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   26836篇
  免费   3232篇
  国内免费   1883篇
电工技术   864篇
综合类   1410篇
化学工业   7479篇
金属工艺   5055篇
机械仪表   1314篇
建筑科学   692篇
矿业工程   639篇
能源动力   817篇
轻工业   1381篇
水利工程   193篇
石油天然气   629篇
武器工业   108篇
无线电   2171篇
一般工业技术   5239篇
冶金工业   2388篇
原子能技术   1307篇
自动化技术   265篇
  2024年   145篇
  2023年   479篇
  2022年   805篇
  2021年   944篇
  2020年   1141篇
  2019年   1067篇
  2018年   1023篇
  2017年   1189篇
  2016年   1083篇
  2015年   1075篇
  2014年   1471篇
  2013年   1594篇
  2012年   1763篇
  2011年   1889篇
  2010年   1348篇
  2009年   1417篇
  2008年   1161篇
  2007年   1665篇
  2006年   1603篇
  2005年   1388篇
  2004年   1237篇
  2003年   1051篇
  2002年   895篇
  2001年   769篇
  2000年   652篇
  1999年   500篇
  1998年   413篇
  1997年   330篇
  1996年   327篇
  1995年   240篇
  1994年   256篇
  1993年   159篇
  1992年   177篇
  1991年   132篇
  1990年   118篇
  1989年   93篇
  1988年   75篇
  1987年   52篇
  1986年   63篇
  1985年   33篇
  1984年   31篇
  1983年   21篇
  1982年   25篇
  1981年   15篇
  1980年   8篇
  1978年   5篇
  1976年   5篇
  1974年   4篇
  1959年   4篇
  1951年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
大庆蜡油在酸性催化剂上反应机理的研究   总被引:11,自引:5,他引:6  
以大庆蜡油为原料,采用两种不同类型的催化剂,在流化床反应器实验装鬣上进行催化裂化反应。结果表明,大庆蜡油在酸性催化剂上反应所产生的干气组成与高烯烃催化裂化汽油相同,干气的产生主要是单分子裂化反应所造成的。从干气产率、组成以及液化气组成可以看出,大庆蜡油在不同类型的催化剂上明显地表现出裂化反应类型的差异。  相似文献   
152.
为了保证进口精对苯二甲酸装置氧化反应器中钛制搅拌器的正常工作,对钛制搅拌器桨叶在运行中断裂脱落的原因进行了分析,并叙述了桨叶修理的方法和要求。经修理后的桨叶投入生产使用,达到了预期的目标。  相似文献   
153.
Chemical shrinkage was used for the in situ measurement of the progressing chemical stabilization reactions and the influence of ozone during the stabilization of polyacrylonitrile. A method for evaluating the activation energy through the sensitivity temperature is presented. The calculated results show that the activation energies were 161.57 kJ/mol in air and 181.23 kJ/mol in ozone-enriched air. Therefore, the chemical reactions were postponed during stabilization in ozone-enriched air. Ozone seemed to act in three ways: first, ozone promoted the formation of the serious skin–core structure. Second, ozone accelerated the chemical reactions and shortened the stabilization time at lower heating rates. Third, ozone postponed the chemical reactions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008  相似文献   
154.
A novel mixed‐mode expanded bed adsorbent with anion‐exchange properties was explored with benzylamine as the functional ligand. The cellulose composite matrix, densified with stainless steel powder, was prepared with the method of water‐in‐oil suspension thermal regeneration. High activation levels of the cellulose matrix were obtained with allyl bromide because of the relative inertness of the allyl group under the conditions of the activation reaction. After the formation of the bromohydrin with N‐bromosuccinimide and coupling with benzylamine, the activated matrix was derived to function as a mixed‐mode adsorbent containing both hydrophobic and ionic groups. The protein adsorption capacity was investigated with bovine serum albumin as a model protein. The results indicated that the prepared adsorbent could bind bovine serum albumin with a high adsorption capacity, and it showed salt tolerance. Effective desorption was achieved by a pH adjustment across the isoelectric point of the protein. The interactions between the cell and adsorbent were studied, and the bioadhesion was shielded by the adjustment of the salt concentration above 0.1M. Stable fluidization in the expanded bed was obtained even in a 2% (dry weight) yeast suspension. The direct capture of target proteins from a biomass‐containing feedstock without extra dilution steps could be expected with the mixed‐mode adsorbent prepared in this work, and this would be especially appropriate for expanded bed adsorption applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   
155.
We have reported an electro‐active paper actuator from regenerated cellulose. After dissolving cellulose fibers with a solution of lithium chloride in N,N‐dimethylacetamide, cellulose was regenerated by combining distillation of cellulose solution along with washing with the mixture of deionized water, isopropyl alcohol, and running water. However, the effect of Li+ ions on structure, properties, and the actuation behavior of the actuator was not studied. This article describes the changes in these parameters when the Li+ ions are removed by subjecting it to different running water exposure time. The structure and properties of cellulose electro‐active paper and its actuation behavior were studied. As Li+ ions content reduced from 4354.17 to 10.26 ppm by increasing the exposure time of running water, crystallinity, Young's modulus, and bending displacement decreased. Details about the investigation have been explained. This elimination of ions is important to increase the piezoelectric effect in EAPap by decreasing the ion migration effect. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008  相似文献   
156.
杨谢军  甄月平 《冶金动力》2003,(6):44-45,48
介绍了WOODWARD505电液控制器原理、功能及在包钢热电厂汽轮鼓风机控制系统的成功应用,大大改善了汽轮机的调节控制品质。  相似文献   
157.
钛硅分子筛催化环己酮氨肟化反应过程--本征动力学   总被引:2,自引:0,他引:2  
对钛硅分子筛(HTS)催化环己酮氨肟化反应本征动力学进行了研究。利用经验方程拟合了试验数据,并采用Marquardt算法对经验方程的参数进行确定,获得了不同试验条件下的反应初速率,然后再用高斯-牛顿法对本征动力学模型进行了参数估计,得出了氨肟化反应以及该反应体系中H2O2分解的本征动力学。并对该模型进行了残差分析和F检验,对氨肟化反应和H2O2分解的动力学模型的计算值与试验值进行了比较,获得相对误差绝对值的平均值分别为5.21%和6.25%。表明该模型能真实反映HTS催化环己酮氨肟化的反应特性,是合理可靠的,能为进一步的过程开发与工程设计提供一些理论上的指导和设计上的依据;而H2O2分解副反应动力学模型仅适用于该反应体系。  相似文献   
158.
纳米掺钼二氧化钛光催化剂研究发展   总被引:1,自引:0,他引:1  
张文钲 《中国钼业》2003,27(3):22-25
介绍了纳米掺钼二氧化钛光催化剂的制备、特性及应用  相似文献   
159.
Fabrication of Ormocer Containing Eu3+ Ion and Their Optical Spectra   总被引:5,自引:0,他引:5  
Eu3 ions were incorporated in sol and gel by a sol-gel processing using 3-glycidoxypropyltrimethoxysilane(CH2OCHCH2O(CH2)3Si(OCH3)3, GPTMS) and ethyl silicate (TEOS) as precursors. The basic chemical-physical properties such as DTA curve, FF-IR spectra and specific surface area were recorded. The characteristics of their optical spectra were measured and investigated. The results indicate that the emission intensity of Eu3 ion in ormocer is much higher and the global line width is wider than those in SiO2 gel. The relationship between the composition and structure of gels and the fluorescence intensity and width were discussed. The obtained ormocer shows good mechanical strength, which can be cut and polished in machine without broken.  相似文献   
160.
总结了电渣 2 0Mn1A钢从电炉冶炼到电渣重熔钢中铝、钛及主要成分的变化情况 ,为该钢的生产提供了控制成分的依据  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