全文获取类型
收费全文 | 30662篇 |
免费 | 70篇 |
国内免费 | 85篇 |
专业分类
系统科学 | 318篇 |
丛书文集 | 661篇 |
教育与普及 | 64篇 |
理论与方法论 | 117篇 |
现状及发展 | 14596篇 |
研究方法 | 1148篇 |
综合类 | 13612篇 |
自然研究 | 301篇 |
出版年
2012年 | 342篇 |
2011年 | 699篇 |
2010年 | 153篇 |
2009年 | 152篇 |
2008年 | 428篇 |
2007年 | 513篇 |
2006年 | 496篇 |
2005年 | 505篇 |
2004年 | 575篇 |
2003年 | 519篇 |
2002年 | 458篇 |
2001年 | 896篇 |
2000年 | 904篇 |
1999年 | 560篇 |
1992年 | 527篇 |
1991年 | 420篇 |
1990年 | 485篇 |
1989年 | 460篇 |
1988年 | 408篇 |
1987年 | 445篇 |
1986年 | 481篇 |
1985年 | 596篇 |
1984年 | 426篇 |
1983年 | 387篇 |
1982年 | 360篇 |
1981年 | 408篇 |
1980年 | 431篇 |
1979年 | 1029篇 |
1978年 | 839篇 |
1977年 | 822篇 |
1976年 | 625篇 |
1975年 | 701篇 |
1974年 | 1044篇 |
1973年 | 823篇 |
1972年 | 806篇 |
1971年 | 983篇 |
1970年 | 1231篇 |
1969年 | 1032篇 |
1968年 | 960篇 |
1967年 | 977篇 |
1966年 | 816篇 |
1965年 | 647篇 |
1964年 | 196篇 |
1959年 | 369篇 |
1958年 | 575篇 |
1957年 | 411篇 |
1956年 | 347篇 |
1955年 | 341篇 |
1954年 | 334篇 |
1948年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
201.
Summary N-(5-Phosphopyridoxyl)-4-aminobutyric acid, a stable adduct of pyridoxal phosphate and 4-aminobutyric acid, has been shown to be a potent inhibitor of rat brain 4-aminobutyric acid aminotransferase (GABA-T) with a Ki of 1.4 M.Acknowledgments. This work was supported in part by the United Parkinson Foundation, l'Association Canadienne l'Ataxie de Friedreich, and the Medical Research Council of Canada. 相似文献
202.
M. Larpent-Gourgaud M. P. Aumaître 《Cellular and molecular life sciences : CMLS》1977,33(12):1601-1602
Summary The radiations coming from Blanc Brillant de Luxe' fluorescent stimulate the growth and ramification of protonema ofCeratodon purpureus (Hedw.) Brid. This stimulation is caused by red light (660 nm). Multidirectional lightening is more favorable than unidirectional exposition. 相似文献
203.
Non-mendelial female sterility in Drosophila melanogaster: demonstration of an inducer chromosome 4]
A Pélisson 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1977,284(23):2399-2402
Crosses between two classes of Drosophila melanogaster strains (reactive and inducer) may lead to partially sterile F1 females. This sterility, called S.F. sterility, can be characterized by its physiological features. It appears to be the result of an interaction between two factors: "R" brought into the initial croos by the reactive mother and "I" by chromosomes of the inducer father. Except for chromosome 4, each chromosome of the well known inducer strains may carry the I factor (inducer chromosomes). The present results provide evidence for the presence of an inducer fourth chromosome in the inducer strain Nagasaki. 相似文献
204.
J P Garrec J Jourdan B Blanchard A Hartmann J P Lassalles M Thellier 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1977,285(5):579-582
The use of the stable isotopes 6 and 7 of lithium, and detection with the ionic analyser, allow the measurement of unidirectional transepithelial Li-fluxes, between "external" and "internal" solutions which both contain 80% Na and 20% Li. Efflux was found to be bigger than influx. An important lag-phase on the curve, reveals the interference of a Li-compartment, with a high capacity, in the epithelium itself. 相似文献
205.
206.
G. Apostol Constanţa Matei-Vladescu Valeria Popescu 《Cellular and molecular life sciences : CMLS》1977,33(3):345-347
Summary Contrary to earlier findings in rats, cerebral lateral ventricular infusions of 1×10–3 M or 2×10–3 M solutions of phloridzin at a rate of 2.5 l/min for 90 min had no significant stimulating effects on food intake and weight gain in hens and cocks. These different responses to intraventricular phloridzin might reflect a difference of sensitivity to the inhibitory action of phloridzin on glucose transport in cerebral cells or certain peculiarities of mechanisms controlling food intake in chickens. 相似文献
207.
Transposable genetic elements as agents of gene instability and chromosomal rearrangements. 总被引:31,自引:0,他引:31
Transposable genetic elements in prokaryotes and eukaryotes, when inserted at a given locus, can control expression of the locus and cause large scale rearrangements of adjacent DNA sequences. Striking similarities in genetic behaviour between the two groups of elements have led to the proposal of a molecular model of eukaryotic controlling elements, and to suggestions about the part such elements may play in evolution and differentiation. 相似文献
208.
209.
An effect which appeared to be pulsating aurora was observed to be associated with explosive releases of barium vapour near 250 km altitude, but only when the explosions were in the path of precipitating electrons associated with the visible aurora. 相似文献
210.
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