全文获取类型
收费全文 | 22181篇 |
免费 | 261篇 |
国内免费 | 298篇 |
专业分类
系统科学 | 291篇 |
丛书文集 | 288篇 |
教育与普及 | 152篇 |
理论与方法论 | 69篇 |
现状及发展 | 7722篇 |
研究方法 | 698篇 |
综合类 | 13359篇 |
自然研究 | 161篇 |
出版年
2014年 | 240篇 |
2013年 | 267篇 |
2012年 | 442篇 |
2011年 | 592篇 |
2010年 | 326篇 |
2009年 | 361篇 |
2008年 | 561篇 |
2007年 | 559篇 |
2006年 | 533篇 |
2005年 | 510篇 |
2004年 | 513篇 |
2003年 | 436篇 |
2002年 | 449篇 |
2001年 | 677篇 |
2000年 | 658篇 |
1999年 | 586篇 |
1998年 | 208篇 |
1996年 | 215篇 |
1995年 | 210篇 |
1994年 | 439篇 |
1992年 | 380篇 |
1991年 | 298篇 |
1990年 | 352篇 |
1989年 | 328篇 |
1988年 | 343篇 |
1987年 | 328篇 |
1986年 | 331篇 |
1985年 | 360篇 |
1984年 | 233篇 |
1983年 | 258篇 |
1982年 | 212篇 |
1981年 | 204篇 |
1980年 | 246篇 |
1979年 | 509篇 |
1978年 | 434篇 |
1977年 | 391篇 |
1976年 | 315篇 |
1975年 | 387篇 |
1974年 | 477篇 |
1973年 | 422篇 |
1972年 | 432篇 |
1971年 | 562篇 |
1970年 | 610篇 |
1969年 | 533篇 |
1968年 | 533篇 |
1967年 | 459篇 |
1966年 | 408篇 |
1965年 | 295篇 |
1958年 | 323篇 |
1957年 | 255篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
H. J. Bestmann J. Erler O. Vostrowsky 《Cellular and molecular life sciences : CMLS》1988,44(9):797-799
Summary By means of closed-loop-stripping and subsequent GC analyses the diel periodicity of release of (Z)-11-hexadecenyl acetate, (E)-8-dodecenyl acetate, and (Z)-9-tetradecenyl acetate, the main constituents of the respective sex pheromone blends ofMamestra brassicae, Cryptophlebia leucotreta andSpodoptera sunia females, was determined.Pheromones, 64. For the 63rd contribution we have taken from: Szöcs, G., Toth, M., Bestmann, H. J., Vostrowsky, O., Heath, R. R., and Tumlinson, J. H., Z. Naturforsch.42c (1987) 165; Pheromones, 62: Bestmann et al.13. 相似文献
33.
E. Flückiger U. Briner B. Clark A. Closse A. Enz P. Gull A. Hofmann R. Markstein L. Tolcsvai H. R. Wagner 《Cellular and molecular life sciences : CMLS》1988,44(5):431-436
Summary The profile of action in animals of CQP 201-403, a novel 8-amino-ergoline, is in most aspects that of a very potent dopaminomimetic, both as a prolactin secretion inhibitor, and at the levels of the CNS and the cardiovascular system. Qualitatively CQP 201-403 differs slightly from bromocriptine and apomorphine in its effects on the CNS (no influence on serotonin metabolism in the rat cortex; induction of masculine mounting behavior in rats) and the cardiovascular system of the dog (reflex tachycardia in response to a blood-pressure fall). In man the new compound proved to be highly active in lowering prolactin serum levels and to be more potent than bromocriptine (Parlodel®).In memory of Dr Annemarie Closse, who died 14 June 1987. 相似文献
34.
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
35.
36.
S. Suzuki S. Kurasawa H. Kitai M. Oba S. Komatsu K. Yoda R. Iizuka 《Cellular and molecular life sciences : CMLS》1986,42(7):795-798
Summary Porcine or human follicular fluid inhibited the spontaneous maturation of isolated hamster oocytes in vitro during the first 1.5 h of culture. Moreover, the presence of 50% follicular fluid combined with 100 M dbcAMP cooperatively reduced the incidence of germinal vesicle breakdown. The addition of FSH also inhibited the resumption of meiosis, and the presence of LH did not overcome the inhibitory effects of follicular fluid and tended to impede isolated hamster oocyte maturation in vitro. 相似文献
37.
38.
Diverse microorganisms ranging from cyanobacteria to eukaryotic algae and fungi live endolithically within ooids, hardgrounds and invertebrate shells on the present-day sea floor. These organisms are involved in the mechanical destruction of carbonates, and are useful ecological indicators of water depth and pollution. The Phanerozoic history of microbial endoliths has been elucidated through the study of microborings (the trace fossils of endolithic microorganisms) and rare cellularly preserved individuals, but nothing was known of the possible Precambrian evolution of comparable microorganisms until Campbell documented the occurrence of microborings in late Proterozoic ooids from central East Greenland. We now report the discovery of large populations of organically preserved endolithic microorganisms in silicified pisolites from 700-800-Myr-old Limestone-Dolomite Series of East Greenland. This fossil assemblage is significant for three reasons: (1) It confirms the prediction that oolites, pisolites and hardgrounds--the substrates for pre-Phanerozoic endoliths--provide a hitherto poorly explored but rewarding set of environments into which the search for early microfossils must be broadened; (2) the assemblage is diverse, containing about 12 taxa of morphologically distinct and previously unknown endolithic cyanobacteria, plus associated epilithic and interstitial populations; and (3) at least six of the fossil populations are indistinguishable in morphology, pattern of development, reproductive biology and inferred ecology from distinctive cyanobacterial species that bore ooids today in the Bahama Banks. 相似文献
39.
R. S. Verma S. Thomas M. Coleman R. T. Silver H. Dosik 《Cellular and molecular life sciences : CMLS》1986,42(4):440-441
Summary A random distribution of the Y-chromosome at somatic metaphase was found in 50 patients with Ph' positive chronic myelogenous leukemia (CML). Thus, it is concluded that the positive of the Y-chromosome at somatic metaphase does not appear to influence the loss from bone marrow cells. 相似文献
40.
Summary Glycosidases like sialidase,-galactosidase, -L-fucosidase, N-acetyl hexosaminidase and proteases were detected in toad testis. Neuraminic acid aldolase activity was also detected. The enzyme activities were found to vary as production of spermatozoa varied. All enzymes, except N-acetyl glucosaminidase, were shown to decrease after injection of toad pituitary extract and they were also found to be absent from testis containing no spermatozoa. The glycosidases were found to act on toad oviduct jelly and they may therefore be involved in the degradation of the jelly after fertilization, into smaller bits, which may be utilized as nutrients by the fertilized zygote.Acknowledgment. We thank Prof. T.R. Ramaiah, Head of the Department of Biochemistry, University of Mysore, for his help. We also acknowledge the financial assistance of University Grants Commission to one of us (MS) and CSIR through a grant No. 9 (165)83/EMR-II to HSS. Please address all correspondence to H.S. Seshadri. 相似文献