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611.
A simulation approach to understanding the masticatory process 总被引:1,自引:0,他引:1
An analysis of the reduction of food particle sizes during human mastication is presented in terms of the probability of a particle being broken (selection function) and the distribution of fragment sizes produced when it fails (breakage function). Both selection and breakage functions are defined and a general equation produced. Several feasible behaviours for these two variables that have been suggested in the literature are modelled by computer simulation and the results are compared to published breakdown patterns. The conclusions are that selection and breakage functions probably behave very simply with respect to particle size, and that these behaviours could be deduced from an analysis of food particle size distributions and the rate at which particle sizes are reduced per chew. 相似文献
612.
Lim KH Chew CM Chen PC Jeyapalina S Ho HN Rappel JK Lim BH 《Journal of biomechanics》2008,41(5):931-936
Biomechanical properties of skin are important for clinical decision making as well as clinical intervention. Measuring these properties in vivo is critical for estimating dimensional behaviour of skin flap or graft after harvest. However, existing methodologies and devices often suffer from lack of standardisation and unwanted peripheral force contribution due to the deformation of surrounding tissues during measurement. This naturally leads to measurement inaccuracies and lack of reproducibility. In order to improve the measurement accuracy, a new portable extensometer, which measures the non-invasive in vivo biomechanical properties of skin, has been designed and constructed. This design incorporates three pads that attach to the skin, including a C-shaped pad to shield the force sensor from peripheral forces. Such design produces data that are significantly closer to in vitro measurements. The results have been verified by finite element analysis, and experiments on rubber sheets and pig skins. This device can be used to obtain biomechanical properties of skin that will aid doctors in measuring skin elasticity and surgical planning, especially in skin flap surgery. 相似文献
613.
Lim KH Jeyapalina S Ho HN Chew CM Chen PC Teo CL Lim BH 《Journal of biomechanics》2008,41(8):1668-1674
A non-invasive, in vivo method has been developed to predict the skin flap shrinkage (retraction) following a harvest. It involves the use of a novel custom-designed extensometer to measure the force-displacement behaviour of skin and subsequent data analysis to estimate the shrinkage. In validation experiments performed on pigs, this method has been shown to produce results with an average absolute error of 6.0% between the actual and predicted shrinkages. This may be close to what an experienced surgeon would estimate subjectively, thus indicating the potential usefulness of this method to predict flap shrinkage of patient's donor sites. 相似文献
614.
Camarata T Bimber B Kulisz A Chew TL Yeung J Simon HG 《The Journal of cell biology》2006,174(3):339-348
615.
Ute Geigenmüller Teri Chew Nancy Ginzton Suzanne M. Matsui 《Journal of virology》2002,76(4):2003-2008
Astrovirus contains three open reading frames (ORF) on its genomic RNA, ORF1a, ORF1b, and ORF2. ORF1a encodes a 920-amino-acid (aa) nonstructural protein, nsP1a, which displays a 3C-like serine protease motif. Little is known about the processing of nsP1a or whether the protease it contains is active and involved in autocatalytic processing. Here we address both of these matters. Intact and N-terminally deleted forms of ORF1a from human astrovirus serotype 1 were expressed in BHK cells, and nsP1a-derived processing products were immunoprecipitated with an nsP1a-specific antibody or an antibody specific for an N-terminally linked epitope tag. The mapping of the main processing products, p20 and p27, suggests cleavage sites near aa 170, 410, and 655 of nsP1a. Cleavages at around aa 410 and 655, but not aa 170, were abolished when a 9-aa substitution was introduced into the protease motif in nsP1a. The p27 processing product was also found in Caco-2 cells that had been infected with human astrovirus serotype 1, confirming the presence of the cleavage sites at approximately aa 410 and 655. 相似文献
616.
Qian Yi Phua Sreeramanan Subramaniam Vuanghao Lim Bee Lynn Chew 《In vitro cellular & developmental biology. Plant》2018,54(4):413-422
Clinacanthus nutans (Burm.F.) Lindau is an herbaceous plant that has long been used for traditional medicinal purposes in Asia. It has recently gained popularity as an alternative treatment for cancer. The aim of this study was to establish cell suspension cultures of C. nutans and to identify targeted bioactive compounds in the cultures. Young leaf explants were cultured on Murashige and Skoog medium supplemented with various combinations of 2,4-dichlorophenoxyacetic acid (2,4-D) and kinetin to identify a suitable medium for callus induction and proliferation. Proliferated, friable calluses were cultured in different combinations of plant growth regulators (2,4-D, naphthaleneacetic acid [NAA], picloram, kinetin, and 6-benzylaminopurine) in liquid medium to establish cell suspension cultures. Three cell lines of suspension culture, callus, and intact plant parts were subjected to ethyl acetate extraction followed by thin layer chromatography for identification of selected bioactive compounds. Medium supplemented with 0.25 mg L?1 2,4-D and 0.75 mg L?1 kinetin was found to be optimal for callus induction, whereas supplementation with 0.50 mg L?1 2,4-D was efficient for callus proliferation. Liquid medium supplemented with 0.25 mg L?1 2,4-D and 0.50 mg L?1 NAA produced the highest growth index (2.52). Quercetin, catechin, and luteolin were present together in the callus and cell suspension cultures of C. nutans, but all three compounds were detected separately in young leaves, mature leaves, and stems. This study is the first to report the establishment of cell suspension culture of C. nutans with both cell and callus cultures producing quercetin, catechin, and luteolin. 相似文献
617.
618.
John Chih Mun Sha Siew Chin Chua Ping Ting Chew Hassan Ibrahim Hock Keong Lua Tze Kwan Fung Peng Zhang 《Primates; journal of primatology》2018,59(2):163-171
Pristine habitats have generally been considered to be the most important ecological resource for wildlife conservation, but due to forest degradation caused by human activities, mosaics of secondary forests have become increasingly prominent. We studied three forest types in a mosaic tropical forest consisting of short secondary forest (SS), tall secondary forest (TS) and freshwater swamp forest (SF). These forests differed in stand structure and floristic composition, as well as phenological productivity of fruits, flowers and young leaves. We examined habitat use of long-tailed macaques (Macaca fascicularis) in relation to indices of phenological activity. The macaques used the SS for feeding/foraging more than the TS and the SF. This was because the SS had higher productivity of fruit, which is a preferred food resource for macaques. Stem densities of young leaves in the SS and the TS also influenced habitat use, as they provided more clumped resources. Use of SF was limited, but these forests provided more species-rich resources. Our results showed that M. fascicularis responded to small-scale variability in phenological activity between forest types found in a heterogeneous mosaic forest, with young secondary regrowth forests likely providing the most important food resources. Mosaic landscapes may be important as they can buffer the effects of temporal food resource variability in any given forest type. In our increasingly human-altered landscapes, a better understanding of the role of secondary forest mosaics is crucial to the conservation and management of wildlife habitats and the animals they support. 相似文献
619.
Nirma D. Perera Rebecca K. Sheean Chew L. Lau Yea Seul Shin Philip M. Beart Malcolm K. Horne 《Autophagy》2018,14(3):534-551
Macroautophagy/autophagy is the main intracellular catabolic pathway in neurons that eliminates misfolded proteins, aggregates and damaged organelles associated with ageing and neurodegeneration. Autophagy is regulated by both MTOR-dependent and -independent pathways. There is increasing evidence that autophagy is compromised in neurodegenerative disorders, which may contribute to cytoplasmic sequestration of aggregation-prone and toxic proteins in neurons. Genetic or pharmacological modulation of autophagy to promote clearance of misfolded proteins may be a promising therapeutic avenue for these disorders. Here, we demonstrate robust autophagy induction in motor neuronal cells expressing SOD1 or TARDBP/TDP-43 mutants linked to amyotrophic lateral sclerosis (ALS). Treatment of these cells with rilmenidine, an anti-hypertensive agent and imidazoline-1 receptor agonist that induces autophagy, promoted autophagic clearance of mutant SOD1 and efficient mitophagy. Rilmenidine administration to mutant SOD1G93A mice upregulated autophagy and mitophagy in spinal cord, leading to reduced soluble mutant SOD1 levels. Importantly, rilmenidine increased autophagosome abundance in motor neurons of SOD1G93A mice, suggesting a direct action on target cells. Despite robust induction of autophagy in vivo, rilmenidine worsened motor neuron degeneration and symptom progression in SOD1G93A mice. These effects were associated with increased accumulation and aggregation of insoluble and misfolded SOD1 species outside the autophagy pathway, and severe mitochondrial depletion in motor neurons of rilmenidine-treated mice. These findings suggest that rilmenidine treatment may drive disease progression and neurodegeneration in this mouse model due to excessive mitophagy, implying that alternative strategies to beneficially stimulate autophagy are warranted in ALS. 相似文献