全文获取类型
收费全文 | 34812篇 |
免费 | 2699篇 |
国内免费 | 6篇 |
专业分类
37517篇 |
出版年
2023年 | 231篇 |
2022年 | 158篇 |
2021年 | 369篇 |
2020年 | 385篇 |
2019年 | 354篇 |
2018年 | 706篇 |
2017年 | 647篇 |
2016年 | 1177篇 |
2015年 | 1867篇 |
2014年 | 1820篇 |
2013年 | 2449篇 |
2012年 | 3250篇 |
2011年 | 2781篇 |
2010年 | 1548篇 |
2009年 | 1196篇 |
2008年 | 2239篇 |
2007年 | 2176篇 |
2006年 | 2224篇 |
2005年 | 1909篇 |
2004年 | 1898篇 |
2003年 | 1727篇 |
2002年 | 1647篇 |
2001年 | 697篇 |
2000年 | 806篇 |
1999年 | 422篇 |
1998年 | 236篇 |
1997年 | 132篇 |
1996年 | 149篇 |
1995年 | 175篇 |
1994年 | 133篇 |
1993年 | 127篇 |
1992年 | 154篇 |
1991年 | 135篇 |
1990年 | 116篇 |
1989年 | 104篇 |
1988年 | 85篇 |
1987年 | 56篇 |
1986年 | 67篇 |
1985年 | 97篇 |
1984年 | 110篇 |
1983年 | 80篇 |
1982年 | 88篇 |
1981年 | 60篇 |
1980年 | 65篇 |
1979年 | 56篇 |
1978年 | 49篇 |
1977年 | 49篇 |
1976年 | 77篇 |
1975年 | 56篇 |
1974年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
André A. Dhondt 《Oecologia》1979,42(2):139-157
Summary Movements and survival of 506 first-brood Great Tit nestlings that fledged in mid-June in an oak wood in southern Sweden were studied by intensive trapping in that wood and in several neighbouring woods between 17 July and 10 September 1977. A total of 1177 captures of 508 individuals was made.Two periods of summer dispersal can be distinguished: the first period, one to one- and-one-half months after fledging, lasts longer in females and results in females moving farther away from their birthplace than males; and the second period in early September. There was no effect of brood-size, fledging date or size on dispersal movements. There is, however, a nest effect in that siblings tend to be more alike in the distance moved than non-siblings.The summer mortality rate is constant but high (13% per week). It is not affected by brood size or fledging date, but during the first month after fledging large individuals survive better than smaller ones. The summer mortality rate of dispersers (birds moving between woods) is not higher than that of non-dispersers.The results contradict two hypotheses proposed to explain when and how postfledging mortality occurs. The mortality rate is not higher during the first month after fledging, as Perrins' and Lack's hypothesis predicts. Since only 22% of the young are still alive at the beginning of September, autumn territorial behaviour cannot be the main factor causing juvenile losses, as proposed by Kluyver.There is some circumstantial evidence that Great Tits compete for food during the summer, and that food therefore could be in short supply, as suggested by Perrins.The observed differential dispersal of adults and young, and of male and female juveniles, may be the result of the dominance relationships in the family flock and later in the summer flocks, with subordinate individuals moving farthest. 相似文献
153.
154.
Mohamed Saïd Hifnawy Jacqueline Vaquette Thierry Sévenet Jean-Louis Pousset André Cavé 《Phytochemistry》1977,16(7):1035-1039
Stems and leaves of Myrtopsis macrocarpa, M. myrtoidea, M. novae-caledoniae and M. sellingii yielded terpenes, sterols, coumarins, alkaloids (furoquinolines and quinolones) and amides. A new quinolone (8-methoxy flindersine) occurs in Myrtopsis macrocarpa, a new amide (N-benzoyltryptamine) in M. myrtoidea, two new coumarins (myrsellin and myrsellinol) and a new dihydrofuroquinoline (myrtopsine) in M. sellingii. Structures of the new compounds are proposed from chemical and spectroscopic evidence. 相似文献
155.
Xanthones with a uniform 1,3,7,8-oxidation pattern, the C-glycosides isoorientin and isovitexin, and in some cases mangiferin, were isolated from the aerial parts of G. nivalis, G. brachyphylla, G. favrati, G. rostani, G. utriculosa and G. schleicheri Kunz. The distribution of these compounds within the section Cyclostigma is given. Comparison of phenolic patterns in other sections of Gentiana is made. 相似文献
156.
157.
Martin Diatewa Yves Boulanger AndréJ.C. Stahl 《Biochemical and biophysical research communications》1982,106(2):520-525
The α and β subunits of yeast mitochondrial Phe-tRNA synthetase are separated and isolated by means of chromatography on DEAE-cellulose, after enzyme alkylation with iodoacetate. The comparison of amino acid compositions of yeast mitochondrial and cytoplasmic native Phe-tRNA synthetases and their components shows significant differences. Results indicate that the two enzymes are coded for by different nuclear genes. 相似文献
158.
159.
Javier Turnay Nieves Olmo José G. Gavilanes María A. Lizarbe 《In vitro cellular & developmental biology. Animal》1991,27(6):447-452
Summary Fibroblastlike primary cells have been obtained from human colon adenocarcinoma explants. Such cells disappear during cell
culture and thus have not been previously studied. These cells have a number of altered phenotypic characteristics: a) morphology;
b) growth behavior and adherence to culture substrate (they required 3 h for 90% attachment and only presented a flattened
morphology 40 h after platting); and c) collagen metabolism. Increased protein biosynthesis (about double than control colon-derived
fibroblasts) and maintained ability for collagen biosynthesis have been observed for the tumor-associated fibroblastlike cells.
Thus, the collagen to noncollagenous proteins ratio was decreased for these cells. They exhibited an altered type I:type III
collagen (5:1 instead of 3:1 in colon fibroblasts) and procollagen (2:1 against 5:1 in colon fibroblasts) ratios as well as
a decreased secretion of collagen with an abnormal deposition of procollagens in the cell layer. These studies show a permanent
phenotypic alteration in the tumor-associated fibroblastlike cells. 相似文献
160.
T Gautier C Dauphin-Villemant C André C Masson J Arnoult D Hernandez-Verdun 《Experimental cell research》1992,200(1):5-15
We investigated the perichromosomal architecture established during mitosis. Entry into mitosis brings about a dramatic reorganization of both nuclear and cytoplasmic structures in preparation for cell division. While the nuclear envelope breaks down, nuclear proteins are redistributed during chromosome condensation. Some of these proteins are found around the chromosomes, but little is known concerning their nature and function. Ten autoimmune sera were used to study the microenvironment of chromosomes and, in particular, the chromosome periphery. They were selected for their anti-nucleolar specificity and were found to recognize three nucleolar proteins that coat the chromosomes during mitosis. The distribution of these antigens was followed through the cell cycle by confocal laser scanning microscopy. The antigens dispersed very early during prophase and simultaneously with the chromosome condensation suggesting a correlation between these two processes. The antigens have apparent molecular weights of 53, 66, and 103 kDa on SDS-PAGE migration. Elution of the antibodies and immunopurification showed that they are RNA-associated proteins. The coimmunoprecipitating RNA moiety involved in these RNPs appeared to be U3, but the antigens are not related to the fibrillarin family. Therefore, small nucleolar RNPs follow the same distribution during mitosis as that described for small nuclear RNPs. Possible functions for these antigens are discussed. 相似文献