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   923217篇
  免费   96989篇
  国内免费   533篇
  2018年   8836篇
  2017年   8617篇
  2016年   13153篇
  2015年   18984篇
  2014年   21400篇
  2013年   28312篇
  2012年   30561篇
  2011年   29027篇
  2010年   20298篇
  2009年   18934篇
  2008年   24919篇
  2007年   25849篇
  2006年   24198篇
  2005年   28674篇
  2004年   27231篇
  2003年   24521篇
  2002年   21913篇
  2001年   40263篇
  2000年   39841篇
  1999年   32043篇
  1998年   10874篇
  1997年   11300篇
  1996年   10503篇
  1995年   9823篇
  1994年   9458篇
  1993年   9486篇
  1992年   26507篇
  1991年   25767篇
  1990年   25222篇
  1989年   24550篇
  1988年   22852篇
  1987年   21599篇
  1986年   20173篇
  1985年   19940篇
  1984年   16326篇
  1983年   13934篇
  1982年   10433篇
  1981年   9427篇
  1980年   8986篇
  1979年   15662篇
  1978年   12129篇
  1977年   11041篇
  1976年   10386篇
  1975年   11440篇
  1974年   12662篇
  1973年   12341篇
  1972年   11416篇
  1971年   10530篇
  1970年   9126篇
  1969年   8882篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The immunization of mice with the protein fraction of B. pertussis strain 305 has made it possible to obtain hybridomas producing monoclonal antibodies to B. pertussis antigens. Ascitic fluids containing monoclonal antibodies react in the ELISA in high titers and actively agglutinate B. pertussis strains 305 and 475.  相似文献   
52.
The preservation of purine ring as purine bases appears to be a common feature of camel liver. Hepatic guanine appears to be actively converted into GMP in the camel rather than further degraded. The limiting step of guanine degradation appears to be the lack of hepatic guanase activity. Higher purine bases over uric acid ratios were found in camel urine with respect to those of zebu.  相似文献   
53.
54.
Abstract. Nutrient conservation in vegetation affects rates of litter decomposition and soil nutrient availability. Although resorption has been traditionally considered one of the most important plant strategies to conserve nutrients in temperate forests, long leaf life‐span and low nutrient requirements have been postulated as better indicators. We aimed at identifying nutrient conservation strategies within characteristic functional groups of NW Patagonian forests on Andisols. We analysed C‐, N‐, P‐, K‐ and lignin‐concentrations in mature and senescent leaves of ten native woody species within the functional groups: broad‐leaved deciduous species, broad‐leaved evergreens and conifers. We also examined mycorrhizal associations in all species. Nutrient concentration in mature leaves and N‐ resorption were higher in broad‐leaved deciduous species than in the other two functional groups. Conifers had low mature leaf nutrient concentrations, low N‐resorption and high lignin/N ratios in senescent leaves. P‐ and K‐resorptions did not differ among functional groups. Broad‐leaved evergreens exhibited a species‐dependent response. Nitrogen in mature leaves was positively correlated with both N resorption and soil N‐fertility. Despite the high P‐retention capacity of Andisols, N appeared to be the more limiting nutrient, with most species being proficient in resorbing N but not P. The presence of endomycorrhizae in all conifers and the broad‐leaved evergreen Maytenus boaria, ectomycorrhizae in all Nothofagus species (four deciduous, one evergreen), and cluster roots in the broad‐leaved evergreen Lomatia hirsuta, would be possibly explaining why P is less limiting than N in these forests.  相似文献   
55.
The study of the specific epidemiological and clinical features of Q fever revealed the existence of an active focus of infection among humans due to their contacts with agricultural animals in one of the districts of the region. The focus was manifested by group morbidity among the cattle-tending personnel of a dairy farm. The source of this infection was cattle. The infection was transferred mainly through the air. The disease took a moderately severe course. The study of the rickettsial contamination of humans, animals and ticks suggested the presence of the active epidemic process and made it possible to work out concrete antiepidemic measures.  相似文献   
56.
57.
58.
59.
60.
Regulation of many cell systems has been shown to be mediated by Inositol 1,4,5-trisphosphate which causes a release of calcium from intracellular sites. We have shown that release of Ca2+ from sarcoplasmic reticulum microsomes was not stimulated by IP3. The phorbol ester, TPA, also had no effect on Ca2+ release or Ca2+ ATPase activity. Thus, it is unlikely that the breakdown of polyphosphatidylinositides serves as a second messenger to mediate release of Ca2+ in skeletal muscle.  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