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   5772篇
  免费   167篇
  国内免费   10篇
电工技术   82篇
综合类   5篇
化学工业   1092篇
金属工艺   115篇
机械仪表   80篇
建筑科学   332篇
矿业工程   8篇
能源动力   165篇
轻工业   386篇
水利工程   45篇
石油天然气   37篇
武器工业   1篇
无线电   394篇
一般工业技术   919篇
冶金工业   1466篇
原子能技术   54篇
自动化技术   768篇
  2021年   63篇
  2020年   60篇
  2019年   62篇
  2018年   72篇
  2017年   64篇
  2016年   82篇
  2015年   83篇
  2014年   89篇
  2013年   365篇
  2012年   204篇
  2011年   235篇
  2010年   168篇
  2009年   185篇
  2008年   226篇
  2007年   231篇
  2006年   198篇
  2005年   189篇
  2004年   171篇
  2003年   158篇
  2002年   166篇
  2001年   92篇
  2000年   100篇
  1999年   114篇
  1998年   99篇
  1997年   87篇
  1996年   100篇
  1995年   76篇
  1994年   72篇
  1993年   83篇
  1992年   75篇
  1991年   56篇
  1990年   69篇
  1989年   81篇
  1988年   69篇
  1987年   86篇
  1986年   82篇
  1985年   103篇
  1984年   111篇
  1983年   84篇
  1982年   77篇
  1981年   86篇
  1980年   63篇
  1979年   99篇
  1978年   73篇
  1977年   79篇
  1976年   58篇
  1975年   67篇
  1974年   60篇
  1973年   76篇
  1972年   55篇
排序方式: 共有5949条查询结果,搜索用时 870 毫秒
51.
94 smokers (mean age 39 yrs) in a 6-wk behavioral smoking-cessation program were administered weekly questionnaires on their use of major program recommendations and other quitting strategies throughout treatment. An "affect-regulation" coping inventory was administered at the beginning and end of treatment. Adequate adherence was reported for most recommendations. Although a composite measure of adherence did not predict quitting success, adherence and coping assessments were associated with maintenance of treatment gains. Short-term maintenance was associated with an extensive affect-regulation repertoire and use of stimulus control strategies; long-term maintenance was associated with consistent self-monitoring of smoking during treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
52.
53.
ABSTRACT: Many analysts argue that important structural conditions exist that discourage city governments from engaging in redistributive policy, especially programs that create direct costs for private developers. Labeled the limited city argument, this logic concludes that only cities with sufficient levels of economic and fiscal well-being can afford to impose upon private developers to meet social needs. Using survey data from 133 cities with populations over 100,000, this paper examines land use regulations that impose obligations or restrictions on the private sector to promote low income housing. The data suggest that the limited city argument is only part of the explanation. The use of regulatory housing policy is also correlated with measures of need and low income housing advocacy.  相似文献   
54.
A three-dimensional (3D) computational fluid dynamics (CFD) model of a contact tank is presented in this paper. The model results are compared against 3D velocities and flow through curve (FTC) data, representing a tracer concentration profile, from a 1:8 scale physical model. The objective is to demonstrate that CFD models can simulate both the FTC and the 3D velocity field quite well. Simultaneous validation of velocities and FTC is important in ascertaining the predictive capabilities of CFD models, as physical model studies indicate that different baffle arrangements can lead to similar FTCs. Therefore, a good prediction of only FTC, as presented in previous 3D CFD model studies, does not necessarily imply a correct simulation of the flow field.  相似文献   
55.
Cell phones are a pervasive new communication technology, especially among college students. This paper examines college students’ cell phone usage from a behavioral and psychological perspective. Utilizing both qualitative (focus groups) and quantitative (survey) approaches, the study suggests these individuals use the devices for a variety of purposes: to help them feel safe, for financial benefits, to manage time efficiently, to keep in touch with friends and family members, et al. The degree to which the individuals are dependent on the cell phones and what they view as the negatives of their utilization are also examined. The findings suggest people have various feelings and attitudes toward cell phone usage. This study serves as a foundation on which future studies will be built.  相似文献   
56.
This article reviews the evidence and theory pertaining to a form of perspective-taking failure--a difficulty in setting aside the privileged information that one knows to be unavailable to another party. The authors argue that this bias (epistemic egocentrism, or EE) is a general feature of human cognition and has been tapped by 2 independent and largely uncommunicating research traditions: the theory-of-mind tradition in developmental psychology and, with more sensitive probes, the "heuristics and biases" tradition in the psychology of human judgment. This article sets the stage for facilitating communication between these traditions as well as for the recognition of EE's breadth and potential interdisciplinary significance. The authors propose a life-span account and a tentative taxonomy of EE; and they highlight the interdisciplinary significance of EE by discussing its implications for normative ethics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
57.
In industrial fluid cokers the feedstock, consisting of heavy bituminous hydrocarbons, is atomized with steam and injected into a hot fluidized bed of coke. Good and uniform contact of the liquid droplets with the solid particles is required to provide heat for the cracking reactions while minimizing mass transfer effects. Experiments in a pilot plant coker have suggested that the initial particle/liquid mixing, in the spray jet, is rather poor. Experiments in a X-ray scanner showed that liquid droplets and entrained particles accumulate just below the tip of the jet plume to form agglomerates.An experimental technique was used to quantitatively determine the quality of mixing with a variety of nozzle configurations including several novel designs. By improving spray stability, redistributing liquid droplets to the solids-rich region of the jet and increasing the surface area of the gas-liquid jet-fluidized bed interface, liquid/solid contact is improved.  相似文献   
58.
This paper reports off-lattice Monte Carlo simulations of highly-branched comb homopolymers weakly adsorbed on a flat, featureless surface showing only covolume and dispersion interactions with the adsorbate. A minimal coarse-grained model, described by hard spheres connected by harmonic springs, was employed. The interaction energy of the adsorbed combs and linear chains is first discussed as a function of the molecular mass and of the number of beads in contact with the surface. The molecular size is then investigated as a function of backbone length and branching density at a fixed arm size. The apparent swelling exponents of the adsorbed combs are larger than those of the corresponding linear chains, and much larger than that of the free molecules. This result indicates a surface-induced stiffening of the comb backbone, further studied through the persistence length lpers. It is found that lpers increases upon adsorption over the free-molecule value, more so the larger is the branching density. Finally, the thickness of the adsorbed layer, the surface-induced molecular anisotropy and the molecular aspect ratio are investigated as a function of branching density and molecular mass.  相似文献   
59.
The NIST 0:45 reflectometer measures the spectral reflectance factor at an influx angle of 0° and an efflux angle of 45° of colored, nonfluorescent specimens at room temperature, with widths ranging from 3 to 10 cm and heights from 3 to 20 cm and with an uncertainty of less than 0.5 in color difference units. Published in 2008 by John Wiley & Sons, Inc. Col Res Appl, 33, 94–99, 2008  相似文献   
60.
Sets of color tiles are available from the National Institute of Standards and Technology calibrated using the NIST 0:45 Reflectometer. The uncertainties associated with the measured values for the color tiles are an indispensable component of the calibration report that accompanies these tiles. A systematic, analytical approach developed previously was applied to the particular case of the reference instrument and color tile set, taking into account the operation and characteristics of the instrument and the spectral properties of the set. The primary sources of uncertainty were identified, and the resulting uncertainties in the color space values L*, a*, and b* were determined. In general, the uncertainties are lowest for those color tiles whose reflectance factors are nearly constant with wavelength. Published in 2008 by John Wiley & Sons, Inc. Col Res Appl, 33, 100–107, 2008  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