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   807篇
  免费   37篇
  国内免费   3篇
电工技术   50篇
综合类   2篇
化学工业   229篇
金属工艺   32篇
机械仪表   24篇
建筑科学   12篇
能源动力   51篇
轻工业   44篇
水利工程   2篇
石油天然气   3篇
无线电   45篇
一般工业技术   178篇
冶金工业   43篇
原子能技术   34篇
自动化技术   98篇
  2023年   9篇
  2022年   7篇
  2021年   26篇
  2020年   11篇
  2019年   16篇
  2018年   12篇
  2017年   19篇
  2016年   25篇
  2015年   17篇
  2014年   32篇
  2013年   49篇
  2012年   37篇
  2011年   69篇
  2010年   56篇
  2009年   41篇
  2008年   56篇
  2007年   48篇
  2006年   31篇
  2005年   33篇
  2004年   26篇
  2003年   36篇
  2002年   23篇
  2001年   12篇
  2000年   12篇
  1999年   8篇
  1998年   33篇
  1997年   11篇
  1996年   8篇
  1995年   11篇
  1994年   8篇
  1993年   5篇
  1992年   10篇
  1991年   5篇
  1990年   2篇
  1989年   9篇
  1988年   1篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1984年   5篇
  1983年   6篇
  1982年   4篇
  1981年   1篇
  1980年   3篇
  1979年   1篇
  1977年   2篇
  1976年   1篇
  1975年   2篇
  1974年   4篇
排序方式: 共有847条查询结果,搜索用时 234 毫秒
91.
Delay of gratification, assessed in a series of experiments when the subjects were in preschool, was related to parental personality ratings obtained a decade later for 95 of these children in adolescence. Clear and consistent patterns of correlations between self-imposed delay time in preschool and later ratings were found for both sexes over this time span. Delay behavior predicted a set of cognitive and social competencies and stress tolerance consistent with experimental analyses of the process underlying effective delay in the preschool delay situation. Specifically, children who were able to wait longer at age 4 or 5 became adolescents whose parents rated them as more academically and socially competent, verbally fluent, rational, attentive, planful, and able to deal well with frustration and stress. Comparisons with related longitudinal research using other delay situations help to clarify the important features of the situations and person variables involved in different aspects of delay of gratification. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
92.
Catalyst aging or formulation changes can cause a perturbation to the rate constant matrix of a monomolecular reaction system. The techniques of determining a perturbation matrix from a knowledge of the original rate constant matrix and the experimental reaction paths are discussed. Kubo's expansion form is shown to be useful for a short reaction time when the magnitude of a perturbation matrix is rather large. For small perturbations, the eigenvalues and eigenvectors of the perturbed system can be expanded into a Taylor series.  相似文献   
93.
The static magnetization of 3He film adsorbed on sintered silver powder has been measured for coverages from 0.10 to 0.54 atoms/»2 in steps of 0.02 atoms/»2 and at a coverage of 4.5 atoms/»2. Below 0.20 atoms/»2 the magnetization well obeys the Curie law, while above that coverage a ferromagnetic tendency appears. The coverage dependence of the magnetization greatly differs from that for graphite. At 0.23 atoms/»2 the magnetization has apeak like that for graphite; however, the magnitude of the peak is not so large. Furthermore, a multipeak structure is found in the isotherm of the magnetization at 0.2 mK. It has two prominent peaks at 0.23 and 0.29 atoms/»2, and two other peaks are found at 0.35 and 0.41 atoms/»2. These appear periodically with an interval of 0.06 atoms/»2, which is nearly equal to the coverage of one liquid layer.  相似文献   
94.
Piezoelectric and ferroelectric properties of bismuth sodium titanate, (Bi1/2Na1/2)TiO3(BNT)-based solid solution, that is, (Bi1/2Na1/2)(1-x)(Pba Bab)xTiO3(a + b = 1) [BNPB(100x-100a/100b)], are studied from the viewpoint of a new group of lead-free or low-lead content piezo-electric ceramics with a rhombohedral(Fa-tetragonal (Fβ) morphotropic phase boundary (MPB). It is evident that the MPB seems to be remarkably efficacious in promoting piezoelectric and pyroelectric activities by electrical poling. X-ray diffraction data, dielectric properties and D-E hysteresis loops show that the MPB exist near (Bi1/2Na1/2)TiO3[BNT] at x = 0.13–0.14, 0.08–0.09 and 0.06–0.07 in the case of b = 0, b = 0.5 and b = 1, respectively. BNPB ceramics are superior for piezoelectric ceramics in high-frequency ultrasonic uses, or special piezoelectric actuator materials with a lower free permittivity ε33Tε0, and a high electromechanical coupling factor k33, along with a high mechanical strength.  相似文献   
95.
The components of self-regulation were analyzed, extending the self-imposed delay of gratification paradigm to older children with social adjustment problems. Delay behavior was related to a network of conceptually relevant cognitive person variables, consisting of attention deployment strategies during delay, knowledge of delay rules, and intelligence. A positive relationship was demonstrated between concurrent indexes of intelligence, attention deployment, and actual delay time. Moreover, attention deployment, measured as an individual differences variable during the delay process, had a direct, positive effect on delay behavior. Specifically, as the duration of delay and the frustration of the situation increased, children who spent a higher proportion of the time distracting themselves from the tempting elements of the delay situation were able to delay longer. The effect of attention deployment on delay behavior was significant even when age, intelligence, and delay rule knowledge were controlled. Likewise, delay rule knowledge significantly predicted delay time, even when age, attention deployment, and intelligence were controlled. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
96.
To examine the effects of the relationships between behavior and the situation in which it occurs, we manipulated such relations and exposed subjects to them. Impressions were similar when based on the behaviors presented with situations unspecified (e.g., child hits) or when the situations in which they naturally occurred were specified (e.g., child hits when provoked). However, when situations were specified, subjects' impressions more accurately predicted individual differences in the children's actual levels of overall aggressive behavior. When the veridical situation–behavior relations were increasingly altered, the targets were perceived as being less plausible and increasingly maladjusted and odd, and correlations decreased between the perceived level of the children's aggressiveness and their actual aggressive behavior. Thus, both personality impressions and predictive accuracy were influenced by the relations between the target's behaviors and their situational contexts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
97.
A compartment model has been used for kinetic analysis of dynamic positron emission tomography (PET) data [e.g., 2-deoxy-2-18F-fluoro-D-glucose (FDG)]. The input function of the model [the plasma time-activity curve (pTAC)] was obtained by serial arterial blood sampling. It is of clinical interest to develop a method for PET studies that estimates the pTAC without needing serial arterial blood sampling. For this purpose, we propose a new method to extract the pTAC from the dynamic brain PET images using a modified independent component analysis [extraction of the pTAC using independent component analysis (EPICA). Source codes of EPICA are freely available at http://www5f.biglobe.ne.jp/?kimura/Software/top.html]. EPICA performs the appropriate preprocessing and independent component analysis (ICA) using an objective function that takes the various properties of the pTAC into account. After validation of EPICA by computer simulation, EPICA was applied to human brain FDG-PET studies. The results imply that the EPICA-estimated pTAC was similar to the actual measured pTAC, and that the estimated blood volume image was highly correlated with the blood volume image measured using 15O-CO inhalation. These results demonstrated that EPICA is useful for extracting the pTAC from dynamic PET images without the necessity of serial arterial blood sampling.  相似文献   
98.
The authors have conducted a laboratory-scale gallery fire test on eight different samples of electric cable in a horizontal airflow. The number of speciments and the distances between them on the trestle were varied for each test. As a result, it was found that both ignitability and flame-propagation properties depended on the distance between the specimens as well as on their number. Such flammability properties obtained for each cable sample were also found to be considerably consistent with the critical oxygen index. In addition, it is proposed that the flammability should be classified largely into five categories in this laboratory-scale gallery fire test for fire-retardance evaluation of solid combustible materials such as electric cables.  相似文献   
99.
A fluorinated self-assembled monolayer (F-SAM) is mainly used as the antisticking layer. To prevent the F-SAM coated on the nanoimprint lithography (NIL) mold from deteriorating, we propose a new form of nanoimprinting using a release-agent-coated resin. The results from measuring the surface free energy and observations by scanning probe microscopy (SPM) confirmed that the surface free energy, frictional force, and adhesion force of the release-agent spray-coated polymethylmethacrylate (PMMA) were lower than those of PMMA. To prove the release-agent spray-coated PMMA had a releasing effect, we tried to undertake thermal nanoimprinting on it using a mold without F-SAM. The pattern was clearly imprinted on the resin without any signs of adhesion.  相似文献   
100.
Polytetrafluoroethylene (PTFE) is a very attractive material for various fields because of its chemical resistance, insulation properties, and hydrophobic properties. However, it is difficult to fabricate PTFE microstructures with conventional techniques such as semiconductor processes or micromachining. We have succeeded in the fabrication of high‐aspect‐ratio microfluidics parts from PTFE by direct in‐vacuum photo‐etching utilizing synchrotron radiation (SR) at energy levels from 2 to 12 keV. This paper presents an analysis of the mechanisms of the PTFE microfabrication process and describes newly discovered processing characteristics of PTFE. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(4): 49–54, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21152  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