全文获取类型
收费全文 | 3723篇 |
免费 | 345篇 |
国内免费 | 1篇 |
出版年
2021年 | 67篇 |
2020年 | 43篇 |
2019年 | 64篇 |
2018年 | 53篇 |
2017年 | 57篇 |
2016年 | 95篇 |
2015年 | 158篇 |
2014年 | 165篇 |
2013年 | 211篇 |
2012年 | 229篇 |
2011年 | 216篇 |
2010年 | 134篇 |
2009年 | 119篇 |
2008年 | 176篇 |
2007年 | 156篇 |
2006年 | 134篇 |
2005年 | 145篇 |
2004年 | 139篇 |
2003年 | 120篇 |
2002年 | 119篇 |
2001年 | 80篇 |
2000年 | 102篇 |
1999年 | 84篇 |
1998年 | 39篇 |
1997年 | 39篇 |
1996年 | 36篇 |
1995年 | 34篇 |
1994年 | 34篇 |
1993年 | 36篇 |
1992年 | 65篇 |
1991年 | 60篇 |
1990年 | 52篇 |
1989年 | 46篇 |
1988年 | 56篇 |
1987年 | 46篇 |
1986年 | 45篇 |
1985年 | 46篇 |
1984年 | 40篇 |
1983年 | 37篇 |
1982年 | 36篇 |
1981年 | 20篇 |
1979年 | 25篇 |
1978年 | 33篇 |
1977年 | 30篇 |
1976年 | 23篇 |
1975年 | 26篇 |
1974年 | 18篇 |
1973年 | 18篇 |
1971年 | 19篇 |
1970年 | 16篇 |
排序方式: 共有4069条查询结果,搜索用时 218 毫秒
1.
Inositol 1,4,5-trisphosphate is not effective in releasing calcium from skeletal sarcoplasmic reticulum microsomes 总被引:2,自引:0,他引:2
Regulation of many cell systems has been shown to be mediated by Inositol 1,4,5-trisphosphate which causes a release of calcium from intracellular sites. We have shown that release of Ca2+ from sarcoplasmic reticulum microsomes was not stimulated by IP3. The phorbol ester, TPA, also had no effect on Ca2+ release or Ca2+ ATPase activity. Thus, it is unlikely that the breakdown of polyphosphatidylinositides serves as a second messenger to mediate release of Ca2+ in skeletal muscle. 相似文献
2.
3.
Verapamil is a calcium-channel blocking agent, commonly used for chronic treatment of heart conditions. We have previously demonstrated that verapamil acts as a co-mutagen in a bacterial mutagenicity test for some experimental anilinoacridine antitumour drugs. Within the anilinoacridines series there are several compounds which are apparently non-mutagenic (or very weak mutagens) in the absence of verapamil, but strong mutagens in its presence. We have now tested a wider range of materials for verapamil enhancement of mutagenicity, to include some of those to which persons on verapamil therapy might be exposed through life-style or occupation. Some verapamil enhancement of mutagenicity was seen with most mutagenic compounds including anticancer drugs, antiparasitic agents, one biological stain and one hair dye. A number of tricyclic antidepressants and biological stains were tested and found to be non-mutagenic. If these results extrapolate to mammalian cells, long-term verapamil therapy could potentially increase the effects of certain environmental mutagens. 相似文献
4.
Laura Cernat Cristina Blaj Rene Jackstadt Lydia Brandl Jutta Engel Heiko Hermeking Andreas Jung Thomas Kirchner David Horst 《PloS one》2014,9(8)
Colonic crypts are stereotypical structures with distinct stem cell, proliferating, and differentiating compartments. Colorectal cancers derive from colonic crypt epithelia but, in contrast, form morphologically disarrayed glands. In this study, we investigated to which extent colorectal cancers phenocopy colonic crypt architecture and thus preserve structural organization of the normal intestinal epithelium. A subset of colon cancers showed crypt-like compartments with high WNT activity and nuclear β-Catenin at the leading tumor edge, adjacent proliferation, and enhanced Cytokeratin 20 expression in most differentiated tumor epithelia of the tumor center. This architecture strongly depended on growth conditions, and was fully reproducible in mouse xenografts of cultured and primary colon cancer cells. Full crypt-like organization was associated with low tumor grade and was an independent prognostic marker of better survival in a collection of 221 colorectal cancers. Our findings suggest that full activation of preserved intestinal morphogenetic programs in colon cancer requires in vivo growth environments. Furthermore, crypt-like architecture was linked with less aggressive tumor biology, and may be useful to improve current colon cancer grading schemes. 相似文献
5.
Nitracrine is used clinically as an antitumour agent, and analogues are actively being developed in some laboratories. The mutagenic activity of 9-[(3-dimethylaminopropyl)amino]-acridine and its 1-nitro (nitracrine), 2-, 3- and 4-nitro derivatives was evaluated at the 6-thioguanine and ouabain resistance loci in cultured Chinese hamster fibroblasts (V79-171b cell line). The des-nitro, 2- and 3-nitro caused no statistically significant mutagenic activity at either locus. Each of these 3 compounds weakly increased (approximately 2-fold) the incidence of micronuclei in the same cell line when tested at cytotoxic doses. Both the 1- and 4-nitro compounds increased the incidence of 6-thioguanine resistant cells from around 1 in 10(-6) to approximately 1 in 10(-4). The former compound significantly increased the frequency of ouabain-resistant cells. Both of these compounds were potent inducers of micronuclei in V79-171b cells, indicating high clastogenic activity. It would appear prudent to regard both of these compounds as potential human carcinogens. 相似文献
6.
7.
Summary The degree of satellite association was found to be significantly higher in phytohemagglutinin (PHA)-stimulated lymphocytes from cystic fibrosis (CF) patients than from those of control individuals. PHA-stimulated lymphocytes from obligatory heterozygotes for the CF mutant allele showed an intermediate degree of satellite association. The degree of satellite association was estimated by the frequency of cells exhibiting associations, by the number of associations per cell, and by the number of chromosomes in an association. The differences in the degree of satellite association were dependent on the concentration of colchicine used for cell arrest. These findings may assist in developing a diagnostic method for the early identification of heterozygotes for the CF allele and for prenatal detection of CF homozygous fetuses.This paper is based on a portion of a dissertation to be submitted by Y. Ravia in partial fulfilment of the Ph. D. requirements in the Graduate School of Tel Aviv University 相似文献
8.
9.
Elizabeth M. A. Valleley Christine J. Harrison Yvonne Cook Mark W. J. Ferguson Paul T. Sharpe 《Chromosoma》1994,103(7):502-507
Comparative mapping studies of X-linked genes in mammals have provided insights into the evolution of the X chromosome. Many reptiles including the American alligator, Alligator mississippiensis, do not appear to possess heteromorphic sex chromosomes, and sex is determined by the incubation temperature of the egg during embryonic development. Mapping of homologues of mammalian X-linked genes in reptiles could lead to a greater understanding of the evolution of vertebrate sex chromosomes. One of the genes used in the mammalian mapping studies was ZFX, an X-linked copy of the human ZFY gene which was originally isolated as a candidate for the mammalian testis-determining factor (TDF). ZFX is X-linked in eutherians, but maps to two autosomal locations in marsupials and monotremes, close to other genes associated with the eutherian X. The alligator homologue of the ZFY/ZFX genes, Zfc, has been isolated and described previously. A detailed karyotype of A. mississippiensis is presented, together with chromosomal in situ hybridisation data localising the Zfc gene to chromosome 3. Further chromosomal mapping studies using eutherian X-linked genes may reveal conserved chromosomal regions in the alligator that have become part of the eutherian X chromosome during evolution. 相似文献
10.
T Henry A Ferguson 《Comparative biochemistry and physiology. B, Comparative biochemistry》1986,85(2):491-496
Informative crosses have verified the genetic basis of a polymorphism at the Ldh-1 locus in brown trout and enzyme activity measurements indicate that the previously described polymorphism at this locus is best explained by a null allele. The LDH-1, LDH-2, LDH-3 and LDH-4 homotetrameric isozymes were purified and subjected to enzyme kinetic analysis. While LDH-1 and LDH-2 displayed catalytic equivalence, important kinetic differences were found between the LDH-3 and LDH-4 isozymes. 相似文献