全文获取类型
收费全文 | 4176篇 |
免费 | 381篇 |
国内免费 | 3篇 |
出版年
2023年 | 28篇 |
2022年 | 50篇 |
2021年 | 131篇 |
2020年 | 80篇 |
2019年 | 95篇 |
2018年 | 118篇 |
2017年 | 111篇 |
2016年 | 175篇 |
2015年 | 311篇 |
2014年 | 282篇 |
2013年 | 276篇 |
2012年 | 453篇 |
2011年 | 363篇 |
2010年 | 234篇 |
2009年 | 189篇 |
2008年 | 275篇 |
2007年 | 245篇 |
2006年 | 200篇 |
2005年 | 191篇 |
2004年 | 132篇 |
2003年 | 139篇 |
2002年 | 113篇 |
2001年 | 23篇 |
2000年 | 24篇 |
1999年 | 17篇 |
1998年 | 27篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 21篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1985年 | 6篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1976年 | 8篇 |
1975年 | 11篇 |
1974年 | 5篇 |
1972年 | 7篇 |
1971年 | 5篇 |
1968年 | 7篇 |
排序方式: 共有4560条查询结果,搜索用时 31 毫秒
71.
Lisa N. Meihls Vinzenz Handrick Gaetan Glauser Hugues Barbier Harleen Kaur Meena M. Haribal Alexander E. Lipka Jonathan Gershenzon Edward S. Buckler Matthias Erb Tobias G. K?llner Georg Jander 《The Plant cell》2013,25(6):2341-2355
Plants differ greatly in their susceptibility to insect herbivory, suggesting both local adaptation and resistance tradeoffs. We used maize (Zea mays) recombinant inbred lines to map a quantitative trait locus (QTL) for the maize leaf aphid (Rhopalosiphum maidis) susceptibility to maize Chromosome 1. Phytochemical analysis revealed that the same locus was also associated with high levels of 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside (HDMBOA-Glc) and low levels of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside (DIMBOA-Glc). In vitro enzyme assays with candidate genes from the region of the QTL identified three O-methyltransferases (Bx10a-c) that convert DIMBOA-Glc to HDMBOA-Glc. Variation in HDMBOA-Glc production was attributed to a natural CACTA family transposon insertion that inactivates Bx10c in maize lines with low HDMBOA-Glc accumulation. When tested with a population of 26 diverse maize inbred lines, R. maidis produced more progeny on those with high HDMBOA-Glc and low DIMBOA-Glc. Although HDMBOA-Glc was more toxic to R. maidis than DIMBOA-Glc in vitro, BX10c activity and the resulting decline of DIMBOA-Glc upon methylation to HDMBOA-Glc were associated with reduced callose deposition as an aphid defense response in vivo. Thus, a natural transposon insertion appears to mediate an ecologically relevant trade-off between the direct toxicity and defense-inducing properties of maize benzoxazinoids. 相似文献
72.
Many existing methods for sustainable technical product design focus on environmental efficiency while lacking a framework for a holistic, sustainable design approach that includes combined social, technical, economic, and environmental aspects in the whole product life cycle, and that provides guidance on a technical product development level. This research proposes a framework for sustainable technical product design in the case of skis. We developed a ski under the Grown brand, benchmarked according to social, environmental, economic, and technical targets, following an initial sustainability assessment, and delivered the first environmental life cycle assessment (ELCA) and the first social life cycle assessment (SLCA) of skis. The framework applies a virtual development process as a combination of ELCA to calculate the environmental footprint as carbon equivalents of all materials and processes and a technical computer‐aided design (CAD) and computer‐aided engineering (CAE) simulation and virtual optimization using parameter studies for the nearly prototype‐free development of the benchmarked skis. The feedback loops between life cycle assessment (LCA) and virtual simulation led to the elimination of highly energy intensive materials, to the pioneering use of basalt fibers in skis, to the optimization of the use of natural materials using protective coatings from natural resins, and to the optimization of the production process. From an environmental perspective, a minimum 32% reduction in carbon equivalent emissions of materials in relation to other comparably performing skis has been achieved, as well as a pioneering step forward toward transparent communication of the environmental performance by the individual, comparable, and first published ski carbon footprint per volume unit. 相似文献
73.
Rufus Turner Tobias Baron Siegfried Wolffram Anne Marie Minihane Aedin Cassidy Gerald Rimbach 《Free radical research》2013,47(2):209-216
Soy isoflavones are thought to have a cardioprotective effect that is partly mediated by an inhibitory influence on the oxidation of low density lipoprotein (LDL). However, the aglycone forms investigated in many previous studies do not circulate in appreciable quantities because they are metabolised in the gut and liver. We investigated effects of various isoflavone metabolites, including for the first time the sulphated conjugates formed in the liver and the mucosa of the small intestine, on copper-induced LDL oxidation. The parent aglycones inhibited oxidation, although only 5% as well as quercetin. Metabolism increased or decreased their effectiveness. Equol inhibited 2.65-fold better than its parent compound daidzein and 8-hydroxydaidzein, not previously assessed, was 12.5-fold better than daidzein. However, monosulphated conjugates of genistein, daidzein and equol were much less effective and disulphates completely ineffective. Since almost all isoflavones circulate as conjugates, these data suggest that despite the increased potency produced by some metabolic changes, isoflavones may not be effective antioxidants in vivo unless they are deconjugated again. 相似文献
74.
Marrit Putker Tobias Madl Harmjan R. Vos Hesther de Ruiter Marieke Visscher Maaike C.W. van den Berg Mohammed Kaplan Hendrik C. Korswagen Rolf Boelens Michiel Vermeulen Boudewijn M.T. Burgering Tobias B. Dansen 《Molecular cell》2013,49(4):730-742
- Download : Download high-res image (206KB)
- Download : Download full-size image
75.
76.
77.
78.
Choimaa Dulamsuren Tobias Wommelsdorf Fengjun Zhao Yaoqin Xue Bulat Z. Zhumadilov Christoph Leuschner Markus Hauck 《Ecosystems》2013,16(8):1536-1549
The larch forests at the southern limit of the Siberian boreal forest in Central Asia have repeatedly experienced strong recent growth declines attributed to decreasing summer precipitation in the course of climate warming. Here, we present evidence from the southernmost Larix sibirica forests in eastern Kazakhstan that these declines are primarily caused by a decrease in effective moisture due to increasing summer temperatures, despite constant annual, and summer precipitation. Tree-ring chronologies (>800 trees) showed a reduction by 50–80% in mean ring width and an increase in the frequency of missing rings since the 1970s. Climate-response analysis revealed a stronger (negative) effect of summer temperature (in particular of the previous year’s June and July temperature) on radial growth than summer precipitation (positive effect). It is assumed that a rise in the atmospheric vapor pressure deficit, which typically increases with temperature, is negatively affecting tree water status and radial growth, either directly or indirectly through reduced soil moisture. Larch rejuvenation ceased in the 1950s, which is partly explained by increasing topsoil desiccation in a warmer climate and a high drought susceptibility of larch germination, as was demonstrated by a germination experiment with variable soil moisture levels. The lack of regeneration and the reduced annual stem increment suggest that sustainable forest management aiming at timber harvesting is no longer feasible in these southern boreal forests. Progressive climate warming is likely to cause a future northward shift of the southern limit of the boreal forest. 相似文献
79.
Sara Borin Francesca Mapelli Eleonora Rolli Bongkeun Song Craig Tobias Markus C. Schmid Gert J. De Lange Gert J. Reichart Stefan Schouten Mike Jetten Daniele Daffonchio 《Extremophiles : life under extreme conditions》2013,17(2):289-299
To extend the knowledge of anaerobic ammonium oxidation (anammox) habitats, bacterial communities were examined in two hypersaline sulphidic basins in Eastern Mediterranean Sea. The 2 m thick seawater–brine haloclines of the deep anoxic hypersaline basins Bannock and L’Atalante were sampled in intervals of 10 cm with increasing salinity. 15N isotope pairing incubation experiments showed the production of 29N2 and 30N2 gases in the chemoclines, ranging from 6.0 to 9.2 % salinity of the L’Atalante basin. Potential anammox rates ranged from 2.52 to 49.65 nmol N2 L?1 day?1 while denitrification was a major N2 production pathway, accounting for more than 85.5 % of total N2 production. Anammox-related 16S rRNA genes were detected along the L’Atalante and Bannock haloclines up to 24 % salinity, and the amplification of the hydrazine synthase genes (hzsA) further confirmed the presence of anammox bacteria in Bannock. Fluorescence in situ hybridisation and sequence analysis of 16S rRNA genes identified representatives of the marine anammox genus ‘Candidatus Scalindua’ and putatively new operational taxonomic units closely affiliated to sequences retrieved in marine environments that have documented anammox activity. ‘Scalindua brodae’ like sequences constituted up to 84.4 % of the sequences retrieved from Bannock. The anammox community in L’Atalante was different than in Bannock and was stratified according to salinity increase. This study putatively extends anammox bacterial habitats to extremely saline sulphidic ecosystems. 相似文献
80.
Jan Plue Pieter De Frenne Kamal Acharya Jrg Brunet Olivier Chabrerie Guillaume Decocq Martin Diekmann Bente J. Graae Thilo Heinken Martin Hermy Annette Kolb Isgard Lemke Jaan Liira Tobias Naaf Anna Shevtsova Kris Verheyen Monika Wulf Sara A. O. Cousins 《Global Ecology and Biogeography》2013,22(10):1106-1117