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   6405篇
  免费   643篇
  国内免费   350篇
电工技术   442篇
技术理论   1篇
综合类   393篇
化学工业   1092篇
金属工艺   438篇
机械仪表   541篇
建筑科学   542篇
矿业工程   204篇
能源动力   191篇
轻工业   437篇
水利工程   124篇
石油天然气   506篇
武器工业   68篇
无线电   553篇
一般工业技术   791篇
冶金工业   272篇
原子能技术   68篇
自动化技术   735篇
  2024年   15篇
  2023年   102篇
  2022年   265篇
  2021年   301篇
  2020年   239篇
  2019年   207篇
  2018年   191篇
  2017年   214篇
  2016年   201篇
  2015年   276篇
  2014年   329篇
  2013年   383篇
  2012年   455篇
  2011年   460篇
  2010年   436篇
  2009年   396篇
  2008年   348篇
  2007年   329篇
  2006年   372篇
  2005年   301篇
  2004年   202篇
  2003年   193篇
  2002年   165篇
  2001年   148篇
  2000年   156篇
  1999年   136篇
  1998年   111篇
  1997年   105篇
  1996年   73篇
  1995年   82篇
  1994年   56篇
  1993年   36篇
  1992年   38篇
  1991年   15篇
  1990年   13篇
  1989年   11篇
  1988年   8篇
  1987年   7篇
  1986年   7篇
  1985年   4篇
  1984年   3篇
  1982年   2篇
  1981年   3篇
  1979年   1篇
  1968年   1篇
  1967年   1篇
  1959年   1篇
排序方式: 共有7398条查询结果,搜索用时 273 毫秒
1.

This paper presents a case study of an optimized combination of mine water control, treatment, utilization and reinjection to achieve the zero discharge of mine water. Mine water has been considered a hazard and pollution source during underground mining, so most mining enterprises directly discharge mine water to the surface after simple treatment, resulting in a serious waste of water. Moreover, discharging a large amount of mine water can destroy the original groundwater balance and cause serious environmental problems, such as surface subsidence, water resource reduction and contamination, and adverse impacts on biodiversity. The Zhongguan iron mine is in the major groundwater source area of the Hundred Springs of Xingtai, which is an area with a high risk of potential subsidence. To optimize the balance between mining and groundwater resources, a series of engineering measures was adopted by the Zhongguan iron mine to realize mine water control, treatment, utilization, and reinjection. The installation of a closed grout curtain has greatly reduced the water yield of deep stopes in the mine; the effective sealing efficiency reaches 80%. Nanofiltration membrane separation was adopted to treat the highly mineralized mine water; the quality of the produced water meets China’s recommended class II groundwater standard. Low-grade heat energy from the mine water is collected and utilized through a water-source heat pump system. Finally, zero mine water discharge is realized through mine water reinjection. This research provides a beneficial reference for mines with similar geological and hydrogeological conditions to achieve environmentally sustainable mining.

  相似文献   
2.
3.
为解决定距螺旋桨与船用主机在船舶运行工况的机桨匹配问题,结合船舶系泊和航行试验的相关标准,分析和归纳船舶运行数据,将实船测试与船机桨匹配理论计算相结合,得出运输船和拖轮在常用工况及特殊工况下定距螺旋桨对主机外特性的定量要求,为配套不同细分市场时船用主机的优化和开发提供参考依据。  相似文献   
4.
本文研究了电波大气折射理论,分析了传播误差因素,阐述了区域导航信号的传播路径与 GNSS 卫星导航的不同,论述了对流层延迟对区域导航信号测量精度的影响,设计了满足区域导航系统应用需求的对流层延迟误差修正模型,并通过仿真研究,验证了所设计区域导航对流层延迟误差修正模型的可行性,并给出了该模型在远距离低仰角和近距离高仰角下的误差修正能力。  相似文献   
5.
本文针对典型高温气冷堆乏燃料厂房在双发商用飞机撞击载荷下的响应及结构完整性开展研究,并探讨结构特性对撞击损伤的影响。对乏燃料厂房及飞机分别建立有限元模型,通过弹体-目标相互作用分析模拟了飞机撞击过程,综合IAEA与NRC的评价准则对乏燃料厂房在飞机撞击下的损伤程度进行评估。数值结果表明:厂房上对应于机身及发动机的撞击位置发生可接受的局部损伤;乏燃料贮存井墙体对于提高构筑物抗飞机撞击能力有重要作用。此外,构筑物外形对损伤有很大影响,圆柱形壳体的抗飞机撞击能力显著强于方形厂房,是核电厂厂房设计的优化方向之一。  相似文献   
6.
对于大宗粉煤灰原灰进行分选加球磨机粉磨,同时添加合适的激发剂进行提质,可以生产出不同细度和活性的粉煤灰产品,提升粉煤灰在水泥及商品砼中的用量。介绍了某发电公司的粉煤灰处置现状,在此基础上,对商品砼的粉煤灰性能要求进行了大量市场调研,针对性地给出了该公司粉煤灰的提质方案,最后进行了提质粉煤灰的应用市场和产品竞争力分析。  相似文献   
7.
8.
Waxy, normal and high-amylose maize starches were subjected to heat-moisture treatment (HMT) and then added to wheat flour (WF) in different ratios (1%, 5% and 10%). The properties of blends and their cooked noodles were studied to investigate the effects of HMT starches. The incorporation of HMT starch in WF led to an increase in swelling power, peak viscosity and breakdown and to a decrease in setback, thus inhibiting retrogradation, hence enhancing resultant noodle softness. Compared to the same addition ratio of native starch to WF, HMT starch led to higher tensile strength and extensibility in resultant noodles. WF with added HMT starch had higher resistant starch than with native starch. This study showed that addition of HMT maize starch has potential to bring nutritional benefits. However, it is necessary to select the proper blending ratio and amylose content of starch to add, in consideration of its effect on noodle quality.  相似文献   
9.
Element doping into the Cu2ZnSn(S,Se)4 (CZTSSe) absorber is an effective method to optimize the performance of thin film solar cells. In this study, the Cu2InxZn1-xSn(S,Se)4 (CIZTSSe) precursor film was deposited by magnetron cosputtering technique using indium (In) and quaternary Cu2ZnSnS4 (CZTS) as targets. Meanwhile, the In content was controlled using the direct current (DC) power on In target (PIn). A single kesterite CIZTSSe alloy was formed by successfully doping a small number of In3+ into the main lattice of CZTSSe. The partial Zn2+ cations were substituted by In3+ ions, resulting in improving properties of CZTSSe films. Morphological analysis showed that large grain CIZTSSe films could be obtained by doping In. The well-distributed, smooth, and dense film was obtained when the PIn was 30 W. The band gap of CIZTSSe could be continuously adjusted from 1.27 to 1.05 eV as PIn increased from 0 to 40 W. In addition, the CIZTSSe alloy thin film at PIn = 30 W exhibited the best p-type conductivity with Hall mobility of 6.87 cm2V?1s?1, which is a potential material as the absorption layer of high-performance solar cells.  相似文献   
10.
Sarcopenia is the loss of skeletal muscle mass and function with advancing age. It involves both complex genetic and modifiable risk factors, such as lack of exercise, malnutrition and reduced neurological drive. Cognitive decline refers to diminished or impaired mental and/or intellectual functioning. Contracting skeletal muscle is a major source of neurotrophic factors, including brain-derived neurotrophic factor, which regulate synapses in the brain. Furthermore, skeletal muscle activity has important immune and redox effects that modify brain function and reduce muscle catabolism. The identification of common risk factors and underlying mechanisms for sarcopenia and cognition may allow the development of targeted interventions that slow or reverse sarcopenia and also certain forms of cognitive decline. However, the links between cognition and skeletal muscle have not been elucidated fully. This review provides a critical appraisal of the literature on the relationship between skeletal muscle health and cognition. The literature suggests that sarcopenia and cognitive decline share pathophysiological pathways. Ageing plays a role in both skeletal muscle deterioration and cognitive decline. Furthermore, lifestyle risk factors, such as physical inactivity, poor diet and smoking, are common to both disorders, so their potential role in the muscle–brain relationship warrants investigation.  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