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   3391篇
  免费   271篇
  国内免费   5篇
  3667篇
  2024年   10篇
  2023年   27篇
  2022年   49篇
  2021年   110篇
  2020年   57篇
  2019年   81篇
  2018年   97篇
  2017年   76篇
  2016年   108篇
  2015年   190篇
  2014年   222篇
  2013年   225篇
  2012年   294篇
  2011年   239篇
  2010年   144篇
  2009年   150篇
  2008年   170篇
  2007年   146篇
  2006年   127篇
  2005年   120篇
  2004年   122篇
  2003年   108篇
  2002年   113篇
  2001年   41篇
  2000年   26篇
  1999年   34篇
  1998年   23篇
  1997年   16篇
  1996年   23篇
  1995年   21篇
  1994年   15篇
  1993年   21篇
  1992年   18篇
  1991年   18篇
  1990年   19篇
  1989年   10篇
  1988年   24篇
  1987年   14篇
  1984年   10篇
  1983年   15篇
  1982年   13篇
  1981年   14篇
  1980年   14篇
  1979年   10篇
  1978年   15篇
  1977年   9篇
  1976年   14篇
  1974年   10篇
  1973年   9篇
  1924年   8篇
排序方式: 共有3667条查询结果,搜索用时 15 毫秒
41.
42.
Despite the considerable progress made in the stent development in the last decades, cardiovascular diseases remain the main cause of death in western countries. Beside the benefits offered by the development of different drug-eluting stents, the coronary revascularization bears also the life-threatening risks of in-stent thrombosis and restenosis. Research on new therapeutic strategies is impaired by the lack of appropriate methods to study stent implantation and restenosis processes. Here, we describe a rapid and accessible procedure of stent implantation in mouse carotid artery, which offers the possibility to study in a convenient way the molecular mechanisms of vessel remodeling and the effects of different drug coatings.  相似文献   
43.
This article reveals a rapid sandwich enzyme-linked immunosorbent assay (ELISA) for the highly sensitive detection of human C-reactive protein (CRP) in less than 30 min. It employs a one-step kinetics-based highly simplified and cost-effective sandwich ELISA procedure with minimal process steps. The procedure involves the formation of a sandwich immune complex on capture anti-human CRP antibody-bound Dynabeads in 15 min, followed by two magnet-assisted washings and one enzymatic reaction. The developed sandwich ELISA detects CRP in the dynamic range of 0.3 to 81 ng ml−1 with a limit of detection of 0.4 ng ml−1 and an analytical sensitivity of 0.7 ng ml−1. It detects CRP spiked in diluted human whole blood and serum with high analytical precision, as confirmed by conventional sandwich ELISA. Moreover, the results of the developed ELISA for the determination of CRP in the ethylenediaminetetraacetic acid plasma samples of patients are in good agreement with those obtained by the conventional ELISA. The developed immunoassay has immense potential for the development of rapid and cost-effective in vitro diagnostic kits.  相似文献   
44.
45.
46.
A number of substituted bradykinin analogs were prepared in which the proline in position 3 was replaced by analogs of proline. All of the bradykinin analogs, with the exception of l-azetidine-2-carboxyl3-bradykinin showed significant ability to inhibit prolyl hydroxylase activity. Addition of an l-glutamyl residue to the amino terminus of 3,4-dehydro-l-prolyl3-bradykinin and trans-4-hydroxy-l-prolyl3-bradykinin resulted in competitive inhibitors of increased effectiveness with Ki, values approximately 10?4m. One of the peptides, l-3,4-dehydro-l-prolyl3-bradykinin, appeared to serve as a substrate for prolyl hydroxylase.  相似文献   
47.
Summary Using immunohistochemical methods, we have investigated the cellular distribution of prothymosin alpha (ProT) in adult rat testis. A policlonal antibody raised against thymosin alpha 1 conjugated to keyhole limpet hemocyanin was used. ProT immunoreactivity was observed in the cytoplasm and nucleus of spermatogonia and primary spermatocytes in initial phases of the first meiotic division, preleptotene, leptotene and zygotene. However, in pachytene phase they already showed a weak or negative staining. On the other hand, secondary spermatocytes, spermatids, spermatozoa and Sertoli cells were not stained. Based on this fact we suggest that ProT is present in the proliferative cycle in the final steps of G1 phase, throughout the S and G2 phases and in initial steps of the prophase.  相似文献   
48.
49.
Habitat fragmentation is a major threat for beneficial organisms and the ecosystem services they provide. Multiple‐habitat users such as wild bees depend on both nesting and foraging habitat. Thus, they may be affected by the fragmentation of at least two habitat types. We investigated the effects of landscape‐scale amount of and patch isolation from both nesting habitat (woody plants) and foraging habitat (specific pollen sources) on the abundance and diet of Osmia bicornis L. Trap‐nests of O. bicornis were studied in 30 agricultural landscapes of the Swiss Plateau. Nesting and foraging habitats were mapped in a radius of 500 m around the sites. Pollen composition of larval diet changed as isolation to the main pollen source, Ranunculus, increased, suggesting that O. bicornis adapted its foraging strategy in function of the nest proximity to main pollen sources. Abundance of O. bicornis was neither related to isolation or amount of nesting habitat nor to isolation or abundance of food plants. Surprisingly, nests of O. bicornis contained fewer larvae in sites at forest edge compared to isolated sites, possibly due to higher parasitism risk. This study indicates that O. bicornis can nest in a variety of situations by compensating scarcity of its main larval food by exploiting alternative food sources.  相似文献   
50.
The biogeographic history of the Chihuahuan Desert is known to be complex, and there is evidence of the effects of physiographic and climatic events in species diversification and demographic population changes in many taxa. Here, using DNA sequence data, we studied the influence of the physiographic and climatic events that occurred in the Chihuahuan Desert during the Pliocene–Pleistocene transition on the speciation and evolutionary history of the sister lizard species Sceloporus cyanostictus and S. gadsdeni. First, based on mtDNA and nDNA sequences, we estimated the divergence times of the sister species. Then, based on mtDNA sequences, we investigated the demographic history of both species within a phylogeographic framework. The divergence time was inferred to be 1.48 Mya, date that corresponds to the existence of a large lake in the Mapimian subprovince, between the current geographic locations of S. cyanostictus and S. gadsdeni. This lake could have acted as a barrier, leading to the speciation of both species. For the demographic history of the two species, we identified two distinct patterns: the population expansion of S. gadsdeni within the Last Glacial Maximum and the potential population decline of S. cyanostictus. Our results can be used as a guide for the study of other aspects that could be critical to developing conservation actions that ensure the survival of not only S. gadsdeni and S. cyanostictus, but also other co‐occurring lizard species.  相似文献   
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