全文获取类型
收费全文 | 14819篇 |
免费 | 1557篇 |
国内免费 | 825篇 |
出版年
2023年 | 146篇 |
2022年 | 251篇 |
2021年 | 568篇 |
2020年 | 420篇 |
2019年 | 480篇 |
2018年 | 467篇 |
2017年 | 379篇 |
2016年 | 566篇 |
2015年 | 846篇 |
2014年 | 943篇 |
2013年 | 986篇 |
2012年 | 1248篇 |
2011年 | 1186篇 |
2010年 | 757篇 |
2009年 | 614篇 |
2008年 | 842篇 |
2007年 | 856篇 |
2006年 | 715篇 |
2005年 | 645篇 |
2004年 | 616篇 |
2003年 | 567篇 |
2002年 | 510篇 |
2001年 | 230篇 |
2000年 | 174篇 |
1999年 | 183篇 |
1998年 | 159篇 |
1997年 | 114篇 |
1996年 | 92篇 |
1995年 | 76篇 |
1994年 | 64篇 |
1993年 | 63篇 |
1992年 | 113篇 |
1991年 | 102篇 |
1990年 | 66篇 |
1989年 | 83篇 |
1988年 | 56篇 |
1987年 | 55篇 |
1986年 | 60篇 |
1985年 | 67篇 |
1984年 | 66篇 |
1983年 | 49篇 |
1982年 | 34篇 |
1981年 | 35篇 |
1980年 | 34篇 |
1979年 | 47篇 |
1978年 | 40篇 |
1977年 | 40篇 |
1976年 | 32篇 |
1974年 | 37篇 |
1972年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
1. As for some other spring‐feeding moths, adult flight of Epirrita autumnata (Lepidoptera: Geometridae) occurs in late autumn. Late‐season flight is a result of a prolonged pupal period. Potential evolutionary explanations for this phenological pattern are evaluated. 2. In a laboratory rearing, there was a weak correlation between pupation date and the time of adult emergence. A substantial genetic difference in pupal period was found between two geographic populations. Adaptive evolution of eclosion time can thus be expected. 3. Metabolic costs of a prolonged pupal period were found to be moderate but still of some ecological significance. Pupal mortality is likely to form the main cost of the prolonged pupal period. 4. Mortality rates of adults, exposed in the field, showed a declining temporal trend from late summer to normal eclosion time in autumn. Lower predation pressure on adults may constitute the decisive selective advantage of late‐season flight. It is suggested that ants, not birds, were the main predators responsible for the temporal trend. 5. Egg mortality was estimated to be low; it is thus unlikely that the late adult period is selected for to reduce the time during which eggs are exposed to predators. 6. In a laboratory experiment, oviposition success was maximal at the time of actual flight peak of E. autumnata, however penalties resulting from sub‐optimal timing of oviposition remained limited. 相似文献
3.
Shashank Hambarde Chi-Lin Tsai Raj K. Pandita Albino Bacolla Anirban Maitra Vijay Charaka Clayton R. Hunt Rakesh Kumar Oliver Limbo Remy Le Meur Walter J. Chazin Susan E. Tsutakawa Paul Russell Katharina Schlacher Tej K. Pandita John A. Tainer 《Molecular cell》2021,81(14):2989-3006.e9
- Download : Download high-res image (222KB)
- Download : Download full-size image
4.
Danielle E. Haulsee Dewayne A. Fox Matthew W. Breece Tonya M. Clauss Matthew J. Oliver 《PloS one》2016,11(2)
We developed a long-term tagging method that can be used to understand species assemblages and social groupings associated with large marine fishes such as the Sand Tiger shark Carcharias taurus. We deployed internally implanted archival VEMCO Mobile Transceivers (VMTs; VEMCO Ltd. Nova Scotia, Canada) in 20 adult Sand Tigers, of which two tags were successfully recovered (10%). The recovered VMTs recorded 29,646 and 44,210 detections of telemetered animals respectively. To our knowledge, this is the first study to demonstrate a method for long-term (~ 1 year) archival acoustic transceiver tag implantation, retention, and recovery in a highly migratory marine fish. Results show low presumed mortality (n = 1, 5%), high VMT retention, and that non-lethal recovery after almost a year at liberty can be achieved for archival acoustic transceivers. This method can be applied to study the social interactions and behavioral ecology of large marine fishes. 相似文献
5.
Andrea Schneider Manuela Ruppert Oliver Hendrich Thomas Giang Maite Ogueta Stefanie Hampel Marvin Vollbach Ansgar Büschges Henrike Scholz 《PloS one》2012,7(12)
The decision to move towards a mating partner or a food source is essential for life. The mechanisms underlying these behaviors are not well understood. Here, we investigated the role of octopamine – the invertebrate analogue of noradrenaline – in innate olfactory attraction to ethanol. We confirmed that preference is caused via an olfactory stimulus by dissecting the function of the olfactory co-receptor Orco (formally known as OR83b). Orco function is not required for ethanol recognition per se, however it plays a role in context dependent recognition of ethanol. Odor-evoked ethanol preference requires the function of Tbh (Tyramine β hydroxalyse), the rate-limiting enzyme of octopamine synthesis. In addition, neuronal activity in a subset of octopaminergic neurons is necessary for olfactory ethanol preference. Notably, a specific neuronal activation pattern of tyraminergic/octopaminergic neurons elicit preference and is therefore sufficient to induce preference. In contrast, dopamine dependent increase in locomotor activity is not sufficient for olfactory ethanol preference. Consistent with the role of noradrenaline in mammalian drug induced rewards, we provide evidence that in adult Drosophila the octopaminergic neurotransmitter functions as a reinforcer and that the molecular dissection of the innate attraction to ethanol uncovers the basic properties of a response selection system. 相似文献
6.
Oliver Goldschmidt Jonathan F. Bard Alexan Takvorian 《Flexible Services and Manufacturing Journal》1997,9(3):251-272
Mixed-model assembly lines are becoming increasingly interesting as the use of just-in-time principles in manufacturing continues to expand. This paper presents, for the first time, complexity results for the underlying problem of product sequencing. It is shown that the problem is intractable for both the single station and the multiple station case. Nevertheless, efficient 1.5-approximation algorithms are developed for the early- and late-start models associated with the former case. Empirical results demonstrate that these algorithms perform extremely well in practice. 相似文献
7.
8.
N Brinkmann M Malissard M Ramuz U R?mer T Schumacher E G Berger L Elling C Wandrey A Liese 《Bioorganic & medicinal chemistry letters》2001,11(18):2503-2506
The alpha-Gal trisaccharide Gal(alpha)(1-->3)Galbeta(1-->4)GlcNAc 11 was synthesized on a homogeneously soluble polymeric support (polyethylene glycol, PEG) by use of a multi-enzyme system consisting of beta-1,4-galactosyltransferase (EC 2.4.1.38), alpha-1,3-galactosyltransferase (EC 2.4.1.151), sucrose synthase (EC 2.4.1.13) and UDP-glucose-4-epimerase (EC 5.1.3.2). In addition workup was simplified by use of dia-ultrafiltration. Thus the advantages of classic chemistry/enzymology and solid-phase synthesis could be united in one. Subsequent hydrogenolytic cleavage afforded the free alpha-Gal trisaccharide. 相似文献
9.
10.