全文获取类型
收费全文 | 109023篇 |
免费 | 13344篇 |
国内免费 | 5396篇 |
专业分类
电工技术 | 6993篇 |
技术理论 | 10篇 |
综合类 | 8537篇 |
化学工业 | 21034篇 |
金属工艺 | 4152篇 |
机械仪表 | 3844篇 |
建筑科学 | 12081篇 |
矿业工程 | 4181篇 |
能源动力 | 3234篇 |
轻工业 | 12399篇 |
水利工程 | 5021篇 |
石油天然气 | 4607篇 |
武器工业 | 1027篇 |
无线电 | 8214篇 |
一般工业技术 | 10565篇 |
冶金工业 | 5837篇 |
原子能技术 | 1248篇 |
自动化技术 | 14779篇 |
出版年
2024年 | 459篇 |
2023年 | 1793篇 |
2022年 | 4812篇 |
2021年 | 5921篇 |
2020年 | 3903篇 |
2019年 | 3620篇 |
2018年 | 3715篇 |
2017年 | 4469篇 |
2016年 | 6096篇 |
2015年 | 6355篇 |
2014年 | 7990篇 |
2013年 | 8301篇 |
2012年 | 7235篇 |
2011年 | 6923篇 |
2010年 | 5430篇 |
2009年 | 5474篇 |
2008年 | 5104篇 |
2007年 | 6689篇 |
2006年 | 6697篇 |
2005年 | 5499篇 |
2004年 | 3944篇 |
2003年 | 3549篇 |
2002年 | 2737篇 |
2001年 | 2020篇 |
2000年 | 1714篇 |
1999年 | 1268篇 |
1998年 | 917篇 |
1997年 | 777篇 |
1996年 | 679篇 |
1995年 | 544篇 |
1994年 | 508篇 |
1993年 | 357篇 |
1992年 | 301篇 |
1991年 | 245篇 |
1990年 | 245篇 |
1989年 | 210篇 |
1988年 | 145篇 |
1987年 | 104篇 |
1986年 | 108篇 |
1985年 | 85篇 |
1984年 | 103篇 |
1983年 | 80篇 |
1982年 | 67篇 |
1981年 | 51篇 |
1980年 | 62篇 |
1979年 | 32篇 |
1966年 | 29篇 |
1965年 | 36篇 |
1964年 | 40篇 |
1962年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Measuring nonlinear optical response of a specific material in a mixture, not only leads to investigate the behavior of a particular component in various circumstances, but also can be a way to select suitable combination and optimum concentration of additives and therefore obtaining the maximum nonlinear optical signals. In this work, by using dual-arm Z-scan technique, the nonlinear refractive index of Disperse Red1 (DR1) organic dye molecules inside the core of prepared polymeric nanocapsules was measured among various materials which prepared nanocapsules were made of them. Then the measured value was compared with nonlinear refractive index of DR1 solved in dichloromethane. 相似文献
82.
Cadmium Sulfide and Ferrous doped Cadmium Sulfide thin films have been prepared on different substrates using an electrodeposition technique. Linear sweep voltammetric analysis has been carried out to determine deposition potential of the prepared films. X-ray diffraction analysis showed that the prepared films possess polycrystalline nature with hexagonal structure. Surface morphology and film composition have been analyzed using Scanning electron microscopy and Energy dispersive analysis by X-rays. Optical absorption analysis showed that the prepared films are found to exhibit Band gap value in the range between 2.3, 2.8 eV for Cadmium Sulfide and Ferrous doped Cadmium Sulfide. 相似文献
83.
The need for feature selection and dimension reduction is felt as a fundamental step in security assessment of large power systems in which the number of features representing the state of power grids dramatically increases. These large amounts of attributes are not proper to be used for computational intelligence (CI) techniques as inputs, because it may lead to a time consuming procedure with insufficient results and they are not suitable for on-line purposes and updates.This paper proposes a combined method for an online voltage security assessment in which the dimension of the token data from phasor measurement units (PMUs) is reduced by principal component analysis (PCA). Then, the features with different stability indices are put into several categories and feature selection is done by correlation analysis in each category. These selected features are then given to decision trees (DTs) for classification and security assessment of power systems.The method is applied to 39-bus test system and a part of Iran power grid. It is seen from the results that the DTs with reduced data have simpler splitting rules, better performance in saving time, reasonable DT error and they are more suitable for constant updates. 相似文献
84.
85.
86.
《Energy Policy》2015
In this paper we construct an indirect measure of the supply marginal cost function for the main generators from the observed bid data in the Italian electricity market in the period 2004–2007. We compute the residual demand function for each generator, taking explicitly into account the issue of transmission line congestion. This procedure allows recovering correct zonal Lerner index and the implied measure of the marginal cost function. We find evidence of a stable U-shaped marginal cost function for three main Italian generators, but a flat function for ENEL, the former national monopolist. The policy relevance of our approach lies in the possibility to offer some empirical knowledge of the marginal cost function of each generator to the regulator to design appropriate policy measures geared to the promotion of competitive market conditions. We propose a new market surveillance mechanism, which is based on the principle of sanctioning excessive deviations from the estimated measure of the marginal cost function presented in this work. 相似文献
87.
基于传统AI-EBG结构,提出了一种小尺寸的增强型电磁带隙结构,实现了从0.5~9.4 GHz的宽频带-40 dB噪声抑制深度,且下截止频率减少到数百MHz,可有效抑制多层PCB板间地弹噪声。文中同时研究了EBG结构在高速电路应用时的信号完整性问题,使用差分信号方案可改善信号完整性。 相似文献
88.
介绍了一种基于高性能浮点DSP芯片TMS320C32、CPLD芯片XC95288和A/D采样芯片AD976组成的多路采集系统的工作原理以及设计方法。通过对第一路施加特殊的电压量,在CCS开发环境下读取采样缓冲区的值,并利用Matlab对采样数据进行了全波傅氏变换。此外,该系统已在继电保护中得到广泛应用,实践表明,该系统能较好地解决多路模拟量的采集,并确保了采样数据的安全可靠性。 相似文献
89.
Metamerism phenomenon can be used in illuminant detection to ensure the accuracy of light source. A method based on Long‐, Middle‐, Short‐ wavelength cones(LMS) weighting algorithm to evaluate metamerism degree is proposed. The chromatic relationship between the degree of metamerism mismatch and the light source is studied. Herein, the consistency between the metameric indices (MIs) and CIE1976 L*a*b* color difference ranking is analyzed by SRCC, KRCC, PLCC and RMSE. A statistically sampling method to obtain practical LMS cone fundamentals to evaluate metamerism degree is employed. The analysis results obtained show that the method based on LMS weighting algorithm has good evaluation ability and stability in simulation experiments and statistically sampling experiments, which are in line with visual characteristics of human. Proposed method meets the requirements of selecting metameric pairs used in light source detection. The analysis results have certain guiding significance. 相似文献
90.
In the early design stage, automotive modeling should both meet the requirements of aesthetics and engineering. Therefore, a vehicle CAD (computer aided design) model that can be easily adjusted by feedbacks is necessary. Based on CE-Bézier surface, this paper presents a set of algorithms for parametric segmentation and fairing surface generation in a car model. This model is defined by a simplified automotive template and relevant control points, shape parameters and segmentation parameters, which can be modified to alter the car form efficiently. With this model and the corresponding adjustment method, more than fifty various vehicle models are established in this research according to different parameters. And two methods for calculating similarity index between car models are constructed, which are suitable for brand design trend analysis and modelling design decisionmaking. 相似文献