全文获取类型
收费全文 | 541篇 |
免费 | 2篇 |
国内免费 | 3篇 |
专业分类
系统科学 | 7篇 |
理论与方法论 | 4篇 |
现状及发展 | 84篇 |
研究方法 | 78篇 |
综合类 | 340篇 |
自然研究 | 33篇 |
出版年
2018年 | 4篇 |
2017年 | 6篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 2篇 |
2012年 | 43篇 |
2011年 | 77篇 |
2010年 | 7篇 |
2009年 | 3篇 |
2008年 | 29篇 |
2007年 | 35篇 |
2006年 | 35篇 |
2005年 | 45篇 |
2004年 | 29篇 |
2003年 | 27篇 |
2002年 | 36篇 |
2001年 | 14篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1995年 | 2篇 |
1993年 | 3篇 |
1991年 | 3篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1971年 | 8篇 |
1970年 | 9篇 |
1969年 | 1篇 |
1968年 | 4篇 |
1967年 | 5篇 |
1966年 | 6篇 |
1965年 | 5篇 |
1961年 | 2篇 |
1958年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有546条查询结果,搜索用时 15 毫秒
171.
A. I. Scott 《Cellular and molecular life sciences : CMLS》1961,17(2):68-69
Zusammenfassung Eine allgemeine Methode für die Berechnung der Hauptabsorptionsbande benzolischer Carbonylverbindungen wird zur Diskussion gestellt. 相似文献
172.
173.
174.
175.
Distribution of acid glycosaminoglycans in human articular cartilage 总被引:11,自引:0,他引:11
176.
Enhancing the crops to feed the poor 总被引:21,自引:0,他引:21
Solutions to the problem of how the developing world will meet its future food needs are broader than producing more food, although the successes of the 'Green Revolution' demonstrate the importance of technology in generating the growth in food output in the past. Despite these successes, the world still faces continuing vulnerability to food shortages. Given the necessary funding, it seems likely that conventional crop breeding, as well as emerging technologies based on molecular biology, genetic engineering and natural resource management, will continue to improve productivity in the coming decades. 相似文献
177.
Variable effects of nitrogen additions on the stability and turnover of soil carbon 总被引:50,自引:0,他引:50
Soils contain the largest near-surface reservoir of terrestrial carbon and so knowledge of the factors controlling soil carbon storage and turnover is essential for understanding the changing global carbon cycle. The influence of climate on decomposition of soil carbon has been well documented, but there remains considerable uncertainty in the potential response of soil carbon dynamics to the rapid global increase in reactive nitrogen (coming largely from agricultural fertilizers and fossil fuel combustion). Here, using 14C, 13C and compound-specific analyses of soil carbon from long-term nitrogen fertilization plots, we show that nitrogen additions significantly accelerate decomposition of light soil carbon fractions (with decadal turnover times) while further stabilizing soil carbon compounds in heavier, mineral-associated fractions (with multidecadal to century lifetimes). Despite these changes in the dynamics of different soil pools, we observed no significant changes in bulk soil carbon, highlighting a limitation inherent to the still widely used single-pool approach to investigating soil carbon responses to changing environmental conditions. It remains to be seen if the effects observed here-caused by relatively high, short-term fertilizer additions-are similar to those arising from lower, long-term additions of nitrogen to natural ecosystems from atmospheric deposition, but our results suggest nonetheless that current models of terrestrial carbon cycling do not contain the mechanisms needed to capture the complex relationship between nitrogen availability and soil carbon storage. 相似文献
178.
Sarrao JL Morales LA Thompson JD Scott BL Stewart GR Wastin F Rebizant J Boulet P Colineau E Lander GH 《Nature》2002,420(6913):297-299
Plutonium is a metal of both technological relevance and fundamental scientific interest. Nevertheless, the electronic structure of plutonium, which directly influences its metallurgical properties, is poorly understood. For example, plutonium's 5f electrons are poised on the border between localized and itinerant, and their theoretical treatment pushes the limits of current electronic structure calculations. Here we extend the range of complexity exhibited by plutonium with the discovery of superconductivity in PuCoGa5. We argue that the observed superconductivity results directly from plutonium's anomalous electronic properties and as such serves as a bridge between two classes of spin-fluctuation-mediated superconductors: the known heavy-fermion superconductors and the high-T(c) copper oxides. We suggest that the mechanism of superconductivity is unconventional; seen in that context, the fact that the transition temperature, T(c) approximately 18.5 K, is an order of magnitude greater than the maximum seen in the U- and Ce-based heavy-fermion systems may be natural. The large critical current displayed by PuCoGa5, which comes from radiation-induced self damage that creates pinning centres, would be of technological importance for applied superconductivity if the hazardous material plutonium were not a constituent. 相似文献
179.
Briggs SD Xiao T Sun ZW Caldwell JA Shabanowitz J Hunt DF Allis CD Strahl BD 《Nature》2002,418(6897):498
The fundamental unit of eukaryotic chromatin, the nucleosome, consists of genomic DNA wrapped around the conserved histone proteins H3, H2B, H2A and H4, all of which are variously modified at their amino- and carboxy-terminal tails to influence the dynamics of chromatin structure and function -- for example, conjugation of histone H2B with ubiquitin controls the outcome of methylation at a specific lysine residue (Lys 4) on histone H3, which regulates gene silencing in the yeast Saccharomyces cerevisiae. Here we show that ubiquitination of H2B is also necessary for the methylation of Lys 79 in H3, the only modification known to occur away from the histone tails, but that not all methylated lysines in H3 are regulated by this 'trans-histone' pathway because the methylation of Lys 36 in H3 is unaffected. Given that gene silencing is regulated by the methylation of Lys 4 and Lys 79 in histone H3, we suggest that H2B ubiquitination acts as a master switch that controls the site-selective histone methylation patterns responsible for this silencing. 相似文献
180.
A physical map of the mouse genome 总被引:1,自引:0,他引:1
Gregory SG Sekhon M Schein J Zhao S Osoegawa K Scott CE Evans RS Burridge PW Cox TV Fox CA Hutton RD Mullenger IR Phillips KJ Smith J Stalker J Threadgold GJ Birney E Wylie K Chinwalla A Wallis J Hillier L Carter J Gaige T Jaeger S Kremitzki C Layman D Maas J McGrane R Mead K Walker R Jones S Smith M Asano J Bosdet I Chan S Chittaranjan S Chiu R Fjell C Fuhrmann D Girn N Gray C Guin R Hsiao L Krzywinski M Kutsche R Lee SS Mathewson C McLeavy C Messervier S Ness S Pandoh P Prabhu AL Saeedi P 《Nature》2002,418(6899):743-750
A physical map of a genome is an essential guide for navigation, allowing the location of any gene or other landmark in the chromosomal DNA. We have constructed a physical map of the mouse genome that contains 296 contigs of overlapping bacterial clones and 16,992 unique markers. The mouse contigs were aligned to the human genome sequence on the basis of 51,486 homology matches, thus enabling use of the conserved synteny (correspondence between chromosome blocks) of the two genomes to accelerate construction of the mouse map. The map provides a framework for assembly of whole-genome shotgun sequence data, and a tile path of clones for generation of the reference sequence. Definition of the human-mouse alignment at this level of resolution enables identification of a mouse clone that corresponds to almost any position in the human genome. The human sequence may be used to facilitate construction of other mammalian genome maps using the same strategy. 相似文献