全文获取类型
收费全文 | 10158篇 |
免费 | 961篇 |
国内免费 | 561篇 |
专业分类
电工技术 | 1079篇 |
综合类 | 915篇 |
化学工业 | 404篇 |
金属工艺 | 255篇 |
机械仪表 | 1187篇 |
建筑科学 | 655篇 |
矿业工程 | 212篇 |
能源动力 | 345篇 |
轻工业 | 297篇 |
水利工程 | 95篇 |
石油天然气 | 228篇 |
武器工业 | 116篇 |
无线电 | 1929篇 |
一般工业技术 | 427篇 |
冶金工业 | 191篇 |
原子能技术 | 154篇 |
自动化技术 | 3191篇 |
出版年
2024年 | 53篇 |
2023年 | 129篇 |
2022年 | 226篇 |
2021年 | 250篇 |
2020年 | 219篇 |
2019年 | 148篇 |
2018年 | 160篇 |
2017年 | 212篇 |
2016年 | 259篇 |
2015年 | 335篇 |
2014年 | 661篇 |
2013年 | 608篇 |
2012年 | 785篇 |
2011年 | 900篇 |
2010年 | 631篇 |
2009年 | 618篇 |
2008年 | 667篇 |
2007年 | 825篇 |
2006年 | 685篇 |
2005年 | 648篇 |
2004年 | 539篇 |
2003年 | 431篇 |
2002年 | 327篇 |
2001年 | 293篇 |
2000年 | 213篇 |
1999年 | 187篇 |
1998年 | 122篇 |
1997年 | 120篇 |
1996年 | 117篇 |
1995年 | 71篇 |
1994年 | 69篇 |
1993年 | 43篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
建筑工程投标报价优选模型 总被引:1,自引:0,他引:1
金季岚 《信息技术与信息化》2007,(5):70-72,59
通过建立区间二次规划数学模型、灰色模型、多目标规划等模型,建立材料价格和用量的选择模型,提供投标单位一种便捷的调整工程造价和控制造价的手段。 相似文献
22.
介绍了国内首次研制的光缆CATV用1.3μmDFB激光器组件。组件工作频带达到1GHz,带内起伏〈1dB,组件的RIN〈-153dB/Hz;出纤光功率〉2mW,载噪比CNR〉50dB。首次实现用低反射尖锥端光纤的DFB激光器耦合。 相似文献
23.
The self-organizing map (SOM) [5] provides a general data approximation method which is suitable for several application domains. The topology preservation is an important feature in data-analysis and may also be advantageous for the evaluation of the data in a function approximation or regression task. For this reason the interpolated self-organizing map (I-SOM) adds an output layer to the SOM architecture which computes a real valued output vector. This paper presents an extension of I-SOM towards a continuous interpolation. It is compared to RBF and to the parametrized self-organizing map. 相似文献
24.
介绍有源声表面波滤波组件的设计思路。报道最新研制的高性能滤波组件,其中心频率40MHz,3dB相对带宽0.8%,阻带抑制优于100dB,矩形系数(Δf100dB/Δf3dB)小于3,输入输出端口电压驻波比接近1。组件体积85mm×35mm×24mm,重量小于115g 相似文献
25.
26.
汪滨琦 《数字社区&智能家居》2006,(5)
以十种函数为例,讨论了在EXCEL电子表格软件中的单元格里粘贴函数的应用要素,即参数的数量、参数的种类、参数之间的关系、函数的书写及粘贴过程等。例举少许易懂函数样例,有助于人们理解、发挥函数功能的强大作用,提高工作效率。 相似文献
27.
介绍了作者研制的应用于固态雷达发射机上的L波段500W固态功放组件的工作原理、用途及其主要技术指标。描述了功放组件的设计过程和测试结果。该功放组件在窄脉宽条件下实现了快速上升沿,性能优良,工作稳定可靠。 相似文献
28.
29.
The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed. 相似文献
30.
岩样自然伽玛能谱的数据库管理系统 总被引:3,自引:0,他引:3
本文阐述了岩样自然伽玛能谱数据库管理系统的功能、结构、特点以及它在研究自然伽玛能谱与岩性参数间关系中的应用,为自然伽玛能谱测井的资料解释奠定了理论基础。 相似文献