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   7034篇
  免费   183篇
  国内免费   18篇
电工技术   265篇
综合类   9篇
化学工业   1526篇
金属工艺   198篇
机械仪表   129篇
建筑科学   239篇
矿业工程   11篇
能源动力   285篇
轻工业   676篇
水利工程   34篇
石油天然气   13篇
无线电   533篇
一般工业技术   1083篇
冶金工业   1375篇
原子能技术   191篇
自动化技术   668篇
  2022年   66篇
  2021年   87篇
  2020年   53篇
  2019年   86篇
  2018年   95篇
  2017年   90篇
  2016年   112篇
  2015年   80篇
  2014年   155篇
  2013年   341篇
  2012年   235篇
  2011年   342篇
  2010年   261篇
  2009年   270篇
  2008年   282篇
  2007年   273篇
  2006年   249篇
  2005年   254篇
  2004年   191篇
  2003年   204篇
  2002年   201篇
  2001年   123篇
  2000年   124篇
  1999年   142篇
  1998年   317篇
  1997年   241篇
  1996年   175篇
  1995年   154篇
  1994年   170篇
  1993年   132篇
  1992年   85篇
  1991年   83篇
  1990年   87篇
  1989年   79篇
  1988年   71篇
  1987年   68篇
  1986年   78篇
  1985年   91篇
  1984年   88篇
  1983年   76篇
  1982年   79篇
  1981年   86篇
  1980年   76篇
  1979年   57篇
  1978年   40篇
  1977年   79篇
  1976年   101篇
  1975年   68篇
  1973年   47篇
  1972年   46篇
排序方式: 共有7235条查询结果,搜索用时 15 毫秒
41.
In this article, a new method for measuring a total spectral radiance factor of a FWA‐treated sample illuminated by a specific standard illuminant is introduced. The method replaces an unstable real fluorescent standard by a bi‐spectral luminescent radiance factor data, which works as a virtual fluorescent standard (VFS) by knowing spectral intensity distributions of illuminations applied to the sample. The method utilizes two illuminations I1 and I2 whose relative spectral intensity distributions are different from each other and synthesizes a virtual illumination presenting the identical fluorescent spectral radiance factor to that presented by the standard illuminant with the VFS of the specific bi‐spectral luminescent radiance factor by linearly combining I1 and I2 with the suitable weighting factors. The applicability of the method is examined in principle by comparing ISO brightness and CIE whiteness index of fluorescent standard paper as a test sample obtained by this new method to the assigned values. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 195–200, 2007  相似文献   
42.
43.
A method for predicting the long-term performance of solar energy systems, based on the analysis of system performance for one particular day—the typical meteorological day (TMD)—is presented. The TMD is constructed from the cumulative time distribution of insolation values on the collector aperture. The TMD method requires little calculational effort and a small data base relative to standard yearly computer simulations. Good agreement is found between the predictions of the new method and the corresponding results of the -f-chart method. The TMD method is of particular value for cases that may often be treated inaccurately by simple calculational methods: (1) high threshold problems; (2) systems with short response times (e.g., due to small storage); and (3) systems in which collectors other than flat plates are used (the method is applicable to all solar collector types).  相似文献   
44.
The surface chemical states of the perovskite-type compounds, strontium doped lanthanum cobalt oxides (La1?x Sr x CoO3), have been investigated using X-ray photoelectron spectroscopy (XPS). Catalytic oxidations of both methane and CO have also been investigated using flow methods. The chemical composition of the surface of La1?x Sr x CoO3 was very different from that in the bulk, which was measured by X-ray fluorescence spectroscopy (XRFS). The catalytic activity of La1?x Sr x CoO3 increased with an increase in the quantity of cobalt atoms on the surface.  相似文献   
45.
A structured in-depth interview employing standardized criteria was used to determine the prevalence of lifetime and current alcohol dependence (alcoholism) in unselected consecutive patients admitted to a regional Level I trauma center. Of 629 patients, 157 (25.0%) were current alcoholics at the time of injury. An additional 87 (13.8%) were diagnosed as lifetime non-current alcoholics. There was no significant difference in the rates of current alcohol dependence among patients injured in vehicular crashes (23.5%), other unintentional trauma victims (29.3%), and those injured as a result of violence (24.6%). Of BAC + (blood alcohol concentration positive) patients, 54.5% were current alcoholics. However, 14.4% of alcohol-negative patients were also diagnosed as alcohol dependent.  相似文献   
46.
In order to estimate the discharge performance of tall lead/acid cells (with tubular positives), changes in current and potential distributions with discharge progress were calculated with a computer on the basis of plate resistance and the current—potential—time relationship between small facing parts of positive and negative plates. The taller the cell, the larger the voltage drop along the plates. Thus, the discharge time became shorter despite a large amount of available active mass remaining in the bottom part of the plates.Various current-collector designs were evaluated, e.g., one with varying resistance at each height; a side conductor placed along the plates and connected to them at the top, centre and bottom, etc. Results revealed an optimum collector design with which the maximum discharge capacity could be obtained. Furthermore, it was shown that the side conductor markedly improved the discharge performance because the active mass near the connecting parts was appreciably used.  相似文献   
47.
Walking without vision results in veering, an inability to maintain a straight path that has important consequences for blind pedestrians. In this study, the authors addressed whether the source of veering in the absence of visual and auditory feedback is better attributed to errors in perceptual encoding or undetected motor error. Three experiments had the following results: No significant differences in the shapes of veering trajectories were found between blind and blindfolded participants; accuracy in detecting curved walking paths was not correlated with simple measures of veering behavior; and explicit perceptual cues to initial walking direction did not reduce veering. The authors present a model that accounts for the major characteristics of participants' veering behavior by postulating 3 independent sources of undetected motor error: initial orientation, consistent biases in step direction, and, most important, variable error in individual steps. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
48.
Truncation of CPC solar collectors and its effect on energy collection   总被引:1,自引:0,他引:1  
Analytic expressions are derived for the angular acceptance function of two-dimensional compound parabolic concentrator solar collectors (CPC's) of arbitrary degree of truncation. Taking into account the effect of truncation on both optical and thermal losses in real collectors, we also evaluate the increase in monthly and yearly collectible energy. Prior analyses that have ignored the correct behavior of the angular acceptance function at large angles for truncated collectors are shown to be in error by 0–2% in calculations of yearly collectible energy for stationary collectors.  相似文献   
49.
50.
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