全文获取类型
收费全文 | 325502篇 |
免费 | 26889篇 |
国内免费 | 16691篇 |
专业分类
电工技术 | 19268篇 |
技术理论 | 52篇 |
综合类 | 41496篇 |
化学工业 | 47286篇 |
金属工艺 | 14252篇 |
机械仪表 | 17091篇 |
建筑科学 | 40329篇 |
矿业工程 | 16437篇 |
能源动力 | 10225篇 |
轻工业 | 24150篇 |
水利工程 | 14840篇 |
石油天然气 | 14734篇 |
武器工业 | 2980篇 |
无线电 | 20578篇 |
一般工业技术 | 26102篇 |
冶金工业 | 18139篇 |
原子能技术 | 3755篇 |
自动化技术 | 37368篇 |
出版年
2024年 | 1083篇 |
2023年 | 3491篇 |
2022年 | 6297篇 |
2021年 | 7886篇 |
2020年 | 8328篇 |
2019年 | 7286篇 |
2018年 | 6784篇 |
2017年 | 8070篇 |
2016年 | 9429篇 |
2015年 | 10256篇 |
2014年 | 18089篇 |
2013年 | 17412篇 |
2012年 | 21844篇 |
2011年 | 22966篇 |
2010年 | 17901篇 |
2009年 | 18737篇 |
2008年 | 17237篇 |
2007年 | 22595篇 |
2006年 | 21436篇 |
2005年 | 18678篇 |
2004年 | 15961篇 |
2003年 | 14430篇 |
2002年 | 11943篇 |
2001年 | 10152篇 |
2000年 | 8536篇 |
1999年 | 7062篇 |
1998年 | 5424篇 |
1997年 | 4753篇 |
1996年 | 4315篇 |
1995年 | 3707篇 |
1994年 | 3251篇 |
1993年 | 2450篇 |
1992年 | 2171篇 |
1991年 | 1641篇 |
1990年 | 1417篇 |
1989年 | 1214篇 |
1988年 | 982篇 |
1987年 | 669篇 |
1986年 | 484篇 |
1985年 | 447篇 |
1984年 | 417篇 |
1983年 | 301篇 |
1982年 | 275篇 |
1981年 | 194篇 |
1980年 | 156篇 |
1979年 | 125篇 |
1978年 | 69篇 |
1977年 | 77篇 |
1976年 | 62篇 |
1975年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
棒状液晶分子相变问题的机械旋转模型研究 总被引:2,自引:1,他引:1
综述一种关于棒状液晶材料的分子结构与液晶相的相关关系的研究成果。介绍了有关液晶分子的机械旋转模型。该模型将液晶分子视作一种高速旋转的转子,通过分子参数计算,对液晶材料的相变温度和分子结构之间的关系给出了一种全新的解释。最新研究表明,含氟三苯液晶材料的分子结构中存在slim和fat现象,能够对液晶材料的相变进行合理解释。该模型能够通过简单的模型方法对新型液晶材料的分子设计与合成提供有用的信息。 相似文献
992.
The boundary knot method (BKM) of very recent origin is an inherently meshless, integration‐free, boundary‐type, radial basis function collocation technique for the numerical discretization of general partial differential equation systems. Unlike the method of fundamental solutions, the use of non‐singular general solution in the BKM avoids the unnecessary requirement of constructing a controversial artificial boundary outside the physical domain. The purpose of this paper is to extend the BKM to solve 2D Helmholtz and convection–diffusion problems under rather complicated irregular geometry. The method is also first applied to 3D problems. Numerical experiments validate that the BKM can produce highly accurate solutions using a relatively small number of knots. For inhomogeneous cases, some inner knots are found necessary to guarantee accuracy and stability. The stability and convergence of the BKM are numerically illustrated and the completeness issue is also discussed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
993.
A. Moropoulou N. Kouloumbi G. Haralampopoulos A. Konstanti P. Michailidis 《Progress in Organic Coatings》2003,48(2-4):259-270
Susceptibility of stone to salt decay is directly related to its microstructural and mechanical characteristics. In the present work, a porous stone from a quarry in Cyprus was examined. Samples of this stone were consolidated and protected with certain conservation materials. The modification of microstructural characteristics of the stone was evaluated by mercury intrusion porosimetry, while its mechanical characteristics were measured by compressive and bending strength tests. From these data, the susceptibility of Cyprus stone to salt (NaCl) decay was estimated. The values of crystallization pressure of NaCl were calculated and compared to the experimentally measured compressive and tensile strength of the stone, in order to examine the probability of stone disruption due to salt crystallization. The development of the phenomenon after coarse pores’ filling with crystals, i.e. crystallization of salts in capillaries or mechanical failure of the stone, was determined by thermodynamic analysis. Additionally, artificial weathering tests of marine salt spray were performed for the evaluation of stone’s durability after the conservation. The treated stone proved to be resistant to salt decay, as it presented ameliorated microstructural and mechanical characteristics, concerning decay due to soluble salt crystallization. The most possible thermodynamic scenario was small pores repletion with crystals, avoiding mechanical failure of the stone. 相似文献
994.
This article theoretically investigates the drying of uncoated paper with gas-fired infrared (IR) emitters installed within the drying section of a given commercial paper machine. Specifically, it presents the ideal location of two opposing IR emitters within the drying section. The ideal location of the two opposing IR emitters corresponds to the highest machine speed with specified average moisture content of paper sheet at the end of the drying section. This article also presents the average evaporation rate, temperature, and moisture content of the paper sheet as it travels through the drying section with the two opposing IR emitters operating at the optimum location. In addition, the temperature and moisture profiles in the sheet thickness direction, before and after the IR emitters, are provided. This article is not concerned with the potential effects of drying with IR emitters on paper sheet properties and machine runnability issues. 相似文献
995.
996.
997.
Acid Green 25, which is a diazoic dye bearing two sulfonic groups, is efficiently sorbed on chitosan. The protonation of chitosan may explain the electrostatic attraction of this anionic dye and that its optimum pH is close to 3. Preliminary protonation of amine groups (obtained by contact with a sulfuric acid solution) reduced the variation of solution pH following sorbent addition but significantly reduced sorption performance: the maximum sorption capacity of raw chitosan, 525 mg dye/g (0.84 mmol dye/g), was halved by acidic preconditioning. The acidic conditioning also reduced the kinetic rate—the time necessary to reach equilibrium increased up to threefold depending on the experimental conditions. The size of sorbent particles influenced sorption kinetics and equilibrium because of resistance to intraparticle diffusion, but the sorption appeared to occur not only at the surface of the sorbent but also in the intraparticle network of the polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1073–1080, 2003 相似文献
998.
This study examines the links between antecedents and consequences of Gabonese teachers' (N= 152) work motivation. The theoretical underpinnings are based on the Motivational Model of Job Burnout (MMJB) which is grounded in Self-Determination Theory (SDT) and states that the more supervisors satisfy an employee's need for self-determination, competence, and relatedness, the more self-determined is the latter's work motivation. The level of self-determined motivation has an impact on job satisfaction, which in turn determines life satisfaction. Higher levels of self-determined motivation also buffer emotional exhaustion and psychological distress. The model was confirmed via structural equation modeling and provides support for the validity and generalizability of the MMJB and SDT. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
程行毛 《石油化工安全环保技术》2003,(2)
分析了NaSCN装置脱色釜爆燃的原因,找出了引起爆燃的主要因素,提出了脱色生产安全防范措施。 相似文献
1000.