全文获取类型
收费全文 | 2242篇 |
免费 | 165篇 |
出版年
2021年 | 32篇 |
2020年 | 18篇 |
2019年 | 22篇 |
2018年 | 29篇 |
2017年 | 21篇 |
2016年 | 40篇 |
2015年 | 76篇 |
2014年 | 96篇 |
2013年 | 131篇 |
2012年 | 149篇 |
2011年 | 151篇 |
2010年 | 83篇 |
2009年 | 79篇 |
2008年 | 108篇 |
2007年 | 138篇 |
2006年 | 110篇 |
2005年 | 114篇 |
2004年 | 119篇 |
2003年 | 113篇 |
2002年 | 83篇 |
2001年 | 34篇 |
2000年 | 18篇 |
1999年 | 24篇 |
1998年 | 30篇 |
1997年 | 25篇 |
1996年 | 22篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 20篇 |
1992年 | 29篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 23篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 17篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1978年 | 15篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 20篇 |
1973年 | 9篇 |
1972年 | 10篇 |
1969年 | 8篇 |
1965年 | 8篇 |
1948年 | 8篇 |
排序方式: 共有2407条查询结果,搜索用时 14 毫秒
91.
92.
93.
This paper reports on the most important non-timber forest products (NTFPs) marketed and used during the dry season in Cinzana, near Ségou, Mali. Data was gathered from villagers through market surveys and interviews with vendors, buyers, and key informants in traditional medicine. In the Sudano-sahelian agricultural region, NTFPs are collected from parklands, comprising of fallows and croplands. Of the 20 species, five were used in handicraft production, 11 yielded human foods, and 11 had medicinal uses. In addition, many tree species have multipurpose value: six of the 20 species were recorded to be food producers in addition to having uses for handicraft production and/or medicine. The contribution of herbaceous species to the NTFPs used and harvested during the dry season is negligible. Only one of the species was non-ligneous, indicating the large significance of tree species for local communities in a region with long seasonal dry periods. 相似文献
94.
Elevational species richness gradients in a hyperdiverse insect taxon: a global meta‐study on geometrid moths 下载免费PDF全文
Jan Beck Christy M. McCain Jan C. Axmacher Louise A. Ashton Florian Bärtschi Gunnar Brehm Sei‐Woong Choi Oldrich Cizek Robert K. Colwell Konrad Fiedler Cristina L. Francois Steven Highland Jeremy D. Holloway Jurie Intachat Tomas Kadlec Roger L. Kitching Sarah C. Maunsell Thomas Merckx Akihiro Nakamura Erica Odell Weiguo Sang Pagi S. Toko Jaroslav Zamecnik Yi Zou Vojtech Novotny 《Global Ecology and Biogeography》2017,26(4):412-424
95.
Few studies address food preference of geese on agricultural land (utilization related to availability) and only a handful so for the breeding season. We studied Greylag geese Anser anser during the breeding season in an intensively farmed area in southern Sweden. Few of 22 available field types were truly preferred. Pastureland was the most consistently preferred, by goslings (with parents) as well as by non-breeders. In some sampling periods, goslings also preferred grazed hay, ley, and carrot fields. Non-breeders exploited a greater variety of crops/fields, feeding also on barley, fallow, grazed hay, lettuce, oats, potatoes, and carrots. Most of these crops were preferred on at least one sampling occasion, except for fallow, grazed hay, and wheat, which were always used less than expected from availability. GLMs revealed that goslings rested more than they fed and preferred shorter vegetation before higher. Moreover, goslings occurred in higher densities in younger age classes than in older and preferred nearshore areas. In contrast, density of non-breeders was only related to field type and sampling occasion (higher densities as the season progressed). The maximum number of broods observed (106) implies a breeding success of 34% based on 311 active nests earlier in the season. Brood size decreased from 3.5 to 2.1 during the study period. Our study shows that goose management during the breeding season should consider goslings and their parents separately from non-breeders, and it implies little potential conflict between Greylag geese and agriculture during the breeding period. 相似文献
96.
97.
Mutational Analysis of the Class IIa Bacteriocin Curvacin A and Its Orientation in Target Cell Membranes 下载免费PDF全文
Heln Sophie Haugen Per Eugen Kristiansen Gunnar Fimland Jon Nissen-Meyer 《Applied microbiology》2008,74(21):6766-6773
To analyze the orientation in target cell membranes of the pediocin-like bacteriocin (antimicrobial peptide) curvacin A, 55 variants were generated by site-directed mutagenesis and their potencies against four different target cells determined. The result suggest that the somewhat hydrophilic short central helix (residues 19 to 24), along with the N-terminal β-sheet-like structure (residues 1 to 16), inserts in the interface region of the target cell membrane, with Ala22 close to the hydrophobic core of the membrane. The following hinge region, with Gly28 as an important residue, may then form a turn wherein Gly28 becomes positioned near the border between the interface and the hydrophobic regions, thus permitting the longer and more-hydrophobic C-terminal helix (residues 29 to 41) to insert into the hydrophobic core of the membrane. This helix contains three glycine residues (G33, G37, and G40) that form a putative helix-helix-interacting GxxxGxxG motif. The replacement of any of these glycines with a larger residue was very detrimental, suggesting their possible involvement in helix-helix interactions with a membrane-embedded receptor protein. 相似文献
98.
Histone H4K20 tri‐methylation at late‐firing origins ensures timely heterochromatin replication 下载免费PDF全文
Charlotte Grimaud Paulina Prorok Christelle Cayrou Gunnar Schotta Alhassan F Abdelsamie Jérôme Déjardin Marcel Méchali Giuseppe Baldacci Claude Sardet Jean‐Charles Cadoret Aloys Schepers Eric Julien 《The EMBO journal》2017,36(18):2726-2741
Among other targets, the protein lysine methyltransferase PR‐Set7 induces histone H4 lysine 20 monomethylation (H4K20me1), which is the substrate for further methylation by the Suv4‐20h methyltransferase. Although these enzymes have been implicated in control of replication origins, the specific contribution of H4K20 methylation to DNA replication remains unclear. Here, we show that H4K20 mutation in mammalian cells, unlike in Drosophila, partially impairs S‐phase progression and protects from DNA re‐replication induced by stabilization of PR‐Set7. Using Epstein–Barr virus‐derived episomes, we further demonstrate that conversion of H4K20me1 to higher H4K20me2/3 states by Suv4‐20h is not sufficient to define an efficient origin per se, but rather serves as an enhancer for MCM2‐7 helicase loading and replication activation at defined origins. Consistent with this, we find that Suv4‐20h‐mediated H4K20 tri‐methylation (H4K20me3) is required to sustain the licensing and activity of a subset of ORCA/LRWD1‐associated origins, which ensure proper replication timing of late‐replicating heterochromatin domains. Altogether, these results reveal Suv4‐20h‐mediated H4K20 tri‐methylation as a critical determinant in the selection of active replication initiation sites in heterochromatin regions of mammalian genomes. 相似文献
99.
100.
Björn Schwanhäusser Manfred Gossen Gunnar Dittmar Matthias Selbach Dr. 《Proteomics》2009,9(1):205-209
Current methods for system‐wide gene expression analysis detect changes in mRNA abundance, but neglect regulation at the level of translation. Pulse labeling with stable isotopes has been used to measure protein turnover rates, but this does not directly provide information about translation rates. Here, we developed pulsed stable isotope labeling by amino acids in cell culture (pSILAC) with two heavy isotope labels to directly quantify protein translation on a proteome‐wide scale. We applied the method to cellular iron homeostasis as a model system and demonstrate that it can confidently identify proteins that are translationally regulated by iron availability. 相似文献