全文获取类型
收费全文 | 7751篇 |
免费 | 921篇 |
国内免费 | 707篇 |
专业分类
电工技术 | 269篇 |
综合类 | 827篇 |
化学工业 | 1455篇 |
金属工艺 | 600篇 |
机械仪表 | 287篇 |
建筑科学 | 1015篇 |
矿业工程 | 312篇 |
能源动力 | 192篇 |
轻工业 | 381篇 |
水利工程 | 222篇 |
石油天然气 | 612篇 |
武器工业 | 87篇 |
无线电 | 762篇 |
一般工业技术 | 1202篇 |
冶金工业 | 518篇 |
原子能技术 | 285篇 |
自动化技术 | 353篇 |
出版年
2024年 | 45篇 |
2023年 | 123篇 |
2022年 | 222篇 |
2021年 | 243篇 |
2020年 | 262篇 |
2019年 | 267篇 |
2018年 | 230篇 |
2017年 | 296篇 |
2016年 | 294篇 |
2015年 | 323篇 |
2014年 | 500篇 |
2013年 | 565篇 |
2012年 | 521篇 |
2011年 | 535篇 |
2010年 | 397篇 |
2009年 | 441篇 |
2008年 | 364篇 |
2007年 | 507篇 |
2006年 | 489篇 |
2005年 | 377篇 |
2004年 | 332篇 |
2003年 | 304篇 |
2002年 | 299篇 |
2001年 | 262篇 |
2000年 | 223篇 |
1999年 | 154篇 |
1998年 | 134篇 |
1997年 | 100篇 |
1996年 | 96篇 |
1995年 | 97篇 |
1994年 | 67篇 |
1993年 | 45篇 |
1992年 | 56篇 |
1991年 | 47篇 |
1990年 | 36篇 |
1989年 | 46篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1976年 | 2篇 |
1964年 | 1篇 |
1959年 | 4篇 |
1951年 | 1篇 |
排序方式: 共有9379条查询结果,搜索用时 15 毫秒
1.
2.
3.
Shi Wei Zhao Xuefeng Ma Conghui Management of the National Development Reform Commission 《中国通信》2008,(3)
After the new round of restructuring of Chinese telecom sector,it's pressing to formulate and implement asymmetric regulation policies so as to shape an effectively competitive market structure in a relatively short term.This paper reviewed the asymmetric regulation policies and practices carried out in foreign telecom market,and then according to the specific situations of Chinese telecom market,proposed the principles and corresponding policies for establishing an asymmetric regulation system fit for Chin... 相似文献
4.
单层开采的圆形定压边界两层油藏压力动态分析 总被引:1,自引:1,他引:0
为更好地分析具有越流的多层油藏的压力动态,采用有效井径的概念,在半透壁模型的基础上建立了圆形定压边界、两层越流油藏单层开采时的渗流数学模型。通过拉氏变换得到了拉氏空间中以Bessel函数表示的精确解。数值反演计算结果表明,单层开采的两层油藏与全部打开的两层油藏的压力动态基本相同,都表现为3个阶段:早期是介于两个渗透层之间的均质流动;中间为过渡段,导数曲线出现下凹特征;晚期表现为整个油藏的均质特征。随着边界距离的增加,压力导数值趋近于0.5。半透率越大过渡段出现得越早。导数曲线下凹程度越小;储容比越大导数曲线峰值越小,导数曲线下凹程度越小;随着两层渗透率比值变小。过渡段变短,导数曲线下凹程度变小。图1参9 相似文献
5.
This paper describes an effective analysis of magnetic shielding based on homogenization. The analyses become time‐consuming if the problems include the magnetic substances having fine structure. The homogenization of the structure makes it possible to analyze effectively the magnetic fields. The authors introduce a method to estimate the effective permeability of the homogenized substance. This method can be applied to any periodic structure made of magnetic substance. The magnetic shielding effects by the structures against direct‐current (DC) fields generated by electric railways are analyzed by using the present method. As a result, it is found that the overhead way and the protective fence near the railway work as a magnetic shield, whose effects can be improved by appropriate arrangement of those constructions. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 7–15, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20310 相似文献
6.
The infiltration of compacted cubic BN (cBN) with molten aluminum has been investigated as a potential route for a cheap and easy method of manufacturing cBN/metal composites. CBN compacts have been infiltrated with molten Al at a temperature between 670 and 800 °C and pressure of 15 MPa in vacuum. At these temperatures no pronounced interactions between hexagonal and cubic BN with Al was observed, allowing the complete infiltration of cBN with 12 μm mean grain size. After infiltration at 800 °C, the temperature was increased without pressure to convert aluminum into borides and AlN. The hardness of the resulting materials depends on the content of hexagonal, cubic BN and the rate of conversion of Al into borides and AlN. The infiltration height of less than 1 mm obtained from infiltrating the 3 μm cBN powder green compacts gave a hardness of 22.0 ± 0.6 GPa after heat treatment. 相似文献
7.
The development of autonomous mobile machines to perform useful tasks in real work environments is currently being impeded
by concerns over effectiveness, commercial viability and, above all, safety. This paper introduces a case study of a robotic
excavator to explore a series of issues around system development, navigation in unstructured environments, autonomous decision
making and changing the behaviour of autonomous machines to suit the prevailing demands of users. The adoption of the Real-Time
Control Systems (RCS) architecture (Albus, 1991) is proposed as a universal framework for the development of intelligent systems. In addition it is explained how the use
of Partially Observable Markov Decision Processes (POMDP) (Kaelbling et al., 1998) can form the basis of decision making in the face of uncertainty and how the technique can be effectively incorporated into
the RCS architecture. Particular emphasis is placed on ensuring that the resulting behaviour is both task effective and adequately
safe, and it is recognised that these two objectives may be in opposition and that the desired relative balance between them
may change. The concept of an autonomous system having “values” is introduced through the use of utility theory. Limited simulation
results of experiments are reported which demonstrate that these techniques can create intelligent systems capable of modifying
their behaviour to exhibit either ‘safety conscious’ or ‘task achieving’ personalities. 相似文献
8.
Yoshinori Nakazawa 《Advanced Performance Materials》1995,2(4):369-384
MITI has actively done R&D on industrial technology for waste and reclamation and so there are many research items from small scale to large scale. However, Ecofactory and researches on recycling of metallic materials are introduced here. Ecofactory was proposed by the Mechanical Engineering Laboratory and is now at the stage of the Leading Research, a new research scheme in AISt. Researches on recycling of metallic materials are being done with subsidy. Those researches should contribute to both the preservatin of the global environment and effective recycling of waste materials.Abbreviations AIST
Agency of Industrial Science and Technology
- MITI
Ministry of International Trade and Industry
- NEDO
New Energy and Industrial Technology Development Organization 相似文献
9.
在实测和分析32、14.6、12.5和9.5mm波段大气衰减的基础上,研究了大气衰减随仰角变化的规律;讨论了仰角为3~90°时计算大气衰减的简化计算公式;给出了大气等效高度与地面水汽密度的关系式,对大气衰减和等效高度的实测值与理论值进行了比较和分析. 相似文献
10.
定量电子晶体学硼对Ni3Al的电荷密度分布的影响 总被引:1,自引:0,他引:1
阐述了定量电子晶体学测定晶体电荷密度分布的基本原理和方法,不足之处和改善途径。以硼对Ni3Al的电荷密度分布的影响为实例,介绍了定量电子晶体学在研究晶体电子结构方面的应用前景。 相似文献