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   925篇
  免费   10篇
电工技术   116篇
综合类   1篇
化学工业   202篇
金属工艺   18篇
机械仪表   22篇
建筑科学   12篇
矿业工程   2篇
能源动力   39篇
轻工业   79篇
水利工程   1篇
石油天然气   2篇
无线电   89篇
一般工业技术   154篇
冶金工业   101篇
原子能技术   24篇
自动化技术   73篇
  2024年   4篇
  2023年   4篇
  2022年   12篇
  2021年   19篇
  2020年   9篇
  2019年   17篇
  2018年   9篇
  2017年   3篇
  2016年   17篇
  2015年   25篇
  2014年   23篇
  2013年   59篇
  2012年   36篇
  2011年   52篇
  2010年   40篇
  2009年   42篇
  2008年   51篇
  2007年   54篇
  2006年   46篇
  2005年   31篇
  2004年   26篇
  2003年   31篇
  2002年   21篇
  2001年   6篇
  2000年   10篇
  1999年   16篇
  1998年   41篇
  1997年   41篇
  1996年   18篇
  1995年   15篇
  1994年   14篇
  1993年   17篇
  1992年   7篇
  1991年   6篇
  1990年   8篇
  1989年   9篇
  1988年   6篇
  1987年   4篇
  1986年   11篇
  1985年   12篇
  1984年   5篇
  1983年   9篇
  1982年   3篇
  1981年   9篇
  1980年   5篇
  1979年   4篇
  1978年   7篇
  1977年   5篇
  1976年   9篇
  1972年   2篇
排序方式: 共有935条查询结果,搜索用时 15 毫秒
101.
In vitro mammalian cytogenetic tests detect chromosomal aberrations and are used for testing the genotoxicity of compounds. This study aimed to identify a supportive genomic biomarker could minimize the risk of misjudgments and aid appropriate decision making in genotoxicity testing. Human lymphoblastoid TK6 cells were treated with each of six DNA damage-inducing genotoxins (clastogens) or two genotoxins that do not cause DNA damage. Cells were exposed to each compound for 4 h, and gene expression was comprehensively examined using Affymetrix U133A microarrays. Toxicogenomic analysis revealed characteristic alterations in the expression of genes included in cyclin-dependent kinase inhibitor 1A (CDKN1A/p21)-centered network. The majority of genes included in this network were upregulated on treatment with DNA damage-inducing clastogens. The network, however, also included kinesin family member 20A (KIF20A) downregulated by treatment with all the DNA damage-inducing clastogens. Downregulation of KIF20A expression was successfully confirmed using additional DNA damage-inducing clastogens. Our analysis also demonstrated that nucleic acid constituents falsely downregulated the expression of KIF20A, possibly via p16 activation, independently of the CDKN1A signaling pathway. Our results indicate the potential of KIF20A as a supportive biomarker for clastogenicity judgment and possible mechanisms involved in KIF20A downregulation in DNA damage and non-DNA damage signaling networks.  相似文献   
102.
103.
This paper first reviews the earthquakes that occurred since 1995 and then outlines the significant lessons learnt from disasters. The discussion then goes into the induced development of engineering practices that were triggered by those disasters. It is clear that major development occurred in design philosophies, soil improvement, and facilities for research. The last section of this paper addresses the compound effects of earthquakes and rainfall that may make the extent of the disasters worse.  相似文献   
104.
105.
    
Experiments were conducted to determine the effects of impeller clearance, impeller diameter, and other operating variables on the minimum agitation speed for off-bottom solid suspension in agitated vessels, Njs, for disc turbines (DTs) and flat-blade turbines (FBTs). Only data for which the impellers produced recirculation flows above and below the impeller (the so-called “double-eight” flow pattern) were considered. Regression equations for Njs were obtained, in which explicit terms for impeller clearance and vessel diameter-to-impeller diameter ratio (T/D) were included. Modified Zwietering equations (Zwietering, 1958) were also obtained, in which Zwietering's parameter S was mathematically expressed as a function of vessel diameter-to-impeller clearance ratio and T/D ratio. When used together with the correlations of Armenante and Uehara Nagamine (1998) for impellers close to the vessel bottom, the equations presented here can be used to calculate Njs for DTs and FBTs for any typical impeller clearance.  相似文献   
106.
  总被引:1,自引:0,他引:1  
The isothermal shrinkage behaviors of fine zirconia powders (containing 2.8–2.9 mol% Y2O3) with specific surface areas of about 6 and 16 m2/g were investigated to clarify the effect of specific surface area on the initial sintering stage. The shrinkage of powder compact was measured under constant temperatures in the range of 1000°–1100°C. The increase in specific surface area enhanced the densification rate with increasing temperature. The values of activation energy ( Q ) and frequency-factor term (β0) of diffusion at initial sintering were estimated by applying the sintering-rate equation to the isothermal shrinkage data. The Q of diffusion changes little but the β0 increases with the increase in specific surface area. It is therefore concluded that the increase in the specific surface area of fine zirconia powder enhances the shrinkage rate because of an increase in the β0 at the initial stage of sintering.  相似文献   
107.
    
Manganese oxides on titanium dioxide were prepared by impregnation method at various calcination temperatures and by deposition-precipitation method and the catalysts were characterized using TG-DTA, XRD, XPS, and N2 adsorption. Various oxidation states for manganese were obtained and activity towards ozone decomposition inside a nonthermal plasma catalysis reactor was investigated. Activity tests show that with increasing manganese oxidation state, the greater the degree of ozone decomposition inside the reactor. MnOx/TiO2 prepared by impregnation method calcined at 350 °C showed the highest decrease in ozone concentration.  相似文献   
108.
    
High‐proton‐conductive polymer electrolyte with a nanomatrix channel was prepared by graft copolymerization of styrene onto deproteinized natural rubber followed by sulfonation with chlorosulfonic acid. First, natural rubber latex was purified with urea in the presence of surfactant to remove almost all proteins present in the rubber. Second, graft copolymerization of styrene onto deproteinized natural rubber was carried out with tert‐butyl hydroperoxide/tetraethylenepentamine as an initiator at 30°C in latex stage. The graft‐copolymerized natural rubber (DPNR‐graft‐PS) was sulfonated with chlorosulfonic acid in chloroform solution at an ambient temperature. The resulting sulfonated DPNR‐graft‐PS was characterized by FTIR spectroscopy, solid state 13C CP/MAS NMR spectroscopy, elemental analysis, and transmission electron microscopy. High proton conductivity of about 0.1 S/cm, less water uptake of 24 wt % and comparatively good stress at break of 9 MPa were accomplished at suitable contents of styrene units and sulfur, i.e., 32 wt % and 75 mol %, respectively. The high proton conductivity, excellent stability, and good mechanical properties were associated with not only the formation of the nanomatrix channel but also a specific concentration of sulfuric acid group. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.  相似文献   
109.
In general, diode rectifiers with electrolytic capacitors on the dc side have been used as dc power supplies for voltage-source inverters. Rectifiers of this type, however, cause many problems such as poor power factor and harmonics. Recently, voltage-source PWM rectifier-inverters have been studied to provide the following advantages: (1) harmonic-free on both ac sides; (2) unity power factor on the input ac side; (3) power flow of either direction or power regeneration; (4) reduction of the dc capacitor. However, it is difficult for a conventional voltage-source PWM rectifier-inverter to regulate the capacitor voltage on transient states because it has only a voltage feedback loop. This paper describes a voltage-source PWM rectifier-inverter with feedforward control of instantaneous power. Based on the pq theory, the instantaneous power which is calculated in the control circuit of the inverter is fed forward to the control circuit of the rectifier. The feedforward control of instantaneous power contributes greatly to sufficiently suppress voltage fluctuation of the dc capacitor on transient states. Transient characteristics are discussed, and some interesting experimental results of a laboratory model are shown.  相似文献   
110.
Three newly found vibrational levels at energies Te(v) = 45127.88(3), 51900.40(4), and 52604.95(3) cm-1 allow the first application of resonance-enhanced multiphoton ionization for detecting the SO radical in its low-energy singlet states, a1Delta and b1Sigma+. The analysis of the spectra is based on the observation of 10 rotationally resolved bands starting from a1Delta v = 0, 6 ellipsis 11 and b1Sigma+ v = 8, covering a typical range of J = 5 ellipsis 40 or 50. Population of these SO singlet states has been achieved by two-photon dissociation of SO2 in a molecular beam environment, applying wavelengths in the 248 to 291 nm range. This paper presents an analysis of the rotational, vibrational, and electronic properties of the new levels. Reviewing earlier works on the singlet states of SO, a revised term energy scheme is provided which connects the singlet and triplet systems of the molecule. Copyright 1998 Academic Press.  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