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   257671篇
  免费   3913篇
  国内免费   1056篇
电工技术   4401篇
综合类   205篇
化学工业   38185篇
金属工艺   8325篇
机械仪表   7334篇
建筑科学   7082篇
矿业工程   548篇
能源动力   7386篇
轻工业   28994篇
水利工程   2156篇
石油天然气   1964篇
武器工业   6篇
无线电   33766篇
一般工业技术   47018篇
冶金工业   47951篇
原子能技术   3411篇
自动化技术   23908篇
  2021年   1862篇
  2020年   1405篇
  2019年   1725篇
  2018年   2638篇
  2017年   2652篇
  2016年   2955篇
  2015年   2240篇
  2014年   3731篇
  2013年   12288篇
  2012年   6940篇
  2011年   9889篇
  2010年   7596篇
  2009年   8562篇
  2008年   9128篇
  2007年   9145篇
  2006年   8452篇
  2005年   7659篇
  2004年   7368篇
  2003年   7246篇
  2002年   6751篇
  2001年   7103篇
  2000年   6412篇
  1999年   6935篇
  1998年   16512篇
  1997年   11476篇
  1996年   8706篇
  1995年   6633篇
  1994年   5778篇
  1993年   5661篇
  1992年   4089篇
  1991年   3836篇
  1990年   3620篇
  1989年   3452篇
  1988年   3351篇
  1987年   2667篇
  1986年   2560篇
  1985年   3254篇
  1984年   2903篇
  1983年   2643篇
  1982年   2427篇
  1981年   2478篇
  1980年   2267篇
  1979年   2137篇
  1978年   1949篇
  1977年   2253篇
  1976年   2787篇
  1975年   1651篇
  1974年   1543篇
  1973年   1623篇
  1972年   1195篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The precautionary principle (PP), according to one of its definitions, says that lack of certainty, given the current scientific and technological knowledge, shall not delay effective and proportionate actions to prevent hazards, taking into account cost-benefit considerations. Rather than being a single principle, a variety of statements of the PP are found in international treaties and other documents. Apart from any specific legal force of the documents, countries (e.g., France) have used these statements as a starting point for their own guidance documents and regulations for addressing specific environmental and health issues, for example regulation of genetically modified organisms. Thus, any discussion of the precautionary principle must address a complex legal and regulatory situation. We briefly review different statements of the PP and important commentary, largely from the European Union. We provide references to the original source documents (many of which are found in English on the World Wide Web).  相似文献   
72.
73.
74.
75.
Surface tension as a controlled variable in mechanical dishwashing   总被引:1,自引:0,他引:1  
Using a continuous, in-line, nondestructive technique based on the maximum bubble pressure method, the surface tension of the wash water in a mechanical dishwashing machine has been monitored. This technique has enabled surface tension to be used as a controlled variable, providing feedback to regulate the amount of surfactant added. Assuming the mechanical force of the water spray is adequate to remove bound soil from the dish surface, the food soil may be titrated against surfactant, providing an indirect indication as to when the dishes are clean. This technique also could be applied to a recirculated wash solution for in-place cleaning.  相似文献   
76.
Some methods determine the non-indolyl glucosinolates content in rapeseed as their hydrolysates: the isothiocyanates and the oxazolidinethiones. These methods in their present form underestimate the amount of the glucosinolates content. In this investigation, a modified method was developed to give a better quantitative estimate, indicating a glucosinolate level five times that obtained by a typical existing method.  相似文献   
77.
78.
Processing methods used in photonics and nanotechnology possess many limitations restricting their application areas such as high cost, inability to produce fine details, problems with scalability, and long processing time. Proximity field nanopatterning is a lithography method which surpasses these limitations. By using interference patterns produced by a two-dimensional phase mask, the technique is able to generate a submicron detailed exposure on a millimeter-size slab of light sensitive photopolymer, which is then developed like a photographic plate to reveal three-dimensional interference patterns from the phase mask. While it is possible to use simulations to obtain the interference patterns produced by a phase mask, realizing the mask dimensions necessary for producing a desired interference pattern is analytically challenging due to the intricacies of light interactions involved in producing the final interference pattern. An alternative method is to iteratively optimize the phase mask until the interference patterns obtained converge to the desired pattern. However, depending on the optimization technique used, one either risks a significant probability of failure or requires a prohibitive number of iterations. We argue that an optimization technique that is to take advantage of the physics of the problem using machine learning methods (here fuzzy learning) can lead to competent mask design. This technique is described in this letter.  相似文献   
79.
A 0.9 V 92 dB Double-Sampled Switched-RC Delta-Sigma Audio ADC   总被引:1,自引:0,他引:1  
A 0.9 V third-order double-sampled delta-sigma audio ADC is presented. A new method using a combination of a switched-RC technique and a floating switched-capacitor double-sampling configuration enabled low-voltage operation without clock boosting or bootstrapping. A three-level quantizer with simple dynamic element matching was used to improve linearity. The prototype IC implemented in a 0.13 CMOS process achieves 92 dB DR, 91 dB SNR and 89 dB SNDR in a 24 kHz audio signal bandwidth, while consuming 1.5 mW from a 0.9 V supply. The prototype operates from 0.65 V to 1.5 V supply with minimal performance degradation.  相似文献   
80.
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