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   487663篇
  免费   47446篇
  国内免费   199篇
  535308篇
  2018年   5055篇
  2017年   4781篇
  2016年   6223篇
  2015年   6905篇
  2014年   8757篇
  2013年   12337篇
  2012年   14311篇
  2011年   14917篇
  2010年   10142篇
  2009年   9305篇
  2008年   13356篇
  2007年   13853篇
  2006年   13353篇
  2005年   12658篇
  2004年   12625篇
  2003年   12250篇
  2002年   12152篇
  2001年   24769篇
  2000年   24819篇
  1999年   19093篇
  1998年   5680篇
  1997年   5855篇
  1996年   5414篇
  1995年   4931篇
  1994年   4870篇
  1993年   4884篇
  1992年   15031篇
  1991年   15105篇
  1990年   14630篇
  1989年   14421篇
  1988年   13427篇
  1987年   12559篇
  1986年   11413篇
  1985年   11451篇
  1984年   9060篇
  1983年   7730篇
  1982年   5383篇
  1981年   4713篇
  1980年   4564篇
  1979年   8299篇
  1978年   6407篇
  1977年   5834篇
  1976年   5408篇
  1975年   6309篇
  1974年   6763篇
  1973年   6634篇
  1972年   5928篇
  1971年   5538篇
  1970年   4825篇
  1969年   4686篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
952.
953.
Trapezonotus dispar Stål, 1872 is subdivided into two subspecies, T. dispar dispar (Europe) and T. dispar breviceps Jakovlev, 1882 (= T. seductor Horváth, 1883) (Caucasus and Asia Minor). T. inglorius Vinokurov, 1990 is synonymized with T. desertus Sedienstücker, 1951.  相似文献   
954.
Efforts to develop molecular tools for genetic analysis and breeding of common bean in the tropics are still limited. The number of microsatellite markers available for the crop is small compared to other crops of similar social and economic importance. As part of a project to broaden the use of molecular tools in bean breeding, a genomic library enriched for AG/TC repeat sequences was constructed for Phaseolus vulgaris. Twenty microsatellite markers were initially developed and 10 were characterized using a panel of 85 representative accessions of the bean gene bank. The number of alleles per marker ranged from three to 10. The polymorphism information content (PIC) varied from 0.23 to 0.80. The results indicate that the new markers can be readily used in genetically analysis of common bean.  相似文献   
955.
Only 20-25% of families screened for BRCA1/2 mutations are found positive. Because only a positive result is informative, we studied the role of BRCA1/2 immunohistochemistry as an additional method for patient selection. From 53 high-risk-affected probands, 18 (34%) had available paraffin blocks of their tumors and were selected for this study. Mutation screening was done by conformation-sensitive gel electrophoresis and multiplex ligation-dependent probe amplification. For immunohistochemistry, 21 neoplastic specimens (15 breast carcinomas, 5 ovary neoplasms, and 1 rectal adenocarcinoma) were analyzed with BRCA1 (monoclonal antibody, Ab-1, oncogene) and BRCA2 (polyclonal antibody, Ab-2, oncogene) antibodies. Absence of the BRCA1 protein was confirmed in negative tumors by Western blotting. Seven patients were positive for BRCA1/2 mutations: 5 for BRCA1 and 2 for BRCA2. Four out of five positive patients had tumors negative for BRCA1 immunostaining, and the remaining 13 BRCA1-negative patients had positive BRCA1 immunostaining in all tumor samples. Sensitivity to predict for BRCA1 mutation carriers was 80%, and specificity was 100%, with a positive predictive value of 100% and a negative predictive value of 93%. This correlation was statistically significant (p=0.001). No correlation was observed for BRCA2. If larger studies confirm these results, high-risk patients with BRCA1-negative tumors should be screened first for this gene.  相似文献   
956.
We demonstrated that the membrane of Acholeplasma laidlawii PG8 and L-form of Staphylococcus aureus, both of which induce cellular immunity in BALB/c mice, were antigenically related each other. Foodpad responses of the mice immunized with a mixture of either antigen and Freund's complete adjuvant showed clearly a cross reaction when challenged with the other antigen. Cross responses to incorporate 3H-thymidine to the spleen lymphocytes of the mice immunized with either antigen occurred in the presence of the other antigen. Furthermore, the purified T cells, but not B cells, of the spleen were activated in the presence of antigen-presenting cells. These antigens existing in the membrane fractions of both microorganisms were purified by Razin's method. Finally, these membrane components of A. laidlawii and L-form of S. aureus were subjected to gel electrophoresis and transferring to nitrocellulose membrane and used to stimulate the spleen lymphocytes of the mice immunized with A. laidlawii or of non-immunized mice. The fractions representing molecular weights of approximately 45 kD, 25 kD, and 13 kD of both microorganisms consistently stimulated the lymphocytes of the immunized mice but not those of non-immunized mice.  相似文献   
957.
958.
959.
960.
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