全文获取类型
收费全文 | 324篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
系统科学 | 2篇 |
教育与普及 | 1篇 |
理论与方法论 | 9篇 |
现状及发展 | 126篇 |
研究方法 | 46篇 |
综合类 | 126篇 |
自然研究 | 16篇 |
出版年
2020年 | 2篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 4篇 |
2013年 | 3篇 |
2012年 | 18篇 |
2011年 | 30篇 |
2010年 | 12篇 |
2009年 | 2篇 |
2008年 | 12篇 |
2007年 | 16篇 |
2006年 | 10篇 |
2005年 | 17篇 |
2004年 | 7篇 |
2003年 | 16篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1992年 | 8篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 8篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1970年 | 10篇 |
1969年 | 2篇 |
1968年 | 7篇 |
1967年 | 5篇 |
1966年 | 4篇 |
1965年 | 2篇 |
1963年 | 2篇 |
1960年 | 1篇 |
1957年 | 3篇 |
1948年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有326条查询结果,搜索用时 15 毫秒
41.
在软件工程中,企业系统最为吸引人也是最为需求的。本书对企业系统建模作概念性的介绍和全面地综述。提出了分析与设计基于表单的企业系统的一种特殊目的建模技术。对特殊领域建模语言一直存在着强烈的需求。本书的作者来自科学家和对此类商业应用程序有兴趣的专业人员,他们以一种创新的方法修改了已被广泛接受的基本建模技术,实现对所需应用程序领域建模框架的优化。 相似文献
42.
L. W. D. Weber 《Cellular and molecular life sciences : CMLS》1987,43(2):176-178
Summary A known ornithine decarboxylase assay working with ion exchang separation of [3H]ornithine and [3H]putrescine has been revised. The assay can be performed in disposable 1.5 ml vessels with a total of four pipetting steps. The separation of enzyme substrate and product, respectively, requires 3 h per 50 samples. The detection limit is about 50 pmoles [3H]putrescine formed. 相似文献
43.
The N-terminal fragments (residues 1-51 and 1-59) obtained by selective tryptic cleavage of native lac repressor retain the ability to bind DNA. These fragments (headpieces) are monomeric and form complexes which resemble those of tetrameric repressor with non-operator DNA. But, they do not show the high specificity of repressor for operator sequences. The DNA binding has been demonstrated by filter-binding assay as well as in solution using absorption, circular dichroism, and fluorescence measurements. 相似文献
44.
J Comsa B Baumann M Zeppezauer H Leonhardt N Weber 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,288(1):185-187
A partially purified thymic extract has determined the development of leucosis in 10 thymectomized irradiated CC57Bl mice out of 25. The pure hormone isolated from the same extract prevented the development of leucosis in intact irradiated Mice. This seems to indicate the presence of a second active substance in the extract (enhancing the development of the leucosis). 相似文献
45.
Summary The aperiodic activity patterns of bilobectomized cockroaches can largely be described by simple stochastic regularities: a) there are no correlations between the lengths of successive activity bursts and rest pauses, b) the probabilities for the transition from activity to rest and from rest to activity are time-independent. The activity sequence is strongly influenced by singular temperature steps or temperature cycles. 相似文献
46.
Primate Alu and rodent Alu-like elements comprise major families of mammalian small dispersed repetitive DNAs. These elements are repeated more than 10(5) times per haploid genome and are found between known genes, in introns and in satellite DNA. Their dispersion throughout the genome and the presence of directly repeated DNA sequences flanking the elements suggest, but do not prove, that they are capable of transposition. We describe here an allelic variation in the 5'-flanking region of the rat prolactin gene that offers the opportunity to examine the sequences of matching regions of two homologous chromosomes which differ in the presence of an Alu-like repetitive DNA element. Our findings support the hypothesis that these elements are integrated into the genome by generating short direct repeats of host DNA. 相似文献
47.
Fractionated X-irradiation of gestational days 11-13 in the mouse, with doses between 3 x 1.05 and 3 x 1.33 Gy resulted in rosette-like clusters of primitive ependym-resembling cells dispersed within the cortex walls. Quantification of these abnormalities showed a general prevalence in the female fetuses, especially due to the larger number of rosettes in the females than in the males. It was concluded that X-irradiation acts on sex-specific differentiation steps, which are fully developed at the beginning of the fetal period. As it was recently speculated that these are linked to an early divergence of gene expression between the sexes, we suggest that X-chromosome damage may be involved in the pathogenesis of the dimorphic lesion pattern. While, in principle, this will valid for any fetal tissue, it only becames evident in the forebrain because of the outstanding relationship between cell necrosis and rosette development in this specific organ. 相似文献
48.
49.
Summary X-Irradiation of pregnant NMRI-mice on gestational days 11–13 with 3×1.05 Gy increased postnatal mortality of the female offspring only. Weights, protein content and acetylcholinesterase, as well as Na, K-ATPase activities in the brains of all treated offspring, were changed. There were, however, no differences between females and males with respect to these parameters.We gratefully acknowledge the assistance of Miss C. Gutmann. 相似文献
50.
Nicole Pasteur 《Cellular and molecular life sciences : CMLS》1972,28(9):1108-1109
Résumé Les protéines présentes dans les glandes salivaires deDrosophila pallidipennis ont été analysées grâce à une technique de microélectrophorèse discale. Les variations observées pendant le développement de la larve et de la jeune pupe on été comparées avec celles deDrosophila pseudoobscura. II semble que certaines variations soient le résultat de phénomènes communs à toutes les espèces du genreDrosophila.
Supported in part by grants No. GM-16 736-03 and No. FR-05 426-09 from the U.S. Department of Health, Education and Welfare. The author was a holder of a University of Texas predoctoral fellowship during the course of this investigation. 相似文献
Supported in part by grants No. GM-16 736-03 and No. FR-05 426-09 from the U.S. Department of Health, Education and Welfare. The author was a holder of a University of Texas predoctoral fellowship during the course of this investigation. 相似文献