全文获取类型
收费全文 | 91518篇 |
免费 | 7786篇 |
国内免费 | 4140篇 |
专业分类
电工技术 | 5825篇 |
技术理论 | 2篇 |
综合类 | 5819篇 |
化学工业 | 14152篇 |
金属工艺 | 4978篇 |
机械仪表 | 5267篇 |
建筑科学 | 6783篇 |
矿业工程 | 1866篇 |
能源动力 | 2696篇 |
轻工业 | 7199篇 |
水利工程 | 1856篇 |
石油天然气 | 3928篇 |
武器工业 | 678篇 |
无线电 | 12116篇 |
一般工业技术 | 11763篇 |
冶金工业 | 4630篇 |
原子能技术 | 1042篇 |
自动化技术 | 12844篇 |
出版年
2024年 | 385篇 |
2023年 | 1416篇 |
2022年 | 2671篇 |
2021年 | 3674篇 |
2020年 | 2565篇 |
2019年 | 2171篇 |
2018年 | 2423篇 |
2017年 | 2853篇 |
2016年 | 2497篇 |
2015年 | 3470篇 |
2014年 | 4503篇 |
2013年 | 5746篇 |
2012年 | 6105篇 |
2011年 | 6800篇 |
2010年 | 5900篇 |
2009年 | 5687篇 |
2008年 | 5611篇 |
2007年 | 5374篇 |
2006年 | 5147篇 |
2005年 | 4197篇 |
2004年 | 2845篇 |
2003年 | 2354篇 |
2002年 | 2372篇 |
2001年 | 2026篇 |
2000年 | 1912篇 |
1999年 | 1941篇 |
1998年 | 1828篇 |
1997年 | 1579篇 |
1996年 | 1413篇 |
1995年 | 1185篇 |
1994年 | 925篇 |
1993年 | 761篇 |
1992年 | 610篇 |
1991年 | 462篇 |
1990年 | 387篇 |
1989年 | 299篇 |
1988年 | 252篇 |
1987年 | 182篇 |
1986年 | 153篇 |
1985年 | 139篇 |
1984年 | 100篇 |
1983年 | 75篇 |
1982年 | 68篇 |
1981年 | 59篇 |
1980年 | 51篇 |
1979年 | 35篇 |
1978年 | 32篇 |
1977年 | 32篇 |
1976年 | 54篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
在互联网服务中,即时通讯已成为了最流行的服务模式之一,人们对即时通讯的依赖程度也与日俱增。但是, 频频出现的病毒和黑客攻击使广大用户深受其害,即时通讯的安全问题也日益严峻。为了从根本上解决问题,本文对即时通讯软件的架构和协议进行了深入分析,目的是找出漏洞根源,给开发者和使用者提供防止漏洞的依据。 相似文献
22.
Yong Xia Rongming Lin 《International journal for numerical methods in engineering》2004,59(1):153-172
Order reduction is a computationally efficient method to estimate some lowest eigenvalues and the corresponding eigenvectors of large structural systems by reducing the order of the original model to a smaller one. But its accuracy is limited to a small range of frequencies that depends on the selection of the retained degrees of freedom. This paper proposes a new iterative order reduction (IOR) technique to obtain accurately the eigensolutions of large structural systems. The technique retains all the inertia terms associated with the removed degrees of freedom. This hence leads to the reduced mass matrix being in an iterated form and the reduced stiffness matrix constant. From these mass and stiffness matrices, the eigensolutions of the reduced system can be obtained iteratively. On convergence the reduced system reproduces the eigensolutions of the original structure. A proof of the convergence property is also presented. Applications of the method to a practical GARTEUR structure as well as a plate have demonstrated that the proposed method is comparable to the commonly used Subspace Iteration method in terms of numerical accuracy. Moreover, it has been found that the proposed method is computationally more efficient than the Subspace Iteration method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
23.
Tsang T.K.K. Kuan-Yu Lin El-Gamal M.N. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2008,55(3):214-218
This paper presents design techniques of CMOS ultra-wide-band (UWB) amplifiers for multistandard communications. The goal of this paper is to propose a compact, simple, and robust topology for UWB low-noise amplifiers, which yet consumes a relatively low power. To achieve this goal, a common-gate amplifier topology with a local feedback is employed. The first amplifier uses a simple inductive peaking technique for bandwidth extension, while the second design utilizes a two-stage approach with an added gain control feature. Both amplifiers achieve a flat bandwidth of more than 6 GHz and a gain of higher than 10 dB with supply voltages of 1.8-2.5 V. Designs with different metal thicknesses are compared. The advantage of using thick-metal inductors in UWB applications depends on the chosen topology. 相似文献
24.
Lei Liu Ying Kong Hong Xu Jin P. Li Jin X. Dong Zhi Lin 《Microporous and mesoporous materials》2008,115(3):624-628
A three-dimensional zinc phosphate compound with DFT topology, designated as ZnPO4-EU1, has been synthesized by an ionothermal approach from the system HF-ZnO–P2O5-choline chloride-imidazolidone. Ethylenediamine, derived from decomposition of the imidazolidone component of the deep-eutectic solvent (DES) itself, is delivered to the synthesis and serves as an appropriate template for ZnPO4-EU1. Experiments in which the synthesis conditions were varied showed that ZnPO4-EU1 may be prepared over a wide molar ratio of P/Zn = 0.55–13.0. Powder X-ray diffraction patterns have been obtained at intervals to track the crystallization process of this material. The experimental data show that Zn3(PO4)2 · 4H2O (a dense phase) was first isolated from the DES after reaction for 1 h. Subsequently, the pure phase of ZnPO4-EU1 was obtained with increasing crystallization time from 12 h to 72 h. The experimental results show that the nucleation and crystallization take place with relatively low levels of solvent degradation, demonstrating that zinc phosphate with a three-dimensional framework can be synthesized by in situ generation of an appropriate template using an unstable DES at high temperatures (150–200 °C). 相似文献
25.
26.
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
27.
Zhiping Lin Xu L. Bose N.K. 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(1):445-461
28.
29.
介绍液态软起动技术在济钢 15000 m3/h制氧机配套的 6000 kW同步电动机上的应用情况,阐述了系统的原理、特点、仿真计算及实际应用后达到的效果. 相似文献
30.