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   649952篇
  免费   20501篇
  国内免费   9519篇
电工技术   19850篇
技术理论   14篇
综合类   11628篇
化学工业   101384篇
金属工艺   28793篇
机械仪表   25047篇
建筑科学   27770篇
矿业工程   6246篇
能源动力   18011篇
轻工业   53500篇
水利工程   6866篇
石油天然气   15440篇
武器工业   1363篇
无线电   82162篇
一般工业技术   110921篇
冶金工业   97600篇
原子能技术   10156篇
自动化技术   63221篇
  2023年   4164篇
  2022年   7950篇
  2021年   11332篇
  2020年   8233篇
  2019年   8104篇
  2018年   10557篇
  2017年   11305篇
  2016年   11062篇
  2015年   11062篇
  2014年   15954篇
  2013年   32610篇
  2012年   22664篇
  2011年   28405篇
  2010年   23429篇
  2009年   24771篇
  2008年   25003篇
  2007年   24512篇
  2006年   23464篇
  2005年   21126篇
  2004年   17564篇
  2003年   17080篇
  2002年   16085篇
  2001年   15973篇
  2000年   15260篇
  1999年   16839篇
  1998年   33585篇
  1997年   24217篇
  1996年   19396篇
  1995年   15021篇
  1994年   13127篇
  1993年   12341篇
  1992年   9049篇
  1991年   8492篇
  1990年   7700篇
  1989年   7344篇
  1988年   7047篇
  1987年   5895篇
  1986年   5752篇
  1985年   6390篇
  1984年   5710篇
  1983年   5336篇
  1982年   4949篇
  1981年   4857篇
  1980年   4653篇
  1979年   4364篇
  1978年   4113篇
  1977年   5094篇
  1976年   7224篇
  1975年   3472篇
  1974年   3330篇
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
71.
本文介绍了一种在微机上实现的印制板自动布线方法──多级线探索法及其编程方法。这种方法是基于完备布线算法的概念,通过分析李氏算法和传统线探索法的不足之处而得到的。虽然它也是一种线探索法,但有较传统线探索法更强的探索能力,不需要结合李氏算法而能单独完成布线任务,是一种较理想的算法,通过实验获得了较为满意的效果。  相似文献   
72.
73.
Fuzzy controller design by using neural network techniques   总被引:2,自引:0,他引:2  
This paper investigates the relationship between the piecewise linear fuzzy controller (PLFC), in which the membership functions for fuzzy variables and the associated inference rules are all in piecewise linear forms, and a Gaussian potential function network based controller (GPFNC), in which the network output is a weighted summation of hidden responses from a series of Gaussian potential function units (GPFU's). Systematic procedures are proposed for transformation from a PLFC to its GPFNC counterpart, and vice versa. Based on these transformation principles, a series of systematic and feasible steps is presented for the design of an optimized PLFC (PLFC*) by using neural network techniques. In the design procedures, the simplified PLFC is used as the initial controller structure, then a GPFNC, which gives the approximate control response to the initially given PLFC, is found for further optimization. A neutralization process is used to demonstrate the feasibility and the potential applicability of these intelligent controllers on the regulation of highly nonlinear chemical processes  相似文献   
74.
Nutrient uptake by the hindlimb was investigated utilising the arteriovenous difference technique in 5 Thoroughbred horses fed to maintenance a diet of 100% roughage or 52% oat grain and 48% roughage. Arterial blood was obtained from a catheter inserted into the carotid artery while venous blood was simultaneously collected from a catheter placed into the iliac vein via the medial saphenous vein. The arteriovenous difference for glucose was significant and represented a mean extraction of 10 +/- 1% with no effect of diet. If fully oxidised, glucose uptake (corrected for lactate and pyruvate arteriovenous difference) was sufficient to account for 78 +/- 13% or 107 +/- 15% of the oxygen consumed by the hindlimb in horses fed a roughage or 52% oat grain diet respectively. Acetate was also a major metabolite of the hindlimb, showing a 39 +/- 5% extraction with no effect of diet. However, the 52% oat grain diet did induce a significant decline in the concentration of acetate in arterial blood. The potential contribution to oxidation in the hindlimb was significantly reduced from 32 +/- 4% in horses fed roughage to 21 +/- 3% when fed 52% oat grain. D-3-Hydroxybutyrate uptake could account for 9 +/- 1% of the oxidation by the hindlimb with no effect of diet. The technique for measuring nutrient uptake across the hindlimb using the arteriovenous difference is relatively simple and would be valuable in investigating fuel use by muscle during exercise.  相似文献   
75.
76.
实验研究了以工业硫酸亚铁及废硫酸为原料,分别采用NaClo_3、KClO_3、H_2O_2及(o_2+NaNO_2)为氧化剂成聚硫酸铁的条件。在以(O_2+NaNO_2)为氧化剂的合成过程中,发现添加微量助催化剂(型号为HG-1、HG-2和HG-3),对提高合成速度及反应过程的稳定性具有重大作用。  相似文献   
77.
78.
Carboxyl-terminated butadiene-acrylonitrile-rubber decreases modulus and yield stress of the studied epoxy but increases fracture toughness. The addition of glass bead compensates for the loss in modulus but has little effect on yield stress. However, it significantly contributes to the fracture toughness by providing additional mechanisms for toughening of both the unmodified and rubber-modified epoxy. For the toughened epoxies studied, fracture surfaces gave only limited information on fracture mechanisms since significant energy absorption also occurs in the material below the fracture surface. Suggestions for suitable material compositions for fiber composite matrices are given.  相似文献   
79.
Schottky diodes of aluminium/poly(3-octylthiophene)(P30T)/indium-tin oxide with large active area are prepared by using the proposed new casting technique. Their rectifying behavior and junction characteristics are dependent on whether the P30T is doped and on the storage time, but independent of the thickness of the P30T layer. The present technique can also be applied in a fabrication of electronic devices with other soluble conjugated polymers.  相似文献   
80.
This paper presents a model of heterogenous diffusion in capillary porous materials during the process of drying. The governing heat and mass transfer equations have been established using the liquid as well as vapor flow. Two models have been presented. Model 1 does not consider the heat conduction while the model 2 has been established by considering the conduction. The developed models and the numerical solutions of the resulting differential equations can take into account the moisture and temperature dependent thermophysical properties of the product. All equations have been established in spherical coordinates but the programme written for the purpose of calculations can be used for other geometries also. Numerical calculations have been performed for gas concrete and tiles using model 1, while model 2 has been used for gas concrete only because of the lack of data for thermophysical properties of the tile. For gas concrete it was seen that conduction has only marginal effect on the drying process and the numerical predictions of the drying process were reasonably accurate.  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