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   1634篇
  免费   202篇
  1836篇
  2022年   17篇
  2021年   36篇
  2020年   21篇
  2018年   31篇
  2017年   30篇
  2016年   38篇
  2015年   52篇
  2014年   54篇
  2013年   75篇
  2012年   73篇
  2011年   77篇
  2010年   58篇
  2009年   42篇
  2008年   69篇
  2007年   75篇
  2006年   71篇
  2005年   53篇
  2004年   50篇
  2003年   67篇
  2002年   43篇
  2001年   44篇
  2000年   48篇
  1999年   38篇
  1998年   19篇
  1997年   13篇
  1996年   15篇
  1995年   14篇
  1993年   14篇
  1992年   30篇
  1991年   34篇
  1990年   26篇
  1989年   35篇
  1988年   29篇
  1987年   40篇
  1986年   29篇
  1985年   27篇
  1984年   22篇
  1983年   15篇
  1982年   15篇
  1981年   14篇
  1980年   15篇
  1979年   25篇
  1978年   22篇
  1977年   17篇
  1976年   16篇
  1975年   22篇
  1973年   21篇
  1972年   21篇
  1971年   14篇
  1970年   14篇
排序方式: 共有1836条查询结果,搜索用时 0 毫秒
11.
This paper describes effects of a sublethal (1.2 mg 1–1) organophosphate, malathion, on the ovary of an air breathing catfish, Heteropneustes fossilis. The study focuses on microscopic changes that occur on ovigerous lamellae, oocytes at different stages of development and the nucleus of the immature oocyte. Also, change in estrogen levels in blood serum is investigated. Clumping of cytoplasm appears after 24 h of exposure to malathion. Clumping intensified after 48 h. Degeneration in the follicular cells was also observed. After 72 h exposure the number of nucleoli increased, nuclear materials shrunk, oocytes became adhered. With 96 h of exposure, nuclear materials of all the oocytes shrunk to a smaller clump. The oocytes fused together, and follicular epithelium became loose and ruptured. A few atretic oocytes were visible. Radioimmunoassay of the estrogen level in blood serum after 72 h of exposure of malathion showed a reduction in the level. This study showed that the histopathological condition of the gonad is reflected in malfunctioning of the endocrine system and hormonal disbalance.  相似文献   
12.
Reverse osmosis is shown to be a viable process for the concentration of highly labile antibiotic solutions. Mathematical n10deJs of antibiotic inactivation by chemical and biological contamination are proposed and correlated with experimental data. Procedures for obtaining high antibiotic recoveries are discussed.  相似文献   
13.
A partially age-related admission policy coupled with a "single-ward" scheme for treatment and rehabilitation was introduced by the Hull geriatric department in 1970. With rare exceptions, elderly patients needing hospital care have been admitted directly to the geriatric unit, and the proportion of the retired population admitted by the general physicians has been greatly reduced. The proportion of inpatients needing continuing care has been reduced to less than 20%, the mean length of inpatient stay has fallen to under 30 days, and separate long-stay wards are no longer needed. More than 91% of patients are admitted without preceding domiciliary assessment, and only 5-6% of admissions are transferred from other units within the area.  相似文献   
14.
Effect of organophosphorus insecticide, phosphomidon (250 and 500 ppm) on human erythrocyte and plasma were studied in vitro to get insight into the cellular antioxidant defence mechanism and malondialdehyde formation. The antioxidant defence system of erythrocyte was altered as evident by depression of glutathione reductase, glucose 6 phosphate dehydrogenase, whereas the level of reduced glutathione, glutathione peroxidase, glutathione-S-transferase, superoxidedismutase and catalase were stimulated. In the case of plasma fraction, glutathione reductase, glutathione peroxidase, glutathione-s-transferase, glucose-6-phosphate dehydrogenase, superoxide dismutase and levels of reduced glutathione were significantly depressed and the malondialdehyde formation and catalase activity were elevated indicating the less adaptive response of plasma to protect it from oxidative damage.  相似文献   
15.
This report documents for the first time the in vitro autophosphorylation of purified 68 kDa hyaluronate binding protein in presence of [32P] ATP. The rate of phosphorylation is proportional to the concentration of protein and to the time of incubation up to 5 min. By both phosphoamino acid and western blot analysis with antiphosphotyrosine antibodies, we have confirmed that the phosphorylation occurs at tyrosine residues. Immunoprecipitation with anti HA binding protein antibody shows a 5 fold increase in the phosphorylation in macrophage histiocytoma compared to normal macrophage. Supplementing hyaluronate with hyaluronate binding protein in the medium is further shown to enhance total protein phosphorylation in rat histiocytoma.  相似文献   
16.
Reclassification of incompatibility group L (IncL) plasmids.   总被引:1,自引:0,他引:1  
H Richards  N Datta 《Plasmid》1979,2(2):293-295
Plasmids classified as IncL are shown to be incompatible with plasmids of IncM and we propose to reclassify them as IncM.  相似文献   
17.
The porphyrin photosensitizer, meso-Tetra (4-N-methylpyridyl) porphine tetraperchlorate binds to calf thymus DNA by intercalation and by external electrostatic association. This was concluded from the results of measruements involving Scatchard analysis, viscometry, thermal denaturation, and circular dichroism.  相似文献   
18.
19.
The present study explains the intraspecific variation in Indian Hill trout (Barilius bendelisis) on the basis of image based truss network system and D‐loop region of mtDNA. A total of 210 samples were collected from three different rivers (Teesta, Kameng and Myntudu River) of North East India in Indo‐Burma Biodiversity Hotspot. By using the software applications (tpsDig version 2.1 and PAST), a total of 25 morphometric measurements were generated from 10 landmarks. The Analysis of Variance (ANOVA), Factor Analysis (FA) and Discriminate Function Analysis (DFA) showed, out of the total variations, factor 1 explained 46.74% while factor 2 and factor 3 explained 27.14% and 11.92%, respectively. Using these variables 83.33% of the cross‐validated specimens were classified into distinct groups. Analysis of Molecular Variance (AMOVA) and pairwise Fst value for D‐loop region of mtDNA also showed high to medium level of genetic variation among the stocks and within the stocks. We conclude that the observed discrete stocks might be the result of changing environmental conditions in different rivers of the hotspot as the rivers are present at different altitudinal labels. It is also believed that the variation might be due to the construction of barrages across the river which hinder the mixing among the stocks.  相似文献   
20.
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