全文获取类型
收费全文 | 19528篇 |
免费 | 41篇 |
国内免费 | 71篇 |
专业分类
系统科学 | 167篇 |
丛书文集 | 288篇 |
教育与普及 | 44篇 |
理论与方法论 | 122篇 |
现状及发展 | 8779篇 |
研究方法 | 1049篇 |
综合类 | 8876篇 |
自然研究 | 315篇 |
出版年
2013年 | 151篇 |
2012年 | 381篇 |
2011年 | 692篇 |
2010年 | 161篇 |
2009年 | 118篇 |
2008年 | 392篇 |
2007年 | 421篇 |
2006年 | 441篇 |
2005年 | 458篇 |
2004年 | 450篇 |
2003年 | 379篇 |
2002年 | 381篇 |
2001年 | 637篇 |
2000年 | 595篇 |
1999年 | 404篇 |
1992年 | 342篇 |
1991年 | 280篇 |
1990年 | 293篇 |
1989年 | 265篇 |
1988年 | 245篇 |
1987年 | 301篇 |
1986年 | 306篇 |
1985年 | 334篇 |
1984年 | 301篇 |
1983年 | 231篇 |
1982年 | 205篇 |
1981年 | 207篇 |
1980年 | 271篇 |
1979年 | 628篇 |
1978年 | 487篇 |
1977年 | 501篇 |
1976年 | 330篇 |
1975年 | 379篇 |
1974年 | 584篇 |
1973年 | 501篇 |
1972年 | 505篇 |
1971年 | 569篇 |
1970年 | 759篇 |
1969年 | 557篇 |
1968年 | 456篇 |
1967年 | 559篇 |
1966年 | 467篇 |
1965年 | 326篇 |
1959年 | 169篇 |
1958年 | 276篇 |
1957年 | 212篇 |
1956年 | 180篇 |
1955年 | 149篇 |
1954年 | 155篇 |
1948年 | 130篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
331.
332.
333.
Snake envenomation is a socio-medical problem of considerable magnitude. About 2.5 million people are bitten by snakes annually,
more than 100,000 fatally. However, although bites can be deadly, snake venom is a natural biological resource that contains
several components of potential therapeutic value. Venom has been used in the treatment of a variety of pathophysiological
conditions in Ayurveda, homeopathy and folk medicine. With the advent of biotechnology, the efficacy of such treatments has
been substantiated by purifying components of venom and delineating their therapeutic properties. This review will focus on
certain snake venom components and their applications in health and disease.
Received 6 July 2006; received after revision 14 August 2006; accepted 28 September 2006 相似文献
334.
335.
Memories become stabilized through a time-dependent process that requires gene expression and is commonly known as consolidation. During this time, memories are labile and can be disrupted by a number of interfering events, including electroconvulsive shock, trauma and other learning or the transient effect of drugs such as protein synthesis inhibitors. Once consolidated, memories are insensitive to these disruptions. However, they can again become fragile if recalled or reactivated. Reactivation creates another time-dependent process, known as reconsolidation, during which the memory is restabilized. Here we discuss some of the questions currently debated in the field of memory consolidation and reconsolidation, the molecular and anatomical requirements for both processes and, finally, their functional relationship. 相似文献
336.
Betaine homocysteine S-methyltransferase: just a regulator of homocysteine metabolism? 总被引:1,自引:0,他引:1
Betaine homocysteine methyltransferase (BHMT), a Zn2+-dependent thiolmethyltransferase, contributes to the regulation of homocysteine levels, increases in which are considered
a risk factor for cardiovascular diseases. Most plasma homocysteine is generated through the liver methionine cycle, in which
BHMT metabolizes approximately 25% of this non-protein amino acid. This process allows recovery of one of the three methylation
equivalents used in phosphatidylcholine synthesis through transmethylation, a major homocysteine-producing pathway. Although
BHMT has been known for over 40 years, the difficulties encountered in its isolation precluded detailed studies until very
recently. Thus, the last 10 years, since the sequence became available, have yielded extensive structural and functional data.
Moreover, recent findings offer clues for potential new functions for BHMT. The purpose of this review is to provide an integrated
view of the knowledge available on BHMT, and to analyze its putative roles in other processes through interactions uncover
to date.
Received 26 May 2006; received after revision 3 July 2006; accepted 24 August 2006 相似文献
337.
Valdar W Solberg LC Gauguier D Burnett S Klenerman P Cookson WO Taylor MS Rawlins JN Mott R Flint J 《Nature genetics》2006,38(8):879-887
Difficulties in fine-mapping quantitative trait loci (QTLs) are a major impediment to progress in the molecular dissection of complex traits in mice. Here we show that genome-wide high-resolution mapping of multiple phenotypes can be achieved using a stock of genetically heterogeneous mice. We developed a conservative and robust bootstrap analysis to map 843 QTLs with an average 95% confidence interval of 2.8 Mb. The QTLs contribute to variation in 97 traits, including models of human disease (asthma, type 2 diabetes mellitus, obesity and anxiety) as well as immunological, biochemical and hematological phenotypes. The genetic architecture of almost all phenotypes was complex, with many loci each contributing a small proportion to the total variance. Our data set, freely available at http://gscan.well.ox.ac.uk, provides an entry point to the functional characterization of genes involved in many complex traits. 相似文献
338.
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
339.
Horvath A Boikos S Giatzakis C Robinson-White A Groussin L Griffin KJ Stein E Levine E Delimpasi G Hsiao HP Keil M Heyerdahl S Matyakhina L Libè R Fratticci A Kirschner LS Cramer K Gaillard RC Bertagna X Carney JA Bertherat J Bossis I Stratakis CA 《Nature genetics》2006,38(7):794-800
Phosphodiesterases (PDEs) regulate cyclic nucleotide levels. Increased cyclic AMP (cAMP) signaling has been associated with PRKAR1A or GNAS mutations and leads to adrenocortical tumors and Cushing syndrome. We investigated the genetic source of Cushing syndrome in individuals with adrenocortical hyperplasia that was not caused by known defects. We performed genome-wide SNP genotyping, including the adrenocortical tumor DNA. The region with the highest probability to harbor a susceptibility gene by loss of heterozygosity (LOH) and other analyses was 2q31-2q35. We identified mutations disrupting the expression of the PDE11A isoform-4 gene (PDE11A) in three kindreds. Tumor tissues showed 2q31-2q35 LOH, decreased protein expression and high cyclic nucleotide levels and cAMP-responsive element binding protein (CREB) phosphorylation. PDE11A codes for a dual-specificity PDE that is expressed in adrenal cortex and is partially inhibited by tadalafil and other PDE inhibitors; its germline inactivation is associated with adrenocortical hyperplasia, suggesting another means by which dysregulation of cAMP signaling causes endocrine tumors. 相似文献
340.
The genetic basis of most conditions characterized by congenital contractures is largely unknown. Here we show that mutations in the embryonic myosin heavy chain (MYH3) gene cause Freeman-Sheldon syndrome (FSS), one of the most severe multiple congenital contracture (that is, arthrogryposis) syndromes, and nearly one-third of all cases of Sheldon-Hall syndrome (SHS), the most common distal arthrogryposis. FSS and SHS mutations affect different myosin residues, demonstrating that MYH3 genotype is predictive of phenotype. A structure-function analysis shows that nearly all of the MYH3 mutations are predicted to interfere with myosin's catalytic activity. These results add to the growing body of evidence showing that congenital contractures are a shared outcome of prenatal defects in myofiber force production. Elucidation of the genetic basis of these syndromes redefines congenital contractures as unique defects of the sarcomere and provides insights about what has heretofore been a poorly understood group of disorders. 相似文献