全文获取类型
收费全文 | 13946篇 |
免费 | 110篇 |
国内免费 | 174篇 |
专业分类
系统科学 | 149篇 |
丛书文集 | 109篇 |
教育与普及 | 60篇 |
理论与方法论 | 36篇 |
现状及发展 | 5447篇 |
研究方法 | 592篇 |
综合类 | 7708篇 |
自然研究 | 129篇 |
出版年
2014年 | 122篇 |
2013年 | 116篇 |
2012年 | 293篇 |
2011年 | 406篇 |
2010年 | 166篇 |
2009年 | 217篇 |
2008年 | 330篇 |
2007年 | 391篇 |
2006年 | 360篇 |
2005年 | 350篇 |
2004年 | 312篇 |
2003年 | 275篇 |
2002年 | 334篇 |
2001年 | 511篇 |
2000年 | 498篇 |
1999年 | 375篇 |
1998年 | 126篇 |
1997年 | 118篇 |
1996年 | 123篇 |
1995年 | 117篇 |
1992年 | 278篇 |
1991年 | 233篇 |
1990年 | 253篇 |
1989年 | 210篇 |
1988年 | 220篇 |
1987年 | 231篇 |
1986年 | 212篇 |
1985年 | 255篇 |
1984年 | 226篇 |
1983年 | 171篇 |
1982年 | 177篇 |
1981年 | 180篇 |
1980年 | 170篇 |
1979年 | 403篇 |
1978年 | 340篇 |
1977年 | 250篇 |
1976年 | 290篇 |
1975年 | 260篇 |
1974年 | 272篇 |
1973年 | 224篇 |
1972年 | 244篇 |
1971年 | 308篇 |
1970年 | 374篇 |
1969年 | 254篇 |
1968年 | 307篇 |
1967年 | 292篇 |
1966年 | 249篇 |
1965年 | 178篇 |
1958年 | 162篇 |
1957年 | 100篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Seed germination in response to diurnal fluctuations of temperature 总被引:20,自引:0,他引:20
Diurnal fluctuations in temperature may initiate or accelerate germination in certain flowering plants, and the effectiveness of the stimulus varies according to the amplitude of fluctuation and the presence or absence of light. Attempts to assess the adaptive significance of the phenomenon, however, have been limited by the scarcity of data for species of contrasted ecology. We report here an investigation of germination responses to fluctuating temperatures, conducted on seeds of herbaceous species collected from native populations near Sheffield. The results suggest that requirements for diurnal fluctuations in temperature are characteristic of the germination of species from particular types of habitat and provide mechanisms which cause seeds to germinate at times and in places favourable for seedling establishment. 相似文献
122.
Proton pump coupled to cytochrome c oxidase in mitochondria. 总被引:1,自引:0,他引:1
M K Wikstrom 《Nature》1977,266(5599):271-273
123.
I. J. Miller N. K. McCallum C. M. Kirk B. M. Peake 《Cellular and molecular life sciences : CMLS》1982,38(2):230-231
Summary The free radical oxidation of 1 and 6-tetrahydrocannabinol has been examined by spin trapping techniques and intermediates that would lead to cannabinol have been trapped. The 1st step in the oxidation of 1-THC involves the removal of 3-H, while for 6-THC, either 2-H or 5-H. Intermediates were isolated which could be pyrolysed to the diene and cannabinol. 相似文献
124.
The identification of ecdysterone (20-hydroxyecdysone) in 3 species of molluscs (Gastropoda: Pulmonata) 总被引:1,自引:0,他引:1
Summary Ecdysterone has been identified in the schistosomiasis vectorBiomphalaria glabrata Say and inHelix aspersa Müller as well as inLymmaea stagnalis L. by chromatography, bioassay, radioimmunoassay, derivatization and by mass spectroscopy. Analysis of the food, faeces and hepatopancreas suggest that the sterol is derived from the diet. The probable function of ecdysterone in relation to calcification of the shell is discussed in this paper.We wish to thank Professor P. Karlson and Dr J. Koolman (Phillips University, Marburg-Lahn, FRG) for providing facilities for RIA. The initial study was begun at the University of Sussex and continued at the Courtauld Institute of Biochemistry, Middlesex Hospital Medical School, London, while D.L.W. was supported by the Ministry of Overseas Development. London and the Medical Research Council of Great Britain (grant G974/525/T). We thank Mr P. Mellon for the mass spectrum and Dr G.B. Russell for his interest in the earlier part of this study. We also thank Professor E. Scherer and Dr Q. Uwe (University of Essen, FRG) for their help in the irradiation ofL. stagnalis.Gauss Str. 82, D-4630 Bochum 5 (Federal Republic of Germany). Research results usingL. stagnalis were submitted for the Philips Europa Wettbewerb für junge Forscher und Erfinder (1979) in a thesis entitled Zur Frage der Existenz von Steroiden und Gonadoliberin bei der Grossen Schlammschnecke (Lymmaea stagnalis L.): ein Beitrag zur Evolution der Insekten- und Wirbeltierhormone. 相似文献
125.
K. R. Middleton F. W. Schaefer H. J. Saz 《Cellular and molecular life sciences : CMLS》1979,35(2):243-244
Summary 4-Isothiocyanato-4-nitrodiphenylamine possessed anthelmintic activity againstNippostrongylus dubius andHymenolepis nana in mice andH. diminuta in rats as determined by both egg counts and recovery of parasites at autopsy. No activity was detected against the cestode,Spirometra mansonoides, in cats.This investigation was supported in part by grants AI-10512 and AI-09483 from the National Institutes of Health. The authors are indebted to Dr P.P. Weinstein for providing animals infected withSpirometra mansonoides. 相似文献
126.
Summary InTambourissa religiosa (Monimiaceae), the flowers are pollinated at a hyperstigma formed by the mouth of the floral cup, and not at the carpels. This is an extraordinary feature in angiosperms.I thank Professor Dr W. Rauh, Institut für Systematische Botanik und Pflanzengeographie der Universität Heidelberg, for providing material from his green house collection (W. Rauh, No. M 138, coll. 1959) and Dr Christa Güssefeld-Schneider for fixing pollinated flowers. 相似文献
127.
A. Borowska S. Sierakowski J. Maćkowiak K. Wiśniewski 《Cellular and molecular life sciences : CMLS》1979,35(10):1368-1370
Summary A correlation between the postirradiation increase of the small intestine motility and the prostaglandin-like activity in this organ during gastrointestinal syndrome was observed. Indomethacin decreased the elevated motility of intestine and reduced the prostaglandin-like activity in this syndrome.Acknowledgments. The work was supported by the Polish Academy of Sciences. 相似文献
128.
The enzymes which were extracted by autodigestion from the microsomal fractions of the pig kidney, liver and submaxillary gland and from the serum showed an immunochemical identity by a double immunodiffusion test. But the kidney enzyme had a different pI-value from the pI-values of the enzymes of other organs. 相似文献
129.
P. J. Müller P. Masner Maria Kälin W. S. Bowers 《Cellular and molecular life sciences : CMLS》1979,35(5):704-705
Summary Corpora allata fromOncopeltus fasciatus incubated in vitro in medium containing 10–5.35 M (1 g/ml) of precocene II lose their ability to secrete juvenile hormone when reimplanted into last instar larvae.Acknowledgments. We thank Mr K. Dorn, Mrs L. Dolezal, Mrs V. Nötzli-Graf, Mr K.H. Trautmann and Mr A. Schuler for technical help, Dr W. Vogel and Dr A. Dübendorfer for valuable discussions. 相似文献
130.
High-frequency generalised transduction by bacteriophage T4 总被引:30,自引:0,他引:30