全文获取类型
收费全文 | 5833篇 |
免费 | 414篇 |
国内免费 | 3篇 |
出版年
2023年 | 43篇 |
2022年 | 85篇 |
2021年 | 186篇 |
2020年 | 78篇 |
2019年 | 116篇 |
2018年 | 151篇 |
2017年 | 118篇 |
2016年 | 219篇 |
2015年 | 243篇 |
2014年 | 293篇 |
2013年 | 376篇 |
2012年 | 397篇 |
2011年 | 382篇 |
2010年 | 211篇 |
2009年 | 201篇 |
2008年 | 246篇 |
2007年 | 255篇 |
2006年 | 200篇 |
2005年 | 199篇 |
2004年 | 174篇 |
2003年 | 135篇 |
2002年 | 149篇 |
2001年 | 139篇 |
2000年 | 123篇 |
1999年 | 99篇 |
1998年 | 44篇 |
1997年 | 43篇 |
1996年 | 34篇 |
1995年 | 42篇 |
1994年 | 40篇 |
1993年 | 29篇 |
1992年 | 89篇 |
1991年 | 69篇 |
1990年 | 87篇 |
1989年 | 70篇 |
1988年 | 80篇 |
1987年 | 74篇 |
1986年 | 72篇 |
1985年 | 67篇 |
1984年 | 56篇 |
1983年 | 33篇 |
1981年 | 27篇 |
1980年 | 35篇 |
1979年 | 45篇 |
1978年 | 31篇 |
1977年 | 35篇 |
1976年 | 34篇 |
1974年 | 31篇 |
1973年 | 33篇 |
1972年 | 31篇 |
排序方式: 共有6250条查询结果,搜索用时 15 毫秒
1.
The photoacoustic spectroscopic studies of purple pigmented leaves revealed the occurrence of anthocyanins and betalains in
some local weed species growing on soils with low moisture levels. The pigmentation intensities were higher in C4 plants than in C3 plants. An inverse correlation was observed between pigmentation intensities and soil moisture levels.
This work is a part of the UNEP Research Project granted to Prof. D. O. Hall, UNEP Coordinator, Department of Plant Sciences,
King’s College; London. 相似文献
2.
A survey of cultivated heirloom tomato varieties identifies four new mutant alleles at the green-flesh locus 总被引:1,自引:0,他引:1
Cornelius S. Barry Priyanka Pandey 《Molecular breeding : new strategies in plant improvement》2009,24(3):269-276
The process of crop domestication occurs through the selection and subsequent propagation of novel alleles that improve traits
of interest. Cultivated tomato (Solanum lycopersicum), particularly heirloom varieties, exhibit a wide range of variation in fruit size, shape and color. The green-flesh mutant of tomato possesses a stay-green phenotype resulting in fruits that ripen to a red-brown color, due to the retention
of chlorophyll and the simultaneous accumulation of lycopene. The recent identification of the GREEN-FLESH gene provides a molecular tool with which to investigate the origin of a subset of cultivated tomato varieties that resemble
the green-flesh mutant. Sequence analysis of the GF locus from 26 varieties revealed the existence of four previously unidentified null alleles. This study illustrates the potential
of cultivated tomato varieties, including heritage cultivars, heirlooms, and land races, for uncovering new alleles in genes
of interest. 相似文献
3.
4.
Influence of duodenal secretions and its components on release and activities of human brush-border enzymes 总被引:1,自引:0,他引:1
The in vitro effects of human duodenal secretions and various combinations of its components on activity and release of enzymes from the human brush border were examined. Sucrase retained activity for 90 min in duodenal secretions, and maltase was almost as stable; lactase lost activity rapidly and alkaline phosphatase was of intermediate stability. Inactivation of lactase could only be partly (50%) attributed to luminal proteases, bile salts and phospholipids played no role. Rate of release of an enzyme from the brush border bore no relationship to its rate of inactivation. When individual proteases were studied, elastase was the most potent for releasing disaccharidases from the brush border; trypsin was ineffective alone but augmented the effect of elastase. Sucrase and maltase were activated by proteolytic release, but activation was abolished by simultaneous exposure of brush borders to bile salts. Lactase was released and rapidly inactivated by proteinases, while alkaline phosphatase appeared to be inactivated without significant release. These results show that there are significant interactions between luminal factors which have been inapparent when studying them in isolation. Loss of functionally useful enzyme does not follow release of sucrase or maltase from the brush border into the lumen but does follow release of lactase. Study of the susceptibility of lactase to inactivation by luminal factors in the various forms of lactose intolerance is warranted. 相似文献
5.
6.
Identification of different protein functions facilitates a mechanistic understanding of Japanese encephalitis virus (JEV) infection and opens novel means for drug development. Support vector machines (SVM), useful
for predicting the functional class of distantly related proteins, is employed to ascribe a possible functional class to Japanese encephalitis virus protein. Our study from SVMProt and available JE virus sequences
suggests that structural and nonstructural proteins of JEV genome possibly belong to diverse protein functions, are expected to occur in the life cycle of JE virus. Protein functions common to both structural and
non-structural proteins are iron-binding, metal-binding, lipid-binding, copper-binding, transmembrane, outer membrane, channels/Pores - Pore-forming toxins (proteins and peptides) group of proteins. Non-structural
proteins perform functions like actin binding, zinc-binding, calcium-binding, hydrolases, Carbon-Oxygen Lyases, P-type ATPase, proteins belonging to major facilitator family (MFS), secreting main terminal branch (MTB)
family, phosphotransfer-driven group translocators and ATP-binding cassette (ABC) family group of proteins. Whereas structural proteins besides belonging to same structural group of proteins (capsid, structural, envelope),
they also perform functions like nuclear receptor, antibiotic resistance, RNA-binding, DNA-binding, magnesium-binding, isomerase (intra-molecular), oxidoreductase and participate in type II (general) secretory pathway (IISP). 相似文献
7.
8.
9.
10.
C M van der Loos P K Das H J Houthoff 《The journal of histochemistry and cytochemistry》1987,35(11):1199-1204
For immunohistological analysis, simultaneous detection of multiple cellular epitopes, as compared to single staining of serial sections, is sometimes needed. Therefore, immunoenzyme triple-staining protocols were tested with polyclonal and monoclonal antibodies on tissue sections and cytospin preparations. Various immunoconjugates were used in different combinations of methods, of which not all proved to be suitable. Of the tested protocols, one yielded superior results for both monoclonal and polyclonal antibodies, with optimal preservation of their original avidity. The method consists of a combination of indirect, direct, and avidin-biotin complex technique. The three antigens can be distinguished clearly and selectively by the reaction products of the enzyme activities of beta-galactosidase (green), alkaline phosphatase (blue), and horseradish peroxidase (red). 相似文献