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   939900篇
  免费   111315篇
  国内免费   435篇
  2018年   8904篇
  2017年   8129篇
  2016年   12169篇
  2015年   17792篇
  2014年   20026篇
  2013年   28260篇
  2012年   32317篇
  2011年   32039篇
  2010年   21041篇
  2009年   19200篇
  2008年   28108篇
  2007年   29096篇
  2006年   26813篇
  2005年   25950篇
  2004年   25516篇
  2003年   24375篇
  2002年   23372篇
  2001年   38708篇
  2000年   39322篇
  1999年   31675篇
  1998年   11860篇
  1997年   12297篇
  1996年   11815篇
  1995年   11089篇
  1994年   11077篇
  1993年   10904篇
  1992年   26539篇
  1991年   25733篇
  1990年   25326篇
  1989年   24703篇
  1988年   22699篇
  1987年   21859篇
  1986年   20209篇
  1985年   20385篇
  1984年   17297篇
  1983年   15155篇
  1982年   11885篇
  1981年   10957篇
  1980年   10287篇
  1979年   16899篇
  1978年   13258篇
  1977年   12165篇
  1976年   11449篇
  1975年   12506篇
  1974年   13249篇
  1973年   12983篇
  1972年   11955篇
  1971年   10757篇
  1970年   9242篇
  1969年   8874篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
The results of this study indicate that urbanization has the effect of significantly altering the Guajiro's sense of ideal and feared identity. It was hypothesized that an attempt would be made to minimize dissonance between the ideal and the real or "true" self which the individual privately acknowledges. However, there is found to be considerable dissonance between ideal and real identities, with the latter actually including many components of feared identity. Defective socialization in the city is suggested as a possible reason for failure to achieve ideal standards.  相似文献   
995.
996.
997.
Six genes that were known to exhibit expression levels that are correlated to drip loss BVES, SLC3A2, ZDHHC5, CS, COQ9, and EGFR have been for candidate gene analysis. Based on in silico analysis SNPs were detected, confirmed by sequencing, and used for genotyping. The SNPs were genotyped in about 1,800 animals from six pig populations including commercial herds of Pietrain (PI) and German Landrace (DL), different commercial herds of Pietrain × (German Large White × German Landrace) (PIF1(a/b/c)), and one experimental F2-population Duroc × Pietrain (DUPI). Comparative and genetic mapping established the location of BVES on SSC1, of SLC3A2 and ZDHHC5 on SSC2, of CS on SSC5, of COQ9 on SSC6 and of EGFR on SSC9, respectively, coinciding with QTL regions for carcass and meat quality traits. BVES, SLC3A2, and CS revealed association at least with drip loss and with several other measures of water holding capacity (WHC). Moreover, COQ9 and EGFR were associated with several meat quality traits such as meat color and/or thawing loss. This study reveals statistic evidence in addition to the functional relationship of these genes to WHC previously evidenced by expression analysis. This study reveals positional and genetic statistical evidence for a link of genetic variation at these loci or close to them and promotes those six candidate genes as functional and/or positional candidate genes for meat quality traits.  相似文献   
998.
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   
999.
Characterizing the architecture of bipartite networks is increasingly used as a framework to study biotic interactions within their ecological context and to assess the extent to which evolutionary constraint shape them. Orchid mycorrhizal symbioses are particularly interesting as they are viewed as more beneficial for plants than for fungi, a situation expected to result in an asymmetry of biological constraint. This study addressed the architecture and phylogenetic constraint in these associations in tropical context. We identified a bipartite network including 73 orchid species and 95 taxonomic units of mycorrhizal fungi across the natural habitats of Reunion Island. Unlike some recent evidence for nestedness in mycorrhizal symbioses, we found a highly modular architecture that largely reflected an ecological barrier between epiphytic and terrestrial subnetworks. By testing for phylogenetic signal, the overall signal was stronger for both partners in the epiphytic subnetwork. Moreover, in the subnetwork of epiphytic angraecoid orchids, the signal in orchid phylogeny was stronger than the signal in fungal phylogeny. Epiphytic associations are therefore more conservative and may co‐evolve more than terrestrial ones. We suggest that such tighter phylogenetic specialization may have been driven by stressful life conditions in the epiphytic niches. In addition to paralleling recent insights into mycorrhizal networks, this study furthermore provides support for epiphytism as a major factor affecting ecological assemblage and evolutionary constraint in tropical mycorrhizal symbioses.  相似文献   
1000.
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