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481.
During 2004, 10 samplings were performed in order to measure dissolved methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) in the surface waters of Río San Pedro, a tidal creek in the salt marsh area of the Bay of Cádiz (SW Spain). The inner partvs of the creek is affected by the inputs coming from an intensive fish farm and the drainage of an extensive salt marsh area.Dissolved CH4, CO2 and N2O concentrations ranged from 11 to 88 nM, 36 to 108 μM and 14 to 50 nM, respectively. Surface waters were in all cases oversaturated with respect to the atmosphere, reaching values of up to 5000% for CH4, 1240% for CO2 and 840% for N2O. Dissolved CH4, CO2 and N2O showed a significant tidal and seasonal variability. Over a tidal cycle, concentrations were always highest during low tide, which points to the influence of the inputs from the fish farm effluent and the drainage of the adjacent salt marsh area, as well as in situ production within the system. Dissolved CH4, CO2 and N2O seasonal patterns were similar and showed maximum concentrations in summer conditions. Using four different parameterizations to calculate the gas transfer coefficients [Liss, P.S. and Merlivat, L., 1986. Air-sea exchange rates: introduction and synthesis. In P. Buat-Ménard (Ed.), The Role of Air-Sea Exchanges in Geochemical Cycling. Reidel, Dordrecht, The Netherlands, p. 113–127.; Clark, J.F., Schlosser, P., Simpson, H.J., Stute, M., Wanninkhof, R., and Ho, D.T., 1995. Relationship between gas transfer velocities and wind speeds in the tidal Hudson River determined by the dual tracer technique. In: B. Jähne and E. Monahan (Eds.), Air-Water Gas Transfer: AEON Verlag and Studio, Hanau, Germany, pp. 785–800.; Carini, S., Weston, N., Hopkinson, G., Tucker, J., Giblin, A. and Vallino, J., 1996. Gas exchanges rates in the Parker River estuary, Massachusetts. Biol. Bull., 191: 333–334.; Kremer, J.N., Reischauer, A. and D'Avanzo, C., 2003. Estuary-specific variation in the air-water gas exchange coefficient for oxygen. Estuaries, 26: 829–836.], the averaged air–water fluxes of CH4, CO2 and N2O from the creek to the atmosphere ranged between 34 and 150 μmol CH4 m− 2 day− 1, 73 and 177 mmol CO2 m− 2 day− 1 and 24 and 62 μmol N2O m−2 day−1, respectively. 相似文献
482.
The prediction of free speeds of vehicles is an integral part of the economic appraisal of highways. It is to be noted that speeds not only govern the travel time costs, but also have major impacts on Vehicle Operating Costs (VOC). The World Bank has proposed a mechanistic free speed model based on the limiting speed concept for Highway Design and Maintenance (HDM)‐III. This model along with some refinements has been included in HDM‐4. The underlying assumption in the HDM free speed prediction model is that the free speed at any given point of time is the minimum of possible constraining speeds. This paper mainly addresses the methodology considered to update the free speed models through mechanistic principles (based on HDM‐4). This is accomplished by calibration of the model using the current data on free speeds, road and vehicle characteristics. Subsequently, the validation of the developed models has been carried out. 相似文献
483.
利用直接边界元法求解兴波问题 总被引:2,自引:0,他引:2
本文描述了利用直接边界元法求解定常兴波问题的理论和数值方法,本方法利用线性化自由面条件,辐射条件基于Dawson的四点差分格式进行处理。本文给出了Wigley船的兴波阻力和波高的数值结果,并与Dawson方法和试验结果进行了比较,结果显示本文的结果合理可靠。 相似文献
484.
The authors have developed a simulation program, CP-System, for multiple cracks propagating in a three-dimensional stiffened
panel structure, where through-the-thickness crack propagation is formulated as a two-dimensional in-plane problem, and the
crack propagation behavior is simulated by step-by-step finite element analyses. In order to evaluate the fatigue lives of
marine structures accurately, it is necessary to take into account the load histories induced by sea waves, which may be composed
of a random sequence of certain clustered loads with variable stress range. In the proposed crack growth model, the crack
opening and closure behavior is simulated by using the modified strip yielding model, and the effective tensile plastic stress
intensity range, ΔK
RP, is calculated by considering the contact of plastic wake along the crack surfaces. The adequacy of the proposed crack growth
model is examined by comparison with fatigue tests under non-constant-amplitude loading. The usefulness of the developed method
is demonstrated for a ship structural detail under certain simulated load sequences. It is shown that the fatigue crack growth
of a ship structure is significantly retarded due to the load interaction effects, so that the conventional method for fatigue
life assessment may predict a relatively conservative fatigue life of a structure. 相似文献
485.
Yoichi Sumi Takuji Yano Anowarul T.M.M. Bashar 《Journal of Marine Science and Technology》2005,10(2):96-102
The weight function method was originally derived for crack problems to calculate stress intensity factors for arbitrary loading conditions. In this article, a numerical weight function method has been extended to formulate the structural response analyses of two-dimensional elasticity, plate-bending, and three-dimensional plate-structures by using the finite-element method. The solution procedure is based on the well-known Maxwell–Betti reciprocal theorem, which is applied to the original and properly defined auxiliary problems. The present numerical weight function may be considered as a finite-element version of a Green’s function in an integral equation solution scheme. Although ship structures are certainly analysed by the finite-element method in a practical design procedure, the weight function approach has not yet been realized. The method is very useful for the analysis of structures subjected to a vast range of loading conditions, because structural responses can simply be calculated by the inner product of the universal weight function and load vectors. The validity and convergence characteristics of the present method are investigated by two-dimensional elastic and plate-bending problems, respectively. Finally, the method is applied to the calculation of the response amplitude operator of a stress component at a critical structural detail of a double-hull tanker, and the speed and efficiency of the method are quantitatively discussed based on the practical results. 相似文献
486.
������������������ϵͳģ�� 总被引:4,自引:0,他引:4
电力是现今大部份铁道系统的动力来源. 可靠、有效率及安全的电力输送对整体铁道服务质素尤为重要,跟其它大型工程系统一样,铁道供电系统的设计,运作及筹划相当倚重计算机仿真.本文将回顾铁道供电系统仿真的模型及一般常规,并通过模拟结果例子及实际应用,介绍最新的模拟方式发展.本文亦对铁道供电系统仿真的未来挑战作出评论. 相似文献
487.
卜昕 《西安交通大学学报(英文版)》1995,(2)
REGULATEDPHOSPHORYLATIONOFTHEGATA-2DNABINDINGPROTEININENDOTHELIALCELLSBuXinE.E.Quertermous,T.Quertermous(DepartmentofMedicine... 相似文献
488.
The main target of this work is to realize the function of pre-oxidizing NO from diesel engine’s exhaust by using self-designed double-dielectric Non-thermal Plasma (NTP) reactor. The majorized discharge frequency and discharge peak to peak voltage (Vp-p) range for NTP reactor were obtained through air discharge test. The diesel engine test bench was established to observe the effect of NTP on the volume fraction of NO. The results showed that there were more active substances and fewer by-products in NTP reactor when discharge frequency was 9 kHz and Vp-p was between 9 kV and 23 kV; Exhaust flows had insignificant effect on the performance of NTP pre-oxidizing NO; The ability of NTP to pre-oxidize NO gradually weakened with the increase of engine load, and when the engine load were 0 % and 25 %, the ratio of NO/NO2 could reach 1. In such working conditions, SCR system could improve the conversion rate of the NOx at low-temperature zone through quick reaction combined with NTP. 相似文献
489.
G. T. Chala A. R. A. Aziz F. Y. Hagos 《International Journal of Automotive Technology》2017,18(1):85-96
There is an increasing interest in supercharging spark ignition engines operating on CNG (compressed natural gas) mainly due to its superior knock resisting properties. However, there is a penalty in volumetric efficiency when directly injecting the gaseous fuel at early and partial injection timings. The present work reports the combined effects of a small boost pressure and injection timing on performance and combustion of CNG fueled DI (direct injection) engine. The experimental tests were carried out on a 4-stroke DI spark ignition engine with a compression ratio of 14. Early injection timing, when inlet valves are still open (at 300°BTDC), and partial injection timing, in which part of the injection occurs after the inlet valves are closed (at 180°BTDC), were varied at each operating speed with variation of the boost pressure from 2.5 to 10 kPa. A narrow angle injector (NAI) was used to increase the mixing rate at engine speeds between 2000 and 5000 rpm. Similar experiments were conducted on a naturally aspirated engine and the results were then compared with that of the boosting system to examine the combined effects of boost pressure and injection timing. It was observed that boost pressure above 7.5 kPa resulted in an improvement of performance and combustion of CNG DI engine at all operating speeds. This was manifested in the faster heat release rates and mass fraction burned that in turn improved combustion efficiency of the boosting system. An increased in cylinder pressure and temperature was also observed with boost pressure compared to naturally aspirated engine. Moreover, the combustion duration was reduced due to concentration of the heat release near to the top dead center as the result of the boost pressure. Supercharging was also found to reduce the penalty of volumetric efficiency at both the simulated port and partial injection timings. 相似文献
490.
H. Yamazaki Y. Karino T. Kamada M. Nagai T. Kimura 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2008,46(4):255-270
It is important to consider the robustness when designing brake control systems, because of the model's uncertainties that result from the nonlinear characteristics of wheel-to-rail adhesion forces and brake material friction coefficients. This paper presents the experimental results from the new wheel-slip prevention control using nonlinear robust control theory. The authors performed experiments for the proposed wheel-slip prevention control to compare it with the conventional control laws. The experimental results proved the comparative effectiveness of the proposed control and showed high brake performance under nonlinear characteristics of brake dynamics. 相似文献