全文获取类型
收费全文 | 6809篇 |
免费 | 424篇 |
国内免费 | 274篇 |
专业分类
电工技术 | 376篇 |
综合类 | 377篇 |
化学工业 | 1546篇 |
金属工艺 | 431篇 |
机械仪表 | 236篇 |
建筑科学 | 221篇 |
矿业工程 | 68篇 |
能源动力 | 207篇 |
轻工业 | 313篇 |
水利工程 | 65篇 |
石油天然气 | 105篇 |
武器工业 | 23篇 |
无线电 | 605篇 |
一般工业技术 | 1288篇 |
冶金工业 | 243篇 |
原子能技术 | 110篇 |
自动化技术 | 1293篇 |
出版年
2024年 | 13篇 |
2023年 | 100篇 |
2022年 | 127篇 |
2021年 | 133篇 |
2020年 | 129篇 |
2019年 | 133篇 |
2018年 | 155篇 |
2017年 | 191篇 |
2016年 | 163篇 |
2015年 | 159篇 |
2014年 | 265篇 |
2013年 | 292篇 |
2012年 | 333篇 |
2011年 | 481篇 |
2010年 | 366篇 |
2009年 | 404篇 |
2008年 | 449篇 |
2007年 | 509篇 |
2006年 | 444篇 |
2005年 | 384篇 |
2004年 | 309篇 |
2003年 | 289篇 |
2002年 | 210篇 |
2001年 | 216篇 |
2000年 | 287篇 |
1999年 | 125篇 |
1998年 | 100篇 |
1997年 | 80篇 |
1996年 | 80篇 |
1995年 | 81篇 |
1994年 | 98篇 |
1993年 | 72篇 |
1992年 | 64篇 |
1991年 | 47篇 |
1990年 | 42篇 |
1989年 | 34篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 25篇 |
1985年 | 22篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有7507条查询结果,搜索用时 0 毫秒
11.
Comparison of different absorption heat cycles is not always made on the correct manner. This also includes comparison of an ideal absorption cycle with a mechanical analogy. A new Carnot model operating with two heat engines and two mechanical heat pumps is defined to be the correct and logical way to describe the mechanical analogy for an absorption heat pump and an absorption heat transformer. General equations for the Carnot coefficient of performance, COPr, are exemplified and simulated for an absorption heat pump and an absorption heat transformer, and an entropy flow fraction diagram is introduced. The important fact that the absorption heat cycles must operate under the same conditions when they are compared is discussed. 相似文献
12.
Zongchang Zhao Fangwei Zhou Xiaodong Zhang Songping Li 《International Journal of Refrigeration》2003,26(3):2088
In this paper, a new solution cycle in the double absorption heat transformer is presented and the thermodynamic performance of this new cycle is simulated based on the thermodynamic properties of aqueous solution of lithium bromide. The results show that this new cycle is superior to the cycle being studied by some researchers. This new solution cycle has a wider range of operation in which the system maintains the high value of COP and has larger temperature lifts and operation stability. The relationship between the absorber and the absorbing evaporator is more independent and this makes the operation and control of the system more easier. 相似文献
13.
OpenType字体技术是Type字体和TrueType字体“大战”的产物,也是响应Unicode字符编码标准的产物,更是Adobe与Microsoft公司合作的产物。单从时间概念上考虑,这种字体技术其实并不新,现在重提OpenType字体,是因为CS2套件对于OpenType字体的全面支持,以及OpenType字体具有许多最要的特征。 相似文献
14.
Calculation methods for comparing the performance of pure and mixed working fluids in heat pump applications 总被引:2,自引:0,他引:2
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
15.
The effect of pressure on transition displacement between trickle and pulsed regimes (TPR: trickle-pulsed transition) in catalytic trickle bed reactors (CTBR) is not properly predicted by existing theoretical models and empirical correlations. Based on high pressure TPR data available to date, a modified Charpentier diagram is proposed to quantify directly the effect of pressure in non-foaming systems. 相似文献
16.
添加尖晶石对氧化锌压敏电阻性能的影响 总被引:1,自引:0,他引:1
通过添加尖晶石(Zn7Sb2O(12))改性研制出电位梯度为100V/mm左右,压敏电压在82~150V,通流容量可达1600A/cm2,漏电流<2μA系列压敏电阻器,从而满足了国内电话交换机行业对82V、100V、120V、150V压敏电阻器的电性能要求。从工艺的角度解释了尖晶石对氧化锌瓷晶粒的作用原理,并分析了尖晶石的微观结构及粒度对瓷片电性能的影响。 相似文献
17.
Maria G Corradini Mark D Normand Micha Peleg 《Journal of the science of food and agriculture》2006,86(5):785-792
Currently, the sterility of heat‐processed food and pharmaceuticals is assessed in terms of an F0 value, based on the equivalence of the heat treatment to an isothermal process at a reference temperature. This F0 value, however, has a meaning if, and only if, the inactivation kinetics of the targeted spores (or cells) follow a first‐order relationship and the temperature dependence of the D value, the reciprocal of the rate constant, is log‐linear. There is growing evidence that these conditions are not satisfied by many spores, including those of Clostridium botulinum and vegetative cells. Consequently, a replacement for the F0 value is proposed in the form of a momentary equivalent time at the reference temperature based on the actual survival pattern of the spores, which need not be log‐linear. This equivalent time can be calculated together with the theoretical survival ratio in real time, thus enabling an operator to monitor the lethality of ongoing industrial heat processes. The concept is demonstrated with published survival data of C. botulinum, for which the Weibullian and log‐logistic models served as primary and secondary models, respectively. The safety factor according to the proposed method is in the number of added minutes of processing, beyond the theoretical time needed to reduce the survival ratio of the targeted spores or cells to a level that would produce practical (or commercial) sterility. Copyright © 2006 Society of Chemical Industry 相似文献
18.
近距无线图像传输系统主要用于无线传感器网络中的图像采集、传输、处理和显示,本文设计并实现了一种具有较强实用性的近距无线图像传输系统。采用OV7670图像传感器作为图像数据采集器,高速低功耗的nRF24L01射频模块作为无线收发器,采用MSP430F14916位超低功耗单片机作为微处理器,所构成的系统具有功耗低、图像传输速度快等优点。作者详细阐述了该系统的硬件结构和软件设计。 相似文献
19.
In this investigation we consider the formation of Cooper pairs near the oxygen-deficient sites in Y-Ba-Cu-O ceramic superconductors which would give rise to an energy-dependent potential as seen by conduction charge carriers. It is shown that Cooper pairs could be formed under such conditions, resulting in a supercurrent. We use the Bogoliubov transformation technique to calculate the energy gap, the energy difference, and the transition temperature of the model superconductor using certain data obtained from previous experiments. Numerical analysis shows that the superconducting current can be explained by the presence of such oscillating Cooper pairs. 相似文献
20.
为了提高水印的鲁棒性和减小对应版权信息的大小,本文提出了一种基于Arnold变换、DWT和SVD的零水印算法。该算法将载体图像进行DWT变换,对低频子带进行分块SVD;比较置乱后的最大奇异值的大小,若大于则对应位为1,否则为0;将结果与预处理过的水印做异或运算,得密钥矩阵。该矩阵为检测水印提供密钥。实验证明,本算法对图像压缩、滤波、模糊、噪声及脏图具有良好的鲁棒性。 相似文献