全文获取类型
收费全文 | 40323篇 |
免费 | 2646篇 |
国内免费 | 1639篇 |
专业分类
电工技术 | 4333篇 |
技术理论 | 1篇 |
综合类 | 2657篇 |
化学工业 | 4110篇 |
金属工艺 | 3528篇 |
机械仪表 | 4536篇 |
建筑科学 | 1908篇 |
矿业工程 | 2080篇 |
能源动力 | 2544篇 |
轻工业 | 1922篇 |
水利工程 | 478篇 |
石油天然气 | 1524篇 |
武器工业 | 465篇 |
无线电 | 3691篇 |
一般工业技术 | 3745篇 |
冶金工业 | 2373篇 |
原子能技术 | 642篇 |
自动化技术 | 4071篇 |
出版年
2024年 | 130篇 |
2023年 | 454篇 |
2022年 | 838篇 |
2021年 | 1042篇 |
2020年 | 1087篇 |
2019年 | 862篇 |
2018年 | 923篇 |
2017年 | 1167篇 |
2016年 | 1253篇 |
2015年 | 1371篇 |
2014年 | 2383篇 |
2013年 | 2159篇 |
2012年 | 2613篇 |
2011年 | 3245篇 |
2010年 | 2201篇 |
2009年 | 2224篇 |
2008年 | 2070篇 |
2007年 | 2491篇 |
2006年 | 2350篇 |
2005年 | 2072篇 |
2004年 | 1650篇 |
2003年 | 1608篇 |
2002年 | 1348篇 |
2001年 | 1245篇 |
2000年 | 1084篇 |
1999年 | 980篇 |
1998年 | 728篇 |
1997年 | 672篇 |
1996年 | 528篇 |
1995年 | 453篇 |
1994年 | 350篇 |
1993年 | 208篇 |
1992年 | 193篇 |
1991年 | 133篇 |
1990年 | 98篇 |
1989年 | 125篇 |
1988年 | 81篇 |
1987年 | 48篇 |
1986年 | 34篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1975年 | 4篇 |
1973年 | 6篇 |
1964年 | 3篇 |
1962年 | 5篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Lithium-ion batteries are becoming more and more important not only for portable electronic devices, but also in prevision of high power electric vehicles. In such an optic, deep studies regarding all the components of a secondary battery are in development. In this study, high voltage cathode materials have been selected. Crystals with spinel structure have a 3D vacancy pathway suitable for Li-ions transport. The material under study was LiNi0.5Mn1.5O4 doped with magnesium replacing the nickel. Various samples were synthesized via three different routes: a solid-state method, a modified sol–gel method and a xerogel method. The structure and morphology of the powders were analyzed with HRTEM and XRD. Electrochemical tests were also performed. A wide range of particle sizes (from micro to nanosize) was the result of the different synthesis routes. Unfortunately pure materials were not always obtained. The electrochemical tests showed improvement of the material's cyclability, by reducing the particle size. The electrochemical tests further confirmed the existence of a Li1+dMn2−dO4 impurity. The results are quite promising, however, further improvement of the purity of the electrode composition are needed. 相似文献
53.
简要介绍了自复中电/机调速器的机械和电气原理,并就使用该调速器的机组在生产运行中容易出现的停机后导叶开度漂移、停机时导叶不能完全关闭和显示开度与实际开度不一致等主要问题,通过修改可编程逻辑控制器(PLC)程序、调节调零杆位置、修改PLC程序参数等方法进行解决,这些方法对同类水电厂处理类似问题有借鉴作用。 相似文献
54.
The Karlsruhe Tritium Neutrino experiment (KATRIN) is going to use a very large electro-static tandem spectrometer to measure the electron spectrum from the tritium beta decay, where several kilometers of non-evaporable getter (NEG) strips (type ST707) are to be used to achieve the UHV requirements. Different geometrical configurations of the NEG strips have been studied by Monte Carlo simulations. It is shown that the resulting pumping speed of the getter pumps will allow to get a pressure below 10−11 mbar in the huge vessel with a volume of 1400 m3. By systematic assessment of the statistics of the pumping surfaces, it could be demonstrated that the design is sound. 相似文献
55.
56.
57.
在每一周期的开始时的速度值V1预设定到传动装置上进行速度预控制,同时,反馈回来的实际值Sj与S1进行比较计算,得出当时偏差值△S,此偏差值△S乘以比例系数Ksp,得到Vk叠加在Vt上,得出传动装置应具有的速度控制信号V,然后V经速度/电压变换和D/A转换向传动系统的速度控制发出控制信号Uα控制执行机构的定位。调节Ksp的值使系统无超调无振荡。 相似文献
58.
随着设备高速化的日益发展,传统的螺杆设计方法及相应的供送特性评价体系已显落后。参照蜗型凸轮动力学性能的评价方法,建立了高速供送螺杆的动态性能评价体系,为高速化供送螺杆的设计提供了性能参照指标。 相似文献
59.
A novel fluorinated bis(ether amine) monomer, 2,3-bis(4-amino-2-trifluoromethylphenoxy)naphthalene, was prepared through the nucleophilic aromatic substitution reaction of 2-chloro-5-nitrobenzotrifluoride and 2,3-dihydroxynaphthalene in the presence of potassium carbonate, followed by catalytic reduction with hydrazine and Pd/C. A series of new fluorine-containing polyimides having inherent viscosities of 0.54 to 1.10 dl/g were synthesized from the diamine with various commercially available aromatic dianhydrides using a standard two-stage process with thermal imidization of poly(amic acid) films. These polyimides were highly soluble in a variety of organic solvents, and most of them afforded transparent, light-colored, and tough films with good tensile strengths. These polyimides exhibited glass transition temperatures (Tgs) of 247-300 °C and showed no significant decomposition below 500 °C under either nitrogen or air atmosphere. Except for the polyimide derived from pyromellitic dianhydride, the polyimide films were almost colorless, with an ultraviolet-visible absorption cutoff wavelength below 400 nm and low b∗ values (a yellowness index) of 10.7-41.9. These polyimides had dielectric constants of 3.09 to 3.65 (1 MHz) and moisture absorptions in the range of 0.2-0.3 wt%. 相似文献
60.
概述污水处理厂的一般工艺,简单介绍了风机、水泵等的节能特点,介绍了变频调速装置在污水处理厂各处理工段的应用。 相似文献