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   113812篇
  免费   11193篇
  国内免费   4278篇
电工技术   4182篇
技术理论   5篇
综合类   10899篇
化学工业   15763篇
金属工艺   13589篇
机械仪表   6817篇
建筑科学   20144篇
矿业工程   4259篇
能源动力   2631篇
轻工业   5959篇
水利工程   2446篇
石油天然气   5740篇
武器工业   1218篇
无线电   6583篇
一般工业技术   13480篇
冶金工业   5963篇
原子能技术   671篇
自动化技术   8934篇
  2025年   968篇
  2024年   2679篇
  2023年   2422篇
  2022年   3314篇
  2021年   3615篇
  2020年   3841篇
  2019年   3140篇
  2018年   2829篇
  2017年   3537篇
  2016年   3623篇
  2015年   3848篇
  2014年   6575篇
  2013年   5677篇
  2012年   7313篇
  2011年   8096篇
  2010年   6170篇
  2009年   6671篇
  2008年   5999篇
  2007年   7213篇
  2006年   6725篇
  2005年   5735篇
  2004年   4807篇
  2003年   4317篇
  2002年   3665篇
  2001年   3064篇
  2000年   2591篇
  1999年   2083篇
  1998年   1665篇
  1997年   1395篇
  1996年   1058篇
  1995年   900篇
  1994年   838篇
  1993年   552篇
  1992年   520篇
  1991年   416篇
  1990年   329篇
  1989年   249篇
  1988年   171篇
  1987年   88篇
  1986年   68篇
  1985年   78篇
  1984年   59篇
  1983年   56篇
  1982年   75篇
  1981年   30篇
  1980年   67篇
  1979年   15篇
  1975年   14篇
  1959年   11篇
  1951年   12篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Chemical Composition and Microstructure of Polymer‐Derived Glasses and Ceramics in the Si–C–O System. Part 2: Characterization of microstructure formation by means of high‐resolution transmission electron microscopy and selected area diffraction Liquid or solid silicone resins represent the economically most interesting class of organic precursors for the pyrolytic production of glass and ceramics materials on silicon basis. As dense, dimensionally stable components can be cost‐effectively achieved by admixing reactive filler powders, chemical composition and microstructure development of the polymer‐derived residues must be exactly known during thermal decomposition. Thus, in the present work, glasses and ceramics produced by pyrolysis of the model precursor polymethylsiloxane at temperatures from 525 to 1550 °C are investigated. In part 1, by means of analytical electron microscopy, the bonding state of silicon was determined on a nanometre scale and the phase separation of the metastable Si–C–O matrix into SiO2, C and SiC was proved. The in‐situ crystallization could be considerably accelerated by adding fine‐grained powder of inert fillers, such as Al2O3 or SiC, which permits effective process control. In part 2, the microstructure is characterized by high‐resolution transmission electron microscopy and selected area diffraction. Turbostratic carbon and cubic β‐SiC precipitate as crystallization products. Theses phases are embedded in an amorphous matrix. Inert fillers reduce the crystallization temperature by several hundred °C. In this case, the polymer‐derived Si–C–O material acts as a binding agent between the powder particles. Reaction layer formation does not occur. On the investigated pyrolysis conditions, no crystallization of SiO2 was observed.  相似文献   
2.
采用电子表格软件EXCEL5.0可以方便地解决许多选煤生产中的线性规划问题。本文通过选煤过程线性规划实例介绍EXCEL5.0在此领域的应用方法。  相似文献   
3.
In order to control a project, construction management requires project information. This is obtained through accounting, estimating, cost management and scheduling functions which produce project reports. These reports are best obtained by subdividing the project into small parts. The ways in which each of these functions subdivides a project in order to produce its reports is discussed, together with a means of interrelating this information with a technique known as the work breakdown structure.  相似文献   
4.
A variable structure model reference adaptive controller (VS-MRAC) using only input and output measurements was recently proposed and shown to be globally asymptotically stable with superior transient behaviour and disturbance rejection properties. In this paper a singular perturbation approach is used in order to establish the robustness of the controller in the presence of unmodelled dynamics (parasitics) and disturbances. We develop a new Lyapunov-based technique to analyse the overall system and show that for sufficiently small parasitics the system remains stable and the output error is small in some sense.  相似文献   
5.
The effect of oxygen content on superconductivity of the 2212 and 2223 phase has been studied. By comparing the excess oxygen, the modulation vector, the XRD patterns, and the electric resistivity of 2212 and 2223 phase samples obtained with different post-annealing conditions, i.e., annealing at 600°C or quenching from 860°C, it was found that the super-conductivity is markedly influenced by both the defect distribution in non-Bi layers and the interstitial oxygens incorporated in the Bi-O layers. A tentative explanation for this is given.  相似文献   
6.
As part of a study of the possible application of polymerisable Langmuir-Blodgett (LB) films as ultra-fine-line e-beam resists, an investigation of the variation of film structure of 22-tricosenoic acid with differing deposition conditions has been made. Unexpected effects with significant implications for deposition speed and resist sensitivity have been observed, and the new techniques for film characterisation developed during the investigation have resulted in a revised model of deposition explaining the observed independence of the disorder causing optical scattering and the macroscopic features observed by polarised microscopy.  相似文献   
7.
8.
Reviews the book, The concept of structure in psychoanalysis by Theodore Shapiro (see record 1991-97355-000). The present volume is a hardcover edition of a previous supplement to the Journal of the American Psychoanalytic Association based on a series of panels presented at meetings of the American on the role of the concept of structure in current psychoanalytic theory and practice. The result can be taken as a more or less authoritative expression of current thinking about structure in orthodox analytic circles. As such, the volume is informative and in many regards thought provoking. But if readers are looking for a coherent, consistent, and consensually endorsed presentation of the idea of structure, or for a uniform conceptualization of the nature of psychic structure and its role in psychoanalytic praxis, they will have to look elsewhere. The volume is more remarkable for its diversity and often contradictory views on the nature of structure and the relevance of structure to clinical work in the analytic setting. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
9.
10.
彭发云 《铸造技术》2004,25(10):785-787
用呋喃树脂石英砂工艺生产牵引电机换向器套筒出现变形、裂纹等铸造缺陷,是由石英砂相变膨胀引起,后用高铬刚玉砂代替石英砂得到解决.  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