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   49392篇
  免费   5475篇
  国内免费   1629篇
电工技术   2396篇
综合类   3826篇
化学工业   9779篇
金属工艺   5370篇
机械仪表   2497篇
建筑科学   5584篇
矿业工程   821篇
能源动力   8522篇
轻工业   2518篇
水利工程   414篇
石油天然气   2290篇
武器工业   332篇
无线电   1197篇
一般工业技术   5713篇
冶金工业   3312篇
原子能技术   1069篇
自动化技术   856篇
  2024年   203篇
  2023年   665篇
  2022年   1367篇
  2021年   1520篇
  2020年   1634篇
  2019年   1298篇
  2018年   1156篇
  2017年   1352篇
  2016年   1674篇
  2015年   1691篇
  2014年   2971篇
  2013年   3054篇
  2012年   3472篇
  2011年   3688篇
  2010年   2697篇
  2009年   2846篇
  2008年   2204篇
  2007年   3138篇
  2006年   2818篇
  2005年   2493篇
  2004年   2181篇
  2003年   1953篇
  2002年   1850篇
  2001年   1488篇
  2000年   1250篇
  1999年   1027篇
  1998年   839篇
  1997年   742篇
  1996年   605篇
  1995年   520篇
  1994年   408篇
  1993年   332篇
  1992年   298篇
  1991年   185篇
  1990年   156篇
  1989年   163篇
  1988年   102篇
  1987年   77篇
  1986年   60篇
  1985年   44篇
  1984年   70篇
  1983年   55篇
  1982年   55篇
  1981年   14篇
  1980年   12篇
  1979年   5篇
  1978年   3篇
  1977年   4篇
  1959年   28篇
  1951年   22篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
In this work, we co‐formulated an oil‐borne copper naphthenate/permethrin wood preservative system with synthetic polymer‐based fire‐retardant additives prior to the impregnation of Pinus radiata sapwood. We evaluated what effect, if any, the preservative had upon the fire performance properties of the fire retardants and whether the fire retardants impacted on the fungicidal and termiticidal efficacy of the preservative. The fire retardants included halogenated and phosphorus‐based systems. A mass loss calorimeter, in conjunction with a thermopile, was used to measure the time to ignition and the peak heat release rate (PHRR) from which the fire performance index (FPI) was determined. The preservative properties were evaluated using termite and soil‐block decay bioassays. In summary, we found that the rate of fire growth was reduced when the fire retardants were used in combination with the wood preservative. We also found that the PHRR was a better determinant of fire performance than the FPI. The performance of the wood preservative was enhanced against fungal decay and termite attack when used in combination with the fire retardants. The fire retardants also demonstrated some wood preservative properties of their own. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
122.
黄晓齐 《节能》2005,(11):32-34
讨论人体新陈代谢发热率及其影响因素;论述节能建筑中舒适的环境温度、空气相对湿度、空气流速以及新鲜空气供给量的最佳值范围;同时考虑皮肤和肺部的显热散热和蒸发潜热散热,建立了传热模型,得出了计算公式。  相似文献   
123.
管内覆丝网强化对流换热及阻力特性的实验研究   总被引:1,自引:1,他引:0  
通过实验对管内覆丝网管进行了强迫对流换热和阻力特性研究。结果表明:管内覆丝网使换热明显增强,阻力也相应增长。菱形丝网对角线距离与平行边距离之比对换热效果有决定作用,丝网厚度对换热的影响比较小,而丝网网格的大小对换热几乎没有影响,在相同的泵功率和几何条件下,换热系数最大增加21%。  相似文献   
124.
铸铝激光熔融处理后的组织与性能   总被引:1,自引:0,他引:1       下载免费PDF全文
朱祖昌  邱Qiu 《激光技术》1996,20(6):335-337
应用光学和电子显微镜及显微硬度计研究了铸造Al-Si合金经激光表面熔融处理后的组织和性能。指出,组织分熔化区、过度区和基体三层。在熔化区中树枝状先共晶α相的平均宽度由原始组织的20~40μm细化到2~3μm,同时共晶组织也被大大细化。这些变化使显微硬度值由67.4提高至109~115.  相似文献   
125.
Three methods for comparing cycle performance of working fluids, pure as well as non-azeotropic mixtures, are investigated for two applications and for two mixture pairs, HCFC22-CFC114 and HCFC22-HCFC142b, and their pure components. The methods differ in the way of calculating the heat exchange processes. They assume, respectively, equal minimum approach temperatures, equal mean temperature differences and equal heat transfer areas. Changes of coefficient of performance (COP) with composition are explained for all methods. It is shown that transport properties must be taken into account when making rigorous comparisons between working fluids. To predict the relations between fluids with high accuracy, one must use the method with equal heat transfer areas. By the method with equal mean temperature differences, the COP can be estimated with the same accuracy for mixtures as for pure fluids, and can be used for rough estimations of the COP level with different fluids. The method of equal minimum approach temperatures should be avoided for non-azeotropic mixtures.  相似文献   
126.
通过力学性能评估和金相组织观察,研究五种热处理制度,两个周期的试验结果,确定了K418B合金细晶铸造整体涡轮的真空热处理工艺。  相似文献   
127.
从烧结矿冷却并回收其余热的角度出发,介绍了利用烧结机尾落矿空间,采用喷吹空气装置对烧结矿进行冷却的小型模拟试验,从测出的结果来看,有可能成为一种新的烧结矿冷却方式。  相似文献   
128.
低温导热绝缘胶粘剂研究   总被引:3,自引:0,他引:3  
吴金林 《低温工程》1998,(3):51-54,59
一种低温导热绝胶粘剂用于氢氧发动机系统表面温度传感器的端封和胶接安装,介绍了胶粘剂的技术要求,研究方案及试验结果。以DW-3超低温胶粘剂为基础,经改性设计后,仍能保持胶粘剂原有的耐低温特性,而且其导热,绝缘等性能均能满足设计和使用要求。  相似文献   
129.
The condition of the surfaces is of crucial importance for the deuterium permeation through materials. In this work a study of the surface constants for the adsorption (σk1) and release (σk2) of deuterium under different surface conditions on the martensitic steel DIN 1.4914 (MANET) has been carried out. The growth of an oxide surface layer (Cr2O3) of about 25–30 nm in a MANET sample, heat treated in an oxidizing environment, compared to the bare MANET that have a ‘natural' oxide of about 5 nm has provoked a reduction of both the permeation rate and the recombination coefficient (about 3 orders of magnitude). In addition, the permeation governing process has changed from diffusion-limited to surface-limited. The measurements of the permeation rate of deuterium were performed by a gas-phase permeation technique over the temperature range 574–746 K and for deuterium driving pressures in the range from 3 to 105 Pa.  相似文献   
130.
In the early eighties, at the Boris Kidrich Institute Vincha, a method for measuring specific heat and electrical resistivity of electrical conductors in the millisecond resolution range was developed for measurements from room temperature to 1900 K. Over a period of nearly 10 years, the method was applied to different materials, including pure metals, ferrous, and nickel/ chromium alloys, and to the characterization of candidate materials for thermophysical property reference standards. This paper describes the method and reviews the results obtained in specific heat and electrical resistivity studies of ferromagnetic and other materials. The paper also demonstrates capabilities of the method for describing phase transitions or anomalies in pure metals (Fe, Co, Ni) or alloys (Nichrome, austenitic stainless steel).Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.  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