首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   801篇
  免费   59篇
  860篇
  2023年   9篇
  2022年   9篇
  2021年   27篇
  2020年   19篇
  2019年   15篇
  2018年   26篇
  2017年   33篇
  2016年   43篇
  2015年   30篇
  2014年   48篇
  2013年   52篇
  2012年   46篇
  2011年   44篇
  2010年   33篇
  2009年   29篇
  2008年   25篇
  2007年   34篇
  2006年   21篇
  2005年   21篇
  2004年   31篇
  2003年   29篇
  2002年   23篇
  2001年   16篇
  2000年   14篇
  1999年   7篇
  1998年   6篇
  1995年   4篇
  1994年   8篇
  1992年   7篇
  1991年   11篇
  1990年   5篇
  1989年   4篇
  1988年   10篇
  1987年   7篇
  1986年   11篇
  1985年   7篇
  1984年   5篇
  1983年   5篇
  1982年   9篇
  1981年   8篇
  1980年   6篇
  1979年   10篇
  1978年   4篇
  1976年   4篇
  1975年   4篇
  1974年   7篇
  1973年   4篇
  1969年   4篇
  1968年   6篇
  1966年   5篇
排序方式: 共有860条查询结果,搜索用时 0 毫秒
141.
This work reports the discovery of an hitherto unknown chemical recognition trait enabling a parasitic life cycle in aquatic habitats. We believe this is the first record of a natural, host-derived chemical molecule identified as a recognition cue for the phylum Myxozoa. The actinospores of these parasites attach to fish hosts via polar filaments that are extruded upon mechanical stimulation after preceding recognition of a chemical trigger contained in surface mucus. Our goal was to identify this signal. We separated compounds from a purified active fraction derived from trout mucus by a novel HPLC method. By subsequent nuclear magnetic resonance analysis of distinct components and testing in bioassays we elicited stimulation of polar filament discharge and sporoplasm emission in actinospores of three myxozoan spp., Myxobolus cerebralis, Myxobolus pseudodispar and Henneguya nuesslini, by the free nucleosides inosine, 2'-deoxyinosine and guanosine. These nucleosides also activated sporoplasm emission. Nucleosides appear to be appropriate cues for rapid host recognition by the waterborne parasite stages since they are continuously released into surface mucus. The recognition mechanism is not specific for susceptible host species, at least in the myxozoan spp. examined. In addition, a novel function of nucleobase derivatives as semiochemicals was uncovered and a wider impact of this molecule class in parasite recognition systems and aquatic chemical ecology is predicted. The relevance for disease prevention and cell culturing remains to be explored.  相似文献   
142.
3-(2-Carboxyethyl)-4,6-dichloro-1H-indole-2-carboxylic acid (MDL-29951), an antagonist of the glycine site of the NMDA receptor, has been found to be an allosteric inhibitor of the enzyme fructose 1,6-bisphosphatase. The compound binds at the AMP regulatory site by X-ray crystallography. This represents a new approach to inhibition of fructose 1,6-bisphosphatase and serves as a lead for further drug design.  相似文献   
143.
144.

Context

Over the last decade, design patterns have been used extensively to generate reusable solutions to frequently encountered problems in software engineering and object oriented programming. A design pattern is a repeatable software design solution that provides a template for solving various instances of a general problem.

Objective

This paper describes a new method for pattern mining, isolating design patterns and relationship between them; and a related tool, DLA-DNA for all implemented pattern and all projects used for evaluation. DLA-DNA achieves acceptable precision and recall instead of other evaluated tools based on distributed learning automata (DLA) and deoxyribonucleic acid (DNA) sequences alignment.

Method

The proposed method mines structural design patterns in the object oriented source code and extracts the strong and weak relationships between them, enabling analyzers and programmers to determine the dependency rate of each object, component, and other section of the code for parameter passing and modular programming. The proposed model can detect design patterns better that available other tools those are Pinot, PTIDEJ and DPJF; and the strengths of their relationships.

Results

The result demonstrate that whenever the source code is build standard and non-standard, based on the design patterns, then the result of the proposed method is near to DPJF and better that Pinot and PTIDEJ. The proposed model is tested on the several source codes and is compared with other related models and available tools those the results show the precision and recall of the proposed method, averagely 20% and 9.6% are more than Pinot, 27% and 31% are more than PTIDEJ and 3.3% and 2% are more than DPJF respectively.

Conclusion

The primary idea of the proposed method is organized in two following steps: the first step, elemental design patterns are identified, while at the second step, is composed to recognize actual design patterns.  相似文献   
145.
1′-Aza-carbocyclic-2′, 3′-dideoxyuridine, 3′-deoxythymidine and 2′, 3′-dideoxycytidine were synthesized from 1-aminopyrrolidine intermediate 13 and evaluated as anti-HIV agents in MT-4 cells.  相似文献   
146.
The molecular phylogeny of the genus Odontobuthus Vachon, 1950 (Scorpiones: Buthidae) in Iran was evaluated using two mitochondrial DNA genes, cytochrome c oxidase, subunit I (COI) and 16S ribosomal RNA (16S rRNA). The molecular phylogenetic analyses were performed using Maximum Parsimony, Maximum Likelihood and Bayesian inference methods. The resulting topologies supported two main clades: the clade comprising Odontobuthus doriae, O. bidentatus, and O. tavighiae, and another one which is the O. tirgari clade. The results clearly presented additional support for the taxonomic validity of the recently described species, O. tirgari and O. tavighiae. In addition, the monophyly of two previously described species O. doriae and O. bidentatus was confirmed. According to the data presented here, three taxonomically valid species belonging to the genus Odontobuthus occur in Iran.  相似文献   
147.
Many laboratories do not have access to a flow cytometer allowing three-color immunofluorescence analysis through the use of multiple light sources. In view of the usefulness of such analyses in the dissection of cell parameters, we describe an approach permitting the study of three labels by using one light source and the two-color immunofluorescence assay. It is useful for the enumeration of cell subpopulations positive for one label and negative for two or more others as well as for qualitative analysis concerning the expression of these labels. This approach is simple and rapid; it does not require additional material and technical steps other than that used in the two-color immunofluorescence assay. Briefly, it consists of the use of a label coupled to a dye (PE or FITC or instance) and two different labels coupled to the other dye. An argon ion laser, operating at 488 nm and 60 mW, excites both fluorescein and phycoerythrin conjugated antibodies. We provided a general example, using three hypothetical labels (X, Y, and Z), and four practical applications: CD3+CD4CD8- and CD8+CD16-CD3- peripheral blood lymphocytes, CD2+CD16-CD3- and CD56+CD16-CD3- peripheral blood, and decidual infiltrating lymphocytes.  相似文献   
148.
149.
Current medical approaches to control the Covid-19 pandemic are either to directly target the SARS-CoV-2 via innovate a defined drug and a safe vaccine or indirectly target the medical complications of the virus. One of the indirect strategies for fighting this virus has been mainly dependent on using anti‐inflammatory drugs to control cytokines storm responsible for severe health complications. We revealed the discovery of novel fused pyrrolopyrimidine derivatives as promising antioxidant and anti-inflammatory agents. The newly synthesised compounds were evaluated for their in vitro anti-inflammatory activity using RAW264.7 cells after stimulation with lipopolysaccharides (LPS). The results revealed that 3a, 4b, and 8e were the most potent analogues. Molecular docking and simulations of these compounds against COX-2, TLR-2 and TLR-4 respectively was performed. The former results were in line with the biological data and proved that 3a, 4b and 8e have potential antioxidant and anti-inflammatory effects.  相似文献   
150.
The development of diabetic cardiomyopathy is a key contributor to heart failure and mortality in obesity and type 2 diabetes (T2D). Current therapeutic interventions for T2D have limited impact on the development of diabetic cardiomyopathy. Clearly, new therapies are urgently needed. A potential therapeutic target is protein kinase D (PKD), which is activated by metabolic insults and implicated in the regulation of cardiac metabolism, contractility and hypertrophy. We therefore hypothesised that PKD inhibition would enhance cardiac function in T2D mice. We first validated the obese and T2D db/db mouse as a model of early stage diabetic cardiomyopathy, which was characterised by both diastolic and systolic dysfunction, without overt alterations in left ventricular morphology. These functional characteristics were also associated with increased PKD2 phosphorylation in the fed state and a gene expression signature characteristic of PKD activation. Acute administration of the PKD inhibitor CID755673 to normal mice reduced both PKD1 and 2 phosphorylation in a time and dose-dependent manner. Chronic CID755673 administration to T2D db/db mice for two weeks reduced expression of the gene expression signature of PKD activation, enhanced indices of both diastolic and systolic left ventricular function and was associated with reduced heart weight. These alterations in cardiac function were independent of changes in glucose homeostasis, insulin action and body composition. These findings suggest that PKD inhibition could be an effective strategy to enhance heart function in obese and diabetic patients and provide an impetus for further mechanistic investigations into the role of PKD in diabetic cardiomyopathy.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号