全文获取类型
收费全文 | 1355篇 |
免费 | 135篇 |
国内免费 | 1篇 |
出版年
2023年 | 7篇 |
2022年 | 5篇 |
2021年 | 21篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 22篇 |
2017年 | 26篇 |
2016年 | 31篇 |
2015年 | 63篇 |
2014年 | 58篇 |
2013年 | 75篇 |
2012年 | 99篇 |
2011年 | 87篇 |
2010年 | 56篇 |
2009年 | 54篇 |
2008年 | 77篇 |
2007年 | 88篇 |
2006年 | 73篇 |
2005年 | 88篇 |
2004年 | 80篇 |
2003年 | 65篇 |
2002年 | 102篇 |
2001年 | 20篇 |
2000年 | 12篇 |
1999年 | 20篇 |
1998年 | 25篇 |
1997年 | 16篇 |
1996年 | 6篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1971年 | 4篇 |
排序方式: 共有1491条查询结果,搜索用时 156 毫秒
101.
In contrast to the macro/mesozooplankton, microzooplankton has received much less attention in ecosystem models. In many modeling studies, microzooplankton has been either entirely neglected, or else, data were often not available for validation, or agreement between the observed and the simulated abundances was rather poor. In this study, we compare the simulation results from several alternative models considering different formulations of ciliate growth in a hydrodynamically driven 1D nutrient-phytoplankton–multiple zooplankton model, with long-term datasets from the deep, monomictic Lake Constance. We show that the parameterization of the limitation of ciliate growth with a constant specific mortality rate and/or predation by copepods leads to uncontrolled ciliate blooms. In contrast, implementation of a density-dependent mortality rate enables reproduction of algae–ciliate dynamics over a variety of environmental settings encompassed by the 14-year dataset spanning 21 years in a lake undergoing oligotrophication. Considering the numerous processes that can be responsible for the dampening of ciliate blooms, our findings suggest that employing a simple density-dependent mortality term offers a pragmatic solution for the challenge of including the microzooplankton, characterized by an overwhelming complexity of trophic interactions, in ecosystem models. 相似文献
102.
Martin H.J. Jaspers Ralf Pflanz Dietmar Riedel Steffen Kawelke Ivo Feussner Reinhard Schuh 《Developmental biology》2014
The transition from a liquid to a gas filled tubular network is the prerequisite for normal function of vertebrate lungs and invertebrate tracheal systems. However, the mechanisms underlying the process of gas filling remain obscure. Here we show that waterproof, encoding a fatty acyl-CoA reductase (FAR), is essential for the gas filling of the tracheal tubes during Drosophila embryogenesis, and does not affect branch network formation or key tracheal maturation processes. However, electron microscopic analysis reveals that in waterproof mutant embryos the formation of the outermost tracheal cuticle sublayer, the envelope, is disrupted and the hydrophobic tracheal coating is damaged. Genetic and gain-of-function experiments indicate a non-cell-autonomous waterproof function for the beginning of the tracheal gas filling process. Interestingly, Waterproof reduces very long chain fatty acids of 24 and 26 carbon atoms to fatty alcohols. Thus, we propose that Waterproof plays a key role in tracheal gas filling by providing very long chain fatty alcohols that serve as potential substrates for wax ester synthesis or related hydrophobic substances that ultimately coat the inner lining of the trachea. The hydrophobicity in turn reduces the tensile strength of the liquid inside the trachea, leading to the formation of a gas bubble, the focal point for subsequent gas filling. Waterproof represents the first enzyme described to date that is necessary for tracheal gas filling without affecting branch morphology. Considering its conservation throughout evolution, Waterproof orthologues may play a similar role in the vertebrate lung. 相似文献
103.
104.
We study the unbiased folding/unfolding thermodynamics of the Trp‐cage miniprotein using detailed molecular dynamics simulations of an all‐atom model of the protein in explicit solvent using the Amberff99SB force field. Replica‐exchange molecular dynamics simulations are used to sample the protein ensembles over a broad range of temperatures covering the folded and unfolded states at two densities. The obtained ensembles are shown to reach equilibrium in the 1 μs/replica timescale. The total simulation time used in the calculations exceeds 100 μs. Ensemble averages of the fraction folded, pressure, and energy differences between the folded and unfolded states as a function of temperature are used to model the free energy of the folding transition, ΔG(P, T), over the whole region of temperatures and pressures sampled in the simulations. The ΔG(P, T) diagram describes an ellipse over the range of temperatures and pressures sampled, predicting that the system can undergo pressure‐induced unfolding and cold denaturation at low temperatures and high pressures, and unfolding at low pressures and high temperatures. The calculated free energy function exhibits remarkably good agreement with the experimental folding transition temperature (Tf = 321 K), free energy, and specific heat changes. However, changes in enthalpy and entropy are significantly different than the experimental values. We speculate that these differences may be due to the simplicity of the semiempirical force field used in the simulations and that more elaborate force fields may be required to describe appropriately the thermodynamics of proteins. Proteins 2010. © 2010 Wiley‐Liss, Inc. 相似文献
105.
Doris Freißmuth Alexander Hiltgartner Christiane Stahl‐Hennig Dietmar Fuchs Klara Tenner‐Racz Paul Racz Klaus Überla Alexander Strasak Manfred P. Dierich Heribert Stoiber Barbara Falkensammer 《Journal of medical primatology》2010,39(2):97-111
Background To determine the correlation between protection and humoral immune response against simian immunodeficiency virus (SIVmac251), 11 macaques were immunized with live‐attenuated SIVmac239Δnef either intravenously or via the tonsils and exposed to SIVmac251 after either 6 or 15 months along with unvaccinated controls. Results Independent of the route of vaccine application, viremia was significantly reduced in vaccinees compared with controls 2 weeks post‐challenge. Concomitantly, viremia correlated inversely with SIV‐specific IgG, complement‐mediated lysis and neutralizing antibodies and these parameters seemed to contribute to reduced viremia. During chronic infection, six monkeys controlled viremia in the circulation (two or fewer infectious units per 106 PBMCs) and showed no signs of trapping in lymphatic tissues (Appendix S1). Conclusions As no significant differences were observed throughout the study, with respect to the humoral immune response and viremia control, between the two vaccinated cohorts, mucosal immunization strategies are recommended due to more simplified application. 相似文献
106.
107.
Clinical studies and animal experiments have shown that the serum protein fetuin-A is a highly effective inhibitor of soft tissue calcification. This inhibition mechanism was elucidated on the basis of an in vitro fetuin-A-mineral model system. In a previous study, we found that in a two-stage process ∼100-nm sized calciprotein particles (CPPs) were formed whose final stage was stabilized by a compact outer fetuin-A monolayer against further growth. Quantitative small-angle neutron scattering data analysis revealed that even at a fetuin-A concentration close to the stability limit, only approximately one-half of the mineral ions and only 5% of the fetuin-A were contained in the CPPs. To uncover the interplay of the remaining supersaturated mineral ion fraction and of the 95% non-CPP fetuin-A, we explored the fetuin-A monomer fraction in solution by contrast variation small-angle neutron scattering. Our results suggest that the mineral ions coalesce to subnanometer-sized clusters, reminiscent of Posner clusters, which are stabilized by fetuin-A monomers. Hence, our experiments revealed a second mechanism of long-term mineral ion stabilization by the fetuin-A that is complementary to the formation of CPPs. 相似文献
108.
Kitti Mueangtoom Roman Kittl Oliver Mann Dietmar Haltrich Roland Ludwig Dr. 《Biotechnology journal》2010,5(8):857-870
In a screening of saprotrophic, ectomycorrhizal and plant pathogen ascomycetes a frequent occurrence of laccase was observed. Lamprospora wrightii, the best producing organism, was chosen to elucidate the properties of a laccase from a moss-associated, saprotrophic ascomycete. The expression of laccase by this bryophilic fungus could be increased by the addition of tomato juice or copper sulfate to the medium. The obtained volumetric activity after optimization was 420 U/mL in either shaking flask or bioreactor-based cultivations. The purified laccase has a molecular mass of 68 kDa and an isoelectric point of 3.4. Although of ascomycete origin, its catalytic properties are similar to typical basidiomycte laccases, and an excellent activity and stability was observed at low pH, which makes it suitable for bioremediation in acidic environments. As an example, the decolorization reactions of azo-, anthraquinone-, trimethylmethane- and indigoid dyes at pH 3.0 and 5.0 were investigated. All ten selected dyes were decolorized, five of them very efficiently. Depending on the dye, the decolorization was found to be a combination of two reactions, degradation of the chromophore and formation of polymerized products, which contributed to the overall process in a dye-specific pattern. 相似文献
109.
Thomas Maischberger Elisabeth Leitner Sunee Nitisinprasert Onladda Juajun Montarop Yamabhai Thu-Ha Nguyen Dr. Dietmar Haltrich 《Biotechnology journal》2010,5(8):838-847
A novel heterodimeric β-galactosidase with a molecular mass of 105 kDa was purified from crude cell extracts of the soil isolate Lactobacillus pentosus KUB-ST10-1 using ammonium sulphate fractionation followed by hydrophobic interaction and affinity chromatography. The electrophoretically homogenous enzyme has a specific activity of 97 UoNPG/mg protein. The Km, kcat and kcat/Km values for lactose and o-nitrophenyl-β-D-galactopyranoside (oNPG) were 38 mM, 20 s-1, 530 M-1·s-1 and 1.67 mM, 540 s-1, 325 000 M-1·s-1, respectively. The temperature optimum of β-galactosidase activity was 60–65°C for a 10-min assay, which is considerably higher than the values reported for other lactobacillal β-galactosidases. Mg2+ ions enhanced both activity and stability significantly. L. pentosus β-galactosidase was used for the production of prebiotic galacto-oligosaccharides (GOS) from lactose. A maximum yield of 31% GOS of total sugars was obtained at 78% lactose conversion. The enzyme showed a strong preference for the formation of β-(1→3) and β-(1→6) linkages, and the main transgalactosylation products identified were the disaccharides β-D-Galp-(1→6)-D -Glc, β-D-Galp-(1→3)-D -Glc, β-D -Galp-(1→6)-D -Gal, β-D -Galp-(1→3)-D -Gal, and the trisaccharides β-D -Galp-(1→3)-D -Lac, β-D -Galp-(1→6)-D -Lac. 相似文献
110.
Clara Salaheddin Yoshimitsu Takakura Masako Tsunashima Barbara Stranzinger Oliver Spadiut Montarop Yamabhai Clemens K Peterbauer Dietmar Haltrich 《Microbial cell factories》2010,9(1):57