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   169921篇
  免费   1402篇
  国内免费   205篇
电工技术   2580篇
综合类   122篇
化学工业   27130篇
金属工艺   9511篇
机械仪表   5761篇
建筑科学   3060篇
矿业工程   1889篇
能源动力   2785篇
轻工业   8941篇
水利工程   2744篇
石油天然气   8708篇
武器工业   12篇
无线电   14645篇
一般工业技术   38527篇
冶金工业   27882篇
原子能技术   6944篇
自动化技术   10287篇
  2018年   3056篇
  2017年   3160篇
  2016年   3409篇
  2015年   1718篇
  2014年   3019篇
  2013年   6476篇
  2012年   4385篇
  2011年   5468篇
  2010年   4497篇
  2009年   4962篇
  2008年   4999篇
  2007年   4918篇
  2006年   4173篇
  2005年   3854篇
  2004年   3654篇
  2003年   3541篇
  2002年   3479篇
  2001年   3479篇
  2000年   3374篇
  1999年   3229篇
  1998年   7046篇
  1997年   5171篇
  1996年   3843篇
  1995年   2929篇
  1994年   2608篇
  1993年   2741篇
  1992年   2269篇
  1991年   2318篇
  1990年   2419篇
  1989年   2334篇
  1988年   2323篇
  1987年   2202篇
  1986年   2260篇
  1985年   2302篇
  1984年   2224篇
  1983年   2147篇
  1982年   1992篇
  1981年   2201篇
  1980年   2070篇
  1979年   2280篇
  1978年   2437篇
  1977年   2440篇
  1976年   3106篇
  1975年   2251篇
  1974年   2311篇
  1973年   2346篇
  1972年   2161篇
  1971年   1914篇
  1970年   1702篇
  1969年   1635篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
A technology for slag formation in the ladle–furnace unit is considered; the slag is based on the CaO–SiO2–MgO–Al2O3–B2O3 system. This technology permits both microalloying of the steel with boron (reduced from the oxide phase) and desulfurization of the steel. The resulting boron content in the steel is 0.001–0.008%; the sulfur content in low-alloy steel and pipe steel is low (0.004–0.010%); and the consumption of manganese ferroalloys is reduced to 0.5 kg/t for 08кп steel and 1.4 kg/t for 09Г2C steel. In addition, the proposed technology increases the strength of the rolled steel, without loss in its plasticity; and reduces the environmental impact thanks to the replacement of fluorspar by colemanite.  相似文献   
73.
Formation and structural transformations of yttrium orthoferrite crystals have been studied using X-ray diffractometry, Mössbauer spectroscopy and transmission electron microscopy combined with electron microdiffraction. Said processes have been studied under heat treatment of glycine-nitrate combustion products. There have been identified formations of three structural yttrium orthoferrite modifications – amorphized hexagonal <h1>-YFeO3 (P63cm) and nanocrystalline hexagonal h2-YFeO3 (P63/mmc), as well as nanocrystalline orthorhombic o-YFeO3 (Pbnm), which are selectively formed depending on available three-dimensional confinements. Based on the analysis of changes in the fluid and size composition formulation, it has been proposed mechanism for formation and transformation of YFeO3 nanocrystals, including growth stage of h2-YFeO3 crystals due to amorphized phase of <h1>-YFeO3 up to critical size of about 15?nm and their subsequent transformation into orthorhombic form o-YFeO3.  相似文献   
74.
75.
Covalent triazine frameworks (CTFs) have been recently employed for visible light-driven photocatalysis due to their unique optical and electronic properties. However, the usually highly hydrophobic nature of CTFs, which originates from their overall aromatic backbone, leads to limitations of CTFs for applications in aqueous media. In this study, we aim to extend the range of the application media of CTFs and design hybrid material of a CTF and mesoporous silica (SBA-15) for efficient photocatalysis in aqueous medium. A thiophene-containing CTF was directly synthesized in mesopores of SBA-15. Due to the high surface area and the added hydrophilic properties by silica, the hybrid material demonstrated excellent adsorption of organic molecules in water. This leads not only to high photocatalytic performance of the hybrid material for the degradation of organic dyes in water, but also for efficient photocatalysis in solvent-free and solid state. Furthermore, the reusability, stability and easy recovery of the hybrid material offers promising metal-free heterogeneous photocatalyst for broader applications in different reaction media.  相似文献   
76.
77.
Excessive energy intake may evoke complex biochemical processes characterized by inflammation, oxidative stress, and impairment of mitochondrial function that represent the main factors underlying noncommunicable diseases. Because cow milk is widely used for human nutrition and in food industry processing, the nutritional quality of milk is of special interest with respect to human health. In our study, we analyzed milk produced by dairy cows fed a diet characterized by a high forage:concentrate ratio (high forage milk, HFM). In view of the low n-6:n-3 ratio and high content of conjugated linoleic acid of HFM, we studied the effects of this milk on lipid metabolism, inflammation, mitochondrial function, and oxidative stress in a rat model. To this end, we supplemented for 4 wk the diet of male Wistar rats with HFM and with an isocaloric amount (82 kJ, 22 mL/d) of milk obtained from cows fed a diet with low forage:concentrate ratio, and analyzed the metabolic parameters of the animals. Our results indicate that HFM may positively affect lipid metabolism, leptin:adiponectin ratio, inflammation, mitochondrial function, and oxidative stress, providing the first evidence of the beneficial effects of HFM on rat metabolism.  相似文献   
78.
Technical Physics Letters - The influence of excitation photons energy on the relaxation times of photoexcited carriers is studied. The involved relaxation mechanisms are evaluated and the...  相似文献   
79.
In this paper, we consider the classical finite mixture model, which is an effective tool for modeling lifetime distributions for random samples from heterogeneous populations. We discuss new results on stochastic comparison for two finite mixtures when each of them is drawn from one of the following semiparametric families, i.e., proportional hazards, accelerated lifetime and proportional reversed hazards.  相似文献   
80.
Technical Physics Letters - We present the results of a comparative investigation of the friction and wear characteristics of MoSx and MoSex coatings in an oxidizing medium (argon–air...  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