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   1902篇
  免费   186篇
  国内免费   1篇
电工技术   34篇
化学工业   411篇
金属工艺   23篇
机械仪表   40篇
建筑科学   64篇
矿业工程   2篇
能源动力   63篇
轻工业   302篇
水利工程   16篇
石油天然气   4篇
无线电   172篇
一般工业技术   375篇
冶金工业   168篇
原子能技术   9篇
自动化技术   406篇
  2024年   5篇
  2023年   15篇
  2022年   35篇
  2021年   49篇
  2020年   54篇
  2019年   65篇
  2018年   75篇
  2017年   67篇
  2016年   72篇
  2015年   64篇
  2014年   97篇
  2013年   155篇
  2012年   118篇
  2011年   140篇
  2010年   95篇
  2009年   115篇
  2008年   122篇
  2007年   80篇
  2006年   70篇
  2005年   54篇
  2004年   50篇
  2003年   53篇
  2002年   42篇
  2001年   30篇
  2000年   32篇
  1999年   26篇
  1998年   68篇
  1997年   43篇
  1996年   29篇
  1995年   21篇
  1994年   24篇
  1993年   25篇
  1992年   5篇
  1991年   14篇
  1990年   9篇
  1989年   9篇
  1988年   12篇
  1987年   5篇
  1986年   5篇
  1985年   7篇
  1984年   8篇
  1983年   4篇
  1981年   2篇
  1980年   2篇
  1979年   4篇
  1978年   3篇
  1977年   3篇
  1976年   5篇
  1969年   1篇
  1956年   1篇
排序方式: 共有2089条查询结果,搜索用时 15 毫秒
1.
Non-alcoholic fatty liver disease (NAFLD) is considered the most common liver disorder, affecting around 25% of the population worldwide. It is a complex disease spectrum, closely linked with other conditions such as obesity, insulin resistance, type 2 diabetes mellitus, and metabolic syndrome, which may increase liver-related mortality. In light of this, numerous efforts have been carried out in recent years in order to clarify its pathogenesis and create new prevention strategies. Currently, the essential role of environmental pollutants in NAFLD development is recognized. Particularly, endocrine-disrupting chemicals (EDCs) have a notable influence. EDCs can be classified as natural (phytoestrogens, genistein, and coumestrol) or synthetic, and the latter ones can be further subdivided into industrial (dioxins, polychlorinated biphenyls, and alkylphenols), agricultural (pesticides, insecticides, herbicides, and fungicides), residential (phthalates, polybrominated biphenyls, and bisphenol A), and pharmaceutical (parabens). Several experimental models have proposed a mechanism involving this group of substances with the disruption of hepatic metabolism, which promotes NAFLD. These include an imbalance between lipid influx/efflux in the liver, mitochondrial dysfunction, liver inflammation, and epigenetic reprogramming. It can be concluded that exposure to EDCs might play a crucial role in NAFLD initiation and evolution. However, further investigations supporting these effects in humans are required.  相似文献   
2.
International Journal of Computer Vision - The original version of this article was unfortunately omitted to publish the footnote “The best result per row is highlighted in bold” in...  相似文献   
3.
4.
The three-phase four-wire shunt active power filter (SAPF) was developed to suppress the harmonic currents generated by nonlinear loads, and for the compensation of unbalanced nonlinear load currents, reactive power, and the harmonic neutral current. In this work, we consider instantaneous reactive power theory (PQ theory) for reference current identification based on the following two algorithms: the classic low-pass filter (LPF) and the second-order generalized integrator (SOGI) filter. Furthermore, since an important process in SAPF control is the regulation of the DC bus voltage at the capacitor, a new controller based on the Lyapunov function is also proposed. A complete simulation of the resultant active filtering system confirms its validity, which uses the SOGI filter to extract the reference currents from the distorted line currents, compared with the traditional PQ theory based on LPF. In addition, the simulation performed also demonstrates the superiority of the proposed approach, for DC bus voltage control based on the Lyapunov function, compared with the traditional proportional-integral (PI) controller. Both novel approaches contribute towards an improvement in the overall performance of the system, which consists of a small rise and settling time, a very low or nonexistent overshoot, and the minimization of the total harmonic distortion (THD).  相似文献   
5.
In this paper we review the results obtained in the last two years with the Orsay free electron laser.  相似文献   
6.
An unexpected experimental finding is reported where the primary morphology developed during polymerization-induced phase separation in a rubber-modified thermoplastic practically disappears at high conversions. This process was evidenced by light scattering (LS) and scanning electron microscopy (SEM) for a particular composition of solutions of polyisobutylene oligomers (PIB) in isobornylmethacrylate (IBoMA), during the free-radical polymerization of the monomer. The primary phase separation produced a dispersion of domains rich in PIB containing significant amounts of the monomer (IBoMA). Polymerization of the monomer in these domains occurred at high overall conversions producing the filling of dispersed domains with a PIBoMA-PIB blend that could not be distinguished from the matrix. Under these conditions the final material had the appearance of a homogeneous blend.  相似文献   
7.
α,β‐Unsaturated nitriles have been synthesized by Knoevenagel condensation of a carbonylic compound with malononitrile, assisted by sonochemical irradiation. Two alkaline‐promoted clays (Li+‐ and Cs+‐exchanged saponites) have been employed as catalysts. The influence of the carbonylic compound (benzaldehyde or cyclohexanone) and the use of a solvent on the catalytic activity have been studied. Remarkable increase in the conversion values has been found when the reaction is activated by ultrasound, as compared with the thermal activation. In this green, solvent‐free procedure, α,β‐unsaturated nitriles have been produced in very high yields (97%) when the Cs+‐saponite is used as catalyst. Copyright © 2004 Society of Chemical Industry  相似文献   
8.
The stabilization problem for selected relative equilibria of an underactuated rigid body, modelling a simple underwater vehicle, moving in an ideal fluid is addressed. State feedback control laws achieving local asymptotic stability of a forward motion and of a diving/rising with forward/reverse motion are proposed. The control design exploits the Hamiltonian nature of the system to be controlled and it is based on the so-called interconnection and damping assignment (IDA) procedure. Simulation results complete the work.  相似文献   
9.
We present the results of modeling the response of a Rotating Polarizer Interferometer (RPI), an actual design and the evaluation of it. The RPI was introduced almost 10 years ago by Erickson [1] and since then it has not received too much attention from the millimeter wave community despite its very attractive characteristics, this is perhaps due to a lack of proven designs to encourage potential users. Here we show that with proper design equations a predictable result can be achieved and that a working device with a low-loss dielectric filling (Teflon) is feasible  相似文献   
10.
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