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   11427篇
  免费   851篇
  国内免费   21篇
电工技术   130篇
综合类   8篇
化学工业   2692篇
金属工艺   431篇
机械仪表   568篇
建筑科学   273篇
矿业工程   11篇
能源动力   391篇
轻工业   1157篇
水利工程   37篇
石油天然气   21篇
无线电   1593篇
一般工业技术   2350篇
冶金工业   1432篇
原子能技术   130篇
自动化技术   1075篇
  2023年   97篇
  2022年   170篇
  2021年   280篇
  2020年   206篇
  2019年   266篇
  2018年   298篇
  2017年   343篇
  2016年   402篇
  2015年   353篇
  2014年   498篇
  2013年   776篇
  2012年   661篇
  2011年   827篇
  2010年   594篇
  2009年   565篇
  2008年   561篇
  2007年   435篇
  2006年   351篇
  2005年   326篇
  2004年   319篇
  2003年   303篇
  2002年   262篇
  2001年   213篇
  2000年   196篇
  1999年   216篇
  1998年   473篇
  1997年   342篇
  1996年   213篇
  1995年   162篇
  1994年   165篇
  1993年   168篇
  1992年   112篇
  1991年   94篇
  1990年   90篇
  1989年   90篇
  1988年   61篇
  1987年   52篇
  1986年   54篇
  1985年   75篇
  1984年   68篇
  1983年   44篇
  1982年   42篇
  1981年   42篇
  1980年   41篇
  1979年   38篇
  1978年   32篇
  1977年   51篇
  1976年   78篇
  1975年   40篇
  1973年   32篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
This paper presents an integrated framework for risk evaluation and risk allocation with bounded data in a critical risk management. A risk evaluation framework using the Imprecise Data Envelopment Analysis (IDEA) method is proposed to be applied to operations of Korean Army helicopters. The risks pertaining to pilots, missions and helicopters are evaluated based on bounded data, and pilots are appropriately allocated to missions and helicopters using goal programming with bounded risk scores. Using bounded data, two risk allocation models are developed to be used with the expected value and lower/upper limit values, resulting in improved reliability of the solutions. Numerical experiments show reasonable solutions and valuable information for risk management.  相似文献   
42.
Bound states and scattering resonances for a 3He-vacancy system in crystalline 4He are shown to exist. For realistic physical parameters the theory yields binding energies of 0.1 K. It is found that the bound states and scattering resonances tend to enhance the diffusion coefficient of 3He. The experimental consequences of this enhanced diffusion are discussed.  相似文献   
43.
Tables in text   总被引:1,自引:0,他引:1  
Tables were inserted into a four page article, and subjects were asked to scan the text which was printed in a two-column or a single-column format. The single-column format was scanned significantly faster than the double-column layout, and there were marked reader preferences for the single-column layout.  相似文献   
44.
A planar monopole antenna with a staircase shape and small volume (25/spl times/26/spl times/1 mm/sup 3/) is proposed in this paper. With the use of a half-bowtie radiating element, the staircase-shape, and a modified ground plane structure, the proposed antenna has a very wide impedance bandwidth measured at about 11.6 GHz (2.9-14.5 GHz, bandwidth ratio about 1:5) below VSWR 2 including the WLAN band notched in the vicinity of 5 GHz. An omnidirectional radiation pattern is obtained. The group delay which is an indication of linearity between two proposed antennas is less than 1 ns. The electrical characteristics in terms of frequency and time domains and physical ones of the proposed antenna make it attractive for use in ultrawideband (UWB) systems.  相似文献   
45.
The LabMatrix is a prototyping system designed to give the user a practical and versatile platform for testing microfluidic applications in the fields of health care and life sciences. The LabMatrix system consists of a microfluidic breadboard and cover that align and secure a series of specially designed LabMatrix microfluidic chips. Chips are easily arranged and rearranged into a user-defined fluidic network. The LabMatrix system is designed with maximum flexibility in mind, providing the user with a means to prototype a wide range of microfluidic applications in a short period.  相似文献   
46.
This paper proposes a heuristic method of constructing multivariate T2 control charts for skewed populations based on ‘weighted standard deviations’, obtained by decomposing the standard deviation into upper and lower deviations according to the direction and degree of skewness. The proposed method adjusts the variance–covariance matrix of quality characteristics and modifies the ellipsoidal probability density function contour of the multivariate normal distribution to a shape similar to that of the skewed distribution. False alarm rates and out‐of‐control average run lengths of the proposed control chart are compared with those of the standard control chart for multivariate lognormal, Weibull and gamma distributions, and the results show that considerable improvement over the standard method can be achieved when the distribution is skewed. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
47.
During the solidification of the AZ91D-alloys, the Al8(Mn, Fe)5 phase is generally precipitated in the melt in advance of the precipitation of the primary α-Mg. The basic principle for manufacturing AZ91D-alloy slurries for semi solid forming is to use the Al8(Mn, Fe)5 precipitates as the heterogeneous nucleation sites for primary α-Mg phases. Microscopic analysis for the location of the Al8(Mn, Fe)5 precipitate explains that the Al8(Mn, Fe)5 precipitate is the effective heterogeneous nucleation site for the primary α-Mg phase. It was also observed that increase of the Mn content in the melt and the cooling rate below to the solid/liquid two-phase region resulted in smaller and more globular primary α-Mg due to the increase of heterogeneous nucleation sites. It was found that the average α-Mg diameter grew as a function of t0.278, where t is the holding time at the solid/liquid two-phase region. This would be attributed to the Ostwald type ripening and coalescence between primary α-Mg phases. The cooling rate below to the solid/liquid two-phase region, Mn content in AZ91D alloy, and the holding time and temperature affected on the quality of slurry.  相似文献   
48.
Although multiphoton fluorescence excitation microscopy has improved the depth at which useful fluorescence images can be collected in biological tissues, the reach of multiphoton fluorescence excitation microscopy is nonetheless limited by tissue scattering and spherical aberration. Scattering can be reduced in fixed samples by mounting in a medium whose refractive index closely matches that of the fixed material. Using optical 'clearing', the effects of refractive index heterogeneity on signal attenuation with depth are investigated. Quantitative measurements show that by mounting kidney tissue in a high refractive index medium, less than 50% of signal attenuates in 100 μm of depth.  相似文献   
49.
Shear horizontal waves are very useful in nondestructive evaluation applications because of their non-dispersive property. The objective of this research is to investigate frequency-tuned shear horizontal wave transduction in plates by using magnetostrictive nickel gratings. Since wireless energy conversion between magnetic energy and acoustic energy in magnetostrictive material can take place, the generation and measurement of waves by the magnetostrictive principle have recently received much attention. In this work, a grating-type magnetostrictive transducer was considered for SH wave transduction; waves can be effectively tuned at desired frequencies by changing grating size and distance. The present experiments showed that the bias field strength and grating width should be selected appropriately to avoid generating unwanted wave modes such as the S0-Lamb wave modes. It is also confirmed from experiments that the grating distance controls the center (or tuning) frequency of the grating transducer.  相似文献   
50.
Genipin is a protein cross-linking agent extracted from Gardenia (Gardenia jasminoides Ellis) fruits. This fruit has conventionally been used as a Chinese herbal medicine for the treatment of inflammation and jaundice and as an edible colorant in oriental countries. Uncoupling protein (UCP)-2 is a member of the family of uncoupling proteins, which are anion transporters positioned in the mitochondrial inner membrane. Genipin has been shown to have hepatoprotective activity, acting as an effective antioxidant and inhibitor of mitochondrial UCP2, and is also reported to exert significant anticancer effects. In this review, the author presents the latest progress of genipin as an anticancer agent and concisely describes its various mechanisms of action. In brief, genipin inhibits UCP2 to attenuate generation of reactive oxygen species (ROS), leading to ROS/c-Jun N-terminal kinase-dependent apoptosis of cancer cells. Genipin also increases the tissue inhibitors of matrix metalloproteases (MMP)-2, a kind of tumor promoter in a variety of cancers, as well as induces caspase-dependent apoptosis in in vitro and in vivo models. These findings suggest that genipin can serve as a promising novel antitumor agent that could be applicable for chemotherapy and/or chemoprevention for cancers.  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