全文获取类型
收费全文 | 915篇 |
免费 | 46篇 |
专业分类
961篇 |
出版年
2023年 | 7篇 |
2022年 | 4篇 |
2021年 | 20篇 |
2020年 | 13篇 |
2019年 | 14篇 |
2018年 | 27篇 |
2017年 | 35篇 |
2016年 | 26篇 |
2015年 | 19篇 |
2014年 | 25篇 |
2013年 | 62篇 |
2012年 | 47篇 |
2011年 | 54篇 |
2010年 | 50篇 |
2009年 | 25篇 |
2008年 | 40篇 |
2007年 | 24篇 |
2006年 | 23篇 |
2005年 | 14篇 |
2004年 | 23篇 |
2003年 | 15篇 |
2002年 | 19篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1971年 | 2篇 |
1955年 | 29篇 |
1954年 | 77篇 |
1953年 | 42篇 |
1952年 | 27篇 |
1951年 | 20篇 |
1950年 | 56篇 |
1949年 | 12篇 |
1948年 | 5篇 |
1947年 | 3篇 |
1937年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有961条查询结果,搜索用时 0 毫秒
1.
2.
3.
High level of divergence of male-reproductive-tract proteins, between Drosophila melanogaster and its sibling species, D. simulans 总被引:1,自引:0,他引:1
We compared male-reproductive-tract polypeptides of Drosophila melanogaster
and D. simulans by using two-dimensional gel electrophoresis. Approximately
64% of male-reproductive-tract polypeptides were identical between two
randomly chosen isofemale lines from these two species, compared with 83%
identity for third-instar imaginal wing-disc polypeptides. Qualitatively
similar differences were found between reproductive tracts and imaginal
discs when D. sechellia was compared with D. melanogaster and with D.
simulans. When genic polymorphism was taken into account, approximately 10%
of male- reproductive-tract polypeptides were apparently fixed for
different alleles between D. melanogaster and D. simulans; this proportion
is the same as that found for soluble enzymes by one-dimensional gel
electrophoresis. Strikingly, approximately 20% of male-reproductive- tract
polypeptides of either D. melanogaster or D. simulans had no detectable
homologue in the other species. We propose that proteins of the Drosophila
male reproductive tract may have diverged more extensively between species
than have other types of proteins and that much of this divergence may
involve large changes in levels of polypeptide expression.
相似文献
4.
Łukasz Wejnerowski Ewa Poniecka Jakub Buda Piotr Klimaszyk Agnieszka Piasecka Marcin Krzysztof Dziuba Gianmarco Mugnai Nozomu Takeuchi Krzysztof Zawierucha 《Journal of phycology》2023,59(5):939-949
Cryoconite, the dark sediment on the surface of glaciers, often aggregates into oval or irregular granules serving as biogeochemical factories. They reduce a glacier's albedo, act as biodiversity hotspots by supporting aerobic and anaerobic microbial communities, constitute one of the organic matter (OM) sources on glaciers, and are a feeder for micrometazoans. Although cryoconite granules have multiple roles on glaciers, their formation is poorly understood. Cyanobacteria are ubiquitous and abundant engineers of cryoconite hole ecosystems. This study tested whether cyanobacteria may be responsible for cryoconite granulation as a sole biotic element. Incubation of Greenlandic, Svalbard, and Scandinavian cyanobacteria in different nutrient availabilities and substrata for growth (distilled water alone and water with quartz powder, furnaced cryoconite without OM, or powdered rocks from glacial catchment) revealed that cyanobacteria bind mineral particles into granules. The structures formed in the experiment resembled those commonly observed in natural cryoconite holes: they contained numerous cyanobacterial filaments protruding from aggregated mineral particles. Moreover, all examined strains were confirmed to produce extracellular polymeric substances (EPS), which suggests that cryoconite granulation is most likely due to EPS secretion by gliding cyanobacteria. In the presence of water as the only substrate for growth, cyanobacteria formed mostly carpet-like mats. Our data empirically prove that EPS-producing oscillatorialean cyanobacteria isolated from the diverse community of cryoconite microorganisms can form granules from mineral substrate and that the presence of the mineral substrate increases the probability of the formation of these important and complex biogeochemical microstructures on glaciers. 相似文献
5.
6.
7.
The aim of this study was to determine the impact of a static magnetic field (MF) of 7 mT on formaldehyde (FA) biodegradation by activated sludge in synthetic wastewater. The MF had a positive effect on activated sludge biomass growth and dehydrogenase activity. The influence of the MF on the degradation process was observed with a FA concentration of 2400-2880 mg/l. Decreases in FA concentration and chemical oxygen demand (COD) were greater, by 30% and 26% respectively, than those in the control sample. At initial FA concentrations in raw wastewater of 2400 and 2880 mg/l, a decrease in the wastewater biodegradation efficiency was observed. This resulted in an increase of the ecotoxicity of the effluent to Daphnia magna. The value of the sludge biotic index (SBI) was dependent on the FA concentration in raw wastewater and the induction of the MF. 相似文献
8.
Lipopeptide biosurfactants are surface active biomolecules that are produced by a variety of microorganisms. Microbial lipopeptides have gained the interest of microbiologists, chemists and biochemists for their high biodiversity as well as efficient action, low toxicity and good biodegradability in comparison to synthetic counterparts. In this report, we review methods for the production, isolation and screening, purification and structural characterization of microbial lipopeptides. Several techniques are currently available for each step, and we describe the most commonly utilized and recently developed techniques in this review. Investigations on lipopeptide biosurfactants in natural products require efficient isolation techniques for the characterization and evaluation of chemical and biological properties. A combination of chromatographic and spectroscopic techniques offer opportunities for a better characterization of lipopeptide structures, which in turn can lead to the application of lipopeptides in food, pharmaceutical, cosmetics, agricultural and bioremediation industries. 相似文献
9.
10.