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   313513篇
  免费   5956篇
  国内免费   2208篇
电工技术   6751篇
技术理论   1篇
综合类   2135篇
化学工业   49302篇
金属工艺   13322篇
机械仪表   10377篇
建筑科学   8946篇
矿业工程   2730篇
能源动力   7486篇
轻工业   28053篇
水利工程   3718篇
石油天然气   8817篇
武器工业   222篇
无线电   34185篇
一般工业技术   59782篇
冶金工业   52595篇
原子能技术   7851篇
自动化技术   25404篇
  2021年   3238篇
  2020年   2444篇
  2019年   2671篇
  2018年   4489篇
  2017年   4510篇
  2016年   4702篇
  2015年   3545篇
  2014年   5686篇
  2013年   13778篇
  2012年   8681篇
  2011年   11337篇
  2010年   9384篇
  2009年   10391篇
  2008年   10701篇
  2007年   10409篇
  2006年   9352篇
  2005年   8682篇
  2004年   7710篇
  2003年   7307篇
  2002年   7336篇
  2001年   7117篇
  2000年   6787篇
  1999年   6798篇
  1998年   15186篇
  1997年   11436篇
  1996年   8901篇
  1995年   6797篇
  1994年   6159篇
  1993年   5951篇
  1992年   4620篇
  1991年   4520篇
  1990年   4346篇
  1989年   4332篇
  1988年   4299篇
  1987年   3624篇
  1986年   3610篇
  1985年   4167篇
  1984年   3975篇
  1983年   3626篇
  1982年   3430篇
  1981年   3565篇
  1980年   3379篇
  1979年   3310篇
  1978年   3406篇
  1977年   3867篇
  1976年   4989篇
  1975年   3114篇
  1974年   2968篇
  1973年   2988篇
  1972年   2621篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
One-third of all proteins are estimated to require metals for structural stability and/or catalytic activity. Desthiobiotin probes containing metal binding groups can be used to capture metalloproteins with exposed active-site metals under mild conditions so as to prevent changes in metallation state. The proof-of-concept was demonstrated with carbonic anhydrase (CA), an open active site, Zn2+-containing protein. CA was targeted by using sulfonamide derivatives. Linkers of various lengths and structures were screened to determine the optimal structure for capture of the native protein. The optimized probes could selectively pull down CA from red blood cell lysate and other protein mixtures. Pull-down of differently metallated CAs was also investigated.  相似文献   
92.
王钦  吴云昌  金意 《城市燃气》2021,561(11):37-41
大力发展天然气对于促进能源结构优化调整和大气污染防治具有重要意义,是实现"碳达峰""碳中和"的重要路径.借力胶东一体化发展战略的提出,引领胶东五市天然气基础设施协同发展,促进胶东一体化战略在能源领域的实施.  相似文献   
93.
Application of brown titanium dioxide (TiO2-x) and its modified composite forms in the photocatalytic decomposition of organic pollutants in the environment is a promising way to provide solutions for environmental redemption. Herein, we report the synthesis of effective and stable TiO2-x nanoparticles with g-C3N4, RGO, and multiwalled carbon nanotubes (CNTs) using a simple hydrothermal method. Among all the as-synthesized samples, excellent photocatalytic degradation activity was observed for RGO-TiO2-x nanocomposite with high rate constants of 0.075 min?1, 0.083 min?1 and 0.093 min?1 for methylene blue, rhodamine-B, and rosebengal dyes under UV–Visible light irradiation, respectively. The altered bandgap (1.8 eV) and the large surface area of RGO-TiO2-x nanocomposite impacts on both absorption of visible light and efficiency of photogenerated charge electron (e?)/hole (h+) pair separation. This resulted in enhanced photocatalytic property of carbon-based TiO2-x nanocomposites. A systematic study on the influence of different carbon nanostructures on the photocatalytic activity of brown TiO2-x is carried out.  相似文献   
94.
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical...  相似文献   
95.
Journal of Communications Technology and Electronics - Approximate formulas for calculating the coefficient of reflection from an artificial magnetic conductor (AMC) based on a capacitive lattice...  相似文献   
96.
Power Technology and Engineering - The monitoring of hydraulic structures as high-risk facilities is discussed. Monitoring should ensure the reliability and functioning of a hydraulic structure...  相似文献   
97.
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   
98.
Oxygen reduction reaction(ORR) plays a critical role in many energy conversion and storage processes.Therein, a comparative study of the electrocatalytic activity for ORR in 0.1 mol/L KOH solution was conducted using layered perovskite-like LaSr_3 Fe_3 O_(10) and LaSr3 Fe_3 O_(10)-graphene oxide(GO) composite as electrodes. Linear sweep voltammetry(LSV) results show that the LaSr3 Fe_3 O_(10)-GO hybrid exhibits higher current density, a more positive onset potential(-0.15 V vs. Hg/HgO) in comparison with LaSr_3 Fe_3 O_(10).The value of the overall transferred electrons for both catalysts implies a dominant two electron process for ORR. Both catalysts under alkalic conditions exhibit a two-step Tafel slope, suggesting a change in the reaction mechanism for ORR. The composite electrode exhibits a higher ORR current density, but inferior durability performances in relative to the LaSr_3 Fe_3 O_(10) electrode.  相似文献   
99.
We deal with the mathematical model of the incremental degradation of the internal coating (e.g. a polymeric material) of a metallic pipe in which a fluid flows relatively fast. The fluid drags solid impurities so that longitudinal scratches, inaccessible to any direct inspection procedure, are produced on the coating. Time evolution of this kind of defects can be reconstructed from the knowledge of a sequence of temperature maps of the external surface. The time-varying orthogonal section of this damaged interface is determined as a function of time and polar angle through the identification of a suitable effective heat transfer coefficient by means of Thin Plate Approximation.  相似文献   
100.
Strength of Materials - The paper addresses the investigation of high-strain rate compressive behavior of Al foams subjected to impact at the intermediate striking velocity ranged from 40 to...  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