全文获取类型
收费全文 | 70603篇 |
免费 | 6398篇 |
国内免费 | 3699篇 |
专业分类
电工技术 | 5272篇 |
技术理论 | 1篇 |
综合类 | 5530篇 |
化学工业 | 11590篇 |
金属工艺 | 7593篇 |
机械仪表 | 4142篇 |
建筑科学 | 6302篇 |
矿业工程 | 1709篇 |
能源动力 | 4354篇 |
轻工业 | 4735篇 |
水利工程 | 1806篇 |
石油天然气 | 3566篇 |
武器工业 | 628篇 |
无线电 | 5874篇 |
一般工业技术 | 7765篇 |
冶金工业 | 4940篇 |
原子能技术 | 1311篇 |
自动化技术 | 3582篇 |
出版年
2024年 | 260篇 |
2023年 | 959篇 |
2022年 | 1868篇 |
2021年 | 2253篇 |
2020年 | 2318篇 |
2019年 | 1906篇 |
2018年 | 1779篇 |
2017年 | 2382篇 |
2016年 | 2575篇 |
2015年 | 2644篇 |
2014年 | 4136篇 |
2013年 | 4352篇 |
2012年 | 5186篇 |
2011年 | 5619篇 |
2010年 | 3907篇 |
2009年 | 4070篇 |
2008年 | 3596篇 |
2007年 | 4659篇 |
2006年 | 4262篇 |
2005年 | 3459篇 |
2004年 | 3091篇 |
2003年 | 2637篇 |
2002年 | 2164篇 |
2001年 | 1936篇 |
2000年 | 1569篇 |
1999年 | 1254篇 |
1998年 | 1015篇 |
1997年 | 873篇 |
1996年 | 780篇 |
1995年 | 595篇 |
1994年 | 525篇 |
1993年 | 369篇 |
1992年 | 359篇 |
1991年 | 303篇 |
1990年 | 230篇 |
1989年 | 157篇 |
1988年 | 132篇 |
1987年 | 79篇 |
1986年 | 82篇 |
1985年 | 70篇 |
1984年 | 63篇 |
1983年 | 48篇 |
1982年 | 35篇 |
1981年 | 20篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1977年 | 11篇 |
1959年 | 14篇 |
1955年 | 5篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
The importance, yet scarcity of the critical constants of thermally unstable fluids warrants the development of reliable methods for the estimation of these essential thermodynamic properties. A thorough investigation undertaken in this study on 1,589 compounds belonging to 83 chemical classes, indicated that the ratio of critical temperature to critical pressure of both low and high molecular weight compounds could be well expressed in terms of their volumetric properties. In addition, two new methodologies are presented for estimating Vc, as well as an indirect approach for prediction of Tc from surface tension data, altogether allowing the calculation of Zc. Moreover, comparative studies are made with five group contribution methods. It is also demonstrated that by employing the Peng-Robinson EOS, and without prior knowledge of the critical properties, it is possible to calculate various thermophysical properties including Psat., Tb, , ∆Hvap. , Cp, and even the Tc and Pc themselves. 相似文献
862.
John W. Drazin James A. Wollmershauser Heonjune Ryou Mason A. Wolak Edward P. Gorzkowski 《Journal of the American Ceramic Society》2020,103(1):60-69
Pressureless sintering approaches provide a simple avenue to manufacture dense ceramic parts with minimal processing equipment, but current pressureless sintering techniques have yet to demonstrate capabilities of producing dense ceramics while maintaining sub-50 nm grain sizes. Nanocrystalline yttria stablized zirconia ceramics were process from 4 mol% yttria stablized zirconia (4YSZ) nanopowders with a crystallite size of 7.5 nm using dry cold isostatic pressing (CIP) where powders are dried immediately prior to green compact formation and CIP vacuum bagging. It is shown that CIP pressures >75 000 psi (517 MPa) effectively remove pores larger than 100 nm and that pressureless sintering occurs at reduced temperatures for green densities ≥50%. Though the sintering kinetics are shown to be similar to other zirconia nanopowder sintering studies, the small initial crystallize size and reduced sintering temperature allowed densities as high as 97.2%, while retaining a ceramic grain size at or below 40 nm. Produced nanocrystalline 4YSZ ceramics with a grain size of 30.3 nm and a density of 96.3% had Vicker's hardnesses as high as 14.2 GPa and Vicker's indentation fracture resistance of 3.43 MPa·, demonstrating that simple processing approaches can be refined to fabricate nanocrystalline ceramics while maintaining high hardness and indentation fracture resistance. 相似文献
863.
864.
CORRELATION OF DIFFUSION COEFFICIENTS FOR LIQUIDS AND DENSE FLUIDS WITH TEMPERATURE AND PRESSURE 下载免费PDF全文
On the basis of the free volume theory and activation energy concept,a fundamental equation whichtakes into account the effects of temperature and pressure has been developed.By introducing differentexpressions for the free volume and activation energy,several equations for fluid diffusion coefficients were derivedaccordingly.With the van der Waals free volume and intermal energy formula,a three-parameter model for fluiddiffusion coeffficients at moderate pressure was obtained.The grand average absolute deviation percent of 345data points (44 systems)for self-and infinite dilute inter-diffusivities is 2.32,against the results of the model ofCohen and Turnbull,4.13.In particular,by means of the modified Carnahan-Starling free volume equation,afour-parameter model with average abosolute deviation percent 2.64(30 systems,644 data points)for theestimation of dense fluid inter-and self-diffusivities at high pressures and in supercritical conditions was derived.The derived model is superior to the method of L 相似文献
865.
Rajmund S. Dybczyński Marta Pyszynska Krzysztof Kulisa Anna Bojanowska-Czajka 《分离科学与技术》2020,55(7):1364-1379
ABSTRACTNew ion interaction chromatographic (IIC) method employing Kromasil 100 C18 column and tetra-n-butylammonium hydroxide (TBAOH) as an ion interaction reagent (IIR) is able to separate yttrium from Rare Earth Elements (REE) as anionic complexes with nitrilotriacetic acid (NTA). New method for the chromatographic determination of Y in REE mixture was devised and validated by the analysis of the certified reference material (CRM). Potential possibilities of the new chromatographic system for larger scale applications including macro-micro events were demonstrated. 相似文献
866.
讨论尿素造粒出塔温度对尿素含水率的影响,对影响尿素造粒出塔温度的因素进行分析,提出通过更换喷头及根据环境温度和空气相对湿度调节百叶窗开度来控制尿素造粒出塔温度。 相似文献
867.
针对光纤制造行业预制棒加热系统温度控制要求,介绍基于西门子S7-300PLC的光纤预制棒温度控制系统的硬件配置、软件流程、人机画面等。 相似文献
868.
869.
设计二级换热站温度智能控制系统,根据室外温度的变化和供热实时情况在线自动调整PID控制器参数,利用变频调速装置进行循环水压力控制,并提出将免疫PID控制策略应用于温度控制中。实验证明该系统具有快速性、鲁棒性以及控制精度高等特点。 相似文献
870.
ZrO2加入物对刚玉—莫来石系烧结材料高温力学性能的影响 总被引:5,自引:0,他引:5
本文研究了加入15~40%ZrO2对刚玉一莫来石系耐火材料高温力学性能的影响及其与显微结构变化的关系。结果表明,在刚玉一莫来石系材料里引进ZrO2,在20~800℃低温阶段降低强度;在1300~1500℃高温阶段提高强度和抗蠕变性;在1000~1200℃,在强度一温度曲线上出现“谷”的特征。这些力学性能变化与相应的显微结构特征(包括结构骨架强度、微裂纹密度、晶界固溶强化等)的变化有密切关系。 相似文献