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   649481篇
  免费   75088篇
  国内免费   358篇
  724927篇
  2016年   7054篇
  2015年   9753篇
  2014年   11347篇
  2013年   16712篇
  2012年   18674篇
  2011年   18833篇
  2010年   12701篇
  2009年   11903篇
  2008年   17017篇
  2007年   17441篇
  2006年   16676篇
  2005年   16089篇
  2004年   15750篇
  2003年   15576篇
  2002年   15042篇
  2001年   27309篇
  2000年   27529篇
  1999年   22427篇
  1998年   8345篇
  1997年   8700篇
  1996年   8479篇
  1995年   7767篇
  1994年   7932篇
  1993年   7770篇
  1992年   19347篇
  1991年   18569篇
  1990年   18440篇
  1989年   18308篇
  1988年   16899篇
  1987年   16349篇
  1986年   15153篇
  1985年   15324篇
  1984年   12624篇
  1983年   11211篇
  1982年   8690篇
  1981年   7983篇
  1980年   7543篇
  1979年   12551篇
  1978年   9849篇
  1977年   9085篇
  1976年   8755篇
  1975年   9451篇
  1974年   10145篇
  1973年   9961篇
  1972年   9179篇
  1971年   8184篇
  1970年   7243篇
  1969年   6992篇
  1968年   6308篇
  1967年   5550篇
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
101.
102.
103.
104.
Synaptonemal complexes and meiosis in myxomycetes   总被引:4,自引:0,他引:4  
Synaptonemal complexes (SC) have been observed in spores 18–24 hr past cleavage in natural fruitings of Physarum cinereum, P. bogoriense, Hemitrichia stipitata, Tubifera ferruginosa, and Arcyria incarnata. Laboratory fruitings of Arcyria cinerea, Stemonitis herbatica, and a homothallic isolate of Physarum pusillum also have SC's present in spores during the same postcleavage period. The presence of these paired chromosomes of meiotic prophase in spores of species collected in nature and in a diversity of taxa suggests that the usual position of meiosis in Myxomycetes is inside the postcleavage spore. Criteria are proposed for evaluating the validity of the SC as an indicator of meiosis.  相似文献   
105.
106.
As part of systematic studies of the genus Porphyrain New Zealand, constituent sugar analyses of cell wall polysaccharidesin situ in dry thalli were found to yield data that weretaxonomically informative. Variation in constituent sugar levels betweenspecieswas sufficient in some cases to be useful in species differentiation. Thereproductive state of thallus regions had a significant impact on the levels ofconstituent sugars, whereas storage of dried thalli for eight months had noeffect. Three epiphytic taxa currently classified as species ofPorphyra appear to be incorrectly placed within the genus,as their constituent sugars and the levels of these sugars differed markedlyfrom those of all other species examined.  相似文献   
107.
Peanut (Arachis hypogaea) agglutinin (PNA) is extensively used as tumour marker as it strongly recognises the cancer specific T antigen (Galβ1→3GalNAc-), but not its sialylated version. However, an additional specificity towards Galβ1→4GlcNAc (LacNAc), which is not tumour specific, had been attributed to PNA. For correct interpretation of lectin histochemical results we examined PNA sugar specificity using naturally occurring or semi-synthetic glycoproteins, matrix-immobilised galactosides and lectin-binding tissue glycoproteins, rather than mono- or disaccharides as ligands. Dot-blots, transfer blots or polystyrene plate coatings of the soluble glycoconjugates were probed with horse-radish peroxidase (HRP) conjugates of PNA and other lectins of known specificity. Modifications of PNA-binding glycoproteins, including selective removal of O-linked oligosaccharides and treatment with glycosidases revealed that Galβ1→4GlcNAc (LacNAc) was ineffective while terminal α-linked galactose (TAG) as well as exposed T antigen (Galβ1→3 GalNAc-) was excellent as sugar moiety in glycoproteins for their recognition by PNA. When immobilised, melibiose was superior to lactose in PNA binding. Results were confirmed using TAG-specific human serum anti-α-galactoside antibody.  相似文献   
108.
109.
110.
A rapid, simple and sensitive reversed-phase high-performance liquid chromatographic (HPLC) method has been developed for the measurement of acyclovir concentrations in human plasma and its use in bioavailability studies is evaluated. Unchanged acyclovir has been quantified without the introduction of an internal standard using the present method. Human plasma proteins were selectively precipitated by the addition of 7% perchloric acid to spiked plasma samples or to the plasma samples obtained after acyclovir administration to human volunteers and the mixture was spun at 1000 g for 10 min. The supernatant was directly injected into a Novaflex C18 column and detected at 254 nm. The mobile phase consisted of octane sulfonic acid buffer (pH 2.5) and methanol (92:08). The limit of quantitation for acyclovir in plasma was 20 ng/ml, which enabled the determination of the area under the curve (AUC) more precisely, that is, it is much closer to its extrapolated value. The present method has been successfully applied to samples from bioavailability studies.  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