全文获取类型
收费全文 | 14086篇 |
免费 | 1259篇 |
国内免费 | 3篇 |
专业分类
15348篇 |
出版年
2022年 | 161篇 |
2021年 | 283篇 |
2020年 | 155篇 |
2019年 | 190篇 |
2018年 | 245篇 |
2017年 | 189篇 |
2016年 | 310篇 |
2015年 | 594篇 |
2014年 | 651篇 |
2013年 | 799篇 |
2012年 | 968篇 |
2011年 | 867篇 |
2010年 | 570篇 |
2009年 | 546篇 |
2008年 | 750篇 |
2007年 | 691篇 |
2006年 | 634篇 |
2005年 | 562篇 |
2004年 | 487篇 |
2003年 | 542篇 |
2002年 | 476篇 |
2001年 | 260篇 |
2000年 | 226篇 |
1999年 | 237篇 |
1998年 | 141篇 |
1997年 | 123篇 |
1996年 | 97篇 |
1995年 | 111篇 |
1994年 | 113篇 |
1993年 | 110篇 |
1992年 | 181篇 |
1991年 | 172篇 |
1990年 | 145篇 |
1989年 | 145篇 |
1988年 | 154篇 |
1987年 | 148篇 |
1986年 | 120篇 |
1985年 | 99篇 |
1984年 | 117篇 |
1983年 | 104篇 |
1981年 | 81篇 |
1979年 | 83篇 |
1978年 | 91篇 |
1977年 | 91篇 |
1975年 | 88篇 |
1974年 | 96篇 |
1973年 | 98篇 |
1972年 | 91篇 |
1971年 | 95篇 |
1969年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
11.
12.
13.
Several physiological stimuli, including neuronal depolarization, increase the production of phosphatidate (PA) from phosphatidylinositol (PI) and increase calcium fluxes across cell membranes. To determine if breakdown of PI is required for neuronal calcium uptake, we tested inhibitors of PI-specific phospholipase C on depolarization-dependent uptake of calcium by isolated brain synaptosomes. At a concentration of 0.1 mM these inhibitors reduced calcium uptake produced by depolarization for 1 to 3 sec, but did not affect uptake due to more prolonged depolarization. Exogenous PA also stimulated calcium accumulation by synaptosomes and this uptake was not reduced by the enzyme inhibitors. These results suggest that the rapid calcium influx produced by neuronal depolarization may be mediated by the breakdown of PI. 相似文献
14.
15.
16.
Caroline van Haaften-Day Peter Russell Susan Carr Lesley Wright 《In vitro cellular & developmental biology. Plant》1988,24(10):965-971
Summary A cell line derived from a human ovarian carcinosarcoma was established in tissue culture and in nude mice. Two sublines,
LDF and HDF, separated by discontinuous density centrifugation were also established from the parent line JoN. The cloning
efficiency of the JoN line was 21%. Morphologic features of adenocarcinoma cells characteristic of the parent JoN cells were
retained in the sublines and clones; all lines showed the same karyotype and DNA content (pseudodiploid and pseudotetraploid).
Keratin, as demonstrated immunohistochemically, was strongly expressed in the parent line JoN and the xenograft tumor, but
not at all in the LDF sublines and only moderately in the HDF sublines. Vimentin, however, was expressed in neither the parent
line JoN nor the xenograft tumor, but was present in both sublines. Transglutaminase and plasminogen activator activity was
high in the parent line JoN. Neither, sublines nor clones showed the same high enzyme activity as the parent line. It is concluded
that this human tumor line JoN is comprised of epithelial cells, capable of multidirectional differentiation. 相似文献
17.
J Fawcett A L Harris R Bicknell 《Biochemical and biophysical research communications》1991,174(2):903-908
The isolation of human adrenal capillary endothelial (HACE) cells without resort to fluorescence activated cell sorting is described, together with their properties in culture. HACE cells were isolated by plating collagenase digests at high dilution in the presence of endothelial cell growth supplement, followed by clonal selection of endothelial colonies. HACE cells exhibit a typical endothelial 'cobblestone' morphology at confluence and formed 'tubes' when seeded onto 'Matrigel'. They are positive for human MHC1, and the endothelial markers ENDOCAM (CD31) and weakly CD34, they also take up dil-acetyl low density lipoprotein but are negative for Factor VIII. Their growth is strongly stimulated by FGF and inhibited by TGF-beta I. Like their much studied bovine counterparts they are robust in culture, retaining the properties described up to senescence. HACE cells provide a readily available alternative to human umbilical vein endothelial cells in that they are easily isolated pure and in quantity. They should be particularly useful in studies where human capillary, as opposed to large vessel endothelium, is required. 相似文献
18.
19.
20.
Transient increase in phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol trisphosphate during activation of human neutrophils 总被引:13,自引:0,他引:13
A E Traynor-Kaplan B L Thompson A L Harris P Taylor G M Omann L A Sklar 《The Journal of biological chemistry》1989,264(26):15668-15673
We recently showed that phosphatidylinositol trisphosphate (PIP3) was present in a unique lipid fraction generated in neutrophils during activation. Here, we demonstrate that the band containing this fraction isolated from thin layer chromatography consists primarily of PIP3 and that only small amounts of radiolabeled PIP3 exist prior to activation. In addition, high performance liquid chromatography of deacylated phospholipids from stimulated cells reveals an increase in a fraction eluting ahead of glycerophosphoinositol 4,5-P2. After removal of the glycerol we found that it coeluted with inositol 1,3,4-P3 when resubjected to high performance liquid chromatography. Thus, we have detected a second, novel form of phosphatidylinositol bisphosphate in activated neutrophils, PI-(3,4)P2. The elevation of PIP3 through the formyl peptide receptor is blocked by pretreatment with pertussis toxin, implicating mediation of the increase in PIP3 by a guanosine triphosphate-binding (G) protein. The rise in PIP3 is not secondary to calcium elevation. Buffering the rise in intracellular calcium did not diminish the increase in PIP3. The elevation of PIP3 appears to occur during activation with physiological agonists, its level varying with the degree of activation. Leukotriene B4, which elicits many of the same responses as stimulation of the formyl peptide receptor but with minimal oxidant production, stimulates a much attenuated rise in PIP3. Isoproterenol, which inhibits oxidant production also reduces the rise in PIP3. Hence formation of PI(3,4)P2 and PIP3 (presumed to be PI(3,4,5)P3) correlates closely with the early events of neutrophil activation. 相似文献