全文获取类型
收费全文 | 210383篇 |
免费 | 2369篇 |
国内免费 | 570篇 |
专业分类
电工技术 | 3677篇 |
综合类 | 143篇 |
化学工业 | 32638篇 |
金属工艺 | 10370篇 |
机械仪表 | 7103篇 |
建筑科学 | 4080篇 |
矿业工程 | 2162篇 |
能源动力 | 4728篇 |
轻工业 | 13247篇 |
水利工程 | 2941篇 |
石油天然气 | 7733篇 |
武器工业 | 22篇 |
无线电 | 21941篇 |
一般工业技术 | 45934篇 |
冶金工业 | 35428篇 |
原子能技术 | 6725篇 |
自动化技术 | 14450篇 |
出版年
2021年 | 2120篇 |
2019年 | 2044篇 |
2018年 | 3732篇 |
2017年 | 3755篇 |
2016年 | 4062篇 |
2015年 | 2271篇 |
2014年 | 3861篇 |
2013年 | 8955篇 |
2012年 | 5787篇 |
2011年 | 7404篇 |
2010年 | 5982篇 |
2009年 | 6645篇 |
2008年 | 6774篇 |
2007年 | 6628篇 |
2006年 | 5719篇 |
2005年 | 5245篇 |
2004年 | 4749篇 |
2003年 | 4692篇 |
2002年 | 4482篇 |
2001年 | 4564篇 |
2000年 | 4258篇 |
1999年 | 4310篇 |
1998年 | 10561篇 |
1997年 | 7434篇 |
1996年 | 5715篇 |
1995年 | 4246篇 |
1994年 | 3707篇 |
1993年 | 3955篇 |
1992年 | 3036篇 |
1991年 | 3047篇 |
1990年 | 2943篇 |
1989年 | 2899篇 |
1988年 | 2908篇 |
1987年 | 2539篇 |
1986年 | 2616篇 |
1985年 | 2906篇 |
1984年 | 2719篇 |
1983年 | 2595篇 |
1982年 | 2335篇 |
1981年 | 2309篇 |
1980年 | 2380篇 |
1979年 | 2384篇 |
1978年 | 2397篇 |
1977年 | 2514篇 |
1976年 | 2917篇 |
1975年 | 2200篇 |
1974年 | 2077篇 |
1973年 | 2177篇 |
1972年 | 1948篇 |
1971年 | 1762篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A. Yu. Pustynnikov V. G. Ryabov D. T. Kalimullin A. N. Nechaev Ya. A. Treskov 《Chemistry and Technology of Fuels and Oils》2006,42(3):188-191
Paving-and roofing-grade asphalts were obtained at LUKOIL-Permnefteorgsintez Ltd. by mixing peroxidized asphalt and a number
of high-boiling unoxidized petroleum products in certain ratios. The asphalts obtained have improved performance characteristics:
high plasticity and low brittleness temperature.
__________
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 26–28, May–June, 2006. 相似文献
52.
Beneficial effects of wettability altering surfactants in oil-wet fractured reservoirs 总被引:3,自引:0,他引:3
Subhash C. Ayirala Chandra S. Vijapurapu Dandina N. Rao 《Journal of Petroleum Science and Engineering》2006,52(1-4):261
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
53.
N. I. Nikolaikin E. Yu. Barzilovich N. E. Nikolaikina 《Chemical and Petroleum Engineering》2006,42(5-6):332-338
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
54.
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
55.
Using a temporary substitution of format, the author offers a fairy tale to demonstrate that we cant expect understanding when computers take the place of humans in our interactions with service providers. 相似文献
56.
Note on B-splines, wavelet scaling functions, and Gabor frames 总被引:3,自引:0,他引:3
Grochenig K. Janssen A.J.E.M. Kaiblinger N. Pfander G.E. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(12):3318-3320
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
57.
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
58.
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(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=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
59.
de Oliveira J.C. Hosseini M. Shirmohammadi S. Malric F. Nourian S. El Saddik A. Georganas N.D. 《Multimedia, IEEE》2003,10(3):18-29
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
60.
Korolev I. A. Alekseenko N. N. Porodnov B. T. Sapunov V. A. Savel'ev D. V. 《Measurement Techniques》2003,46(9):865-871
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