全文获取类型
收费全文 | 406921篇 |
免费 | 5998篇 |
国内免费 | 2346篇 |
专业分类
电工技术 | 8176篇 |
技术理论 | 5篇 |
综合类 | 1255篇 |
化学工业 | 65042篇 |
金属工艺 | 17297篇 |
机械仪表 | 11955篇 |
建筑科学 | 10345篇 |
矿业工程 | 2439篇 |
能源动力 | 9540篇 |
轻工业 | 38643篇 |
水利工程 | 4246篇 |
石油天然气 | 8515篇 |
武器工业 | 245篇 |
无线电 | 44047篇 |
一般工业技术 | 76306篇 |
冶金工业 | 75427篇 |
原子能技术 | 8986篇 |
自动化技术 | 32796篇 |
出版年
2021年 | 3534篇 |
2019年 | 3108篇 |
2018年 | 5016篇 |
2017年 | 4974篇 |
2016年 | 5414篇 |
2015年 | 4100篇 |
2014年 | 6731篇 |
2013年 | 17811篇 |
2012年 | 11303篇 |
2011年 | 15276篇 |
2010年 | 12162篇 |
2009年 | 13398篇 |
2008年 | 14105篇 |
2007年 | 14296篇 |
2006年 | 12453篇 |
2005年 | 11150篇 |
2004年 | 10233篇 |
2003年 | 9588篇 |
2002年 | 9585篇 |
2001年 | 9661篇 |
2000年 | 9143篇 |
1999年 | 9225篇 |
1998年 | 21551篇 |
1997年 | 15730篇 |
1996年 | 12052篇 |
1995年 | 9165篇 |
1994年 | 8126篇 |
1993年 | 7958篇 |
1992年 | 6114篇 |
1991年 | 5885篇 |
1990年 | 5840篇 |
1989年 | 5836篇 |
1988年 | 5520篇 |
1987年 | 4833篇 |
1986年 | 4774篇 |
1985年 | 5442篇 |
1984年 | 5143篇 |
1983年 | 4791篇 |
1982年 | 4290篇 |
1981年 | 4547篇 |
1980年 | 4162篇 |
1979年 | 4346篇 |
1978年 | 4223篇 |
1977年 | 4648篇 |
1976年 | 6013篇 |
1975年 | 3757篇 |
1974年 | 3574篇 |
1973年 | 3674篇 |
1972年 | 3105篇 |
1971年 | 2829篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Stormwater quality simulation models are useful tools for the design and management of sewer systems. Modelling results are highly sensitive to experimental data used for calibration. This sensitivity is examined for three modelling approaches of various complexities (site mean concentration approach, event mean concentration approach and build-up, washoff and transport modelling approach) applied to a typical case study (design of a dry detention tank), accounting for the variability of calibration data and their effect on simulation results. Calibrated models with different calibration data sets were used to simulate 3 years of rainfall with different retention tank specific volumes. Annual pollutant load interception efficiencies were determined. Simulations results revealed (i) that there is no advantage in using the EMC model compared to the SMC model and (ii) that the BWT model resulted in higher design ratios than those given by the SMC/hydraulic approach. For both EMC and BWT models, using an increasing number n of events for calibration leads to narrower confidence intervals for the design ratios. It is crucial for design ratios to account for successive storm events in chronological order and to account for the maximum allowable flow to be transferred to the downstream WWTP. 相似文献
13.
It was found that vanadyl porphyrin complexes synthesized from petroleum metal porphyrin concentrates stimulated epoxidation during the olefin oxygenation process. The yields of obtained oxiranes turned out to be 38–75%, depending on the olefin structure. An epoxidation mechanism that suggests the formation of a protonated dioxygen adduct as an intermediate during oxygenation of olefins in the presence of vanadyl porphyrin complexes was proposed. An analogy is drawn between the epoxide formation reaction upon the catalytic oxygenation of olefins and the Prilezhaev reaction. 相似文献
14.
The Magnitogorsk Metallurgical Combine has conducted a study of the effect of technological factors on the hydrogen content
of chromium-nickel-molybdenum steel after vacuum degassing. It was established that the most important factor is the hydrogen
content of the steel before the degassing operation. The study also determined the effects of the circulation coefficient,
the duration of the degassing operation, and the vacuum used in the treatment.
__________
Translated from Metallurg, No. 7, pp. 68–69, July, 2006. 相似文献
15.
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
16.
L. Gao P. Hrter Ch. Linsmeier J. Gstttner R. Emling D. Schmitt-Landsiedel 《Materials Science in Semiconductor Processing》2004,7(4-6):331
Deposition of Ag films by direct liquid injection-metal organic chemical vapor deposition (DLI-MOCVD) was chosen because this preparation method allows precise control of precursor flow and prevents early decomposition of the precursor as compared to the bubbler-delivery. Silver(I)-2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionato-triethylphosphine [Ag(fod)(PEt3)] as the precursor for Ag CVD was studied, which is liquid at 30 °C. Ag films were grown on different substrates of SiO2/Si and TiN/Si. Argon and nitrogen/hydrogen carrier gas was used in a cold wall reactor at a pressure of 50–500 Pa with deposition temperature ranging between 220 °C and 350 °C. Ag films deposited on a TiN/Si diffusion barrier layer have favorable properties over films deposited on SiO2/Si substrate. At lower temperature (220 °C), film growth is essentially reaction-limited on SiO2 substrate. Significant dependence of the surface morphology on the deposition conditions exists in our experiments. According to XPS analysis pure Ag films are deposited by DLI-MOCVD at 250 °C by using argon as carrier gas. 相似文献
17.
Popular biorthogonal wavelet filters via a lifting scheme and its application in image compression 总被引:2,自引:0,他引:2
Cheng L. Liang D.L. Zhang Z.H. 《Vision, Image and Signal Processing, IEE Proceedings -》2003,150(4):227-232
A technique using a lifting scheme is presented for constructing compactly supported wavelets whose coefficients are composed of free variables locating in an interval. An efficient approach-based wavelet for image compression is developed by selecting the coefficients of the 9-7 wavelet filter and associated lifting scheme. Furthermore, the rationalised coefficients wavelet filter that can be implemented with simple integer arithmetic is achieved and its characteristic is close to the well known original irrational coefficients 9-7 wavelet filters developed by A. Cohen et al. (Commun. Pure Appl. Maths., vol.45, no.1, p.485-560, 1992). To reduce the computational cost of image coding applications further, an acceleration technique is proposed for the lifting steps. Software and hardware simulations show that the new method has very low complexity, and simultaneously preserves the high quality of the compressed image. 相似文献
18.
At some point in their careers, clinicians who work or consult in forensic and correctional settings will almost certainly encounter individuals who exhibit psychopathic personality features. Because of the widespread use of this disorder to inform legal and clinical decision making, psychologists should be exceedingly familiar with the relevant research literature on this topic before venturing into these settings. This article reviews the empirical bases of several clinically relevant claims and assertions regarding psychopathy and concludes that many areas of research are decidedly more equivocal in their findings than is commonly perceived. Although there is much to be gained by assessing psychopathy in various contexts, clinicians need to be cautious about drawing overzealous and empirically questionable conclusions about an important disorder that also has great potential for abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
19.
The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit. 相似文献
20.
Ciofi C. Crupi F. Pace C. Scandurra G. 《IEEE transactions on instrumentation and measurement》2003,52(5):1533-1536
Low-frequency noise measurements represent an interesting investigation technique for the characterization of the quality and reliability of microelectronic materials and devices. Performing meaningful noise measurements at low and very low (f<1 Hz) frequencies, however, may be quite challenging, particularly because of the many sources of interference that superimpose on the noise signal. For this reason, packaged samples are preferred because they allow accurate shielding from the external environment, and because keeping the sample in close proximity to the low-noise biasing system and amplifier reduces microphonic and electromagnetic disturbances. Notwithstanding this, the possibility of performing low-frequency noise measurements at wafer level would be quite interesting, both because of the ease of obtaining wafer-level samples from industries with respect to packaged samples, and because this would avoid possible packaging-process induced device degradation. The purpose of this work is to demonstrate that it is, in fact, possible to design and build a dedicated probe system for performing high-sensitivity, low-frequency noise measurements on metal-oxide-semiconductor devices at wafer level. 相似文献