全文获取类型
收费全文 | 40261篇 |
免费 | 3716篇 |
国内免费 | 3705篇 |
出版年
2024年 | 27篇 |
2023年 | 573篇 |
2022年 | 731篇 |
2021年 | 2193篇 |
2020年 | 1565篇 |
2019年 | 2006篇 |
2018年 | 1848篇 |
2017年 | 1353篇 |
2016年 | 1797篇 |
2015年 | 2604篇 |
2014年 | 3143篇 |
2013年 | 3356篇 |
2012年 | 3850篇 |
2011年 | 3487篇 |
2010年 | 2113篇 |
2009年 | 1837篇 |
2008年 | 2136篇 |
2007年 | 1846篇 |
2006年 | 1592篇 |
2005年 | 1350篇 |
2004年 | 1189篇 |
2003年 | 1031篇 |
2002年 | 904篇 |
2001年 | 726篇 |
2000年 | 641篇 |
1999年 | 606篇 |
1998年 | 358篇 |
1997年 | 347篇 |
1996年 | 334篇 |
1995年 | 327篇 |
1994年 | 288篇 |
1993年 | 215篇 |
1992年 | 298篇 |
1991年 | 201篇 |
1990年 | 171篇 |
1989年 | 171篇 |
1988年 | 102篇 |
1987年 | 91篇 |
1986年 | 66篇 |
1985年 | 76篇 |
1984年 | 32篇 |
1983年 | 36篇 |
1982年 | 24篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Industrial aquaculture wastewater contains large quantities of suspended particles that can be easily broken down physically. Introduction of macro-bio-filters, such as bivalve filter feeders, may offer the potential for treatment of fine suspended matter in industrial aquaculture wastewater. In this study, we employed two kinds of bivalve filter feeders, the Pacific oyster Crassostrea gigas and the blue mussel Mytilus galloprovincialis, to deposit suspended solids from marine fish aquaculture wastewater in flow-through systems. Results showed that the biodeposition rate of suspended particles by C. gigas (shell height: 8.67±0.99 cm) and M. galloprovincialis (shell height: 4.43±0.98 cm) was 77.84±7.77 and 6.37±0.67 mg ind−1•d−1, respectively. The total solid suspension (TSS) deposition rates of oyster and mussel treatments were 3.73±0.27 and 2.76±0.20 times higher than that of the control treatment without bivalves, respectively. The TSS deposition rates of bivalve treatments were significantly higher than the natural sedimentation rate of the control treatment (P<0.001). Furthermore, organic matter and C, N in the sediments of bivalve treatments were significantly lower than those in the sediments of the control (P<0.05). It was suggested that the filter feeders C. gigas and M. galloprovincialis had considerable potential to filter and accelerate the deposition of suspended particles from industrial aquaculture wastewater, and simultaneously yield value-added biological products. 相似文献
42.
43.
Splicing and alternative splicing in rice and humans 总被引:1,自引:0,他引:1
Rice is a monocot gramineous crop, and one of the most important staple foods. Rice is considered a model species for most gramineous crops. Extensive research on rice has provided critical guidance for other crops, such as maize and wheat. In recent years, climate change and exacerbated soil degradation have resulted in a variety of abiotic stresses, such as greenhouse effects, lower temperatures, drought, floods, soil salinization and heavy metal pollution. As such, there is an extremely high demand for additional research, in order to address these negative factors. Studies have shown that the alternative splicing of many genes in rice is affected by stress conditions, suggesting that manipulation of the alternative splicing of specific genes may be an effective approach for rice to adapt to abiotic stress. With the advancement of microarrays, and more recently, next generation sequencing technology, several studies have shown that more than half of the genes in the rice genome undergo alternative splicing. This mini-review summarizes the latest progress in the research of splicing and alternative splicing in rice, compared to splicing in humans. Furthermore, we discuss how additional studies may change the landscape of investigation of rice functional genomics and genetically improved rice. [BMB Reports 2013; 46(9): 439-447] 相似文献
44.
Qingrong Sun Hongyan Sun Richard L. Bell Huifeng Li Li Xin 《Plant Cell, Tissue and Organ Culture》2011,107(1):131-140
A wide range of phenotypic variation was observed among neopolyploids obtained from the diploid pear cultivar ‘Fertility’
by in vitro colchicine treatment. The variant plantlets had alterations in leaf characteristics. Neopolyploids had significantly
different ratios of leaf length to leaf width compared to the diploid control. Shoot regeneration from leaf explants and rooting
ability from in vitro shoots of neopolyploids was examined. Regeneration frequencies of shoots from leaf explants of seven
of the nine neopolyploids were significantly decreased compared to the diploid control. The organogenic potential of neopolyploids
was highly genotype-dependent for both shoots and roots. Tetraploid clone 4x − 4 failed to regenerate shoots from leaf explants
and the pentaploid clone 5x − 2 failed to root from in vitro shoots. The results suggest that polyploidization caused the
decrease in or loss of in vitro organogenic potential. Regenerated shoots derived from neopolyploids showed different phenotypes,
depending on the ploidy of the donor plant. 相似文献
45.
The genes encoding the six polypeptide components of the alkene monooxygenase from Xanthobacter Py2 have been sequenced. The predicted amino acid sequence of the first ORF shows homology with the iron binding subunits of binuclear non-haem iron containing monooxygenases including benzene monooxygenase, toluene 4-monooxygenase (>60% sequence similarity) and methane monooxygenase (>40% sequence similarity) and that the necessary sequence motifs associated with iron co-ordination are also present. Secondary structure prediction based on the amino acid sequence showed that the predominantly α-helical structure that surrounds the binuclear iron binding site was conserved allowing the sequence to be modelled on the co-ordinates of the methane monooxygenase α-subunit. Significant differences in the residues forming the hydrophobic cavity which forms the substrate binding site are discussed with reference to the differences in reaction specificity and stereospecificity of binuclear non-haem iron monooxygenases. 相似文献
46.
47.
X. M. Zhou P. H.-S. Jen 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2000,186(4):389-398
This study examines the role of neural inhibition in auditory spatial selectivity of inferior collicular neurons of the big
brown bat, Eptesicus fuscus, using a two-tone inhibition paradigm. Two-tone inhibition decreases auditory spatial response areas but increases the slopes
of directional sensitivity curves of inferior collicular neurons. Inferior collicular neurons have either directionally-selective
or hemifield directional sensitivity curves. A directionally-selective curve always has a peak which is at least 50% larger
than the minimum. A hemifield directional sensitivity curve rises from an ipsilateral angle by more than 50% and either reaches
a plateau or declines by less than 50% over a range of contralateral angles. Two-tone inhibition does not change directionally-selective
curves but changes most hemifield directional sensitivity curves into directionally-selective curves. Auditory spatial selectivity
determined both with and without two-tone inhibition increases with increasing best-excitatory frequency. Sharpening of auditory
spatial selectivity by two-tone inhibition is larger for neurons with smaller differences between excitatory and inhibitory
best frequencies. The effect of two-tone inhibition on auditory spatial selectivity increases with increasing inhibitory tone
intensity but decreases with increasing intertone interval. The implications of these findings in bat echolocation are discussed.
Accepted: 18 January 2000 相似文献
48.
Zac Yates Kannan Gunasekaran Hongxing Zhou Zhonghua Hu Zhi Liu Randal R. Ketchem Boxu Yan 《The Journal of biological chemistry》2010,285(24):18662-18671
Hydroxyl radicals induce hinge cleavage in a human IgG1 molecule via initial radical formation at the first hinge Cys231 followed by electron transfer to the upper hinge residues. To enable engineering of a stable monoclonal antibody hinge, we investigated the role of the hinge His229 residue using structure modeling and site-directed mutagenesis. Direct involvement of His229 in the reaction mechanism is suggested by a 75–85% reduction of the hinge cleavage for variants in which His229 was substituted with either Gln, Ser, or Ala. In contrast, mutation of Lys227 to Gln, Ser, or Ala increased hinge cleavage. However, the H229S/K227S double mutant shows hinge cleavage levels similar to that of the single H229S variant, further revealing the importance of His229. Examination of the hinge structure shows that His229 is capable of forming hydrogen bonds with surrounding residues. These observations led us to hypothesize that the imidazole ring of His229 may function to facilitate the cleavage by forming a transient radical center that is capable of extracting a proton from neighboring residues. The work presented here suggests the feasibility of engineering a new generation of monoclonal antibodies capable of resisting hinge cleavage to improve product stability and efficacy. 相似文献
49.
The effect of established infection on microvascular surgery 总被引:6,自引:0,他引:6
The success of microvascular anastomoses in the presence of staphylococcal infection was studied using rat femoral arteries. There was a spontaneous thrombosis rate of 19 percent in normal vessels that traversed the area of infection. Vessels with an anastomosis outside the area of infection had a similar thrombosis rate, but if the anastomotic site was within the infected area itself, the thrombosis rate increased to 75 percent. Inflammatory changes with subsequent fibrosis in the media and adventitia appeared responsible for the thrombosis. The intima was unaffected by the presence of infection. This study suggests that when a microvascular anastomosis is necessary in the presence of infection, the anastomosis should be placed outside the area of infection with a pedicle to traverse the infected area. 相似文献
50.
Yi Ting Zhou Li Li Chew Sheng-cai Lin Boon Chuan Low 《Molecular biology of the cell》2010,21(18):3232-3246
The BNIP-2 and Cdc42GAP homology (BCH) domain is a novel regulator for Rho GTPases, but its impact on p50-Rho GTPase-activating protein (p50RhoGAP or Cdc42GAP) in cells remains elusive. Here we show that deletion of the BCH domain from p50RhoGAP enhanced its GAP activity and caused drastic cell rounding. Introducing constitutively active RhoA or inactivating GAP domain blocked such effect, whereas replacing the BCH domain with endosome-targeting SNX3 excluded requirement of endosomal localization in regulating the GAP activity. Substitution with homologous BCH domain from Schizosaccharomyces pombe, which does not bind mammalian RhoA, also led to complete loss of suppression. Interestingly, the p50RhoGAP BCH domain only targeted RhoA, but not Cdc42 or Rac1, and it was unable to distinguish between GDP and the GTP-bound form of RhoA. Further mutagenesis revealed a RhoA-binding motif (residues 85-120), which when deleted, significantly reduced BCH inhibition on GAP-mediated cell rounding, whereas its full suppression also required an intramolecular interaction motif (residues 169-197). Therefore, BCH domain serves as a local modulator in cis to sequester RhoA from inactivation by the adjacent GAP domain, adding to a new paradigm for regulating p50RhoGAP signaling. 相似文献