全文获取类型
收费全文 | 37126篇 |
免费 | 3898篇 |
国内免费 | 2187篇 |
专业分类
电工技术 | 2638篇 |
综合类 | 2638篇 |
化学工业 | 5490篇 |
金属工艺 | 2466篇 |
机械仪表 | 2736篇 |
建筑科学 | 2366篇 |
矿业工程 | 1271篇 |
能源动力 | 1233篇 |
轻工业 | 3335篇 |
水利工程 | 831篇 |
石油天然气 | 1482篇 |
武器工业 | 441篇 |
无线电 | 4463篇 |
一般工业技术 | 4828篇 |
冶金工业 | 1862篇 |
原子能技术 | 475篇 |
自动化技术 | 4656篇 |
出版年
2024年 | 197篇 |
2023年 | 717篇 |
2022年 | 1390篇 |
2021年 | 1886篇 |
2020年 | 1388篇 |
2019年 | 1096篇 |
2018年 | 1241篇 |
2017年 | 1241篇 |
2016年 | 1260篇 |
2015年 | 1581篇 |
2014年 | 1958篇 |
2013年 | 2421篇 |
2012年 | 2709篇 |
2011年 | 2993篇 |
2010年 | 2647篇 |
2009年 | 2493篇 |
2008年 | 2345篇 |
2007年 | 2201篇 |
2006年 | 1964篇 |
2005年 | 1602篇 |
2004年 | 1186篇 |
2003年 | 1036篇 |
2002年 | 904篇 |
2001年 | 827篇 |
2000年 | 694篇 |
1999年 | 551篇 |
1998年 | 484篇 |
1997年 | 394篇 |
1996年 | 347篇 |
1995年 | 277篇 |
1994年 | 227篇 |
1993年 | 148篇 |
1992年 | 125篇 |
1991年 | 89篇 |
1990年 | 89篇 |
1989年 | 78篇 |
1988年 | 54篇 |
1987年 | 39篇 |
1986年 | 40篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 26篇 |
1980年 | 22篇 |
1979年 | 16篇 |
1977年 | 16篇 |
1976年 | 12篇 |
1965年 | 17篇 |
1959年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
SUNShou-qun ZHAOSan-xing ZHANGWei CHANGXin-long 《国际设备工程与管理》2003,8(2):80-87
The multi-fault phenomena are common in the turbo-rotor system of a liquid rocket engine.As it has many excellent qualities,the neural network might be used to solve the problems of multi-fault diagnasis of a turbo-rotor system.First,the feature expression of a common turbo-rotor fault was studied in order to build up the standard fault pattern and satisfy the need of neural network studying and diagnosing.Then.the turbo-rotor fault identification and diagnosis problems were investigated by using a BP(back-propaga-tion)neural network.According to the BP neural network problems,the parallel BP neural network method of multi-fault diagnosis and classification was presented and investigated.The results indicated that the parallel Bp neural network method could solve the turbo-rotor multi-fault diagnosis problems. 相似文献
42.
This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem. 相似文献
43.
44.
为了在非平稳、非线性条件下能得到真实风场的良好估计,提出了一种用空间分布天线(SA)雷达信号的增量累积量测量大气风场参数的方法。该方法基于结构函数方法,利用高阶累计量在信息处理中的特性,用零延迟的增量累计量求解平均水平风速等具体参量,并在大气散射模型基础上对增量累积量方法进行了数值模拟,得出了同理论分析一致的结果.分析和计算表明,该方法完全适用于局地平稳条件,可以减小风场参量估计对天线间距的敏感度;阶数k≥3时,对高斯噪声有很强抑制;同时可以得到风场参量的高阶估计,这是普通的二阶方法(如全相关分析、全谱分析)不具备的。 相似文献
45.
To determine three‐dimensional fiber orientation states in injection‐molded short‐fiber composites, a confocal laser scanning microscope (CLSM) is used. Since the CLSM optically sections the specimen, more than two images of the cross sections on and below the surface of the composite can be obtained. Three‐dimensional fiber orientation states can be determined by using geometric parameters of fiber images obtained from two parallel cross sections. For experiments, carbon‐fiber‐reinforced polystyrene is examined by the CLSM and geometric parameters of fibers on each cross‐sectional plane are measured by an image analysis. In order to describe fiber orientation states compactly, orientation tensors are determined at different positions of the prepared specimen. Three‐dimensional orientation states are obtained without any difficulty by determining the out‐of‐plane angles utilizing fiber images on two parallel planes acquired by the CLSM. Orientation states are different at different positions and show the shell–core structure along the thickness of the specimen. Fiber orientation tensors are predicted by a numerical analysis and the numerically predicted orientation states show good agreement with measured ones. However, some differences are found at the end of cavity. They may result from the fountain flow effects, which are not considered in the numerical analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 500–509, 2003 相似文献
46.
Boundary element analysis of thermal stress intensity factors for interface griffith and cusp cracks
Kang Yong Lee
Woon Cheon Baik
《Engineering Fracture Mechanics》1994,47(6):909-918The thermal stress intensity factors for interface cracks of Griffith and symmetric lip cusp types under vertical uniform heat flow in a finite body are calculated by the boundary element method. The boundary conditions on the crack surfaces are insulated or fixed to constant temperature. The relationship between the stress intensity factors and the displacements on the nodal point of a crack-tip element is derived. The numerical values of the thermal stress intensity factors for an interface Griffith crack in an infinite body are compared with the previous solutions. The thermal stress intensity factors for a symmetric lip cusp interface crack in a finite body are calculated with respect to various effective crack lengths, configuration parameters, material property ratios and the thermal boundary conditions on the crack surfaces. Under the same outer boundary conditions, there are no appreciable differences in the distribution of thermal stress intensity factors with respect to each material property. However, the effect of crack surface thermal boundary conditions on the thermal stress intensity factors is considerable. 相似文献
47.
介绍了一种日常参数智能控制器的研制及研制过程中的几个重要问题的解决方法。特别是用于城市照明及美化城市的彩灯的开、关时间智能控制方面,给出了依据当地绝对时间、经度、纬度进行昼夜时间计算的方法,使之在不接光电传感器情况下可跟踪季节的昼夜变化。控制系统采用89C2051单片机,配有时钟日历芯片DS12887,系统体积小、功能强、可靠性高。 相似文献
48.
Ki Hyun Kim Yong Hoon Kang Byoungho Lee 《Photonics Technology Letters, IEEE》1997,9(12):1610-1612
A photorefractive volume hologram was recorded and probed using light diffracted from a tapered optical fiber as a reference beam. A single-mode fiber (SMF) was chemically etched and tapered to give a complicated beam pattern, and it is shown that the tapered optical fiber can be utilized to increase the storage density of the volume hologram. Spatial selectivity of the volume hologram with this method was increased by two times compared to the normal SMF referencing, which is due to the fact that the complicated beam pattern has little correlation with its shifted version 相似文献
49.
DH Kang CL Coe DO McCarthy NN Jarjour EA Kelly RR Rodriguez WW Busse 《Canadian Metallurgical Quarterly》1997,17(8):481-487
T cell cytokines play an important role in mediating airway inflammation in asthma. The predominance of a Th2 cytokine profile, particularly interleukin (IL)-4 and IL-5, is associated with the pathogenesis and course of asthma. The aim of this study was to test the hypothesis that a stressful life event alters the pattern of cytokine release in asthmatic individuals. Thirteen healthy controls and 21 asthmatic adolescents gave blood samples three times over a semester: midsemester, during the week of final examinations, and 2-3 weeks after examinations. Interferon-gamma (IFN-gamma), IL-2, IL-4, and IL-5 were measured from supernatants of cells stimulated with PHA/PMA for 24 h. Cells from asthmatic subjects released significantly more IL-5 during the examination and postexamination periods, whereas cells from healthy controls released significantly more IL-2 during the midsemester and examination periods, thereby indicating a bias for a Th2-like pattern in asthmatics and a Th1-like pattern in healthy controls. IL-4 and IL-5 production showed a marked decrease during and after examinations in healthy controls, whereas this decline was absent in asthmatics. The ratios of IFN-gamma:IL-4 and IFN-gamma:IL-5 also revealed significant changes in the profile of cytokine release across the semester. These results indicate differential cytokine responses in asthmatics that may become pronounced during periods of cellular activation. 相似文献
50.
2Mbit/s高速信令链路在移动通信七号信令网中的应用 总被引:1,自引:0,他引:1
通过对2Mbit/s高速信令链路原理、特点的介绍,阐明了该技术在现阶段使用的实际意义,并给出了2Mbit/s高速信令链路在移动通信七号信令网中的应用。 相似文献