全文获取类型
收费全文 | 5820篇 |
免费 | 439篇 |
国内免费 | 2篇 |
出版年
2023年 | 31篇 |
2022年 | 53篇 |
2021年 | 147篇 |
2020年 | 64篇 |
2019年 | 96篇 |
2018年 | 127篇 |
2017年 | 100篇 |
2016年 | 185篇 |
2015年 | 207篇 |
2014年 | 273篇 |
2013年 | 336篇 |
2012年 | 379篇 |
2011年 | 364篇 |
2010年 | 213篇 |
2009年 | 208篇 |
2008年 | 259篇 |
2007年 | 274篇 |
2006年 | 211篇 |
2005年 | 213篇 |
2004年 | 190篇 |
2003年 | 143篇 |
2002年 | 174篇 |
2001年 | 159篇 |
2000年 | 144篇 |
1999年 | 122篇 |
1998年 | 54篇 |
1997年 | 54篇 |
1996年 | 42篇 |
1995年 | 52篇 |
1994年 | 45篇 |
1992年 | 92篇 |
1991年 | 80篇 |
1990年 | 92篇 |
1989年 | 72篇 |
1988年 | 84篇 |
1987年 | 79篇 |
1986年 | 77篇 |
1985年 | 72篇 |
1984年 | 62篇 |
1983年 | 39篇 |
1981年 | 32篇 |
1980年 | 41篇 |
1979年 | 49篇 |
1978年 | 33篇 |
1977年 | 37篇 |
1976年 | 36篇 |
1975年 | 30篇 |
1974年 | 33篇 |
1973年 | 34篇 |
1972年 | 33篇 |
排序方式: 共有6261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.
3.
Lina Long Douglas R. McCabe M. Eileen Dolan 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1999,731(2):128
A highly sensitive and selective method for determining 8-oxoguanine in plasma and urine was developed by high-performance liquid chromatography with electrochemical detection. The compound was separated by gradient elution on a C18 reversed-phase column with a mobile phase of acetonitrile and 0.1 M sodium acetate, pH 5.2. 8-Hydroxy-2′-deoxyguanosine was used as internal standard. 8-Oxoguanine was detected electrochemically by setting the potential to +300 mV vs. Pd reference. The sensitivity of the assay was 22 ng/ml with a signal-to-noise ratio of 7:1. The within-day relative standard deviations for 8-oxoguanine quality control samples with concentrations of 3340, 1340 and 84 ng/ml were 3.6, 4.3 and 5.7% for plasma, and 4.1, 4.6 and 6.2% for urine, respectively. The day-to-day relative standard deviations for the same samples were 3.8, 6.8 and 7.1% for plasma, and 3.9, 7.0 and 7.9% for urine, respectively. The method is designed to study the pharmacokinetics and metabolic fate of O6-benzylguanine in a phase I clinical trial. Previously, O6-benzyl-8-oxoguanine was identified as the primary metabolite of O6-benzylguanine in humans. We now demonstrate that 8-oxoguanine is a further metabolite of O6-benzylguanine. 相似文献
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.
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.
Dolan TT 《Parasitology today (Personal ed.)》1987,3(1):4-6; discussion 4