全文获取类型
收费全文 | 5632篇 |
免费 | 458篇 |
国内免费 | 2篇 |
专业分类
6092篇 |
出版年
2023年 | 44篇 |
2022年 | 110篇 |
2021年 | 188篇 |
2020年 | 82篇 |
2019年 | 110篇 |
2018年 | 144篇 |
2017年 | 112篇 |
2016年 | 204篇 |
2015年 | 309篇 |
2014年 | 349篇 |
2013年 | 409篇 |
2012年 | 471篇 |
2011年 | 482篇 |
2010年 | 292篇 |
2009年 | 270篇 |
2008年 | 299篇 |
2007年 | 326篇 |
2006年 | 286篇 |
2005年 | 247篇 |
2004年 | 235篇 |
2003年 | 202篇 |
2002年 | 186篇 |
2001年 | 38篇 |
2000年 | 33篇 |
1999年 | 39篇 |
1998年 | 60篇 |
1997年 | 39篇 |
1996年 | 28篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 31篇 |
1992年 | 26篇 |
1991年 | 16篇 |
1990年 | 27篇 |
1989年 | 21篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1985年 | 15篇 |
1984年 | 23篇 |
1983年 | 19篇 |
1982年 | 18篇 |
1981年 | 19篇 |
1980年 | 27篇 |
1979年 | 21篇 |
1978年 | 24篇 |
1977年 | 19篇 |
1975年 | 9篇 |
1974年 | 12篇 |
1970年 | 9篇 |
1968年 | 8篇 |
排序方式: 共有6092条查询结果,搜索用时 15 毫秒
51.
Michael E. Joesten Moira E. Royston Marlene Jimenez Axel Wadewitz Diana Melian Richard A. Lockshin 《Journal of insect physiology》1982,28(7):589-599
Larvae of Manduca sexta, (Sphingidae) increase their weight approx. 50% just before pupation and then secrete this fluid during the formation of their burrows. Time-lapse cinematography indicates that the fluid is ejected into the walls of the final burrow. It may offer some mechanical support; it is not particularly repellent to ants or mice, and it contains only small amounts of the alkaloids ingested from its preferred food plants. Comparison to other species indicates that the gain and loss of water is associated with burrowing behaviour; the fluid appears to be used in providing hydraulic pressure for burrowing, in forming and cementing the pupal chamber, and in acting as a CO2 trap underground. The secretion is a hypertonic, highly alkaline solution containing KHCO3 and small amounts of Na+, Ca2+, Mg2+, PO4?3 and some proteins. Haemolymph levels of K+ decrease, and those of Ca2+ increase, during the secretory phase. When radioactive calcium is injected into mature larvae, it appears promptly in the secretion. If however, the injection is given more than 24 hr before the animal begins secreting, then the calcium is bound to haemolymph protein and does not appear in the secretion. 相似文献
52.
53.
Diana M. Downs 《Molecular microbiology》2020,113(1):1-3
Building a robust, stable network must include strategies to minimize perturbations caused by environmental stress, while optimizing cellular fitness. The introduction of oxygen into the Earth's atmosphere brought challenges for the microbes that had evolved enzyme machinery and metabolic network stability in the anoxic world. Unable to generate new enzyme paradigms and metabolic networks de novo, organisms have evolved strategies to neutralize the impact of oxygen that can be added to and integrated into the existing metabolic framework. This issue of Molecular Microbiology includes a paper by Korshunov et al. in which the authors describe an elegant strategy that Escherichia coli has evolved to minimize metabolic stress that results from the acquisition and use of cystine, the oxidized form of cysteine, as a source of cellular sulfur. This study highlights how a strategy involving both cost and benefit can result in a functional, but energy intensive mechanism for this bacterium to thrive in an oxic world. 相似文献
54.
Sáenz-de la O Diana Cedillo-Jimenez Christopher Alexis García-Ortega Luis F. Martínez-Reséndiz Mariela Arné-Robles Diego Cruz-Hernandez Andrés Guevara-Gonzalez Ramón Gerardo 《Physiology and Molecular Biology of Plants》2020,26(1):3-13
Physiology and Molecular Biology of Plants - Transgenic tobacco (N. tabacum cv. Xanthi nc) expressing Capsicum chinense CchGLP gene that encodes an Mn-SOD, constitutively produces hydrogen... 相似文献
55.
Kathleen M. Kay Tania Jogesh Diana Tataru Sami Akiba 《Proceedings. Biological sciences / The Royal Society》2020,287(1941)
Heteranthery, the presence of two or more anther types in the same flower, is taxonomically widespread among bee-pollinated angiosperms, yet has puzzled botanists since Darwin. We test two competing hypotheses for its evolution: the long-standing ‘division of labour'' hypothesis, which posits that some anthers are specialized as food rewards for bees whereas others are specialized for surreptitious pollination, and our new hypothesis that heteranthery is a way to gradually release pollen that maximizes pollen delivery. We examine the evolution of heteranthery and associated traits across the genus Clarkia (Onagraceae) and study plant–pollinator interactions in two heterantherous Clarkia species. Across species, heteranthery is associated with bee pollination, delayed dehiscence and colour crypsis of one anther whorl, and movement of that anther whorl upon dehiscence. Our mechanistic studies in heterantherous species show that bees notice, forage on and export pollen from each anther whorl when it is dehiscing, and that heteranthery promotes pollen export. We find no support for division of labour, but multifarious evidence that heteranthery is a mechanism for gradual pollen presentation that probably evolved through indirect male–male competition for siring success. 相似文献
56.
Robert B. Page Claire Conarroe Diana Quintanilla Andriea Palomo Joshua Solis Ashley Aguilar Kelly Bezold Andrew M. Sackman David M. Marsh 《Ecology and evolution》2020,10(18):9948-9967
Climate change poses several challenges to biological communities including changes in the frequency of encounters between closely related congeners as a result of range shifts. When climate change leads to increased hybridization, hybrid dysfunction or genetic swamping may increase extinction risk—particularly in range‐restricted species with low vagility. The Peaks of Otter Salamander, Plethodon hubrichti, is a fully terrestrial woodland salamander that is restricted to ~18 km of ridgeline in the mountains of southwestern Virginia, and its range is surrounded by the abundant and widespread Eastern Red‐backed Salamander, Plethodon cinereus. In order to determine whether these two species are hybridizing and how their range limits may be shifting, we assessed variation at eight microsatellite loci and a 1,008 bp region of Cytochrome B in both species at allopatric reference sites and within a contact zone. Our results show that hybridization between P. hubrichti and P. cinereus either does not occur or is very rare. However, we find that diversity and differentiation are substantially higher in the mountaintop endemic P. hubrichti than in the widespread P. cinereus, despite similar movement ability for the two species as assessed by a homing experiment. Furthermore, estimation of divergence times between reference and contact zone populations via approximate Bayesian computation is consistent with the idea that P. cinereus has expanded into the range of P. hubrichti. Given the apparent recent colonization of the contact zone by P. cinereus, future monitoring of P. cinereus range limits should be a priority for the management of P. hubrichti populations. 相似文献
57.
58.
Le Roux Johannes J. Crous Pedro W. Kamutando Casper N. Richardson David M. Strasberg Dominique Wingfield Michael J. Wright Mark G. Valverde Angel 《Plant and Soil》2021,459(1-2):277-288
Plant and Soil - The hydrolysis of organic P in soils is a relevant aspect contributing to the supply P to plants, which is affected by adsorbent capacity and biological properties of soils. This... 相似文献
59.
60.
Diana Pinto Stefania Sut Stefano Dall'Acqua Cristina Delerue-Matos Francisca Rodrigues 《化学与生物多样性》2021,18(3):e2000925
Hardy kiwifruit (Actinidia arguta) is a highly appreciated exotic fruit endowed with outstanding bioactive compounds. The present work proposes to characterize the pulp from A. arguta organic fruits, emphasizing its radicals scavenging capacity and effects on intestinal cells (Caco-2 and HT29-MTX). The physicochemical properties and phenolic profile were also screened. The total phenolic and flavonoid contents (TPC and TFC, respectively) of pulp were 12.21 mg GAE/g on dry weight (DW) and 5.92 mg CE/g DW, respectively. A high antioxidant activity was observed (FRAP: 151.41 μmol FSE/g DW; DPPH: 12.17 mg TE/g DW). Furthermore, the pulp did not induce a toxic effect on Caco-2 and HT29-MTX cells viability up to 1000 μg/mL. Regarding in vitro scavenging capacity, the pulp revealed the highest scavenging power against NO. (IC50=3.45 μg/mL) and HOCl (IC50=12.77 μg/mL). These results emphasize the richness of A. arguta fruit pulp to be used in different food products. 相似文献