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   50246篇
  免费   4659篇
  国内免费   2333篇
电工技术   2850篇
技术理论   2篇
综合类   3422篇
化学工业   8735篇
金属工艺   2792篇
机械仪表   2813篇
建筑科学   3850篇
矿业工程   1381篇
能源动力   1252篇
轻工业   4230篇
水利工程   905篇
石油天然气   3017篇
武器工业   368篇
无线电   6029篇
一般工业技术   5916篇
冶金工业   2148篇
原子能技术   598篇
自动化技术   6930篇
  2024年   302篇
  2023年   970篇
  2022年   1735篇
  2021年   2467篇
  2020年   1885篇
  2019年   1495篇
  2018年   1645篇
  2017年   1904篇
  2016年   1647篇
  2015年   2225篇
  2014年   2749篇
  2013年   3337篇
  2012年   3389篇
  2011年   3724篇
  2010年   3124篇
  2009年   2740篇
  2008年   2673篇
  2007年   2448篇
  2006年   2525篇
  2005年   2145篇
  2004年   1424篇
  2003年   1210篇
  2002年   1137篇
  2001年   1006篇
  2000年   1025篇
  1999年   1133篇
  1998年   852篇
  1997年   772篇
  1996年   737篇
  1995年   608篇
  1994年   499篇
  1993年   383篇
  1992年   283篇
  1991年   218篇
  1990年   170篇
  1989年   158篇
  1988年   128篇
  1987年   88篇
  1986年   61篇
  1985年   32篇
  1984年   21篇
  1983年   26篇
  1982年   34篇
  1981年   22篇
  1980年   22篇
  1979年   12篇
  1977年   11篇
  1976年   7篇
  1975年   5篇
  1959年   5篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
31.
电动车制动能量再生反馈控制研究   总被引:7,自引:0,他引:7  
研究了电动汽车制动过程中的能量回馈,设计了混合励磁无刷电动机在汽车制动过程的能量再生反馈控制系统。以脉宽调制调压调速系统为例,研究各种制动态下的能量回馈过程。并将其安装在EV6600电动汽车上进行试验,结果表明:该控制系统可达到10%左右的能量回收效率。  相似文献   
32.
A series of phosphorus‐containing, wholly aromatic thermotropic copolyesters from acetylated 2‐(6‐oxide‐6H‐dibenz〈c,e〉〈1,2〉oxa phosphorin‐6‐yl)‐1,4‐dihydroxy phenylene, p‐acetoxybenzoic acid, terephthalic acid, and isophthalic acid were prepared by melting polycondensation. The structure and basic properties of the polymers, such as the glass‐transition temperature (Tg), melting temperature (Tm), thermal stability, crystallinity, and liquid crystallinity, were investigated with Fourier transform infrared, elemental analysis, differential scanning calorimetry (DSC), thermogravimetric analysis, wide‐angle X‐ray diffraction, and hot‐stage polarizing optical microscopy. The copolyesters had relatively high Tg values ranging from 183 to 192°C. The Tm values obtained from DSC curves for samples P‐20 and P‐25 were 290 and 287°C, respectively (where the number in the sample name indicates the molar fraction of the phosphorus‐containing monomer in the reactants). The initial flow temperatures of other samples observed with hot‐stage polarizing microscopy were 271–290°C. The 5% degradation temperatures in nitrogen ranged from 431 to 462°C, and the char yields at 640°C were 41–52%. All the copolyesters, except P‐40, were thermotropic and nematic. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1278–1284, 2002  相似文献   
33.
初步探索了SO_4~2-/ZrO2固体超强酸的失活机理.并着重研究了催化剂的两种再生方法:灼烧法和溶剂洗涤法。催化剂主要是因结焦而失活,高温灼烧能基本恢复催化剂原有活性.且再生效果与灼烧温度有关。溶剂洗涤法有一定的再生能力,但不显著.  相似文献   
34.
Gas phase propylene epoxidation on gold catalysts has attracted wide attention from industry and academia due to its high selectivity. However, it suffers from low propylene conversion and rapid catalyst deactivation. Experiments showed that propylene conversion could be increased by raising H2, O2, or C3H6 concentration in the feed, but the feed compositions were within the explosion limit. It was also shown that the activity of the used catalyst could be fully recovered, but the regeneration temperature was 280 °C, much higher than that for reaction. Therefore a microchannel reactor was devised to suppress explosion and was constructed with Fecralloy, to raise the temperature rapidly for catalyst regeneration by electric heating. In two minutes the temperature of the reactor could be raised from 50 to 300 °C. Catalysts were coated on the alloy belt by dip coating, and the performance of the reactor was evaluated under different operating conditions. Results showed that in the microreactor the overall reaction rate was controlled mainly by the intrinsic reaction rate, and also influenced by film diffusion to a certain extent. The deactivated catalyst was regenerated in the microchannel reactor and the activity was fully recovered.  相似文献   
35.
罗奎 《化肥工业》2002,29(5):20-23
介绍了改良MEA脱碳技术的基本原理、工艺特点以及在工业中的应用情况,实践表明,改良MEA提高了溶液的吸收能力,降低了再生热耗,解决了MEA易降解损耗等问题。  相似文献   
36.
本文提出了确定化工用搅拌器搅拌时间的一种简单试验方法,并用正交表安排寻找最佳搅拌参数的试验和整理试验数据,得到了有实用价值的结果。  相似文献   
37.
α,ω‐Dihydroxy‐polydimethylsiloxane/polystyrene (PDMS/PS) blends were prepared by the solution polymerization of styrene (St) in the presence of α,ω ‐dihydroxy‐polydimethylsiloxane (PDMS), using toluene as solvent and benzoyl peroxide (BPO) as initiator. The PDMS/PS blends obtained by this method are a series of stable, white gums, which were vulcanized to elastomers at room temperature with methyl‐triethoxysilicane (MTES). The use level of MTES was far more than the necessary amount used to end‐link hydroxy‐terminated chains of PDMS, with the excess being hydrolyzed to crosslinked networks, which were similar to SiO2 and acted as filler. Investigations were carried out on the elastomeric materials by extraction measurement, swelling measurement, and scanning electron microscopy. The extraction data show that at each composition the amount of soluble fraction is less than expected and the difference between experimental and theoretical values becomes more and more significant as PS content increases. This is mainly due to the grafting of PS onto PDMS and the entanglement of PS in the interpenetrating polymer network (IPN), which consists of either directly linked PDMS chains or chains linked via PS grafts and is formed by free radical crosslinking of PDMS during the radical polymerization of St. PS grafted on PDMS is insoluble and PS entangled in the IPN is difficult to extract. Both render the soluble fraction to be less than expected. As the St content in preparing PDMS/PS blends increases, the probability of grafting PS onto PDMS also increases, which may subsequently produce a higher crosslinking level of PDMS networks that linked via PS grafts by radical crosslinking. As a result, not only the amount of insoluble PS increases but also PS entangled in the IPN is more difficult to extract. Scanning electron microscopy demonstrates that the elastomer system has a microphase‐separated structure and a certain amount of PS remains in the PDMS networks after extraction, which is in accordance with the extraction data. Moreover, the mechanical properties of the elastormeric materials have been studied in detail. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3542–3548, 2004  相似文献   
38.
为了保证广角摄像机在现代机器人视觉定位应用中的准确性,以广角摄像机像素坐标的反畸变过程为研究对象,提出一种在畸变对应表的基础上使用中心迭代法以及区域插值法确定物体实际位置的方法。通过实验证明了该方法能够测量物体的位置,其精度能够满足工业使用要求。  相似文献   
39.
本文是在10kg/h固体热载体干馏实验装置上用扎赉诺尔褐煤制取高炉喷吹料和中热值煤气的研究结果。在干馏温度450℃~650℃范围制得煤气110Nm3/t~400Nm3/t,煤气热值为14.7MJ/Nm3~17.5MJ/Nm3,属中热值煤气。可供民用,也可用于补充钢铁企业燃气不足,平衡能源。得低温焦油2%~9%,可加工成化工产品和燃料油。半焦可用于高炉喷吹。  相似文献   
40.
现阶段地球物理三维勘探面临越来越复杂的问题,其要求更精细的三维网格剖分,现有的一些方法随着网格节点的增加其收敛速度相应减慢。对于应用中更复杂实际模型、更细密网格剖分以及更快收敛速度要求,难于有进一步提高。要有所突破,需借助计算数学最新进展,引入新的高效算法。多重网格法是近二十年迅速发展的一种求解微分方程近乎最优的新算法。本文首先简单介绍了多重网格法基本原理和运算格式,着重介绍了当前国内外多重网格法在地球物理正反演中的应用成果和发展现状。此外,对多重网格法在地球物理正反演中的应用前景及发展趋势进行了展望。  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