全文获取类型
收费全文 | 18923篇 |
免费 | 1996篇 |
国内免费 | 1185篇 |
专业分类
电工技术 | 577篇 |
综合类 | 1615篇 |
化学工业 | 3946篇 |
金属工艺 | 775篇 |
机械仪表 | 2130篇 |
建筑科学 | 994篇 |
矿业工程 | 507篇 |
能源动力 | 1088篇 |
轻工业 | 526篇 |
水利工程 | 409篇 |
石油天然气 | 586篇 |
武器工业 | 563篇 |
无线电 | 771篇 |
一般工业技术 | 2979篇 |
冶金工业 | 600篇 |
原子能技术 | 349篇 |
自动化技术 | 3689篇 |
出版年
2024年 | 106篇 |
2023年 | 423篇 |
2022年 | 734篇 |
2021年 | 842篇 |
2020年 | 767篇 |
2019年 | 661篇 |
2018年 | 581篇 |
2017年 | 756篇 |
2016年 | 797篇 |
2015年 | 804篇 |
2014年 | 1145篇 |
2013年 | 1341篇 |
2012年 | 1168篇 |
2011年 | 1455篇 |
2010年 | 919篇 |
2009年 | 1079篇 |
2008年 | 1009篇 |
2007年 | 1156篇 |
2006年 | 1021篇 |
2005年 | 811篇 |
2004年 | 712篇 |
2003年 | 599篇 |
2002年 | 468篇 |
2001年 | 426篇 |
2000年 | 334篇 |
1999年 | 327篇 |
1998年 | 263篇 |
1997年 | 243篇 |
1996年 | 187篇 |
1995年 | 159篇 |
1994年 | 117篇 |
1993年 | 116篇 |
1992年 | 94篇 |
1991年 | 89篇 |
1990年 | 64篇 |
1989年 | 86篇 |
1988年 | 53篇 |
1987年 | 32篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1976年 | 4篇 |
1959年 | 8篇 |
1955年 | 5篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
PDC钻头水力结构优化设计研究 总被引:9,自引:0,他引:9
在PDC钻头工作过程中,钻井液对钻头体表面的冲洗、冷却和润滑是保证钻头正常工作的一个非常重要的条件。对PDC钻头而言,水力结构(主要是中心水眼和冠部水道)设计的重要性尤其突出。以前,对钻头水力系统研究只能通过实验的方法进行,研究周期长、成本高、结构调整不方便,而数值模拟的方法在几年前还不成熟,甚至静态的复杂结构流场问题基本无法解决。为此,在提出PDC钻头水力结构优化设计原则的基础上,对PDC钻头的三维流场进行了数值模拟。模拟中考虑了钻头的喷嘴布置位置、直径、数量以及切削齿对流场的影响。计算结果表明,原设计在喷嘴布置位置和喷射角度上存在不足,以此为基础进行了水力结构的优化设计。文中的研究成果成功地应用在新型钻头水力结构的设计中,研究方法为PDC钻头水力结构优化分析奠定了理论基础。 相似文献
32.
33.
Nonlinear Propagation of Coupling Optical Pulse under Compton Scattering in Laser Medium 总被引:1,自引:1,他引:0
HAO Dong-shan ZHANG Xiao-fu 《半导体光子学与技术》2006,12(3):178-183,204
After considering Kerr nonlinear effect,group velocity dispersion of host and gain distribution of active particle in laser amplifying medium,a basic equation describing propagation of the coupling optical pulse under the multi-photon nonlinear Compton scattering in the laser amplifying medium has been deduced. Besides,the profile and power spectrum of a picosecond-level super-Gaussian coupling pulse in the laser amplifying medium have been discussed when its central frequency coincides with the gain peak frequency of the laser amplifying medium. 相似文献
34.
A stochastic model for local disturbances, particularly for a temporal harmonic with random modulations in amplitude and/or phase, is proposed in this paper. Results for the second moment responses of a linear single-degree-of-freedom system to this type of stochastic loading demonstrate a significant change in response characteristics due to a small uncertainty. A local phenomenon may last much longer and resonance may be smeared to a broad range. Integrated with wavelet transform, the proposed approach may be used to model a random process with non-stationary frequency content. Especially, it can be effectively used for Monte Carlo simulation to generate large size of samples that have similar characteristics in time and frequency domains as a pre-selected mother sample has. The technique has a great potential for the case where uncertainty study is warranted but the available samples are limited. 相似文献
35.
36.
37.
Dynamics of liquid-filled spacecraft 总被引:1,自引:0,他引:1
A method is presented for simulating coupled liquid-solid dynamics. An important example of a coupled liquid-solid system is a satellite carrying fuel. The dynamics of the satellite and the onboard fuel influence each other, which may lead to satellite motion that is uncontrollable. For better understanding of the complex dynamics of coupled systems, a numerical model is developed. The model consists of two parts. The first part that solves the liquid motion is only briefly discussed here. The focus in this paper is on the way in which the dynamics of the liquid and the solid body are coupled. For this, the governing equations are presented in which terms appear that represent the force and torque on the solid body due to the sloshing liquid. The governing equations are rewritten such that the discrete approximation of these equations can be integrated in a stable manner for arbitrary liquid/solid mass ratios. Results are presented demonstrating the stability of the present model. A grid-refinement study and a time-step analysis are performed. Finally, the flat-spin motion of a satellite, partially filled with liquid, that flew in 1992 as part of the Wet Satellite Model experiment is studied. Results from the simulation are compared with the actual flight data. 相似文献
38.
Dissolved organic carbon (DOC) dynamics were investigated over a two year period in the Upper Rhǒne River to examine the role of side-arms in providing DOC to the main channel in relation to discharge fluctuations, especially floods. Concentrations of DOC are shown to remain low in space and in time (average 1.5 mg ?1) and to be more related to global hydrological events (precipitation) than to any local flushing for backwaters during floods. The results do not support the general assumption that side-arms are the providers of DOC to the main channel. 相似文献
39.
40.
YOU Deyi 《计算机辅助绘图.设计与制造(英文版)》1991,(1)
The TangShan Research Institute of Group Technology has been engaged in the develop-ment of GT for the light industry machinery building factories since 1980.Under its overall supervisionmore than 8 factories have applied GT to drawing control and process planning,while 4 of them reorga-nized their machine shops into GT cells and the throughput capabilities were raisd immediately by 15 toeven 49%.Since the existing GT coding systems predict only the global characteristics of machine parts,theirapplication alone is unable to transfer all the information needed for the CAD/CAM integration in aCIM environment.From the very beginning of 1989,we started to study the feasibility of introducingconcepts of Functional Form Features into GT codes.Based on the exhaustive study of nearly 100,000part drawings from machineries for making pottery and porcelain appliances,cigarette,paper pulp,glass bottles,plastics moulding,beer and beverage filling etc.,a new GT/FFF coding system wasworked out and a corresponding set of standard drawings assembled from FFF primitives Was formulat-ed which can cover up to 65—75% of existing parts from light industry machineries.FFF based GTcodes greatly facilitate the standardization control of released drawings,accelerate the engineering de-sign and process planning,and certainly will play an important role in the future CIM organization. 相似文献