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   3098篇
  免费   100篇
  国内免费   2篇
电工技术   44篇
综合类   1篇
化学工业   583篇
金属工艺   124篇
机械仪表   104篇
建筑科学   53篇
矿业工程   13篇
能源动力   53篇
轻工业   131篇
水利工程   25篇
石油天然气   195篇
无线电   307篇
一般工业技术   772篇
冶金工业   278篇
原子能技术   161篇
自动化技术   356篇
  2022年   64篇
  2021年   77篇
  2020年   55篇
  2019年   73篇
  2018年   78篇
  2017年   80篇
  2016年   103篇
  2015年   60篇
  2014年   82篇
  2013年   181篇
  2012年   136篇
  2011年   140篇
  2010年   115篇
  2009年   120篇
  2008年   115篇
  2007年   98篇
  2006年   99篇
  2005年   80篇
  2004年   71篇
  2003年   62篇
  2002年   89篇
  2001年   49篇
  2000年   35篇
  1999年   35篇
  1998年   67篇
  1997年   61篇
  1996年   43篇
  1995年   42篇
  1994年   30篇
  1993年   23篇
  1992年   26篇
  1989年   27篇
  1988年   25篇
  1985年   34篇
  1984年   26篇
  1983年   23篇
  1982年   35篇
  1981年   27篇
  1980年   25篇
  1979年   26篇
  1978年   37篇
  1977年   43篇
  1976年   50篇
  1975年   28篇
  1974年   32篇
  1973年   32篇
  1972年   38篇
  1971年   37篇
  1970年   35篇
  1966年   28篇
排序方式: 共有3200条查询结果,搜索用时 46 毫秒
1.
This study deals with the formulation of natural drugs into hydrogels. For the first time, compounds from the sage essential oil were formulated into chitosan hydrogels. A sample preparation procedure for hydrophobic volatile analytes present in a hydrophilic water matrix along with an analytical method based on the gas chromatography coupled with the mass spectrometry (GC-MS) was developed and applied for the evaluation of the identity and quantity of essential oil components in the hydrogels and saline samples. The experimental results revealed that the chitosan hydrogels are suitable for the formulation of sage essential oil. The monoterpene release can be effectively controlled by both chitosan and caffeine concentration in the hydrogels. Permeation experiment, based on a hydrogel with the optimized composition [3.5% (w/w) sage essential oil, 2.0% (w/w) caffeine, 2.5% (w/w) chitosan and 0.1% (w/w) Tween-80] in donor compartment, saline solution in acceptor compartment, and semi-permeable cellophane membrane, demonstrated the useful permeation selectivity. Here, (according to lipophilicity) an enhanced permeation of the bicyclic monoterpenes with antiflogistic and antiseptic properties (eucalyptol, camphor and borneol) and, at the same time, suppressed permeation of toxic thujone (not exceeding its permitted applicable concentration) was observed. These properties highlight the pharmaceutical importance of the developed chitosan hydrogel formulating sage essential oil in the dermal applications.  相似文献   
2.
Atomic Energy - The results of calculations and experimental determination of the neutronics characteristics of the IRT-T research reactor are presented. The IRT-T reactor is a pool reactor with...  相似文献   
3.
The enzymatic conversion of lignins, possibly in combination with electrochemical oxidation, makes aromatics such as syringol, guaiacol, vanillin and catechol available in the qualities required by the fragrance industry. The lignins were obtained by soda digestion from wheat straw and Miscanthus, characterized and then converted with laccases. The overall yield amounted up to 9 wt % with a product spectrum confined to four substances. Catechol was the major product, with a fraction of ≈75 %. It can easily be isolated by extraction with acetone.  相似文献   
4.
5.
6.
The authors discuss the results of experimental investigation of structural degradation of gray cast iron at various stages of static tensile deformation. Analysis of the deformation process has revealed that damageability of a material under loading can be assessed by both a special strain parameter and scatter of hardness characteristics or a ratio of the modulus deviation to the current value of the elastic modulus. A correlation between these parameters has been established.  相似文献   
7.
8.
The ozonation of two differently substituted azo dyes (Schwarz GRS and Orange Acid 8) in water media is studied. The influence of pH on the effectiveness of the ozonation at various initial concentrations of each dye is explored. It was found out that the rates of decolorization for amino-group substituted dyes reflect the considerable influence by the widely varying initial pH from 4.5 to 10. Specifically, the highest effect of decolorization of this dye was obtained at the highest pH studied (pH 10) for all initial concentrations of the solutions. Considering the dye without an amino-group substitute, the rates of color disappearance in ozonation reflected to a lower degree the variations of the initial pH. Pseudo-first-order trends of decolorization were observed in all the experimental runs. Regarding the kinetic results obtained, an attempt to explain the different dyes reactivity was made based on the absolute electronegativity (Elumo + Ehomo) of both dyes. The COD/BOD analysis shows that the ozonation of both azo dyes can reduce the sample COD but it could not improve the biodegradability ratio (BOD5/COD). BOD decrease with ozonation time indicates that the intermediates of the ozonation are of lower biodegradability. Oxalic acid was found as the final product of ozonation of both dyes.  相似文献   
9.
Healthcare institutions typically post their privacy practices online as privacy policy documents. We conducted a longitudinal study that examines the effects of HIPAA's enactment on a collection of privacy policy documents for a fixed set of organizations over a four-year period. We present our analysis of 24 healthcare privacy policy documents from nine healthcare Web sites, analyzed using goal mining, a content-analysis method that supports extraction of useful information about institutions' privacy practices from documents. We compare our results to our pre-HIPAA study of these same institutions' online privacy practices and evaluate their evolution in the presence of privacy laws  相似文献   
10.
Set out is a brief account of the two major accomplishments by the Russian Research Center ‘Kurchatov Institute’ in creating the full-scope simulators and mathematical modeling technologies. Presented are the basic specifications of one of the world's largest simulators—the full-scope simulator for the Leningrad NPP which is the new-generation one. Owing to the extended modeling scope accomplished is the possibility of training personnel to act in terms of not only the design-basis but rather beyond the design-basis accidents. To minimize the expenditures for creating the simulators, analyzers and other modeling and control means, the RRC ‘Kurchatov Institute' has created the unique technology of mathmodeling automation. Thanks to its versatility and application at its creation of the ELUD philosophy (easy to learn, use and develop) good use is made of this technology both in nuclear and thermal power engineering, as well as in gas industry.  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