全文获取类型
收费全文 | 17903篇 |
免费 | 793篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 213篇 |
综合类 | 18篇 |
化学工业 | 3674篇 |
金属工艺 | 321篇 |
机械仪表 | 403篇 |
建筑科学 | 1004篇 |
矿业工程 | 49篇 |
能源动力 | 501篇 |
轻工业 | 1675篇 |
水利工程 | 120篇 |
石油天然气 | 56篇 |
武器工业 | 1篇 |
无线电 | 1579篇 |
一般工业技术 | 3053篇 |
冶金工业 | 3019篇 |
原子能技术 | 188篇 |
自动化技术 | 2842篇 |
出版年
2023年 | 140篇 |
2022年 | 224篇 |
2021年 | 457篇 |
2020年 | 341篇 |
2019年 | 366篇 |
2018年 | 424篇 |
2017年 | 388篇 |
2016年 | 491篇 |
2015年 | 423篇 |
2014年 | 520篇 |
2013年 | 1072篇 |
2012年 | 856篇 |
2011年 | 1115篇 |
2010年 | 765篇 |
2009年 | 821篇 |
2008年 | 861篇 |
2007年 | 756篇 |
2006年 | 701篇 |
2005年 | 590篇 |
2004年 | 484篇 |
2003年 | 435篇 |
2002年 | 420篇 |
2001年 | 295篇 |
2000年 | 317篇 |
1999年 | 347篇 |
1998年 | 730篇 |
1997年 | 475篇 |
1996年 | 391篇 |
1995年 | 286篇 |
1994年 | 268篇 |
1993年 | 265篇 |
1992年 | 182篇 |
1991年 | 154篇 |
1990年 | 135篇 |
1989年 | 135篇 |
1988年 | 123篇 |
1987年 | 115篇 |
1986年 | 113篇 |
1985年 | 138篇 |
1984年 | 132篇 |
1983年 | 115篇 |
1982年 | 89篇 |
1981年 | 102篇 |
1980年 | 85篇 |
1979年 | 96篇 |
1978年 | 87篇 |
1977年 | 115篇 |
1976年 | 137篇 |
1975年 | 79篇 |
1974年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
961.
Pavani Kotakonda Izabela Naydenova Robert Howard Suzanne Martin Vincent Toal 《Journal of Materials Science: Materials in Electronics》2009,20(Z1):198-201
Holographically recorded surface relief gratings in dry, self-developing acrylamide based photopolymer were used to fabricate
two types of switchable liquid crystal (LC) device. One is an electrically switchable LC diffraction grating and the other
is an electrically switchable polarization rotator. The electrically switchable diffraction grating was characterized by measuring
the dependence of the intensity in the first diffracted order on the applied electric field. The polarization rotator was
characterized by studying the influence of the applied electric field on the twist angle and the variation of intensity in
the zero and the first orders of diffraction. 相似文献
962.
963.
This paper considers homogeneous networks of general, linear time-invariant, second-order systems. We consider linear feedback controllers and require that the directed graph associated with the network contains a spanning tree and systems are stabilisable. We show that consensus with a guaranteed rate of convergence can always be achieved using linear state feedback. To achieve this, we provide a new and simple derivation of the conditions for a second-order polynomial with complex coefficients to be Hurwitz. We apply this result to obtain necessary and sufficient conditions to achieve consensus with networks whose graph Laplacian matrix may have complex eigenvalues. Based on the conditions found, methods to compute feedback gains are proposed. We show that gains can be chosen such that consensus is achieved robustly over a variety of communication structures and system dynamics. We also consider the use of static output feedback. 相似文献
964.
Agglomeration and productivity: evidence from firm-level data 总被引:1,自引:1,他引:0
Do agglomerations stimulate productivity? An extensive literature on agglomeration economies, or urban increasing returns, has analyzed this question with aggregated spatial data. This paper estimates the relationship between agglomeration and productivity at the firm level using static and dynamic models. It makes use of a rich dataset comprising register information on all manufacturing firms in Sweden with 10 or more employees over the period 1997–2004. Three things emerge. First, firms located in larger regions are more productive when controlling for size, human capital, physical capital, ownership structure, import and export, industry classification, and time trend. Second, results from dynamic panel estimations suggests a learning effect in that agglomeration enhances firms’ productivity. Third, the role of agglomeration phenomena does not seem to have a clear coupling to firm size. 相似文献
965.
Operational remote monitoring of snowpack stratigraphy, melt water intrusions and their evolution with time for forecasting snowpack stability is not possible to date. Determination of the spatial variability of snowpack conditions on various scales requires a number of point measurements with various methods. These methods are either destructive or do not provide information about the internal structure of the snowpack. The application of a remotely controlled non-destructive sensor system would help to gain a higher spatio-temporal resolution about information of the snowpack. In this study we present results from upward-looking ground-penetrating radar (GPR) surveys from horizontal caves dug in the front wall of snow pits at the bottom of the snowpack. GPR data are compared with vertical profiles of snow hardness and density, obtained in the snow pit. Data were acquired in different areas with varying snow conditions with various GPR impulse systems, frequencies and polarizations. Radar experiments with high frequencies (> 1 GHz) detect internal layers in the snowpack in dry snow, but fail to provide clear reflections at the upper snow-air transition because of attenuation. In wet snow, the radar signals < 1 GHz are capable to penetrate a meter-thick snowpack and detect the snow surface, although the signal is strongly attenuated. Analysis of reflection phases and magnitudes allows interpretation of their physical origin in terms of changes in electrical permittivity. Varying antenna polarization causes a strongly different signal response, likely caused by the snow-pit wall present in our set-up. Forward calculation of density-based reflection coefficients between neighboring layers of varying hardness yields ambiguous results in terms of correspondence with observed radar reflections apart except for interferences of neighboring reflections. Moreover, we identify several pitfalls for future applications. The system set-up used here represents a basis for further developments towards a system, which is capable of improving information on the spatial and temporal snowpack characteristics. 相似文献
966.
A. Martin J. C. Poignet J. Fouletier M. Allibert D. Lambertin G. Bourgès 《Journal of Applied Electrochemistry》2010,40(3):533-542
This article is devoted to the study of the stability of an yttria-stabilized zirconia membrane used in the electrolysis of
molten CaCl2–CaO mixtures at 850 °C. Intensiostatic and potentiostatic electrolysis were carried for periods ranging from 10 to 20 h.
Post-mortem composition profiles across the zirconia membrane were determined using Raman spectroscopy and microprobe analysis.
The membrane degradation was analyzed in terms of synergetic parameters, i.e., chemical, electrochemical, and thermomechanical
effects. 相似文献
967.
Martin Oschatz Marcus Rose Nicole Klein Thomas Freudenberg Gleb Yushin 《Carbon》2010,48(14):3987-3992
A hierarchical and highly porous carbide-derived carbon (CDC) was obtained by nanocasting of pre-ceramic precursors into cubic ordered silica (KIT-6) and subsequent chlorination. Resulting CDC replica materials show high methane and n-butane uptake and excellent performance as electrode materials in supercapacitors. 相似文献
968.
Jesse Carter E.G. Fu G. Bassiri B.M. Dvorak N. David Theodore Guoqiang Xie D.A. Lucca Michael Martin Mark Hollander Xinghang Zhang Lin Shao 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(8-9):1518-1521
Application of metallic glasses as structural materials has been limited by their poor ductility. To overcome brittle failure, nanocrystals are intentionally introduced to stabilize the glasses. In this study, we report on the application of ion irradiation to induce nanocrystalization in a Cu50Zr45Ti5 (CZT) alloy. Transmission electron microcopy, microindentation and nanoindentation have been used to characterize the CZT alloy irradiated with 140 keV He ions at room temperature. Hardness enhancement was observed near the projected range of the He ions, coinciding with the formation of nanocrystals. Such microstructural changes, however, were not observed in the near surface region, where the electronic stopping process is dominant. 相似文献
969.
Michael Noeth Prasun Ratn Frank Mueller Martin Schulz Bronis R. de Supinski 《Journal of Parallel and Distributed Computing》2009
Characterizing the communication behavior of large-scale applications is a difficult and costly task due to code/system complexity and long execution times. While many tools to study this behavior have been developed, these approaches either aggregate information in a lossy way through high-level statistics or produce huge trace files that are hard to handle. 相似文献
970.
Clint Alex CottrellScott E. Grasman Mathew ThomasKevin Braun Martin John W. Sheffield 《International Journal of Hydrogen Energy》2011,36(13):7969-7975
In the future, hydrogen-based stationary and portable fuel cell systems can help supply some or all of the power demanded with additional advantages of higher reliability, lower emissions, independence from the general grid, and cogeneration capability. In order to understand how to prepare the future for this technology, this paper describes a thorough investigation of past alternative stationary and portable power projects in order for an assessment of the opportunities for stationary and portable fuel cell markets, as well as interactions with transportation hydrogen systems. The lessons learned from the programs are used to establish best practices and recommendations for a hydrogen strategy that addresses opportunities for hydrogen in power generation systems, as well as to make recommendations for market transformation within the hydrogen fuel cell industry. 相似文献