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991.
For both cells and tissues, shape is closely correlated with function presumably via geometry-dependent distribution of tension. In this study, we identify common shape determinants spanning cell and tissue scales. For cells whose sites of adhesion are restricted to small adhesive islands on a micropatterned substrate, shape resembles a sequence of inward-curved circular arcs. The same shape is observed for fibroblast-populated collagen gels that are pinned to a flat substrate. Quantitative image analysis reveals that, in both cases, arc radii increase with the spanning distance between the pinning points. Although the Laplace law for interfaces under tension predicts circular arcs, it cannot explain the observed dependence on the spanning distance. Computer simulations and theoretical modeling demonstrate that filamentous network mechanics and contractility give rise to a modified Laplace law that quantitatively explains our experimental findings on both cell and tissue scales. Our model in conjunction with actomyosin inhibition experiments further suggests that cell shape is regulated by two different control modes related to motor contractility and structural changes in the actin cytoskeleton. 相似文献
992.
The Toxoplasma gondii type-II NADH dehydrogenase TgNDH2-I is inhibited by 1-hydroxy-2-alkyl-4(1H)quinolones 总被引:1,自引:0,他引:1
Lin SS Kerscher S Saleh A Brandt U Gross U Bohne W 《Biochimica et biophysica acta》2008,1777(11):1455-1462
The apicomplexan parasite Toxoplasma gondii does not possess complex I of the mitochondrial respiratory chain, but has two genes encoding rotenone-insensitive, non-proton pumping type-II NADH dehydrogenases (NDH2s). The absence of such "alternative" NADH dehydrogenases in the human host defines these enzymes as potential drug targets. TgNDH2-I and TgNDH2-II are constitutively expressed in tachyzoites and bradyzoites and are localized to the mitochondrion as shown by epitope tagging. Functional expression of TgNDH2-I in the yeast Yarrowia lipolytica as an internal enzyme, with the active site facing the mitochondrial matrix, permitted growth in the presence of the complex I inhibitor DQA. Bisubstrate kinetics of TgNDH2-I measured within Y. lipolytica mitochondrial membrane preparations were in accordance with a ping-pong mechanism. Using inhibition kinetics we demonstrate here that 1-hydroxy-2-alkyl-4(1)quinolones with long alkyl chains of C(12) (HDQ) and C(14) are high affinity inhibitors for TgNDH2-I, while compounds with shorter side chains (C(5) and C(6)) displayed significantly higher IC(50) values. The efficiency of the various quinolone derivatives to inhibit TgNDH2-I enzyme activity mirrors their inhibitory potency in vivo, suggesting that a long acyl site chain is critical for the inhibitory potential of these compounds. 相似文献
993.
Understanding protein folding: small proteins in silico 总被引:1,自引:0,他引:1
Recent improvements in methodology and increased computer power now allow atomistic computer simulations of protein folding. We briefly review several advanced Monte Carlo algorithms that have contributed to this development. Details of folding simulations of three designed mini proteins are shown. Adding global translations and rotations has allowed us to handle multiple chains and to simulate the aggregation of six beta-amyloid fragments. In a different line of research we have developed several algorithms to predict local features from sequence. In an outlook we sketch how such biasing could extend the application spectrum of Monte Carlo simulations to structure prediction of larger proteins. 相似文献
994.
Three cellulosic substrates: lyocell (CLY), viscose (CV), and modal (CMD) in the form of fibers and fabrics were subjected to wet/dry or wash/dry treatments. The accessibility of untreated and treated substrates to water and iodine was investigated using dynamic water-vapor sorption, moisture retention, and iodine sorption methods, to study the influence of treatments on sorption-desorption hysteresis, fraction of moisture sorbed as a monomolecular layer, water retention, and iodine sorption. It was found that the sorption properties of untreated and treated substrates differed with sorbate type as well as substrate type and form. 相似文献
995.
Mathara JM Schillinger U Kutima PM Mbugua SK Guigas C Franz C Holzapfel WH 《Current microbiology》2008,56(4):315-321
Lactobacillus plantarum was the major species among the lactic acid bacterial strains isolated from traditional fermented milk of the Maasai in Kenya.
Selected strains were characterized for their functional properties using in vitro standard procedures. All strains expressed
acid tolerance at pH 2.0 after 2-h exposure of values that ranged from 1% to 100%, while bile tolerance of acid-stressed cells
at 0.3% oxgal varied from 30% to 80%. In vitro adhesion to the mucus-secreting cell line HT 29 MTX and binding capacity to
extracellular protein matrices was demonstrated for several strains. The four strains tested in a simulated stomach duodenum
passage survived with recovery rates ranging from 17% to 100%. Strains were intrinsically resistant to several antibiotics
tested. From these in vitro studies, a number of Lb. plantarum strains isolated from the Maasai traditional fermented milk showed probiotic potential. The strains are good candidates for
multifunctional starter culture development. 相似文献
996.
Münch C Zhu BG Mink A Seefried U Riepe MW Ludolph AC Meyer T 《Neurochemical research》2008,33(6):1005-1010
Hypoxia is one of the major common components of vascular risk factors for pathogenesis of Alzheimer’s disease. This study
investigated the possible relationship between hypoxia and alternative splicing of the excitatory amino acid transporter 2
(EAAT2) in a transgenic model for Alzheimer’s disease. We used an APP23 mouse model prior to amyloid deposition and subjected
it to chemical hypoxia treatment as induced by 3-nitropropionic acid. One hour after administration of 3-nitropropionic acid
changes in the expression of the 5′-splice forms mEAAT2/5UT3, mEAAT2/5UT4, and mEAAT2/5UT5 were found in the frontal cortex,
hippocampus and cerebellum of the APP23 model. In untreated APP23 animals the expression of EAAT2 splice variants was unchanged.
Our results demonstrate that hypoxia facilitates alternative splicing of EAAT2 in the APP23 model. This may be a molecular
mechanism linking vascular factors to early pathophysiology of Alzheimer’s disease. 相似文献
997.
Limits to the estimation of species richness: The use of relative abundance distributions 总被引:1,自引:0,他引:1
The present study demonstrates the possibility of estimating species numbers of animal or plant communities from samples using relative abundance distributions. We use log‐abundance–species‐rank order plots and derive two new estimators that are based on log‐series and lognormal distributions. At small to moderate sample sizes these estimators appear to be more precise than previous parametric and nonparametric estimators. We test our estimators using samples from 171 published medium‐sized to large animal and plant communities taken from the literature. By this we show that our new estimators define also limits of precision. 相似文献
998.
Predicting the consequences of species loss requires extending our traditional understanding of simpler dynamic systems of few interacting species to the more complex ecological networks found in natural ecosystems. Especially important is the scaling up of our limited understanding of how and under what conditions loss of ‘keystone’ species causes large declines of many other species. Here we explore how these keystone effects vary among simulations progressively scaled up from simple to more complex systems. Simpler simulations of four to seven interacting species suggest that species up to four links away can strongly alter keystone effects and make the consequences of keystone loss potentially indeterminate in more realistically complex communities. Instead of indeterminacy, we find that more complex networks of up to 32 species generally buffer distant influences such that variation in keystone effects is well predicted by surprisingly local ‘top‐down’, ‘bottom‐up’, and ‘horizontal‘ constraints acting within two links of the keystone subsystem. These results demonstrate that: (1) strong suppression of the competitive dominant by the keystone may only weakly affect subordinate competitors; (2) the community context of the target species determines whether strong keystone effects are realized; (3) simple, measurable, and local attributes of complex communities may explain much of the empirically observed variation in keystone effects; and (4) increasing network complexity per se does not inherently make the prediction of strong keystone effects more complicated. 相似文献
999.
We studied the variation of small-scale swimming behaviour in eight Bosmina cornuta and ten B. pellucida clones in response to key environmental factors to test whether swimming behaviour and genotypes are linked in non-Daphnia cladocerans. We quantified (1) the short-term responses to changes in temperature, light intensity and pH, (2) the response to long-term temperature acclimation, and (3) the pH-related survival rates. Vertical swimming activity S was quantified in cuvette experiments as crossings of a line at 2 cm height per individual an hour. S differed significantly among species and conspecific clones. At any temperature, light intensity and pH tested, B. cornuta (clone variation: 40-58 crossings/ind.× h) showed a higher vertical swimming activity than B. pellucida (clone variation: 25-48 crossings/ind.× h). A short-term change of water temperature (range tested: 10-25°C) only affected S of B. cornuta, whereas that of B. pellucida remained unaltered. In contrast, S increased with rising temperature following long-term temperature acclimation (range tested: 10-20°C) in both species. Swimming activity was inversely related to the light intensity (range tested: 60-60,000 lux), but decrease of activity was stronger in B. pellucida (44 → 12 crossings/ind × h) than in B. cornuta (50 → 40 crossings/ind.× h). Short-term changes of pH (range tested: 4-6) did not influence swimming activity in any species, although a prolonged exposure (24 h) to pH 4 was lethal. Thus, Bosmina showed behavioural responses which permit to distinguish between the species and which are related to their seasonal succession and distribution pattern. 相似文献
1000.
Rolf Stoeckli Robin Chanda Igor Langer Ulrich Keller 《Obesity (Silver Spring, Md.)》2004,12(2):346-350
Objective: Ghrelin is an enteric peptide with strong orexigenic and adipogenic effects. Plasma ghrelin levels are decreased in obese subjects but increase after weight loss; this increase is not observed after Roux‐en‐Y gastric bypass (RYGB). Prospective and comparative data after adjustable silicone gastric banding (ASGB) have not been reported previously. Research Methods and Procedures: Overnight fasting plasma ghrelin concentration was measured in morbidly obese subjects at baseline and 3, 6, 12, and 24 months after ASGB (n = 8) or RYGB (n = 5) and in nonoperated controls (n = 7). Results: After RYGB, body weight (BW) decreased by 29.5 ± 5.5 kg (mean ± SE, p < 0.001), whereas plasma ghrelin failed to increase significantly (+167 ± 119 pg/mL, not significant). In contrast, after ASGB, BW decreased less (by 22.8 ± 5.9 kg; p < 0.001), and plasma ghrelin significantly increased by 377 ± 201 pg/mL (p = 0.025). Neither BW nor plasma ghrelin changed in nonoperated controls. Plasma leptin decreased in both operated groups (similarly p < 0.05) but not in nonoperated controls. Plasma growth hormone and insulin‐like growth factor 1 were not correlated with changes in plasma ghrelin concentrations. Discussion: Plasma ghrelin levels failed to increase during substantial weight loss after RYGB, but did increase in response to lesser weight loss after ASGB. These findings suggest that the plasma ghrelin response after weight loss is impaired after exclusion of major parts of the stomach and the duodenum (RYGB), and the smaller long‐term weight loss after ASGB compared with RYGB may be due, at least in part, to an absent increase in plasma ghrelin after RYGB. 相似文献