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   119433篇
  免费   10159篇
  国内免费   4884篇
电工技术   7056篇
技术理论   7篇
综合类   7528篇
化学工业   20853篇
金属工艺   6436篇
机械仪表   7316篇
建筑科学   9715篇
矿业工程   3391篇
能源动力   3553篇
轻工业   7977篇
水利工程   2127篇
石油天然气   7178篇
武器工业   876篇
无线电   13441篇
一般工业技术   14545篇
冶金工业   5905篇
原子能技术   1294篇
自动化技术   15278篇
  2024年   439篇
  2023年   1945篇
  2022年   3341篇
  2021年   4935篇
  2020年   3713篇
  2019年   3160篇
  2018年   3418篇
  2017年   3929篇
  2016年   3344篇
  2015年   4692篇
  2014年   5760篇
  2013年   6910篇
  2012年   7561篇
  2011年   8198篇
  2010年   7110篇
  2009年   6804篇
  2008年   6574篇
  2007年   6225篇
  2006年   6459篇
  2005年   5584篇
  2004年   3848篇
  2003年   3359篇
  2002年   3123篇
  2001年   2841篇
  2000年   2986篇
  1999年   3169篇
  1998年   2684篇
  1997年   2281篇
  1996年   2108篇
  1995年   1834篇
  1994年   1473篇
  1993年   1054篇
  1992年   857篇
  1991年   666篇
  1990年   500篇
  1989年   440篇
  1988年   352篇
  1987年   236篇
  1986年   153篇
  1985年   92篇
  1984年   58篇
  1983年   40篇
  1982年   62篇
  1981年   39篇
  1980年   31篇
  1979年   14篇
  1947年   8篇
  1944年   11篇
  1943年   7篇
  1942年   10篇
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
81.
Zhang  Huawei  Yang  Zhi  Wu  Zhaoyu  Hong  Xiaoyu  Li  Zhong  Xu  Yulai  Li  Jun  Ni  Gaojin  Xiao  Xueshan 《Oxidation of Metals》2019,92(1-2):49-65
Oxidation of Metals - The isothermal oxidation behavior and oxide-scale evolution on a newly developed Ni–Fe-based superalloy were investigated. Three oxidation stages were generally...  相似文献   
82.
以用户为中心的可见光通信协作传输是近年来出现的新架构,这导致虚拟小区之间出现重叠。为避免导频污染问题,每个虚拟小区中的光接入点(AP)或者虚拟小区中选择相同AP的用户发送的训练序列应该是正交的。针对可见光通信中以用户为中心的协作网络,研究训练资源的正交分配问题,提出了一种新的导频分配算法,联合导频分配和用户选择问题,以期最大限度地增加虚拟小区内可被接入的用户数。分析和仿真结果表明,该导频分配方案可以有效改善导频污染问题,提高训练资源利用率,并且相比已有的导频分配方案,性能有所改进。  相似文献   
83.
The synergistic effects of activated carbon (AC) and molybdenum oxide (MoO3) in improving the flame retardancy of poly(vinyl chloride) (PVC) were investigated. The effects of AC, MoO3 and their mixture with a mass ratio of 1:1 on the flame retardancy and smoke suppression properties of PVC were studied using the limiting oxygen index and cone calorimeter tests. It was found that the flame retardancy of the relatively cheaper AC was slightly weaker than that of MoO3. In addition, the incorporation of AC and MoO3 greatly reduced the total heat release and improved smoke suppressant property of PVC composites. When the total content of AC and MoO3 was 10 phr, PVC/AC/MoO3 had the lowest peak heat release rate and peak smoke production rate values of 173.80 kW m?2 and 0.1472 m2 s?1, which represented reductions of 47.3 and 59.9%, respectively, compared with those of PVC. Furthermore, thermogravimetric analysis and gel content tests were used to analyze the flame retardant mechanism of AC and MoO3, with results showing that AC could promote early crosslinking in PVC. Char residue left after heating at 500 °C was analyzed using scanning electron microscopy and Raman spectroscopy, and the results showed that MoO3 produced the most compact char, with the smallest and most organized carbonaceous microstructures. © 2017 Society of Chemical Industry  相似文献   
84.
85.
张旭 《建筑学报》2021,(12):35-41
通过对宜兴丁蜀镇青龙山公园多功能馆项目设计和建造历程的回顾,在自然与人工、城市与建筑、可见与消隐、开放与持存的多重辩证关系中推进和展开关于地景、地方以及边界的讨论,试图进一步探讨在现有的空间规划和土地政策下,建筑基础设施化作为一种设计策略、将特殊场地再次纳入城市结构的可能性.  相似文献   
86.
87.
Rapid and sensitive point-of-care testing (POCT) is an extremely critical mission in practical applications, especially for rigorous military medicine, home health care, and in the third world. Here, we report a visual POCT method for adenosine triphosphate (ATP) detection based on Taylor rising in the corner of quadratic geometries between two rod surfaces. We discuss the principle of Taylor rising, demonstrating that it is significantly influenced by contact angle, surface tension, and density of the sample, which are controlled by ATP-dependent rolling circle amplification (RCA). In the presence of ATP, RCA reaction effectively suppresses Taylor-rising behavior, due to the increased contact angle, density, and decreased surface tension. Without addition of ATP, untriggered RCA reaction is favorable for Taylor rising, resulting in a significant height. With this proposed method, visual sensitive detection of ATP without the aid of other instruments is realized with only a 5 μL droplet, which has good selectivity and a low detection limit (17 nM). Importantly, this visual method provides a promising POCT tool for user-friendly molecular diagnostics.  相似文献   
88.
This paper discusses the compressive performance of perforated brick masonry after fire exposure. Compressive strength tests of the mortar, clay perforated brick, and perforated brick masonry specimens were performed in accordance with ISO834 fire tests of different durations. The temperature distribution of the masonry materials and specimens was simulated using the finite element software ABAQUS, with the thermal parameters of masonry materials recommended by European standard Eurocode 6 and related literature. The compressive strength reduction factors of mortar and clay perforated brick exposed to different fire durations were calculated via the layered method suggested by European standard Eurocode 1. In addition, the compressive strength reduction factors after cooldown were obtained from the experimental data of the masonry materials, and by considering further reductions in the compressive strength after cooling from high temperatures. Experimental data of the masonry specimens were compared with the numerical results obtained using the reduction factors proposed in this work. The comparison revealed an overall acceptable approximation. Thus, the method presented in this paper can be used to evaluate the residual capacity of masonry structures after fire.  相似文献   
89.
90.
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