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   278187篇
  免费   4663篇
  国内免费   1834篇
电工技术   5609篇
技术理论   5篇
综合类   1179篇
化学工业   44322篇
金属工艺   11235篇
机械仪表   8053篇
建筑科学   7444篇
矿业工程   1690篇
能源动力   6001篇
轻工业   27518篇
水利工程   3129篇
石油天然气   6025篇
武器工业   243篇
无线电   29264篇
一般工业技术   51301篇
冶金工业   52465篇
原子能技术   5757篇
自动化技术   23444篇
  2021年   2710篇
  2019年   2313篇
  2018年   3631篇
  2017年   3591篇
  2016年   3922篇
  2015年   3031篇
  2014年   4933篇
  2013年   11975篇
  2012年   8273篇
  2011年   11041篇
  2010年   8703篇
  2009年   9295篇
  2008年   10116篇
  2007年   10192篇
  2006年   8964篇
  2005年   7898篇
  2004年   7098篇
  2003年   6613篇
  2002年   6599篇
  2001年   6608篇
  2000年   6191篇
  1999年   6273篇
  1998年   14706篇
  1997年   10651篇
  1996年   8029篇
  1995年   5985篇
  1994年   5528篇
  1993年   5383篇
  1992年   4113篇
  1991年   3935篇
  1990年   3998篇
  1989年   3950篇
  1988年   3709篇
  1987年   3138篇
  1986年   3177篇
  1985年   3575篇
  1984年   3443篇
  1983年   3160篇
  1982年   2791篇
  1981年   2996篇
  1980年   2720篇
  1979年   2925篇
  1978年   2799篇
  1977年   2971篇
  1976年   3835篇
  1975年   2525篇
  1974年   2357篇
  1973年   2364篇
  1972年   2007篇
  1971年   1810篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
New nanolayered coatings are designed and deposited on flexible plastic substrate having the thickness of 100 /spl mu/m, in order to realize lightweight ultrathin transparent shielding foils. The structure of the coating is optimized considering three figures of merit: the average transmittance in the visible range for normal incidence, the normalized average transmittance for oblique incidence at 550 nm, and the transmittance quality factor. The nanotechnology exploited for the deposition of the transparent metals is the dual ion beam sputtering. Tests of durability, optical transmission, and shielding effectiveness demonstrate that the film has a high adhesion under mechanical solicitation, high resistance against aging, peak transmittance in the visible range higher than 70%, omnidirectional properties in the range 0/spl deg/-60/spl deg/, and shielding effectiveness of 40 dB up to 6 GHz.  相似文献   
72.
73.
The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance.  相似文献   
74.
Indoor body-area channel model for narrowband communications   总被引:1,自引:0,他引:1  
Using wireless sensors placed on a person to continuously monitor health information is a promising new application. At the same time, new low-power wireless standards such as Bluetooth and Zigbee have been proposed for short range, low data-rate communication matching the requirements of these bio-medical applications. However, there are currently few measurements or models describing propagation around the body. To address this problem, electromagnetic waves near the torso are measured and a statistical model is derived for communication in the 915 MHz and 2.45 GHz industrial, scientific and medical bands associated with Zigbee and Bluetooth. Measurement setup and statistical analysis are described.  相似文献   
75.
The structure of the recently introduced Brazilian government programme for monitoring pesticide residues in six major agricultural products is described. Residues found from the analysis of samples of tomatoes and strawberries are discussed in detail. The much greater frequency of detection of pesticide residues, many of which are not approved for use in Brazil, in produce being sold on the domestic market, as opposed to that produced for export, is of major concern. It is perceived that this new monitoring programme will become permanent and be used to underpin enforcement actions that will need to be taken to reduce the numbers of incidents of illegal residues occurring, particularly in fresh fruits and vegetables.  相似文献   
76.
77.
78.
The effect of the composition of sensitizing–activating solutions on the activation efficiency and the chemical coppering of diamond powders is studied. The results demonstrate that stabilizing additives improve the stability of the solutions, influence the average coppering rate, and play a key role in determining the morphology and quality of the resultant coatings. The most effective stabilizing additive is synthamid-10, which ensures the deposition of high-quality copper coatings.  相似文献   
79.
The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem.  相似文献   
80.
Polystyrene packaging material taint was sensorily evaluated in cocoa powder for drinks and chocolate flakes using short-cut signal detection measures on differences between control and test samples and on recognition of styrene. No differences were observed in cocoa powder for drinks and plain chocolate flakes treated with 0.5 dm2 polystyrene of 1 mm thickness. However, differences were detected in milk chocolate flakes and plain chocolate flakes, which were in contact with a larger area or thicker polystyrene packaging material. The latter results were confirmed by the styrene recognition test, so polystyrene is a potential source of off-flavour for chocolate products. The amount of residual styrene in the polystyrene used was about 320 ppm, while the amounts of styrene ranged from 7 to 132 ppb in cocoa drinks and from 414 to 1447 ppb in chocolate flakes.  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