全文获取类型
收费全文 | 3590篇 |
免费 | 220篇 |
国内免费 | 4篇 |
专业分类
3814篇 |
出版年
2023年 | 14篇 |
2022年 | 16篇 |
2021年 | 46篇 |
2020年 | 29篇 |
2019年 | 38篇 |
2018年 | 42篇 |
2017年 | 42篇 |
2016年 | 76篇 |
2015年 | 104篇 |
2014年 | 147篇 |
2013年 | 186篇 |
2012年 | 216篇 |
2011年 | 225篇 |
2010年 | 248篇 |
2009年 | 228篇 |
2008年 | 230篇 |
2007年 | 249篇 |
2006年 | 215篇 |
2005年 | 205篇 |
2004年 | 214篇 |
2003年 | 223篇 |
2002年 | 203篇 |
2001年 | 45篇 |
2000年 | 39篇 |
1999年 | 42篇 |
1998年 | 48篇 |
1997年 | 39篇 |
1996年 | 36篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 28篇 |
1992年 | 25篇 |
1991年 | 26篇 |
1990年 | 13篇 |
1989年 | 22篇 |
1988年 | 25篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 12篇 |
1975年 | 7篇 |
1974年 | 7篇 |
排序方式: 共有3814条查询结果,搜索用时 15 毫秒
81.
82.
83.
Graham RL Pollock CE O'Loughlin SN Ternan NG Weatherly DB Jackson PJ Tarleton RL McMullan G 《Journal of proteome research》2006,5(11):3145-3153
We report the first large-scale gel-free proteomic analysis of the soluble subproteome of the emerging pathogen Ochrobactrum anthropi. Utilizing our robust offline multidimensional protein identification protocol, a total of 57 280 peptides were initially identified utilizing automated MS/MS analysis software. We describe our investigation of the heuristic protein validation tool PROVALT and demonstrate its ability to increase the speed and accuracy of the curation process of large-scale proteomic datasets. PROVALT reduced our peptide list to 8517 identified peptides and further manual curation of these peptides led to a final list of 984 uniquely identified peptides that resulted in the positive identification of 249 proteins. These identified proteins were functionally classified and physiochemically characterized. A variety of typical "housekeeping" functions identified within the proteome included nucleic acid, amino and fatty acid anabolism and catabolism, glycolysis, TCA cycle, and pyruvate and selenoamino acid metabolism. In addition, a number of potential virulence factors of relevance to both plant and human disease were identified. 相似文献
84.
Combe JP Basran J Hothi P Leys D Rigby SE Munro AW Scrutton NS 《The Journal of biological chemistry》2006,281(26):17977-17988
Dihydroorotate dehydrogenase B (DHODB) catalyzes the oxidation of dihydroorotate (DHO) to orotate and is found in the pyrimidine biosynthetic pathway. The Lactococcus lactis enzyme is a dimer of heterodimers containing FMN, FAD, and a 2Fe-2S center. Lys-D48 is found in the catalytic subunit and its side-chain adopts different positions, influenced by ligand binding. Based on crystal structures of DHODB in the presence and absence of orotate, we hypothesized that Lys-D48 has a role in facilitating electron transfer in DHODB, specifically in stabilizing negative charge in the reduced FMN isoalloxazine ring. We show that mutagenesis of Lys-D48 to an alanine, arginine, glutamine, or glutamate residue (mutants K38A, K48R, K48Q, and K48E) impairs catalytic turnover substantially (approximately 50-500-fold reduction in turnover number). Stopped-flow studies demonstrate that loss of catalytic activity is attributed to poor rates of FMN reduction by substrate. Mutation also impairs electron transfer from the 2Fe-2S center to FMN. Addition of methylamine leads to partial rescue of flavin reduction activity. Nicotinamide coenzyme oxidation and reduction at the distal FAD site is unaffected by the mutations. Formation of the spin-interacting state between the FMN semiquinone-reduced 2Fe-2S centers observed in wild-type enzyme is retained in the mutant proteins, consistent with there being little perturbation of the superexchange paths that contribute to the efficiency of electron transfer between these cofactors. Our data suggest a key charge-stabilizing role for Lys-D48 during reduction of FMN by dihydroorotate, or by electron transfer from the 2Fe-2S center, and establish a common mechanism of FMN reduction in the single FMN-containing A-type and the complex multicenter B-type DHOD enzymes. 相似文献
85.
Plants frequently suffer attack from herbivores and microbial pathogens, and have evolved a complex array of defence mechanisms to resist defoliation and disease. These include both preformed defences, ranging from structural features to stores of toxic secondary metabolites, and inducible defences, which are activated only after an attack is detected. It is well known that plant defences against pests and pathogens are commonly affected by environmental conditions, but the mechanisms by which responses to the biotic and abiotic environments interact are only poorly understood. In this review, we consider the impact of light on plant defence, in terms of both plant life histories and rapid scale molecular responses to biotic attack. We bring together evidence that illustrates that light not only modulates defence responses via its influence on biochemistry and plant development but, in some cases, is essential for the development of resistance. We suggest that the interaction between the light environment and plant defence is multifaceted, and extends across different temporal and biological scales. 相似文献
86.
Groome JR Alexander HM Fujimoto E Sherry M Petty D 《Cellular and molecular neurobiology》2007,27(1):87-106
Summary 1. Mutations in the S4 segment of domain III in the voltage gated skeletal muscle sodium channel hNaV1.4 were constructed to test the roles of each charged residue in deactivation gating. Mutations comprised charge reversals
at K1-R6, charge neutralization, and substitution at R4 and R5.
2. Charge-reversing mutations at R4 and R5 produced the greatest alteration of activation parameters compared to hNaV1.4. Effects included depolarization of the conductance/voltage (g/V) curve, decreased valence and slowing of kinetics.
3. Reversal of charge at R2 to R4 hyperpolarized, and reversal at R5 or R6 depolarized the h
∞ curve. Most DIIIS4 mutations slowed inactivation from the open state. R4E slowed closed state fast inactivation and R5E inhibited
its completion.
4. Deactivation from the open and/or inactivated state was prolonged in mutations reversing charge at R2 to R4 but accelerated
by reversal of charge at R5 or R6. Effects were most pronounced at central charges R4 and R5.
5. Charge and structure each contribute to effects of mutations at R4 and R5 on channel gating. Effects of mutations on activation
and deactivation at R4 and, to a lesser extent R5, were primarily owing to charge alteration, whereas effects on fast inactivation
were charge independent. 相似文献
87.
W. Ellis Penning Marit Mjelde Bernard Dudley Seppo Hellsten Jenica Hanganu Agnieszka Kolada Marcel van den Berg Sandra Poikane Geoff Phillips Nigel Willby Frauke Ecke 《Aquatic Ecology》2008,42(2):237-251
Aquatic macrophytes are one of the biological quality elements in the Water Framework Directive (WFD) for which status assessments
must be defined. We tested two methods to classify macrophyte species and their response to eutrophication pressure: one based
on percentiles of occurrence along a phosphorous gradient and another based on trophic ranking of species using Canonical
Correspondence Analyses in the ranking procedure. The methods were tested at Europe-wide, regional and national scale as well
as by alkalinity category, using 1,147 lakes from 12 European states. The grouping of species as sensitive, tolerant or indifferent
to eutrophication was evaluated for some taxa, such as the sensitive Chara spp. and the large isoetids, by analysing the (non-linear) response curve along a phosphorous gradient. These thresholds
revealed in these response curves can be used to set boundaries among different ecological status classes. In total 48 taxa
out of 114 taxa were classified identically regardless of dataset or classification method. These taxa can be considered the
most consistent and reliable indicators of sensitivity or tolerance to eutrophication at European scale. Although the general
response of well known indicator species seems to hold, there are many species that were evaluated differently according to
the database selection and classification methods. This hampers a Europe-wide comparison of classified species lists as used
for the status assessment within the WFD implementation process. 相似文献
88.
This study on human cytochrome P450 reductase (CPR) presents a comprehensive analysis of the thermodynamic and kinetic effects of pH and solvent on two- and four-electron reduction in this diflavin enzyme. pH-dependent redox potentiometry revealed that the thermodynamic equilibrium between various two-electron reduced enzyme species (FMNH*,FADH*; FMN,FADH2; FMNH2,FAD) is independent of pH. No shift from the blue, neutral di-semiquinone (FMNH*,FADH*) towards the red, anionic species is observed upon increasing the pH from 6.5 to 8.5. Spectrophotometric analysis of events following the mixing of oxidized CPR and NADPH (1 to 1) in a stopped-flow instrument demonstrates that the establishment of this thermodynamic equilibrium becomes a very slow process at elevated pH, indicative of a pH-gating mechanism. The final level of blue di-semiquinone formation is found to be pH independent. Stopped-flow experiments using excess NADPH over CPR provide evidence that both pH and solvent significantly influence the kinetic exposure of the blue di-semiquinone intermediate, yet the observed rate constants are essentially pH independent. Thus, the kinetic pH-gating mechanism under stoichiometric conditions is of no significant kinetic relevance for four-electron reduction, but rather modulates the observed semiquinone absorbance at 600 nm in a pH-dependent manner. The use of proton inventory experiments and primary kinetic isotope effects are described as kinetic tools to disentangle the intricate pH-dependent kinetic mechanism in CPR. Our analysis of the pH and isotope dependence in human CPR reveals previously hidden complexity in the mechanism of electron transfer in this complex flavoprotein. 相似文献
89.
William R. Harcombe Nigel F. Delaney Nicholas Leiby Niels Klitgord Christopher J. Marx 《PLoS computational biology》2013,9(6)
The most powerful genome-scale framework to model metabolism, flux balance analysis (FBA), is an evolutionary optimality model. It hypothesizes selection upon a proposed optimality criterion in order to predict the set of internal fluxes that would maximize fitness. Here we present a direct test of the optimality assumption underlying FBA by comparing the central metabolic fluxes predicted by multiple criteria to changes measurable by a 13C-labeling method for experimentally-evolved strains. We considered datasets for three Escherichia coli evolution experiments that varied in their length, consistency of environment, and initial optimality. For ten populations that were evolved for 50,000 generations in glucose minimal medium, we observed modest changes in relative fluxes that led to small, but significant decreases in optimality and increased the distance to the predicted optimal flux distribution. In contrast, seven populations evolved on the poor substrate lactate for 900 generations collectively became more optimal and had flux distributions that moved toward predictions. For three pairs of central metabolic knockouts evolved on glucose for 600–800 generations, there was a balance between cases where optimality and flux patterns moved toward or away from FBA predictions. Despite this variation in predictability of changes in central metabolism, two generalities emerged. First, improved growth largely derived from evolved increases in the rate of substrate use. Second, FBA predictions bore out well for the two experiments initiated with ancestors with relatively sub-optimal yield, whereas those begun already quite optimal tended to move somewhat away from predictions. These findings suggest that the tradeoff between rate and yield is surprisingly modest. The observed positive correlation between rate and yield when adaptation initiated further from the optimum resulted in the ability of FBA to use stoichiometric constraints to predict the evolution of metabolism despite selection for rate. 相似文献
90.