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   18266篇
  免费   2631篇
  国内免费   874篇
电工技术   1119篇
技术理论   3篇
综合类   897篇
化学工业   6077篇
金属工艺   1376篇
机械仪表   726篇
建筑科学   541篇
矿业工程   352篇
能源动力   1080篇
轻工业   322篇
水利工程   86篇
石油天然气   744篇
武器工业   106篇
无线电   1585篇
一般工业技术   2184篇
冶金工业   956篇
原子能技术   138篇
自动化技术   3479篇
  2024年   68篇
  2023年   407篇
  2022年   357篇
  2021年   524篇
  2020年   684篇
  2019年   791篇
  2018年   722篇
  2017年   764篇
  2016年   851篇
  2015年   834篇
  2014年   994篇
  2013年   1135篇
  2012年   1023篇
  2011年   1087篇
  2010年   823篇
  2009年   893篇
  2008年   888篇
  2007年   1084篇
  2006年   958篇
  2005年   928篇
  2004年   744篇
  2003年   762篇
  2002年   826篇
  2001年   818篇
  2000年   631篇
  1999年   481篇
  1998年   351篇
  1997年   216篇
  1996年   284篇
  1995年   160篇
  1994年   140篇
  1993年   117篇
  1992年   93篇
  1991年   76篇
  1990年   57篇
  1989年   40篇
  1988年   26篇
  1987年   15篇
  1986年   14篇
  1985年   15篇
  1984年   30篇
  1983年   17篇
  1982年   20篇
  1981年   3篇
  1978年   2篇
  1977年   1篇
  1975年   7篇
  1974年   4篇
  1958年   1篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
采用化学共沉淀法作为钴蓝颜料的制备方法,探讨了主要工艺因素对制备钴蓝颜料性能的影响,对制备的样品进行了测试与表征。结果表明:Co2+和Al3+物质的量比为1∶2.5时,制备的钴蓝样品颜色饱和度与明度最高,沉淀剂为尿素时制得的样品的粒度最小,粒度分布比较均匀。前驱体的洗涤过程采取水洗加醇洗的方法可有效减少样品的硬团聚现象,且前驱体的最佳煅烧温度为950℃左右。  相似文献   
72.
The technical characters of mobile agent (MA) originated in the distributional artificial intelligence domain is introduced. A network management construction based on agent (NMCA) is then proposed. The NMCA structure features are elaborated in detail. A prototype design of NMCA is given by using the jKQML programming. The establishment of NMCA platform will be helpful to reduce the correspondence load of network management and improves the efficiency and the expansion ability of network management systems.  相似文献   
73.
This study examined partner violence in the year before and the year after individually based, outpatient alcoholism treatment for 301 married or cohabiting male alcoholic patients and used a demographically matched nonalcoholic comparison sample. In the year before treatment, 56% of the alcoholic patients had been violent toward their female partner, 4 times the rate of 14% in the comparison sample. In the year after treatment, violence decreased significantly to 25% of the alcoholic sample but remained higher than in the comparison group. Among remitted alcoholics after treatment, violence prevalence of 15% was nearly identical to the comparison sample and half the rate among relapsed patients (32%). Thus, partner violence decreased after alcoholism treatment, and clinically significant violence reductions occurred for patients whose alcoholism was remitted after treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
74.
Modified (α‐diimine)nickel(II) catalysts are suitable for ethylene oligomerization reactions. Due to the mechanism (“chain running”), the formation of double‐bond isomers and branched olefins can be observed. The obtained oligomer mixtures show a Schulz–Flory distribution. Increasing ethylene pressure favors the selectivity of α‐olefin formation. The same effect can be observed when Lewis bases like thiophene or furane are added to the oligomerization reaction mixture. These results can be related to an interaction of the additives with the catalytic active species during the oligomerization process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1356–1361, 2003  相似文献   
75.
Polyester‐based polyurethane/nano‐silica composites were obtained via in situ polymerization and investigated by Fourier‐transform infrared spectroscopy (FTIR), or FTIR coupled with attenuated total reflectance (FTIR‐ATR), Transmission electron microscopy (TEM), atomic force microscopy (AFM), an Instron testing machine, dynamic mechanical analysis (DMA) and ultraviolet‐visible spectrophotometry (UV‐vis). FTIR analysis showed that in situ polymerization provoked some chemical reactions between polyester molecules and nano‐silica particles. FTIR‐ATR, TEM and AFM analyses showed that both surface and interface contained nano‐silica particles. Instron testing and DMA data showed that introducing nano‐silica particles into polyurethane enhanced the hardness, glass temperature and adhesion strength of polyurethane to the substrate, but also increased the resin viscosity. UV‐vis spectrophotometry showed that nano‐silica obtained by the fumed method did not shield UV radiation in polyurethane films. Copyright © 2003 Society of Chemical Industry  相似文献   
76.
硅表面上的纳米量子点的自组织生长   总被引:1,自引:1,他引:0  
纳米半导体量子点以其所具有的新颖光电性质与输运特性正在受到人们普遍重视。作为制备高质量纳米量子点的工艺技术 ,自组织生长方法倍受材料物理学家的青睐。而如何制备尺寸大小与密度分布可控的纳米量子点更为人们所注目。因为这是关系到纳米量子点最终能否器件实用化的关键。文中以此为主线 ,着重介绍了各种 Si表面 ,如常规表面、氧化表面、台阶表面以及吸附表面上 ,不同纳米量子点的自组织生长及其形成机理 ,并展望了其未来发展前景  相似文献   
77.
Alumina-supported vanadium oxide, VOx/Al2O3, and binary vanadium–antimony oxides, VSbOx/Al2O3, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by SBET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO2 pulse methods. VSbOx/Al2O3 exhibited enhanced catalytic activity and especially on-stream stability compared to VOx/Al2O3 catalyst. Incorporation of antimony into VOx/Al2O3 increased dispersion of active VOx species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V0.43Sb0.57Ox/Al2O3 system.  相似文献   
78.
Phase equilibria in the Ta-Co-O and Nb-Co-O systems have been studied at 1200°C at oxygen partial pressures from 10−0.68 to 10−13.50 atm for the former and from 10−0.68 to 10−13.30 atm for the latter. In both systems, M2CoO6 and M2Co4O9 are stable ternary compounds under the experimental conditions, and a new phase, Nb5Co2O14, has been identified. The Ta-Co-O system is simple, whereas the Nb-Co-O system is somewhat more complicated because of the extra phase. The lattice constants of the ternary compounds have been determined and compared with previous values. The standard Gibbs energies of reactions have been determined using oxygen partial pressures in equilibrium with three solid phases.  相似文献   
79.
研究了杂多酸催化无水乙醇和环氧乙烷(EO)制备乙醇乙醚的醚化反应,考察了不同种类的杂多酸以及醚化反应工艺条件对反应活性和选择性的影响.结果表明,PW_(12)催化剂的反应活性高、反应温度低、选择性好,当用PW_(12)作催化剂,乙醇与环氧化乙烷之比为3.0(mol),反应温度45℃,反应时间1h时,转化率和选择性均超过97%.  相似文献   
80.
XANES of vanadium and niobium oxide on silica or alumina have been analyzed quantitatively by a deconvolution technique. Based on the results for reference compounds, local structures of supported vanadium and niobium species were identified. The composition was estimated from difference spectra for the samples which consisted of two kinds of species.  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