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   115122篇
  免费   10061篇
  国内免费   5510篇
电工技术   7042篇
技术理论   13篇
综合类   8120篇
化学工业   19279篇
金属工艺   6256篇
机械仪表   7155篇
建筑科学   9761篇
矿业工程   3401篇
能源动力   3557篇
轻工业   7893篇
水利工程   2218篇
石油天然气   6897篇
武器工业   990篇
无线电   13014篇
一般工业技术   13716篇
冶金工业   5253篇
原子能技术   1303篇
自动化技术   14825篇
  2024年   494篇
  2023年   2016篇
  2022年   3526篇
  2021年   4858篇
  2020年   3649篇
  2019年   3122篇
  2018年   3461篇
  2017年   3867篇
  2016年   3493篇
  2015年   4560篇
  2014年   5874篇
  2013年   6818篇
  2012年   7623篇
  2011年   8007篇
  2010年   7287篇
  2009年   6926篇
  2008年   6747篇
  2007年   6267篇
  2006年   6306篇
  2005年   5251篇
  2004年   3658篇
  2003年   3190篇
  2002年   3050篇
  2001年   2829篇
  2000年   2726篇
  1999年   2867篇
  1998年   2206篇
  1997年   1854篇
  1996年   1699篇
  1995年   1432篇
  1994年   1219篇
  1993年   862篇
  1992年   708篇
  1991年   529篇
  1990年   453篇
  1989年   347篇
  1988年   252篇
  1987年   165篇
  1986年   147篇
  1985年   92篇
  1984年   64篇
  1983年   43篇
  1982年   50篇
  1981年   35篇
  1980年   30篇
  1979年   10篇
  1976年   3篇
  1970年   2篇
  1959年   4篇
  1951年   8篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
当今纳米科学技术飞速发展,其中纳米管已构成了纳米材料的一个非常重要的类别。本文介绍近几年来由化学键结合的纳米管以及由分子间力形成的一些纳米或具有中观尺度的管状结构材料的合成研究进展。  相似文献   
92.
利用本地瓷石和厂内废料代替河北邢台碱、长石和部分石英生产卫生瓷,可降低产品烧成温度,提高产品质量。  相似文献   
93.
The thermal stability of seven organically modified montmorillonites (‘organoclays’) has been investigated using differential thermal analysis, differential scanning calorimetry, and thermogravimetry in conjunction with X-ray diffractometry. Six organoclays were synthesised by replacing the interlayer inorganic cations, initially present, with quaternary phosphonium and ammonium surfactant cations. The samples modified with tetrabutylphosphonium (TBP), and butyltriphenylphosphonium (BTPP) ions have an appreciably higher thermal stability than the octadecyltrimethylammonium (ODTMA)-modified clays. Thus, in the case of TBP- and BTPP-modified montmorillonites, the onset temperature of decomposition is close to 300 °C. Samples modified with hexadecyltributylphosphonium (HDTBP) ions have a lower onset temperature of decomposition of 225 °C. In comparison, the onset temperature for ODTMA-montmorillonites (obtained at different concentrations of ODTMA-bromide) ranges from 158 to 222 °C, being highest where the concentration of intercalated surfactant is lowest. The onset temperature for a commercial alkylsilane-treated quaternary ammonium-modified organoclay (S-BEN N-400FP) is 207 °C. The basal spacing of the TBP- and BTPP-modified clays is 1.7–1.8 nm, indicating a monolayer arrangement of quaternary phosphonium ions in the interlayer space, while the value of 2.5 nm for HDTBP-montmorillonite indicates a more open structure. The ODTMA-modified samples have basal spacings ranging from 1.9 to 2.1 nm, indicative of a bilayer to pseudo-trilayer arrangement. The exceptionally high basal spacing of 3.4 nm for the S-BEN N-400FP organoclay might be due to interlayer penetration of organosilane hydrolysis products during synthesis. The thermal properties of organoclays are apparently related to the nature of the surfactants and their arrangement in the interlayer space of montmorillonite.  相似文献   
94.
Zhang  Weiwei  Zhao  Hongyong  Sha  Chunlin  Wang  Yuan 《Neural Processing Letters》2021,53(5):3607-3618
Neural Processing Letters - In this article, the finite time (FT) synchronization problem of fractional order quaternion valued neural networks with time delay is investigated. Without separating...  相似文献   
95.
International Journal of Control, Automation and Systems - The reinforcement learning problem of complex action control in multiplayer online battlefield games has brought considerable interest in...  相似文献   
96.
Uncertainties existing in the acoustic metamaterial may strongly affect its unusual properties. Aiming at this actuality, the interval model is introduced to treat with uncertainties existing in the acoustic metamaterial with Helmholtz resonators. Frequency intervals in which the sound intensity transmission coefficients are certainly less than the required value and the effective bulk moduli are certainly negative are defined as conservative approximations. Frequency intervals in which the sound intensity transmission coefficients may be less than the required value and the effective bulk moduli may be negative are defined as unsafe approximations. The proportion of the conservative approximation and the unsafe approximation is defined as an approximate precision. Based on the quantification of uncertainties of the sound intensity transmission coefficients and the negative effective bulk moduli, an optimization model for the interval acoustic metamaterial with Helmholtz resonators is constructed. Numerical results showed that even suffering from effects of interval parameters, unusual properties of the optimized acoustic metamaterial (such as the bandgap of the sound transmission and the negative effective bulk modulus) could be improved.  相似文献   
97.
残疾人通常根据其政治、经济、精神和社会保障等利益需要进行利益表达。当残疾人的利益表达机制不完善、缺乏利益表达意识、社会利益输出不平衡等因素造成制度化利益表达受阻,残疾人只能无奈地选择非常规的、非制度化利益表达方式。通过健全残疾人社会保障服务体系、保证残疾人制度化利益表达渠道畅通、引导残疾人合理运用网络新媒体进行利益表达,是规避由非制度化利益表达造成的社会不和谐因子的有效途径。  相似文献   
98.
The applicability of the rapid iodide migration test was systematically studied. Comparative experimental tests of different test conditions, including several external voltages, test durations, concrete ages and mixing proportions, were carried out to make clear the transport behaviors of iodide under parallel electric fields. Numerical simulations were also done using the finite element method to found the correlation between chloride and iodide transport behaviors. The test and numerical results show that the chloride transport behaviors of RIM and RCM tests have a good correlation under the several conditions used in the present paper. Moreover, the influence of external conditions (external voltages, test durations) on the test results is small. Thus, it can be concluded that the RIM method is available to determine the chloride penetration resistance of the chloride-eroded structural concrete.  相似文献   
99.
根据城市居民对供水的可靠性、稳定性、经济节能性的需求,课题组提出了一种基于"双储"模式的供水系统,并按照本市德胜住宅小区的供水要求,设计了一套由储水池、气压罐、变频器、多台水泵机组等主要设备构成的全自动变频恒压供水系统.经过近半年的运行测试,系统有效地解决了传统供水方式中存在的问题,增强了系统的总体性能,有明显的节能效果.  相似文献   
100.
Cheng  Jiaqi  Gong  Junyi  Yue  Shuai  Jiang  Yao  Hou  Xiangjun  Ma  Jianjun  Yao  Yali  Jiang  Cairong 《Journal of Applied Electrochemistry》2021,51(8):1175-1188
Journal of Applied Electrochemistry - La-doped titanate materials have been widely investigated as alternative Ni-free anodes for solid oxide fuel cells (SOFCs). In this study, La0.4Sr0.6TiO3 (LST)...  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