全文获取类型
收费全文 | 1675篇 |
免费 | 19篇 |
专业分类
公路运输 | 463篇 |
综合类 | 223篇 |
水路运输 | 527篇 |
铁路运输 | 194篇 |
综合运输 | 287篇 |
出版年
2022年 | 15篇 |
2021年 | 26篇 |
2020年 | 14篇 |
2019年 | 21篇 |
2018年 | 22篇 |
2017年 | 29篇 |
2016年 | 34篇 |
2015年 | 38篇 |
2014年 | 44篇 |
2013年 | 174篇 |
2012年 | 103篇 |
2011年 | 84篇 |
2010年 | 92篇 |
2009年 | 104篇 |
2008年 | 98篇 |
2007年 | 88篇 |
2006年 | 105篇 |
2005年 | 65篇 |
2004年 | 38篇 |
2003年 | 35篇 |
2002年 | 27篇 |
2001年 | 40篇 |
2000年 | 31篇 |
1999年 | 18篇 |
1998年 | 25篇 |
1997年 | 21篇 |
1996年 | 30篇 |
1995年 | 31篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 19篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 5篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 18篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 13篇 |
1974年 | 5篇 |
1973年 | 7篇 |
排序方式: 共有1694条查询结果,搜索用时 15 毫秒
251.
252.
赛车的每一场比赛都是一场赌博。车手做了最好的准备,车队夜以继日地工作,在现有条件下努力打造赛车,但最后获得的,可能只是个教训。但是赛车运动的魅力也在此,有时候不管你扔进去多少钱,但结果并不会按照个人意愿顺利实现。 相似文献
253.
谭祥国 《国防交通工程与技术》2014,(1):20-22,14
移动模架造桥机施工为逐跨段原位现浇施工。以DSZ32/900上承式移动模架造桥机为例介绍该设备在桥隧相连隧道出口处的后退式拼装方法,即通过对移动模架造桥机主梁进行简单的改造,实现主梁在后支腿和前支腿托辊机构之间的纵向移动,则可逐节将在隧道口拼装好的主梁和导梁向隧道内后退,如此反复将移动模架的主梁和导梁全部拼装完成,最后将退入隧道内的主梁及导梁向隧道外走行移动,再完成外模挑梁、吊挂外肋、模板及其他附属结构等的拼装。采用此方法不需要对场地进行大范围回填、平整、硬化,从而节约大量施工成本,缩短安装工期。可为以后类似工程提供借鉴。 相似文献
254.
郑时春 《西安交通大学学报(英文版)》1995,(2)
LEISHMANIAPROMASTIGOTESEVADEINTERLEUKIN12INDUCTIONBYMACROPHAGESANDSTIMULATEABROAD RANGEOFCYTOKINESFROM CD_(4)~(+)TCELLSDURINGI... 相似文献
255.
为了更好的分析小半径曲线段沥青路面病害特征,对重载交通条件下直线段和不同半径(35m/50m/65m)弯道段汽车横向轮迹荷载分布进行了调研和分析,得出了直线段和不同半径弯道段轮迹荷载横向分布特征,以此为依据分析认为小半径弯道沥青路面病害主要为疲劳网裂、水损害,研究了病害的产生机理,并结合沥青路面设计、施工给出了相应的建... 相似文献
256.
Numerical artifacts can limit accurate simulation of turbulent particle motion when Lagrangian particle-tracking models are implemented in hydrodynamic models with stratified conditions like fronts. Yet, modeling of individual particle motion in frontal regions is critical for understanding sediment dynamics as well as the transport and retention of planktonic organisms. The objective of this research was to develop a numerical technique to accurately simulate turbulent particle motions in a particle-tracking model embedded within a hydrodynamic model of a frontal zone. A new interpolation scheme, the ‘water column profile’ scheme, was developed and used to implement a random displacement model for turbulent particle motions. A new interpolation scheme was necessary because linear interpolation schemes caused artificial aggregation of particles where abrupt changes in vertical diffusivity occurred. The new ‘water column profile’ scheme was used to fit a continuous function (a tension spline) to a smoothed profile of vertical diffusivities at the x–y particle location. The new implementation scheme was checked for artifacts and compared with a standard random walk model using (1) Well Mixed Condition tests, and (2) dye-release experiments. The Well Mixed Condition tests confirmed that the use of the ‘water column profile’ interpolation scheme for implementing the random displacement model significantly reduced numerical artifacts. In dye-release experiments, high concentrations of Eulerian tracer and Lagrangian particles were released at the same location up-estuary of the salt front and tracked for 4 days. After small differences in initial dispersal rates, tracer and particle distributions remained highly correlated (r = 0.84 to 0.99) when a random displacement model was implemented in the particle-tracking model. In contrast, correlation coefficients were substantially lower (r = 0.07 to 0.58) when a random walk model was implemented. In general, model performance tests indicated that the ‘water column interpolation’ scheme was an effective technique for implementing a random displacement model within a hydrodynamic model, and both could be used to accurately simulate diffusion in a highly baroclinic frontal region. The new implementation scheme has the potential to be a useful tool for investigating the influence of hydrodynamic variability on the transport of sediment particles and planktonic organisms in frontal zones. 相似文献
257.
Macrobenthic surveys are an expensive, slow and labour intensive means to establish the health of benthic communities. Sediment profile imagery (SPI) is a means of rapid reconnaissance for monitoring large areas of the benthos. SPI has often been used to monitor gross anthropogenic disturbance. The aim of this study is to determine if SPI can be used as a tool to reliably map change in communities along natural estuarine gradients. Macrobenthic sampling was carried out at five stations along an established estuarine gradient. This faunal data was analysed using standard multivariate techniques and to ground truth a concurrent SPI survey. Faunal analysis showed that habitat quality in Inner Galway Bay was generally good, with some localised disturbance from the River Corrib and the sewage out flow exterior to the city dock. Four distinct groups were identified with a degree of overlap occurring between stations 3 and 4. While existing SPI indices mapped habitat quality in the same manner as the faunal data for end member stations, the level of distinction between the habitats of an intermediate staging was found to be poor. This lack of distinction amongst the stage 2 and 3 stations was overcome by developing a tailored index, the Galway Bay index of habitat quality (GBHQ). This index was derived from the 5 observed variables in the SPI data that were determined to best match the faunal distribution by permutative mantel testing. The 5 observed variables from the SPI data were the depth of the apparent redox potential discontinuity (aRPD), the depth of penetration by the prism, and the presence/absence of infauna, surface faecal pellet layer and biogenic mounding. The GBHQ was able to distinguish between the 5 stations to a greater extent than previously described indices, showing clearly the separate groupings defined by the faunal data. The index was tested on a follow up SPI survey and shown to be applicable in mapping a broader range of habitats in Galway Bay. Indices generated for localised mapping of estuarine gradients should be derived from observed features and be ground truthed using faunal data. Some aspects of the GBHQ should be generally applicable to fine grained boreal estuarine sediments (aRPD/penetration), while others may be of limited utility in other locations depending on the digging characteristics of the particular SPI camera, and local factors influencing the persistence of biogenic features in the profile. This derivation technique provides a simple way to optimise SPI to particular studies and localities. 相似文献
258.
Carlos Jerome Lawrence A. Howard Ezgi Uzel Jameela R. Androulidakis 《WMU Journal of Maritime Affairs》2017,16(1):89-98
Protection against on-ship infectious disease—whether due to mishap or to harmful purpose—faces special situational problems. Sometimes, when infection levels on board have reached threshold levels, emergency actions are required. Often, the most thorough strategies for responding to threat are not feasible. A rapid first-stage test (RFT) is a fast, minimally invasive procedure used to rule out from possible infection a large percentage of an infection-threatened group. Prevention and control of on-ship infection need to combine various interconnected tactics. When timely criterion tests are not possible, the medical team must adopt fast alternative measures. The methods used to summarize protection against on-ship infectious agents included a scientific literature review and a web search. The fields of the review were maritime, health, and technology sources. Special attention was paid to material dealing with risks and threats of on-ship penetration by infectious agents, on-ship infection prevalence thresholds, and rapid diagnostic screens. The Bayes rule and the law of large numbers were applied to the analysis, for large on-ship populations, of RFT indications of crossing of an infection prevalence threshold. The increasing risk of serious on-ship infection—either accidental or purposeful—calls for a multi-layered protection approach. RFTs are a key part of the outer layer of such a defense. Well-designed and well-administered RFTs provide several advantages for defense against on-ship infection: low-cost, non-invasive, fast, and focuses on a drastically smaller number of infection possibilities. 相似文献
259.
Navigating in confined waters with a pilot aboard requires that the pilot’s intention and plan is understood by all present on the bridge. The present study investigates the effect of having a detailed route plan and monitoring it in the context of pilotage. The aim was to see how the presence of a shared pilot passage plan in the Electronic Chart Display and Information System (ECDIS) affects the identification and recovery from navigational errors made by a pilot. Twenty participants, 10 with a shared route plan and 10 without, participated as navigators in a simulator scenario involving pilotage in the Oslofjord. Participants were bachelor students in nautical science. The navigation scenarios involved the intentional error by the pilot just before a predefined way point. Three measurements of relevance to navigational safety were recorded: (1) the time it took the participant to express concern, (2) the time it took the participant to correct the error (‘time to recovery’), and (3) the number of groundings. The study revealed that time to express concern and time to recovery were significantly much shorter for the group with a shared pilot passage plan presented in ECDIS than for the group without such a plan. Providing a bridge team with a shared pilot passage plan in ECDIS during pilotage might improve the ability to identify and correct navigational errors. 相似文献
260.
本文用三维有限元方法对东风_4型内燃机车的整个牵引电机传动系统进行了计算。其计算模型利用假想的二力杆连接齿轮副的啮合点,人为地造成了均匀传递啮合力的力学条件,从而计算出了合理的齿轮修形量。 相似文献