全文获取类型
收费全文 | 844篇 |
免费 | 4篇 |
专业分类
公路运输 | 240篇 |
综合类 | 21篇 |
水路运输 | 276篇 |
铁路运输 | 22篇 |
综合运输 | 289篇 |
出版年
2022年 | 16篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 20篇 |
2017年 | 22篇 |
2016年 | 28篇 |
2015年 | 11篇 |
2014年 | 30篇 |
2013年 | 116篇 |
2012年 | 30篇 |
2011年 | 37篇 |
2010年 | 41篇 |
2009年 | 34篇 |
2008年 | 41篇 |
2007年 | 15篇 |
2006年 | 22篇 |
2005年 | 22篇 |
2004年 | 12篇 |
2003年 | 24篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 13篇 |
1999年 | 18篇 |
1998年 | 29篇 |
1997年 | 20篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 10篇 |
1972年 | 5篇 |
排序方式: 共有848条查询结果,搜索用时 390 毫秒
811.
A combined observational-modeling study was conducted to investigate turbulence mixing, and the relation to surface forcing, in the surface boundary layer (SBL) of a tropical, high-altitude, freshwater reservoir. A suite of vertical profiles of temperature microstructure, collected at three different stations of one-day duration each, provided estimates of dissipation rates of turbulence kinetic energy, , and temperature variance, χ. Numerical simulations of and χ, using state-of-the-art, public domain, two-equation turbulence closure models, compared favorably with the observations and reproduced the dynamics of daytime wind mixing as well as the vertical and temporal turbulence structure during nighttime convective conditions.Two independent estimates of vertical eddy diffusivities in the stably stratified (daytime) SBL, computed from the microstructure measurements, agreed closely, and the near surface heat and buoyancy fluxes, computed from the diffusivities, were similar to those computed independently from surface meteorology. Model generated eddy diffusivities agreed closely with the observed values, except those generated by K profile parameterization (KPP) model simulations. The good agreement provides confidence that nutrient fluxes in the SBL may be accurately computed from the models when forced with regularly measured surface meteorological parameters. The consequences are important for estimation of daily primary productivity rates in the euphotic zone and the ability to predict algal blooms such as those observed in the present reservoir. 相似文献
812.
P. Bolzern F. Cheli G. Falciola F. Resta 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1999,31(1):23-34
The paper discusses the application to real data of an identification procedure based on an Extended Kalman Filter, for estimating the equivalent non-linear suspension tyre cornering forces of a road vehicle from a single standard manoeuvre. In particular, both the steady-state and the dynamic handling characteristics can be evaluated. 相似文献
813.
Realistic predictions of the likely safety performance of advanced transport systems will need to draw on the knowledge accumulated from a large number of safety evaluations which have already been undertaken for existing transport systems. In particular, safety evaluations of future technologies must avoid the methodological pitfalls experienced in extensively researched areas, such as road safety, if such evaluations are to be meaningful. This paper reviews the use of exposure for a broad range of road safety studies, and concludes that unsatisfactory treatment of exposure is a common failing in past evaluations of the effectiveness of road accident countermeasures. Whilst a broad range of safety analyses is discussed, the use of exposure in site safety studies is emphasized. A follow-up paper will extend the discussion to other aspects of accident exposure including exposure measures for large groups of transport system users. 相似文献
814.
815.
G. Levikov 《Maritime Policy and Management》1988,15(3):247-254
In light of the Reveiw Conference on the UN Code of Conduct for Liner Conferences to be in November 1988, this paper highlights some of the Major problems impinging upon the universal acceptability of the Code. These include the reservation (known as the Brussels Package) by EC and certain other OECD countries that discriminates aganist developing and Socialist countries; reservations of a controversial nature with regard to the establishment of joint shipping lines established on the basis of intergovernmental bilateral agreement; and the question of compctition by non-conference lines that diminishes the share of cargo available to National Lines by virtue of the Code. 相似文献
816.
This paper undertakes a comparative analysis of the stock market perception of risk in US listed water transportation companies and seven other main sectors, air transportation; rail transportation; trucks; electricity; gas; petroleum refining; and real estate over the period July 1984-June 1995. This is done by employing the Capital Asset Pricing Model (CAPM) to model the stock returns of each industry and hence compare their betas (systematic risk). Multiequation Regression Models are used for estimation. The findings suggest that the water transportation industry exhibits significantly lower market risk than the average stock and the rail transportation industry, significantly higher systematic risk than the real estate industry, while its systematic risk is insignificantly different from the rest of the industries. These results are useful to investors basing their decisions on relative market exposures to risk in different industries. 相似文献
817.
G. F. Mazepova 《Journal of Marine Systems》1998,15(1-4)
This describes a study of the pelagic zone of Lake Baikal with particular reference to copepods. In addition the cycling of matter and energy in lacustrine basins is described. 相似文献
818.
An experimental technique for exploring the sensitivity of transportation plan evaluations to forecasting and community value uncertainties is described. Three kinds of uncertainty — goal-achievement impacts, costs, and goal-weights — are included. Within a cost-effectiveness evaluation framework, an on-line capability for interactively and iteratively testing plan comparisons is outlined. A series of user-oriented computer instructions is developed to test plan comparison outcomes according to a wide variety of user-selected changes in impact forecasts, goal weights, and cost forecasts. A sample, hypothetical application of the technique is described. The technique is currently under further development by the San Diego Region Comprehensive Planning Organization. 相似文献
819.
E.J Murphy P.W Boyd R.J.G Leakey A Atkinson E.S Edwards C Robinson J Priddle S.J Bury D.B Robins P.H Burkill G Savidge N.J.P Owens D Turner 《Journal of Marine Systems》1998,17(1-4)
Most analyses of marine microbial systems in the seasonally ice covered areas of the Southern Ocean have been based on data from the major embayment areas of the Ross and Weddell Seas. In this study data were collected at stations covering a range of regimes from full ice cover through to open water in the Bellingshausen Sea. A major feature of the production system was a rapid retreat of the ice-edge, which uncoupled the marginal ice zone from a phytoplankton bloom which remained associated with a frontal system. This bloom was maintained, and probably initiated, in an unusual environment generated by the interaction between the marginal ice zone and the front. Size-based analyses of the microbial system were derived for ice-covered, recently ice-covered and open water sites. Estimates of standing stocks and key rate processes were combined to produce a single food web network for each station. The under-ice system was one of low production and low recycling but apparently high retention. As the ice retreated the microbial systems to the north began to develop, but these were constrained by grazing pressure. The bloom in the area appeared to be sustained even though estimated losses were far higher than production, although the high sedimentation losses expected were not observed. The carbon flow networks are discussed in relation to the environmental changes and the interaction of the marginal ice zone and the frontal system appears crucial to the phytoplankton. Microzooplankton grazing is implicated as a major controlling factor. The local microbial dynamics are strongly influenced by material which was produced at an earlier time and somewhere else in the Southern Ocean. 相似文献
820.