全文获取类型
收费全文 | 1407篇 |
免费 | 68篇 |
国内免费 | 5篇 |
专业分类
1480篇 |
出版年
2024年 | 4篇 |
2023年 | 24篇 |
2022年 | 49篇 |
2021年 | 103篇 |
2020年 | 48篇 |
2019年 | 47篇 |
2018年 | 71篇 |
2017年 | 47篇 |
2016年 | 58篇 |
2015年 | 78篇 |
2014年 | 84篇 |
2013年 | 95篇 |
2012年 | 101篇 |
2011年 | 91篇 |
2010年 | 46篇 |
2009年 | 46篇 |
2008年 | 48篇 |
2007年 | 52篇 |
2006年 | 27篇 |
2005年 | 43篇 |
2004年 | 36篇 |
2003年 | 35篇 |
2002年 | 22篇 |
2001年 | 3篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 9篇 |
1991年 | 17篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有1480条查询结果,搜索用时 15 毫秒
81.
In the current study, fifteen halophilic and halotolerant bacteria were isolated from salt-affected soil of ?anl?urfa, Turkey. The isolates were characterized by conventional and molecular techniques (16S rDNA sequence analyses) as belonging to seven different genus including Bacillus (5 isolates), Halobacillus (1 isolate), Oceanobacillus (2 isolates), Halomonas (3 isolate), Nesterenkonia (1 isolate), Chromohalobacter (2 isolates) and Jeotgalibacillus (2 isolates). According to the results obtained, the investigated bacterial strains have high salt tolerance and significant enzyme activities which can improve soil nutrient cycling and fertility. Furthermore, these bacterial strains have been investigated for their ability to dissolve common salts available in salt-affected soils. Salt dissolving experiments showed that two Chromohalobacter isolates were able to dissolve CaCO3 and one of the Halomonas isolate was able to dissolve both CaCO3 and MgCO3. As these bacterial isolates can dissolve CaCO3 and MgCO3, the availability of Ca2+ and Mg2+ ions may increase which can enhance the removal of the excess Na+ in soil profile. 相似文献
82.
Hend H. A. M. Abdullah Nadia Amanzougaghene Handi Dahmana Meriem Louni Didier Raoult Oleg Mediannikov 《PLoS neglected tropical diseases》2021,15(9)
Vector Borne Diseases (VBDs) are considered emerging and re-emerging diseases that represent a global burden. The aim of this study was to explore and characterize vector-borne pathogens in different domestic animal hosts in Egypt. A total of 557 blood samples were collected from different animals using a convenience sampling strategy (203 dogs, 149 camels, 88 cattle, 26 buffaloes, 58 sheep and 33 goats). All samples were tested for multiple pathogens using quantitative PCR and standard PCR coupled with sequencing. We identified Theileria annulata and Babesia bigemina in cattle (15.9 and 1.1%, respectively), T. ovis in sheep and buffaloes (8.6 and 7.7%, respectively) and Ba. canis in dogs (0.5%) as well as Anaplasma marginale in cattle, sheep and camels (20.4, 3.4 and 0.7%, respectively) and Coxiella burnetii in sheep and goats (1.7 and 3%; respectively). New genotypes of An. centrale, An. ovis, An. platys-like and Borrelia theileri were found in cattle (1.1,3.4, 3.4 and 3.4%, respectively), An. platys-like in buffaloes (7.7%), An. marginale, An. ovis, An. platys-like and Bo. theileri in sheep (3.4, 1.7, 1.7 and 3.4%, respectively), An. platys, An. platys-like and Setaria digitata in camels (0.7, 5.4 and 0.7%, respectively) and Rickettsia africae-like, An. platys, Dirofilaria repens and Acanthocheilonema reconditum in dogs (1.5, 3.4, 1 and 0.5%, respectively). Co-infections were found in cattle, sheep and dogs (5.7, 1.7, 0.5%, respectively). For the first time, we have demonstrated the presence of several vector-borne zoonoses in the blood of domestic animals in Egypt. Dogs and ruminants seem to play a significant role in the epidemiological cycle of VBDs. 相似文献
83.
Lettuce is a commercially important leafy vegetable that is cultivated worldwide, and it is also a target crop for plant factories.
In this study, lettuce was selected as an alternative platform for recombinant miraculin production because of its fast growth,
agronomic value, and wide availability. The taste-modifying protein miraculin is a glycoprotein extracted from the red berries
of the West African native shrub Richadella dulcifica. Because of its limited natural availability, many attempts have been made to produce this protein in suitable alternative
hosts. We produced transgenic lettuce with miraculin gene driven either by the ubiquitin promoter/terminator cassette from
lettuce or a 35S promoter/nos terminator cassette. Miraculin gene expression and miraculin accumulation in both cassettes
were compared by quantitative real-time PCR analysis, Western blotting, and enzyme-linked immunosorbent assay. The expression
level of the miraculin gene and protein in transgenic lettuce was higher and more genetically stable in the ubiquitin promoter/terminator
cassette than in the 35S promoter/nos terminator cassette. These results demonstrated that the ubiquitin promoter/terminator
cassette is an efficient platform for the genetically stable expression of the miraculin protein in lettuce and hence this
platform is of benefit for recombinant miraculin production on a commercial scale. 相似文献
84.
85.
Sener MK Jolley C Ben-Shem A Fromme P Nelson N Croce R Schulten K 《Biophysical journal》2005,89(3):1630-1642
With the availability of structural models for photosystem I (PSI) in cyanobacteria and plants it is possible to compare the excitation transfer networks in this ubiquitous photosystem from two domains of life separated by over one billion years of divergent evolution, thus providing an insight into the physical constraints that shape the networks' evolution. Structure-based modeling methods are used to examine the excitation transfer kinetics of the plant PSI-LHCI supercomplex. For this purpose an effective Hamiltonian is constructed that combines an existing cyanobacterial model for structurally conserved chlorophylls with spectral information for chlorophylls in the Lhca subunits. The plant PSI excitation migration network thus characterized is compared to its cyanobacterial counterpart investigated earlier. In agreement with observations, an average excitation transfer lifetime of approximately 49 ps is computed for the plant PSI-LHCI supercomplex with a corresponding quantum yield of 95%. The sensitivity of the results to chlorophyll site energy assignments is discussed. Lhca subunits are efficiently coupled to the PSI core via gap chlorophylls. In contrast to the chlorophylls in the vicinity of the reaction center, previously shown to optimize the quantum yield of the excitation transfer process, the orientational ordering of peripheral chlorophylls does not show such optimality. The finding suggests that after close packing of chlorophylls was achieved, constraints other than efficiency of the overall excitation transfer process precluded further evolution of pigment ordering. 相似文献
86.
87.
Md. Abdullahil Baque Abdullah Elgirban Eun-Jung Lee Kee-Yoeup Paek 《Acta Physiologiae Plantarum》2012,34(2):405-415
The effect of initial sucrose concentration was investigated in root suspension cultures of Morinda citrifolia to improve root growth and secondary metabolites production, i.e. anthraquinone, phenolics and flavonoids. Besides, oxidative
stress level, antioxidant enzymes activity and membranes damage under different sucrose concentration were estimated. A 5%
sucrose supply was shown to be optimal for the production of root dry mass, but higher sucrose concentrations of 7–9% inhibited
the accumulation of root dry weight (DW). However, the maximum production of anthraquinone (251.89 g L−1 DW), phenolics (165.14 g L−1 DW) and flavonoids (163.56 g L−1 DW) were achieved at 1% sucrose-treated culture, which may be a source carbon skeletons for secondary metabolism. At the
same time was observed low oxidative damage, which could be associated with high levels of secondary metabolites and the increased
activity of catalase. Although, catalase (CAT) activity were stimulated at 7–9% sucrose-treated cultures, high accumulation
of hydrogen peroxide (H2O2) and peroxidation of lipid (MDA) was induced. The observed high activity of CAT and guaiacol peroxidase (G-POD) were not
sufficient enough to mitigate the toxic effect of H2O2. 相似文献
88.
Oh RS Pan WC Yalcin A Zhang H Guilarte TR Hotamisligil GS Christiani DC Lu Q 《The Journal of biological chemistry》2012,287(8):6025-6034
89.
Branched chain alpha-ketoacid dehydrogenase and pyruvate dehydrogenase activity in isolated rat pancreatic islets 总被引:1,自引:0,他引:1
Branched-chain alpha-ketoacid dehydrogenase and pyruvate dehydrogenase in isolated rat pancreatic islets were shown to be regulated by a phosphorylation/dephosphorylation mechanism. Broad-specificity phosphoprotein phosphatase treatment stimulated and ATP addition inhibited their activities. The kinases responsible for inactivating these complexes were shown to be sensitive to inhibition by known inhibitors, alpha-chloroisocaproate and dichloroacetate. Total activity (nmol/min/islet / 37 degrees C) of branched-chain alpha-ketoacid dehydrogenase and pyruvate dehydrogenase was 0.86 and 5.09, with a % active form (activity before phosphatase treatment divided by activity after phosphatase treatment X 100) of 36% and 94%, respectively. Incubation of intact isolated islets with alpha-chloroisocaproate affected neither insulin release nor flux through branched-chain alpha-ketoacid dehydrogenase. 相似文献
90.
F Malaisse-Lagae M H Giroix A Sener W J Malaisse 《Biological chemistry Hoppe-Seyler》1986,367(5):411-416
The phosphorylation of alpha- and beta-D-glucose by either yeast hexokinase or beef heart hexokinase was measured at both 10 and 30 degrees C. At 30 degrees C, the anomeric specificity of yeast hexokinase represented a mirror image of that of bovine hexokinase, in terms of both maximal velocity and affinity. A decrease in temperature apparently accentuated the anomeric difference in both maximal velocity and affinity of bovine hexokinase. Such a difference consisted in a higher maximal velocity with beta- than alpha-D-glucose, but a greater affinity for the alpha- than beta-anomer. In yeast hexokinase, however, the decrease in temperature suppressed the anomeric difference in maximal velocity and inversed the anomeric difference in affinity. In the case of both enzymes, the fall in temperature decreased more the maximal velocity recorded with alpha-D-glucose than that measured with beta-D-glucose, and severely lowered the Km for alpha-D-glucose, whilst failing to affect significantly the Km for beta-D-glucose. These findings, which allow to reconcile prior apparently conflicting data, reveal that the anomeric behaviour of hexokinase is affected by the ambient temperature. Our data also support the view that hexokinase underwent a phylogenic evolution in terms of its anomeric specificity. 相似文献