全文获取类型
收费全文 | 2586篇 |
免费 | 93篇 |
专业分类
公路运输 | 781篇 |
综合类 | 685篇 |
水路运输 | 652篇 |
铁路运输 | 474篇 |
综合运输 | 87篇 |
出版年
2024年 | 8篇 |
2023年 | 15篇 |
2022年 | 69篇 |
2021年 | 127篇 |
2020年 | 92篇 |
2019年 | 32篇 |
2018年 | 32篇 |
2017年 | 33篇 |
2016年 | 45篇 |
2015年 | 89篇 |
2014年 | 105篇 |
2013年 | 144篇 |
2012年 | 197篇 |
2011年 | 203篇 |
2010年 | 182篇 |
2009年 | 185篇 |
2008年 | 192篇 |
2007年 | 245篇 |
2006年 | 219篇 |
2005年 | 139篇 |
2004年 | 44篇 |
2003年 | 49篇 |
2002年 | 44篇 |
2001年 | 53篇 |
2000年 | 40篇 |
1999年 | 19篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有2679条查询结果,搜索用时 168 毫秒
471.
Outliers in point clouds affect the performance of surface reconstruction directly. Most of outlier removal methods just remove
those outliers far away from the real surface and are only applied to handle watertight surface. In this paper, a two-step
outlier removal procedure is proposed to filter the point clouds acquired from the gray code and line-shifting technique.
The first step is to remove the outliers far away from the real surface. Some feature points are extracted from the point
clouds to construct an initial surface. The points with distances to the initial surface greater than a given threshold are
removed as distant outliers. The retained points are linked into lines in each structured light sheet using their Voronoi
diagrams. Some of lines which are very close to the real surface are removed as near outliers in the second step. The experimental
results show that the proposed method is very effective in removing outliers for surface reconstruction.
Foundation item: the National Natural Science Foundation of China (No. 30470488) 相似文献
472.
Metal-oxide-semiconductor field effect transistor (MOSFET) intrinsic gain degradation caused by channel length modulation
(CLM) effect is examined. A simplified model based on Berkeley short-channel insulator-gate field effect transistor model
version 4 (BSIM4) current expression for sub-100 nm MOSFET intrinsic gain is deduced, which only needs a few technology parameters.
With this transistor intrinsic gain model, complementary metal-oxide-semiconductor (CMOS) operational amplifier (op amp) DC
gain could be predicted. A two-stage folded cascode op amp is used as an example in this work. Non-minimum length device is
used to improve the op amp DC gain. An improvement of 20 dB is proved when using doubled channel length design. Optimizing
transistor bias condition and using advanced technology with thinner gate dielectric thickness and shallower source/drain
junction depth can also increase the op amp DC gain. After these, a full op amp DC gain scaling roadmap is proposed, from
130 nm technology node to 32 nm technology node. Five scaled op amps are built and their DC gains in simulation roll down
from 69.6 to 41.1 dB. Simulation shows transistors biased at higher source-drain voltage will have more impact on the op amp
DC gain scaling over technology. The prediction based on our simplified gain model agrees with SPICE simulation results. 相似文献
473.
�����ʩ�н�ͨӵ���ѵĽ�ͨӰ����� 总被引:2,自引:0,他引:2
交通拥挤费作为缓解城市交通拥堵的直接而有效的需求管理方法,已在国外部分城市实施. 本文对北京市旧城区实行交通拥挤收费的预期交通影响进行分析. 首先根据旧城区的区位特征,土地利用性质,以及目前交通运行状况,提出在旧城区实行交通拥挤收费的必要性. 然后借鉴国内外城市实行交通拥挤收费的经验,结合北京市实际的出行时间价值调查结论,提出旧城区交通拥挤收费的可行方案. 最后基于北京市宏观交通模型测试了施行拥挤费后的预期交通影响,并对施行拥挤费政策提出了相关建议. 相似文献
474.
Objective To investigate the biological function of NS5ABP37 and to look for proteins interacting with NS5ABP37 protein in hepatocytes. Methods We constructed bait plasmid expressing NS5ABP37 protein of hepatitis C virus (HCV) by cloning the gene of NS5ABP37 protein into pGBKT7, then the recombinant plasmid DNA was transformed into yeast AH109 (α type). The transformed yeast AH109 was mated with yeast Y187 (α type) containing liver cDNA library plasmid in 2×YPDA medium. Diploid yeast was plated on synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) containing X-α-gal for selection and screening. After extracting and sequencing of plasmids from positive (blue) colonies, we made a sequence analysis by bioinformatics. Results We screened twenty-five proteins binding to NS5ABP37, including Homo sapiens cyclin Ⅰ (CCNI) gene, Homo sapiens matrix metallopeptidase 25 (MMP25) and Homo sapiens talin 1. Conclusion The yeast-two hybrid system is an effective method for identifying hepatocyte proteins interacting with NS5ABP37 of HCV. And the biological function of NS5ABP37 may be associated with glycometabolism, lipid metabolism and apoptosis. 相似文献
475.
对高速公路安全管理系统进行了研究,重点讨论了影响高速公路交通安全的因素,如人、车、路、管理等因素,并针对这些因素,对高速公路安全管理提出了一些建议. 相似文献
476.
477.
478.
对文献[1]中的主导公式进行了梳理,并在其中增补了可以用来分析具有双层桥面、单室梯形箱梁畸变的几何参数,然后建立了用弹性地基相似梁法分析畸变的计算模型.通过两个示例表明,作这样的调理,不但可以大大节省计算时间,而且还扩大了文献[1]的应用范围. 相似文献
479.
480.