全文获取类型
收费全文 | 8797篇 |
免费 | 914篇 |
国内免费 | 5篇 |
出版年
2023年 | 40篇 |
2021年 | 165篇 |
2020年 | 107篇 |
2019年 | 143篇 |
2018年 | 192篇 |
2017年 | 164篇 |
2016年 | 292篇 |
2015年 | 395篇 |
2014年 | 441篇 |
2013年 | 504篇 |
2012年 | 658篇 |
2011年 | 667篇 |
2010年 | 393篇 |
2009年 | 350篇 |
2008年 | 488篇 |
2007年 | 472篇 |
2006年 | 441篇 |
2005年 | 354篇 |
2004年 | 392篇 |
2003年 | 313篇 |
2002年 | 339篇 |
2001年 | 141篇 |
2000年 | 144篇 |
1999年 | 132篇 |
1998年 | 120篇 |
1997年 | 92篇 |
1996年 | 82篇 |
1995年 | 76篇 |
1994年 | 69篇 |
1993年 | 57篇 |
1992年 | 104篇 |
1991年 | 83篇 |
1990年 | 100篇 |
1989年 | 89篇 |
1988年 | 78篇 |
1987年 | 75篇 |
1986年 | 54篇 |
1985年 | 73篇 |
1984年 | 86篇 |
1983年 | 46篇 |
1982年 | 54篇 |
1981年 | 41篇 |
1980年 | 27篇 |
1979年 | 40篇 |
1978年 | 31篇 |
1977年 | 43篇 |
1973年 | 33篇 |
1972年 | 28篇 |
1970年 | 33篇 |
1969年 | 28篇 |
排序方式: 共有9716条查询结果,搜索用时 125 毫秒
1.
2.
Signal crayfish (Pacifastacus leniusculus) are an invasive species of global significance because of their detrimental impacts on freshwater environments and native organisms. The movement of signal crayfish was continuously monitored for 150-days through a 20-m reach of an alluvial stream in the UK. Passive integrated transponder-tags were attached to crayfish, allowing their location to be monitored relative to 16 antennae which were buried beneath the river bed. The activity of crayfish was related to water depth and temperature, which were continuously monitored within the instrumented reach. Crayfish were highly nocturnal, with less than 6% of movements recorded during daylight hours. Activity declined from September and was minimal in November when water temperature was low and flow depth was high. However, relations between environmental parameters and crayfish activity had poor explanatory power which may partly reflect biological processes not accounted for in this study. Water depth and temperature had a limiting relationship with crayfish activity, quantified using quantile regression. The results extend existing data on signal crayfish nocturnalism and demonstrate that, although signal crayfish can tolerate a range of flows, activity becomes limited as water temperature declines seasonally and when water depth remains high in autumn and winter months. 相似文献
3.
Tim Schwarting Philipp Lechler Johannes Struewer Marius Ambrock Thomas Manfred Frangen Steffen Ruchholtz Ewgeni Ziring Michael Frink 《PloS one》2015,10(2)
IntroductionSuccessful graft ingrowth following reconstruction of the anterior cruciate ligament is governed by complex biological processes at the tendon-bone interface. The aim of this study was to investigate in an in vitro study the effects of bone morphogenetic protein 7 (BMP-7) on tendon-bone integration.ResultsIn both models, positive effects of BMP-7 on ALP enzyme activity were observed (p<0.001). Additionally, similar results were noted for LDH activity and lactate concentration. BMP-7 stimulation led to a significant increase in OCN expression. Whereas the effects of BMP-7 on tendon monoculture peaked during an early phase of the experiment (p<0.001), the cocultures showed a maximal increase during the later stages (p<0.001). The histological analysis showed a stimulating effect of BMP-7 on extracellular matrix formation. Organized ossification zones and calcium carbonate-like structures were only observed in the BMP-stimulated cell cultures.DiscussionThis study showed the positive effects of BMP-7 on the biological process of tendon-bone integration in vitro. Histological signs of improved mineralization were paralleled by increased rates of osteoblast-specific protein levels in primary bovine osteoblasts and fibroblasts.ConclusionOur findings indicated a role for BMP-7 as an adjuvant therapeutic agent in the treatment of ligamentous injuries, and they emphasized the importance of the transdifferentiation process of tendinous fibroblasts at the tendon-bone interface. 相似文献
4.
Mohammed Mamdani Vernell Williamson Gowon O. McMichael Tana Blevins Fazil Aliev Amy Adkins Laura Hack Tim Bigdeli Andrew D. van der Vaart Bradley Todd Web Silviu-Alin Bacanu Gursharan Kalsi COGA Consortium Kenneth S. Kendler Michael F. Miles Danielle Dick Brien P. Riley Catherine Dumur Vladimir I. Vladimirov 《PloS one》2015,10(9)
5.
6.
7.
Background
Twelve populations of E. coli were serially propagated for 20,000 generations in a glucose-supplemented minimal medium in order to study the dynamics of evolution. We sought to find and characterize one of the beneficial mutations responsible for the adaptation and other phenotypic changes, including increased cell size, in one of these populations. 相似文献8.
9.
10.