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   43860篇
  免费   4574篇
  国内免费   2998篇
电工技术   2459篇
技术理论   1篇
综合类   4014篇
化学工业   7279篇
金属工艺   3291篇
机械仪表   1857篇
建筑科学   2925篇
矿业工程   1943篇
能源动力   2141篇
轻工业   3548篇
水利工程   1398篇
石油天然气   2589篇
武器工业   591篇
无线电   4468篇
一般工业技术   4974篇
冶金工业   3056篇
原子能技术   1102篇
自动化技术   3796篇
  2024年   178篇
  2023年   599篇
  2022年   1177篇
  2021年   1426篇
  2020年   1589篇
  2019年   1334篇
  2018年   1319篇
  2017年   1706篇
  2016年   1852篇
  2015年   1872篇
  2014年   2833篇
  2013年   3092篇
  2012年   3375篇
  2011年   3463篇
  2010年   2561篇
  2009年   2499篇
  2008年   2226篇
  2007年   2778篇
  2006年   2331篇
  2005年   2011篇
  2004年   1773篇
  2003年   1505篇
  2002年   1291篇
  2001年   1119篇
  2000年   943篇
  1999年   783篇
  1998年   667篇
  1997年   559篇
  1996年   517篇
  1995年   432篇
  1994年   321篇
  1993年   259篇
  1992年   237篇
  1991年   180篇
  1990年   152篇
  1989年   105篇
  1988年   73篇
  1987年   46篇
  1986年   48篇
  1985年   38篇
  1984年   36篇
  1983年   19篇
  1982年   19篇
  1981年   16篇
  1980年   17篇
  1979年   5篇
  1978年   6篇
  1975年   10篇
  1959年   9篇
  1951年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
钢样成分化验分析结果网络传输系统将碳硫分析仪、光谱分析仪和相应的计算机控制系统按以太网络结构组联,形成"炉前分析网络",采用分析网主服务器系统软件和网络分析系统软件实现网络传输。该系统可将炉前钢样化验分析结果实时传输到炉前大屏,具有传输速度快、准确率高的特点,提高了工作效率和产品合格率,降低了生产成本。  相似文献   
73.
The degree to which real and hypothetical rewards were discounted across delays ranging from 6 hr to 1 year was explored in a within-subjects design. An adjusting-amounts procedure was used to estimate the subjective value of real and hypothetical rewards at each delay. A hyperbolic discounting function provided a significantly better fit to individual participants' preferences than did an exponential function. No significant effect of reward type on degree of hyperbolic discounting or area under the discounting curves was detected. These findings offer some support for the validity of using hypothetical rewards to estimate discounting rates in substance-abusing and other populations, but caution is suggested because this support is gleaned from a failure to detect an effect of reward type. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
74.
Prediction of the energy dissipation rate in ductile crack propagation   总被引:1,自引:0,他引:1  
In this paper, energy dissipation rate D vs. Δa curves in ductile fracture are predicted using a ‘conversion’ between loads, load‐point displacements and crack lengths predicted by NLEFM and those found in real ELPL propagation. The NLEFM/ELPL link was recently discovered for the DCB testpiece, and we believe it applies to other cracked geometries. The predictions for D agree with experimental results. The model permits a crack tip toughness Ra) which rises from Jc and saturates out when (if) steady state propagation is reached after a transient stage in which all tunnelling, crack tip necking and shear lip formation is established. JR is always greater than the crack tip Ra) and continues to rise even after Ra) levels off. The analysis is capable of predicting the usual D vs. Δa curves in the literature which have high initial values and fall monotonically to a plateau at large Δa. It also predicts that D curves for CCT testpieces should be higher than those for SENB/CT, as found in practice. The possibility that D curves at some intermediate Δa may dip to a minimum below the levelled‐off value at large Δa is predicted and confirmed by experiment. Recently reported D curves that have smaller initial D than the D‐values after extensive propagation can also be predicted. The testpiece geometry and crack tip Ra) conditions required to produce these different‐shaped D vs. Δa curves are established and confirmed by comparison with experiment. The energy dissipation rate D vs. Δa is not a transferable property as it depends on geometry. The material characteristic Ra) may be the ‘transferable property’ for scaling problems in ELPL fracture. How it can be deduced from D vs. Δa curves (and by implication, JR vs. Δa curves) is established.  相似文献   
75.
分析了高温复合固硫剂各成分的作用,实验研究了在不同配比的燃烧试验下,各成分对燃煤着火和燃烧以及对炉渣固硫的影响,得出了该煤种高温复合固硫剂的最佳配方。  相似文献   
76.
Electrochemical implantation was performed at Ni electrodes to form DyNi2 films at 0.55 V (vs. Li+/Li), 0.62 V, and 0.70 V for 0.5-5.0 h in a molten LiCl-KCl-DyCl3 (0.50 mol%) system at 700 K. It was found that the DyNi2 films grew linearly with time with coulomb efficiency of about 100%. The obtained growth rates were higher at more negative potentials, i.e., 0.47 μm min−1 at 0.55 V, 0.32 μm min−1 at 0.62 V, and 0.14 μm min−1 at 0.70 V. On the analogy of the metal oxide growth, the observed rapid and linear growth of DyNi2 films may be explained by the existence of the outer and inner DyNi2 layers.  相似文献   
77.
A semi-empirical mathematical model for the acid-oxygen pressure leaching of Ni–Cu matte is presented, based on data from batch leaching experiments. The primary controlling factor in the leaching process is found to be galvanic inhibition of the more highly oxidized copper and nickel sulfide species by less oxidized species, particularly Ni alloy and Ni3S2. The leaching rate of many species is greatly reduced by the presence of one or both of these phases, and others will not commence leaching until neither is present. The mathematical model is based on first-order chemical reaction controlled rate expressions, as the reactions occurring are electrochemical in nature. Mass transfer effects are included only empirically. Some possibly diffusion-related phenomena are noted, although the model is not extended to incorporate these effects on a fundamental level. The model is verified and extended by the inclusion of several different factors that were tested experimentally. The effects of variations in O2 flow rate and partial pressure, initial particle size, reaction pulp density and initial acid concentration were all studied, and included in the model. Variations in O2 flow rate and partial pressure are found to affect the reaction rates via the dissolved oxygen concentration in the solution phase.  相似文献   
78.
We present some new lower bounds on the optimal information rate and on the optimal average information rate of secret sharing schemes with homogeneous access structure. These bounds are found by using some covering constructions and a new parameter, the k-degree of a participant, that is introduced in this paper. Our bounds improve the previous ones in almost all cases.  相似文献   
79.
本文采用 2只扩散杯 ,一只选择渗透率较大的滤膜 ,使2 2 2 Rn和2 2 0 Rn能很容易的进入。另一只选择渗透率较小的滤膜 ,该滤膜只允许2 2 2 Rn进入 ,半衰期较短的2 2 0 Rn被阻挡在外面。通过不同滤膜扩散率的差异 ,改变探测器的空气交换率 ,从而达到同时测量2 2 2 Rn和2 2 0 Rn的目的  相似文献   
80.
任小军 《通信技术》2003,(12):112-113
提出种基于TEMIC射频卡Manchester编码的速率自适应读卡算法,并对该算法进行了说明和示例。  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