全文获取类型
收费全文 | 82084篇 |
免费 | 8880篇 |
国内免费 | 5230篇 |
专业分类
电工技术 | 6794篇 |
技术理论 | 6篇 |
综合类 | 6479篇 |
化学工业 | 11737篇 |
金属工艺 | 4779篇 |
机械仪表 | 5664篇 |
建筑科学 | 6574篇 |
矿业工程 | 2768篇 |
能源动力 | 2464篇 |
轻工业 | 6442篇 |
水利工程 | 2003篇 |
石油天然气 | 4531篇 |
武器工业 | 988篇 |
无线电 | 10100篇 |
一般工业技术 | 8338篇 |
冶金工业 | 3242篇 |
原子能技术 | 1130篇 |
自动化技术 | 12155篇 |
出版年
2024年 | 480篇 |
2023年 | 1526篇 |
2022年 | 3020篇 |
2021年 | 4173篇 |
2020年 | 3118篇 |
2019年 | 2375篇 |
2018年 | 2619篇 |
2017年 | 2964篇 |
2016年 | 2664篇 |
2015年 | 3917篇 |
2014年 | 4765篇 |
2013年 | 5550篇 |
2012年 | 6407篇 |
2011年 | 6618篇 |
2010年 | 5924篇 |
2009年 | 5547篇 |
2008年 | 5407篇 |
2007年 | 5139篇 |
2006年 | 4775篇 |
2005年 | 3838篇 |
2004年 | 2638篇 |
2003年 | 2077篇 |
2002年 | 2116篇 |
2001年 | 1731篇 |
2000年 | 1367篇 |
1999年 | 1211篇 |
1998年 | 822篇 |
1997年 | 668篇 |
1996年 | 600篇 |
1995年 | 527篇 |
1994年 | 391篇 |
1993年 | 252篇 |
1992年 | 227篇 |
1991年 | 142篇 |
1990年 | 130篇 |
1989年 | 95篇 |
1988年 | 61篇 |
1987年 | 52篇 |
1986年 | 41篇 |
1985年 | 30篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 26篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 18篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
A newly developed catalyst type DVR-1 for catalytic cracking of Daqing vacuum resid was put into use in a commercial VRFCC unit,This catalyst features uniquely active matrix and modified ultra-stable zeolite.The commercial application results show that the DVR-1 type catalyst has the advantage of high heavy oil conversion,good metal tolerance nd gooed stability for catalyst regeneration,The FCC tests have shown Favorable product distribution,acceptable product quality and enormaous economic benefits whe processing the feedstock containin 75%-100% Daqing VR. 相似文献
54.
铝电解槽磁流体稳定性有限元分析 总被引:2,自引:0,他引:2
本文采用有限元法求解分层磁流体小扰动方程系统特征值,研究铝电解槽稳定性。研究结果表明,在没有电磁力时,铝液表面波动(内波)是稳定的。存在电磁力时,它会激发铝液表面波动的某些低频长波分量不稳定性,高频短波不受影响。被激发的不稳定波动频率和扰动增长率与电流密度,磁感应强度垂直分量,铝电解槽长宽比,电解质和铝液的密度差,厚度等因素密切相关。减少电流密度,磁感应强度,增加电极距离和铝液厚度可以提高铝电解槽的稳定性。这对铝电解槽优化设计和在线控制有重要意义。 相似文献
55.
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
56.
57.
This paper deals with the trajectory planning problem for redundant manipulators. A genetic algorithm (GA) using a floating point representation is proposed to search for the optimal end-effector trajectory for a redundant manipulator. An evaluation function is defined based on multiple criteria, including the total displacement of the end-effector, the total angular displacement of all the joints, as well as the uniformity of Cartesian and joint space velocities. These criteria result in minimized, smooth end-effector motions. Simulations are carried out for path planning in free space and in a workspace with obstacles. Results demonstrate the effectiveness and capability of the proposed method in generating optimized collision-free trajectories. 相似文献
58.
Direct sequence code-division multiple access has been shown as the predominant access technology to provide high-speed multimedia services in next-generation wireless cellular networks. The DS-CDMA cellular network significantly differentiates itself from the traditional narrowband TDMA/FDMA system, in which great capacity gain can be explored by taking advantage of its unique characteristics. This article addresses resource management in DS-CDMA cellular networks. We first provide an overview of the DS-CDMA network and discuss the main challenges in the design of resource management schemes. We then examine several critical issues within the scope of resource management, including congestion control, rate and power control, and cell planning, with the emphasis on call admission control. Finally, we offer some insights and discussions on the performance aspects, strengths, and weaknesses of existing proposals. 相似文献
59.
Polyester‐based polyurethane/nano‐silica composites were obtained via in situ polymerization and investigated by Fourier‐transform infrared spectroscopy (FTIR), or FTIR coupled with attenuated total reflectance (FTIR‐ATR), Transmission electron microscopy (TEM), atomic force microscopy (AFM), an Instron testing machine, dynamic mechanical analysis (DMA) and ultraviolet‐visible spectrophotometry (UV‐vis). FTIR analysis showed that in situ polymerization provoked some chemical reactions between polyester molecules and nano‐silica particles. FTIR‐ATR, TEM and AFM analyses showed that both surface and interface contained nano‐silica particles. Instron testing and DMA data showed that introducing nano‐silica particles into polyurethane enhanced the hardness, glass temperature and adhesion strength of polyurethane to the substrate, but also increased the resin viscosity. UV‐vis spectrophotometry showed that nano‐silica obtained by the fumed method did not shield UV radiation in polyurethane films. Copyright © 2003 Society of Chemical Industry 相似文献
60.
按照2000年示范电厂的思路,电厂MIS已经作为电厂建设的一部分被列入基建程序。面对电力行业重组的新局面,为了提高电厂MIS设计水平,更好地为业主服务,以适应当前日益激烈的竞争,适时地总结电厂MIS设计中的共性问题是很有必要的。文中叙述的内容不是探讨如何设计电厂MIS,而是就设计中容易出现的问题进行研讨。 相似文献