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   131571篇
  免费   13138篇
  国内免费   8557篇
电工技术   5194篇
技术理论   4篇
综合类   13235篇
化学工业   23216篇
金属工艺   11200篇
机械仪表   7183篇
建筑科学   23726篇
矿业工程   4269篇
能源动力   3175篇
轻工业   10057篇
水利工程   2785篇
石油天然气   5135篇
武器工业   1516篇
无线电   7405篇
一般工业技术   19569篇
冶金工业   4709篇
原子能技术   670篇
自动化技术   10218篇
  2024年   520篇
  2023年   1876篇
  2022年   3495篇
  2021年   4164篇
  2020年   4065篇
  2019年   3461篇
  2018年   3191篇
  2017年   4095篇
  2016年   4355篇
  2015年   4566篇
  2014年   7673篇
  2013年   6932篇
  2012年   9204篇
  2011年   10025篇
  2010年   7790篇
  2009年   8389篇
  2008年   7343篇
  2007年   9161篇
  2006年   8414篇
  2005年   7274篇
  2004年   5938篇
  2003年   5410篇
  2002年   4588篇
  2001年   3930篇
  2000年   3355篇
  1999年   2740篇
  1998年   2187篇
  1997年   1842篇
  1996年   1444篇
  1995年   1226篇
  1994年   1082篇
  1993年   780篇
  1992年   646篇
  1991年   494篇
  1990年   376篇
  1989年   257篇
  1988年   200篇
  1987年   108篇
  1986年   68篇
  1985年   98篇
  1984年   73篇
  1983年   67篇
  1982年   81篇
  1981年   22篇
  1980年   78篇
  1979年   29篇
  1978年   17篇
  1975年   14篇
  1959年   12篇
  1951年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
结合结构支撑理论,探究节点网络结构支持力的一些性质,提出了社交网络结构中的全网支持力和被支持力的总量一致性,并进一步提出计算节点支持力的方法。谣言作为特殊信息,在支持力不同节点之间的传播特性有所不同,借鉴随机游走模型中的PageRank计算方法,对不同节点支持力的谣言传播以及传播后的辟谣状况进行了仿真模拟,结果表明支持力不同的节点对于谣言传播和辟谣影响明显。  相似文献   
42.
43.
Zinc (Zn), the second-most necessary trace element, is abundant in the human body. The human body lacks the capacity to store Zn; hence, the dietary intake of Zn is essential for various functions and metabolism. The uptake of Zn during its transport through the body is important for proper development of the three major accessory sex glands: the testis, epididymis, and prostate. It plays key roles in the initial stages of germ cell development and spermatogenesis, sperm cell development and maturation, ejaculation, liquefaction, the binding of spermatozoa and prostasomes, capacitation, and fertilization. The prostate releases more Zn into the seminal plasma during ejaculation, and it plays a significant role in sperm release and motility. During the maternal, labor, perinatal, and neonatal periods, the part of Zn is vital. The average dietary intake of Zn is in the range of 8–12 mg/day in developing countries during the maternal period. Globally, the dietary intake of Zn varies for pregnant and lactating mothers, but the average Zn intake is in the range of 9.6–11.2 mg/day. The absence of Zn and the consequences of this have been discussed using critical evidence. The events and functions of Zn related to successful fertilization have been summarized in detail. Briefly, our current review emphasizes the role of Zn at each stage of human reproduction, from the spermatogenesis process to childbirth. The role of Zn and its supplementation in in vitro fertilization (IVF) opens opportunities for future studies on reproductive biology.  相似文献   
44.
The multilayer ceramic composites (MLC) consist of two ceramic materials insoluble in each other and sequentially piled in a symmetric manner whereas they can be divided into two groups: multilayer composites with weak interfaces and composites with strong interfaces. The graphene added multilayer ceramic sandwich (GMCS) composite was developed. The multilayer stack of Si3N4 with 5 and 30 wt% graphene addition were stratified in sandwich structure. So formed multilayer stacks with 5 and 7 layers were sintered by hot issostatic pressing (HIP). The homogenity of graphene addition, the effect of layered structures and the position of layers with lower and higher graphene content on the final properties were studied.  相似文献   
45.
The top illuminated organic photodetectors (OPDs) with a Dielectric/Metal/Dielectric (DMD) transparent anode are fabricated. The transparent electrode is composed of molybdenum trioxide (MoO3)/silver (Ag)/MoO3 layers and zinc oxide (ZnO)/aluminum (Al) is used for bottom cathode. The optimized DMD electrode has an optical transmittance of 85.7% at the wavelength of 546 nm and sheet resistance of ∼6 Ω/sq. The fabricated OPDs exhibit a high detectivity and wide range linearity.  相似文献   
46.
47.
通过制备不同晶相结构〔单斜相(m-ZrO_2)、四方相(t-ZrO_2)和无定型(a-ZrO_2)〕ZrO_2载体,再通过沉积沉淀法制得Cu/m-ZrO_2、Cu/t-ZrO_2和Cu/a-ZrO_2催化剂,分别用于催化二乙醇胺脱氢合成亚氨基二乙酸反应。采用XRD、氮气物理吸附脱附、XPS、H_2-TPR、CO_2-TPD对催化剂的结构进行了表征。结果表明,Cu/m-ZrO_2催化剂界面更加有利于Cu~+/Cu~0稳定存在,具有更多的碱性位点,且抗氧化性较好。在二乙醇胺脱氢反应中,Cu/m-ZrO_2催化剂性能最好,反应时间为2.5 h,亚氨基二乙酸收率为97.64%。  相似文献   
48.
49.
A simple, cost-effective, and novel chemical sensor for ammonia (NH3) gas detection was developed from polyaniline (PANI)/quail eggshell (QES) composites. QES is a natural waste enriched in calcium carbonate. In this work, pure PANI was synthesized from chemical oxidation method and PANI/QES composites were prepared from physical mixing of QES with the synthesized PANI at different mass ratio. A series of complementary techniques including Fourier transform infrared and ultraviolet-visible spectrometers, scanning electron microscope with energy dispersive detection coupled with mapping, thermogravimetric analysis, and X-ray diffractometer were used to characterize the physicochemical and textural properties of the biocomposites. From the results, PANI/QES composite with a mass ratio of 1 exhibited the lowest NH3 detection limit of 5.24 ppm with a linear correlation coefficient (R2) of close to unity (0.9932) between the signal and NH3 gas concentration. As a whole, the PANI/QES biocomposites synthesized from this work exhibited excellent selectivity toward NH3 gas even in the presence of other gas impurities, such as acetone, ethanol, and hexane. For the sensor reusability, the PANI/QES biocomposites can be reused in the application of NH3 gas detection for at least 4 cycles.  相似文献   
50.
以多晶硅锭中硬质点为研究对象,通过实验研究和数值模拟的方法,对多晶硅锭中硬质点进行形貌和成分分析,并提出改善控制方法。研究结果表明硅锭中部的硬质点较细小,主要由SiC组成;硅锭头部的硬质点较粗大,主要由SiC和Si3N4组成,还有少量O的存在。进一步研究发现多晶硅定向凝固铸锭炉的热场结构对于多晶硅锭硬质点形成有直接影响,通过改进热场结构,优化晶体生长界面,显著减少了铸锭中硬质点的数量。  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