全文获取类型
收费全文 | 6213篇 |
免费 | 442篇 |
国内免费 | 2篇 |
专业分类
6657篇 |
出版年
2023年 | 38篇 |
2022年 | 80篇 |
2021年 | 177篇 |
2020年 | 85篇 |
2019年 | 128篇 |
2018年 | 161篇 |
2017年 | 125篇 |
2016年 | 217篇 |
2015年 | 239篇 |
2014年 | 304篇 |
2013年 | 380篇 |
2012年 | 423篇 |
2011年 | 399篇 |
2010年 | 260篇 |
2009年 | 219篇 |
2008年 | 276篇 |
2007年 | 273篇 |
2006年 | 226篇 |
2005年 | 229篇 |
2004年 | 193篇 |
2003年 | 147篇 |
2002年 | 178篇 |
2001年 | 153篇 |
2000年 | 139篇 |
1999年 | 111篇 |
1998年 | 50篇 |
1997年 | 46篇 |
1996年 | 34篇 |
1995年 | 44篇 |
1994年 | 44篇 |
1993年 | 34篇 |
1992年 | 92篇 |
1991年 | 77篇 |
1990年 | 90篇 |
1989年 | 71篇 |
1988年 | 81篇 |
1987年 | 78篇 |
1986年 | 73篇 |
1985年 | 70篇 |
1984年 | 60篇 |
1983年 | 33篇 |
1981年 | 27篇 |
1980年 | 36篇 |
1979年 | 45篇 |
1978年 | 32篇 |
1977年 | 36篇 |
1976年 | 34篇 |
1974年 | 33篇 |
1973年 | 33篇 |
1972年 | 31篇 |
排序方式: 共有6657条查询结果,搜索用时 0 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.
3.
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
4.
Chromosome characterization in Acestrorhynchinae and Cynopotaminae (Pisces, Characidae) 总被引:1,自引:0,他引:1
The karyotypes of six species of Acestrorhynchinae ( Acestrorhynchus alus, A. lacustris, Oligosarcus hepsetus, O. jenynsii, O. macrolepis and O. pinloi ) and of one species of Cynopotaminae ( Galeocharax knerii ) were studied. The six Acestrorhynchinae species have 2 n = 50, while Galeocharax knerii has 2 n = 52 chromosomes. Some chromosomal characteristics were detected which permit establishing some karyotypic relationships among the different species investigated. Thus, among the Acestrorhynchinae, the four Oligosarcus species are relatively more related to one another than the two Acestrorhynchus species, at least with respect to the cytogenetic data considered. On the basis of the methods used, no sex chromosome heteromorphism was detected in the species for which a comparative study between male and female specimens was possible. 相似文献
5.
Leandro Neves Faria Marlon Gomes Da Rocha Quirijn De Jong Van Lier Derblai Casaroli 《Plant and Soil》2010,331(1-2):299-311
Correct modeling of root water uptake partitioning over depth is an important issue in hydrological and crop growth models. Recently a physically based model to describe root water uptake was developed at single root scale and upscaled to the root system scale considering a homogeneous distribution of roots per soil layer. Root water uptake partitioning is calculated over soil layers or compartments as a function of respective soil hydraulic conditions, specifically the soil matric flux potential, root characteristics and a root system efficiency factor to compensate for within-layer root system heterogeneities. The performance of this model was tested in an experiment performed in two-compartment split-pot lysimeters with sorghum plants. The compartments were submitted to different irrigation cycles resulting in contrasting water contents over time. The root system efficiency factor was determined to be about 0.05. Release of water from roots to soil was predicted and observed on several occasions during the experiment; however, model predictions suggested root water release to occur more often and at a higher rate than observed. This may be due to not considering internal root system resistances, thus overestimating the ease with which roots can act as conductors of water. Excluding these erroneous predictions from the dataset, statistical indices show model performance to be of good quality. 相似文献
6.
7.
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
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