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   6408篇
  免费   502篇
  国内免费   112篇
电工技术   256篇
综合类   203篇
化学工业   1083篇
金属工艺   207篇
机械仪表   243篇
建筑科学   386篇
矿业工程   49篇
能源动力   320篇
轻工业   502篇
水利工程   97篇
石油天然气   177篇
武器工业   4篇
无线电   810篇
一般工业技术   1018篇
冶金工业   442篇
原子能技术   23篇
自动化技术   1202篇
  2024年   11篇
  2023年   101篇
  2022年   152篇
  2021年   230篇
  2020年   184篇
  2019年   197篇
  2018年   226篇
  2017年   216篇
  2016年   249篇
  2015年   226篇
  2014年   255篇
  2013年   482篇
  2012年   383篇
  2011年   510篇
  2010年   385篇
  2009年   394篇
  2008年   314篇
  2007年   271篇
  2006年   281篇
  2005年   217篇
  2004年   158篇
  2003年   177篇
  2002年   231篇
  2001年   162篇
  2000年   121篇
  1999年   85篇
  1998年   131篇
  1997年   87篇
  1996年   78篇
  1995年   74篇
  1994年   61篇
  1993年   49篇
  1992年   34篇
  1991年   14篇
  1990年   18篇
  1989年   14篇
  1988年   22篇
  1987年   21篇
  1986年   15篇
  1985年   15篇
  1984年   28篇
  1983年   15篇
  1982年   14篇
  1981年   12篇
  1980年   13篇
  1979年   11篇
  1978年   11篇
  1977年   12篇
  1976年   18篇
  1975年   8篇
排序方式: 共有7022条查询结果,搜索用时 359 毫秒
991.
Clean Technologies and Environmental Policy - In this paper, an optimal sizing of a grid-connected PV system to accommodate the load demands of a public building (i.e., Faculty of Sciences and...  相似文献   
992.
镍镀层具有较好的耐蚀性和耐磨性,单纯的镍镀层易存在孔隙、晶粒粗大等缺陷,在镀镍时加入少量稀土元素可以显著提高镀层的性能.为此,通过改变电镀液成分和电流密度,在Q235基底上电镀形成一系列NiCoCe合金层,通过浸泡试验及电化学试验评价表面处理前后耐蚀性能的变化.结果 表明:添加0~0.4 g/L Ce元素可以通过细化晶粒有效增强镀层的耐蚀性,当电流密度小于0.04 A/cm2时,电流密度的增加可以使镀层中的晶粒细化,提高镀层的致密性和耐腐蚀性.当Ce元素的添加量为0.4 g/L,电流密度为0.03 A/cm2,电镀温度为50℃时,试验效果最佳.  相似文献   
993.
This paper describes the reversible chemical locking of sypiropyran switches bound to metallic surfaces to enable the encoding of nonvolatile information. Data are encoded spatially by selectively locking the spiropyran moieties in their merocyanine form using a combination of exposure to acid and UV light. Without exposure to acid, the merocyanine form spontaneously converts back to the spiropyran form. Bits are resolved by defining the regions of the monolayer that are exposed to acid, using a “soft punchcard” fabricated from a silicone elastomer. Information is read by measuring the tunneling charge–transport through the monolayer using eutectic Ga–In top‐contacts. The merocyanine form is more than three orders of magnitude more conductive than the spiropyran form, allowing the differentiation of bits. Photoelectron spectroscopy shows that the monolayers are undamaged by exposure to light, acid, base, and applied bias, enabling proof‐of‐concept devices in which an 8‐bit ASCII encoded six‐character string is written, erased, and rewritten.  相似文献   
994.
Ma  Ben  Huang  Xiao  Liu  Zhaofeng  Tian  Xiaohui  Zhou  Yingke 《Journal of Materials Science》2022,57(4):2857-2869
Journal of Materials Science - The LiNi0.6Co0.2Mn0.2O2 (NCM) cathode material is highly potential for the wide application in lithium-ion batteries due to its moderate cost and high specific...  相似文献   
995.
Jaouali  M.  Nouiri  M.  Ihzaz  N.  Sagna  A.  Mejnoun  K.  Zouaoui  M.  Bouloufa  A.  El Haskouri  J.  Djessas  K.  El Mir  L.  Ayadi  Z. Ben 《Journal of Materials Science: Materials in Electronics》2022,33(26):20867-20883

This work aims to highlight the beneficial effect of annealing of Cu2ZnSn(S,Se)4 (CZTSSe) nanoparticles (NPs) on the properties of the obtained films by RF-magnetron sputtering at room temperature (RT) and at 200 °C. The CZTSSe targets used for the deposition are obtained using nanoparticles synthesized by solvothermal technique. It is denoted that the elemental composition of thin films becomes independent of the growth temperature in the case of annealed CZTSSe NPs. The optical investigation gives that the gap energy is ranging between 1.26 and 1.40 eV with an Urbach’s energy between 100 and 200 meV. By using the Wemple and Didominico model to analyze the refractive index spectra, we have identified common oscillator energy for all CZTSSe thin films and dispersion energy ranging from 2.63 to 5.81 eV. CZTSSe thin films obtained by means of annealed NPs exhibit higher dielectric constant and refractive index. The dispersion of different parameters with experimental conditions is analyzed via a common relationship that illustrates the linear dependence of n0, Ed, εs, and εL on the square of the valence difference (ΔZ). The conductivity spectra are deduced, and a theoretical model was identified to fit the permittivity spectra. The obtained results are promising for solar cell applications.

  相似文献   
996.
The accurate evaluation of electrical energy demanded by a CNC toolpath during a machining process is essential to determine its efficiency. Actually, the dynamic behavior of cutting forces seems to be neglected by investigators despite its influence on the consumed cutting energy during a face milling operation. This paper aims to investigate the effect of dynamic behavior of the machining system in order to take into account the dynamic response of the cutting forces on the axis feed power prediction. A dynamic cutting power model is developed in order to predict the consumed cutting energy. A parametric study is performed in order to show the impact of cutting conditions on the consumed energy values. The numerical results are compared to experimental ones.  相似文献   
997.
Nonlinear optical microscopy has become a powerful tool in bioimaging research due to its unique capabilities of deep optical sectioning, high‐spatial‐resolution imaging, and 3D reconstruction of biological specimens. Developing organic fluorescent probes with strong nonlinear optical effects, in particular third‐harmonic generation (THG), is promising for exploiting nonlinear microscopic imaging for biomedical applications. Herein, a simple method for preparing organic nanocrystals based on an aggregation‐induced emission (AIE) luminogen (DCCN) with bright near‐infrared emission is successfully demonstrated. Aggregation‐induced nonlinear optical effects, including two‐photon fluorescence (2PF), three‐photon fluorescence (3PF), and THG, of DCCN are observed in nanoparticles, especially for crystalline nanoparticles. The nanocrystals of DCCN are successfully applied for 2PF microscopy at 1040 nm NIR‐II excitation and THG microscopy at 1560 nm NIR‐II excitation, respectively, to reconstruct the 3D vasculature of the mouse cerebral vasculature. Impressively, the THG microscopy provides much higher spatial resolution and brightness than the 2PF microscopy and can visualize small vessels with diameters of ≈2.7 µm at the deepest depth of 800 µm in a mouse brain. Thus, this is expected to inspire new insights into the development of advanced AIE materials with multiple nonlinearity, in particular THG, for multimodal nonlinear optical microscopy.  相似文献   
998.
李琴  陈奔  黄志强  何磊  李刚 《材料保护》2019,52(4):66-72
为得到轨道与埋地管道并行情况下杂散电流对管道电腐蚀的影响规律,建立了基于电路原理和电力系统接地极理论的双边供电直流电车杂散电流对管地电位干扰模型,并求得了轨道电位和管地电位的分布变化函数以及杂散电流泄漏量分布函数。采用MATLAB进行了数值模拟,得到了杂散电流泄露规律及其对管地电位干扰规律,并对管道防腐蚀层单破损点、双破损点情况下管道的电腐蚀规律进行了分析。结果表明:轨道杂散电流泄露量与轨道电位大小成正比,降低轨道电阻可减小杂散电流泄露量。防腐蚀层单破损点不易产生腐蚀,双破损点导致局部腐蚀较严重,且变电站附近的点腐蚀严重。因此,应重点监测保护变电站处下方管道以减少产生多破损点的概率。  相似文献   
999.
BACKGROUND: Scabies is not a notifiable disease in most countries. Thus, the reported rates of the disease in large populations are usually inaccurate and based on estimations. Scabies is usually reported only when large outbreaks occur. OBJECTIVE: This article describes the global epidemiology of scabies in the Israel Defense Force. The data used in this study are based on the routine and mandatory reporting of every individual case of scabies to the Army Health Branch Epidemiology Department since 1968. RESULTS: There was a period of 13 years of quiescence from the implementation of reporting in 1968 until 1981. This period was followed by an epidemic of 15 years, peaking in 1985 and 1986, and returning to the baseline rates of the quiescent period by 1996. This prospectively observed pattern of at least 13 years of quiescence followed by a peak of 15 years is consistent with other, mostly retrospective, reports. Although the peak may have been triggered by the "Lebanon" war of 1982, it is noticeable that no peak was observed during the "Yom Kippur" war (1973). CONCLUSIONS: Prospective, mandatory reporting of the kind described here should help to better understand the epidemiology of scabies.  相似文献   
1000.
协同开发技术是进行控制系统软件开发的重要方法, 其中的软件集成部署是协同开发技术的重要一环. 随着软件规模越来越大, 复杂性越来越高, 现有的软件集成部署方法由于缺乏标准统一的部署规范和安全机制, 所以会存在集成部署效率低下和安全性较差的问题. 针对上述问题, 提出了一种基于度量认证的协同集成部署方法, 解决在分布式协同开发环境下集成部署工作带来的安全和效率问题. 本文的主要思想是利用一种安全关联协议, 在软件部署双方之间建立可信的安全传输通道, 继而根据统一的打包部署规范, 完成软件的集成和部署工作. 理论分析和实验结果表明, 该方案统一了软件打包部署规范, 优化了完整性度量算法, 减少了认证和软件部署的时间, 并且由于部署双方在准备阶段已建立了安全关联, 所以提高了整个软件部署过程的安全性. 本文的研究内容能够在分布式开发环境下完成安全且高效的软件集成部署工作.  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