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   52793篇
  免费   3432篇
  国内免费   431篇
电工技术   930篇
综合类   508篇
化学工业   9371篇
金属工艺   1238篇
机械仪表   1329篇
建筑科学   1935篇
矿业工程   224篇
能源动力   1167篇
轻工业   6496篇
水利工程   574篇
石油天然气   439篇
武器工业   79篇
无线电   4035篇
一般工业技术   8819篇
冶金工业   11759篇
原子能技术   354篇
自动化技术   7399篇
  2024年   128篇
  2023年   563篇
  2022年   773篇
  2021年   1521篇
  2020年   1202篇
  2019年   1067篇
  2018年   1930篇
  2017年   1918篇
  2016年   1975篇
  2015年   1598篇
  2014年   2015篇
  2013年   3485篇
  2012年   3156篇
  2011年   3075篇
  2010年   2378篇
  2009年   2137篇
  2008年   2409篇
  2007年   2072篇
  2006年   1613篇
  2005年   1321篇
  2004年   1195篇
  2003年   1073篇
  2002年   1008篇
  2001年   678篇
  2000年   651篇
  1999年   815篇
  1998年   3779篇
  1997年   2289篇
  1996年   1534篇
  1995年   888篇
  1994年   783篇
  1993年   762篇
  1992年   286篇
  1991年   307篇
  1990年   283篇
  1989年   284篇
  1988年   232篇
  1987年   207篇
  1986年   221篇
  1985年   259篇
  1984年   225篇
  1983年   175篇
  1982年   198篇
  1981年   204篇
  1980年   188篇
  1979年   151篇
  1978年   136篇
  1977年   242篇
  1976年   484篇
  1975年   106篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
C-axis textured thin films of gallium-doped indium zinc oxide (GIZO) with a 2% ratio of Ga/Zn, were obtained via RF-magnetron sputtering with high transparency and electrical conductivity. A Box-Behnken response surface design was used to evaluate the effects of the deposition parameters (In2O3 target power, deposition time, and substrate temperature) on the chemical composition, optical, electrical, and structural properties of the GIZO films. The optical constants and the electrical properties were obtained using optical models. The GIZO stoichiometry, and therefore the In/Zn atomic ratio, affected the crystallinity, crystalline parameters, band gap, and charge carrier mobility of the GIZO films. The charge carrier density was related to the change in the crystalline parameters of the hexagonal structure and the In/Zn atomic ratio. The best electrical conductivity values (1.75?×?103 Ω?1 cm?1) were obtained for GIZO films with In/Zn ratio ≥?1. Several figures of merit (FOM) defined for the visible and solar regions were comparatively used to select the optimal In/Zn atomic ratio that provided the best balance between the conductivity and the transparency. The optimal In/Zn ratio was in a range of 0.85–0.90 for the GIZO films.  相似文献   
52.
53.
Chiral molecules, especially enantiomers and diastereomers of purity > 99 %, present a significant market share within the chemical, pharmaceutical, and flavor industries. Antisolvent precipitations, both batch and semicontinuous operations to serve the current trends in flow chemistry were demonstrated to be environmentally benign and efficient tools in achieving high optical purities. Although salts are known to be insoluble in supercritical CO2, instabilities of the nascent salts were detected and applied for increasing efficiency. Diastereomeric excess values of the crystalline products exceeded 99 % in maximum of three consecutive steps both by repeated resolution with half molar equivalent of the amine to the acid and by direct recrystallization of the salts.  相似文献   
54.
A simple but comprehensive model considering homogeneous and micellar nucleation, coagulation, entry of radicals to particles and to micelles and radicals' exit from particles, is presented. The model is validated, in a starved semicontinuous heterophase polymerization of ethyl methacrylate, at three monomer addition rates. The model accurately describes the overall and instantaneous conversion, the average particle density and diameter, and the number and weight average molar masses evolutions over time. It is found that even though the average number of radicals is much smaller than 0.5, the system is not 0-1. An empirical function was used to describe the gel effect. The homogeneous nucleation was the prevailing mechanism for particle formation and large exit rates of radicals were observed. POLYM. ENG. SCI., 60: 223–232, 2019. © 2019 Society of Plastics Engineers  相似文献   
55.
Vu  Hoa T.  Nguyen  Manh B.  Vu  Tan M.  Le  Giang H.  Pham  Trang T. T.  Nguyen  Trinh Duy  Vu  Tuan A. 《Topics in Catalysis》2020,63(11-14):1046-1055
Topics in Catalysis - Nano Fe-BTC/graphene oxide (GO) composites were successfully synthesized by hydrothermal treatment with a microwave-assisted method. Samples were characterized by X-ray...  相似文献   
56.
The Journal of Supercomputing - Deadlock-free dynamic network reconfiguration process is usually studied from the routing algorithm restrictions and resource reservation perspective. The dynamic...  相似文献   
57.
58.

This paper presents a PVS development of relevant results of the theory of rings. The PVS theory includes complete proofs of the three classical isomorphism theorems for rings, and characterizations of principal, prime and maximal ideals. Algebraic concepts and properties are specified and formalized as generally as possible allowing in this manner their application to other algebraic structures. The development provides the required elements to formalize important algebraic theorems. In particular, the paper presents the formalization of the general algebraic-theoretical version of the Chinese remainder theorem (CRT) for the theory of rings, as given in abstract algebra textbooks, proved as a consequence of the first isomorphism theorem. Also, the PVS theory includes a formalization of the number-theoretical version of CRT for the structure of integers, which is the version of CRT found in formalizations. CRT for integers is obtained as a consequence of the general version of CRT for the theory of rings.

  相似文献   
59.
60.
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