全文获取类型
收费全文 | 1142篇 |
免费 | 160篇 |
专业分类
1302篇 |
出版年
2022年 | 15篇 |
2021年 | 18篇 |
2020年 | 14篇 |
2019年 | 17篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 21篇 |
2015年 | 26篇 |
2014年 | 28篇 |
2013年 | 50篇 |
2012年 | 55篇 |
2011年 | 69篇 |
2010年 | 40篇 |
2009年 | 29篇 |
2008年 | 55篇 |
2007年 | 55篇 |
2006年 | 42篇 |
2005年 | 51篇 |
2004年 | 47篇 |
2003年 | 44篇 |
2002年 | 44篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 16篇 |
1998年 | 24篇 |
1997年 | 21篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1993年 | 17篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1989年 | 15篇 |
1988年 | 17篇 |
1987年 | 18篇 |
1986年 | 10篇 |
1984年 | 13篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 19篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1974年 | 20篇 |
1973年 | 16篇 |
1972年 | 10篇 |
1970年 | 12篇 |
1969年 | 17篇 |
1968年 | 11篇 |
1967年 | 9篇 |
1964年 | 9篇 |
排序方式: 共有1302条查询结果,搜索用时 15 毫秒
61.
Anita Tragler Lakshmi Srinivasan Olga Shenderova Melvin McClauren Donald W. Brenner 《Molecular simulation》2013,39(1-2):121-130
Abstract A novel simulation interface is being developed as an educational tool to help students better understand fundamentals of materials science. This interface makes use of virtual reality (VR) technology consisting of PC-based graphics and a force-feedback haptic device. Visualization of atomistic processes with simultaneous tactile sensation via the haptic provides a powerful method for understanding complex phenomena that are otherwise difficult to comprehend. Modules are described that allow students to interactively explore interatomic bonding and single-atom diffusion through materials. 相似文献
62.
Aung Than Melvin Khee-Shing Leow Peng Chen 《The Journal of biological chemistry》2013,288(22):15520-15531
Angiotensin II (AngII), a peptide hormone released by adipocytes, can be catabolized by adipose angiotensin-converting enzyme 2 (ACE2) to form Ang(1–7). Co-expression of AngII receptors (AT1 and AT2) and Ang(1–7) receptors (Mas) in adipocytes implies the autocrine regulation of the local angiotensin system upon adipocyte functions, through yet unknown interactive mechanisms. In the present study, we reveal the adipogenic effects of Ang(1–7) through activation of Mas receptor and its subtle interplays with the antiadipogenic AngII-AT1 signaling pathways. Specifically, in human and 3T3-L1 preadipocytes, Ang(1–7)-Mas signaling promotes adipogenesis via activation of PI3K/Akt and inhibition of MAPK kinase/ERK pathways, and Ang(1–7)-Mas antagonizes the antiadipogenic effect of AngII-AT1 by inhibiting the AngII-AT1-triggered MAPK kinase/ERK pathway. The autocrine regulation of the AngII/AT1-ACE2-Ang(1–7)/Mas axis upon adipogenesis has also been revealed. This study suggests the importance of the local regulation of the delicately balanced angiotensin system upon adipogenesis and its potential as a novel therapeutic target for obesity and related metabolic disorders. 相似文献
63.
David C. Kombo Terry A. Hauser Vladimir P. Grinevich Matthew S. Melvin Jon-Paul Strachan Serguei S. Sidach Joseph Chewning Nikolai Fedorov Kartik Tallapragada Scott R. Breining Craig H. Miller 《Bioorganic & medicinal chemistry letters》2013,23(5):1450-1455
We have carried out a pharmacological evaluation of arylmethylene quinuclidine derivatives interactions with human α3β4 nAChRs subtype, using cell-based receptor binding, calcium-influx, electrophysiological patch-clamp assays and molecular modeling techniques. We have found that the compounds bind competitively to the α3β4 receptor with micromolar affinities and some of the compounds behave as non-competitive antagonists (compounds 1, 2 and 3), displaying submicromolar IC50 values. These evidences suggest a mixed mode of action for these compounds, having interactions at the orthosteric site and more pronounced interactions at an allosteric site to block agonist effects. One of the compounds, 1-benzyl-3-(diphenylmethylene)-1-azoniabicyclo[2.2.2]octane chloride (compound 3), exhibited poorly reversible use-dependent block of α3β4 channels. We also found that removal of a phenyl group from compound 1 confers a partial agonism to the derived analog (compound 6). Introducing a hydrogen-bond acceptor into the 3-benzylidene quinuclidine derivative (compound 7) increases agonism potency at the α3β4 receptor subtype. Docking into the orthosteric binding site of a α3β4 protein structure derived by comparative modeling accurately predicted the experimentally-observed trend in binding affinity. Results supported the notion that binding requires a hydrogen bond formation between the ligand basic nitrogen and the backbone carbonyl oxygen atom of the conserved Trp-149. 相似文献
64.
Kerry E. Uebel Gina Joubert Edwin Wouters Willie F. Mollentze Dingie H. C. J. van Rensburg 《PloS one》2013,8(1)
Background
Integration of human immunodeficiency virus (HIV) care into primary care services is one strategy proposed to achieve universal access to antiretroviral treatment (ART) for HIV-positive patients in high burden countries. There is a need for controlled studies of programmes to integrate HIV care with details of the services being integrated.Methods
A semi-quantitative questionnaire was developed in consultation with clinic staff, tested for internal consistency using Cronbach''s alpha coefficients and checked for inter-observer reliability. It was used to conduct four assessments of the integration of HIV care into referring primary care clinics (mainstreaming HIV) and into the work of all nurses within ART clinics (internal integration) and the integration of pre-ART and ART care during the Streamlining Tasks and Roles to Expand Treatment and Care for HIV (STRETCH) trial in South Africa. Mean total integration and four component integration scores at intervention and control clinics were compared using one way analysis of variance (ANOVA). Repeated measures ANOVA was used to analyse changes in scores during the trial.Results
Cronbach''s alpha coefficients for total integration, pre-ART and ART integration and mainstreaming HIV and internal integration scores showed good internal consistency. Mean total integration, mainstreaming HIV and ART integration scores increased significantly at intervention clinics by the third assessment. Mean pre-ART integration scores were almost maximal at the first assessment and showed no further change. There was no change in mean internal integration score.Conclusion
The questionnaire developed in this study is a valid tool with potential for monitoring integration of HIV care in other settings. The STRETCH trial interventions resulted in increased integration of HIV care, particularly ART care, by providing HIV care at referring primary care clinics, but had no effect on integrating HIV care into the work of all nurses with the ART clinic. 相似文献65.
Continuous, anaerobic fermentations of D-xylose were performed by Actinobacillus succinogenes 130Z in a custom, biofilm reactor at dilution rates of 0.05, 0.10 and 0.30 h?1. Succinic acid yields on xylose (0.55–0.68 g g?1), titres (10.9–29.4 g L?1) and productivities (1.5–3.4 g L?1 h?1) were lower than those of a previous study on glucose, but product ratios (succinic acid/acetic acid = 3.0–5.0 g g?1) and carbohydrate consumption rates were similar. Also, mass balance closures on xylose were up to 18.2 % lower than those on glucose. A modified HPLC method revealed pyruvic acid excretion at appreciable concentrations (1.2–1.9 g L?1) which improved the mass balance closure by up to 16.8 %. Furthermore, redox balances based on the accounted xylose consumed and the excreted metabolites, indicated an overproduction of reducing power. The oxidative pentose phosphate pathway was shown to be a plausible source of the additional reducing power. 相似文献
66.
We propose Turing Learning, a novel system identification method for inferring the behavior of natural or artificial systems. Turing Learning simultaneously optimizes two populations of computer programs, one representing models of the behavior of the system under investigation, and the other representing classifiers. By observing the behavior of the system as well as the behaviors produced by the models, two sets of data samples are obtained. The classifiers are rewarded for discriminating between these two sets, that is, for correctly categorizing data samples as either genuine or counterfeit. Conversely, the models are rewarded for ‘tricking’ the classifiers into categorizing their data samples as genuine. Unlike other methods for system identification, Turing Learning does not require predefined metrics to quantify the difference between the system and its models. We present two case studies with swarms of simulated robots and prove that the underlying behaviors cannot be inferred by a metric-based system identification method. By contrast, Turing Learning infers the behaviors with high accuracy. It also produces a useful by-product—the classifiers—that can be used to detect abnormal behavior in the swarm. Moreover, we show that Turing Learning also successfully infers the behavior of physical robot swarms. The results show that collective behaviors can be directly inferred from motion trajectories of individuals in the swarm, which may have significant implications for the study of animal collectives. Furthermore, Turing Learning could prove useful whenever a behavior is not easily characterizable using metrics, making it suitable for a wide range of applications. 相似文献
67.
Yamanaka Akihiro Beuckmann Carsten T. Willie Jon T. Hara Junko Tsujino Natsuko Goto Katsutoshi Yanagisawa Masashi Sakurai Takeshi 《Sleep and biological rhythms》2016,2(1):S57-S57
Sleep and Biological Rhythms - 相似文献
68.
Hugh F. Davies Willie Rioli Jos Puruntatameri Willie Roberts Colin Kerinaiua Vivian Kerinauia Kim Brooks Womatakimi Graeme R. Gillespie Brett P. Murphy 《Austral ecology》2019,44(5):868-879
Since European settlement, many granivorous birds of northern Australia's savanna landscapes have declined. One such example, the partridge pigeon (Geophaps smithii), has suffered a significant range contraction, disappearing from at least half of its pre‐European range. Multiple factors have been implicated in this decline, including the loss of traditional Aboriginal burning practices, grazing by large exotic herbivores and predation by feral cats (Felis catus). While populations of partridge pigeon on the Tiwi Islands may be particularly important for the long‐term persistence of this species, they too may be at risk of decline. However, as a reliable method to detect this species has not yet been developed and tested, we lack the ability to identify, at an early stage, the species' decline in a given location or region. This severely limits our capacity to make informed management decisions. Here, we demonstrate that the standard camera trapping approach for native mammal monitoring in northern Australia attained an overall probability of detecting partridge pigeon greater than 0.98. We thus provide a robust estimate of partridge pigeon site occupancy (0.30) on Melville Island, the larger of the two main Tiwi Islands. The information presented here for the partridge pigeon represents a critical first step towards the development of optimal monitoring programmes with which to gauge population trajectories, as well as the response to remedial management actions. In the face of ongoing biodiversity loss, such baseline information is vital for management agencies to make informed decisions and should therefore be sought for as many species as possible. 相似文献
69.
Suresh Anand Sadananthan Mya Thway Tint Navin Michael Izzuddin M. Aris See Ling Loy Kuan Jin Lee Lynette Pei‐Chi Shek Fabian Kok Peng Yap Kok Hian Tan Keith M. Godfrey Melvin Khee‐Shing Leow Yung Seng Lee Michael S. Kramer Peter D. Gluckman Yap Seng Chong Neerja Karnani Christiani Jeyakumar Henry Marielle Valerie Fortier S. Sendhil Velan 《Obesity (Silver Spring, Md.)》2019,27(3):470-478
70.
Bei Gao Mo-Xian Chen Xiao-Shuang Li Yu-Qing Liang Dao-Yuan Zhang rew J. Wood Melvin J. Oliver Jian-Hua Zhang 《植物分类学报:英文版》2022,60(1):144-159
Mosses (Bryophyta) are a key group occupying an important phylogenetic position in land plant (embryophyte) evolution. The class Bryopsida represents the most diversified lineage, containing more than 95% of modern mosses, whereas other classes are species‐poor. Two branches with large numbers of gene duplications were elucidated by phylogenomic analyses, one in the ancestry of all mosses and another before the separation of the Bryopsida, Polytrichopsida, and Tetraphidopsida. The analysis of the phylogenetic progression of duplicated paralogs retained on genomic syntenic regions in the Physcomitrella patens genome confirmed that the whole‐genome duplication events WGD1 and WGD2 were re‐recognized as the ψ event and the Funarioideae duplication event, respectively. The ψ polyploidy event was tightly associated with the early diversification of Bryopsida, in the ancestor of Bryidae, Dicranidae, Timmiidae, and Funariidae. Together, four branches with large numbers of gene duplications were unveiled in the evolutionary past of P. patens. Gene retention patterns following the four large‐scale duplications in different moss lineages were analyzed and discussed. Recurrent significant retention of stress‐related genes may have contributed to their adaption to distinct ecological environments and the evolutionary success of this early‐diverging land plant lineage. 相似文献