全文获取类型
收费全文 | 19058篇 |
免费 | 60篇 |
国内免费 | 57篇 |
专业分类
系统科学 | 303篇 |
丛书文集 | 446篇 |
教育与普及 | 36篇 |
理论与方法论 | 75篇 |
现状及发展 | 9095篇 |
研究方法 | 795篇 |
综合类 | 8200篇 |
自然研究 | 225篇 |
出版年
2012年 | 250篇 |
2011年 | 498篇 |
2010年 | 128篇 |
2009年 | 114篇 |
2008年 | 316篇 |
2007年 | 382篇 |
2006年 | 332篇 |
2005年 | 355篇 |
2004年 | 321篇 |
2003年 | 379篇 |
2002年 | 308篇 |
2001年 | 640篇 |
2000年 | 631篇 |
1999年 | 362篇 |
1992年 | 349篇 |
1991年 | 268篇 |
1990年 | 313篇 |
1989年 | 281篇 |
1988年 | 268篇 |
1987年 | 291篇 |
1986年 | 290篇 |
1985年 | 356篇 |
1984年 | 265篇 |
1983年 | 232篇 |
1982年 | 219篇 |
1981年 | 258篇 |
1980年 | 277篇 |
1979年 | 599篇 |
1978年 | 493篇 |
1977年 | 509篇 |
1976年 | 384篇 |
1975年 | 399篇 |
1974年 | 615篇 |
1973年 | 496篇 |
1972年 | 456篇 |
1971年 | 546篇 |
1970年 | 708篇 |
1969年 | 618篇 |
1968年 | 573篇 |
1967年 | 591篇 |
1966年 | 491篇 |
1965年 | 369篇 |
1964年 | 126篇 |
1959年 | 213篇 |
1958年 | 303篇 |
1957年 | 206篇 |
1956年 | 180篇 |
1955年 | 176篇 |
1954年 | 166篇 |
1948年 | 97篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
51.
52.
T lymphocytes recognize antigen in the form of peptides that associate with specific alleles of class I or class II major histocompatibility (MHC) molecules. By contrast with the clear MHC allele-specific binding of peptides to purified class II molecules purified solubilized class I molecules either bind relatively poorly or show degenerate specificity. Using photo-affinity labelling, we demonstrate here the specific interaction of peptides with cell-associated MHC class I molecules and show that this involves metabolically active processes. 相似文献
53.
European blackcaps,Sylvia atricapilla, with one breeding season per year, have a single-peaked annual testes cycle. However, African conspecifics from the Cape Verde Islands with two breeding seasons per annum demonstrate a two-peaked cycle. Both population-specific cycles reflect differences in the respective endogenous circannual rhythms. Experimental hybridization of birds of the two populations resulted in an intermediate pattern of testes cycle, thus demonstrating that there are genetic components for some temporal aspects in an avian reproductive cycle. Another characteristic of the African birds, their extremely rapid juvenile development and early sexual maturity (at an age of 5–6 months) proved largely to be a photoperiodic (short-day) effect in birds hatched in autumn. The same effect could also be induced in European conspecifics exposed to correspondingly short day-lengths. 相似文献
54.
The rough endoplasmic reticulum membranes of mammalian cells contain specific ribosome-binding sites. A purification to apparent homogeneity of a negatively charged protein (ERp180) of relative molecular mass 180,000 (180 K) was reported which was proposed to function as a rough endoplasmic reticulum ribosome receptor. We report here that ribosome-binding site activity quantitatively solubilized from rough endoplasmic reticulum membranes does not cofractionate with ERp180. By contrast, ribosome-binding site activity fractionates as a much smaller, positively charged protein. 相似文献
55.
56.
Dhar-Chowdhury P Malester B Rajacic P Coetzee WA 《Cellular and molecular life sciences : CMLS》2007,64(23):3069-3083
Glycolysis is an evolutionary conserved metabolic pathway that provides small amounts of energy in the form of ATP when compared
to other pathways such as oxidative phosphorylation or fatty acid oxidation. The ATP levels inside metabolically active cells
are not constant and the local ATP level will depend on the site of production as well as the respective rates of ATP production,
diffusion and consumption. Membrane ion transporters (pumps, exchangers and channels) are located at sites distal to the major
sources of ATP formation (the mitochondria). We review evidence that the glycolytic complex is associated with membranes;
both at the plasmalemma and with membranes of the endo/sarcoplasmic reticular network. We examine the evidence for the concept
that many of the ion transporters are regulated preferentially by the glycolytic process. These include the Na+/K+-ATPase, the H+-ATPase, various types of Ca2+-ATPases, the Na+/H+ exchanger, the ATP-sensitive K+ channel, cation channels, Na+ channels, Ca2+ channels and other channels involved in intracellular Ca2+ homeostasis. Regulation of these pumps, exchangers and ion channels by the glycolytic process has important consequences
in a variety of physiological and pathophysiological processes, and a better understanding of this mode of regulation may
have important consequences for developing future strategies in combating disease and developing novel therapeutic approaches.
Received 20 July 2007; received after revision 30 July 2007; accepted 17 August 2007 相似文献
57.
58.
59.
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
60.
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