全文获取类型
收费全文 | 13107篇 |
免费 | 1149篇 |
国内免费 | 618篇 |
专业分类
电工技术 | 786篇 |
技术理论 | 1篇 |
综合类 | 802篇 |
化学工业 | 2052篇 |
金属工艺 | 846篇 |
机械仪表 | 751篇 |
建筑科学 | 908篇 |
矿业工程 | 342篇 |
能源动力 | 409篇 |
轻工业 | 824篇 |
水利工程 | 231篇 |
石油天然气 | 754篇 |
武器工业 | 91篇 |
无线电 | 1660篇 |
一般工业技术 | 1617篇 |
冶金工业 | 781篇 |
原子能技术 | 163篇 |
自动化技术 | 1856篇 |
出版年
2024年 | 35篇 |
2023年 | 188篇 |
2022年 | 292篇 |
2021年 | 480篇 |
2020年 | 362篇 |
2019年 | 326篇 |
2018年 | 405篇 |
2017年 | 422篇 |
2016年 | 380篇 |
2015年 | 483篇 |
2014年 | 626篇 |
2013年 | 688篇 |
2012年 | 791篇 |
2011年 | 815篇 |
2010年 | 717篇 |
2009年 | 712篇 |
2008年 | 709篇 |
2007年 | 729篇 |
2006年 | 700篇 |
2005年 | 613篇 |
2004年 | 403篇 |
2003年 | 472篇 |
2002年 | 460篇 |
2001年 | 403篇 |
2000年 | 378篇 |
1999年 | 371篇 |
1998年 | 340篇 |
1997年 | 320篇 |
1996年 | 299篇 |
1995年 | 214篇 |
1994年 | 178篇 |
1993年 | 130篇 |
1992年 | 98篇 |
1991年 | 82篇 |
1990年 | 64篇 |
1989年 | 47篇 |
1988年 | 34篇 |
1987年 | 25篇 |
1986年 | 20篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
91.
92.
93.
机械合金化制备金属难熔化合物 总被引:2,自引:0,他引:2
在介绍机械合金化特点的同时,重点研究和讨论了机械合金化制备金属难熔化合物的过程及机理,并认为机械合金化是制备难熔化合物及其材料的一种行之有效的方法。 相似文献
94.
本文针对我国表面活性剂/聚合物驱油的实际,研究了石油磺酸盐(PS)、正丁醇(R_4OH)和矿化水对水解聚丙烯酰胺(HPAM)溶液流变性的影响。结果表明,PS对HPAM溶液流变性的影响与介质的矿化度有关:非矿化水介质中,PS对HPAM溶液性质的影响类似于无机盐,能降低HPAM溶液的表现粘度(η_α)和稠度系数(k);当系统中含有一定浓度矿化水时,PS却能升高系统的η_α和k值,降低流型指数(n),使系统的非牛顿性增强。在含有PS和矿化水的HPAM系统中加入R_4OH,系统的η_α和k值会有所增加。 相似文献
95.
本文研究了在以电子加速器的电子射线为辐射源时,剂量率对PTFE辐射裂解的影响。在剂量相同的条件下,剂量率从1.44×10~4 rad/s增至5.75×10~4 rad/s,裂解效率提高3.3倍。剂量率和各断裂参数(单位剂量裂解度a_0,G(s)值等)均成线性关系。当裂解度一定时,剂量率与剂量成反变关系。 相似文献
96.
97.
The influence volume approach (IVA) is often utilized for modeling the mass transfer process dictating bubble growth dynamics in physical foaming. However, the assumed concentration profile in the IVA method is only valid when the changes in dissolved gas concentration are small (less than 5%). In addition, the validity of the IVA method is difficult to justify in chemical foaming applications because of the difficulties involved in defining the dissolved gas concentration profile.In the present work, we define two distinct stages of bubble growth for physical foaming. These two stages are termed as free and limited expansion and are controlled by the bubble nucleation rate. Bubble nucleation is assumed to occur only in the free expansion stage. In this stage, the bubble pressure drops substantially from an initially high pressure in the supersaturated state while the dissolved gas concentration changes very little. The second stage of our two-stage mass transfer model is termed the limited expansion stage and accounts for bubble growth in the late stages of foam evolution, when the pressure changes become small. However, in the limited stage of bubble growth the dissolved gas concentration drops significantly, as the available dissolved gas is depleted. To summarize our two-stage mass transfer model of foam expansion, the pressure difference between the bubble phase and the liquid phase is the primary mechanism for driving mass transfer in the early (free) stages of foam growth and the concentration difference is the driver for bubble growth in the late (limited) stages of growth. The first stage can be regarded as the nucleation stage and it is relatively short; while the second stage can be regarded as the bubble growth stage and is much longer. Most of the bubble volume expansion takes place in the second stage.The concentration gradient at the bubble edge, which is often ignored in other models, is analyzed in detail in this paper. The details of our novel mass transfer model are also presented. 相似文献
98.
在过去几年里,小型PCB诸如硅芯片级以及便携式移动电话的生产者和设计者们已经发现:如果要保持自己的竞争力并具备生产高密度封装板能力,就必须采用微孔技术。微孔技术的出现要求针对微孔缺陷的有效检测手段对工艺进行过程控制。本文对激光微孔的自动光学检测进行了详细介绍。 相似文献
99.
Miniaturized Hexagonal Stepped-Impedance Resonators and Their Applications to Filters 总被引:1,自引:0,他引:1
Rui-Jie Mao Xiao-Hong Tang Ling Wang Guo-Hong Du 《Microwave Theory and Techniques》2008,56(2):440-448
Miniaturized hexagonal stepped-impedance resonators and their applications to bandpass filters are presented. Based on the odd- and even-mode equivalent circuits, the resonance characteristics of these resonators are investigated. A series of circuit configurations, including the third-order Chebyshev, trisection, and fifth-order cascaded trisection filters, are constructed by the proposed resonators. These filters are very compact and have good stopband responses. Measured results validate the analysis and theoretical prediction with good agreement. 相似文献
100.
Yanhan Shen Rongrong Qi Qiaochu Liu Yanling Wang Yapeng Mao Juan Yu 《应用聚合物科学杂志》2008,110(4):2261-2266
The grafting of a polymer can lead to the improvement and modification of the polymer and thus expand its applications. Grafting methods include solution grafting in organic solvents, melt grafting at high temperatures, and light grafting with radioactive sources. These methods have their advantages and disadvantages. The disadvantages include waste treatment, consumption of energy, and so on. In this study, a hydrothermal process which is called the green approach, was developed to prepare graft copolymers. The effect of various factors on the grafting degree was investigated in detail. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献