全文获取类型
收费全文 | 52472篇 |
免费 | 4853篇 |
国内免费 | 2805篇 |
专业分类
电工技术 | 3434篇 |
技术理论 | 5篇 |
综合类 | 4472篇 |
化学工业 | 8246篇 |
金属工艺 | 2774篇 |
机械仪表 | 3184篇 |
建筑科学 | 4209篇 |
矿业工程 | 1459篇 |
能源动力 | 1449篇 |
轻工业 | 6049篇 |
水利工程 | 1234篇 |
石油天然气 | 2257篇 |
武器工业 | 533篇 |
无线电 | 5619篇 |
一般工业技术 | 5201篇 |
冶金工业 | 2005篇 |
原子能技术 | 668篇 |
自动化技术 | 7332篇 |
出版年
2024年 | 258篇 |
2023年 | 849篇 |
2022年 | 1635篇 |
2021年 | 2228篇 |
2020年 | 1635篇 |
2019年 | 1283篇 |
2018年 | 1436篇 |
2017年 | 1633篇 |
2016年 | 1505篇 |
2015年 | 2171篇 |
2014年 | 2716篇 |
2013年 | 3227篇 |
2012年 | 3868篇 |
2011年 | 4106篇 |
2010年 | 3706篇 |
2009年 | 3624篇 |
2008年 | 3673篇 |
2007年 | 3336篇 |
2006年 | 3133篇 |
2005年 | 2647篇 |
2004年 | 1856篇 |
2003年 | 1364篇 |
2002年 | 1311篇 |
2001年 | 1110篇 |
2000年 | 1005篇 |
1999年 | 942篇 |
1998年 | 741篇 |
1997年 | 609篇 |
1996年 | 530篇 |
1995年 | 461篇 |
1994年 | 337篇 |
1993年 | 252篇 |
1992年 | 225篇 |
1991年 | 162篇 |
1990年 | 114篇 |
1989年 | 106篇 |
1988年 | 87篇 |
1987年 | 47篇 |
1986年 | 59篇 |
1985年 | 24篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 8篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
本文主要介绍了在动态汽车衡的试验过程中不确定度来源,并以动态试验为例重点介绍了计算各分量的标准不确定度、合成标准不确定度以及扩展不确定度的方法. 相似文献
13.
提出一种基于二维多波束形成的蜂窝网覆盖方法,该方法旨在通过对平面阵阵元权矢量的控制,使所形成的波束在空域上呈非均匀蜂窝网结构,达到重点地区覆盖密度高,非重点区域覆盖密度低的目的,减小资源利用率,并重点分析了波束设计思路和权值的计算方法,仿真结果表明:该覆盖方法是有效的. 相似文献
14.
憎水性栀子蓝色素制备的研究 总被引:1,自引:0,他引:1
以浓盐酸为催化剂,采用乙酸酐酯化处理水溶性栀子蓝色素,制备了憎水性栀子蓝色素.探讨了栀子蓝色素与乙酸酐料液比、反应时间和反应温度等因素对憎水性栀子蓝色素色价的影响.结果表明:采用料液比1:20,在常温下反应4 h,为制备憎水性栀子蓝色素的最优条件.同时,通过红外光谱、可见吸收光谱及溶解性对栀子蓝色素的酯化改性进行了初步的探讨. 相似文献
15.
Local residence time,residence revolution,and residence volume distributions in twin‐screw extruders
Xian‐Ming Zhang Lian‐Fang Feng Sandrine Hoppe Guo‐Hua Hu 《Polymer Engineering and Science》2008,48(1):19-28
This work was aimed at studying the overall, partial, and local residence time distributions (RTD); overall, partial and local residence revolution distributions (RRD) and overall, partial and local residence volume distributions (RVD) in a co‐rotating twin screw extruder, on the one hand; and establishing the relationships among them, on the other hand. Emphasis was placed on the effects of the type and geometry of mixing elements (a gear block and various types of kneading elements differing in staggering angle) and process parameters on the RTD, RRD and RVD. The overall and partial RTD were directly measured in‐line during the extrusion process and the local ones were calculated by deconvolution based on a statistical theory. The local RTD allowed comparing the mixing performance of mixing elements. Also it was confirmed both experimentally and theoretically that specific throughput, defined as a ratio of throughput (Q) over screw speed (N), controlled all the above three types of residence distributions, be they local, partial or overall. The RRD and RVD do not provide more information on an extrusion process than the corresponding RTD. Rather they are different ways of representing the same phenomena. POLYM. ENG. SCI., 48:19–28, 2008. © 2007 Society of Plastics Engineers 相似文献
16.
Haijun Fang Zongli Lin 《Automatic Control, IEEE Transactions on》2006,51(7):1177-1184
In this note, we revisit the problem of global practical stabilization for planar linear systems subject to actuator saturation and input additive disturbances. A parameterized linear state feedback law is designed such that, by tuning the value of the parameter, all trajectories of the closed-loop system converge to an arbitrarily small neighborhood of the origin in a finite time and remain in there. 相似文献
17.
Mixtures of Cr and Mo elemental powders, with the nominal compositions Cr25Mo75, Cr50Mo50, and Cr75Mo25, are processed by high-energy ball milling at ambient temperature. Milling is observed to force the mixing of the immiscible
bcc elements Cr and Mo into solid solutions. The lattice parameter of these solid solutions, measured by X-ray diffraction
(XRD), displays the expected positive deviation from Vegard’s law. These deviations are compared to the ones predicted by
Eshelby’s inclusion model for dilute alloys. The conventional Williamson-Hall approach is shown to fail to determine the grain
size in as-milled samples, probably due to the high density of dislocations. Annealing at 700 °C for 10 hours under argon
leads to a large reduction in structural defect density, without inducing any significant decomposition. The mixing measured
in Cr-Mo is discussed in the broader context of the mechanical mixing forced by ball milling in moderately immiscible systems. 相似文献
18.
19.
Fang Wu Yaojiang Zhang Zaw Zaw Oo Erping Li 《Antennas and Propagation Magazine, IEEE》2005,47(4):110-118
The Multilevel Fast Multipole Method (FMM) is a well-established method and can be applied to solve electromagnetic (EM) scattering problems. Compared with other traditional methods, it requires less computational time and memory. However, constrained by a single processor's speed and memory limitations, the problem size that can be solved by serial implementation is still relatively small. For a million-unknown target, the computational time on a single processor is intolerable, and memory could be easily exhausted. Parallel-computing technology, which can utilize multiprocessors, provides an efficient way to solve electrically large-scale EM problems. This paper will focus on discussing the parallel methodologies applied to a multilevel FMM code, as well as demonstrating the computational efficiency of the parallel approach. 相似文献
20.
本文研究了具有典型分解特征的Al-Zn-Ce非晶合金的形成和晶化过程,探讨了各种相的生成顺序。XRD和DSC测试结果表明强烈的化合物短程序有利于Al-Zn-Ce非晶合金的形成。在Al-Zn-Ce非晶合金的晶化过程中存在复杂的相选择行为,多种相的竞争形核和有限生长使其具有复杂的结构特点。同时,结果也表明冷速对该体系非晶的形成有很大影响。 相似文献