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   247908篇
  免费   3175篇
  国内免费   855篇
电工技术   4755篇
综合类   187篇
化学工业   33724篇
金属工艺   9453篇
机械仪表   7420篇
建筑科学   5616篇
矿业工程   874篇
能源动力   7132篇
轻工业   20565篇
水利工程   2193篇
石油天然气   3216篇
武器工业   15篇
无线电   34160篇
一般工业技术   49399篇
冶金工业   48540篇
原子能技术   5075篇
自动化技术   19614篇
  2021年   2061篇
  2020年   1557篇
  2019年   1914篇
  2018年   3270篇
  2017年   3307篇
  2016年   3399篇
  2015年   2218篇
  2014年   3954篇
  2013年   11474篇
  2012年   6233篇
  2011年   8572篇
  2010年   6904篇
  2009年   7883篇
  2008年   8404篇
  2007年   8294篇
  2006年   7361篇
  2005年   6500篇
  2004年   6282篇
  2003年   6452篇
  2002年   5729篇
  2001年   6123篇
  2000年   5467篇
  1999年   6009篇
  1998年   16155篇
  1997年   11087篇
  1996年   8457篇
  1995年   6540篇
  1994年   5860篇
  1993年   5781篇
  1992年   4081篇
  1991年   3967篇
  1990年   3822篇
  1989年   3589篇
  1988年   3500篇
  1987年   2954篇
  1986年   2897篇
  1985年   3153篇
  1984年   2882篇
  1983年   2775篇
  1982年   2589篇
  1981年   2492篇
  1980年   2416篇
  1979年   2260篇
  1978年   2079篇
  1977年   2562篇
  1976年   3510篇
  1975年   1728篇
  1974年   1700篇
  1973年   1631篇
  1972年   1445篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
Multidimensional Systems and Signal Processing - In medical Image processing, the chief objective is to detect Neoplasm effectively. Neoplasm is basically a sort of abnormal excessive cell growth...  相似文献   
102.
103.
The micro-powder injection molding (micro-PIM) process has the potential to bridge the gap between the design and manufacturing of micro-components that are often used in small and handy devices. Numerical modeling helps to analyze and overcome various difficulties of micro-PIM. In the present work, a numerical model is developed to predict the powder–binder separation (a common defect in PIM and especially severe in micro-PIM) during the injection of an alumina feedstock. A powder–binder separation criterion is proposed dealing with applied injection pressure and friction force between the powder and binder. An indirect comparison of feedstock travel time between two locations is used to validate the model. The predicted segregation from the simulated result is supported by a qualitative experimental measurement. The developed model can be used to optimize injection parameters to get a defect-free product.  相似文献   
104.
Glass Physics and Chemistry - This article presents the results of a study of the effect on the adsorption properties of microporous glass of its modification with ZnO–Ag nanocrystals. The...  相似文献   
105.
Strength of Materials - Creep constitutive equations have been derived for the materials that exhibit the properties of orthotropy (transversal isotropy) and transient creep under cyclic loading. A...  相似文献   
106.
Singh  A. K.  Chandra  Devesh  Kattayat  Sandhya  Kumar  Shalendra  Alvi  P. A.  Rathi  Amit 《Semiconductors》2019,53(12):1584-1592
Semiconductors - Compositional variations in GaAs based ternary alloys have exhibited wide range alterations in electronic properties. In the present paper, first-principles study of...  相似文献   
107.
Type 316LN stainless steel (SS) is the principal structural material for the components of sodium cooled fast reactors operating under elevated temperature conditions. In order to assess the degradation in strength of service exposed components using a small specimen testing technique such as automated ball indentation (ABI), it is necessary to carry out prior detailed ABI studies on the virgin material. In this investigation, the tensile behaviour of as-received 316LN SS were investigated at several temperatures in the range 298–973 K using ABI technique. The load-depth of indentation data measured from ABI tests was analyzed using semi-empirical relationships to obtain the tensile properties. The yield stress and the flow curves were determined by correlating ABI results with corresponding uniaxial tensile test results. Trend curve for tensile strength with temperature, as estimated from ABI tests, exhibited a plateau region in the temperature around 823 K, similar to uniaxial tensile tests. The variations of strength coefficient, strain hardening exponent, yield ratio, hardness and uniform ductility with temperature were evaluated from ABI tests. The ABI technique was found to estimate the influence of temperature on tensile properties sensitively.  相似文献   
108.
Thermal flow characteristics and the methane conversion reaction in a low power arc plasma reactor for efficient storage and transport of methane, which is the main component of shale gas, were simulated. The temperature and velocity distributions were calculated according to the type of discharge gases and arc current level by a self-developed magnetohydrodynamics (MHD) code and a commercial ANSYS-FLUENT code; the transport of chemical species was analyzed as including the chemical reactions of methane conversion. The simulated results were verified by the comparison of calculated and measured arc voltages with permissible low error as under 4%. Three C2 hydrocarbon gases with ethane (C2H6), ethylene (C2H4), and acetylene (C2H2) were selected as the converted species of methane from experimental data. The mass fraction of C2 hydrocarbons and hydrogen as the product of the conversion reaction at the reactor was also calculated. Those values show good agreement with the actual experimental results in that the major conversion reaction occurred in C2H2 and hydrogen, and the conversions to C2H6, C2H4, and hydrogen were minor reactions of methane pyrolysis conversion.  相似文献   
109.
The synergistic interactions and corrosion protection properties of 2-amino 4-methyl benzothiazole, (AMBT) and 1, 2, 3-benzotriazole (BTZ) have been studied for mild steel in HCl at elevated temperatures. The extent of synergistic interaction increases with temperature. The methods of study include the conventional weight loss studies, computational screening, surface characterization and electrochemical studies. Quantum chemical approach was used to calculate some electronic properties of the molecules and to ascertain the synergistic interaction, inhibitive effect and molecular structures. The corrosion inhibition efficiencies and the global chemical reactivity relate to parameters like total energy, EHOMO, ELUMO and gap energy (ΔE). Condensed atom Fukui functions also calculated using DFT at B3LYP/6-31G* level, and were found to be correlating with the experimental results.  相似文献   
110.
This article presents a metaheuristic approach, the binary whale optimization algorithm (BWOA), to solve complex, constrained, non-convex, binary-nature profit-based unit commitment (PBUC) optimization problems of a price-taking generation company (GenCo) in the electricity market. To simulate the binary-nature PBUC problem, the continuous, real-value whale position/location is mapped into binary search space through various transfer functions. This article introduces three variants of BWOA using tangential hyperbolic, inverse tangent (arctan) and sigmoidal transfer functions. The effectiveness of the BWOA approaches is examined in test systems with different market mechanisms, i.e. an energy-only market, and energy and reserve market participation with different reserve payment methods. The simulation results are presented, discussed and compared with other existing approaches. The convergence characteristics, solution quality and consistency of the results across different BWOA variants are discussed. The superiority and statistical significance of the proposed approaches with respect to existing approaches is also presented.  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