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   259799篇
  免费   3601篇
  国内免费   818篇
电工技术   5130篇
综合类   328篇
化学工业   37060篇
金属工艺   10253篇
机械仪表   8488篇
建筑科学   6118篇
矿业工程   1076篇
能源动力   6396篇
轻工业   22876篇
水利工程   2560篇
石油天然气   3906篇
武器工业   68篇
无线电   34753篇
一般工业技术   50172篇
冶金工业   46597篇
原子能技术   5425篇
自动化技术   23012篇
  2021年   2033篇
  2019年   2044篇
  2018年   3472篇
  2017年   3538篇
  2016年   3739篇
  2015年   2319篇
  2014年   4057篇
  2013年   11299篇
  2012年   6578篇
  2011年   8901篇
  2010年   7000篇
  2009年   7870篇
  2008年   8703篇
  2007年   8631篇
  2006年   7825篇
  2005年   7152篇
  2004年   6900篇
  2003年   6738篇
  2002年   6377篇
  2001年   6475篇
  2000年   6175篇
  1999年   6261篇
  1998年   14263篇
  1997年   10281篇
  1996年   8123篇
  1995年   6421篇
  1994年   5716篇
  1993年   5591篇
  1992年   4557篇
  1991年   4212篇
  1990年   4053篇
  1989年   3782篇
  1988年   3626篇
  1987年   3172篇
  1986年   3067篇
  1985年   3613篇
  1984年   3383篇
  1983年   3031篇
  1982年   2850篇
  1981年   2951篇
  1980年   2763篇
  1979年   2650篇
  1978年   2503篇
  1977年   2948篇
  1976年   3558篇
  1975年   2316篇
  1974年   2313篇
  1973年   2318篇
  1972年   1849篇
  1971年   1745篇
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
101.
102.
103.
Processing lithium-ion battery (LIB) electrode dispersions with water as the solvent during primary drying offers many advantages over N-methylpyrrolidone (NMP). An in-depth analysis of the comparative drying costs of LIB electrodes is discussed for both NMP- and water-based dispersion processing in terms of battery pack $/kWh. Electrode coating manufacturing and capital equipment cost savings are compared for water vs. conventional NMP organic solvent processing. A major finding of this work is that the total electrode manufacturing costs, whether water- or NMP-based, contribute about 8–9% of the total pack cost. However, it was found that up to a 2?×?reduction in electrode processing (drying and solvent recovery) cost can be expected along with a $3–6?M savings in associated plant capital equipment (for a plant producing 100,000 10-kWh Plug-in Hybrid Electric Vehicle (PHEV) batteries) using water as the electrode solvent. This paper shows a different perspective in that the most important benefits of aqueous electrode processing actually revolve around capital equipment savings and environmental stewardship and not processing cost savings.  相似文献   
104.
The molten salt method was used to synthesise the MAX phase compounds Ti2AlC and Ti3AlC2 from elemental powders. Between 900–1000?°C, Ti2AlC was formed alongside ancillary phases TiC and TiAl, which decreased in abundance with increasing synthesis temperature. Changing the stoichiometry and increasing the synthesis temperature to 1300?°C resulted in formation of Ti3AlC2 alongside Ti2AlC and TiC. The type of salt flux used had little effect on the product formation. The reaction pathway for Ti2AlC was determined to be the initial formation of TiC1-x templating on the graphite and titanium aluminides.  相似文献   
105.
A novel glass-ceramic material based on albite type Na-rich feldspar has been synthesized by conventional ceramic process. High crystallinity, >94%?Vol.% is obtained by fast sintering which allows energy saving processing. Albite is the main crystalline phase and tetragonal SiO2 is a secondary phase. Electrical properties were examined by complex impedance, DC measurements, and dielectric breakdown test. Dielectric characterization shows a non-Debye type dielectric behavior with low dielectric constant, 4.6 at 1?MHz, low dielectric losses, (~10?3 at 1?MHz, and a large dielectric strength, ~60?kV/mm), that it is the largest value reported in ceramic insulators. Those dielectric properties are attained by the low glassy phase content in the samples and their unique micro-nanostructure. All these properties make this novel material a very promising candidate in the market of ceramic electrical insulator, highlighting for high-voltage applications.  相似文献   
106.
Russian Engineering Research - The theoretically possible reconfigurable parallel mechanisms are classified, in terms of the layout of guides on the base. Formulas are derived for the...  相似文献   
107.
108.
109.
110.
This study addresses the thermo‐diffusion and the diffusion‐thermo phenomena in a semi‐infinite absorbent channel whose walls are contracting/expanding, with heat source/sink effects. The governing partial differential equations with suitable boundary conditions are transformed to a system of dimensionless ordinary differential equations. An analytic solution of the problem has been found using a technique called homotopy analysis method (HAM). HAM gives consistently valid answers to the problem over an extensive variety of parameters and also provides better accuracy. To validate the analytical results, a comparison has been presented with a numerical solution calculated by using the parallel shooting method. The effects of dimensionless parameters, that is, deformation parameter, Reynolds number, Soret and Dufour numbers, and heat source/sink parameter on the expressions of velocity, temperature, and concentration profiles are analyzed graphically to understand the physics of the deformable channel. It has been noted that the velocity across the channel is higher for the expanding channel, as compared to that for the contracting channel. Also the Soret and Dufour number increases the temperature of the fluid, and decreases the concentration. The temperature profile has an increasing behavior in the case of heat source, and a decreasing behavior in the case of heat sink.  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