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   1128869篇
  免费   93145篇
  国内免费   1356篇
  2021年   17569篇
  2020年   12525篇
  2019年   16084篇
  2018年   16628篇
  2017年   15369篇
  2016年   27222篇
  2015年   41758篇
  2014年   49740篇
  2013年   76010篇
  2012年   29511篇
  2011年   16224篇
  2010年   40949篇
  2009年   43123篇
  2008年   16381篇
  2007年   13633篇
  2006年   20377篇
  2005年   21542篇
  2004年   20959篇
  2003年   18690篇
  2002年   16911篇
  2001年   21055篇
  2000年   17991篇
  1999年   21565篇
  1998年   23902篇
  1997年   23686篇
  1996年   23502篇
  1995年   21617篇
  1994年   21491篇
  1993年   20505篇
  1992年   19358篇
  1991年   17819篇
  1990年   16594篇
  1989年   17747篇
  1988年   16187篇
  1987年   15275篇
  1986年   14634篇
  1985年   16740篇
  1984年   18001篇
  1983年   16084篇
  1982年   18164篇
  1981年   17777篇
  1980年   16515篇
  1979年   13963篇
  1978年   14334篇
  1977年   14032篇
  1976年   13383篇
  1975年   12336篇
  1974年   12400篇
  1973年   12856篇
  1972年   10608篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Studies of HIV prevention interventions such as pre-exposure prophylaxis (PREP) and circumcision in India are limited. The present study sought to investigate Indian truck-drivers initial commitment to PREP and circumcision utilizing the AIDS Risk Reduction Model. Ninety truck-drivers completed an in-depth qualitative interview and provided a blood sample for HIV and HSV-2 testing. Truck-drivers exhibited low levels of initial commitment towards PREP and even lower for circumcision. However, potential leverage points for increasing commitment were realized in fear of infecting family rather than self, self-perceptions of risk, and for PREP focusing on cultural beliefs towards medication and physicians. Cost was a major barrier to both HIV prevention interventions. Despite these barriers, our findings suggest that the ARRM may be useful in identifying several leverage points that may be used by peers, health care providers and public health field workers to enhance initial commitment to novel HIV prevention interventions in India.  相似文献   
952.
953.
Six acapsular strains ofCryptococcus neoformans obtained by chemical mutagenesis failed to produce a capsulein vivo and were avirulent in mice following high dose intramuscular, intraperitoneal or intravenous inoculation. Peritoneal granulomas were observed in all animals inoculated with the acapsular mutants. These granulomas were characterized by a large central mass consisting of intact, degenerating and necrotic yeast cells. This was surrounded by concentric layers of a broad band of histiocytes, a narrow band of fibroblasts, and around the periphery, a mass of lymphocytes and plasma cells. These isolates did not revert to an encapsulated or virulent state after more than a year of subculturing or 18 passages through mice.  相似文献   
954.
955.
A gel filtration method has been developed for the complete removal of sodium dodecyl sulfate (SDS) from proteins and peptides. The protein or peptide (20 μg–10 mg) containing SDS (up to 30–60 mg) is dissolved in a mixture of propionic acid, formic acid, and water (2:1:2, vv). Under these conditions, protein-SDS (or peptide-SDS) complexes, as well as SDS micelles, are dissociated. Subsequently, protein and SDS can be separated on a small Sephadex G-25 superfine column. The recovery of protein is typically 90% or more.  相似文献   
956.
957.
958.
Summary The production of acetate from the fermentation of lactate by Gluconobacter oxydans was studied. Batch experiments showed that glucose was the preferred substrate compared to lactate. A fed-batch culture was fed with a mixture of glucose and lactate followed by periodic addition of lactate. The maximum productivity of acetate was 0.16 g/l h but this value decreased during the fedbatch culture due to growth inhibition by acetate.  相似文献   
959.
A key environmental factor in inducing final fruiting body differentiation in the migrating slugs of cellular slime molds is loss of contact with a surface film of water. If the slug tip reaches above the water film, fruiting tends to occur, but if it stays in contact with the surface water, continued migration is favored. Light is effective in promoting fruiting only if the phototactic slugs orient away from surface (as with overhead light) and therefore, only indirectly affects differentiation.  相似文献   
960.
The pericarp of Chinese gooseberries is green due to the presenceof low concentrations of chlorophylls. On a f. wt basis thereis about 1.5 times more tetrapyrollic pigments (chlorophyllsand related compounds) in the outer pericarp than in the innerpericarp, whereas the carotenoid pigment values only showed1.25 times more in the outer than in the inner part of the fruit.The drying of Chinese gooseberries at 40 °C for 40 h resultedin the loss of at least half the tetrapyrollic pigments andof carotenoids. Chlorophylls a and b were converted to chlorophyllides,pheophytins and pheophorbides. Chloroplasts in the outer pericarp are clustered closely aroundthe nucleus and have a well-defined grana and inter-granal membranesystem. In the inner pericarp the chloroplasts are again clusteredaround the nucleus and there is a proliferation of inter-granalmembranes. In dried tissue the limiting membrane of chloroplastswas completely dispersed whereas some of the internal membranesremained intact. Actinidia chinensis Planch., Chinese gooseberry, Kiwi fruit, pigments, chloroplast structure  相似文献   
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