全文获取类型
收费全文 | 236篇 |
免费 | 18篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 17篇 |
2012年 | 17篇 |
2011年 | 16篇 |
2010年 | 12篇 |
2009年 | 13篇 |
2008年 | 10篇 |
2007年 | 10篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有254条查询结果,搜索用时 31 毫秒
251.
Present knowledge in the field of vascular endothelial cells is reviewed. The role of endothelial cells in the synthesis of
matrix proteins and glycosaminoglycans is described. Endothelial cells play a considerable role in the processes of coagulation
and fibrinolysis. They also interact with neurotransmitters and vasomotoric substances, and participate in inflammation and
immunological responses. They procuce several different growth factors. Their role in lipoprotein metabolism is of special
importance to research into atherosclerosis. 相似文献
252.
Ingrid Olsen Seetha V. Balasingham Tonje Davidsen Ephrem Debebe Einar A. Rødland Dick van Soolingen Kristin Kremer Ingrun Alseth & Tone Tønjum 《FEMS immunology and medical microbiology》2009,56(2):151-161
The ability to repair DNA damage is likely to play an important role in the survival of facultative intracellular parasites because they are exposed to high levels of reactive oxygen species and nitrogen intermediates inside phagocytes. Correcting oxidative damage in purines and pyrimidines is the primary function of the enzymes formamidopyrimidine (faPy)–DNA glycosylase (Fpg) and endonuclease VIII (Nei) of the base excision repair pathway, respectively. Four gene homologs, belonging to the fpg/nei family, have been identified in Mycobacterium tuberculosis H37Rv. The recombinant protein encoded by M. tuberculosis Rv2924c , termed Mtb-Fpg1, was overexpressed, purified and biochemically characterized. The enzyme removed faPy and 5-hydroxycytosine lesions, as well as 8-oxo-7,8-dihydroguanine (8oxoG) opposite to C, T and G. Mtb-Fpg1 thus exhibited substrate specificities typical for Fpg enzymes. Although Mtb-fpg1 showed nearly complete nucleotide sequence conservation in 32 M. tuberculosis isolates, the region upstream of Mtb-fpg1 in these strains contained tandem repeat motifs of variable length. A relationship between repeat length and Mtb-fpg1 expression level was demonstrated in M. tuberculosis strains, indicating that an increased length of the tandem repeats positively influenced the expression levels of Mtb-fpg1 . This is the first example of such a tandem repeat region of variable length being linked to the expression level of a bacterial gene. 相似文献
253.
Kjell Einar Erikstad Hanno Sandvik Tone Kristin Reiertsen Jan Ove Bustnes Hallvard Str?m 《Proceedings. Biological sciences / The Royal Society》2013,280(1769)
In long-lived species, any negative effect of pollution on adult survival may pose serious hazards to breeding populations. In this study, we measured concentrations of various organochlorines (OCs) (polychlorinated biphenyl and OC pesticides) in the blood of a large number of adult glaucous gulls (Larus hyperboreus) breeding on Bjørnøya (Bear Island) in the Norwegian Arctic, and modelled their local survival using capture–recapture analysis. Survival was negatively associated with concentrations of OCs in the blood. The effect of OCs was nonlinear and evident only among birds with the highest concentrations (the uppermost deciles of contamination). The threshold for depressed survival differed between the sexes, with females being more sensitive to contamination. For birds with lower OC concentration, survival was very high, i.e. at the upper range of survival rates reported from glaucous and other large gull species in other, presumably less contaminated populations. We propose two non-exclusive explanations. First, at some threshold of OC concentration, parents (especially males) may abandon reproduction to maximize their own survival. Second, high contamination of OC may eliminate the most sensitive individuals from the population (especially among females), inducing a strong selection towards high-quality and less sensitive phenotypes. 相似文献
254.
Does collembolan grazing influence nitrogen fixation by cyanobacteria in the high Arctic? 总被引:1,自引:1,他引:0
A field experiment was performed to test whether cyanobacterial nitrogen fixation rates increase or decrease when exposed
to low and moderate microarthropod grazing intensities. The densities of naturally occurring Collembola, i.e. Hypogastrura viatica, were manipulated on a salt marsh covered with cyanobacteria in the high Arctic, Svalbard. Nitrogen-fixation rates in grazed
cyanobacterial crust were measured and used as an indirect measurement of cyanobacterial biomass on three dates during one
summer. After 30 days, a second order polynomial regression gave a good fit to the data, indicating an increase in nitrogen-fixation
rates at low/intermediate grazing pressures and a decrease at high grazing pressures. Thus, grazing collembolans may influence
the nitrogen-fixation rates in an arctic salt-marsh community. Although based on a small set of data, the study indicates
a compensatory fixation at low grazing pressures followed by a reduction at high grazing pressures.
Accepted: 21 March 2000 相似文献