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   6413篇
  免费   479篇
  国内免费   72篇
电工技术   162篇
综合类   108篇
化学工业   1465篇
金属工艺   201篇
机械仪表   224篇
建筑科学   229篇
矿业工程   40篇
能源动力   297篇
轻工业   1024篇
水利工程   68篇
石油天然气   98篇
武器工业   5篇
无线电   538篇
一般工业技术   1083篇
冶金工业   454篇
原子能技术   66篇
自动化技术   902篇
  2024年   27篇
  2023年   75篇
  2022年   147篇
  2021年   324篇
  2020年   251篇
  2019年   237篇
  2018年   300篇
  2017年   314篇
  2016年   275篇
  2015年   212篇
  2014年   316篇
  2013年   493篇
  2012年   416篇
  2011年   440篇
  2010年   321篇
  2009年   317篇
  2008年   287篇
  2007年   221篇
  2006年   216篇
  2005年   160篇
  2004年   149篇
  2003年   219篇
  2002年   201篇
  2001年   158篇
  2000年   102篇
  1999年   84篇
  1998年   139篇
  1997年   84篇
  1996年   78篇
  1995年   67篇
  1994年   38篇
  1993年   43篇
  1992年   32篇
  1991年   29篇
  1990年   24篇
  1989年   15篇
  1988年   26篇
  1987年   11篇
  1986年   14篇
  1985年   15篇
  1984年   8篇
  1982年   5篇
  1981年   8篇
  1980年   6篇
  1979年   6篇
  1977年   10篇
  1976年   14篇
  1975年   6篇
  1974年   4篇
  1973年   7篇
排序方式: 共有6964条查询结果,搜索用时 31 毫秒
991.
This paper presents an exercise in the formalization of political principles, by taking as its theme the concept of distributive justice that Karl Marx advanced in his Critique of the Gotha Programme. We first summarize the content of the Critique of the Gotha Programme. Next, we transcribe the core of Marx’s presentation of the concept of distributive justice. Following, we present our formalization of Marx’s conception. Then, we make use of that formal analysis to confront Marx’s principle of distributive justice with John Rawls’ conception of justice as fairness, and the principles of distributive justice that derive from it. Finally, we discuss methodological issues relative to, and implications of, the way of formalizing political principles introduced here.  相似文献   
992.
We present the development of an experimentally validated computational fluid dynamics model for liquid micro jets. Such jets are produced by focusing hydrodynamic momentum from a co-flowing sheath of gas on a liquid stream in a nozzle. The numerical model based on laminar two-phase, Newtonian, compressible Navier–Stokes equations is solved with finite volume method, where the phase interface is treated by the volume of fluid approach. A mixture model of the two-phase system is solved in axisymmetry using?~?300,000 finite volumes, while ensuring mesh independence with the finite volumes of the size 0.25 µm in the vicinity of the jet and drops. The numerical model is evaluated by comparing jet diameters and jet lengths obtained experimentally and from scaling analysis. They are not affected by the strong temperature and viscosity changes in the focusing gas while expanding at nozzle outlet. A range of gas and liquid-operating parameters is investigated numerically to understand their influence on the jet performance. The study is performed for gas and liquid Reynolds numbers in the range 17–1222 and 110–215, and Weber numbers in the range 3–320, respectively. A reasonably good agreement between experimental and scaling results is found for the range of operating parameters never tackled before. This study provides a basis for further computational designs as well as adjustments of the operating conditions for specific liquids and gases.  相似文献   
993.
The location optimization of sensors is a essential problem in structural health monitoring systems. Taking the cost of sensors into account, it is uneconomical to install sensors on every part of a structure and moreover in aeronautical industry, the weight is a crucial factor. In this paper, a optimal placement optimization of sensor locations for structural health monitoring systems is studied. Several techniques of optimization of sensors are approached and applied in a shell structure. The structure, a laminate of carbon fiber, was modeled by the finite element method (FEM) and then subject to free vibration. Genetic algorithms (GAs) are then employed to locate the best sensor distribution to cover a specific number of low frequency modes. Numerical results have demonstrated the overall efficiency of sensor delivery methods. Specific problems occurred, especially regarding the method of effective independence, being less efficient and discrepant in relation to the other methods employed. In summary, the results obtained in this paper provide an optimal position for sensors in real SHM systems and experiments.  相似文献   
994.
Since its first emergence in 2004, the high-entropy alloy (HEA) concept has aimed at stabilizing single- or dual-phase multi-element solid solutions through high mixing entropy. Here, this strategy is changed and renders such massive solid solutions metastable, to trigger spinodal decomposition for improving the alloys’ magnetic properties. The motivation for starting from a HEA for this approach is to provide the chemical degrees of freedom required to tailor spinodal behavior using multiple components. The key idea is to form Fe-Co enriched regions which have an expanded volume (relative to unconstrained Fe-Co), due to coherency constraints imposed by the surrounding HEA matrix. As demonstrated by theory and experiments, this leads to improved magnetic properties of the decomposed alloy relative to the original solid solution matrix. In a prototype magnetic FeCoNiMnCu HEA, it is shown that the modulated structures, achieved by spinodal decomposition, lead to an increase of the Curie temperature by 48% and a simultaneous increase of magnetization by 70% at ambient temperature as compared to the homogenized single-phase reference alloy. The findings thus open a pathway for the development of advanced functional HEAs.  相似文献   
995.
3D printing and nanotechnology have been two important tools in the development of therapeutic approaches for personalized medicine. More recently, their alliance has been improved in an effort to build innovative, versatile, multifunctional, and/or smart medical and pharmaceutical products. Therefore, an extensive review about scientific studies that ally 3D printing and nanomaterials in the development of new approaches for pharmaceutical and medical applications for the treatment and prevention of diseases is presented here. The articles are classified into five categories according to their main application: Cell growth and tissue engineering, antimicrobial, drug delivery, stimulus-response, and theranostics. Semisolid extrusion, inorganic nanoparticles, and cell growth and tissue engineering are the most reported 3D printing technique, type of nanomaterial, and application, respectively. The increase in papers dedicated to these areas is also notable, especially in the 2019 and 2020, when semisolid extrusion became the most used technique, overcoming fused deposition modelling. In fact, this review highlights that the possibility of an alliance between 3D printing and nanotechnology for the production of multiscale materials is undoubtedly a great opportunity for knowledge and innovation in the pharmaceutical and medical area.  相似文献   
996.
Wireless Personal Communications - In the present study, the results obtained by incoherent scatter radar (ISR) and empirical models (NeQuick2 and IRI-2016) of the variations in mid-latitude...  相似文献   
997.
Wireless Personal Communications - This paper presents the development of a compact monopole antenna bioinspired in the Opuntia ficus-indica plant-shape, generated by Gielis formula, built in...  相似文献   
998.

This paper is concerned with the investigation of the shear effect on the dynamic behavior of a thin microcantilever beam with manufacturing process defects. Unlike the Rayleigh beam model (RBM), the Timoshenko beam model (TBM) takes in consideration the shear effect on the resonance frequency. This effect become significant for thin microcantilever beams with larger slenderness ratios that are normally encountered in MEMS devices such as sensors. The TBM model is presented and analyzed by numerical simulation using Finite Element Method (FEM) to determine corrective factors for the correction of the effect of manufacturing process defects like the underetching at the clamped end of the microbeam and the nonrectangular cross section of the area. A semi-analytical approach is proposed for the extraction of the Young’s modulus from 3D FEM simulation with COMSOL Multiphysics software. This model was tested on measurements of a thin chromium microcantilever beam of dimensions (80 × 2 × 0.95 μm3). Final results indicate that the correction of the effect of manufacturing process defects is significant where the corrected value of Young’s modulus is very close to the experimental results and it is about 280.81 GPa.

  相似文献   
999.
The objective of this investigation was to study the functional properties of Pigeon pea (Cajanus cajan (L.) Millsp) flour and protein concentrate. The solubility of both samples were superior than 70% at pH above 6.7 and below 3.5. The water and oil absorption were 1.2 and 1.07 ml/g of sample and 0.87 and 1.73 ml/g of flour and protein concentrate samples, respectively. The minimum concentration of flour and protein concentrate needed for gelation was 20% and 12%, respectively. The emulsifying capacity of flour and concentrate was 129.35 g and 191.66 g oil/g of protein and the emulsion stability 87.50 and 97.97%, respectively, after 780 minutes. The foam capacity and stability of flour foam were 36.0% and 18.61, while of the concentrate were 44.70% and 78.97% after 90 minutes. These properties indicate that the flour as well as the concentrate could have application in various food systems.  相似文献   
1000.
刘卅  贾德民 《弹性体》2004,14(5):47-50
研究了共轭二烯烃类聚合物在贮氢合金氢化物存在下双键加氢的情况。结果表明AB;型贮氢合金[包括LaNi5和MINi5-x(CoMnAl)8]可催化NBR、NR、BR、SBS等共轭二烯烃聚合物双键加氢,其氢化度分别可达33.5%、31.1%、45.8%、32.3%。采用IR、^1H NMR、碘量分析法等手段对加氢产物进行了分析,表明聚合物中双键加氢的同时,NBR中的-C≡N和SBS中的苯环不受影响。此外。研究结果还表明合金组成、表面处理方式等对贮氢合金催化共轭二烯烃类聚合物双键加氢活性有影响。合金氢化物在共轭二烯烃类聚合物双键加氢过程中具有提供氢源与催化双重功能。  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