全文获取类型
收费全文 | 37534篇 |
免费 | 3409篇 |
国内免费 | 5366篇 |
专业分类
46309篇 |
出版年
2024年 | 128篇 |
2023年 | 530篇 |
2022年 | 1237篇 |
2021年 | 1982篇 |
2020年 | 1428篇 |
2019年 | 1803篇 |
2018年 | 1661篇 |
2017年 | 1290篇 |
2016年 | 1750篇 |
2015年 | 2551篇 |
2014年 | 3042篇 |
2013年 | 3165篇 |
2012年 | 3813篇 |
2011年 | 3471篇 |
2010年 | 2208篇 |
2009年 | 1962篇 |
2008年 | 2201篇 |
2007年 | 1961篇 |
2006年 | 1716篇 |
2005年 | 1403篇 |
2004年 | 1145篇 |
2003年 | 1078篇 |
2002年 | 917篇 |
2001年 | 580篇 |
2000年 | 505篇 |
1999年 | 474篇 |
1998年 | 297篇 |
1997年 | 278篇 |
1996年 | 243篇 |
1995年 | 191篇 |
1994年 | 184篇 |
1993年 | 132篇 |
1992年 | 144篇 |
1991年 | 119篇 |
1990年 | 95篇 |
1989年 | 85篇 |
1988年 | 64篇 |
1987年 | 48篇 |
1986年 | 56篇 |
1985年 | 63篇 |
1984年 | 27篇 |
1983年 | 32篇 |
1982年 | 30篇 |
1981年 | 27篇 |
1980年 | 16篇 |
1979年 | 32篇 |
1978年 | 18篇 |
1977年 | 15篇 |
1974年 | 14篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
1.
Food availability is important to the dynamics of animal social organizations or populations. However, the role of winter
food availability in animal population dynamics is still controversial. We carried out an experimental study to test Lack’s
hypothesis that reduced food in winter limits survival and spring numbers of breeding individuals of social groups, using
the Mongolian gerbil (Meriones unguiculatus) as model species. We established 24 gerbil social groups in 24, 10 × 10 m, pens in September 2008. We provided wheat seeds
as supplemental food in 12 enclosures from September 2008 to March 2009; the other 12 enclosures, not provided with supplemental
food, served as controls. We live-trapped gerbils at a 2-week interval from September to April. Supplemental food during winter
increased biweekly survival by 10% relative to that in control groups. Only four control social groups survived to the end
of our study whereas all 12 food-supplemented social groups survived through our study period. Supplemental food also increased
cumulative numbers of recruits and group sizes of gerbils. We conclude that winter food availability limits winter survival
and spring social groups or population sizes of Mongolian gerbils. 相似文献
2.
3.
Bing Xia Haiping Ke Wei Jiang Masayori Inouye 《The Journal of biological chemistry》2002,277(8):6005-6011
The 5'-end region of cspA mRNA contains a Cold Box sequence conserved among several cold-shock mRNAs. This region forms a stable stem-loop structure followed by an AU-rich sequence. Here we show that the Cold Box region is essential for the normal scale of cspA mRNA induction after cold shock because a deletion of the stem-loop significantly destabilizes the mRNA and reduces the cold shock-induced cspA mRNA amount by approximately 50%. The AU-rich track, however, slightly destabilizes the mRNA. The integrity of the stem is essential for the stabilizing function, whereas that of the loop sequence is less important. Overexpression of a mutant cspA mRNA devoid of both the AUG initiation codon and the coding sequence results in a severe growth inhibition at low temperature along with a derepression of the chromosomal cspA expression. Furthermore, the overexpressed RNA is stably associated with the 30 S and 70 S ribosomes. Our results demonstrate that the AUG initiation codon and the coding region containing the downstream box are not required for cspA mRNA to bind ribosomes and that the 5'-untranslated region by itself has a remarkable affinity to ribosomes at low temperature. 相似文献
4.
5.
6.
Xu Liu Ben Chen Lulan Chen Wan-Ting Ren Juan Liu Guoxiang Wang Wei Fan Xin Wang Yun Wang 《PloS one》2013,8(4)
Phenol red is widely used in cell culture as a pH indicator. Recently, it also has been reported to have estrogen-like bioactivity and be capable of promoting cell proliferation in different cell lines. However, the effect of phenol red on primary neuronal culture has never been investigated. By using patch clamp technique, we demonstrated that hippocampal pyramidal neurons cultured in neurobasal medium containing no phenol red had large depolarization-associated epileptiform bursting activities, which were rarely seen in neurons cultured in phenol red-containing medium. Further experiment data indicate that the suppressive effect of the phenol red on the abnormal epileptiform burst neuronal activities was U-shape dose related, with the most effective concentration at 28 µM. In addition, this concentration related inhibitory effect of phenol red on the epileptiform neuronal discharges was mimicked by 17-β-estradiol, an estrogen receptor agonist, and inhibited by ICI-182,780, an estrogen receptor antagonist. Our results suggest that estrogen receptor activation by phenol red in the culture medium prevents formation of abnormal, epileptiform burst activity. These studies highlight the importance of phenol red as estrogen receptor stimulator and cautions of careful use of phenol red in cell culture media. 相似文献
7.
8.
9.
The androgen-dependent mouse seminal vesicle secretory protein IV: characterization and complementary deoxyribonucleic acid cloning 总被引:4,自引:0,他引:4
Y H Chen B T Pentecost J A McLachlan C T Teng 《Molecular endocrinology (Baltimore, Md.)》1987,1(10):707-716
Seminal vesicle secretory protein IV of a mouse has been isolated, and the cDNA coding for its mRNA has been cloned and sequenced. The 556-nucleotides encode 16 amino acid signal peptides and 92 residues of mature protein. Considerable homology between mouse and rat SVS IV cDNA was found. In the leader peptide and 3'-noncoding region there is 92% and 85% homology, respectively. The other regional homologies are 86% for the first 12, 68.5% for the last 35, and 40% for the middle 44 amino acids. The expression of mouse SVS IV mRNA is under the control of androgen. Administration of testosterone to castrated mice resulted in induction of the mRNA level to 50% of the mature male in 96 h of hormone treatment. Secretion of the protein after testosterone injection follows a similar pattern. 相似文献