全文获取类型
收费全文 | 5665篇 |
免费 | 727篇 |
国内免费 | 4篇 |
出版年
2022年 | 41篇 |
2021年 | 68篇 |
2019年 | 52篇 |
2018年 | 73篇 |
2017年 | 74篇 |
2016年 | 98篇 |
2015年 | 176篇 |
2014年 | 186篇 |
2013年 | 256篇 |
2012年 | 318篇 |
2011年 | 322篇 |
2010年 | 201篇 |
2009年 | 180篇 |
2008年 | 263篇 |
2007年 | 280篇 |
2006年 | 231篇 |
2005年 | 235篇 |
2004年 | 229篇 |
2003年 | 229篇 |
2002年 | 214篇 |
2001年 | 132篇 |
2000年 | 146篇 |
1999年 | 175篇 |
1998年 | 84篇 |
1997年 | 67篇 |
1996年 | 51篇 |
1995年 | 59篇 |
1994年 | 57篇 |
1993年 | 47篇 |
1992年 | 101篇 |
1991年 | 81篇 |
1990年 | 92篇 |
1989年 | 91篇 |
1988年 | 80篇 |
1987年 | 82篇 |
1986年 | 80篇 |
1985年 | 73篇 |
1984年 | 63篇 |
1983年 | 68篇 |
1982年 | 47篇 |
1981年 | 54篇 |
1980年 | 42篇 |
1979年 | 66篇 |
1978年 | 41篇 |
1976年 | 40篇 |
1974年 | 50篇 |
1973年 | 45篇 |
1972年 | 42篇 |
1970年 | 46篇 |
1968年 | 49篇 |
排序方式: 共有6396条查询结果,搜索用时 31 毫秒
1.
J M Clements S Craig A J Gearing M G Hunter C M Heyworth T M Dexter B I Lord 《Cytokine》1992,4(1):76-82
The murine macrophage inflammatory proteins-1 alpha (MIP-1 alpha) and MIP-1 beta are distinct but closely related cytokines. Partially purified mixtures of the two proteins affect neutrophil function and cause local inflammation and fever. The particular properties of MIP-1 alpha have not been well studied, although it has been identified as being identical to an inhibitor of haemopoietic stem cell growth. We have expressed MIP-1 alpha in yeast cells and purified it to sequence homogeneity. Structural analysis of this biologically active material by circular dichroism and fluorescence spectroscopy confirms that MIP-1 alpha has a very similar secondary and tertiary structure to platelet factor 4 and interleukin 8 with which it shares limited sequence homology. The in-vitro stem cell inhibitory properties have been confirmed using a range of murine progenitor cells including purified bone marrow progenitor cells (FACS-1), the FDCP-mix A4 cell line, and spleen colony forming unit (CFU-S) populations. Plateau levels of inhibition of stem cell growth were achieved using concentrations of 0.15 micrograms/ml MIP-1 alpha. We have also demonstrated that MIP-1 alpha is active in vivo: 5 micrograms of MIP-1 alpha per mouse given as a bolus injection, protects stem cells from subsequent in-vitro killing by tritiated thymidine. MIP-1 alpha was also shown to enhance the proliferation of more committed progenitor granulocyte macrophage-colony forming cells (GM-CFC) in response to granulocyte macrophage-colony stimulating factor (GM-CSF). 相似文献
2.
The products of mitochondrial protein synthesis have been investigated in Tetrahymena after labelling with [35S]methionine in the presence of cycloheximide. The labelled proteins were analyzed by sodium dodecyl sulfate slab polyacrylamide gel electrophoresis. We have identified 13 electrophoretically discrete bands as well as 4 other bands with a more variable occurrence. These proteins ranged in apparent molecular weight from 8100 to 57,500. The cycloheximide-resistant incorporation could be blocked with chloramphenicol. The mitochondrial proteins appeared to be in a disaggregated state and were stable to agents such as trichloroacetic acid (hot or cold) and chloroform-methanol. The pattern of proteins was similar following labelling times ranging from 30 min to 3 h. 相似文献
3.
4.
5.
6.
We have analysed the lineage of olfactory receptor neurons usinga replication-incompetent retrovirus injected beneath the olfactoryepithelium of young rats. There are two major types of clustersof infected cells seen at 540 days after infection: (i)horizontal basal cells (HBCs); (ii) variable numbers of globosebasal cells (GBCs), and immature and mature sensory neurons.Olfactory nerve lesion increased the frequency of the globose/sensoryneuron clusters, as well as the number of cells/cluster, butdid not change the number of HBC clusters or cells/cluster.No clusters contained sustentacular cells. These data indicatethat, at least in young rats: (i) HBCs are not precursors ofolfactory neurons; (ii) there is a lineage path from GBCs tomature neurons; and (iii) sustentacular cells arise from a separatelineage. 相似文献
7.
8.
9.
The recycling of a secretory granule membrane protein 总被引:2,自引:0,他引:2
We have used N-hydroxysuccinimido-d-biotin as a reagent for labeling proteins exposed at the surface of cultured bovine adrenal chromaffin cells during Ba2+-stimulated secretion. A specific secretory granule membrane constituent, dopamine-beta-hydroxylase (DBH), has been investigated using immunoprecipitation followed by electrophoresis. Within 30 min of stimulation, exposed DBH had been cleared from the cell surface. Nevertheless, quantitation of labeled DBH using [125I] streptavidin suggested that it remained undegraded over a period of 24 h, a time during which secretory granule stores of catecholamines were being replenished. Subcellular fractionation of the cultured cells suggested that, after 3 or 4 h, the biotinylated DBH, which was still membrane-bound, was located in particulate material that also contained cytochrome b561, another major secretory granule membrane component. 相似文献
10.