全文获取类型
收费全文 | 2457篇 |
免费 | 254篇 |
国内免费 | 8篇 |
出版年
2021年 | 40篇 |
2019年 | 25篇 |
2017年 | 27篇 |
2016年 | 44篇 |
2015年 | 49篇 |
2014年 | 60篇 |
2013年 | 80篇 |
2012年 | 97篇 |
2011年 | 112篇 |
2010年 | 65篇 |
2009年 | 68篇 |
2008年 | 89篇 |
2007年 | 95篇 |
2006年 | 99篇 |
2005年 | 79篇 |
2004年 | 78篇 |
2003年 | 81篇 |
2002年 | 102篇 |
2001年 | 76篇 |
2000年 | 57篇 |
1999年 | 70篇 |
1998年 | 26篇 |
1997年 | 22篇 |
1996年 | 31篇 |
1995年 | 22篇 |
1994年 | 30篇 |
1993年 | 16篇 |
1992年 | 55篇 |
1991年 | 50篇 |
1990年 | 56篇 |
1989年 | 48篇 |
1988年 | 48篇 |
1987年 | 41篇 |
1986年 | 40篇 |
1985年 | 50篇 |
1984年 | 48篇 |
1983年 | 50篇 |
1982年 | 41篇 |
1981年 | 28篇 |
1980年 | 33篇 |
1979年 | 43篇 |
1978年 | 46篇 |
1977年 | 49篇 |
1976年 | 33篇 |
1975年 | 29篇 |
1974年 | 26篇 |
1973年 | 44篇 |
1972年 | 28篇 |
1971年 | 22篇 |
1968年 | 27篇 |
排序方式: 共有2719条查询结果,搜索用时 15 毫秒
51.
We have constructed and tested several new vectors for P element-mediated gene transfer. These vectors contain restriction sites for cloning a wide variety of DNA fragments within a small, non-autonomous P element and can be used to efficiently transduce microinjected DNA sequences into the germ line chromosomes of D. melanogaster. The P element in one vector also carries the rosy gene which serves as an easily scored marker to facilitate the transfer of DNA fragments that do not themselves confer a recognizable phenotype. The failure of certain P element constructs to function as vectors suggests that P element sequences, in addition to the 31 bp inverse terminal repeats, are required in cis for transposition. Moreover, removal of the first 38 bp of the autonomous 2.9 kb P element appears to destroy its ability to provide a trans-acting factor (s) required for the transposition of non-autonomous P elements. Finally, we describe a genomic sequence arrangement that apparently arose by the transposition of a 54 kb composite P element from a tetramer plasmid. 相似文献
52.
Lymphocytes obtained from CLL patients exhibited a delayed and reduced response to PHA when cultured in diffusion chambers. DNA synthesis (8–10 hr) and general time (15–19 hr) of the late-developing CLL blasts were consistent with normal values ( T s : 8–10 hr; T c : 14–17 hr). However, the G2 period of CLL blasts seemed more variable, and their mitotic index during the response at 5–6 days was 30–50% of the values determined for normal blasts during their peak response at 2–3 days. 相似文献
53.
Uridine transport and RNA synthesis in growing and in density-inhibited animal cells 总被引:19,自引:0,他引:19
Both chick embryo fibroblasts and mouse 3T3 cells reduce the rate at which they incorporate H3 uridine into RNA as their growth becomes inhibited at high cell density. This reduction occurs as a function of the cell population density, and with chick embryo cells (in contrast to 3T3 cells) it is not accompanied by significant medium alterations. This indicates the importance of the cell population density in the control of cellular metabolism. The decline in H3 uridine incorporation is paralleled by a decline in the rate of uptake of the isotope into the acid-soluble pool, suggesting that decreased entry of H3 uridine into the cell, rather than a decreased rate of RNA synthesis, is responsible for the reduced rate of incorporation into RNA of density-inhibited cells. This suggestion was confirmed by finding that when the restriction on uridine uptake was overcome by increasing the concentration of uridine in the medium, the density-dependent inhibition of uridine incorporation was largely reversed. We conclude that, even though the rate of H3 uridine incorporation into RNA is reduced three- to five-fold in density-inhibited cells, the rate of synthesis of pulse-labeled RNA continues at 70 to 85% of the rapidly-growing rate. 相似文献
54.
pH AND POPULATION DENSITY IN THE REGULATION OF ANIMAL CELL MULTIPLICATION 总被引:14,自引:2,他引:12
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
H. Rubin 《The Journal of cell biology》1971,51(3):686-702
Sparse and dense cultures of chick embryo cells were affected differently by pH. The rates of cell multiplication and of thymidine-3H incorporation into DNA of dense cultures were increased as the pH was increased from 6.6 to 7.6. At pH higher than 7.6 the rate of multiplication decreased slightly in the dense cultures, but the rate of thymidine-3H incorporation continued to increase. The discrepancy was due in part to cell death and detachment at very high pH, and in part to a more rapid uptake of thymidine-3H at very high pH. Sparse cultures were much less sensitive to pH reduction and, when a suitably conditioned medium was used to minimize cell damage, very sparse cultures grew almost as well at pH 6.7 as at higher pH. The rates of cell multiplication and thymidine-3H incorporation at low pH decreased in the initially sparse cultures before they reached confluent cell densities. There was no microscope evidence of direct contact between plasma membranes of cells at these densities although the parallel orientation indicated that the cells were influencing locally each other's behavior. Even at much higher cell densities, electron microscopy revealed large intercellular gaps partly filled with a fragmentary electron-opaque material suspected to be glycoprotein. Wounding experiments showed that pH affected cell migration in a manner similar to its effects on cell multiplication. Low pH inhibited cell migration, but those cells which migrated into the denuded region multiplied as rapidly at low pH as at high pH. The effects of pH on growth were correlated with effects on the uptake of 2-deoxyglucose-3H. Dense populations of cells inhibited by low pH were stimulated to incorporate thymidine-3H by the addition of small amounts of diethylaminoethyl-dextran. Rous sarcoma cells at high cell density were less sensitive to pH than were normal cells at the same density, but were more sensitive than sparse normal cultures. The results suggest that cell growth is inhibited through the combined effects of both lowered pH and high cell density on cell surface permeability. 相似文献
55.
Biosynthesis of mitochondrial enzymes 总被引:18,自引:0,他引:18
56.
57.
58.
59.
A new micro method for determination of cholesterol in serum 总被引:6,自引:0,他引:6
60.
Human keratinocyte growth factor activity on proliferation and differentiation of human keratinocytes: differentiation response distinguishes KGF from EGF family. 总被引:15,自引:0,他引:15
C Marchese J Rubin D Ron A Faggioni M R Torrisi A Messina L Frati S A Aaronson 《Journal of cellular physiology》1990,144(2):326-332
Human keratinocyte growth factor (KGF) is an epithelial cell specific mitogen which is secreted by normal stromal fibroblasts. In the present studies, we demonstrate that KGF is as potent as EGF in stimulating proliferation of primary or secondary human keratinocytes in tissue culture. Exposure of KGF- or EGF-stimulated keratinocytes to 1.0 mM calcium, an inducer of differentiation, led to cessation of cell growth. However, immunologic analysis of early and late markers of terminal differentiation, K1 and filaggrin, respectively, revealed striking differences in keratinocytes propagated in the presence of these growth factors. With KGF, the differentiation response was associated with expression of both markers whereas their appearance was retarded or blocked by EGF. TGF alpha, which also interacts with the EGF receptor, gave a similar response to that observed with EGF. These findings functionally distinguish KGF from the EGF family and support the role of KGF in the normal proliferation and differentiation of human epithelial cells. 相似文献