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   4210篇
  免费   131篇
  国内免费   5篇
电工技术   57篇
综合类   14篇
化学工业   1045篇
金属工艺   85篇
机械仪表   84篇
建筑科学   257篇
矿业工程   21篇
能源动力   82篇
轻工业   637篇
水利工程   22篇
石油天然气   3篇
无线电   361篇
一般工业技术   747篇
冶金工业   473篇
原子能技术   52篇
自动化技术   406篇
  2022年   33篇
  2021年   62篇
  2020年   41篇
  2019年   56篇
  2018年   46篇
  2017年   55篇
  2016年   93篇
  2015年   94篇
  2014年   99篇
  2013年   158篇
  2012年   192篇
  2011年   181篇
  2010年   140篇
  2009年   171篇
  2008年   160篇
  2007年   161篇
  2006年   176篇
  2005年   130篇
  2004年   122篇
  2003年   105篇
  2002年   103篇
  2001年   76篇
  2000年   59篇
  1999年   74篇
  1998年   126篇
  1997年   101篇
  1996年   70篇
  1995年   73篇
  1994年   71篇
  1993年   53篇
  1992年   67篇
  1991年   52篇
  1990年   44篇
  1989年   53篇
  1988年   54篇
  1987年   61篇
  1986年   53篇
  1985年   46篇
  1984年   58篇
  1983年   51篇
  1982年   44篇
  1981年   53篇
  1980年   41篇
  1979年   42篇
  1978年   42篇
  1977年   44篇
  1976年   55篇
  1975年   30篇
  1973年   33篇
  1971年   32篇
排序方式: 共有4346条查询结果,搜索用时 15 毫秒
101.
A group of 344 cervices, produced by conisation within a period of 5 1/2 years, were examined for specific effects of contraceptives. In half of all women, who used oral contraceptives, specific lesions such as "siebartige polypoide Hyperplasie" (cribriform polypoid hyperplasia) were found. The findings and their etiology and importance are discussed.  相似文献   
102.
Quasi‐periodic oscillations and invariant tori play an important role in the study of forced or coupled oscillators. This paper presents two new numerical methods for the investigation of quasi‐periodic oscillations. Both algorithms can be regarded as generalizations of the averaging and the harmonic (spectral) balance methods. The algorithms are easy to implement and require only minimal a priori knowledge of the system. Most importantly, the methods do not depend on an a priori co‐ordinate transformation. The methods are applied to a number of illustrative examples from non‐linear electrical engineering and the results show that the methods are efficient and reliable. In addition, these examples show that the presented algorithms can also continue through regions of sub‐harmonic (phase‐locked) resonance even though they are designed only for the quasi‐periodic case. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
103.
The authors investigated the influence of patients' social support on subjective and objective stress indicators before, during, and after surgery. The sample consisted of 42 male and 42 female patients. Social support as perceived by the patients was measured by a surgery-specific inventory with the Emotional Support and Informational Support subscales. Perioperative adaptation was assessed by self-reported anxiety, the amount of narcotics needed for anesthesia induction, and the length of the postoperative stay. Results demonstrated that patients who scored high on social support showed less anxiety, received lower doses of narcotics, and had a shorter hospital stay than did patients with low support. However, gender was a moderator of some of these associations. Compared with men, women exhibited more relationships that were in accordance with the hypotheses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
104.
105.
Summary We operationalize scientific output in a region by means of the number of articles (as in the SciSearch database) per year and technology output by means of the number of patent applications (as in the database of the European Patent Office) per priority year. All informetric analyses were done using the DIALOG online-system. The main research questions are the following: Which scientific and technological fields or topics are most influent within a region and which institutions or companies are mainly publishing articles or holding patents? Do the distributions of regional science and technology fields and of publishing institutions follow the well-known informetric function? Are there - as it is expected - only few fields and few institutions which dominate the region? Is there a connection between the economic power of a region and the regional publication and patent output? Examples studied in detail are seven German regions: Aachen, Düsseldorf, Hamburg, Köln (Cologne), Leipzig - Halle - Dessau, München (Munich), and Stuttgart. Three different indicators were used, science and technology attraction of a region (number of scientific articles and patents), science and technology intensity (articles and patents per 1,000 inhabitants), and science and technology density (articles and patents per 1 billion EURO gross value added). Top region concerning both attraction and intensity is Munich, concerning density it is Aachen.  相似文献   
106.
107.
This paper considers two-machine open shop problems with secondary criteria where the primary criterion is the minimization of makespan and the secondary criterion is the minimization of the total flow time, total weighted flow time, or total weighted tardiness time. In view of the strongly NP-hard nature of these problems, two polynomially solvable special cases are given and constructive heuristic algorithms based on insertion techniques are developed. A strongly connected neighborhood structure is derived and used to develop effective iterative heuristic algorithms by incorporating iterative improvement, simulated annealing and multi-start procedures. The proposed insertion and iterative heuristic algorithms are empirically evaluated by solving problem instances with up to 80 jobs.  相似文献   
108.
We have developed a self-consistent quantum mechanical Monte Carlo device simulator that takes electron transport in quantized states into consideration. Two-dimensional quantized states in MOSFET channels are constructed from one-dimensional solutions of the Schrödinger equation at different positions along the channel, and the Schrödinger and Poisson equations are solved self-consistently in terms of electron concentration and electrostatic potential distribution. The channel electron concentration, velocity and drain currents are calculated with the one particle Monte Carlo approach incorporating the intra-valley acoustic phonon and inter-valley phonon scattering mechanisms. This simulator was applied to a 70 nm n-MOSFET transistor, and we found that current mostly flows through the lowest subband and transport is quasi-ballistic near the source junction. To quantitatively estimate the performance of advanced devices, we have developed an inversion carrier transport simulator based on a full-band model. Our simulation method enables us to evaluate device characteristics and analyze the transport properties of ultra-small MOSFETs.  相似文献   
109.
Microsystems are on their way out of laboratories into production. One of these microsystems, a piezoresistive pressure sensor developed by Robert Bosch GmbH, is examined within this paper. Obviously, one can detect undesirable temperature effects resulting from the sensor package, which influence the electrical characteristics of the sensor. By means of finite-element modelling (FEM), a simulation of the temperature effects can be managed. It is also possible to search for alternative designs of the sensor package.  相似文献   
110.
Recurrent relationships for the definitions of fully normalized spherical harmonic coefficients C?n,m and S?n,m are derived and integrated analytically to yield the gravitational potential of a constant-density polyhedron. The algorithm is expressed in a C language computer program.  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