全文获取类型
收费全文 | 424710篇 |
免费 | 47822篇 |
国内免费 | 163篇 |
专业分类
472695篇 |
出版年
2018年 | 3902篇 |
2016年 | 5279篇 |
2015年 | 6895篇 |
2014年 | 8143篇 |
2013年 | 11229篇 |
2012年 | 12782篇 |
2011年 | 13230篇 |
2010年 | 9073篇 |
2009年 | 8426篇 |
2008年 | 12110篇 |
2007年 | 12606篇 |
2006年 | 11821篇 |
2005年 | 11300篇 |
2004年 | 11342篇 |
2003年 | 10628篇 |
2002年 | 10450篇 |
2001年 | 17417篇 |
2000年 | 17427篇 |
1999年 | 13910篇 |
1998年 | 5020篇 |
1997年 | 5269篇 |
1996年 | 4910篇 |
1995年 | 4616篇 |
1994年 | 4483篇 |
1993年 | 4536篇 |
1992年 | 11606篇 |
1991年 | 11533篇 |
1990年 | 11292篇 |
1989年 | 10906篇 |
1988年 | 10486篇 |
1987年 | 10075篇 |
1986年 | 9362篇 |
1985年 | 9231篇 |
1984年 | 7746篇 |
1983年 | 6702篇 |
1982年 | 5160篇 |
1981年 | 4616篇 |
1980年 | 4462篇 |
1979年 | 7419篇 |
1978年 | 5863篇 |
1977年 | 5396篇 |
1976年 | 5201篇 |
1975年 | 5594篇 |
1974年 | 6300篇 |
1973年 | 6166篇 |
1972年 | 5764篇 |
1971年 | 5226篇 |
1970年 | 4633篇 |
1969年 | 4574篇 |
1968年 | 4421篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
851.
852.
Up regulation of the transforming growth factor-beta 1 (TGF-β1) axis has been recognized as a pathogenic event for progression of glomerulosclerosis in diabetic nephropathy. We demonstrate that glomeruli isolated from diabetic rats accumulate up to sixfold more extracellular adenosine than normal rats. Both decreased nucleoside uptake activity by the equilibrative nucleoside transporter 1 and increased AMP hydrolysis contribute to raise extracellular adenosine. Ex vivo assays indicate that activation of the low affinity adenosine A2B receptor subtype (A2BAR) mediates TGF-β1 release from glomeruli of diabetic rats, a pathogenic event that could support progression of glomerulopathy when the bioavailability of adenosine is increased. 相似文献
853.
854.
E Shistik T Keren-Raifman G H Idelson Y Blumenstein N Dascal T Ivanina 《The Journal of biological chemistry》1999,274(44):31145-31149
The first 46 amino acids (aa) of the N terminus of the rabbit heart (RH) L-type cardiac Ca(2+) channel alpha(1C) subunit are crucial for the stimulating action of protein kinase C (PKC) and also hinder channel gating (Shistik, E., Ivanina, T., Blumenstein, Y., and Dascal, N. (1998) J. Biol. Chem. 273, 17901-17909). The mechanism of PKC action and the location of the PKC target site are not known. Moreover, uncertainties in the genomic sequence of the N-terminal region of alpha(1C) leave open the question of the presence of RH-type N terminus in L-type channels in mammalian tissues. Here, we demonstrate the presence of alpha(1C) protein containing an RH-type initial N-terminal segment in rat heart and brain by using a newly prepared polyclonal antibody. Using deletion mutants of alpha(1C) expressed in Xenopus oocytes, we further narrowed down the part of the N terminus crucial for both inhibitory gating and for PKC effect to the first 20 amino acid residues, and we identify the first 5 aa as an important determinant of PKC action and of N-terminal effect on gating. The absence of serines and threonines in the first 5 aa and the absence of phosphorylation by PKC of a glutathione S-transferase-fusion protein containing the initial segment suggest that the effect of PKC does not arise through a direct phosphorylation of this segment. We propose that PKC acts by attenuating the inhibitory action of the N terminus via phosphorylation of a remote site, in the channel or in an auxiliary protein, that interacts with the initial segment of the N terminus. 相似文献
855.
856.
E R Morey-Holton B P Halloran L P Garetto S B Doty 《Journal of applied physiology》2000,88(4):1303-1309
The rat has been used extensively as an animal model to study the effects of spaceflight on bone metabolism. The results of these studies have been inconsistent. On some missions, bone formation at the periosteal bone surface of weight-bearing bones is impaired and on others it is not, suggesting that experimental conditions may be an important determinant of bone responsiveness to spaceflight. To determine whether animal housing can affect the response of bone to spaceflight, we studied young growing (juvenile) rats group housed in the animal enclosure module and singly housed in the research animal holding facility under otherwise identical flight conditions (Spacelab Life Science 1). Spaceflight reduced periosteal bone formation by 30% (P < 0.001) and bone mass by 7% in single-housed animals but had little or no effect on formation (-6%) or mass (-3%) in group-housed animals. Group housing reduced the response of bone to spaceflight by as much as 80%. The data suggest that housing can dramatically affect the skeletal response of juvenile rats to spaceflight. These observations explain many of the discrepancies in previous flight studies and emphasize the need to study more closely the effects of housing (physical-social interaction) on the response of bone to the weightlessness of spaceflight. 相似文献
857.
A number of motile strains of Azospirillum brasilense, A. lipoferum, and A. irakense, were found to possess tyrosinase activity both on the surface of and inside the cells. A. brasilense Sp245, Sp7, and A. irakense KBC-1 each possessed two forms of tyrosinase of different molecular masses; A. lipoferum 43, A. lipoferum 59b, and A. irakense KA-3 each had a single tyrosinase form of approximately the same molecular mass; and A. brasilense Sp107 possessed a single form of tyrosinase different from all the other forms. 相似文献
858.
I R Eshba N A Kochanova K M Popov T V Bulargina E S Severin 《Biulleten' eksperimental'no? biologii i meditsiny》1987,103(5):567-569
Monoclonal antibodies against regulatory subunit of cAMP-dependent protein kinase, type II, were obtained from pig brain (R II). The immune-affinity sorbent has been synthesized on the basis of monoclonal antibodies against R II. The method was proposed for the purification of homogeneous R II with high cAMP-binding activity using immune-affinity sorbent. 相似文献
859.
In order to verify the applicability of biochemical methods for species identification of Trypanosomatidae, 13 species of monoxenic trypanosomatids plus the heteroxenous Trypanosoma cruzi were comparatively analyzed by three different biochemical methods. Insect trypanosomatids examined were: Crithidia acanthocephali, C. fasciculata (three varieties), C. luciliae luciliae, C. luciliae thermophila, C. deanei, C. oncopelti, Herpetomonas muscarum muscarum, H. megaseliae, H. samuelpessoai, H. mariadeanei, Leptomonas seymouri, L. collosoma, L. samueli, and Blastocrithidia culicis. Also included in the survey were aposymbiotic strains of C. deanei and C. oncopelti. Methods used were: electrophoretic profiling of endonuclease-generated fragments of k-DNA, esterase isoenzymes profiling, and polyacrylamide-gel electrophoresis (SDS-PAGE) of radioiodinated cell surface proteins. Interspecific but not intraspecific differences were detected by all three methods among the 13 monoxenic species examined. Thus, it is concluded that these methods can be successfully used, in addition to classical criteria, for species identification of insect trypanosomatids. 相似文献
860.