全文获取类型
收费全文 | 3676篇 |
免费 | 12篇 |
国内免费 | 20篇 |
专业分类
系统科学 | 84篇 |
丛书文集 | 24篇 |
教育与普及 | 7篇 |
理论与方法论 | 9篇 |
现状及发展 | 1604篇 |
研究方法 | 199篇 |
综合类 | 1724篇 |
自然研究 | 57篇 |
出版年
2012年 | 87篇 |
2011年 | 148篇 |
2010年 | 28篇 |
2008年 | 85篇 |
2007年 | 98篇 |
2006年 | 90篇 |
2005年 | 94篇 |
2004年 | 150篇 |
2003年 | 126篇 |
2002年 | 100篇 |
2001年 | 102篇 |
2000年 | 98篇 |
1999年 | 66篇 |
1993年 | 22篇 |
1992年 | 83篇 |
1991年 | 47篇 |
1990年 | 44篇 |
1989年 | 37篇 |
1988年 | 26篇 |
1987年 | 41篇 |
1986年 | 46篇 |
1985年 | 51篇 |
1984年 | 58篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 26篇 |
1980年 | 45篇 |
1979年 | 96篇 |
1978年 | 61篇 |
1977年 | 80篇 |
1976年 | 53篇 |
1975年 | 53篇 |
1974年 | 102篇 |
1973年 | 86篇 |
1972年 | 75篇 |
1971年 | 83篇 |
1970年 | 117篇 |
1969年 | 104篇 |
1968年 | 113篇 |
1967年 | 97篇 |
1966年 | 106篇 |
1965年 | 74篇 |
1964年 | 31篇 |
1959年 | 27篇 |
1958年 | 49篇 |
1957年 | 39篇 |
1956年 | 44篇 |
1955年 | 31篇 |
1954年 | 25篇 |
1948年 | 33篇 |
排序方式: 共有3708条查询结果,搜索用时 15 毫秒
1.
Paul D. Taylor Silviu O. Martha Dennis P. Gordon 《Journal of Natural History》2018,52(25-26):1657-1721
Genera assigned to the cheilostome bryozoan family Onychocellidae are revised based on the skeletal morphology of the type species and, when possible, the type material of these species. All genera are illustrated using scanning electron micrographs, some for the first time. Onychocellidae, which ranges from the Cenomanian stage of the Cretaceous to the Recent, has been a particularly troublesome family because of poorly defined generic concepts correlating at least in part with a paucity of morphological characters. Thirty-five genera are described in this review. Of these, two are recognised as subjective synonyms of other onychocellid genera (Rhebasia and Semieschara), one cannot be sufficiently characterised from the type material (Collura), and two are new: Aechmellina gen. nov. (type species Aechmella falcifera) and Kamilocella gen. nov. (type species Eschara latilabris). A neotype is chosen for Rhagasostoma hexagonum, the type species of Rhagasostoma. A key is provided to assist in the identification of onychocellid genera. Phylogenetic relationships between genera remain obscure and are unlikely to be fully resolved based on skeletal morphology alone. The family as an entity is loosely circumscribed and almost certainly paraphyletic, containing stem genera of other anascan familes such as Lunulitidae, Coscinopleuridae and Aspidostomatidae.
www.zoobank.org/urn:lsid:org:pub:63A31AD2-F049-42CB-A45B-557014DC286E 相似文献
2.
3.
系统地总结和介绍了我国高性能计算机,包括“银河”系列巨型机、“曙光”系列巨型机、“神威”系列巨型机、“深腾”系列巨型机以及“深超”系列巨型机的开发研制以及应用情况。 相似文献
4.
董文伟 《科技情报开发与经济》2004,14(6):296-297
以具体工程为例,介绍了建筑物地基处理的设计、施工中遵循的原则,施工中遇到特殊情况时采取的处理方法和必要的检测方法,对几种桩基的设计要求、施工工艺及过程、质量控制等情况进行了简单阐述。 相似文献
5.
关于21世纪图书馆员继续教育问题的思考 总被引:4,自引:1,他引:3
罗雪晴 《科技情报开发与经济》2004,14(6):14-15
论述了21世纪对图书馆员进行继续教育的必要性,介绍了图书馆员继续教育的内容,针对我国图书馆员继续教育的状况,提出了应采取加大投入、进行针对性培训、运用激励机制等措施来加强对图书馆员的继续教育。 相似文献
6.
Romeo S Pennacchio LA Fu Y Boerwinkle E Tybjaerg-Hansen A Hobbs HH Cohen JC 《Nature genetics》2007,39(4):513-516
Resequencing genes provides the opportunity to assess the full spectrum of variants that influence complex traits. Here we report the first application of resequencing to a large population (n = 3,551) to examine the role of the adipokine ANGPTL4 in lipid metabolism. Nonsynonymous variants in ANGPTL4 were more prevalent in individuals with triglyceride levels in the lowest quartile than in individuals with levels in the highest quartile (P = 0.016). One variant (E40K), present in approximately 3% of European Americans, was associated with significantly lower plasma levels of triglyceride and higher levels of high-density lipoprotein cholesterol in European Americans from the Atherosclerosis Risk in Communities Study and in Danes from the Copenhagen City Heart Study. The ratio of nonsynonymous to synonymous variants was higher in European Americans than in African Americans (4:1 versus 1.3:1), suggesting population-specific relaxation of purifying selection. Thus, resequencing of ANGPTL4 in a multiethnic population allowed analysis of the phenotypic effects of both rare and common variants while taking advantage of genetic variation arising from ethnic differences in population history. 相似文献
7.
Hellgren M Strömberg P Gallego O Martras S Farrés J Persson B Parés X Höög JO 《Cellular and molecular life sciences : CMLS》2007,64(4):498-505
The metabolism of all-trans- and 9-cis-retinol/ retinaldehyde has been investigated with focus on the activities of human, mouse and rat alcohol dehydrogenase 2
(ADH2), an intriguing enzyme with apparently different functions in human and rodents. Kinetic constants were determined with
an HPLC method and a structural approach was implemented by in silico substrate dockings. For human ADH2, the determined Km values ranged from 0.05 to 0.3 μM and kcat values from 2.3 to 17.6 min−1, while the catalytic efficiency for 9-cis-retinol showed the highest value for any substrate. In contrast, poor activities
were detected for the rodent enzymes. A mouse ADH2 mutant (ADH2Pro47His) was studied that resembles the human ADH2 setup.
This mutation increased the retinoid activity up to 100-fold. The Km values of human ADH2 are the lowest among all known human retinol dehydrogenases, which clearly support a role in hepatic
retinol oxidation at physiological concentrations.
Received 12 October 2006; received after revision 6 December 2006; accepted 8 January 2007 相似文献
8.
Wang E Lenferink A O'Connor-McCourt M 《Cellular and molecular life sciences : CMLS》2007,64(14):1752-1762
Genomic alterations lead to cancer complexity and form a major hurdle for comprehensive understanding of the molecular mechanisms underlying oncogenesis. In this review, we describe recent advances in studying cancer-associated genes from a systems biology point of view. The integration of known cancer genes onto protein and signaling networks reveals the characteristics of cancer genes within networks. This approach shows that cancer genes often function as network hub proteins which are involved in many cellular processes and form focal nodes in information exchange between many signaling pathways. Literature mining allows constructing gene-gene networks, in which new cancer genes can be identified. The gene expression profiles of cancer cells are used for reconstructing gene regulatory networks. By doing so, genes which are involved in the regulation of cancer progression can be picked up from these networks, after which their functions can be further confirmed in the laboratory. 相似文献
9.
KERMACK WO 《Science progress》1948,36(142):288-292
10.
Association scan of 14,500 nonsynonymous SNPs in four diseases identifies autoimmunity variants 总被引:2,自引:0,他引:2
Wellcome Trust Case Control Consortium;Australo-Anglo-American Spondylitis Consortium 《Nature genetics》2007,39(11):1329-1337
We have genotyped 14,436 nonsynonymous SNPs (nsSNPs) and 897 major histocompatibility complex (MHC) tag SNPs from 1,000 independent cases of ankylosing spondylitis (AS), autoimmune thyroid disease (AITD), multiple sclerosis (MS) and breast cancer (BC). Comparing these data against a common control dataset derived from 1,500 randomly selected healthy British individuals, we report initial association and independent replication in a North American sample of two new loci related to ankylosing spondylitis, ARTS1 and IL23R, and confirmation of the previously reported association of AITD with TSHR and FCRL3. These findings, enabled in part by increased statistical power resulting from the expansion of the control reference group to include individuals from the other disease groups, highlight notable new possibilities for autoimmune regulation and suggest that IL23R may be a common susceptibility factor for the major 'seronegative' diseases. 相似文献