全文获取类型
收费全文 | 12057篇 |
免费 | 24篇 |
国内免费 | 43篇 |
专业分类
系统科学 | 36篇 |
丛书文集 | 80篇 |
教育与普及 | 32篇 |
理论与方法论 | 43篇 |
现状及发展 | 5162篇 |
研究方法 | 590篇 |
综合类 | 5992篇 |
自然研究 | 189篇 |
出版年
2013年 | 97篇 |
2012年 | 198篇 |
2011年 | 368篇 |
2010年 | 87篇 |
2009年 | 59篇 |
2008年 | 196篇 |
2007年 | 231篇 |
2006年 | 213篇 |
2005年 | 231篇 |
2004年 | 223篇 |
2003年 | 216篇 |
2002年 | 210篇 |
2001年 | 381篇 |
2000年 | 375篇 |
1999年 | 268篇 |
1992年 | 237篇 |
1991年 | 181篇 |
1990年 | 204篇 |
1989年 | 190篇 |
1988年 | 205篇 |
1987年 | 209篇 |
1986年 | 162篇 |
1985年 | 251篇 |
1984年 | 174篇 |
1983年 | 150篇 |
1982年 | 166篇 |
1981年 | 135篇 |
1980年 | 171篇 |
1979年 | 385篇 |
1978年 | 295篇 |
1977年 | 291篇 |
1976年 | 254篇 |
1975年 | 288篇 |
1974年 | 312篇 |
1973年 | 313篇 |
1972年 | 349篇 |
1971年 | 349篇 |
1970年 | 435篇 |
1969年 | 361篇 |
1968年 | 382篇 |
1967年 | 356篇 |
1966年 | 322篇 |
1965年 | 205篇 |
1959年 | 107篇 |
1958年 | 204篇 |
1957年 | 137篇 |
1956年 | 122篇 |
1955年 | 105篇 |
1954年 | 81篇 |
1948年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
从“十四五”保护与发展的生态关系角度,探讨了生态保护与绿色发展的十大生态关系,阐述了生态保护和绿色发展中的一系列有关生态关系的生态智慧及生态技术,并对长江、黄河等流域的生态保护和修复提出了相关建议。 相似文献
2.
Ten-day treatment with nicotine (5, 25 or 50 micrograms/ml drinking water) dose-dependently intensified gastric ulceration induced by cold-restraint, and emptying rate. Stomach contractions produced by graded doses of bethanechol i.v. were elevated further by nicotine treatment. It is suggested that chronic nicotine administration produces hypersensitivity of the gastric muscarinic receptors; stomach hypermotility contributes to the ulcer-worsening action of the alkaloid. 相似文献
3.
4.
5.
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
6.
7.
Houlden H Johnson J Gardner-Thorpe C Lashley T Hernandez D Worth P Singleton AB Hilton DA Holton J Revesz T Davis MB Giunti P Giunti P Wood NW 《Nature genetics》2007,39(12):1434-1436
The microtubule-associated protein tau (encoded by MAPT) and several tau kinases have been implicated in neurodegeneration, but only MAPT has a proven role in disease. We identified mutations in the gene encoding tau tubulin kinase 2 (TTBK2) as the cause of spinocerebellar ataxia type 11. Affected brain tissue showed substantial cerebellar degeneration and tau deposition. These data suggest that TTBK2 is important in the tau cascade and in spinocerebellar degeneration. 相似文献
8.
Recombination and linkage disequilibrium in Arabidopsis thaliana 总被引:4,自引:0,他引:4
Kim S Plagnol V Hu TT Toomajian C Clark RM Ossowski S Ecker JR Weigel D Nordborg M 《Nature genetics》2007,39(9):1151-1155
Linkage disequilibrium (LD) is a major aspect of the organization of genetic variation in natural populations. Here we describe the genome-wide pattern of LD in a sample of 19 Arabidopsis thaliana accessions using 341,602 non-singleton SNPs. LD decays within 10 kb on average, considerably faster than previously estimated. Tag SNP selection algorithms and 'hide-the-SNP' simulations suggest that genome-wide association mapping will require only 40%-50% of the observed SNPs, a reduction similar to estimates in a sample of African Americans. An Affymetrix genotyping array containing 250,000 SNPs has been designed based on these results; we demonstrate that it should have more than adequate coverage for genome-wide association mapping. The extent of LD is highly variable, and we find clear evidence of recombination hotspots, which seem to occur preferentially in intergenic regions. LD also reflects the action of selection, and it is more extensive between nonsynonymous polymorphisms than between synonymous polymorphisms. 相似文献
9.
Risheg H Graham JM Clark RD Rogers RC Opitz JM Moeschler JB Peiffer AP May M Joseph SM Jones JR Stevenson RE Schwartz CE Friez MJ 《Nature genetics》2007,39(4):451-453
Opitz-Kaveggia syndrome (also known as FG syndrome) is an X-linked disorder characterized by mental retardation, relative macrocephaly, hypotonia and constipation. We report here that the original family for whom the condition is named and five other families have a recurrent mutation (2881C>T, leading to R961W) in MED12 (also called TRAP230 or HOPA), a gene located at Xq13 that functions as a thyroid receptor-associated protein in the Mediator complex. 相似文献
10.
Lindahl E Nyman U Melles E Sigmundsson K Ståhlberg M Wahren J Obrink B Shafqat J Joseph B Jörnvall H 《Cellular and molecular life sciences : CMLS》2007,64(4):479-486
Proinsulin C-peptide is known to bind specifically to cell membranes and to exert intracellular effects, but whether it is
internalized in target cells is unknown. In this study, using confocal microscopy and immunostained or rhodamine-labeled peptide,
we show that C-peptide is internalized and localized to the cytosol of Swiss 3T3 and HEK-293 cells. In addition, transport
into nuclei was found using the labeled peptide. The internalization was followed at 37°C for up to 1 h, and was reduced at
4°C and after preincubation with pertussis toxin. Hence, it is concluded to occur via an energy-dependent, pertussis toxin-sensitive
mechanism and without detectable degradation within the experimental time course. Surface plasmon resonance measurements demonstrated
binding of HEK-293 cell extract components to C-peptide, and subsequent elution of bound material revealed the components
to be intracellular proteins. The identification of C-peptide cellular internalization, intracellular binding proteins, absence
of rapid subsequent C-peptide degradation and apparent nuclear internalization support a maintained activity similar to that
of an intracrine peptide hormone. Hence, the data suggest the possibility of one further C-peptide site of action.
Received 31 October 2006; received after revision 27 December 2006; accepted 30 December 2006 相似文献