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   122637篇
  免费   7805篇
  国内免费   2931篇
电工技术   4574篇
技术理论   6篇
综合类   4492篇
化学工业   23092篇
金属工艺   6064篇
机械仪表   8053篇
建筑科学   6298篇
矿业工程   2428篇
能源动力   4321篇
轻工业   8550篇
水利工程   1271篇
石油天然气   5373篇
武器工业   462篇
无线电   15410篇
一般工业技术   19908篇
冶金工业   7804篇
原子能技术   1409篇
自动化技术   13858篇
  2024年   349篇
  2023年   1825篇
  2022年   2957篇
  2021年   4352篇
  2020年   3241篇
  2019年   3111篇
  2018年   3690篇
  2017年   3883篇
  2016年   3798篇
  2015年   3968篇
  2014年   5489篇
  2013年   7193篇
  2012年   7551篇
  2011年   8677篇
  2010年   6944篇
  2009年   6847篇
  2008年   6628篇
  2007年   5877篇
  2006年   5799篇
  2005年   5154篇
  2004年   3841篇
  2003年   3573篇
  2002年   3184篇
  2001年   2762篇
  2000年   2799篇
  1999年   2983篇
  1998年   3326篇
  1997年   2422篇
  1996年   2210篇
  1995年   1740篇
  1994年   1423篇
  1993年   1124篇
  1992年   842篇
  1991年   707篇
  1990年   593篇
  1989年   496篇
  1988年   434篇
  1987年   315篇
  1986年   243篇
  1985年   210篇
  1984年   161篇
  1983年   104篇
  1982年   80篇
  1981年   68篇
  1980年   55篇
  1979年   44篇
  1978年   34篇
  1977年   47篇
  1976年   69篇
  1975年   25篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
本文从开放性原理出发,描述了计算机通信网络系统开放性体系的思想及其实现技术。  相似文献   
92.
PURPOSE: Normal retina is firmly attached to the retinal pigment epithelium, but the force of this adhesion drops precipitously within the first 2-3 min after enucleation. The purpose was to study metabolic factors that might be relevant to this postmortem failure of adhesion. METHODS: Dutch rabbit retina was manually peeled from the retinal pigment epithelium on strips of enucleated eyecup within a 37 degrees C bath. Retinal adhesiveness was measured by observing the amount of retinal pigment epithelium that remained adherent to the retina. RESULTS: Autologous whole blood in place of salt solution retarded the decrease in adhesiveness. A solution of hemoglobin alone was similarly effective, whereas methemoglobin solution failed to help the persistence of retinal adhesion. Bubbling oxygen into the salt solution and circulating it to avoid oxygen depletion at the tissue boundary also proved effective at sustaining retinal adhesiveness. Eyes made ischemic in vivo for 5 min or longer, by elevating intraocular pressure, showed virtually no retinal adhesion when enucleated immediately thereafter. However, eyes made ischemic for 10 min, but allowed to regain circulation for 5 min before enucleation, showed a return of retinal adhesiveness to 80% of normal. CONCLUSIONS: Oxidative metabolism is critical to the maintenance of retinal adhesiveness, and the effects of oxygen deprivation on adhesion are reversible within a certain time period.  相似文献   
93.
94.
ATM局域网仿真体系结构的研究   总被引:4,自引:0,他引:4  
本文在简要叙述了基于ATM技术进行局域网仿真的原理后,对局域网仿真体系结构作了一些探讨。考虑的重点是无连接服务和群播功能的实现  相似文献   
95.
本文详细叙述了海上靶场角度量录取糸统的组成、测试原理及其功能设计,简要介绍了该系统在靶扬的应用情况.  相似文献   
96.
When a heterogeneous elastic material is represented by an effective homogeneous elastic solid, average stress and strain fields are used. The meaning of the J-integral in the effective homogeneous solid is investigated. A periodically layered medium is considered. The relation between the J-integrals in the original layered medium and the effective medium is derived.  相似文献   
97.
An alternative approach is presented in this article for the calculation of the activity of FeO, Fe2O3, and the other component in ternary oxide slags when the redox behavior of iron oxides is known. The approach avoids the use of the “tangent intercepts” to the iso-oxygen activity curves as required in Schuhmann's method. Favorable comparisons were obtained for the systems of FeO-Fe2O3-CaO and FeO-Fe2O3-SiO2 between the isoactivity curves derived using this method and those established in previous work using Schuhmann's method. Direct calculation of the free energy of mixing from the redox data is also possible. An example is given for the FeO-Fe2O2-CaO system.  相似文献   
98.
The aim of this study was to design a modified atmosphere package for a mixed vegetable salad consisting of 75 g of cut carrot, 55 g of cut cucumber, 20 g of sliced garlic and 50 g of whole green pepper. Respiration data of all the components were combined with film permeability data to predict package atmospheres and design optimal packages for experimental testing for improved shelf-life of the produce. The optimal package avoided minimum O2 and maximum CO2 tolerance limits, and chilling injury temperatures for any component. A pouch form package made of 27 mm low density polyethylene developed a modified atmosphere of 2.0–2.1% O2 and 5.5–5.7% CO2, which was beneficial for all components and provided better quality retention than other test packages.  相似文献   
99.
100.
A novel reaction scheme for transforming certain metal sulfides to the corresponding oxides has been developed. In this process, steam oxidizes the sulfide into the oxide, and the hydrogen sulfide produced reacts with lime to form calcium sulfide and regenerate steam. There is no net consumption or generation of gaseous species. Thus, the overall reaction can be carried out in a closed system as far as the gas phase is concerned. This eliminates the possibility of emitting hydrogen sulfide out of the reactor. Only certain metal sulfides are thermodynamically amenable to this treatment. In this paper, the reaction of ZnS to ZnO by this scheme is described, together with a detailed formulation of the rate equation for the overall reaction based on the kinetics of the component gas-solid reactions. Although the present work was done with CaO, other suitable oxides may be used in its place. A further potential application of this process is to the selective oxidation of certain sulfide(s) from complex sulfide ores as a treatment prior to the separation of minerals.  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