全文获取类型
收费全文 | 43464篇 |
免费 | 3091篇 |
国内免费 | 2037篇 |
出版年
2024年 | 75篇 |
2023年 | 750篇 |
2022年 | 1018篇 |
2021年 | 1506篇 |
2020年 | 1443篇 |
2019年 | 1938篇 |
2018年 | 1603篇 |
2017年 | 1091篇 |
2016年 | 1209篇 |
2015年 | 1569篇 |
2014年 | 2389篇 |
2013年 | 3111篇 |
2012年 | 1696篇 |
2011年 | 2163篇 |
2010年 | 1589篇 |
2009年 | 1863篇 |
2008年 | 1881篇 |
2007年 | 1990篇 |
2006年 | 1776篇 |
2005年 | 1691篇 |
2004年 | 1513篇 |
2003年 | 1312篇 |
2002年 | 1301篇 |
2001年 | 1091篇 |
2000年 | 915篇 |
1999年 | 836篇 |
1998年 | 787篇 |
1997年 | 733篇 |
1996年 | 693篇 |
1995年 | 655篇 |
1994年 | 612篇 |
1993年 | 564篇 |
1992年 | 546篇 |
1991年 | 510篇 |
1990年 | 391篇 |
1989年 | 397篇 |
1988年 | 362篇 |
1987年 | 295篇 |
1986年 | 248篇 |
1985年 | 309篇 |
1984年 | 396篇 |
1983年 | 223篇 |
1982年 | 296篇 |
1981年 | 286篇 |
1980年 | 223篇 |
1979年 | 206篇 |
1978年 | 147篇 |
1977年 | 102篇 |
1976年 | 111篇 |
1974年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
51.
52.
The influence of contact guidance on the orientation of colonies of subcultured vascular smooth muscle cells 总被引:1,自引:0,他引:1
Robert C. Buck 《In vitro cellular & developmental biology. Plant》1982,18(9):783-788
Summary Subcultures of smooth muscle cells derived from rat thoracic aorta were grown on plane plastic substrata and on plastic substrata
having ridges molded in them by a heated, ruled template. The cells were found to have a very high degree of contact guidance
when distributed sparsely on the ridged substrata. When the cell density increased multilayered, elongated colonies formed.
On plane substrata these were irregular, curved, and disposed in all directions. On the ridged substrata, however, the colonies
were straight, evenly spaced, and positioned at right angles to the ridges.
Supported by Grant MT1011 from the Medical Research Council of Canada. 相似文献
53.
Charles E. Wenner John C. Cheney L. David Tomei 《Journal of cellular biochemistry》1981,15(2):161-168
The introduction of either PGF2α (10?7 M) or TPA (10?7 M) stimulated, ouabain-sensitive 86Rb+ influx at 30 min in postconfluent 3T3-4 mouse fibroblast cultures by 117% and 124%, respectively. Both TPA and PGF2α at these concentrations stimulated the incorporation of 3H-TdR into DNA. TPA had the greatest stimulatory effect, which was similar to that obtained with 10% fetal calf serum. In accord with the idea that modulation of membrane processes such as Na+/K+ pump activity in fibroblasts may reflect important events related to the initiation of DNA synthesis, it was observed that in both 3T3-4 and C3H-1 0T½ cells there were parallel increases in 3H-TdR incorporation and ouabain-sensitive 86Rb+ influxes with 10?7 M TPA, whereas PGF2α stimulated a significant increase in 3H-TdR incorporation in 3T3-4 but not C3H-10T½ cells and only marginal increases in ouabain-sensitive 86Rb+ influx in both. Therefore, although there appears to be a close correlation between Na+/K+ pump activation and subsequent S-phase entry following TPA stimulation, a similar correlation for PGF2α cannot be confirmed. 相似文献
54.
《Molecular cell》2021,81(24):5099-5111.e8
55.
56.
J.N. Beresford J.A. Gallagher M. Gowen M. Couch J. Poser D.D. Wood R.G.G. Russell 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,801(1):58-65
Cultural adherent human mononuclear cells produce factor(s) which stimulate the release of calcium from new-born mouse calvaria in organ culture. This stimulation of bone resorption is accompanied by an inhibition of the incorporation of [3H]proline into collagen which is independent of increased prostaglandin production by the bone. When human osteoblast-like cells are treated with conditioned medium from human mononuclear cells, collagen accounts for a decreased proportion of the protein synthesised. This effect on matrix synthesis is not accompanied by an inhibitory action of the monocyte-conditioned medium preparations on net cell proliferation. In human osteoblast-like cell cultures, partially purified human interleukin 1 also inhibits the production of the bone-specific protein osteocalcin in a dose-dependent fashion. These observations are consistent with the hypothesis that products of human monocytes similar to, or identical with, human interleukin 1 may be important regulators of bone metabolism and may contribute to the bone loss seen in diseases such as chronic rheumatoid arthritis. 相似文献
57.
Preparation of chloroplast DNA from pea plastids isolated in a medium of high ionic strength 总被引:8,自引:0,他引:8
A simple, rapid, and inexpensive method for the preparation and purification of chloroplast DNA (cpDNA) from pea has been developed. The crucial step is the isolation of chloroplasts in a medium of high ionic strength (I congruent equal to 1.40 M). CpDNA from pea prepared according to this method has successfully been used for restriction enzyme mapping, Southern transfers, and cloning. 相似文献
58.
59.
《Molecular & cellular proteomics : MCP》2020,19(3):444-455
Highlights
- •Human spermatozoa possess cells of poor morphology that lack nuclear integrity.
- •These cells can be isolated by density separation.
- •Mass spectrometry reveals their nuclei contain excess protein.
- •TOP2A is a promising marker of this poor nuclear development.
60.
Summary Equivalent-circuit impedance analysis experiments were performed on the urinary bladders of freshwater turtles in order to quantify membrane ionic conductances and areas, and to investigate how changes in these parameters are associated with changes in the rate of proton secretion in this tissue. In all experiments, sodium reabsorption was inhibited thereby unmasking the electrogenic proton secretion process. We report the following: (1) transepithelial impedance is represented exceptionally well by a simple equivalent-circuit model, which results in estimates of the apical and basolateral membrane ionic conductances and capacitances; (2) when sodium transport is inhibited with mucosal amiloride and serosal ouabain, the apical and basolateral membrane conductances and capacitances exhibit a continual decline with time; (3) this decline in the membrane parameters is most likely caused by subtle time-dependent changes in cell volume, resulting in changes in the areas of the apical and basolateral membranes; (4) stable membrane parameters are obtained if the tissue is not treated with ouabain, and if the oncotic pressure of the serosal solution is increased by the addition of 2% albumin; (5) inhibition of proton secretion using acetazolamide in CO2 and HCO
3
–
-free bathing solutions results in a decrease in the area of the apical membrane, with no significant change in its specific conductance; (6) stimulation of proton transport with CO2 and HCO
3
–
-containing serosal solution results in an increase in the apical membrane area and specific conductance. These results show that our methods can be used to measure changes in the membrane electrophysiological parameters that are related to changes in the rate of proton transport. Notably, they can be used to quantify in the live tissue, changes in membrane area resulting from changes in the net rates of endocytosis and exocytosis which are postulated to be intimately involved in the regulation of proton transport. 相似文献