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   5307篇
  免费   440篇
  国内免费   258篇
  2023年   50篇
  2022年   58篇
  2021年   230篇
  2020年   175篇
  2019年   207篇
  2018年   188篇
  2017年   135篇
  2016年   211篇
  2015年   341篇
  2014年   384篇
  2013年   414篇
  2012年   504篇
  2011年   444篇
  2010年   270篇
  2009年   243篇
  2008年   267篇
  2007年   242篇
  2006年   189篇
  2005年   177篇
  2004年   166篇
  2003年   120篇
  2002年   109篇
  2001年   106篇
  2000年   93篇
  1999年   96篇
  1998年   40篇
  1997年   50篇
  1996年   42篇
  1995年   38篇
  1994年   29篇
  1993年   33篇
  1992年   41篇
  1991年   37篇
  1990年   46篇
  1989年   36篇
  1988年   23篇
  1987年   24篇
  1986年   13篇
  1985年   14篇
  1984年   10篇
  1983年   10篇
  1982年   9篇
  1981年   8篇
  1979年   14篇
  1978年   8篇
  1975年   5篇
  1973年   9篇
  1972年   6篇
  1971年   9篇
  1968年   5篇
排序方式: 共有6005条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
We have detected an RNA species, containing sequences complementary to pre-albumin intron V in poly(A)+ RNA from rat liver cytoplasm (but not in nuclear RNA). Its relative abundance roughly parallels that of mature albumin mRNA, when comparing control with acute phase preparations.  相似文献   
7.
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   
8.
Summary A laboratory experiment was conducted to study inhibition of soil urease activity by amido derivatives of phosphoric and thiophosphoric acids. Results showed that derivatives with higher amido substitutions have greater inhibitory effect on urea hydrolysis in the soils used in our study. Triamides of phosphoric and thiophosphoric acids were found to be very effective inhibitors of soil urease. These compounds seem to have potential as fertilizer amendments for inhibiting soil urease activity and for improving the efficiency of nitrogen use from urea.  相似文献   
9.
Four of six human monoclonal IgM proteins were found to react best with Klebsiella polysaccharides containing 3,4py beta DGal (pyruvic acetalated D-galactopyranose), one with Klebsiella polysaccharides with 4,6pyDGlc; the sixth is uncharacterized. The combining sites of two of these (IgMWEA and IgMNAE) were essentially indistinguishable by quantitative precipitin studies at varying pH and by quantitative precipitin inhibition assays, but the other two differed in specificity of their combining sites from these and from each other. These differences were detected by precipitin inhibition assays with 3,4py beta DGal-containing oligosaccharide alditols, the R and S isomers of methyl 4,6py alpha DGal, the R isomer of methyl 4,6py beta DGal, or the R and S isomers of methyl 4,6py alpha DGlc, and -beta DGlc. In all of these except the S isomer of methyl 4,6pyDGal and R isomer of methyl 4,6pyDGlc, the carboxyl group is axial to the plane of the acetal ring. Their specificity appears to be determined by the nonreducing ends of chains and is considered to be cavity-type.  相似文献   
10.
Additive reagents have been investigated to improve the stability of methanolic Wright's stain. The addition of ammonium halides, monoalkyiamine hydrochlorides, dialkylamine hydrochlorides or trialkylamine hydrochlorides to methanolic Wright's stain was found to enhance the stability of stain components in methanol. No change in performance is observed with these additives present. Random precipitation in the stain solution was still observed with the addition of ammonium halides and monoalkyiamine hydrochlorides. No precipitation was found in stain solutions containing hydrochlorides of most dialkylamines and trialkylamines. Of the compounds evaluated, 0.6% diethylamine hydrochloride added to methanolic stain solutions produced the most desirable overall results. Mechanisms of stabilization and precipitation in these stain solutions are proposed, Essentially, separation of the thiazine-eosinate ion pair through interaction with an appropriate additive increases stain stability. The solubilities of thiazine-eosinate or additive cation-eosinate ion pairs in methanol determine the formation of precipitate in such stain solutions.  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