全文获取类型
收费全文 | 1904篇 |
免费 | 60篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 39篇 |
综合类 | 1篇 |
化学工业 | 460篇 |
金属工艺 | 65篇 |
机械仪表 | 32篇 |
建筑科学 | 19篇 |
矿业工程 | 3篇 |
能源动力 | 91篇 |
轻工业 | 69篇 |
水利工程 | 15篇 |
石油天然气 | 43篇 |
无线电 | 246篇 |
一般工业技术 | 408篇 |
冶金工业 | 234篇 |
原子能技术 | 2篇 |
自动化技术 | 246篇 |
出版年
2023年 | 11篇 |
2022年 | 35篇 |
2021年 | 39篇 |
2020年 | 29篇 |
2019年 | 41篇 |
2018年 | 62篇 |
2017年 | 49篇 |
2016年 | 43篇 |
2015年 | 29篇 |
2014年 | 65篇 |
2013年 | 168篇 |
2012年 | 78篇 |
2011年 | 97篇 |
2010年 | 72篇 |
2009年 | 65篇 |
2008年 | 76篇 |
2007年 | 87篇 |
2006年 | 50篇 |
2005年 | 55篇 |
2004年 | 41篇 |
2003年 | 53篇 |
2002年 | 44篇 |
2001年 | 30篇 |
2000年 | 35篇 |
1999年 | 25篇 |
1998年 | 72篇 |
1997年 | 53篇 |
1996年 | 32篇 |
1995年 | 33篇 |
1994年 | 29篇 |
1993年 | 37篇 |
1992年 | 24篇 |
1991年 | 33篇 |
1990年 | 35篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 19篇 |
1986年 | 17篇 |
1985年 | 16篇 |
1984年 | 19篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 18篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 5篇 |
1973年 | 6篇 |
排序方式: 共有1973条查询结果,搜索用时 0 毫秒
11.
Kevin E. Spaulding Geoffrey J. Woolfe Rajan L. Joshi 《Color research and application》2003,28(4):251-266
Image sources, such as digital camera captures and photographic negatives, typically have more information than can be reproduced on a photographic print or a video display. The information that is lost during the tone/color rendering process relates to both the extended dynamic range and color gamut of the original scene. In conventional photographic systems, most of this additional information is archived on the photographic negative and can be accessed by adjusting the way the negative is printed. However, most digital imaging systems have traditionally archived only a rendered video RGB image. As a result, it is not possible to make the same sorts of image manipulations that historically have been possible with conventional photographic systems. This suggests that there would be an advantage to storing images using an extended dynamic range/color gamut color encoding. However, because of file compatibility issues, digital imaging systems that store images using color encoding other than a standard video RGB representation (e.g., sRGB) would be significantly disadvantaged in the marketplace. In this article, we describe a solution that has been developed to maintain compatibility with existing file formats and software applications, while simultaneously retaining the extended dynamic range and color gamut information associated with the original scenes. With this approach, the input raw digital camera image or film scan is first transformed to the scene‐referred ERIMM RGB color encoding. Next, a rendered sRGB image is formed in the usual way and stored in a conventional image file (e.g., a standard JPEG file). A residual image representing the difference between the original extended dynamic range image and the final rendered image is formed and stored in the image file using proprietary metadata tags. This provides a mechanism for archiving the extended dynamic range/color gamut information, which is normally discarded during the rendering process, without sacrificing interoperability. Appropriately enabled applications can decode the residual image metadata and use it to reconstruct the ERIMM RGB image, whereas applications that are not aware of the metadata will ignore it and only have access to the sRGB image. The residual image is formed such that it will have negligible pixel values for those portions of the image that lie within the sRGB gamut, and will therefore be highly compressible. Tests on a population of 950 real customer images have demonstrated that the extended dynamic range scene information can be stored with an average file size overhead of about 8% compared to the sRGB images alone. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 251–266, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10160 相似文献
12.
A two-stage balanced Ku-band coplanar waveguide amplifier design is presented which has been miniaturised by using impedance transforming couplers which considerably reduce the required matching networks to the MESFETs. The amplifier, measuring only 2*1.7 mm/sup 2/, exhibits a gain of 13.7 dB with less than +or-0.2 dB of ripple over the range 14-16 GHz.<> 相似文献
13.
STATISTICAL ANALYSIS OF REACTION RATE DATA OF LIQUID PHASE SYNTHESIS OF DIMETHYL ETHER FROM METHANOL
Makarand R. Gogate 《Petroleum Science and Technology》1993,11(9):1251-1268
The liquid phase catalytic dehydration of methanol to dimethyl ether (DME) is a key reaction step in the single-step synthesis of DME from CO-rich syngas in a slurry reactor. The effect of process variables including temperature, pressure, impeller speed, and feed methanol flow rate on DME synthesis rate has been studied by a systematic 24 full factorial experimental design with single replicate. The significant effects and interactions have been quantified by F-tests. The estimates of significant effects have been obtained by Yates' algorithm. Residual probability and normal probability dots have been obtained to test model adequacy. Finally, a computational model has been developed to predict the DME synthesis rate alt various values of process variables. The model has excellent interpolational predictive capability as evidenced by parity plots. 相似文献
14.
15.
The scalar transform is a new representation for signals, offering a perspective that is different from the Fourier transform. We introduce the notion of a scalar periodic function. These functions are then represented through the discrete scale series. We also define the notion of a strictly scale-limited signal. Analogous to the Shannon interpolation formula, we show that such signals can be exactly reconstructed from exponentially spaced samples of the signal in the time domain. As an interesting, practical application, we show how properties unique to the scale transform make it very useful in computing depth maps of a scene 相似文献
16.
17.
2',4'-Dihydroxyacetophenone, also known as resoacetophenone, is a commercially important intermediate which is generally
prepared by the acylation of resorcinol with acetic acid in the presence of a molar excess of zinc chloride, which leads to
waste disposal problems. The most frequently used acylating agents such as acetic anhydride and acetyl chloride have several
disadvantages and need to be replaced by cheap and benign agents. In this connection, acetic acid is a better choice but with
a non-polluting and reusable catalyst. The synthesis of 2',4'-dihydroxyacetophenone from resorcinol and acetic acid was carried
out in the presence of a variety of solid acid catalysts such as montmorillonite clay (K-10), dodecatungstophosphoric acid
(DTP) supported on K-10, sulfated zirconia and ion exchange resins. Amongst these catalysts, Amberlyst-36, an ion exchange
resin, was found to be the most effective. The effects of various parameters on the rate of reaction and selectivity were
investigated to establish the intrinsic kinetics of the reaction. It was possible to deduce the adsorption equilibrium constant
and rate constant simultaneously for the reaction including the corresponding energies of activation. The catalyst is reusable.
The process is in consonance with the principles of green chemistry.
Electronic Publication 相似文献
18.
In this paper we report the impact of hot-carrier stress on analog performance of n- and p-MOSFET's with conventional oxide, NH3-nitrided oxide (RTN) and reoxidized nitrided oxide (RTN/RTO) as gate dielectrics. Changes due to hot-carrier stress in crucial analog parameters viz., drain output resistance, voltage gain, and input offset voltage of a source coupled differential MOSFET pair are investigated. Results show that RTN/RTO gate dielectrics suppress degradation of analog parameters in n-MOSFET's but increase it slightly in p-MOSFET's, as compared to conventional oxide MOSFET's 相似文献
19.
Qingbin Cui Mehmet Emre Bayraktar Makarand Hastak Issam Minkarah 《Canadian Metallurgical Quarterly》2004,20(3):118-125
Since the introduction of warranty provisions in federal highway jobs, more and more state departments of transportation (DOTs) have considered the use of such provisions to protect their initial investment. This paper describes the pros and cons of warranty contracting in highway construction based on a survey of warranty practices in the United States. In particular, the need for state DOTs to buy a warranty for a well-built project is questioned. As an alternative, this paper introduces the warranty option, which gives the DOT the right to buy a warranty only if it becomes necessary at the end of construction. This option is exercised if the performance on site warrants it. This paper describes the mechanics of the warranty option and its advantages over the conventional warranty. A bid evaluation model is also developed for the warranty option approach. 相似文献
20.