首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   206167篇
  免费   2338篇
  国内免费   565篇
电工技术   3510篇
综合类   141篇
化学工业   31846篇
金属工艺   10268篇
机械仪表   7028篇
建筑科学   3998篇
矿业工程   2161篇
能源动力   4631篇
轻工业   12876篇
水利工程   2921篇
石油天然气   7737篇
武器工业   22篇
无线电   21502篇
一般工业技术   45192篇
冶金工业   34471篇
原子能技术   6620篇
自动化技术   14146篇
  2021年   2051篇
  2019年   1999篇
  2018年   3681篇
  2017年   3719篇
  2016年   3999篇
  2015年   2233篇
  2014年   3782篇
  2013年   8754篇
  2012年   5681篇
  2011年   7217篇
  2010年   5857篇
  2009年   6491篇
  2008年   6614篇
  2007年   6493篇
  2006年   5573篇
  2005年   5119篇
  2004年   4630篇
  2003年   4555篇
  2002年   4369篇
  2001年   4472篇
  2000年   4187篇
  1999年   4201篇
  1998年   10212篇
  1997年   7204篇
  1996年   5510篇
  1995年   4133篇
  1994年   3600篇
  1993年   3841篇
  1992年   2985篇
  1991年   2995篇
  1990年   2894篇
  1989年   2856篇
  1988年   2870篇
  1987年   2512篇
  1986年   2571篇
  1985年   2858篇
  1984年   2688篇
  1983年   2556篇
  1982年   2301篇
  1981年   2270篇
  1980年   2349篇
  1979年   2360篇
  1978年   2383篇
  1977年   2490篇
  1976年   2882篇
  1975年   2191篇
  1974年   2069篇
  1973年   2167篇
  1972年   1942篇
  1971年   1756篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
In fractured reservoirs, an effective matrix-fracture mass transfer is required for oil recovery. Surfactants have long been considered for oil recovery enhancement, mainly in terms of their ability to reduce oil–water interfacial tension. These surfactants are effective when the fractured formations are water-wet, where capillary imbibition of surfactants from the fracture into the matrix contributes to oil recovery. However, another beneficial aspect of surfactants, namely their ability to alter wettability, remains to be explored and exploited. Surfactants capable of altering wettability can be especially beneficial in oil-wet fractured formations, where the surfactant in the fracture diffuses into the matrix and alters the wettability, enabling imbibition of even more surfactant into the matrix. This sequential process of initial diffusion followed by imbibition continues well into the matrix yielding significant enhancements in oil recovery.In order to test this hypothesis of sequential diffusion–imbibition phenomenon, Dual-Drop Dual-Crystal (DDDC) contact angle experiments have been conducted using fractured Yates dolomite reservoir fluids, two types of surfactants (nonionic and anionic) and dolomite rock substrates. A new experimental procedure was developed in which crude oil equilibrated with reservoir brine has been exposed to surfactant to simulate the matrix-fracture interactions in fractured reservoirs. This procedure enables the measurements of dynamic contact angles and oil–water interfacial tensions, in addition to providing the visual observations of the dynamic behavior of crude oil trapped in the rock matrix as it encounters the diffusing surfactant from the fractures. Both the measurements and visual observations indicate wettability alterations of the matrix surface from oil-wet to less oil-wet or intermediate wet by the surfactants. Thus this study is of practical importance to oil-wet fractured formations where surfactant-induced wettability alterations can result in significant oil recovery enhancements. In addition, this study has also identified the need to include contact angle term in the dimensionless Bond number formulations for better quantitative interpretation of rock–fluids interactions.  相似文献   
82.
The paper discusses optimal control of ecosystem state for observation of a generalized monotonically varying random parameter. A model is proposed for the controlled vector random process, whose components are assigned acceptable ranges and the observations are performed discretely. __________ Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 6, pp. 40–44, June, 2006.  相似文献   
83.
Co-browsing is an activity in which a group of users navigate their way through of a set of Web pages together for a shared purpose. Effective co-browsing among users with different device capabilities requires a shared understanding of those Web pages. This paper demonstrates the concept of shared viewpoints (SVPs), and personal viewpoints (PVPs), for co-browsing, before detailing a framework for implementing these concepts. Finally, the effectiveness of the framework is presented through a perceptual experiment.  相似文献   
84.
Holmes  N. 《Computer》2006,39(2):112-111
Using a temporary substitution of format, the author offers a fairy tale to demonstrate that we can’t expect understanding when computers take the place of humans in our interactions with service providers.  相似文献   
85.
Note on B-splines, wavelet scaling functions, and Gabor frames   总被引:3,自引:0,他引:3  
Let g be a continuous, compactly supported function on such that the integer translates of g constitute a partition of unity. We show that the Gabor system (g,a,b), with window g and time-shift and frequency-shift parameters a,b>0 has no lower frame bound larger than 0 if b=2,3,... and a>0. In particular, (g,a,b) is not a Gabor frame if g is a continuous, compactly supported wavelet scaling function and if b=2,3,... and a>0. We give an example for our result for the case that g=B/sub 1/, the triangle function supported by [-1,1], by showing pictures of the canonical dual corresponding to (g,a,b) where ab=1/4 and b crosses the lines N=2,3,.  相似文献   
86.
The basic methods of verifying continuous automatic belt weighers are described. A comparative analysis of these methods on the basis of experimental studies is made and ways of implementing the results in industry are recommended.  相似文献   
87.
Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(tγ), shows a decreasing trend with step strain. The experimental results indicate that G(tγ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(tγ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(tγ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior.  相似文献   
88.
Using Java-based tools in multimedia collaborative environments accessed over the Internet can increase an application's client base. Most operating systems support Java, and its "compile once-run everywhere" architecture is easy to maintain and update. The Java-based tools presented here let users share Internet resources, including resources originally designed for single use.  相似文献   
89.
The design of a sylphon bellows sensor and the basic circuits of an LC-generator and of a microprocessor unit are presented. An analytical pressure–frequency conversion function and a special method of adjusting the sensor ensure an error of less than 0.05%. The dynamic range is up to 105. The instruments developed cover the ranges 103, 104, and 105 Pa.  相似文献   
90.
The phenomenon of persistent tunneling photoconductivity was studied using the tunneling spectroscopy technique at liquid-helium temperature: the separation between the unoccupied levels in a δ-doped layer at the GaAs surface decreased after illumination. This decrease was due to an increase in the width of the quantum well of the δ-doped layer. For photon energies hv exceeding the GaAs band gap E g , this increase in the width of the quantum well was related to the accumulation of positive charge in the depth of GaAs induced by the generation of the electron-hole pairs and photoionization of deep centers. For hv < E g (including the case of CO2 laser), only photoionization is important. The experimental data agree with the self-consistent calculations. The critical temperature for the effect has been determined (T c = 45 K); at higher temperatures, the effect disappears.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号