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   101422篇
  免费   6997篇
  国内免费   2843篇
电工技术   4282篇
技术理论   6篇
综合类   4459篇
化学工业   18960篇
金属工艺   5079篇
机械仪表   6404篇
建筑科学   5726篇
矿业工程   2413篇
能源动力   3318篇
轻工业   7140篇
水利工程   1121篇
石油天然气   5299篇
武器工业   461篇
无线电   12263篇
一般工业技术   15390篇
冶金工业   6006篇
原子能技术   1089篇
自动化技术   11846篇
  2024年   328篇
  2023年   1608篇
  2022年   2625篇
  2021年   3788篇
  2020年   2816篇
  2019年   2592篇
  2018年   3156篇
  2017年   3369篇
  2016年   3098篇
  2015年   3502篇
  2014年   4659篇
  2013年   6027篇
  2012年   6205篇
  2011年   7197篇
  2010年   5862篇
  2009年   5639篇
  2008年   5352篇
  2007年   4906篇
  2006年   4847篇
  2005年   4328篇
  2004年   3111篇
  2003年   2831篇
  2002年   2568篇
  2001年   2272篇
  2000年   2358篇
  1999年   2577篇
  1998年   2667篇
  1997年   1957篇
  1996年   1889篇
  1995年   1493篇
  1994年   1182篇
  1993年   911篇
  1992年   688篇
  1991年   545篇
  1990年   419篇
  1989年   362篇
  1988年   313篇
  1987年   215篇
  1986年   186篇
  1985年   146篇
  1984年   112篇
  1983年   79篇
  1982年   77篇
  1981年   62篇
  1980年   61篇
  1979年   32篇
  1977年   36篇
  1976年   50篇
  1975年   24篇
  1974年   22篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
文章采用模糊规划的方法证明了期望放出体在放矿中的合理性,从而使放矿这个复杂的过程能方便地采用数学手段来处理。同时说明了如何在崩落法矿山利用期望体来解决实际生产中的放矿问题。  相似文献   
102.
Dongsheng Tang  Lianfeng Sun  Weiya Zhou 《Carbon》2005,43(13):2812-2816
By investigating the morphologies and microstructures of the cathode deposits prepared by self-sustained arc discharge between graphite rods, we consider that there are two electron emission mechanisms occurring on the cathode: field emission and thermionic emission. The former occurs mainly on the edge of the growing surface, by which we can explain the formation of the outer hard shell of the cathode deposit; while the latter occurs mainly on the growing surface except for the edge area and it is the main cause for the growth of carbon nanotubes.  相似文献   
103.
When priorities to message streams are assigned using Rate Monotonic (RM) for a Controller Area Network (CAN), the utilization bound is known to be about 25% for CAN 2.0A and 29% for CAN 2.0B. In this letter, we present a higher utilization bound than the existing ones with a reasonable constraint. The new utilization bounds are approximately 34% for CAN 2.0A and 41% for CAN 2.0B if no single message stream's utilization exceeds 46% or 27% of the total utilization for CAN 2.0A or CAN 2.0B, respectively.  相似文献   
104.
105.
Semi-annual cycles of the sea-surface temperature (SST) in the East/Japan Sea (EJS) and their forcings were examined by analysing National Oceanic and Atmospheric Administration/Advanced Very-High-Resolution Radiometer data, scatterometer wind vectors, and heat flux data. The semi-annual cycle contributed to the total variance of the SST by 8% and amounted to 25% of the amplitudes of the annual SST cycle, particularly in the Tatarskiy Strait and along the continental shelf off Russia. The lowest phase, corresponding to the minimum SST, occurred during early November and 6 months earlier in May or June depending on the position. The forcings of the semi-annual cycle were not semi-annual but substantially annual with a lag of 6 months, which gave rise to SST cooling in spring and autumn. Our analyses illustrated that SST cooling in autumn was caused by direct, local atmospheric wind forcings, whereas the cooling with large amplitudes of the semi-annual cycle in spring was caused by the non-local, remotely forced cold water advection of the Liman Current associated with sea-ice melting in the Tatarskiy Strait. The phase lag of 1–2 months between the complete melting of the sea ice in the Tatarskiy Strait and the surface cooling along the Russian continental shelf was related to the advection of cold water from sea ice in the form of the Liman Cold Current. The semi-annual cycle also resulted from asymmetry of the time series of the SST due to a long cold winter and a short warm summer. To understand how SST curves are distorted and asymmetric, we suggested two mathematical parameters of kurtosis and skewness. In addition, we suggest that the ratio of the semi-annual amplitude to the annual amplitude of SST harmonics can be used as a typical indicator of the asymmetry in year-to-year SST variations.  相似文献   
106.
填充母料及其他常用塑料母料   总被引:1,自引:0,他引:1  
塑料母料对推动塑料工业的迅猛发展起了很大作用,其主要特点是:可以简化生产工艺过程:原料混合方便,混炼质量均匀,提高生产效率及制品性能指标;减少粉尘飞扬及对设备的磨损;降低制品在换色时清洗螺杆的用料量;延长原料储存的保质期等。  相似文献   
107.
As a result of developments in spectrophotometry, together with improved accuracy in computer colour matching and laboratory dyeing, non–physical standards (reflectance data) can now be used for the successful communication, matching and quality control of colour. In colour palette generation, ‘matching by numbers’ has become a reality.  相似文献   
108.
Adsorption and desorption characteristics of the 2-methyl-4-chlorophenoxyacetic acid (MCPA) from aqueous solution onto the activated carbon (GAC, F-400) were studied. Adsorption equilibrium capacities of the MCPA increased with decreasing pH and temperature of the solution. Adsorption equilibrium of the MCPA could be represented by the Sips equation. The internal diffusion coefficients were determined by comparing the experimental concentration decay curves with those predicted from surface diffusion model and pore diffusion model. The adsorption model based on the linear driving force approximation (LDFA) was used for simulating the adsorption behavior of the MCPA in a fixed bed. Over ninety five percent desorption of the MCPA could be obtained using distilled water.  相似文献   
109.
Micron‐sized polymer particles were coated with layers of nickel compounds by plating electrolessly in the presence of aqueous solutions of nickel chloride, sodium hypophosphite, sodium citrate, and ammonium chloride at elevated temperature. The uniform functional polymer particle could be obtained by seeded polymerization. To investigate the effect of surface functionality on the conditions for nickel deposition, the polymer particle was functionalized with the thiol group. From morphological observation, it was found that the mode of nickel deposition was greatly dependent on the surface functionality of the polymer particle. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 420–424, 2003  相似文献   
110.
Nano-sized silicon carbide (SiC) powder was prepared by thermal plasma process using silicon tetrachloride (SiCl4) and methane (CH4). The synthesized powder was characterized by X-ray diffraction pattern, scanning electron microscopy, transmission electron microscopy, FT-IR spectroscopy and particle size analyzer. The powder was dominated by β-SiC including some of α-SiC and free carbon species. The quality of the powder was varied with process conditions such as the molar ratio of H/Si and C/Si, and collecting positions. It was known that the conversion to SiC was mainly affected by the addition of hydrogen gas because it promoted the decomposition and reduction of SiCL. CH4 was easily decomposed to carbon species for the formation of SiC as well as removal of impure oxygen, but excessive carbon suppressed the formation of crystalline SiC and resulted in the solid carbon contamination. The optimum ratio of H/Si was approx. 26 and that of C/Si was 1.1. For collecting positions, the powder collected at the vessel and filter was preferable to that at the reaction tube. The average size of the powder synthesized was estimated to be below 100 nm and uniform in distribution.  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