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   27530篇
  免费   3383篇
  国内免费   2107篇
电工技术   2072篇
综合类   3333篇
化学工业   3817篇
金属工艺   1432篇
机械仪表   2052篇
建筑科学   4002篇
矿业工程   1072篇
能源动力   1463篇
轻工业   872篇
水利工程   1666篇
石油天然气   1200篇
武器工业   329篇
无线电   2388篇
一般工业技术   2895篇
冶金工业   825篇
原子能技术   636篇
自动化技术   2966篇
  2024年   98篇
  2023年   370篇
  2022年   725篇
  2021年   793篇
  2020年   919篇
  2019年   816篇
  2018年   771篇
  2017年   1078篇
  2016年   1080篇
  2015年   1162篇
  2014年   1580篇
  2013年   1864篇
  2012年   2099篇
  2011年   2115篇
  2010年   1601篇
  2009年   1681篇
  2008年   1659篇
  2007年   1926篇
  2006年   1646篇
  2005年   1407篇
  2004年   1164篇
  2003年   954篇
  2002年   841篇
  2001年   723篇
  2000年   644篇
  1999年   524篇
  1998年   436篇
  1997年   399篇
  1996年   343篇
  1995年   307篇
  1994年   262篇
  1993年   179篇
  1992年   170篇
  1991年   142篇
  1990年   142篇
  1989年   108篇
  1988年   78篇
  1987年   48篇
  1986年   38篇
  1985年   33篇
  1984年   22篇
  1983年   8篇
  1982年   17篇
  1981年   9篇
  1980年   14篇
  1979年   4篇
  1976年   3篇
  1975年   4篇
  1959年   3篇
  1951年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
对某底层为架空层的教学楼进行了底层柱顶隔震设计和动力响应分析。时程分析表明:在7度(0.15g)中震下,减震系数为0.36,减震效果明显,上部结构可以降低半度设计;底层的柱子按8度(0.20g)罕遇地震作用下受到的内力进行强度设计,分析表明底层柱子具有足够的刚度和强度。  相似文献   
994.
《国际计算机数学杂志》2012,89(7):1321-1333
In this study, we investigate the consistency of half supervised coefficient regularization learning with indefinite kernels. In our setting, the hypothesis space and learning algorithms are based on two different groups of input data which are drawn i.i.d. according to an unknown probability measure ρ X . The only conditions imposed on the kernel function are the continuity and boundedness instead of a Mercer kernel and the output data are not asked to be bounded uniformly. By a mild assumption of unbounded output data and a refined integral operator technique, the generalization error is decomposed into hypothesis error, sample error and approximation error. By estimating these three parts, we deduce satisfactory learning rates with proper choice of the regularization parameter.  相似文献   
995.
本文首先介绍了真空玻璃平板光伏构件,然后根据相关标准测试该种构件的光学物理性能,最后分析该种构件在全国各气候分区的应用适宜性。  相似文献   
996.
Source rocks generate and expel hydrocarbon with thermal evolution, which lead to a decrease of total organic carbon (TOC) content. A new quantitative model for original total organic carbon (TOCo) content evolution and recovery was proposed, and then was used to the carbonate source rocks with different TOCs (CSRDTOC) in the Tazhong area, Tarim Basin, China. Studies showed that the higher the TOC of source rocks, the bigger the range of TOC reduction and recovery coefficient. When vitrinite reflectance (VR) is equal to 2.5%, recovery coefficients of TOCo = 0.2%, 0.4%, and 1.0% are 1.43, 1.66, and 2.01, respectively. It must restore TOCo when we evaluate source rocks at the stage of high overmaturity and predict oil and gas resources.  相似文献   
997.
In order to implement process analytical technology in beer manufacturing, an ultrasound‐based in‐line sensor was developed which is capable to determine sound velocity and density via the multiple reflection method. Based on a systematic study of the ternary system water–maltose–ethanol, two models were established to estimate the critical process parameters: sugar and ethanol mass fraction. The sound velocity‐based model showed unreasonable high errors although temperature variations and deviations due to dissolved CO2 were corrected. In contrast, the sound velocity–density–temperature model provided an average root mean square error of 0.53%g/g sugar and 0.26%g/g ethanol content for the main fermentation. Method, sensor and model showed the capability to capture the process signature which may be related to product and process quality.  相似文献   
998.
The multiphase microstructure and properties of low carbon steel by IQ&PB process under different partitioning temperatures and time were studied by means of SEM, EPMA, XRD and tensile testing. Results show that the microstructures of experimental steel consist of ferrite, bainite and retained austenite. With the increase of the holding time in two- phase region, the C and Mn contents apparently increase in martensite which transformed from austenite, and C and Mn content are 1. 47 times and 1. 16 times than average value of the base. With the decrease of the quenching and partitioning temperature, the volume fraction of the bainite increases, the microstructure is refined, and the content of M/A islands increases. With the temperature and time increased, the volume fraction of retained austenite at room temperature increases, the tensile strength decreases, the total elongation increases, and work hardening behavior occurrs continuously. When the partitioning time is 30min and the partitioning temperature is 400??, the tensile strength of the steel is 1107MPa, the elongation is 24%, the product of strength and elongation reaches above 26568MPa??%.  相似文献   
999.
中国不少地方政府采取BT模式建设公共项目,但许多BT项目最终并未取得成功,因此有必要对BT项目关键成功因素进行研究。首先梳理BT项目实施流程及工作内容,结合BT项目成功标准,初步归纳影响BT项目成功的关键因素,然后用问卷调查方法对初步关键成功因素进行修正和确认,得到关键成功因素清单,然后扩大问卷调查范围确定各关键成功因素的重要性,并对重要性的调查结果从整体和按角色进行对比分析,所得结果对BT项目中的业主、实施方、监理等各参与方都有借鉴作用。  相似文献   
1000.
Electrolyte effects on the oxygen surface exchange coefficients of strontium-doped lanthanum manganates (LSM) are investigated using electrical conductivity relaxation technique. Introducing electrolytes can significantly reduce the re-equilibration time, demonstrating the substantial promotion in the surface exchange kinetics. The coefficient at 1000 °C increases from 9.00 × 10−5 cm s−1 for pure LSM to 2.45 × 10−4 cm s−1 for LSM coated with yttria-stabilized zirconia, and further increases to 7.92 × 10−4 cm s−1 for LSM with samaria-doped ceria. The nearly one order of magnitude increase in the coefficient demonstrates that introducing electrolytes can effectively increase the electrochemical performance of solid-oxide-fuel-cell cathodes by enhancing the surface exchange reaction in addition to extending the reaction sites.  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