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   111881篇
  免费   147893篇
  国内免费   45684篇
  305458篇
  2022年   3000篇
  2021年   3329篇
  2020年   3363篇
  2019年   5141篇
  2018年   3876篇
  2017年   3541篇
  2016年   3830篇
  2015年   4820篇
  2014年   5979篇
  2013年   5521篇
  2012年   7210篇
  2011年   7727篇
  2010年   8342篇
  2009年   13421篇
  2008年   7694篇
  2007年   7213篇
  2006年   6274篇
  2005年   5666篇
  2004年   4848篇
  2003年   4132篇
  2002年   4622篇
  2001年   5618篇
  2000年   3303篇
  1999年   7389篇
  1998年   9219篇
  1997年   9320篇
  1996年   8655篇
  1995年   8882篇
  1994年   8270篇
  1993年   7922篇
  1992年   7849篇
  1991年   7880篇
  1990年   8690篇
  1989年   7914篇
  1988年   7236篇
  1987年   6318篇
  1986年   5833篇
  1985年   5289篇
  1984年   4076篇
  1983年   3280篇
  1982年   3635篇
  1981年   3243篇
  1980年   3150篇
  1979年   3262篇
  1978年   2968篇
  1977年   2899篇
  1976年   2721篇
  1973年   2465篇
  1972年   2815篇
  1971年   2593篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
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   
93.
94.
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   
95.
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   
96.
97.
Polypeptides released into the culture medium of herpesvirus sylvilagus-infected cells were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of extracellular fluid from [35S]methionine- and [3H]glucosamine-labeled cell cultures. Virus-induced glycoproteins 31, 32, and 33 (molecular weights of 62,000, 59,000, and 54,000, respectively) were the most abundant species and appeared predominantly in the culture medium. This observation, together with the known cell-associated nature of herpesvirus sylvilagus, suggested that virus-induced glycoproteins 31, 32, and 33 were specifically released. Immunization of rabbits with virus-induced glycoproteins 13 (molecular weight of 130,000) and 32 resulted in the production of antibodies that neutralized viral infectivity in vitro. Both antiserum to gp13 and antiserum to gp32 immunoprecipitated gp13, gp26, gp33a, gp45, and virus-induced polypeptide 39 (molecular weights of 130,000, 77,000, 49,000, 27,000, and 36,000, respectively) from [35S]methionine-labeled cell extracts as well as virus-induced glycoproteins 31, 32, and 33 from the culture medium. In addition, membrane immunofluorescence assays indicate that an antigen(s) reactive with anti-gp13/32 serum was located on the plasma membrane of infected cells.  相似文献   
98.
99.
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