全文获取类型
收费全文 | 3260篇 |
免费 | 208篇 |
出版年
2023年 | 14篇 |
2022年 | 43篇 |
2021年 | 57篇 |
2020年 | 39篇 |
2019年 | 79篇 |
2018年 | 77篇 |
2017年 | 59篇 |
2016年 | 99篇 |
2015年 | 173篇 |
2014年 | 146篇 |
2013年 | 230篇 |
2012年 | 267篇 |
2011年 | 252篇 |
2010年 | 158篇 |
2009年 | 117篇 |
2008年 | 185篇 |
2007年 | 187篇 |
2006年 | 179篇 |
2005年 | 171篇 |
2004年 | 166篇 |
2003年 | 138篇 |
2002年 | 157篇 |
2001年 | 30篇 |
2000年 | 27篇 |
1999年 | 35篇 |
1998年 | 24篇 |
1997年 | 21篇 |
1996年 | 24篇 |
1995年 | 25篇 |
1994年 | 16篇 |
1993年 | 16篇 |
1992年 | 15篇 |
1991年 | 24篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 17篇 |
1983年 | 12篇 |
1982年 | 23篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1971年 | 5篇 |
1968年 | 6篇 |
1966年 | 7篇 |
排序方式: 共有3468条查询结果,搜索用时 15 毫秒
1.
Abstract In Arabidopsis thaliana, cell fate in developing ovules is determined by the action of the homeodomain factor BELL1 (BEL1) and of the MADS-box factors SEEDSTICK (STK), SHATTERPROOF1 (SHP1) and SHP2. The analysis of the bel1 and the stk shp1 shp2 mutants revealed that the functional megaspore is formed, however, it does not proceed into megagametogenesis. In the bel1 stk shp1 shp2, quadruple mutant megasporogenesis does not take place. In this article we describe a detailed morphological analysis of the quadruple mutant, and we discuss the possibility that BELL1, STK, SHP1 and SHP2 not only control integument identity determination and development, but that they might also play a role during megasporogenesis. 相似文献
2.
3.
Roberta L. Millstein 《Journal of the history of biology》2008,41(2):339-367
Biologists and philosophers have been extremely pessimistic about the possibility of demonstrating random drift in nature,
particularly when it comes to distinguishing random drift from natural selection. However, examination of a historical case
– Maxime Lamotte’s study of natural populations of the land snail, Cepaea nemoralis in the 1950s – shows that while some pessimism is warranted, it has been overstated. Indeed, by describing a unique signature
for drift and showing that this signature obtained in the populations under study, Lamotte was able to make a good case for
a significant role for␣drift. It may be difficult to disentangle the causes of drift and selection acting in a population,
but it is not (always) impossible. 相似文献
4.
Francesca Passaretta Domenico Bosco Lucia Centurione Maria Antonietta Centurione Fabio Marongiu Roberta Di Pietro 《Journal of cellular and molecular medicine》2020,24(7):4350-4355
Human Amniotic Epithelial Cells (hAEC) isolated from term placenta are a promising source for regenerative medicine. However, it has long been debated whether the hAEC population consists of heterogeneous or homogeneous cells. In a previous study, we investigated the characteristics of hAEC isolated from four different regions of the amniotic membrane finding significant heterogeneity. The aim of this study was to evaluate the hepatic differentiation capability of hAEC isolated from these four regions. Human term placentae were collected after caesarean section and hAEC were isolated from four regions of the amniotic membrane (R1-R4, according to their relative distance from the umbilical cord) and treated in hepatic differentiation conditions for 14 days. hAEC-derived hepatocyte-like cells showed marked differences in the expression of hepatic markers: R4 showed higher levels of Albumin and Hepatocyte Nuclear Factor (HNF) 4α whereas R1 expressed higher Cytochrome P450 enzymes, both at the gene and protein level. These preliminary results suggest that hAEC isolated from R1 and R4 of the amniotic membrane are more prone to hepatic differentiation. Therefore, the use of hAEC from a specific region of the amniotic membrane should be taken into consideration as it could have an impact on the outcome of therapeutic applications. 相似文献
5.
6.
7.
8.
9.
Mutagenicity of 4-hydroxynonenal in V79 Chinese hamster cells 总被引:2,自引:0,他引:2
4-Hydroxynonenal (HNE), a major product of the peroxidation of liver microsomal lipids, was examined for mutagenic activity at the hypoxanthine-guanine phosphoribosyltransferase locus in V79 Chinese hamster lung cells. At concentrations ranging from 10 to 45 microM, HNE induced a dose-dependent increase in the number of mutations to 6-thioguanine resistance, which reached the level of 4.7X baseline at the highest concentration tested. 相似文献
10.