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   1177篇
  免费   67篇
  国内免费   15篇
电工技术   25篇
综合类   4篇
化学工业   275篇
金属工艺   28篇
机械仪表   41篇
建筑科学   30篇
能源动力   82篇
轻工业   126篇
水利工程   4篇
石油天然气   4篇
武器工业   1篇
无线电   119篇
一般工业技术   292篇
冶金工业   64篇
原子能技术   22篇
自动化技术   142篇
  2023年   30篇
  2022年   80篇
  2021年   93篇
  2020年   76篇
  2019年   69篇
  2018年   84篇
  2017年   61篇
  2016年   70篇
  2015年   41篇
  2014年   58篇
  2013年   92篇
  2012年   55篇
  2011年   67篇
  2010年   32篇
  2009年   43篇
  2008年   33篇
  2007年   38篇
  2006年   24篇
  2005年   27篇
  2004年   11篇
  2003年   8篇
  2002年   6篇
  2001年   7篇
  2000年   7篇
  1999年   6篇
  1998年   18篇
  1997年   12篇
  1996年   9篇
  1995年   6篇
  1994年   12篇
  1993年   7篇
  1992年   4篇
  1991年   7篇
  1990年   6篇
  1989年   8篇
  1988年   4篇
  1987年   4篇
  1986年   2篇
  1985年   3篇
  1984年   3篇
  1983年   4篇
  1982年   2篇
  1981年   2篇
  1980年   4篇
  1979年   5篇
  1978年   8篇
  1977年   3篇
  1976年   3篇
  1969年   1篇
  1966年   1篇
排序方式: 共有1259条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Agriculture crop development and production may be hampered in the modern era because of the increasing prevalence of ecological problems around the world. In the last few centuries, plant and agrarian scientific experts have shown significant progress in promoting efficient and eco-friendly approaches for the green synthesis of nanoparticles (NPs), which are noteworthy due to their unique physio-biochemical features as well as their possible role and applications. They are thought to be powerful sensing molecules that regulate a wide range of significant physiological and biochemical processes in plants, from germination to senescence, as well as unique strategies for coping with changing environmental circumstances. This review highlights current knowledge on the plant extract-mediated synthesis of NPs, as well as their significance in reprogramming plant traits and ameliorating abiotic stresses. Nano particles-mediated modulation of phytohormone content in response to abiotic stress is also displayed. Additionally, the applications and limitations of green synthesized NPs in various scientific regimes have also been highlighted.  相似文献   
995.
996.
The effects of rapid solidification on the microstructure and electrochemical properties of Nd0.8Mg0.2(Ni0.8Co0.2)3.8 alloy were systematically investigated.The microstructure of alloys was characterized by scanning electron microscopy(SEM),X-ray diffractometer(XRD) and transmission electron microscopy(TEM).It was found that the melt-spun Nd0.8Mg0.2(Ni0.8Co0.2)3.8 ribbons became thinner and the average grain size of the ribbons became smaller with increasing wheel speed.A fraction of amorphous phase was observed for the ribbons melt-spun at high wheel speed(≥20 m/s).Microstructural characterization revealed that two phases:(Nd,Mg)2(Ni,Co)7 main phase(Ce2Ni7 type structure) and NdNi5 second phase(CaCu5 type structure),existed in the samples in cast state and melt-spun.The cycle stability of the melt-spun alloys was significantly enhanced as compared with cast alloy,and the sample prepared at wheel speed of 20 m/s exhibited good comprehensive electrochemical properties.  相似文献   
997.
Neutron energy spectrum in Miniature Neutron Source Reactor (MNSR), called Pakistan Research Reactor (PARR-2), is measured employing threshold neutron activation detectors. The calculated neutron spectrum was obtained through modeling the core in detail in three-dimensions employing the transport theory based code WIMS-D/4 and the diffusion theory based code CITATION which was also used as pre-information in the adjustment procedure. A Number of threshold detectors in the form of thin foils are used for spectrum measurements. Gamma activity of irradiated foils was measured with the help of a gamma spectroscopic system consisting of a high efficiency HPGe detector and 8000 channels PC based multi-channel analyzer. STAYNL computer code supplied by International Atomic Energy Agency (IAEA) was used for neutron spectrum adjustment. The group cross-section values and their covariance matrices were derived from the data given in preprocessed cross section libraries in ENDF–6 format of IRDF-90/NMF-G. The comparison between theoretical and experimental work shows good agreement.  相似文献   
998.
In this study response surface methodology (RSM) was applied to study the effect of H2SO4 concentration, temperature, and time on the production of reducing sugars, total sugars, and total phenolic compounds from pine needles. Three variables with three levels showed that maximum release of total phenolic compounds (31.20 ± 0.002 mM) was observed at 1% H2SO4 concentration, 130°C temperature for 75 min of residence time. Under these conditions, the predicted value of total phenolic compounds was 31.27 mM, which indicated that the model is valid, having negligible variation in observed and predicted values. These results suggested that this substrate could be potentially used as substrate for bioethanol production.  相似文献   
999.
Novel robustness and performance parameters are established for Smooth Super Twisting Algorithm (SSTA). The stability of SSTA is well established for arbitrary gains using homogeneity approach. The design and tuning of the controller parameters is a major issue and no analytic design method is available so far. A novel Lyapunov function is proposed and by the virtue of stability analysis, the stability bounds for a certain class of uncertainties are determined. In addition, the issue of finite time convergence is also explored, resulting in determination of the settling time as a function of the controller parameters. The proposed settling time formulation suggests a methodical approach to SSTA design in contrast to the available rules of thumb. Unlike the literature available for Higher Order Sliding Mode (HOSM) controllers, the proposed design framework is validated against a challenging problem of the Underground Coal Gasification (UCG) process control. Like the other process control problems the chosen problem is nonlinear and contains significant uncertainties.  相似文献   
1000.
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