全文获取类型
收费全文 | 6340篇 |
免费 | 612篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 73篇 |
综合类 | 4篇 |
化学工业 | 1661篇 |
金属工艺 | 196篇 |
机械仪表 | 364篇 |
建筑科学 | 90篇 |
矿业工程 | 4篇 |
能源动力 | 269篇 |
轻工业 | 619篇 |
水利工程 | 16篇 |
石油天然气 | 17篇 |
无线电 | 996篇 |
一般工业技术 | 1477篇 |
冶金工业 | 420篇 |
原子能技术 | 70篇 |
自动化技术 | 685篇 |
出版年
2023年 | 55篇 |
2022年 | 74篇 |
2021年 | 169篇 |
2020年 | 163篇 |
2019年 | 213篇 |
2018年 | 221篇 |
2017年 | 221篇 |
2016年 | 254篇 |
2015年 | 246篇 |
2014年 | 303篇 |
2013年 | 419篇 |
2012年 | 507篇 |
2011年 | 548篇 |
2010年 | 399篇 |
2009年 | 381篇 |
2008年 | 354篇 |
2007年 | 277篇 |
2006年 | 263篇 |
2005年 | 210篇 |
2004年 | 198篇 |
2003年 | 193篇 |
2002年 | 161篇 |
2001年 | 129篇 |
2000年 | 95篇 |
1999年 | 129篇 |
1998年 | 165篇 |
1997年 | 129篇 |
1996年 | 98篇 |
1995年 | 77篇 |
1994年 | 44篇 |
1993年 | 42篇 |
1992年 | 30篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 17篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 9篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有6961条查询结果,搜索用时 15 毫秒
31.
Preparation and characterisation of vanadium catalysts supported over alumina-pillared clays 总被引:1,自引:0,他引:1
M. A. Vicente C. Belver R. Trujillano M. A. Baares-Muoz V. Rives S. A. Korili A. Gil L. M. Gandía J. -F. Lambert 《Catalysis Today》2003,78(1-4):181-190
Supported vanadium-containing catalysts were prepared by impregnation of Al-pillared clays with NaVO3 precursor aqueous solutions. A montmorillonite and a saponite, both natural as well as previously pillared with Al13-Keggin polycations, were used as supports, being impregnated with solutions of the precursor by means of the incipient wetness technique. The layered structure of the supports is maintained after impregnation, and even after calcination of the impregnated solids at 500 °C, although with a significant worsening of the textural properties of the solids, in particular, a loss of specific surface area. Three crystalline vanadium-containing phases were identified in the impregnated solids, namely, NaV3O8, AlVO4 and V2O5 (shcherbinaite). The reduction of these phases to V3+ species was observed as wide processes in the 450–750 °C range, all of them centred at ca. 600 °C. 相似文献
32.
JaeHyunKim JounHoLee JiChulLim ChangHoonLee MooHyoungSong JuYeonYoon HeeDongChoi JeomJaeKim ChangHoOh SangDeogYeo 李路海 《现代显示》2004,31(5):31-33
薄膜晶体管液晶电视(TFT-LCD TV)因为具有薄、轻、紧凑和可随意放置的特点,已经占据了大部分电视机市场。除了这些物理特性以外,最重要的特性是已具有了良好像质的对比度。为了将对比度提高到1:600以上,对偏振片膜、背光源板、滤色片树脂、电极锥角和摩擦条件等都进行了研究。优化的背光板组合,光滑的电极锥角和摩擦方法的控制是提高对比度的主要控制因素。应用新开发的滤色片树脂,对获得高对比度最为有效。 相似文献
33.
With video compression standards such as MPEG‐4, a transmission error happens in a video‐packet basis, rather than in a macroblock basis. In this context, we propose a semantic error prioritization method that determines the size of a video packet based on the importance of its contents. A video packet length is made to be short for an important area such as a facial area in order to reduce the possibility of error accumulation. To facilitate the semantic error prioritization, an efficient hardware algorithm for face tracking is proposed. The increase of hardware complexity is minimal because a motion estimation engine is efficiently re‐used for face tracking. Experimental results demonstrate that the facial area is well protected with the proposed scheme. 相似文献
34.
韩国许多城市指定了专项旅游区,通过提供若干激励政策来促进城市旅游.汉城的梨泰院1997年被指定为专项旅游区并成为CBD的一部分.本研究追溯了它作为旅游购物区的变化过程,并通过调查其土地使用找出城市空间结构的变化特征.最后,作者提出了对发展城市旅游的政策性建议,包括减少指定性区域和特殊政策. 相似文献
35.
Kum‐Il Lee Yong‐Sik Yim Sang‐Wook Chung Jiaqiu Wei Jong Il Rhee 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(9):1036-1045
A two‐dimensional (2D) spectrofluorometer was used to monitor various fermentation processes with recombinant E coli for the production of 5‐aminolevulinic acid (ALA). The whole fluorescence spectral data obtained during a process were analyzed using artificial neural networks, ie self‐organizing map (SOM) and feedforward backpropagation neural network (BPNN). The SOM‐based classification of the whole spectral data has made it possible to qualitatively associate some process parameters with the normalized weights and variances, and to select some useful combinations of excitation and emission wavelengths. Based on the classified fluorescence spectra a supervised BPNN algorithm was used to predict some of the process parameters. It was also shown that the BPNN models could elucidate some sections of the process's performance, eg forecasting the process's performance. Copyright © 2005 Society of Chemical Industry 相似文献
36.
Alvaro E. Gil Author Vitae Author Vitae 《Automatica》2006,42(2):245-250
Resource allocation involves deciding how to divide a resource of limited availability among multiple demands in a way that optimizes current objectives. In this brief paper we focus on one type of distributed resource allocation problem where via an imperfect communication network multiple processors can share the load presented by multiple task types. We introduce asynchronous “cooperative” resource allocation strategies, and show that they lead to a bounded cumulative demand. 相似文献
37.
The rate of filtration and the water content of cake are influenced by the existence of a dense skin in a highly compressible
cake. The phenomenon of the dense skin has been rarely studied, and its existence has not been verified experimentally. In
this study, the porosity variation in a very compressible cake is measured by using a new experimental apparatus, and with
this the existence of dense skin has been established experimentally. ‘Unified theory on solid-liquid separation’, a recently
developed theory, is utilized for calculating the porosity variation in a very compressible cake. 相似文献
38.
Uniaxial tensile tests in various directions following uniaxial extension, equibiaxial stretching or plane strain rolling have been performed to study the effects of changes in strain path on the anisotropy of yield stresses of aluminium-killed low-carbon steel and 70-30 brass sheets. The anisotropy could be predicted from the specimen textures, if dislocation structure were equiaxed, as in the case of equibiaxial stretching. However, elongated dislocation cell structures, developed in the steel specimens prestrained in uniaxial tension or plane strain rolling, gave rise to the second-stage yield stresses higher than predicted from textures in the directions different from the maximum prestrain direction. Planar dislocation structures in the brass specimens prestrained in uniaxial tension or plane strain rolling gave the second-stage yield stresses lower than predicted from the textures in the directions different from the maximum prestrain direction. The phenomena are discussed based on textures and dislocation structures. 相似文献
39.
A new physics analysis procedure has been developed for a prismatic very high temperature gas-cooled reactor based on a conventional two-step procedure for the PWR physics analysis. The HELIOS and MASTER codes were employed to generate the coarse group cross sections through a transport lattice calculation, and to perform the 3-dimensional core physics analysis by a nodal diffusion calculation, respectively. Physics analysis of the prismatic VHTRs involves particular modeling issues such as a double heterogeneity of the coated fuel particles, a neutron streaming in the coolant channels, a strong core-reflector interaction, and large spectrum shifts due to changes of the surrounding environment and state parameters. Double heterogeneity effect was considered by using a recently developed reactivity-equivalent physical transformation method. Neutron streaming effect was quantified through 3-dimensional Monte Carlo transport calculations by using the MCNP code. Strong core-reflector interaction could be handled by applying an equivalence theory to the generation of the reflector cross sections. The effects of a spectrum shift could be covered by optimizing the coarse energy group structure. A two-step analysis procedure was established for the prismatic VHTR physics analysis by combining all the methodologies described above. The applicability of our code system was tested against core benchmark problems. The results of these benchmark tests show that our code system is very accurate and practical for a prismatic VHTR physics analysis. 相似文献
40.
Pharmacologic profile of survivors of acute myocardial infarction at United States academic hospitals 总被引:1,自引:0,他引:1
BG Phillips JM Yim EJ Brown N Bittar TJ Hoon C Celestin PH Vlasses JL Bauman 《Canadian Metallurgical Quarterly》1996,131(5):872-878
Optimal drug therapy for patients with acute myocardial infarction (AMI) is well described in the medical literature. However, data on the actual pharmacologic management of patients surviving AMI at academic hospitals is unavailable. The purpose of this study was to document treatment profiles in 500 patients surviving AMI at 12 academic hospitals in the United States. These profiles were compared with established guidelines and were evaluated for trends. Overall, thrombolytics (streptokinase > or = tissue-type plasminogen activator) were administered in 29% of the patients, with a greater proportion of patients receiving beta-blockers than calcium channel antagonists in the initial 72 hours (61% vs 40%; p < 0.005) and at discharge (51% vs 35%; p < 0.005). Further, women were less likely than men to receive thrombolytic therapy (odds ratio [OR] = 0.61; confidence interval [CI], 0.54 to 0.69) or beta-blocker therapy within the first 72 hours (OR = 0.61; CI, 0.55 to 0.67) or at hospital discharge (OR = 0.53; CI, 0.48 to 0.58). Overall, improvements could still be made in the number of patients who receive thrombolytic and acute and chronic beta-blocker therapies after AMI, particularly in women. Changes in treatment profiles may be a reflection of the publication of large clinical trials. 相似文献