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   32875篇
  免费   376篇
  国内免费   159篇
电工技术   359篇
综合类   288篇
化学工业   4613篇
金属工艺   2524篇
机械仪表   2991篇
建筑科学   832篇
矿业工程   291篇
能源动力   6963篇
轻工业   506篇
水利工程   75篇
石油天然气   101篇
武器工业   26篇
无线电   1180篇
一般工业技术   7316篇
冶金工业   799篇
原子能技术   310篇
自动化技术   4236篇
  2024年   311篇
  2023年   1202篇
  2022年   703篇
  2021年   846篇
  2020年   1536篇
  2019年   1291篇
  2018年   811篇
  2017年   1482篇
  2016年   1727篇
  2015年   1738篇
  2014年   2098篇
  2013年   2240篇
  2012年   1510篇
  2011年   1426篇
  2010年   1552篇
  2009年   1675篇
  2008年   709篇
  2007年   1185篇
  2006年   1134篇
  2005年   777篇
  2004年   476篇
  2003年   538篇
  2002年   696篇
  2001年   665篇
  2000年   385篇
  1999年   473篇
  1998年   226篇
  1997年   154篇
  1996年   196篇
  1995年   174篇
  1994年   162篇
  1993年   117篇
  1992年   104篇
  1991年   129篇
  1990年   132篇
  1989年   96篇
  1988年   214篇
  1987年   516篇
  1986年   475篇
  1985年   154篇
  1984年   104篇
  1983年   67篇
  1982年   70篇
  1981年   68篇
  1979年   72篇
  1972年   69篇
  1970年   78篇
  1967年   73篇
  1966年   73篇
  1965年   63篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
An experimental investigation on heat and fluid flow characteristics of fully developed turbulent flow in a rectangular duct having repeated integral transverse chamfered rib-groove roughness on one broad wall has been carried out. Experiments encompassed the Reynolds number range of 3000–21,000; relative roughness pitch of 4.5–10, chamfer angle of 5°–30°, relative groove position of 0.3–0.6 and relative roughness height of 0.022–0.04. The effect of roughness parameters on Nusselt number and friction factor have been discussed and the results are compared with the results of square rib-grooved and smooth duct under similar flow conditions. The conditions for the best performance have been determined. Correlations for the Nusselt number and friction factor have been developed as a function of roughness parameters and flow Reynolds number.  相似文献   
2.
3.
There is no good method to measure the shape and the strain distributions of a structure changing with time. We have previously proposed the Fourier transform grid method (FTGM) to measure the three-dimensional shape and surface strain distributions of stationary objects by analysing the two-dimensional grating images recorded with two cameras. In the stereoscopic method, it is very important to determine the accurate geometric parameters of the camera system. In this paper, the positions and the directions of cameras are accurately determined using the FTGM applied to images of a reference object on which a two-dimensional grating is drawn. Applications for analysing shape and strain distributions of vibrating rubber plates and a moving human skin are shown.  相似文献   
4.
In order to analyze the effect of an epoxidized natural rubber (ENR) and filler treatment on the morphology and behavior of natural rubber (NR) nanocomposites, blends of these polymers have been prepared. The nature and extent of the clay dispersions in the filled samples were evaluated by X-ray diffraction. In the presence of ENR, an exfoliated structure was obtained which suggests that enough rubbery polymer was incorporated into the interlayer spacing. The effect of clay in rubber compounds was analyzed through rheological, mechanical and swelling characterization. A sensible improvement in the nanocomposite properties was observed by the addition of organoclay. It has been deduced that the properties of the compounds strongly depend on the extent of the silicate nanolayers dispersion into the rubber matrices as well as on the organoclay type and elastomer compatibility.  相似文献   
5.
Information granules, such as e.g., fuzzy sets, capture essential knowledge about data and the key dependencies between them. Quite commonly, we may envision that information granules (fuzzy sets) have become a result of fuzzy clustering and therefore could be succinctly represented in the form of some fuzzy partition matrices. Interestingly, the same data set could be represented from various standpoints and this multifaceted view yields a collection of different partition matrices being reflective of the higher-order granular knowledge about the data. The levels of specificity of the clusters the data are organized into could be quite different—the larger the number of clusters, the more detailed insight into the structure of data becomes available. Given the granularity of the resulting constructs (rather than plain data themselves), one could view a collection of partition matrices as a certain type of a network of knowledge. Considering a variety of sources of knowledge encountered across the network, we are interested in forming consensus between them. In a nutshell, this leads to the construction of certain fuzzy partition matrices which “reconcile” the knowledge captured by the individual partition matrices. Given that the granularity of the sources of knowledge under consideration could vary quite substantially, we develop a unified optimization perspective by introducing fuzzy proximity matrices that are induced by the corresponding partition matrices. In the sequel, the optimization is realized on a basis of these proximity matrices. We offer a detailed algorithm and illustrate its performance using a series of numeric experiments.  相似文献   
6.
《Materials Letters》2007,61(11-12):2419-2421
The effect of the addition of cerium in potassium dihydrogen phosphate, grown from aqueous solution by the temperature lowering method using bi-direction seed rotation technique has been studied. The optimal addition of trivalent cerium ions considerably prevents other bivalent transition metal ions (Co, Ni, Mn) from entering into the crystal lattice and results in reduced defects and dislocations. A simple microcontroller based bi-directional accelerated seed rotation control setup is designed and employed to avoid stagnant regions or re-circulating flows in the solution. High-resolution XRD analysis of the (002) plane reveals that the Ce3+ added KDP exhibited better crystalline perfection and contains less dislocation.  相似文献   
7.
Closed-form expressions are presented for effective material properties of human dentine in this paper. The derivation is based a Generalized Self Consistent Method and the strain energy principle. The Generalized Self Consistent Model for cell model of fiber-reinforced composites is extended to the case of hollow cylinder model and the corresponding cell model is chosen to consist of a circular hollow cylinder filled with liquid or gas phase, which surrounded by a circular cylindrical shell of matrix phase. Each layer of cylindrical shell is here considered as a kind of composite consisting of collagen fibrils, with mineralized hydroxyapatite, loosely connected to their neighbours, and water (or gas in the case of dry dentine composite). Using the cell model, the effect of Poisson’s ratio and volume fraction of intertubular dentine on effective mechanical constants is analyzed. Results obtained from the proposed model are compared with those from other models such as nano-indentation method.  相似文献   
8.
This paper deals with a new boundary element method for analysis of the quasistatic problems in coupled thermoelasticity. Through some mathematical manipulation of the Navier equation in elasticity, the heat conduction equation is transformed into a simpler form, similar to the uncoupled-type equation with the modified thermal conductivity which shows the coupling effects. This procedure enables us to treat the coupled thermoelastic problems as an uncoupled one, A few examples are computed by the proposed BEM, and the results obtained are compared with the analytical ones available in the literature, whereby the accuracy and versatility of the proposed method are demonstrated.  相似文献   
9.
An easy to use method for an approximate creep life prediction for pipe bends was developed within a recent R & D-project in Germany. The new algorithm is based on a Finite-Element parameter study comprising approximately 200 pipe bends. The creep behaviour of the materials primarily used for main steam and hot reheat piping is described using the Graham–Walles creep law. Since the new algorithm considers the time dependent out-of-roundness and stress redistribution of the pipe bend, it yields a more precise creep life prediction, compared to standard piping codes. It is possible to integrate this new calculation into existing online lifetime-monitoring-systems.  相似文献   
10.
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