全文获取类型
收费全文 | 324715篇 |
免费 | 82270篇 |
国内免费 | 56997篇 |
专业分类
电工技术 | 39966篇 |
技术理论 | 3篇 |
综合类 | 36124篇 |
化学工业 | 40711篇 |
金属工艺 | 34394篇 |
机械仪表 | 16658篇 |
建筑科学 | 23366篇 |
矿业工程 | 17848篇 |
能源动力 | 11883篇 |
轻工业 | 36536篇 |
水利工程 | 11647篇 |
石油天然气 | 17286篇 |
武器工业 | 5197篇 |
无线电 | 44464篇 |
一般工业技术 | 41445篇 |
冶金工业 | 12276篇 |
原子能技术 | 3718篇 |
自动化技术 | 70460篇 |
出版年
2024年 | 3518篇 |
2023年 | 6557篇 |
2022年 | 10076篇 |
2021年 | 12191篇 |
2020年 | 13183篇 |
2019年 | 20519篇 |
2018年 | 22096篇 |
2017年 | 24037篇 |
2016年 | 23399篇 |
2015年 | 24537篇 |
2014年 | 24851篇 |
2013年 | 25649篇 |
2012年 | 27182篇 |
2011年 | 24258篇 |
2010年 | 22563篇 |
2009年 | 19549篇 |
2008年 | 18153篇 |
2007年 | 17554篇 |
2006年 | 14876篇 |
2005年 | 12742篇 |
2004年 | 13688篇 |
2003年 | 11040篇 |
2002年 | 11329篇 |
2001年 | 10014篇 |
2000年 | 8106篇 |
1999年 | 6081篇 |
1998年 | 4713篇 |
1997年 | 4206篇 |
1996年 | 3988篇 |
1995年 | 3948篇 |
1994年 | 3260篇 |
1993年 | 2972篇 |
1992年 | 2835篇 |
1991年 | 2058篇 |
1990年 | 1615篇 |
1989年 | 1510篇 |
1988年 | 1160篇 |
1987年 | 410篇 |
1986年 | 344篇 |
1985年 | 241篇 |
1984年 | 161篇 |
1983年 | 128篇 |
1982年 | 160篇 |
1981年 | 179篇 |
1980年 | 155篇 |
1976年 | 230篇 |
1975年 | 210篇 |
1972年 | 237篇 |
1971年 | 128篇 |
1960年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
分析了韩国、日本及国内运营商手机游戏业务的发展状况.探讨了手机游戏业务的模式.论述了该业务的战略定位和市场前景。从地区提供给移动通信市场对外部环境、产业链的准备是否充分以及运营商内部的资源和运营状况等三个方面阐明了手机游戏业务发展的关键因素。 相似文献
22.
Javier Ramírez Antonio García Uwe Meyer-Bäse Fred Taylor Antonio Lloris 《The Journal of VLSI Signal Processing》2003,33(1-2):171-190
Currently there are design barriers inhibiting the implementation of high-precision digital signal processing (DSP) objects with field programmable logic (FPL) devices. This paper explores overcoming these barriers by fusing together the popular distributed arithmetic (DA) method with the residue number system (RNS) for use in FPL-centric designs. The new design paradigm is studied in the context of a high-performance filter bank and a discrete wavelet transform (DWT). The proposed design paradigm is facilitated by a new RNS accumulator structure based on a carry save adder (CSA). The reported methodology also introduces a polyphase filter structure that results in a reduced look-up table (LUT) budget. The 2C-DA and RNS-DA are compared, in the context of a FPL implementation strategy, using a discrete wavelet transform (DWT) filter bank as a common design theme. The results show that the RNS-DA, compared to a traditional 2C-DA design, enjoys a performance advantage that increases with precision (wordlength). 相似文献
23.
24.
吐哈油田部分区块地层压力系数小于0.9,常规水基压井液对储层伤害大,若使用油基压井液成本高,环境污染严重。通过实验优选出了一种低密度水基微泡沫压井液。该压井液具有密度低、泡沫强度高、稳定性好、携砂能力强等优点。现场应用表明,低密度微泡沫压井液稳定时间大于48 h,密度在0.70~0.99 g/cm3之间可调,抗油污染能力强,抗油大于8%,抗温在100℃以上,岩心污染后渗透率恢复值大于80%;并且施工方便,成本低,具有储层保护能力,使用微泡沫压井液的井表皮系数在0.20~2.34之间。 相似文献
25.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
26.
M. Riad Manaa Laurence E. Fried Evan J. Reed 《Journal of Computer-Aided Materials Design》2003,10(2):75-97
In this article, we review recent atomistic computational techniques to study the electronic structure aspects and chemistry
of energetic materials at high-pressure and/or high temperature. While several mechanisms have been proposed for the initial
events of energetic materials at high-pressure, we explore the validity of a proposed shear-induced local metallization via
molecular bond bending in the insensitive explosive TATB. We study the effect of high-stress (both uniform and uniaxial) on
the electronic energy band-gap and the first chemical event of a prototypical energetic material, that of nitromethane. We
also determine chemical reactions rate laws and decomposition mechanisms from a quantum-based molecular dynamics simulation
of HMX, a widely used explosive material, at conditions of high density and temperature similar to that encounter under detonation.
Finally, we review a new multi-scale computational tool recently developed to model the shock-induced chemistry of energetic
materials at the atomistic level, and report its applicability to shocked solid nitromethane.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
27.
28.
本文提出了一种基于信息融合的物体三维特征的提取方法,该方法利用两幅互相配准的三维测距图像和灰度图像,来提取多面体的三维特征。首先,通过分析灰度图像中的灰度变化及测距图像中的测距值变化,分别求取各自图像中物体的特征点及特征边;然后,利用两配准图像之间的对应关系,求得所有特征点、面与多边形在三维测距图像中的三维表示;接着,通过分析三维测距图像中所测得的各候选平面上特定点与边处的曲率及法向,验证候选平面 相似文献
29.
W. Lim C. K. Wang 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,370(2-3):568-572
The one-dimensional (1D) position-sensitive superheated-liquid-droplet dosimeter (SLDD) has been fabricated and tested in the laboratory. The 1D SLDD is fabricated from a 9.525-mm OD, 6.35-mm ID, 20-cm long, Plexiglas-walled tube filled with a mixture of superheated-liquid Freon droplets and host medium glycerol. Washer-shaped piezoelectric acoustic transducers are positioned at both ends of the tube; they determine the number and positions of the acoustic events when the superheated-liquid droplets evaporate upon neutron irradiation. The SLDD is irradiated with the 137Cs and 60Co γ-sources, as well as 252Cf neutron source to test for its radiation response and spatial resolution. The SLDD based on the Freon-134a superheated-liquid droplets operating at 20°C and 1 atm is found to be ideal for measuring absorbed neutron dose. This study also proves that the positions of the radiation-induced nucleation acoustic events can be linearly determined from the differences in the transmission times received by the acoustic transducers on the 1D SLDD. The spatial resolution of the neutron depth-dose is 1 mm due the finite response time (1 μs) of the piezoelectric acoustic transducers. 相似文献
30.