全文获取类型
收费全文 | 12857篇 |
免费 | 1071篇 |
国内免费 | 9篇 |
专业分类
13937篇 |
出版年
2023年 | 52篇 |
2022年 | 99篇 |
2021年 | 235篇 |
2020年 | 138篇 |
2019年 | 203篇 |
2018年 | 239篇 |
2017年 | 219篇 |
2016年 | 313篇 |
2015年 | 608篇 |
2014年 | 638篇 |
2013年 | 778篇 |
2012年 | 1062篇 |
2011年 | 1020篇 |
2010年 | 636篇 |
2009年 | 583篇 |
2008年 | 825篇 |
2007年 | 847篇 |
2006年 | 727篇 |
2005年 | 721篇 |
2004年 | 685篇 |
2003年 | 638篇 |
2002年 | 640篇 |
2001年 | 125篇 |
2000年 | 88篇 |
1999年 | 137篇 |
1998年 | 158篇 |
1997年 | 132篇 |
1996年 | 119篇 |
1995年 | 121篇 |
1994年 | 102篇 |
1993年 | 78篇 |
1992年 | 86篇 |
1991年 | 60篇 |
1990年 | 62篇 |
1989年 | 67篇 |
1988年 | 41篇 |
1987年 | 45篇 |
1986年 | 46篇 |
1985年 | 47篇 |
1984年 | 49篇 |
1983年 | 38篇 |
1982年 | 66篇 |
1981年 | 43篇 |
1980年 | 45篇 |
1979年 | 31篇 |
1978年 | 37篇 |
1977年 | 36篇 |
1976年 | 21篇 |
1975年 | 22篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Pollen dispersal in sugar beet production fields 总被引:1,自引:0,他引:1
Henri Darmency Etienne K. Klein Thierry Gestat De Garanbé Pierre-Henri Gouyon Marc Richard-Molard Claude Muchembled 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2009,118(6):1083-1092
Pollen-mediated gene flow has important implications for biodiversity conservation and for breeders and farmers’ activities.
In sugar beet production fields, a few sugar beet bolters can produce pollen as well as be fertilized by wild and weed beet.
Since the crop, the wild beets, and the weed beets are the same species and intercross freely, the question of pollen flow
is an important issue to determine the potential dispersal of transgenes from field to field and to wild habitats. We report
here an experiment to describe pollen dispersal from a small herbicide-resistant sugar beet source towards male sterile target
plants located along radiating lines up to 1,200 m away. Individual dispersal functions were inferred from statistical analyses
and compared. Pollen limitation, as expected in root-production fields, was confirmed at all the distances from the pollen
source. The number of resistant seeds produced by bait plants best fitted a fat-tailed probability distribution curve of pollen
grains (power–law) dependent on the distance from the pollen source. A literature survey confirmed that power–law function
could fit in most cases. The b coefficient was lower than 2. The number of fertilized flowers by background (herbicide-susceptible) pollen grains was uniform
across the whole field. Airborne pollen had a fertilization impact equivalent to that of one adjacent bolter. The individual
dispersal function from different pollen sources can be integrated to provide the pollen cloud composition for a given target
plant, thus allowing modeling of gene flow in a field, inter-fields in a small region, and also in seed-production area. Long-distance
pollen flow is not negligible and could play an important role in rapid transgene dispersal from crop to wild and weed beets
in the landscape. The removing of any bolting, herbicide-resistant sugar beet should be compulsory to prevent the occurrence
of herbicide-resistant weed beet, thus preventing gene flow to wild populations and preserving the sustainable utility of
the resistant varieties. Whether such a goal is attainable remains an open question and certainly would be worth a large scale
experimental study. 相似文献
122.
123.
Enrichment and characterization of marine anammox bacteria associated with global nitrogen gas production 总被引:2,自引:0,他引:2
van de Vossenberg J Rattray JE Geerts W Kartal B van Niftrik L van Donselaar EG Sinninghe Damsté JS Strous M Jetten MS 《Environmental microbiology》2008,10(11):3120-3129
Microbiological investigation of anaerobic ammonium oxidizing (anammox) bacteria has until now been restricted to wastewater species. The present study describes the enrichment and characterization of two marine Scalindua species, the anammox genus that dominates almost all natural habitats investigated so far. The species were enriched from a marine sediment in the Gullmar Fjord (Sweden) using a medium based on Red Sea salt. Anammox cells comprised about 90% of the enrichment culture after 10 months. The enriched Scalindua bacteria displayed all typical features known for anammox bacteria, including turnover of hydrazine, the presence of ladderane lipids, and a compartmentalized cellular ultrastructure. The Scalindua species also showed a nitrate-dependent use of formate, acetate and propionate, and performed a formate-dependent reduction of nitrate, Fe(III) and Mn(IV). This versatile metabolism may be the basis for the global distribution and substantial contribution of the marine Scalindua anammox bacteria to the nitrogen loss from oxygen-limited marine ecosystems. 相似文献
124.
Fuchs Marc Klas Ferdinand E. McFerson James R. Gonsalves Dennis 《Transgenic research》1998,7(6):449-462
Transgenic melon and squash containing the coat protein (CP) gene of the aphid transmissible strain WL of cucumber mosaic cucumovirus (CMV) were grown under field conditions to determine if they would assist the spread of the aphid non-transmissible strain C of CMV, possibly through heterologous encapsidation and recombination. Transgenic melon were susceptible to CMV strain C whereas transgenic squash were resistant although the latter occasionally developed chlorotic blotches on lower leaves. Transgenic squash line ZW-20, one of the parents of commercialized cultivar Freedom II, which expresses the CP genes of the aphid transmissible strains FL of zucchini yellow mosaic (ZYMV) and watermelon mosaic virus 2 (WMV 2) potyviruses was also tested. Line ZW-20 is resistant to ZYMV and WMV 2 but is susceptible to CMV. Field experiments conducted over two consecutive years showed that aphid-vectored spread of CMV strain C did not occur from any of the CMV strain C-challenge inoculated transgenic plants to any of the uninoculated CMV-susceptible non- transgenic plants. Although CMV was detected in 3% (22/764) of the uninoculated plants, several assays including ELISA, RT- PCR-RFLP, identification of CP amino acid at position 168, and aphid transmission tests demonstrated that these CMV isolates were distinct from strain C. Instead, they were non-targeted CMV isolates that came from outside the field plots. This is the first report on field experiments designed to determine the potential of transgenic plants expressing CP genes for triggering changes in virus-vector specificity. Our results indicate that transgenic plants expressing CP genes of aphid transmissible strains of CMV, ZYMV, and WMV 2 are unlikely to mediate the spread of aphid non-transmissible strains of CMV. This finding is of practical relevance because transgenic crops expressing the three CP genes are targeted for commercial release, and because CMV is economically important, has a wide host range, and is widespread worldwide. 相似文献
125.
126.
Samit Kumar Dutta Pedro Serrano Michael Geralt Herbert L. Axelrod Qingping Xu Scott A. Lesley Adam Godzik Ashley M. Deacon Marc‐André Elsliger Ian A. Wilson Kurt Wüthrich 《Protein science : a publication of the Protein Society》2015,24(10):1600-1608
Flavodoxins in combination with the flavin mononucleotide (FMN) cofactor play important roles for electron transport in prokaryotes. Here, novel insights into the FMN‐binding mechanism to flavodoxins‐4 were obtained from the NMR structures of the apo‐protein from Lactobacillus acidophilus (YP_193882.1) and comparison of its complex with FMN. Extensive reversible conformational changes were observed upon FMN binding and release. The NMR structure of the FMN complex is in agreement with the crystal structure (PDB ID: 3EDO ) and exhibits the characteristic flavodoxin fold, with a central five‐stranded parallel β–sheet and five α‐helices forming an α/β‐sandwich architecture. The structure differs from other flavoproteins in that helix α2 is oriented perpendicular to the β‐sheet and covers the FMN‐binding site. This helix reversibly unfolds upon removal of the FMN ligand, which represents a unique structural rearrangement among flavodoxins. 相似文献
127.
In this study, the role of SNARE-mediated membrane traffic in regulating integrin localization was examined and the requirement for SNARE function in cellular spreading was quantitatively assessed. Membrane traffic was inhibited with the VAMP-specific catalytic light chain from tetanus toxin (TeTx-LC), a dominant-negative form (E329Q) of N-ethylmaleimide-sensitive fusion protein (NSF), and brefeldin A (BfA). Inhibition of membrane traffic with either E329Q-NSF or TeTx-LC, but not BfA, significantly inhibited spreading of CHO cells on fibronectin. Spreading was rescued in TeTx-LC-expressing cells by co-transfection with a TeTx-resistant cellubrevin/VAMP3. E329Q-NSF, a general inhibitor of SNARE function, was a more potent inhibitor of cell spreading than TeTx-LC, suggesting that tetanus toxin-insensitive SNAREs contribute to adhesion. It was found that E329Q-NSF prevented trafficking of alpha5beta1 integrins from a central Rab11-containing compartment to sites of protrusion during cell adhesion, while TeTx-LC delayed this trafficking. These results are consistent with a model of cellular adhesion that implicates SNARE function as an important component of integrin trafficking during the process of cell spreading. 相似文献
128.
Jespersen T Gavillet B van Bemmelen MX Cordonier S Thomas MA Staub O Abriel H 《Biochemical and biophysical research communications》2006,348(4):1455-1462
In order to identify proteins interacting with the cardiac voltage-gated sodium channel Na(v)1.5, we used the last 66 amino acids of the C-terminus of the channel as bait to screen a human cardiac cDNA library. We identified the protein tyrosine phosphatase PTPH1 as an interacting protein. Pull-down experiments confirmed the interaction, and indicated that it depends on the PDZ-domain binding motif of Na(v)1.5. Co-expression experiments in HEK293 cells showed that PTPH1 shifts the Na(v)1.5 availability relationship toward hyperpolarized potentials, whereas an inactive PTPH1 or the tyrosine kinase Fyn does the opposite. The results of this study suggest that tyrosine phosphorylation destabilizes the inactivated state of Na(v)1.5. 相似文献
129.
Robo4 maintains vessel integrity and inhibits angiogenesis by interacting with UNC5B 总被引:1,自引:0,他引:1
Koch AW Mathivet T Larrivée B Tong RK Kowalski J Pibouin-Fragner L Bouvrée K Stawicki S Nicholes K Rathore N Scales SJ Luis E del Toro R Freitas C Bréant C Michaud A Corvol P Thomas JL Wu Y Peale F Watts RJ Tessier-Lavigne M Bagri A Eichmann A 《Developmental cell》2011,20(1):33-46
Robo4 is an endothelial cell-specific member of the Roundabout axon guidance receptor family. To identify Robo4 binding partners, we performed a protein-protein interaction screen with the Robo4 extracellular domain. We find that Robo4 specifically binds to UNC5B, a vascular Netrin receptor, revealing unexpected interactions between two endothelial guidance receptors. We show that Robo4 maintains vessel integrity by activating UNC5B, which inhibits signaling downstream of vascular endothelial growth factor (VEGF). Function-blocking monoclonal antibodies against Robo4 and UNC5B increase angiogenesis and disrupt vessel integrity. Soluble Robo4 protein inhibits VEGF-induced vessel permeability and rescues barrier defects in Robo4(-/-) mice, but not in mice treated with anti-UNC5B. Thus, Robo4-UNC5B signaling maintains vascular integrity by counteracting VEGF signaling in endothelial cells, identifying a novel function of guidance receptor interactions in the vasculature. 相似文献
130.