全文获取类型
收费全文 | 40686篇 |
免费 | 3556篇 |
国内免费 | 5577篇 |
专业分类
49819篇 |
出版年
2024年 | 133篇 |
2023年 | 578篇 |
2022年 | 1318篇 |
2021年 | 2147篇 |
2020年 | 1504篇 |
2019年 | 1929篇 |
2018年 | 1786篇 |
2017年 | 1376篇 |
2016年 | 1868篇 |
2015年 | 2720篇 |
2014年 | 3242篇 |
2013年 | 3437篇 |
2012年 | 4099篇 |
2011年 | 3678篇 |
2010年 | 2344篇 |
2009年 | 2098篇 |
2008年 | 2330篇 |
2007年 | 2121篇 |
2006年 | 1863篇 |
2005年 | 1545篇 |
2004年 | 1234篇 |
2003年 | 1151篇 |
2002年 | 980篇 |
2001年 | 660篇 |
2000年 | 563篇 |
1999年 | 549篇 |
1998年 | 331篇 |
1997年 | 319篇 |
1996年 | 282篇 |
1995年 | 212篇 |
1994年 | 214篇 |
1993年 | 152篇 |
1992年 | 170篇 |
1991年 | 139篇 |
1990年 | 107篇 |
1989年 | 98篇 |
1988年 | 80篇 |
1987年 | 53篇 |
1986年 | 69篇 |
1985年 | 73篇 |
1984年 | 31篇 |
1983年 | 35篇 |
1982年 | 35篇 |
1981年 | 34篇 |
1980年 | 14篇 |
1979年 | 21篇 |
1976年 | 9篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1971年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 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.
Substance P-like immunoreactive nerve fibers in the pars distalis of the anterior pituitary in the dog 总被引:1,自引:0,他引:1
Summary The pars distalis of the anterior pituitary is known to be regulated by hypothalamic hormones. Recently, we have discovered the presence of substance P-like immunoreactive nerve fibers in the pars distalis of the monkeys. Substance P-like immunoreactivity in the pars distalis of the dog was investigated in this study. A substantial amount of substance P-like immunoreactive nerve fibers with a large amount of varicosities were found. They were widely distributed in the gland, more abundant along its periphery. Most of them were closely related to the glandular tissue, some were located on vascular walls. Substance P-like immunoreactive nerve fibers were also found in the meningeal sheath of the anterior pituitary. They could be followed into the parenchyma of the gland. 相似文献
6.
7.
8.
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
9.
10.
A 14 kDa polypeptide in rat ileal cytosol has been identified as the major intestinal cytosolic bile acid-binding protein (I-BABP) by photoaffinity labeling with the radiolabeled 7,7-azo derivative of taurocholate (7,7-azo-TC). To further characterize I-BABP, the protein was purified by lysylglycocholate Sepharose 4B affinity and DE-52 anion-exchange chromatography. The purified I-BABP contained a single 14 kDa band on SDS-PAGE. The 14 kDa protein showed a 26-fold increase in binding affinity for [3H]7,7-azo-TC compared to cytosolic protein. Immunoblotting of protein fractions separated by affinity chromatography showed that neither liver fatty acid binding protein (L-FABP) nor intestinal fatty acid binding protein (I-FABP) bind to the affinity column and that the 14 kDa protein which bound to the column and was subsequently eluted with detergent did not cross-react with anti-L-FABP or anti-I-FABP. The 14 kDa protein labeled with [3H]7,7-azo-TC was radioimmunoprecipitated from cytosol by rabbit antiserum raised against purified I-BABP. I-BABP was shown to have a blocked N-terminus; however, its mixed internal sequence generated from cyanogen bromide-cleaved protein and amino acid composition indicated that it was related to (although clearly distinct from) both I-FABP and L-FABP. These studies have isolated a 14 kDa bile acid-binding protein from rat ileal cytosol which is immunologically and biochemically distinct from I-FABP and L-FABP. 相似文献