全文获取类型
收费全文 | 1551篇 |
免费 | 100篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 19篇 |
2021年 | 61篇 |
2020年 | 33篇 |
2019年 | 40篇 |
2018年 | 44篇 |
2017年 | 43篇 |
2016年 | 47篇 |
2015年 | 102篇 |
2014年 | 84篇 |
2013年 | 110篇 |
2012年 | 166篇 |
2011年 | 139篇 |
2010年 | 73篇 |
2009年 | 83篇 |
2008年 | 97篇 |
2007年 | 104篇 |
2006年 | 78篇 |
2005年 | 83篇 |
2004年 | 58篇 |
2003年 | 57篇 |
2002年 | 41篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有1651条查询结果,搜索用时 562 毫秒
1.
2.
3.
Hydroboration of 5 alpha-cholest-8-ene, 5 alpha,14 beta-cholest-8-ene and 5 alpha,14 beta-cholest-7-ene provides a simple route to oxygenated steroids with 14 beta- and 8 alpha,14 beta- unnatural stereochemistry. 相似文献
4.
A C-glucoside of cholic acid was synthesized by the introduction of an acetyl group at position 3 alpha and direct one-pot C-glucosidation using 2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranosyl chloride. 相似文献
5.
Mallomonas paluestrica sp. nov., a new member of sect. Torquatae ser. Pumilae , was found in a small Danish pond and is described and illustrated with TEM and SEM micrographs. 相似文献
6.
Anastasia Klimova Ricardo Rodríguez-Estrella Guanliang Meng Jesús Neftalí Gutiérrez-Rivera María Luisa Jimenez-Jimenez Shanlin Liu 《Diversity & distributions》2023,29(3):438-461
Aim
Desert springs or oases are the only permanent mesic environments in highly water-limited arid regions. Oases have immense cultural, evolutionary and ecological importance for people and a high number of endemic and relic species. Nevertheless, they are also highly vulnerable ecosystems, with invasive species, overexploitation and climate change being the primary threats. We used the arthropod communities' spatiotemporal diversity and distribution patterns as a proxy to understand biodiversity dynamics in two geographically close but ecologically contrasting and highly threatened ecosystems: deserts and oases.Location
Baja California Peninsula, Mexico.Methods
Arthropod communities at five oases and surrounding desert scrub areas were sampled in two seasons. Using DNA metabarcoding and traditional taxonomic surveys, we tried to identify what biotic and abiotic characteristics of the habitat are important drivers of arthropod diversity and how these characteristics can change across spatial and temporal scales.Results
Over 6200 individuals representing 23 orders were collected. In oasis samples, the community composition fluctuated more in space (i.e. among sites) than in time (i.e. seasons). Thus, seasonal changes did not affect oasis community diversity and composition, but the dissimilarity among sites increased with geographic distance. Moreover, anthropic activities negatively correlated with arthropod diversity in oases. On the other hand, the season, geography (e.g. latitude) and biotic characteristics of the habitat (e.g. sampled scrub species) significantly affected the diversity and composition of the desert arthropod communities.Main Conclusions
Neutral dynamics (e.g. historical climatic events, dispersal limitation and spatial component) and human impact significantly influenced the biodiversity patterns of each oasis. In contrast, the habitat's seasonal variation and biotic characteristics were the most important variables influencing the diversity of the desert communities. Baja California oases harbour distinct invertebrate communities; therefore, each oasis should be conserved individually to preserve these unique assemblages. 相似文献7.
Charlotte Schou Erik R. Ottosen Hans Jørgen Petersen Fredrik Björkling Scilla Latini Pernille V. Hjarnaa Erik Bramm Lise Binderup 《Bioorganic & medicinal chemistry letters》1997,7(24):616-3100
4-Pyridyl cyanoguanidines with hydrophobic aromatic side chains showed potent antiproliferative activity in the human breast and lung cancer cell lines MCF-7, NYH and H460. In vivo, treatment with N-(6-chlorophenoxyhexyl)-N′-cyano-N″-4-pyridylguanidine (18, 20 mg/kg/day po.), gave a complete remission of tumours in a model of NYH inoculated nude mice. 相似文献
8.
C Lauritzen E Tüchsen P E Hansen O Skovgaard 《Protein expression and purification》1991,2(5-6):372-378
A recombinant gene for BPTI (bovine pancreatic trypsin inhibitor) is expressed in Escherichia coli using a MBP (maltose-binding protein) fusion vector. BPTI is fused through an FXa (blood coagulation factor Xa protease) target sequence (Ile-Glu-Gly-Arg) to the C-terminus of MBP. The MBP moiety of the hybrid protein enables purification in one step utilizing MBP's affinity to cross-linked amylose, and the FXa target sequence allows specific cleavage of the hybrid protein. Effective FXa cleavage is achieved by spacing the FXa target sequence and Arg-1 of the BPTI sequence with four residues (Met-Glu-Ala-Glu). The resulting N-terminal extended BPTI is readily converted to the wild-type sequence by trimming with cathepsin C exopeptidase, for the activity of which the spacing tetrapeptide is optimized. FXa cleavage is prohibited when the target sequence is placed next to Arg-1. In this construction, off-target cleavage at a somewhat homologous sequence (Val-Pro-Gly-Arg) results in five- or six-residue extended BPTI, indicating new details of the FXa specificity. The yield of highly purified recombinant BPTI is 3-6 mg/liter of culture, making the MBP-BPTI expression system convenient for the production of sufficient amounts of protein for NMR studies. 1H NMR is used to analyze the N-extended BPTI analogues. 相似文献
9.
Lapeña David Olsen Pernille M. Arntzen Magnus Ø. Kosa Gergely Passoth Volkmar Eijsink Vincent G. H. Horn Svein J. 《Bioprocess and biosystems engineering》2020,43(4):723-736
Bioprocess and Biosystems Engineering - The production of microbial protein in the form of yeast grown on lignocellulosic sugars and nitrogen-rich industrial residues is an attractive approach for... 相似文献
10.
Kitashova Anastasia Schneider Katja Fürtauer Lisa Schröder Laura Scheibenbogen Tim Fürtauer Siegfried Nägele Thomas 《Photosynthesis research》2021,147(1):49-60
Photosynthesis Research - Photosynthesis and carbohydrate metabolism of higher plants need to be tightly regulated to prevent tissue damage during environmental changes. The intracellular position... 相似文献