全文获取类型
收费全文 | 284篇 |
免费 | 14篇 |
国内免费 | 18篇 |
专业分类
化学 | 31篇 |
力学 | 185篇 |
综合类 | 7篇 |
数学 | 32篇 |
物理学 | 61篇 |
出版年
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 11篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 15篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 12篇 |
2013年 | 8篇 |
2012年 | 10篇 |
2011年 | 14篇 |
2010年 | 6篇 |
2009年 | 12篇 |
2008年 | 15篇 |
2007年 | 12篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 16篇 |
2003年 | 13篇 |
2002年 | 16篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有316条查询结果,搜索用时 203 毫秒
31.
32.
水硬性石灰在欧洲石质文物修复和加固中获得了很大成功。我国的石质文物主要是砂岩,水硬性石灰的修复效果不好。为满足我国石质文物修复和加固的需求,本文以石灰石和黏土为原料,在950℃煅烧不同时间,制备出水硬性石,对试样的成分、微观形貌、收缩率、抗拉强度和拉破坏过程等进行了研究。结果表明:(1)试样中含有水硬性成分2CaO·SiO2(C2S);煅烧8h时,成分与欧洲水硬性石灰NHL5接近;1.5CaO·SiO2·xH2O(C-S-H)和CaCO3的含量随龄期的增加逐渐增加。(2)龄期1~3d,收缩率较小;龄期4~6d,收缩率以线性规律增加;7d以后,收缩率趋于稳定。(3)局部变形区随拉应力的增加而变大,邻近局部变形区逐渐合并,形成面积更大的应变局部化带;载荷超过峰值后,产生微裂隙;随载荷进一步增加,微裂隙扩展,贯穿整个试件,发展成宏观裂隙,使试件破坏。(4)抗拉强度随龄期的增加而增加,水硬性石灰中C-S-H、CaCO3等相互交织,构成空间致密体,使试件力学强度提高。合成的水硬性石灰物理力学性能与欧洲水硬性石灰NHL5相近,并且成分均匀、可控,在石质文物修复和加固工程中具有良好应用前景。 相似文献
33.
34.
《先进技术聚合物》2018,29(3):1022-1029
In this article, a novel kind of temperature‐resistant thickening agent (LK) was copolymerized with acrylamide, acrylic acid, sodium p‐styrenesulfonate, and dimethyl diallyl ammonium chloride via free radical copolymerization. The polymerization conditions were optimized by the single‐variable method. Subsequently, the structure of the copolymer was characterized through Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. Thermal gravimetric analysis demonstrates that the thickening agent LK has an excellent ability of temperature‐resistance and the degradation temperature of the copolymer is higher than 300°C. The 3‐dimensional network structure formed in the fracturing fluid was observed via experimental results of scanning electron microscopy. Several aspects of the properties of fracturing gel system, such as temperature and shear tolerance, salt resistance and viscoelasticity, and gel breaking and filter loss were evaluated. Results indicates that the fracturing gel system presents good comprehensive performances under high‐temperature condition. 相似文献
35.
B. Essiger 《Journal of Thermal Analysis and Calorimetry》1998,52(1):73-80
Different methods of thermal analysis (TG/DTG, pressure- and cooling-DSC) were used for a comparative characterization of the thermal-oxidative stabilities and low-temperature behaviour of vegetable and mineral oil-based hydraulic fluids. The mineral oil-based hydraulic fluids proved to have markedly higher thermal-oxidative stabilities than those of the vegetable oils, but they were much less biodegradable.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
36.
B. Pacewska G. Blonkowski I. Wilińska 《Journal of Thermal Analysis and Calorimetry》2008,94(2):469-476
In this work, the pozzolanic and hydraulic properties of ashes originating from various sources were studied in model systems
such as ash and ash-lime pastes. The sources of studied ashes were: fluidized combustion of brown coal, pulverized combustion
of brown coal and pulverized combustion of hard coal. This article is a continuation of our previously published studies on
cement pastes with mentioned ashes.
The following experimental techniques were applied: calorimetry, thermal analysis (TG, DTG) and infrared absorption (IR).
Previously drawn conclusions relating to the reactivity of ashes in an environment containing Ca2+ ions were confirmed. According to these conclusions, an ash originating from fluidized combustion of coal exhibited higher
reactivity compared to other ashes from pulverized combustion. Pozzolanic and hydraulic properties of this ash were also confirmed.
Differences in the behaviour of ashes originating from pulverized combustion of various types of coal in the presence of water
and Ca2+ rich environment were demonstrated. 相似文献
37.
Hydraulic hoses are components of umbilical cables and others subsea equipments. They are manufactured from thermoplastic polymers and are susceptible to collapse under external pressure, which can cause plastic strains around the circumference, leading to failure under internal pressure (bursting). This work studies an alternative hydraulic hose liner capable of support such load history, even after long time exposure to the hydraulic fluid. It is based on the comparison between the material currently used (Polyamide 11) and a fluorinated elastomer, Viton®. Mechanical characterization, ageing tests as well as nonlinear finite elements simulations were accomplished to issue both performances. The results obtained showed that Viton® liners are mechanically more suitable than Polyamide 11 liners to such hoses. The ageing tests showed compatibility between Viton® and the hydraulic fluid. Considering that the external aramid layer is responsible to withstand the internal pressure in both cases, Viton® can successfully replace Polyamide 11 for this application as well as others involving layered hoses under combined internal and external pressure. 相似文献
38.
准确地描述煤岩体压裂裂缝的形成与演化规律对煤层气井开采具有重要意义.本文以煤岩体压裂裂缝演化过程的微裂缝演化数目、裂缝尖端区域的径向应力与周向应力作为描述裂缝演化的特征指标,引入关联维数、最大Lyapunov指数和Ko1mogorov熵作为裂缝演化系统的混沌特征量,计算与描述煤岩体压裂裂缝的损伤演化过程.以黑龙江省某一煤岩开采区块岩体作为研究对象,计算分析煤岩体压裂裂缝的形成的混沌特征,为后续煤岩体压裂裂缝形成规律的研究提供了新的思路. 相似文献
40.
关于颗粒悬浮机理和悬浮动的讨论 总被引:7,自引:1,他引:6
从分析气体分子的悬浮和静水中Brown微粒的悬浮之机理出发,论述了重力场中粒子(分子、微粒等)的悬浮不一定需要其它外力,粒子本身的任何形式的无规则运动,达到一定强度后都能使粒子弥散悬浮.河流中的泥沙颗粒和气(水)力输送管道中的颗粒的悬浮也主要靠颗粒物的无规则运动.作用于颗粒的升力和其它力可改变颗粒悬浮沿高度的分布,但仅用这些力(若无任何无规则运动)无法解释颗粒的弥散悬浮状态.讨论了颗粒对流动阻力的双重作用:支持颗粒悬浮的湍流脉动因引入颗粒而削弱,这是颗粒的减阻作用;颗粒增阻的一个主要机制是,流体给予颗粒的水平动量在颗粒一壁面碰撞中不断地损失.用悬浮动概念解释颗粒引起的增阻是不正确的. 相似文献