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   1393篇
  免费   78篇
电工技术   15篇
综合类   1篇
化学工业   397篇
金属工艺   27篇
机械仪表   28篇
建筑科学   136篇
矿业工程   7篇
能源动力   49篇
轻工业   174篇
水利工程   20篇
石油天然气   5篇
无线电   97篇
一般工业技术   162篇
冶金工业   129篇
原子能技术   16篇
自动化技术   208篇
  2023年   14篇
  2022年   43篇
  2021年   52篇
  2020年   38篇
  2019年   44篇
  2018年   60篇
  2017年   50篇
  2016年   56篇
  2015年   41篇
  2014年   69篇
  2013年   92篇
  2012年   73篇
  2011年   88篇
  2010年   67篇
  2009年   65篇
  2008年   51篇
  2007年   67篇
  2006年   46篇
  2005年   31篇
  2004年   32篇
  2003年   17篇
  2002年   20篇
  2001年   20篇
  2000年   20篇
  1999年   30篇
  1998年   32篇
  1997年   23篇
  1996年   18篇
  1995年   16篇
  1994年   18篇
  1993年   17篇
  1992年   12篇
  1991年   8篇
  1990年   12篇
  1989年   5篇
  1988年   10篇
  1987年   10篇
  1985年   9篇
  1983年   7篇
  1982年   5篇
  1981年   5篇
  1980年   4篇
  1979年   5篇
  1978年   6篇
  1977年   5篇
  1976年   4篇
  1975年   6篇
  1974年   4篇
  1966年   4篇
  1940年   4篇
排序方式: 共有1471条查询结果,搜索用时 15 毫秒
71.
Mammary neoplasms are the tumors most affecting female dogs and women. Formalin-fixed, paraffin-embedded (FFPE) tissues are an invaluable source of archived biological material. Fresh frozen (FF) tissue is considered ideal for gene expression analysis. However, strategies based on FFPE material offer several advantages. Branched-DNA assays permit a reliable and fast workflow when analyzing gene expression. The aim of this study was to assess the comparability of the branched-DNA assay when analyzing certain gene expression patterns between FF and FFPE samples in canine mammary tumors. RNA was isolated from 109 FFPE samples and from 93 FF samples of different canine mammary tissues. Sixteen (16) target genes (Tp53; Myc; HMGA1; Pik3ca; Mcl1; MAPK3; FOXO3; PTEN; GATA4; PFDN5; HMGB1; MAPK1; BRCA2; BRCA1; HMGA2; and Her2) were analyzed via branched-DNA assay (b-DNA). ACTB, GAPDH, and HPRT1 were used as data normalizers. Overall, the relative gene expression of the two different origins of samples showed an agreement of 63%. Still, care should be taken, as FFPE specimens showed lower expression of the analyzed targets when compared to FF samples. The fact that the gene expression in FFPE proved to be lower than in FF specimens is likely to have been caused by the effect of storage time. ACTB had the best performance as a data normalizer.  相似文献   
72.
Palladium supported on sulfated zirconia (PdSZ) has been characterized by the n-butane isomerization reaction in the presence of hydrogen, X-ray absorption spectroscopy (XAS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) of adsorbed carbon monoxide. Catalyst calcination at 873 K followed by hydrogen reduction at 513 K results in the formation of 30–40 Å Pd metal clusters, but the surface can only weakly adsorb CO, though stronger than Pd-free, sulfated zirconia catalysts. In the presence of hydrogen, PdSZ has a lower n-butane isomerization activity than SZ, and the Pd function cannot stabilize the reaction at low H2/n-butane ratios.  相似文献   
73.
The paper presents a multi-fluid Eulerian model derived from binary kinetic theory of granular flows, free path theory and an empirical friction theory. The effects of the inter- and inner-particle collisions, particle translational motions and particle–particle friction are included. As the effects due to fluiddynamic particle velocity differences and particle–particle friction are considered, some unconventional terms are produced compared with the previous models. Model validation using the data from Mathiesen et al. (2000) shows that the coupling terms give a stronger and more realistic particle–particle coupling because the effects due to the fluiddynamic velocity differences are considered. The model gives reasonable predictions of the particle volume fraction, particle velocities and velocity fluctuations. The model analysis reveals that the basic particle velocity fluctuations constitute 2 terms: the velocity fluctuations of the discrete particles, and the velocity fluctuations of the continuous fluid flow. Furthermore, the simulation results show that the velocity fluctuations of the continuous fluid flow are dominant in a binary riser flow.  相似文献   
74.
Steryl glucosides (SG) are common contaminants in biodiesel that form precipitates, which form and cause problems due to fouling during transport and storage. Therefore, their quantification is necessary to assess the quality of this fuel. The methods currently available for SG analysis require expensive instrumentation, need a previous concentration step by solid‐phase extraction (SPE) or are of limited use for the quantitative assessment. We developed an enzymatic method for SG quantification in biodiesel samples based on the hydrolysis of the glucoside catalyzed by a broadly specific beta glucosidase and the subsequent determination of the glucose released by the reaction. The method is non‐expensive, sensitive and was adapted to 96‐well format fluorescence plate reader, making it useful for the parallel assay of multiple samples. The enzymatic assay presented here represent a valuable tool for both quality control and the development of improved biodiesel production and purification procedures.  相似文献   
75.
MATISSE is a design environment intended for developing systems characterized by a tight interaction between control and data-flow behavior, intensive data storage and transfer, and stringent real-time requirements. Matisse bridges the gap from a system specification, using a concurrent object-oriented language, to an optimized embedded single-chip hardware/software implementation. Matisse supports stepwise exploration and refinement of dynamic memory management, memory architecture exploration, and gradual incorporation of timing constraints before going to traditional tools for hardware synthesis, software compilation, and inter-processor communication synthesis. With this approach, specifications of embedded systems can be written in a high-level programming language using data abstraction. Application of MATISSE on telecom protocol processing systems in the ATM area shows significant improvements in area usage and power consumption.  相似文献   
76.
During last few decades, emerging environmental regulations worldwide, more notably in Europe and Japan, have targeted the elimination of Pb usage in electronic assemblies due to the inherent toxicity of this element. This situation drives to the replacement of the Sn–Pb solder alloy of eutectic composition commonly used as joining material to suitable lead-free solders for microelectronic assembly. Sn-based alloys containing Ag, Cu, Bi, and Zn are potential lead-free solders, usually close to the binary or ternary eutectic composition. For this reason a great effort was directed to establish reliable thermophysical data fundamental to interpret the solidification process and fluidity of alloys belonging to these systems. In this work, an analysis of the solidification process of pure Sn, binary Sn–Ag, Sn–Cu, Sn–Bi, Sn–Zn, Sn–Pb and ternary Sn–Ag–Cu eutectic alloys was carried out using computer aided-cooling curve analysis and differential scanning calorimetry.  相似文献   
77.
Regional innovation systems (RSI) concept is an important theoretical framework to analyse regional profiles of regions when trying to understand Innovation but it has also been used by practioners to design and implement policies. This study hopes to contribute to the understanding of the Algarve RSI, a peripheral Portuguese region in the National and European framework, where an economic growth is supported by Tourism, which leaves it out of the group of poorest regions when the GDPpc indicator is taken in account. The regional profile, the comparison with the other European regions and the characterisation of RSI following developed typologies are discussed in this paper. Through the analysis of 175 regions of the EU 15 the study seeks to find the dimensions underlying the innovative phenomena and to create homogeneous groups of regions that display similar profiles. Factorial Analysis was used to reduce the dimension of data from a barrage of regional indicators such as: Critical Mass of Territories, Economic Performance, Level of Wealth, Employment Market, Sectoral Structure of the Economy, Age Group Structure, Education and Training, Technological Employment, R&D and Patents. Having determined the four main factors with significant results (Technological Innovation, Human Capital, Economic Structure and Availability of the Employment Market) what followed was a hierarchical analysis of Clusters, resulting in five groupings of regions: Disadvantaged Regions, Average Regions, Central Regions, Large Economic Centres and Innovating Regions. A synthesis of the recent Regional Innovation Strategies for the Algarve is presented including previous experiences (Ettirse and INOVAlgarve) and the Algarve’s Regional Innovation Plan, which will try to create a pathway for regional development supported by knowledge-based activities for a more diversified regional economy.  相似文献   
78.
The influence of the temperature and precursor pressure on the defect density of single-walled carbon nanotubes (SWCNTs) grown by catalytic chemical vapor deposition was studied for several catalyst–precursor couples. The SWCNT defect density was assessed by studying the Raman D band. In situ Raman monitoring was used to determine experimental conditions allowing the preparation of samples free of pyrolytic carbon and not altered by air exposure. The most striking feature is that the Arrhenius plots of the IG/ID ratio systematically display a convex shape, i.e. the apparent activation energy decreases with increasing temperature. From HRTEM observations and oxidation experiments, this evolution of the D band features is ascribed to the catalytic growth of long SWCNTs with few defects at high temperature and of short and defective SWCNTs and carbon structures at low temperature. The convex Arrhenius behavior is well accounted by two kinetic models: (i) a model considering a change of intermediate states as a function of the temperature (for instance due to a phase transition of the catalyst particle or a change of intermediate carbon species) and (ii) a model considering a high-temperature process of defect creation (for instance by reaction with reactive gas species).  相似文献   
79.
Reachability, joinability and confluence properties are known to be undecidable for flat term rewrite systems (TRS). We give shorter and conceptually simpler proofs of these results. We also prove undecidability of weak normalization and unique normalization properties for flat TRS. The first author was supported by Spanish Ministry of Education and Science by the FORMALISM project (TIN2007-66523) and by the LOGICTOOLS-2 project (TIN2007-68093-C02-01). The second author was supported by Spanish Ministry of Education and Science by the FORMALISM project (TIN2007-66523).  相似文献   
80.
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