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   1368篇
  免费   9篇
  国内免费   1篇
电工技术   14篇
化学工业   130篇
金属工艺   29篇
机械仪表   30篇
建筑科学   61篇
矿业工程   1篇
能源动力   26篇
轻工业   131篇
水利工程   13篇
石油天然气   1篇
无线电   95篇
一般工业技术   212篇
冶金工业   483篇
原子能技术   18篇
自动化技术   134篇
  2021年   6篇
  2018年   7篇
  2016年   7篇
  2015年   6篇
  2014年   16篇
  2013年   54篇
  2012年   38篇
  2011年   52篇
  2010年   23篇
  2009年   32篇
  2008年   42篇
  2007年   37篇
  2006年   37篇
  2005年   48篇
  2004年   35篇
  2003年   36篇
  2002年   36篇
  2001年   21篇
  2000年   30篇
  1999年   32篇
  1998年   137篇
  1997年   72篇
  1996年   52篇
  1995年   40篇
  1994年   34篇
  1993年   40篇
  1992年   18篇
  1991年   24篇
  1990年   20篇
  1989年   21篇
  1988年   13篇
  1987年   13篇
  1986年   15篇
  1985年   20篇
  1984年   21篇
  1983年   15篇
  1982年   21篇
  1981年   6篇
  1980年   16篇
  1979年   16篇
  1978年   20篇
  1977年   10篇
  1976年   22篇
  1975年   15篇
  1974年   6篇
  1973年   15篇
  1972年   5篇
  1971年   11篇
  1970年   10篇
  1965年   7篇
排序方式: 共有1378条查询结果,搜索用时 15 毫秒
41.
This paper describes five successive interventions in the rearing of infants at an orphanage in Tehran, with their outcomes. The outcomes were assessed longitudinally. The first of the successive groups, here called "waves", numbered 15. These Ss constitute the controls. The only intervention consisted of examining the infants every other week during the first year and every fourth week thereafter with the ordinal, sensorimotor scales of Uzgiris and Hunt. The audio-visual intervention intended for the second wave of 10 infants was tape-recorded mother talk and music under the control of the infants and mobiles that the infants could activate. This plan was never adequately implemented because of inadequate supervision. The third wave of 10 infants got extra untutored human care. The fourth wave of 20 infants got the kind of audio-visual intervention originally intended for the second wave plus access to responsive inanimate materials. For the fifth wave, numbering 11, the infant-caretaker ratio was reduced to two or three to one and the caretakers were taught the Badger program supplemented with procedures to foster vocal imitation and semantic mastery of body parts, clothing, toys, and other objects and events regularly encountered. The results show that each successive wave, excepting the second, achieved the top steps of nearly all seven of the ordinal scales at mean ages younger than the preceding wave, and the fifth wave surpassed even home-reared American children from predominantly professional families in achieving the top steps on five of the seven scales. The findings show that infants need not advance along all branches simultaneously and that the kinds of experience encountered determine the branch along which advancement occurs. A number of theoretical implications are examined. Especially important is the idea that a dependable educational psychology for infancy and early childhood calls for much more knowledge than we now have of the kinds of experience that advance development along each of the various branches.  相似文献   
42.
Condition assessment is a term that is used to describe the process of characterizing the physical condition of constructed systems. This paper summarizes a condition assessment (CA) procedure based on a complete system of field-testing, finite element (FE) modeling, and load rating. Experimental techniques, including both modal testing and truckload testing, are used to collect measurements of the constructed systems. The basic mechanism and procedure of the FE modeling and calibration are presented. Different physical parameters of FE models are adjusted during the calibration process using both static and dynamic responses as criteria to achieve convergence between experimental measurements and analytical results using carefully developed objective functions. Finally, a bridge load rating is completed on the basis of the calibrated model. These developments are described and illustrated using a representative bridge as an example.  相似文献   
43.
Thomas  D. Hunt  A. 《Software, IEEE》2003,20(4):82-83
Software development seems to be a discipline of artifacts; the developers spend their time producing products and attempting to find ways to measure just how well and how fast they make that product. We get pleasure from the act of creation and from activities that surround the creation process. But as time goes on, we start to lose sight of this. Companies are not interested in the process as much as the product. Managers cannot measure the thought that goes into a specification; they only see the document.  相似文献   
44.
Finding changed identifiers is important for understanding the difference between two versions of a program and for detecting and resolving conflicts while merging variants of a program together. Standard practice for differencing and merging relies on line based techniques that do not recognize renamed identifiers. The design and implementation of a tool to automatically detect renamed identifiers between two versions of a program is presented. The system uses an abstract representation of language constructs to enable language awareness without introducing language dependence. Modules for Java and Scheme have been written. The detector works with multiple file pairs, taking into account renamings that span several files. A case study is presented that demonstrates proof of concept. The detector is part of a suite of intelligent differencing and merging programs that exploit the static semantics of programming languages.  相似文献   
45.
46.
As part of the process of automatically guiding an aircraft, we have been successful in using stable inversion to compute a desired bounded state trajectory and corresponding bounded control. In addition to this feedforward control, we must also construct a regulator to address modeling errors and disturbances. With respect to modeling errors we find that the stable inversion procedures used are so accurate that the regulator can assume a simple form, say a linear regulator about the desired trajectory. We show that under the appropriate assumptions, the bounded state trajectory and bounded control computed through stable inversion depend continuously on the parameters of the system. This is a consequence of a mathematical result that we prove about the continuous dependence of the “particular solution” of a time varying nonlinear system driven by a bounded input. This is distinct from the usual continuous dependence of the initial value problem for systems.  相似文献   
47.
In an effort to assess the constructability and performance of bridges with fiber-reinforced polymer (FRP) composite decks, the short-term and long-term responses of a 207 m, five-span bridge retrofitted with four different FRP panel systems were monitored. The overall aspects of the panel systems, connection details, and construction techniques are presented prior to presentation of the observed and measured responses. Key design parameters (impact factors, girder distribution factors, and level of composite action) for FRP and reinforced concrete decks are evaluated. This paper demonstrates that FRP replacement decks are a viable alternative to reinforced concrete decks and identifies the differences in performances of various FRP deck systems. Two of the FRP panel systems were found to perform considerably better than the other deck systems. Issues that may reduce the service life of FRP deck systems are presented and discussed.  相似文献   
48.
Degradation rates of electrical current during constant voltage operation of SOFCs with anodes made using NiO precursor powders from two different manufacturers with and without the addition of aluminum titanate (ALT) added by either mechanical mixing or anode infiltration have been quantified using a novel MATLAB algorithm. Because the algorithm has been used to quantify degradation rates for many different SOFC tests, it is thought that the method can be applied to most measured SOFC data to quantify the instantaneous cell degradation rate as a function of time for the entire SOFC performance measurement. Degradation rates determined at different times have been plotted against varying concentrations of ALT addition, facilitating the estimation of optimum ALT concentration for SOFC anodes made with NiO from a specific manufacturer. The algorithm used to determine degradation rates is available upon request to the corresponding author.  相似文献   
49.
Trehalose, a natural disaccharide with bioprotective properties, is widely recognized for its ability to preserve biological membranes during freezing and dehydration events. Despite debate over the molecular mechanisms by which this is achieved, and that different mechanisms imply quite different distributions of trehalose molecules with respect to the bilayer, there are no direct experimental data describing the location of trehalose within lipid bilayer membrane systems during dehydration. Here, we use neutron membrane diffraction to conclusively show that the trehalose distribution in a dioleoylphosphatidylcholine (DOPC) system follows a Gaussian profile centred in the water layer between bilayers. The absence of any preference for localizing near the lipid headgroups of the bilayers indicates that the bioprotective effects of trehalose at physiologically relevant concentrations are the result of non-specific mechanisms that do not rely on direct interactions with the lipid headgroups.  相似文献   
50.
Data were obtained for the colour appearance of unrelated colours under photopic and mesopic conditions. The effects of changes in luminance level and stimulus size were investigated. The method used was magnitude scaling of brightness, colourfulness, and hue. Two stimulus sizes (10° and 0.5°) and four starting luminance levels (60, 5, 1, and 0.1, cd/m2) were used. The results at 0.1 cd/m2 had large variations, so data were obtained for two additional stimulus sizes (1° and 2°) at this luminance level. Ten observers judged 50 unrelated colours. A total of 17,820 estimations were made. The observations were carried out in a completely darkened room, after 20 min adaptation; each test colour was presented on its own. Brightness and colourfulness were found to decrease with decreases of both luminance level and stimulus size. The CAM97u model predicted brightness more accurately than CIECAM02 but gave worse performance in predicting colorfulness. For hue, CAM97u and CIECAM02 both gave satisfactory predictions. Using the brightness correlate from CAM97u, a new colour‐appearance model based on CIECAM02 was developed specifically for unrelated colours under photopic and mesopic conditions, with parameters to allow for the effects of luminance level and stimulus size. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2011;  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