全文获取类型
收费全文 | 26013篇 |
免费 | 57篇 |
国内免费 | 87篇 |
专业分类
系统科学 | 287篇 |
丛书文集 | 611篇 |
教育与普及 | 70篇 |
理论与方法论 | 97篇 |
现状及发展 | 12230篇 |
研究方法 | 1013篇 |
综合类 | 11579篇 |
自然研究 | 270篇 |
出版年
2013年 | 137篇 |
2012年 | 320篇 |
2011年 | 650篇 |
2010年 | 151篇 |
2008年 | 411篇 |
2007年 | 492篇 |
2006年 | 434篇 |
2005年 | 466篇 |
2004年 | 412篇 |
2003年 | 464篇 |
2002年 | 417篇 |
2001年 | 795篇 |
2000年 | 794篇 |
1999年 | 462篇 |
1992年 | 452篇 |
1991年 | 363篇 |
1990年 | 405篇 |
1989年 | 387篇 |
1988年 | 385篇 |
1987年 | 388篇 |
1986年 | 409篇 |
1985年 | 517篇 |
1984年 | 351篇 |
1983年 | 331篇 |
1982年 | 276篇 |
1981年 | 320篇 |
1980年 | 375篇 |
1979年 | 870篇 |
1978年 | 684篇 |
1977年 | 711篇 |
1976年 | 530篇 |
1975年 | 544篇 |
1974年 | 851篇 |
1973年 | 693篇 |
1972年 | 669篇 |
1971年 | 786篇 |
1970年 | 1017篇 |
1969年 | 880篇 |
1968年 | 804篇 |
1967年 | 813篇 |
1966年 | 683篇 |
1965年 | 508篇 |
1964年 | 147篇 |
1959年 | 300篇 |
1958年 | 480篇 |
1957年 | 347篇 |
1956年 | 318篇 |
1955年 | 278篇 |
1954年 | 275篇 |
1948年 | 183篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
RNA polymerase is poised for activation across the genome 总被引:2,自引:0,他引:2
Muse GW Gilchrist DA Nechaev S Shah R Parker JS Grissom SF Zeitlinger J Adelman K 《Nature genetics》2007,39(12):1507-1511
93.
Mutations in the gene encoding the basal body protein RPGRIP1L, a nephrocystin-4 interactor, cause Joubert syndrome 总被引:7,自引:0,他引:7
Arts HH Doherty D van Beersum SE Parisi MA Letteboer SJ Gorden NT Peters TA Märker T Voesenek K Kartono A Ozyurek H Farin FM Kroes HY Wolfrum U Brunner HG Cremers FP Glass IA Knoers NV Roepman R 《Nature genetics》2007,39(7):882-888
Protein-protein interaction analyses have uncovered a ciliary and basal body protein network that, when disrupted, can result in nephronophthisis (NPHP), Leber congenital amaurosis, Senior-L?ken syndrome (SLSN) or Joubert syndrome (JBTS). However, details of the molecular mechanisms underlying these disorders remain poorly understood. RPGRIP1-like protein (RPGRIP1L) is a homolog of RPGRIP1 (RPGR-interacting protein 1), a ciliary protein defective in Leber congenital amaurosis. We show that RPGRIP1L interacts with nephrocystin-4 and that mutations in the gene encoding nephrocystin-4 (NPHP4) that are known to cause SLSN disrupt this interaction. RPGRIP1L is ubiquitously expressed, and its protein product localizes to basal bodies. Therefore, we analyzed RPGRIP1L as a candidate gene for JBTS and identified loss-of-function mutations in three families with typical JBTS, including the characteristic mid-hindbrain malformation. This work identifies RPGRIP1L as a gene responsible for JBTS and establishes a central role for cilia and basal bodies in the pathophysiology of this disorder. 相似文献
94.
Loss of GLIS2 causes nephronophthisis in humans and mice by increased apoptosis and fibrosis 总被引:4,自引:0,他引:4
95.
From endoderm to pancreas: a multistep journey 总被引:2,自引:0,他引:2
Spagnoli FM 《Cellular and molecular life sciences : CMLS》2007,64(18):2378-2390
The formation of the vertebrate pancreas is a complex process that typifies the basic steps of embryonic development. It involves the establishment of competence, specification, signaling from neighboring tissues, morphogenesis, and the elaboration of tissue-specific genetic networks. A full analysis of this multistep process will help us to understand classic principles of embryonic development. Furthermore, this will provide the blueprint for experimental programming of pancreas formation from embryonic stem cells in the context of diabetes cell-therapy. Although in the past decade many studies have contributed to a solid foundation for understanding pancreatogenesis, important gaps persist in our knowledge of early pancreas formation. This review will summarize the current understanding of the early mechanisms coming into play to pattern the "pre-pancreatic" region within the endoderm and, gradually, specify the pancreatic tissue. 相似文献
96.
97.
Epigenetic asymmetry of imprinted genes in plant gametes 总被引:12,自引:0,他引:12
Gutiérrez-Marcos JF Costa LM Dal Prà M Scholten S Kranz E Perez P Dickinson HG 《Nature genetics》2006,38(8):876-878
Plant imprinted genes show parent-of-origin expression in seed endosperm, but little is known about the nature of parental imprints in gametes before fertilization. We show here that single differentially methylated regions (DMRs) correlate with allele-specific expression of two maternally expressed genes in the seed and that one DMR is differentially methylated between gametes. Thus, plants seem to have developed similar strategies as mammals to epigenetically mark imprinted genes. 相似文献
98.
By considering an exciplex system consisting of collective molecules in interaction with both the 'pumping' fields and the biophoton fields, the two-level exciplex model and the three-level exciplex model are presented. They are useful for the investigation of the quasi-stationary behaviour of biophoton emission, and biophoton emission as a dynamic process in the presence of external perturbations. Our theoretical results predict a series of nonlinear effects, such as chaos, fractal behaviour, and non-equilibrium phase transition. These effects characterize the coherence nature of living systems. In our approaches, there are two important quantities f and x, which can be used to mark the working points of the two-level and three-level exciplex systems. All the influences of external perturbations on the exciplex systems, e.g. change of temperature, the addition of agents, exposure to light, etc., can be interpreted as shifts of the working points of the systems, leading to a diversity of nonlinear response of biophoton emission. In addition, the agreements of the theoretical results and the corresponding experimental observations on biophoton emission from biological systems in the presence of external perturbations are demonstrated. 相似文献
99.
A New Discipline of Science-The Study of Open Complex Giant System and Its Methodology 总被引:2,自引:0,他引:2
Qian XuesenChina Association for Science Technology Beijing ChinaYu JingyuanBeijing Institute of Information Control P.O.Box Beijing ChinaDai RuweiInstitute of Automation Chinese Academy of Sciences Beijing China 《系统工程与电子技术(英文版)》1993,(2)
This paper introduces the conception of open complex giant system and the methodology for dealing with the system, with stress on its profound significance in development of science and technology. The authors conclude that the reductionism underlying the exact science is not suitable to open complex giant system, and the only feasible alternative is the meta-synthetic engineering from the qualitative to the quantitative. 相似文献
100.
J E Landegent N Jansen in de Wal G J van Ommen F Baas J J de Vijlder P van Duijn M Van der Ploeg 《Nature》1985,317(6033):175-177
During the past few years, several methods have been developed for the detection of specific nucleic acid sequences by in situ hybridization using non-radioactive labels such as fluorochromes, cytochemically detectable enzymes and electron-dense markers. These methods are preferable to autoradiography in terms of speed of performance and topological resolution. Their limited sensitivity, however, has so far restricted their use to the detection of repeated sequences. Here we report single gene detection with a procedure using 2-acetylaminofluorene (AAF)-modified probes, immunoperoxidase cytochemistry and reflection-contrast microscopy. We confirmed the autoradiographic data on the localization of the human thyroglobulin (Tg) gene to the distal end of the long arm of chromosome 8. A mixture of cosmid cHT2-derived subclones of the 3' part of the Tg gene, 22.3 kilobase pairs (kbp) in total, was used as a hybridization probe. This procedure can be used to map other unique sequences, if genomic clones are available from which clones with an appropriate amount of inserts can be isolated. 相似文献