全文获取类型
收费全文 | 426641篇 |
免费 | 53583篇 |
国内免费 | 230篇 |
出版年
2018年 | 3909篇 |
2017年 | 3771篇 |
2016年 | 5202篇 |
2015年 | 7308篇 |
2014年 | 8287篇 |
2013年 | 12074篇 |
2012年 | 13029篇 |
2011年 | 13277篇 |
2010年 | 9147篇 |
2009年 | 8483篇 |
2008年 | 11732篇 |
2007年 | 12018篇 |
2006年 | 11173篇 |
2005年 | 10697篇 |
2004年 | 10195篇 |
2003年 | 10116篇 |
2002年 | 9678篇 |
2001年 | 19774篇 |
2000年 | 20063篇 |
1999年 | 15800篇 |
1998年 | 5533篇 |
1997年 | 6092篇 |
1996年 | 5783篇 |
1995年 | 5391篇 |
1994年 | 5275篇 |
1993年 | 5399篇 |
1992年 | 13383篇 |
1991年 | 13199篇 |
1990年 | 12572篇 |
1989年 | 12381篇 |
1988年 | 11284篇 |
1987年 | 10938篇 |
1986年 | 10216篇 |
1985年 | 10174篇 |
1984年 | 8519篇 |
1983年 | 7345篇 |
1982年 | 5655篇 |
1981年 | 5036篇 |
1980年 | 4862篇 |
1979年 | 8008篇 |
1978年 | 6401篇 |
1977年 | 5831篇 |
1976年 | 5496篇 |
1975年 | 6032篇 |
1974年 | 6223篇 |
1973年 | 6155篇 |
1972年 | 5555篇 |
1971年 | 5108篇 |
1970年 | 4260篇 |
1969年 | 4103篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Purification of transcription factor IIIB from HeLa cells 总被引:17,自引:0,他引:17
912.
A Santagostino G Giagnoni P Fumagalli D Pavesi E Torretta 《Biochemical and biophysical research communications》1982,104(2):577-582
The isoelectric point of the camel and the human β-endorphin, of the α-endorphin and the enkephalins were determined by analytical isoelectric focusing on 1 mm thin polyacrylamide gel slab. The difficulty of staining peptides as short as β-endorphin or smaller was overcomed using a modification of Bibring and Baxandall's or Faupel and Von Arx's staining method. The camel β-endorphin gives two bands having isoelectric point of 10.3 and 10.4, the human β-endorphin focus at pH 9.9, while α-endorphin, leu and met-enkephalin at pH 5.9, 5.5 and 5.45 respectively. The staining method described coupled with the isoelectric focusing seems to be fit for discriminating β-endorphin in a crude rat pituitary extract. 相似文献
913.
Sonia Coni Silvia Maria Serrao Zuleyha Nihan Yurtsever Laura Di Magno Rosa Bordone Camilla Bertani Valerio Licursi Zaira Ianniello Paola Infante Marta Moretti Marialaura Petroni Francesca Guerrieri Alessandro Fatica Alberto Macone Enrico De Smaele Lucia Di Marcotullio Giuseppe Giannini Marella Maroder Enzo Agostinelli Gianluca Canettieri 《Cell death & disease》2020,11(12)
914.
James J. Krupa Kevin R. Hopper Samuel B. Gruber Jason M. Schmidt James D. Harwood 《Ecology and evolution》2020,10(11):4762-4772
- Plant–animal interactions are diverse and widespread shaping ecology, evolution, and biodiversity of most ecological communities. Carnivorous plants are unusual in that they can be simultaneously engaged with animals in multiple mutualistic and antagonistic interactions including reversed plant–animal interactions where they are the predator. Competition with animals is a potential antagonistic plant–animal interaction unique to carnivorous plants when they and animal predators consume the same prey.
- The goal of this field study was to test the hypothesis that under natural conditions, sundews and spiders are predators consuming the same prey thus creating an environment where interkingdom competition can occur.
- Over 12 months, we collected data on 15 dates in the only protected Highland Rim Wet Meadow Ecosystem in Kentucky where sundews, sheet‐web spiders, and ground‐running spiders co‐exist. One each sampling day, we attempted to locate fifteen sites with: (a) both sheet‐web spiders and sundews; (b) sundews only; and (c) where neither occurred. Sticky traps were set at each of these sites to determine prey (springtails) activity–density. Ground‐running spiders were collected on sampling days. DNA extraction was performed on all spiders to determine which individuals had eaten springtails and comparing this to the density of sundews where the spiders were captured.
- Sundews and spiders consumed springtails. Springtail activity–densities were lower, the higher the density of sundews. Both sheet‐web and ground‐running spiders were found less often where sundew densities were high. Sheet‐web size was smaller where sundew densities were high.
- The results of this study suggest that asymmetrical exploitative competition occurs between sundews and spiders. Sundews appear to have a greater negative impact on spiders, where spiders probably have little impact on sundews. In this example of interkingdom competition where the asymmetry should be most extreme, amensalism where one competitor experiences no cost of interaction may be occurring.
915.
N.m.r. studies of metabolism in perfused organs 总被引:1,自引:0,他引:1
J J Ackerman P J Bore D G Gadian T H Grove G K Radda 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1980,289(1037):425-436
Several metabolites and intracellular pH in intact organs can be studied in a non-destructive manner by phorphorus nuclear magnetic resonance (31P n.m.r.). This possibility was demonstrated by us nearly five years ago. Since then we have developed the appropriate physiological techniques and improved the n.m.r. method for the study of animal hearts and kidneys. Here we described measurements aimed at clarifying three problesm. (1) Having measured the enzyme-catalysed fluxes between phosphocreatine and ATP by the method of saturation transfer n.m.r., we examine the relations between energy supply and heart rate in the isolated perfused rat heart. (2) We describe experiments to establish the validity of the perfusion model. For the first time, we report 31P n.m.r. measurements of an in vivo rat heart and compare the results with those obtained for the perfused rat heart. (3) Ischaemia and metabolism in rabbit kidneys is investigated to establish the relation between functional and metabolic recovery after a renal transplant operation. 相似文献
916.
917.
Interaction of spin-labeled myosin with substrate 总被引:1,自引:0,他引:1
D B Stone 《Archives of biochemistry and biophysics》1970,141(1):378-380
918.
CD40 ligand-activated human monocytes amplify glomerular inflammatory responses through soluble and cell-to-cell contact-dependent mechanisms. 总被引:3,自引:0,他引:3
T Kuroiwa E G Lee C L Danning G G Illei I B McInnes D T Boumpas 《Journal of immunology (Baltimore, Md. : 1950)》1999,163(4):2168-2175
Monocytes/macrophages play a critical role in the initiation and progression of a variety of glomerulonephritides. We sought to define the interactions between physiologically activated human monocytes and glomerular mesangial cells (MC) by employing a cell culture system that permits the accurate assessment of the contribution of soluble factors and cell-to-cell contact. Human peripheral blood monocytes, primed with IFN-gamma and GM-CSF, were activated with CD40 ligand (CD40L) or TNF-alpha and cocultured with MC. CD40L-activated monocytes induced higher levels of IL-6, monocyte chemoattractant protein-1 (MCP-1) and ICAM-1 synthesis by MC. Separation of CD40L-activated monocytes from MC by a porous membrane decreased the mesangial synthesis of IL-6 by 80% and ICAM-1 by 45%, but had no effect on MCP-1. Neutralizing Abs against the beta 2 integrins, LFA-1 and Mac-1, decreased IL-6 production by 40 and 50%, respectively. Ligation of mesangial surface ICAM-1 directly enhanced IL-6, but not MCP-1, production. Simultaneous neutralization of soluble TNF-alpha and IL-1 beta decreased MCP-1 production by 55% in membrane-separated cocultures of MC/CD40L-activated monocytes. Paraformaldehyde-fixed CD40L-activated monocytes (to preserve membrane integrity but prevent secretory activity), cocultured with MC at various ratios, induced IL-6, MCP-1, and ICAM-1 synthesis by MC. Plasma membrane preparations from activated monocytes also induced mesangial IL-6 and MCP-1 synthesis. The addition of plasma membrane enhanced TNF-alpha-induced mesangial IL-6 production by approximately 4-fold. Together, these data suggest that the CD40/CD40L is essential for optimal effector function of monocytes, that CD40L-activated monocytes stimulate MC through both soluble factors and cell-to-cell contact mediated pathways, and that both pathways are essential for maximum stimulation of MC. 相似文献
919.
Using affinity capillary electrophoresis to study the interaction of the extracellular binding domain of erythropoietin receptor with peptides. 总被引:1,自引:0,他引:1
G W Caldwell P A McDonnell J A Masucci D L Johnson L K Jolliffe 《Journal of biochemical and biophysical methods》1999,40(1-2):17-25
We have shown that affinity capillary electrophoresis (ACE) can be utilized to screen peptides that bind to the extracellular binding domain of the erythropoietin receptor (EBP). The comparison of the cyclic peptides GGTYSCHFGPLTWVCKPQGG (EMP1) GGTYSCHFGPLTAVCKPQGG (EMP13), and LGRKYSCHFGPLTWVCQPAKKD (EMP37) with the linear peptides HFGPLTWV (EMP26) and FMRF as ACE buffer additives were investigated. When EMP1 and EMP37 were the buffer additives, an abrupt change in the electrophoretic mobility of EBP was observed in the electropherogram. When EMP13, EMP26, and FMRF were examined under identical ACE conditions as EMP1 and EMP37, no significant change in the electrophoretic mobility of EBP was observed. These results correlate well with previously reported IC50 competitive binding data; that is, EMP1 and EMP37 bind to EBP while EMP13 and EMP26 bind very weakly. These observations strongly infer that peptide.EBP dimerization were induced by EMP1, and EMP37 but not by EMP13, EMP26 or FMRF. This ACE method provides a rapid tool for the detection of small peptides or drugs that bind to EBP. 相似文献
920.
Mutational, kinetic, and chemical modification experiments show that one of the three-way helical junctions in the Neurospora VS ribozyme contains a uridine turn that is important for organizing the functional three-dimensional structure of this junction. Disruption of the uridine turn disrupts the structure of the junction and decreases the self-cleavage activity of the ribozyme; however, substitution of the uridine turn with a variety of different hairpins, thereby transforming the three-way junction into a four-way junction, maintains catalytic activity. Chemical modification structure probing reveals that both the native junction and the hairpin-containing junction support the same tertiary interactions required elsewhere in the ribozyme for catalysis. These observations show that functionally equivalent three-dimensional RNA structures can be built from different secondary structure elements. 相似文献