全文获取类型
收费全文 | 34889篇 |
免费 | 2708篇 |
国内免费 | 6篇 |
专业分类
37603篇 |
出版年
2023年 | 231篇 |
2022年 | 157篇 |
2021年 | 368篇 |
2020年 | 387篇 |
2019年 | 354篇 |
2018年 | 705篇 |
2017年 | 651篇 |
2016年 | 1179篇 |
2015年 | 1871篇 |
2014年 | 1822篇 |
2013年 | 2452篇 |
2012年 | 3255篇 |
2011年 | 2782篇 |
2010年 | 1547篇 |
2009年 | 1194篇 |
2008年 | 2243篇 |
2007年 | 2179篇 |
2006年 | 2227篇 |
2005年 | 1911篇 |
2004年 | 1902篇 |
2003年 | 1731篇 |
2002年 | 1649篇 |
2001年 | 698篇 |
2000年 | 807篇 |
1999年 | 424篇 |
1998年 | 237篇 |
1997年 | 134篇 |
1996年 | 151篇 |
1995年 | 177篇 |
1994年 | 133篇 |
1993年 | 127篇 |
1992年 | 161篇 |
1991年 | 138篇 |
1990年 | 122篇 |
1989年 | 104篇 |
1988年 | 87篇 |
1987年 | 56篇 |
1986年 | 67篇 |
1985年 | 96篇 |
1984年 | 111篇 |
1983年 | 80篇 |
1982年 | 88篇 |
1981年 | 62篇 |
1980年 | 66篇 |
1979年 | 58篇 |
1978年 | 50篇 |
1977年 | 49篇 |
1976年 | 77篇 |
1975年 | 58篇 |
1974年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
J Lacour F Lacour A Spira M Michelson J Y Petit G Delage D Sarrazin G Contesso J Viguier 《BMJ (Clinical research ed.)》1984,288(6417):589-592
The results of a randomised trial of polyadenylic-polyuridylic acid given as adjuvant treatment for operable breast cancer were reviewed after a mean follow up period of 87 months. Of the 300 patients included in the original trial, 145 had been allocated to conventional treatment alone and served as controls. At the time of review the overall survival of the group given polyadenylic-polyuridylic acid was significantly improved (p less than 0.05) as compared with that of the controls given conventional treatment alone. Significant benefit (p less than 0.02) was also observed among patients with evidence of disease in lymph nodes, the best results occurring in those with up to three invaded nodes, who showed a significant increase in both overall and relapse free survival. No evidence of toxicity was recorded. These findings confirm the value of polyadenylic-polyuridylic acid as adjuvant treatment for operable breast cancer. Results in an experimental model and in patients receiving the adjuvant suggested a possible role of interferon and natural killer (NK) cells in the mechanism of action. 相似文献
62.
B-cells of the synovial membrane. II. Differentiation during development of the synovial cavity in the mouse 总被引:1,自引:0,他引:1
Summary Study of pre- and postnatal development of the metatarsophalangeal joint of the mouse shows that the synovial cavity (SC) forms before any differentiation of the synovial mesenchyme. The primitive cleft results from degradation of a thin vascular mesenchymal layer in direct contact with the chondrogenic layers. Differentiation of the synovial membrane coincides with clarification of the SC (3rd to 6th day of postnatal life). When dilatation of the SC occurs (6th to 8th day), the two intimal cells types (A- and B-cells) are well identified. The B-cells already show typical features at day 6; their content of typical dense secretory vesicles is comparable to that of the adult B-cells at day 13. The specific secretory function of B-cells could be correlated with the particular structure of the intimal interstitial tissue and could account for the origin of some protein(s) of the synovial fluid.ERA 178 (Neuroendocrinologie Comparée) du CNRS et INSERM 相似文献
63.
64.
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
65.
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
66.
67.
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
68.
69.
An extensive search for recombination between mitochondrial markers was carried out in Paramecium tetraurelia. Thirty-two combinations, altogether involving 24 different markers, were studied. The markers belonged to the three main categories of mitochondrial mutations presently available in this organism, (a) Spontaneous or UV-induced antibiotic resistance mutations, most probably affecting mitochondrial ribosomes, (b) nitrosoguanidine-induced antibiotic resistance markers displaying thermosensitivity or slow growth, enabling easy selection of possible wild-type recombinants, and (c) mitochondrial partial suppressors of a nuclear gene, probably corresponding to molecular alterations distinct from the preceding two categories. In addition, different genetic configurations were analyzed (i.e., mutant X mutant, double-mutant X wild-type, etc.).--None of the combinations yielded any evidence for the occurrence of recombined genomes despite the fact that: (1) all of them were studied on a large scale involving the screening of at least several thousand mitochondrial genomes (often several millions), (2) in many of them the detection level was sufficiently high to enable the isolation of spontaneous mutants in control cells, and (3) in several of them, reconstitution experiments carried out in parallel show that the conditions were fully adequate to detect recombinant genotypes. The results are in marked contrast with those obtained on the few other organisms in which mitochondrial recombination has been studied, particularly Saccharomyces cerevisiae, in which mitochondrial recombination is intense.--The most likely basis for the various manifestations of mitochondrial genetic autonomy in Paramecium, described in this as well as in previous publications, is that the chondriome of this organism is made up of thousands of structurally discrete, noninteracting units. 相似文献
70.
Synchronous growth of a freshwater diatom Melosira italica under natural environment 总被引:1,自引:0,他引:1
Summary A filamentous diatom Melosira italica was collected at the beginning of rainy season from a shallow lake in the tropical savanna region in Brazil. Even the sample taken from surface water contained empty cells in high percentages. The number of cells per filament of M. italica showed a peculiar pulse-like frequency distribution with peak values at 4, 8, 12 and 16. Evidences of the synchronous cell division in this planktonic diatom under natural environment are discussed. 相似文献