全文获取类型
收费全文 | 3958篇 |
免费 | 322篇 |
出版年
2022年 | 23篇 |
2021年 | 48篇 |
2020年 | 34篇 |
2019年 | 36篇 |
2018年 | 62篇 |
2017年 | 47篇 |
2016年 | 95篇 |
2015年 | 161篇 |
2014年 | 186篇 |
2013年 | 205篇 |
2012年 | 298篇 |
2011年 | 271篇 |
2010年 | 180篇 |
2009年 | 163篇 |
2008年 | 213篇 |
2007年 | 198篇 |
2006年 | 202篇 |
2005年 | 211篇 |
2004年 | 192篇 |
2003年 | 189篇 |
2002年 | 200篇 |
2001年 | 28篇 |
2000年 | 31篇 |
1999年 | 47篇 |
1998年 | 56篇 |
1997年 | 30篇 |
1996年 | 37篇 |
1995年 | 28篇 |
1994年 | 41篇 |
1993年 | 35篇 |
1992年 | 29篇 |
1991年 | 25篇 |
1990年 | 20篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 29篇 |
1984年 | 45篇 |
1983年 | 18篇 |
1982年 | 39篇 |
1981年 | 28篇 |
1980年 | 30篇 |
1979年 | 21篇 |
1978年 | 21篇 |
1977年 | 28篇 |
1976年 | 27篇 |
1975年 | 22篇 |
1974年 | 21篇 |
1973年 | 27篇 |
1970年 | 18篇 |
排序方式: 共有4280条查询结果,搜索用时 15 毫秒
41.
42.
The effects of enzymatic attack and of shear during the isolation and deproteinization of DNA have been investigated. Different methods of disaggregating DNA have been studied, and conditions under which reaggregation can occur are discussed. It was found that shaking with chloroform-octanol does not degrade DNA from the seven sources studied; that light scattering yields valid weight-average molecular weights for these samples; and that, when disaggregated, the molecular weights of these samples are in the range 1.2-2.4 million and the length-to-mass ratios are high. 相似文献
43.
44.
45.
46.
Cora-Jean S. Edgell Jill E. Haizlip C. Robert Bagnell Joan P. Packenham Paul Harrison Barry Wilbourn Victoria J. Madden 《In vitro cellular & developmental biology. Plant》1990,26(12):1167-1172
Summary Weibel-Palade bodies are ultrastructurally defined organelles found only in vascular endothelial cells. Because endothelium
in corpo is very dispersed, isolation and further characterization of this organelle has been dependent on increasing the
number of cells in culture. However, primary isolates of endothelial cells have a limited replication potential and tend to
senesce in culture. In this report, EA.hy926, a continuously replicating cell line derived from human endothelium, is shown
to contain Weibel-Palade bodies. Electron micrographs demonstrate the ultrastructural characteristics of these tissue-specific
organelles and their cytoplasmic distribution in EA.hy926 cells. Von Willebrand factor, which has been shown to exist in Weibel
Palade bodies, is demonstrated by immunofluorescence in discrete rod-shaped organelles whose size, shape, and distribution
are consistent with that of Weibel-Palade bodies in primary endothelial cell cultures. Rapid release of von Willebrand factor
can be induced by calcium ionophore, and large multimeric forms of the protein are found in EA.hy926 cells. These two properties
are consistent with the function currently ascribed to Weibel Palade bodies: storage of multimerized von Willebrand factor.
Thus ultrastructural, immunologic, and functional data establish the existence of this as yet poorly understood tissue-specific
organelle in a continuous, vigorously replicating human cell line. 相似文献
47.
Functional Expression of P-Glycoprotein in an Immortalised Cell Line of Rat Brain Endothelial Cells, RBE4 总被引:5,自引:3,他引:2
David J. Begley Delphine Lechardeur Zheng-Duan Chen Christopher Rollinson †Michèle Bardoul †Françoise Roux Daniel Scherman N. Joan Abbott 《Journal of neurochemistry》1996,67(3):988-995
Abstract: The presence of P-glycoprotein in the cell plasma membrane limits the penetration of many cytotoxic substances into cells that express the gene product. There is considerable evidence also to indicate that P-glycoprotein is expressed as part of the normal blood-brain barrier in the luminal membranes of the cerebral capillary endothelial cells, where it presumably performs a protective function for the brain. This report describes the functional expression of P-glycoprotein in an immortalised cell line, RBE4, derived from rat cerebral capillary endothelial cells. The expression of P-glycoprotein is demonstrated by western immunoblotting and by immunogold and fluorescent staining with monoclonal antibodies. The cellular accumulation of [3 H]colchicine and [3 H]vinblastine is investigated and shown to be enhanced by the presence of azidothymidine, chlorpromazine, verapamil, cyclosporin A, and PSC 833 ([3'-keto-Bmt1 ]-[Val2 ]-cyclosporin) at 50 or 100 µ M concentration. It is concluded that the RBE4 cell line is a valuable tool for investigating the mechanisms of P-glycoprotein activity both in the blood-brain barrier and in multidrug resistance in general. 相似文献
48.
Dahlia Minc-Golomb Gal Yadid Ilan Tsarfaty James H. Resau Joan P. Schwartz 《Journal of neurochemistry》1996,66(4):1504-1509
Abstract: In the CNS, nitric oxide (NO) functions as both neuromodulator and neurotoxic agent. In vivo neuronal expression of NO synthase (NOS) has been attributed to constitutive NOS—both the neuronal and the endothelial types. The other class of NOS—the inducible NOS (iNOS)—is known to mediate toxic effects of NO in various tissues. In this study, we show for the first time that direct intracerebellar injection of endotoxin and cytokine (lipopolysaccharide and interferon-γ) induced in vivo neuronal expression of the iNOS gene, as demonstrated by fluorescent in situ hybridization and immunohistochemical staining analyzed by confocal laser-scanning microscopy. This raises the possibility that neuronal iNOS might contribute significantly to the vulnerability of the brain to various insults. 相似文献
49.
Analysis of total aromatic amino acid (free and bound) in some cucumber accessions selected previously for resistance to western flower thrips, Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae], indicated that low concentrations of these essential nutrients, relative to total leaf protein, were correlated with a reduction in damage by the insect. Further analysis of samples of four important horticultural crops (lettuce, tomato, pepper and cucumber) with unknown levels of resistance to thrips showed a significant genotypic variation in the concentrations of total aromatic amino acids relative to the total leaf protein. Accessions from each crop with low or high concentrations of aromatic amino acids in proteins were exposed to thrips larvae. Regression analysis showed a highly significant positive correlation between aromatic amino acid concentration in leaf protein and thrips damage, regardless of crop species. It is concluded that higher concentrations of aromatic amino acids in plant proteins are important for successful thrips development. These results provide plant breeders with a promising tool for indirect selection without using undesirable insect bioassays. 相似文献
50.
The effects of mycorrhizal roots on litter decomposition, soil biota, and nutrients in a spodosolic soil 总被引:1,自引:0,他引:1
We studied the effects of mycorrhizal pitch pine (Pinus rigida) roots on litter decomposition, microbial biomass, nematode abundance and inorganic nutrients in the E horizon material of a spodosolic soil, using field microcosms created in a regenerating pitch pine stand in the New Jersey Pinelands. Pine roots stimulated litter decomposition by 18.7% by the end of the 29 month study. Both mass loss and N and P release from the litter were always higher in the presence of roots than in their absence. Nutrient concentrations in decomposing litter were similar, however, in the presence and absence of roots, which suggests that the roots present in the with-root treatment did not withdraw nutrients directly from the litter. The soil was slightly drier in the presence of roots, but there was no discernible effect on soil microbial biomass. The effects of roots on soil extractable inorganic nutrients were inconsistent. Roots, however, were consistently associated with higher numbers of soil nematodes. These results suggest that, in soils with low total C and N contents, roots stimulate greater activity of the soil biota, which contribute, in turn, to faster litter decomposition and nutrient release.Contribution No. 95-22 from the Institute of Marine and Coastal Sciences.Contribution No. 95-22 from the Institute of Marine and Coastal Sciences. 相似文献