全文获取类型
收费全文 | 3940篇 |
免费 | 439篇 |
出版年
2023年 | 22篇 |
2022年 | 59篇 |
2021年 | 109篇 |
2020年 | 64篇 |
2019年 | 86篇 |
2018年 | 88篇 |
2017年 | 57篇 |
2016年 | 119篇 |
2015年 | 175篇 |
2014年 | 203篇 |
2013年 | 250篇 |
2012年 | 299篇 |
2011年 | 289篇 |
2010年 | 169篇 |
2009年 | 132篇 |
2008年 | 194篇 |
2007年 | 178篇 |
2006年 | 179篇 |
2005年 | 185篇 |
2004年 | 156篇 |
2003年 | 149篇 |
2002年 | 146篇 |
2001年 | 59篇 |
2000年 | 38篇 |
1999年 | 50篇 |
1998年 | 44篇 |
1997年 | 26篇 |
1996年 | 37篇 |
1995年 | 34篇 |
1994年 | 30篇 |
1993年 | 34篇 |
1992年 | 22篇 |
1991年 | 32篇 |
1990年 | 28篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 21篇 |
1986年 | 24篇 |
1985年 | 31篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 29篇 |
1981年 | 25篇 |
1980年 | 37篇 |
1979年 | 22篇 |
1978年 | 19篇 |
1977年 | 34篇 |
1976年 | 28篇 |
1975年 | 26篇 |
1973年 | 30篇 |
排序方式: 共有4379条查询结果,搜索用时 31 毫秒
1.
2.
Keith G. Danielson Janice E. Knepper Frances S. Kittrell Janet S. Butel Daniel Medina Elisa M. Durban 《In vitro cellular & developmental biology. Plant》1989,25(6):535-543
Summary Clonal populations were isolated from the mouse mammary cell line, COMMA-D, by transfection with a dominant-selectable gene,
pSV2Neo, which confers resistance to the antibiotic, G418. Seven of twenty-four clones isolated retained the ability of the
parental line to repopulate cleared mammary fat pads in vivo as ductal-alveolar hyperplasias. Two sublines designated CDNR2
and CDNR4 retained hyperplastic growth potential after multiple passages in vitro with low incidence of tumor formation. A
third subpopulation, CDNR1, contained a single integration site for the pSV2Neo plasmid indicating a bonafide clonal origin
for this subline. CDNR1 cells displayed heterogeneous growth phenotypes in vivo including hyperplasia, adenocarcinoma, and
bone formation. Functional differentiation of CDNR1 cells organized as alveolarlike structures in vivo or on floating collagen
gels in vitro was observed as determined by immunoperoxidase staining for the milk-specific protein, casein. Overall, the
results indicate that a subset of cells from the COMMA-D cell line may be functionally analogous to stem cells existing in
the mammary gland.
Supported by NCI research grants CA-38650, CA-33369, CA-39017, and CA-25215. 相似文献
3.
4.
5.
6.
Alan B Oelkers Erick J Schutte David R Tyler 《Photochemical & photobiological sciences》2008,7(2):228-234
The photochemistry of the [(CpR)Mo(CO)(3)](2) molecules, where CpR = eta(5)-C(5)H(4)(CH(2))(2)C(O)NCH(3)(CH(2))(n)CH(3) (n = 3, 8, 13, and 18), was examined using femtosecond pump-probe transient absorption spectroscopy. The goal of this study was to investigate the importance of radical size and mass on the dynamics and efficiency of geminate radical-radical recombination. The femtosecond results demonstrated the lack of any size/mass dependence of the recombination efficiency. This finding contrasts with results from a prior study that did find a size/mass dependence using a steady-state photochemical technique. To explain these conflicting results, it is proposed that the femtosecond pump-probe results are a measurement of the efficiency of primary geminate recombination whereas the steady-state method results are a measurement of the sum of primary and secondary geminate recombination efficiencies. The size/mass dependence is evident in the latter because secondary geminate recombination is a slower diffusive recombination process and therefore depends on the steric properties of the radicals. Although the existence of primary and secondary recombination channels is often taken for granted, experimental differentiation of primary and secondary caging has proven to be difficult because it is not possible for a single experimental technique to span the entire timescale for recombination of a radical cage pair and adequately resolve these recombination pathways. 相似文献
7.
8.
Effect of citric acid-cycle intermediates on oxaloacetate utilization and succinate oxidation 总被引:2,自引:1,他引:1 下载免费PDF全文
D. B. Tyler 《The Biochemical journal》1960,76(2):293-297
9.
Abstract The effects of an unusual high frequency mowing regime, which involved the removal of slash, were compared to moderate grazing through the method of paired quadrats across a fenceline, which was orthogonal to a weak environmental gradient. The mown plots proved superior in their conservation characteristics to the moderately grazed plots. The mowing regime produced greater cover of rare or threatened species, greater native cover and lesser exotic grass cover. It thus presents an opportunity for maintaining or improving the condition of previously grazed remnants in reserves without resorting to the use of stock or fire for biomass reduction. 相似文献
10.