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   34325篇
  免费   2412篇
  国内免费   1251篇
电工技术   1576篇
技术理论   1篇
综合类   1980篇
化学工业   6115篇
金属工艺   1611篇
机械仪表   1934篇
建筑科学   3085篇
矿业工程   643篇
能源动力   1069篇
轻工业   2098篇
水利工程   505篇
石油天然气   1875篇
武器工业   218篇
无线电   4185篇
一般工业技术   4459篇
冶金工业   1852篇
原子能技术   436篇
自动化技术   4346篇
  2024年   136篇
  2023年   487篇
  2022年   843篇
  2021年   1171篇
  2020年   901篇
  2019年   770篇
  2018年   836篇
  2017年   996篇
  2016年   896篇
  2015年   1148篇
  2014年   1490篇
  2013年   1921篇
  2012年   2006篇
  2011年   2182篇
  2010年   1834篇
  2009年   1825篇
  2008年   1789篇
  2007年   1751篇
  2006年   1799篇
  2005年   1622篇
  2004年   1113篇
  2003年   1004篇
  2002年   994篇
  2001年   837篇
  2000年   919篇
  1999年   992篇
  1998年   978篇
  1997年   789篇
  1996年   788篇
  1995年   648篇
  1994年   506篇
  1993年   458篇
  1992年   320篇
  1991年   233篇
  1990年   237篇
  1989年   165篇
  1988年   138篇
  1987年   94篇
  1986年   78篇
  1985年   56篇
  1984年   48篇
  1983年   34篇
  1982年   32篇
  1981年   20篇
  1980年   19篇
  1979年   10篇
  1977年   10篇
  1976年   12篇
  1973年   8篇
  1970年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
A reconfigurable FACTS system for university laboratories   总被引:1,自引:0,他引:1  
To fully understand the dynamic performance of the multiple flexible ac transmission systems (FACTS) devices, a hardware setup is needed to complement software simulation for university research laboratories. This paper presents the schematic and basic controls of a reconfigurable FACTS system that can be used to realize the major voltage-sourced-converter FACTS topologies: the StatCom, the static synchronous series compensator (SSSC), and the unified power-flow controller (UPFC). Furthermore, the state models and control algorithms for the FACTS devices are proposed. The digital signal processor (DSP)-based control system enables new control methods to be rapidly implemented. The comparison of the experimental and simulation results is also provided to verify the proposed controls. The paper culminates in a list of suggested experiments appropriate for an elective/graduate course in electric power systems.  相似文献   
112.
Polycrystalline samples LaBa2Cu3?xCo x O y (0 ≤ x ≤ 1.0) were synthesized by solid state reaction method. The structure, phonon vibration, conduction, and spin correlation were investigated by means of X-ray diffraction, infrared spectra, resistivity, and electron spin resonance. It is found that there are orthorhombic–tetragonal and tetragonal–orthorhombic structural transitions with Co doping, and the conduction behavior changes from metallic to semiconducting. With the increase of Co content, the Cu(1)—O(1) phonon mode around 531 cm?1 softens, the Cu(2)—O(2) phonon mode around 657 cm?1 hardens, and the Cu(1)—O(4) mode around 583 cm?1 is nearly unchanged. The Cu2+ spins tend to localize with Co doping. The changes in structure, phonon vibration, and spin correlation with Co doping are analyzed and discussed.  相似文献   
113.
114.
The magnetic liquid was prepared with ferric salt by inorganic gel technology. The effect of the doped rare earth elements on the properties of magnetic particles was analyzed. The magnetic liquid was composed with clay mineral into magnetic mineral composites. The crystal structure and micro-morphology of the nanoparticles were studied by XRD and TEM. The results show that the crystal structure of the magnetic particles doped 0.5 % of lanthanum is more complete, and the magnetic response capability is higher with doping agent. At the same time, the possibility of the clay mineral magnetic composites as the carrier of target drug was probed.  相似文献   
115.
Fluxing agents of zinc borate, antimony oxide, galss frit A and glass frit B, with different melting or softening point temperatures, were added into MgO-Al2O3-SiO2/boron phenol formaldehyde resin (MAS/BPF) composites to lower the formation temperature of eutectic liquid phase and promote the ceramification of ceramifiable composites. The effects of fluxing agents on the thermogravimetric properties, phase evolution, and microstructure evolution of MAS / BPF composites were characterized by TG-DSC, XRD and SEM analyses. The results reveal that the addition of a fluxing agent highly reduces the decomposition rate of MAS / BPF composites. Fluxing agents lower the formation temperatures of liquid phases of ceramifiable MAS / BPF composites obviously, and then promote the ceramification and densification process. The final residues of composites are ceramic surrounded by large amount of glass phases.  相似文献   
116.
本文研究了两个系列的热塑型聚氨酯—聚醚酯氨(ET)和聚酯氨酯(ES)的结构形态与相分离程度,提出了一种确定硬段含量(W_h)的IR方法。与NMR法、投料比法比较,三者得到非常吻合的结果。此外本文还研究了W_h、M_(n·■)、拉伸及热历史对相分离程度的影响。  相似文献   
117.
本工作测定了不同温度下硫酸高铈与对二甲苯反应的速率常数及表观活化能Ea= 111.5kJ·m ol- 1。在动力学测定的的基础上确定了此反应的速率方程为d[PTAL]/dt= k[PX][Ce(IV)]  相似文献   
118.
提供了人工神经网络的一种算法-误差反向传播算法的数学推导方法及上机实现步骤.  相似文献   
119.
本文介绍6例在苏联切尔诺贝利核电站事故期间受到放射性铯内污染的我国驻外人员,在本实验室接受活体测量和服用普鲁士蓝促排的观察结果。6例内污染者分两组分别于受污染后的第114天和第272天开始用药,在大约一个月期间,每人共服药54g(给药方式:每次服1g,每日3次,6天为一个疗程,间隔6天,共用药3个疗程)。观测结果表明,在促排期间,6例内污染者体内铯的生物半排期均明显缩短,~(131)Cs 的生物半排期由对照期(用药前)的54—123d 缩短到28—65d,~(134)Cs 由对照期的42—117d 缩短到23—69d;6例体内放射性铯的累积活度相对于同期未用药条件下的累积活度减少2—21%。  相似文献   
120.
ICF target quality control in the laser fusion program is vital to ensure that the energy deposition from the lasers results in uniform compression and minimization of Rayleigh–Taylor instabilities, which requires surface finishes on the order of submicron-scale. During target fabrication process the surface finish and the dimensions of the hohlraum need be well controlled. Density variations and nonspherical or nonconcentric shells might be produced. Scanning transmission ion microscopy computed tomography (STIM-CT) is able to reconstruct the three-dimensional quantitative structure of ICF targets a few tens of micrometers in size. Compared to other types of probe techniques, the main advantage of STIM-CT is that quantitative information about mass density and sphericity can be obtained directly and non-destructively, utilizing specific reconstruction codes. We present a case of ICF target (composed of polyvinyl alcohol) characterization by STIM-CT in order to demonstrate the STIM-CT potential impact in assessing target fabrication processes.  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