全文获取类型
收费全文 | 17579篇 |
免费 | 2217篇 |
国内免费 | 1054篇 |
专业分类
电工技术 | 2995篇 |
技术理论 | 1篇 |
综合类 | 1574篇 |
化学工业 | 1737篇 |
金属工艺 | 1056篇 |
机械仪表 | 1093篇 |
建筑科学 | 326篇 |
矿业工程 | 603篇 |
能源动力 | 293篇 |
轻工业 | 556篇 |
水利工程 | 100篇 |
石油天然气 | 483篇 |
武器工业 | 432篇 |
无线电 | 4681篇 |
一般工业技术 | 2583篇 |
冶金工业 | 538篇 |
原子能技术 | 559篇 |
自动化技术 | 1240篇 |
出版年
2024年 | 98篇 |
2023年 | 327篇 |
2022年 | 415篇 |
2021年 | 577篇 |
2020年 | 588篇 |
2019年 | 490篇 |
2018年 | 398篇 |
2017年 | 623篇 |
2016年 | 659篇 |
2015年 | 716篇 |
2014年 | 1086篇 |
2013年 | 1122篇 |
2012年 | 1271篇 |
2011年 | 1419篇 |
2010年 | 1059篇 |
2009年 | 1120篇 |
2008年 | 922篇 |
2007年 | 1125篇 |
2006年 | 1028篇 |
2005年 | 888篇 |
2004年 | 716篇 |
2003年 | 703篇 |
2002年 | 547篇 |
2001年 | 454篇 |
2000年 | 436篇 |
1999年 | 316篇 |
1998年 | 237篇 |
1997年 | 240篇 |
1996年 | 205篇 |
1995年 | 192篇 |
1994年 | 153篇 |
1993年 | 128篇 |
1992年 | 104篇 |
1991年 | 84篇 |
1990年 | 72篇 |
1989年 | 77篇 |
1988年 | 43篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 43篇 |
1984年 | 36篇 |
1983年 | 28篇 |
1982年 | 39篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1959年 | 3篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
We have studied electron energy relaxation in GaInAs/AlInAs heterojunctions and GaAs/AlGaAs multiple quantum wells using mobility measurements as a function of electric field and temperature, in the range 3K to 300K. The results in the range 3 to 20K show a power loss rate which is dependent on (Te − Tl), suggesting that the energy relaxation occurs through acoustic phonon scattering. At electron temperatures greater than 20K, the experimental results are modelled using a standard expression for polar optical phonons. This modelling yields 30meV and 31meV for the polar optical phonon energy in GaAs and InGaAs respectively. 相似文献
102.
本文在综述近年来有关光孤子研究成果的基础上,对单模光纤中受激喇曼散射的喇曼孤子产生进行了详细地描述。从理论上分析了喇曼互作用及喇曼孤子的形成过程,讨论了喇曼孤子产生的实验方法及有关应用。 相似文献
103.
《Information Systems Management》2007,24(4):305-310
Most organizations have measures to protect their network infrastructure from intruders. With the growth AND AVAILABILITY of wireless, some intruders now are aiming their attacks there. The potential for damage from these types of attacks is significant due to their nature. However, there is another type of wireless attack on organizational resources that also poses a significant vulnerability. That is electromagnetic radiation, also called radio frequency emissions (RFE), from unprotected systems and networks. 相似文献
104.
The laser-induced thermal grating technique has been used to determine the thermal diffusivity of liquids and liquid mixtures. But the dynamic behaviour of the transient thermal grating has not yet been thoroughly investigated, and the systematic errors, which result from the departures from one-dimensional heat conduction, have scarcely been studied quantitatively. In this paper. a three-dimensional numerical simulation and results of the transient thermal grating technique are presented, which enable a good understanding of the dynamic behaviour of the transient thermal grating. The results of this simulation are important for the proper design of the experimental setup to keep the systematic errors for the diffusivity measurement small. Based on the simulation method, the systematic errors were analyzed quantitatively. Here, the following effects were studied: (I) sample thickness, (2) intersection angle, (3) absorption, (4) Gaussian beam intensity distribution and focusing of heating laser beam, and (5) heating pulse duration and laser power. This error analysis makes it possible to specify the criteria for optimum measuring conditions, to correct the measured thermal-diffusivity values for systematic errors, and to estimate the accuracy of the measurements. 相似文献
105.
Jean-Christophe Autrique 《Computers & Structures》2007,85(9):518-525
This work is devoted to a study of a conjugated infinite element method for Helmholtz problems in exterior domains. A formulation of this method with Lagrange multipliers defined on (semi-)infinite space is presented and analyzed in a domain decomposition context. The implementation aspects of this method in a parallel industrial acoustic software (SYSNOISE) are described in details. Numerical results show the computational efficiency of this method on acoustic scattering problems. 相似文献
106.
L. FAN‡ D. PATERSON† I. McNULTY‡ M. M. J. TREACY & J. M. GIBSON‡ 《Journal of microscopy》2007,225(1):41-48
Measuring medium‐range order is a challenging and important problem in the structural study of disordered materials. We have developed a new technique, fluctuation x‐ray microscopy, that offers quantitative insight into medium‐range correlations in disordered materials at nanometre and larger length scales.In this technique, which requires a spatially coherent x‐ray beam, a series of speckle patterns are measured at a large number of locations in a sample using various illumination sizes. Examination of the speckle variance as a function of the illumination spot size allows the structural correlation length to be measured. To demonstrate this technique we have studied polystyrene latex spheres, which serve as a model for a dense random‐packed glass, and for the first time have measured the correlation length in a disordered system by fluctuation X‐ray microscopy. We discuss data analysis and procedures to correct for shot noise and detector noise. This approach could be used to explore medium‐range order and subtle spatial structural changes in a wide range of disordered materials, from soft matter to nanowire arrays, semiconductor quantum dot arrays and magnetic materials. 相似文献
107.
工作在北京正负电子对撞机(BEPC)上的北京谱议(BES),于2003年12月在质心系能量从3.660到3.897 GeV区间内67个能量点上收集了数据,我们测量了此67个能量点数据样本的积分亮度.数据样本对应的总的积分亮度为(5550.96±13.56±108.24)nb-1. 相似文献
108.
提取系统的冲击响应函数(impulse response function,IRF)是测量雷达系统性能指标的前提,IRF来自理想点目标的雷达图像。对于低频超宽带合成孔径雷达(ultra wide band synthetic aperture radar,UWB SAR),参考点目标的电磁散射特性是频率和方位角的函数,不满足理想点目标的散射特性要求。本文从IRF的定义出发,结合低频UWBSAR系统处理模型,利用二维数字聚焦方法消除杂波的影响,同时利用低频电磁散射数值建模的方法计算参考点目标的电磁散射特性,最后给出了计算系统IRF的方法。 相似文献
109.
110.
本文探讨了TEM室测量电话通信设备辐射干扰的原理、方法,得出了在线电话终端0.15~30MHz频段辐射干扰测量结果,并进行了分析。 相似文献