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   86714篇
  免费   8486篇
  国内免费   4768篇
电工技术   6108篇
技术理论   1篇
综合类   6466篇
化学工业   13448篇
金属工艺   5328篇
机械仪表   6050篇
建筑科学   6977篇
矿业工程   2881篇
能源动力   2340篇
轻工业   5704篇
水利工程   1810篇
石油天然气   4373篇
武器工业   871篇
无线电   10480篇
一般工业技术   9688篇
冶金工业   3713篇
原子能技术   1040篇
自动化技术   12690篇
  2024年   286篇
  2023年   1170篇
  2022年   2445篇
  2021年   3515篇
  2020年   2633篇
  2019年   2141篇
  2018年   2398篇
  2017年   2702篇
  2016年   2518篇
  2015年   3799篇
  2014年   4574篇
  2013年   5507篇
  2012年   6290篇
  2011年   6729篇
  2010年   6205篇
  2009年   6141篇
  2008年   5881篇
  2007年   5662篇
  2006年   5194篇
  2005年   4432篇
  2004年   2999篇
  2003年   2509篇
  2002年   2351篇
  2001年   2062篇
  2000年   1740篇
  1999年   1675篇
  1998年   1180篇
  1997年   1032篇
  1996年   892篇
  1995年   725篇
  1994年   597篇
  1993年   428篇
  1992年   347篇
  1991年   271篇
  1990年   213篇
  1989年   190篇
  1988年   144篇
  1987年   92篇
  1986年   75篇
  1985年   34篇
  1984年   33篇
  1983年   17篇
  1982年   23篇
  1981年   14篇
  1980年   22篇
  1979年   12篇
  1978年   9篇
  1977年   8篇
  1976年   15篇
  1951年   12篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Pyrethroid esters are widely used as insecticides worldwide. In this study, we aimed to evaluate the harmful effect of deltamethrin on the male reproductive system through the assessment of reproductive hormones, inflammatory markers, and testicular function. To achieve our aim, eighty male 7-9-week-old, Wistar rats were taken, weighed, and divided into four experimental groups. The first group was kept as a control group, and the other three groups were given deltamethrin orally at different concentrations (0.87, 8.7, and 17.4 mg/kg body weight) for nine weeks. The results indicated that deltamethrin administration associated with a significant decrease in reproductive hormones, especially FSH, LH, and significant elevation in the interleukin 2 (IL2), interleukin 6 (IL6), histamine, and cortisol levels. Also, the significance of inhibition of sperm motility and viability, decreased testis weights, sperm count, and fructose in semen were noted. These findings clarify the harmful effect of deltamethrin on the male reproductive system by producing a significant alteration in reproductive hormones, inflammatory markers as well as testicular function.  相似文献   
62.
63.
The hippocampus is crucial in learning, memory and emotion processing, and is involved in the development of different neurological and neuropsychological disorders. Several epigenetic factors, including DNA methylation, histone modifications and non-coding RNAs, have been shown to regulate the development and function of the hippocampus, and the alteration of epigenetic regulation may play important roles in the development of neurocognitive and neurodegenerative diseases. This review summarizes the epigenetic modifications of various cell types and processes within the hippocampus and their resulting effects on cognition, memory and overall hippocampal function. In addition, the effects of exposure to radiation that may induce a myriad of epigenetic changes in the hippocampus are reviewed. By assessing and evaluating the current literature, we hope to prompt a more thorough understanding of the molecular mechanisms that underlie radiation-induced epigenetic changes, an area which can be further explored.  相似文献   
64.
通过对CSFB语音方案原理的分析,结合业务模型及网络安全等方面的考虑,提出了一种支持4G CSFB的MSC改造规模预测方法,为端局后续建设提供了参考.  相似文献   
65.
The {100} facet of single-crystalline TiO2(B) is an ideal platform for inserting Li ions, but it is hard to be obtained due to its high surface energy. Here, the single-crystalline TiO2(B) nanobelts from H2Ti3O7 with nearly 70% {100} facets exposed are synthesized, which significantly enhances Li-storage capacity. The first-principle calculations demonstrate an ab in-plane 2D diffusion through the exposed {100} facets. As a consequence, the nanobelts can significantly accommodate Li ions in LiTiO2 formula with specific capacity up to 335 mAh g−1, which is in good agreement with the electrochemical characterizations. Coating with conductive and protective poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), the cut-off discharge voltage is as low as 0.5 V, leading to a capacity of 160.7 mAh g−1 after 1500 cycles with a retention rate of 66% at 1C. This work provides a practical strategy to increase the Li-ion capacity and cycle stability by tailoring the crystal orientation and nanostructures.  相似文献   
66.
Ethanol steam reforming (ESR) is one of the potential processes to convert ethanol into valuable products. Hydrogen produced from ESR is considered as green energy for the future and can be an excellent alternative to fossil fuels with the aim of mitigating the greenhouse gas effect. The ESR process has been well studied, using transition metals as catalysts coupled with both acidic and basic oxides as supports. Among various reported transition metals, Ni is an inexpensive material with activity comparable to that of noble metals, showing promising ethanol conversion and hydrogen yields. Additionally, different promoters and supports were utilized to enhance the hydrogen yield and the catalyst stability. This review summarizes and discusses the influences of the supports and promoters of Ni-based catalysts on the ESR process.  相似文献   
67.
该文针对当前矿井炮掘巷道大断面掘进普遍存在掘进施工较慢的实际,结合公司实际情况,有针对性地提出了解决的办法。  相似文献   
68.
69.
International Journal of Control, Automation and Systems - There is a class of typical nonlinear industrial process, which can be characterized by a first-order inertia plus pure delay model in an...  相似文献   
70.
Structural and Multidisciplinary Optimization - The overall layout optimization design of an orbital propellant depot involves the optimization of shape, size, and positions of propellant tanks in...  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