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   108280篇
  免费   148200篇
  国内免费   49638篇
  2022年   3236篇
  2021年   3279篇
  2020年   3419篇
  2019年   4937篇
  2018年   3654篇
  2017年   3471篇
  2016年   3447篇
  2015年   4377篇
  2014年   5767篇
  2013年   5095篇
  2012年   6971篇
  2011年   7579篇
  2010年   8464篇
  2009年   13881篇
  2008年   8078篇
  2007年   7519篇
  2006年   6617篇
  2005年   5936篇
  2004年   5002篇
  2003年   4143篇
  2002年   4705篇
  2001年   5800篇
  2000年   3515篇
  1999年   7531篇
  1998年   9220篇
  1997年   9302篇
  1996年   8626篇
  1995年   8895篇
  1994年   8271篇
  1993年   7931篇
  1992年   7836篇
  1991年   7845篇
  1990年   8663篇
  1989年   7902篇
  1988年   7210篇
  1987年   6301篇
  1986年   5840篇
  1985年   5284篇
  1984年   4085篇
  1983年   3267篇
  1982年   3646篇
  1981年   3241篇
  1980年   3159篇
  1979年   3250篇
  1978年   2962篇
  1977年   2895篇
  1976年   2718篇
  1973年   2465篇
  1972年   2810篇
  1971年   2591篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Nucleotide sequence of pheW; a third gene for E. coli tRNAPhe.   总被引:2,自引:0,他引:2       下载免费PDF全文
  相似文献   
93.
Natural relationship between bacteroides and flavobacteria.   总被引:34,自引:18,他引:16       下载免费PDF全文
Comparisons among 16S rRNA sequences from various eubacteria reveal a natural relationship between the bacteroides (represented by the Bacteroides fragilis sequence) and a phylogenetic unit that comprises the flavobacteria, cytophagae, flexibacteria, and others (represented by the Flavobacterium heparinum sequence). Although the relationship is not a close one, it is, nevertheless, specific. rRNAs from these two organisms are not only closer to one another in overall sequence than they are to outgroup species (such as Bacillus subtilis, Escherichia coli, Desulfovibrio desulfuricans, and Agrobacterium tumefaciens), but they show common idiosyncrasies (i.e., derived characteristics) in both rRNA sequences and higher-order structures.  相似文献   
94.
A LIM motif is present in a pollen-specific protein.   总被引:5,自引:2,他引:3       下载免费PDF全文
R Baltz  J L Evrard  C Domon    A Steinmetz 《The Plant cell》1992,4(12):1465-1466
  相似文献   
95.
96.
Bacopa monniera Wettst. (BM, syn. Herpestis monniera L; Scrophulariaceae), is an Ayurvedic drug used as a rasayana. Its fresh juice was earlier reported to have significant antiulcerogenic activity. In continuation, methanolic extract of BM (BME) standardized to bacoside-A content (percentage-38.0 ± 0.9), when given in the dose of 10–50 mg/kg, twice daily for 5 days, showed dose-dependent anti-ulcerogenic on various gastric ulcer models induced by ethanol, aspirin, 2 h cold restraint stress and 4 h pylorus ligation. BME in the dose of 20 mg/kg, given for 10 days, twice daily showed healing effects against 50% acetic acid-induced gastric ulcers. Further work was done to investigate the possible mechanisms of its action by studying its effect on various mucosal offensive acid-pepsin secretion and defensive factors like mucin secretion, mucosal cell shedding, cell proliferation and antioxidant activity in rats. BME 20 mg/kg showed no effect on acid-pepsin secretion, increased mucin secretion, while it decreased cell shedding with no effect on cell proliferation. BME showed significant antioxidant effect per se and in stressed animals. Thus, the gastric prophylactic and curative effects of BME may be due to its predominant effect on mucosal defensive factors.  相似文献   
97.
98.
Summary The frequency of large granular lymphocytes (LGL) in the peripheral blood of healthy persons (n=56) and breast cancer patients (31 cases with stage-I and -II disease and 42 cases with stage-III and -IV disease) was studied. The frequency of LGL in peripheral blood was significantly depressed in cancer patients, and particularly in patients with advanced breast cancer.  相似文献   
99.
The murine cytomegalovirus m02 gene family encodes putative type I membrane glycoproteins named m02 through m16. A subset of these genes were fused to an epitope tag and cloned into an expression vector. In transfected and murine cytomegalovirus-infected cells, m02, m04, m05, m06, m07, m09, m10, and m12 localized to cytoplasmic structures near the nucleus, whereas m08 and m13 localized to a filamentous structure surrounding the nucleus. Substitution mutants lacking the m02 gene (SMsubm02) or the entire m02 gene family (SMsubm02-16) grew like their wild-type parent in cultured cells. However, whereas SMsubm02 was as pathogenic as the wild-type virus, SMsubm02-16 was markedly less virulent. SMsubm02-16 produced less infectious virus in most organs compared to wild-type virus in BALB/c and C57BL/6J mice, but it replicated to wild-type levels in the organs of immunodeficient gamma(c)/Rag2 mice, lacking multiple cell types including natural killer cells, and in C57BL/6J mice depleted of natural killer cells. These results argue that one or more members of the m02 gene family antagonize natural killer cell-mediated immune surveillance.  相似文献   
100.
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