首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   15149篇
  免费   939篇
  国内免费   33篇
  2023年   142篇
  2022年   410篇
  2021年   690篇
  2020年   420篇
  2019年   565篇
  2018年   629篇
  2017年   481篇
  2016年   650篇
  2015年   773篇
  2014年   888篇
  2013年   1164篇
  2012年   1197篇
  2011年   1110篇
  2010年   703篇
  2009年   583篇
  2008年   675篇
  2007年   684篇
  2006年   558篇
  2005年   544篇
  2004年   433篇
  2003年   377篇
  2002年   339篇
  2001年   197篇
  2000年   216篇
  1999年   160篇
  1998年   119篇
  1997年   59篇
  1996年   69篇
  1995年   68篇
  1994年   41篇
  1993年   44篇
  1992年   69篇
  1991年   63篇
  1990年   61篇
  1989年   67篇
  1988年   59篇
  1987年   49篇
  1986年   51篇
  1985年   54篇
  1984年   58篇
  1983年   51篇
  1982年   41篇
  1981年   40篇
  1980年   49篇
  1979年   43篇
  1978年   49篇
  1977年   39篇
  1976年   35篇
  1975年   29篇
  1973年   24篇
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
1.
2.
3.
4.
5.
Perspective texture synthesis has great significance in many fields like video editing, scene capturing etc., due to its ability to read and control global feature information. In this paper, we present a novel example-based, specifically energy optimization-based algorithm, to synthesize perspective textures. Energy optimization technique is a pixel-based approach, so it’s time-consuming. We improve it from two aspects with the purpose of achieving faster synthesis and high quality. Firstly, we change this pixel-based technique by replacing the pixel computation with a little patch. Secondly, we present a novel technique to accelerate searching nearest neighborhoods in energy optimization. Using k- means clustering technique to build a search tree to accelerate the search. Hence, we make use of principal component analysis (PCA) technique to reduce dimensions of input vectors. The high quality results prove that our approach is feasible. Besides, our proposed algorithm needs shorter time relative to other similar methods.  相似文献   
6.
Δ7-5-Desaturase catalyses one of the last steps in ergosterol biosynthesis in fungi. Moreover Δ5-unsaturation is necessary for the sparking function. Synthesis of three pairs of C-6 epimeric cholestanol derivatives are described as potential growth inhibitors. Preliminary results suggest that 6β-aminocholestanol is a potent antifungal agent.  相似文献   
7.
One novel approach for the biological delivery of peptide drugs is to incorporate the sequence of the peptide into the structure of a natural transport protein such as human serum transferrin (HST). However, a potential drawback is that the HST may increase the immunoreactivity of the peptide, in the same way that carrier proteins can be used to generate highly immunogenic peptide hapten conjugates. In this study we have generated a recombinant HST carrier protein that contains a peptide substrate of HIV-1 protease (VSQNYPIVL). The protein retained native HST function, and the peptide was surface exposed since it was immunoreactive in native dot blots, and was cleaved by HIV-1 protease. Immunisation of rabbits with the recombinant protein elicited only a very poor anti-peptide immune response. In contrast, strong anti-peptide immune responses were raised against both the peptide alone, and a chemical conjugate of the peptide with HST. These data demonstrate that it is possible to attenuate the immune response normally directed against an immunogenic peptide sequence by engineering into a surface exposed loop of HST. These findings may have an important impact on the future design of peptide delivery systems.  相似文献   
8.
9.
Camera trapping studies have become increasingly popular to produce population estimates of individually recognisable mammals. Yet, monitoring techniques for rare species which occur at extremely low densities are lacking. Additionally, species which have unpredictable movements may make obtaining reliable population estimates challenging due to low detectability. Our study explores the effectiveness of intensive camera trapping for estimating cheetah (Acinonyx jubatus) numbers. Using both a more traditional, systematic grid approach and pre-determined, targeted sites for camera placement, the cheetah population of the Northern Tuli Game Reserve, Botswana was sampled between December 2012 and October 2013. Placement of cameras in a regular grid pattern yielded very few (n = 9) cheetah images and these were insufficient to estimate cheetah density. However, pre-selected cheetah scent-marking posts provided 53 images of seven adult cheetahs (0.61 ± 0.18 cheetahs/100km²). While increasing the length of the camera trapping survey from 90 to 130 days increased the total number of cheetah images obtained (from 53 to 200), no new individuals were recorded and the estimated population density remained stable. Thus, our study demonstrates that targeted camera placement (irrespective of survey duration) is necessary for reliably assessing cheetah densities where populations are naturally very low or dominated by transient individuals. Significantly our approach can easily be applied to other rare predator species.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号