全文获取类型
收费全文 | 58976篇 |
免费 | 5363篇 |
国内免费 | 3082篇 |
专业分类
电工技术 | 3358篇 |
技术理论 | 2篇 |
综合类 | 4091篇 |
化学工业 | 9639篇 |
金属工艺 | 3098篇 |
机械仪表 | 3728篇 |
建筑科学 | 4667篇 |
矿业工程 | 1740篇 |
能源动力 | 1629篇 |
轻工业 | 4559篇 |
水利工程 | 1249篇 |
石油天然气 | 3219篇 |
武器工业 | 479篇 |
无线电 | 7204篇 |
一般工业技术 | 7018篇 |
冶金工业 | 2581篇 |
原子能技术 | 760篇 |
自动化技术 | 8400篇 |
出版年
2024年 | 314篇 |
2023年 | 984篇 |
2022年 | 1726篇 |
2021年 | 2390篇 |
2020年 | 1830篇 |
2019年 | 1570篇 |
2018年 | 1776篇 |
2017年 | 1911篇 |
2016年 | 1756篇 |
2015年 | 2283篇 |
2014年 | 2925篇 |
2013年 | 3619篇 |
2012年 | 3924篇 |
2011年 | 4002篇 |
2010年 | 3701篇 |
2009年 | 3609篇 |
2008年 | 3391篇 |
2007年 | 3379篇 |
2006年 | 3339篇 |
2005年 | 2842篇 |
2004年 | 2023篇 |
2003年 | 1905篇 |
2002年 | 1959篇 |
2001年 | 1738篇 |
2000年 | 1451篇 |
1999年 | 1339篇 |
1998年 | 1035篇 |
1997年 | 906篇 |
1996年 | 845篇 |
1995年 | 675篇 |
1994年 | 541篇 |
1993年 | 397篇 |
1992年 | 334篇 |
1991年 | 252篇 |
1990年 | 184篇 |
1989年 | 160篇 |
1988年 | 110篇 |
1987年 | 70篇 |
1986年 | 46篇 |
1985年 | 38篇 |
1984年 | 27篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 17篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1977年 | 3篇 |
1973年 | 3篇 |
1959年 | 10篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
在传统异步电动机直接转矩控制方案中,由于负载的变化规律不可预测,因此其常会带来较大的开关频率的变化,为此提出了一种基于预前控制的异步电动机直接转矩控制的方法。该方法依据前一个周期的磁链和转矩误差,对下一个开关周期所应施加到异步电动机的定子电压矢量进行预测,然后借助空间矢量PWM的方法,合成此开关电压矢量。样机实验结果表明,该方案不但能维持逆变器的开关频率基本恒定,而且还具有比传统直接转矩控制更为优良的动静态特性。 相似文献
42.
针对WCDMA运营中的系统问互操作问题,首先给出了系统间互操作行为的分类,并从互操作的触发开始,分析了所涉及的关键参数以及系统间重选、切换和引入HSDPA之后的重配置流程,然后总结了互操作过程中所使用的测量事件,最后说明在不同运营阶段,双模终端的驻留与切换策略. 相似文献
43.
44.
热物理性质测试技术研究现状和发展趋势 总被引:3,自引:0,他引:3
本文在对热物理性质研究在热能工程、材料科学、信息科学、航天工程、环境工程、生物科学、微电子技术和计量学等众多科技领域中的重要性进行探讨的基础上,评述了热物理性质测试技术的研究现状和发展趋势。鉴于薄膜材料在微电子器件、集成电路和微电子机械系统等领域中日益广泛的应用,本文还综述了亚微米-纳米尺度薄膜材料热导率和热扩散率的测试新技术。 相似文献
45.
Spectral slope (S), describing the exponential decrease of the absorption spectrum over a given wavelength range, is an important parameter in the study of of chromophoric dissolved organic matter (CDOM) dynamics, and also an essential input parameter in remote sensing models. Furthermore, S is often used as a proxy for CDOM composition, including the ratio of fulvic to humic acids and molecular weight. The relative broad range in S values reported in the literature can be explained by the different spectral ranges and fitting methods used. A single exponential model is used to fit the S values for 17 investigations involving 458 samples in Lake Taihu from January to October in 2004. The average S value was 15.18 ± 1.39 μm−1 for the range of 280–500 nm, which fell within the range reported in the literature. The frequency distribution of S value basically obeyed a normal distribution. Significant differences in S values between summer and other seasons showed that phytoplankton degradation was one of the important sources of CDOM in summer, whereas CDOM mainly came from the river input in other seasons. Furthermore, the estimated S value decreased with increasing wavelength range used in regression. The maximum and minimum values derived from the regression were 17.89 ± 1.25 μm−1 and 13.62 ± 2.11 μm−1 for the wavelength ranges of 280–380 nm and 400–500 nm, respectively, a decrease of 23.9%. S values significantly decreased with the increase of CDOM absorption coefficients. CDOM absorption coefficients could be more appropriately estimated from exponential model introducing the variation of S with absorption coefficients, making them useful for a remote sensing bio-optical model of Lake Taihu. DOC-specific absorption coefficient a*(λ) and the parameter M describing molecular size of the humic molecules could also be used as a proxy for the sources and types of CDOM. A general relationship was found between S and a*(λ), and M values. S increased with the decrease of DOC-specific absorption coefficient and the increase of M corresponding to the decrease of molecular weight. 相似文献
46.
Yiping Wang Na Chen Binfeng Yun Yiping Cui 《Photonics Technology Letters, IEEE》2007,19(16):1242-1244
A measurement method has been developed to determine the full-field deformation of a simply supported plane plate under transverse load. The method utilizes strain information provided by a set of four fiber Bragg grating sensors mounted on the plate in a way that all sensors measure strains along one certain direction. The sensors were interrogated using a wavelength swept fiber laser. Utilizing the strain information and the first four terms of Navier solution of simply supported rectangular plate, the necessary parameters for determining the deflection could be computed. By substituting the values of x- and -y- coordinates of each position on the rectangle plate, the full-field deformation information can be obtained. Single-point loading tests were experimentally performed to verify the accuracy of the method. 相似文献
47.
国内主要参展商
1.益阳橡机
益阳橡胶塑料机械集团有限公司在本次展会上,推出了一款GE-5实验室用密炼机,容积5升,啮合型转子,用于橡胶制品、白炭黑、特种胶的混炼. 相似文献
48.
49.
Mushroom-like ZnO microcrystals have been prepared via a solution calcination route, using Zn(NO3)2 as Zn source in the absence of any surfactants, templates or catalysts. This is the first example to prepare mushroom-like crystals as semiconductors, which are expected to show particular physical properties. The ZnO products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) spectrum measurements. A suitable concentration of Zn(NO3)2 solution was important for the growth of the mushroom-like products. The reported synthetic procedure is straightforward and inexpensive, and thus can be readily adopted to produce large quantities of mushroom-like ZnO microcrystals. 相似文献
50.