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   113888篇
  免费   8862篇
  国内免费   4434篇
电工技术   6029篇
技术理论   11篇
综合类   6771篇
化学工业   19343篇
金属工艺   6077篇
机械仪表   6832篇
建筑科学   8856篇
矿业工程   3183篇
能源动力   3156篇
轻工业   6720篇
水利工程   1800篇
石油天然气   6410篇
武器工业   731篇
无线电   14176篇
一般工业技术   14606篇
冶金工业   6007篇
原子能技术   1280篇
自动化技术   15196篇
  2024年   442篇
  2023年   1804篇
  2022年   3001篇
  2021年   4121篇
  2020年   3155篇
  2019年   2671篇
  2018年   3101篇
  2017年   3499篇
  2016年   3041篇
  2015年   4011篇
  2014年   5039篇
  2013年   6454篇
  2012年   6762篇
  2011年   7407篇
  2010年   6395篇
  2009年   6328篇
  2008年   6290篇
  2007年   5858篇
  2006年   6182篇
  2005年   5510篇
  2004年   3759篇
  2003年   3257篇
  2002年   2901篇
  2001年   2806篇
  2000年   2913篇
  1999年   3439篇
  1998年   2953篇
  1997年   2570篇
  1996年   2300篇
  1995年   1939篇
  1994年   1564篇
  1993年   1228篇
  1992年   971篇
  1991年   743篇
  1990年   604篇
  1989年   504篇
  1988年   390篇
  1987年   299篇
  1986年   207篇
  1985年   176篇
  1984年   108篇
  1983年   81篇
  1982年   87篇
  1981年   58篇
  1980年   48篇
  1979年   35篇
  1978年   25篇
  1977年   25篇
  1976年   40篇
  1973年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
User Modeling and User-Adapted Interaction - Personality plays a pivotal role at work. Many scholars have investigated the association between personality and language usage habits in the English...  相似文献   
105.
The Caputo and Caputo–Fabrizio derivative are applied to study a second‐grade nanofluid over a vertical plate. A comparative analysis is presented to study the unsteady free convection of a second‐grade nanofluid with a new time–space fractional heat conduction. The governing equations with mixed time–space fractional derivatives are non‐dimensionalized and solved numerically, and a comparison between the Caputo and the Caputo–Fabrizio models is made. It is found that the temperature is higher for the Caputo–Fabrizio fractional model than the Caputo model, but the higher velocity only exists near the vertical plate for the Caputo–Fabrizio model than the Caputo model. Moreover, the velocity for the Caputo model will exceed the Caputo–Fabrizio model as y evolves.  相似文献   
106.
Abstract

The reabsorption characteristics of the lignite treated by low and high temperature drying process were addressed in the paper. The information about the moisture form, functional groups, effective water-filled porosities and equilibrium moisture content of the lignite before and after the drying process was investigated using Differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and a self-made reabsorption device, respectively. The results show that the low drying temperature (140, 190, 230?°C, 10?min, N2) has little impact on the effective water-filled porosities of the resulted samples, whereas it has a great influence on the main oxygen-containing functional groups, which amount firstly decreases and then increases with the drying temperature increasing. In the case of the lignite samples dried under high-temperature (600, 700, 800?°C, 30?s, N2), the amount of the effective water-filled porosity of the sample decreases and the amount of oxygen-containing functional groups increases as the temperature increasing. The reabsorption capability of the high temperature dried sample is much lower than that of the sample treated under low drying temperature. The reabsorption characteristics of the low-temperature dried samples are affected by the amount of the oxygen-containing functional groups, while the effective water-filled porosity is main factor for the lignite samples derived from high temperature drying process. Moreover, the work gives a good evidence that the high-temperature drying process is an effective choose for lignite upgrading.  相似文献   
107.
108.
从今年3月初以来,钢材市场行情呈现明显恢复性上扬态势。据中国钢铁工业协会财务资产部和冶金价格信息中心发布的钢材价格指数,5月15日-5月19日板材平均已恢复到110.34点,比去年末上升17.92点,价格恢复性上涨19.38%,但比去年5月份的146.1点仍低24.5%;长材价格指数略有同升,在94.37点,比去年末只回升3.56点,价格只恢复性上涨3.92%,比去年5月份的102.19点仍低7.65。掘国家统计局数据,一季度全国规模以上工业企业销售收入同比增长25.3%,实现利润同比增长21.3%,但钢铁企业由于去年下半年价格大幅度下降,今年一季度钢协会员企业(钢产量占全国81.8%)销售收入同比下降5.18%,实现利润同比下降  相似文献   
109.
A tunable dual-band quadrature hybrid coupler for mobile GSM bands (900 and 1800MHz) is proposed and characterized. The structure is composed of four quarter-wavelength sections at a frequency located between the two operating frequencies and two pairs of open-ended stubs. Frequency tuning is achieved by modifying the electrical length of the open-ended stubs with varactor-diode capacitors. A dual-band tunability of 33% and 10% is obtained for the first and the second bands, respectively  相似文献   
110.
The homogenization of Ni in powder metal (PM) steel compacts is usually difficult even after high-temperature sintering at 1250°C. An earlier study by the authors demonstrated that this problem can be alleviated through the addition of 0.5 wt pct Cr in the form of stainless steel powders. To further improve the microstructure and mechanical properties of Ni-containing PM steels and to understand the mechanisms, an attempt was made in this study using the Fe-3Cr-0.5Mo prealloyed powder as the base material. The results showed that the distribution of the Ni additives was significantly improved. As a result, the tensile strength of the Fe-3Cr-0.5Mo-4Ni-0.5C compact sintered at 1250°C reached 1323 MPa. The elongation was higher than 1 pct. These sinter-hardened properties, which were attained using a slow furnace cooling rate, were comparable to those of the sinter-hardened alloys reported in the literature using accelerated cooling and were equivalent to those of the best quenched-and-tempered alloys registered in the Metal Powder Industries Federation (MPIF) standards. These improvements were attributed to the positive effect of Cr addition on alloy homogenization due to the reduction of the repelling effect between Ni and C, as was demonstrated through the thermodynamic analysis using the Thermo-Calc program.  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