全文获取类型
收费全文 | 25193篇 |
免费 | 58篇 |
国内免费 | 72篇 |
专业分类
系统科学 | 107篇 |
丛书文集 | 295篇 |
教育与普及 | 65篇 |
理论与方法论 | 104篇 |
现状及发展 | 10278篇 |
研究方法 | 1064篇 |
综合类 | 12983篇 |
自然研究 | 427篇 |
出版年
2013年 | 232篇 |
2012年 | 351篇 |
2011年 | 780篇 |
2010年 | 154篇 |
2008年 | 402篇 |
2007年 | 487篇 |
2006年 | 477篇 |
2005年 | 482篇 |
2004年 | 450篇 |
2003年 | 434篇 |
2002年 | 447篇 |
2001年 | 883篇 |
2000年 | 860篇 |
1999年 | 494篇 |
1992年 | 466篇 |
1991年 | 376篇 |
1990年 | 404篇 |
1989年 | 435篇 |
1988年 | 403篇 |
1987年 | 383篇 |
1986年 | 419篇 |
1985年 | 493篇 |
1984年 | 373篇 |
1983年 | 349篇 |
1982年 | 277篇 |
1981年 | 281篇 |
1980年 | 336篇 |
1979年 | 818篇 |
1978年 | 628篇 |
1977年 | 613篇 |
1976年 | 482篇 |
1975年 | 526篇 |
1974年 | 778篇 |
1973年 | 616篇 |
1972年 | 647篇 |
1971年 | 763篇 |
1970年 | 961篇 |
1969年 | 732篇 |
1968年 | 766篇 |
1967年 | 669篇 |
1966年 | 649篇 |
1965年 | 452篇 |
1964年 | 110篇 |
1959年 | 245篇 |
1958年 | 411篇 |
1957年 | 310篇 |
1956年 | 257篇 |
1955年 | 234篇 |
1954年 | 229篇 |
1948年 | 186篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
A E Davis K Aulak R B Parad H P Stecklein E Eldering C E Hack J Kramer R C Strunk J Bissler F S Rosen 《Nature genetics》1992,1(5):354-358
Heterozygosity for a mutant dysfunctional C1 inhibitor protein, a member of the serine proteinase inhibitor (serpin) superfamily, results in type II hereditary angioneurotic oedema. We identified a "hinge" region mutation in C1 inhibitor with a Val to Glu replacement at P14 Val-432. Recombinant C1 inhibitors P10 Ala-->Thr and P14Val-->Glu did not form stable complexes with fluid phase C1s or kallikrein. The P14 Val-->Glu mutant, however, was cleaved to a 96K form by C1s, while the P10 Ala-->Thr mutant was not. The recombinant P10 mutant also did not complex with C1s, kallikrein or beta-factor Xlla-Sepharose. The two mutations, therefore, result in dysfunction by different mechanisms: in one (P14 Val-->Glu), the inhibitor is converted to a substrate, while in the other (P10 Ala-->Thr), interaction with target protease is blocked. 相似文献
82.
D. Porquet M. Appel T. Fournier O. Bertaux D. Biou J. Féger 《Cellular and molecular life sciences : CMLS》1992,48(3):257-261
Both in vivo and in vitro models have certain disadvantages for the study of the chronic hepatotoxicity of drugs. The aim of this work was to evaluate a new approach based on an in vivo/in vitro model. After chronic in vivo treatment of rats with Vincamine and Vindeburnol (an eburnamenine derivative which exhibits hepatotoxic properties in man) liver cells were isolated, and functional and metabolic disorders (metabolic utilization of fructose and protein biosynthesis) were studied to determine injury. The results showed no modification of blood parameters, but a direct relationship between the dose of Vindeburnol administered in vivo and the metabolic disorders observed in vitro, evidencing the high sensitivity and reliability of this model. 相似文献
83.
R. Wiesendanger B. Martinoni T. Boller D. Arigoni 《Cellular and molecular life sciences : CMLS》1986,42(2):207-209
Summary Under the action of the appropriate synthase from ripe tomatoes a 11 mixture of (3S, 4R)-[3,4-2H2] and (3R, 4S)-[3,4-2H2]-(2S)-adenosylmethionine is transformed into a 11 mixture of the two meso forms of [2H2]-1-aminocyclopropanecarboxylic acid, a result which proves the operation of an inversion mechanism and which is consistent with direct nucleophilic displacement of the leaving group in the substrate. 相似文献
84.
D. Dubourdieu 《Cellular and molecular life sciences : CMLS》1986,42(8):914-921
Conclusion Current enological research does not aim at developing technological wines whose organoleptic characteristics are basically determined by the methods used in the transformation of grape wine, but rather to refine methods which will highlight the original qualities of different cultivars and viticultural conditions. 相似文献
85.
The median procedure for n-trees 总被引:2,自引:2,他引:0
Let (X,d) be a metric space The functionM:X
k 2
x
defined by
is the minimum } is called themedian procedure and has been found useful in various applications involving the notion of consensus Here we present axioms that characterizeM whenX is a certain class of trees (hierarchical classifications), andd is the symmetric difference metricWe would like to thank the referees and Editor for helpful comments 相似文献
86.
Evolution of the atmosphere and oceans 总被引:1,自引:0,他引:1
The residence times of most constituents of the atmosphere and oceans are small fractions of the age of the Earth and, in general, their rate of output has been nearly equal to their rate of input. We are disturbing a number of these dynamic equilibria quite severely. The mineralogy of marine evaporites rules out drastic changes in the composition of sea water during the last 900 Myr. The chemistry of soils formed more than 1,000 Myr ago suggests that the atmosphere then contained significantly more CO2 and less O2 than at present. Hydrogen peroxide may well have been the principal oxidant and formaldehyde the main reductant in rain water between 3,000 and 1,000 Myr ago. Major changes in atmospheric chemistry since that time are almost certainly related to the evolution of the biosphere. 相似文献
87.
Antidiuretic effects of oxytocin in the Brattleboro rat 总被引:1,自引:0,他引:1
J. Lyness A. G. Robinson M. N. Sheridan D. M. Gash 《Cellular and molecular life sciences : CMLS》1985,41(11):1444-1446
Summary The antidiuretic activity of oxytocin (OT) was measured in Brattleboro rats with congenital diabetes insipidus. A dose dependent antidiuretic response was found in animals receiving chronic infusions of 0.1 g/h, 1.0 g/h, and 5 g/h of OT. OT infused at the rate of 5 g/h over a 7-day period completely reversed the symptoms of diabetes insipidus. The results support the concept that OT serves as a weak agonist of vasopressin at the level of the kidney and at pharmacological levels exhibits antidiuretic activity. 相似文献
88.
J. R. Aldrich J. P. Kochansky J. D. Sexton 《Cellular and molecular life sciences : CMLS》1985,41(3):420-422
Summary Workers and queens of the eastern yellowjacket,Vespula maculifrons, are attracted to the artificial long-range attractant pheromone of the predaceous pentatomid,Podisus maculiventris. A 11 mixture of linalool or -terpineol and (E)-2-hexenal is as attractive toV. maculifrons workers as the pheromone.We thank A.S. Menke of the Systematic Entomology Laboratory, USDA, for identifying the yellowjackets. Mention of a company name does not imply endorsement by the US Department of Agriculture. 相似文献
89.
N. Akaike K. Hattori Y. Oomura D. O. Carpenter 《Cellular and molecular life sciences : CMLS》1985,41(1):70-71
Summary Using isolated, internally perfused bullfrog dorsal root ganglion cells we have studied the dose-response curves for -aminobutyric acid (GABA) in the presence of internally or externally applied GABA antagonists. With external application of antagonists the inhibition of the GABA current by bicuculline was competitive and that by picrotoxin was noncompetitive. Picrotoxin but not bicuculline blocked when internally perfused.To whom reprint requests should be addressed.Acknowledgments. We thank Drs S. Minakami and S. Yasui for helpful discussions and comments. 相似文献
90.
S. S. Tobe R. P. Ruegg B. A. Stay F. C. Baker C. A. Miller D. A. Schooley 《Cellular and molecular life sciences : CMLS》1985,41(8):1028-1034
Summary Titres of juvenile hormone (JH) have been determined in both hemolymph and whole body extracts of femaleDiploptera punctata during the first gonotrophic cycle using a method employing gas chromatography/mass spectrometry for qualitative and quantitative analysis. JH III is the sole JH found in both adult and last instarD. punctata. Maximum values of 1500 ng/ml (6M) were observed at the middle of the gonotrophic cycle, when basal oocyte growth rate was greatest. Changes in rates of JH release in vitro by corpora allata paralleled closely the changes in JH titre, suggesting that biosynthesis is a major regulator of titre. JH levels per animal were calculated from observed JH titres, and at certain time points in the gonotrophic cycle JH levels obtained from analysis of whole bodies were significantly greater than those predicted from hemolymph titres. These results suggest the existence of a nonhemolymph JH pool inD. punctata. Decay in JH titre after allatectomy of 5 day females has also been studied. Following a rapid initial decline, the rate of decay slowed appreciably 4 h post-operation. Thus, use of a first-order rate constant to estimate half-life of JH significantly underestimated the longevity of the hormone. The apparent persistence of JH following allatectomy may be due to the existence of a nonhemolymph JH pool. 相似文献