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   169963篇
  免费   1439篇
  国内免费   193篇
电工技术   2593篇
综合类   119篇
化学工业   26803篇
金属工艺   9513篇
机械仪表   5748篇
建筑科学   3050篇
矿业工程   1888篇
能源动力   2749篇
轻工业   8982篇
水利工程   2749篇
石油天然气   8707篇
武器工业   12篇
无线电   14731篇
一般工业技术   38522篇
冶金工业   28186篇
原子能技术   6951篇
自动化技术   10292篇
  2018年   3012篇
  2017年   3146篇
  2016年   3412篇
  2015年   1724篇
  2014年   3026篇
  2013年   6422篇
  2012年   4370篇
  2011年   5498篇
  2010年   4494篇
  2009年   4968篇
  2008年   5017篇
  2007年   4951篇
  2006年   4208篇
  2005年   3874篇
  2004年   3687篇
  2003年   3573篇
  2002年   3514篇
  2001年   3501篇
  2000年   3391篇
  1999年   3246篇
  1998年   7149篇
  1997年   5216篇
  1996年   3883篇
  1995年   2970篇
  1994年   2630篇
  1993年   2759篇
  1992年   2275篇
  1991年   2323篇
  1990年   2430篇
  1989年   2334篇
  1988年   2328篇
  1987年   2210篇
  1986年   2268篇
  1985年   2306篇
  1984年   2221篇
  1983年   2146篇
  1982年   1986篇
  1981年   2204篇
  1980年   2058篇
  1979年   2277篇
  1978年   2427篇
  1977年   2427篇
  1976年   3098篇
  1975年   2243篇
  1974年   2297篇
  1973年   2336篇
  1972年   2153篇
  1971年   1904篇
  1970年   1700篇
  1969年   1625篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
11.
Refractories and Industrial Ceramics - Technology for producing alumina-periclase-carbon refractories of the brands APUK-D and APU-D is developed and implemented. Use of complex antioxidant and...  相似文献   
12.
The solid solutions based on the pyrochlore-type system Bi2MgNb2-xTaxO9 were formed in the compositional range х = 0–2.0 (Bi1·6Mg0·8Nb1.6-tTatO7.2, t = 0–1.6). The Rietveld method was used to refine the structure for Bi2MgNb2-xTaxO9 (x = 0, 1.0, 2.0). The increasing tantalum content led to the slight decrease in the cubic unit cell parameters from 10.56934 (4) Å for x = 0 and 10.54607 (3) Å for x = 2 (sp.gr. Fd-3m:2). At the same time, tantalum additions suppressed grain growth in the pyrochlore ceramics during sintering and made it possible to obtain materials with an average grain size of 1–2 μm (Bi1·6Mg0·8Ta1·6O7.2). The increase in the Ta5+ concentration led to the decrease in the dielectric permeability from 104 (Bi1·6Mg0·8Nb1·6O7.2) to 20 (Bi1·6Mg0·8Ta1·6O7.2) at room temperature, while the dielectric loss tangent remained lower than 0.002, which is due to the small grain size and the high porosity of the samples. An increase in temperature has practically no effect on the values of the dielectric permittivity in the entire frequency range. The samples have weak through conductivity. The activation energies of electrical conductivity varied in the range of 0.84–1.00 eV, and the less tantalum, the lower the activation energy. The electrical properties of the samples at 200 Hz to 1 MHz are described by the simplest parallel scheme.  相似文献   
13.
Chemical and Petroleum Engineering - The hydrodynamics of oxidation towers used for bitumen production were studied using a model tower having transparent walls. Experiments were carried out in two...  相似文献   
14.
Journal of Engineering Physics and Thermophysics - Results of investigation into the influence of a corrosion process on thermotechnical characteristics of heat pipes of low-temperature range are...  相似文献   
15.
Russian Engineering Research - The stability of robot-mower motion in a specific direction is considered. The direction is regulated by means of an angular sensor and a programmable controller...  相似文献   
16.
Theoretical Foundations of Chemical Engineering - The effect of the electrolyte composition, mass-transfer conditions, pore diameter, interpore distance, and electric parameters on the formation of...  相似文献   
17.
Chronic stress is a combination of nonspecific adaptive reactions of the body to the influence of various adverse stress factors which disrupt its homeostasis, and it is also a corresponding state of the organism’s nervous system (or the body in general). We hypothesized that chronic stress may be one of the causes occurence of several molecular and cellular types of stress. We analyzed literary sources and considered most of these types of stress in our review article. We examined genes and mutations of nuclear and mitochondrial genomes and also molecular variants which lead to various types of stress. The end result of chronic stress can be metabolic disturbance in humans and animals, leading to accumulation of reactive oxygen species (ROS), oxidative stress, energy deficiency in cells (due to a decrease in ATP synthesis) and mitochondrial dysfunction. These changes can last for the lifetime and lead to severe pathologies, including neurodegenerative diseases and atherosclerosis. The analysis of literature allowed us to conclude that under the influence of chronic stress, metabolism in the human body can be disrupted, mutations of the mitochondrial and nuclear genome and dysfunction of cells and their compartments can occur. As a result of these processes, oxidative, genotoxic, and cellular stress can occur. Therefore, chronic stress can be one of the causes forthe occurrence and development of neurodegenerative diseases and atherosclerosis. In particular, chronic stress can play a large role in the occurrence and development of oxidative, genotoxic, and cellular types of stress.  相似文献   
18.
Kirovskaya  I. A.  Filatova  T. N.  Nor  P. E. 《Semiconductors》2021,55(2):228-233
Semiconductors - According to developed methods, in the fields of the mutual solubility of initial binary compounds (InP, InSb, and CdS), solid solutions of the InP–CdS and InSb–CdS...  相似文献   
19.
Trofimova  Elena G.  Lomovsky  Oleg I. 《SILICON》2021,13(2):433-439
Silicon - The products of solid-phase mechanochemical interaction between pyrocatechol and silicon dioxide yielding a powdered composite were studied using a number of physicochemical methods. This...  相似文献   
20.
Treating neuroinflammation-related injuries and disorders through manipulation of neuroinflammation functions is being heralded as a new therapeutic strategy. In this study, a novel pectic galactan (PG) polysaccharide based gene therapy approach is developed for targeting reactive gliosis in neuroinflammation. Galectin-3 (Gal-3) is a cell protein with a high affinity to β-galactoside sugars and is highly expressed in reactive gliosis. Since PG carries galactans, it can target reactive gliosis via specific carbohydrate interaction between galactan and Gal-3 on the cell membrane, and therefore can be utilized as a carrier for delivering genes to these cells. The carrier is synthesized by modifying quaternary ammonium groups on the PG. The resulting quaternized PG (QPG) is found to form complexes with plasmid DNA with a mean diameter of 100 nm and have the characteristics required for targeted gene therapy. The complexes efficiently condense large amounts of plasmid per particle and successfully bind to Gal-3. The in vivo study shows that the complexes are biocompatible and safe for administration and can selectively transfect reactive glial cells of an induced cortical lesion. The results confirm that this PG-based delivery system is a promising platform for targeting Gal-3 overexpressing neuroinflammation cells for treating neuroinflammation-related injuries and neurodegenerative diseases.  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