全文获取类型
收费全文 | 1273篇 |
免费 | 32篇 |
国内免费 | 258篇 |
专业分类
化学 | 982篇 |
力学 | 29篇 |
综合类 | 1篇 |
数学 | 31篇 |
物理学 | 160篇 |
综合类 | 360篇 |
出版年
2024年 | 13篇 |
2023年 | 76篇 |
2022年 | 29篇 |
2021年 | 33篇 |
2020年 | 38篇 |
2019年 | 33篇 |
2018年 | 25篇 |
2017年 | 32篇 |
2016年 | 25篇 |
2015年 | 28篇 |
2014年 | 53篇 |
2013年 | 85篇 |
2012年 | 57篇 |
2011年 | 83篇 |
2010年 | 54篇 |
2009年 | 65篇 |
2008年 | 77篇 |
2007年 | 88篇 |
2006年 | 66篇 |
2005年 | 79篇 |
2004年 | 55篇 |
2003年 | 43篇 |
2002年 | 43篇 |
2001年 | 32篇 |
2000年 | 47篇 |
1999年 | 34篇 |
1998年 | 31篇 |
1997年 | 28篇 |
1996年 | 29篇 |
1995年 | 23篇 |
1994年 | 22篇 |
1993年 | 21篇 |
1992年 | 17篇 |
1991年 | 24篇 |
1990年 | 11篇 |
1989年 | 18篇 |
1988年 | 18篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
排序方式: 共有1563条查询结果,搜索用时 0 毫秒
991.
The redox reaction between the 12-tungstocobaltate(III) ion and carbohydrazide is first order with respect to both the oxidant and the substrate. The observed pseudo first-order rate constant, kobs, is retarded by increasing the concentrations of H+ and alkali metal ion (Li+, Na+ and K+). There is a linear correlation between the kobs and the concentrations of carbohydrazide and H+ ion, but the plots of kobs against the concentrations of the alkali metal ions is non-linear. However, the same data is applicable to the Davies equation for the effect of the ionic strength on the kobs. 相似文献
992.
本文提出了两种智能步行轮的腿机构,对机构的运动特性进行研究,详细讨论了在各种道路条件下实现智能步行轮预定运动规迹的控制方式和控制规律.以及机构设计参数对控制规律的影响. 相似文献
993.
Qingyin?WuEmail author Shouli?Zhao Jianming?Wang Jianqing?Zhang 《Journal of Solid State Electrochemistry》2007,11(2):240-243
In this work, the polyethylene glycol (PEG) hybrid material composited with tungstovanadogermanic heteropoly acid was prepared. Infrared (IR) spectrum revealed that the Keggin structure characteristic of the anion was present in PEG hybrid material. At room temperature (20°C), the conductivity of the sample is 4.07×10−3 S cm−1. The results indicated that it is a new kind of excellent high-proton conductor. According to the experimental results, we proposed a possible mechanism of the proton conduction of the hybrid materials. 相似文献
994.
Prospects and application of ultrasound and magnetic fields in the fermentation of rare edible fungi
Ultrasound has the potential to be broadly applied in the field of agricultural food processing due to advantages such as environmental friendliness, low energy costs, no need for exogenous additives and ease of operation. High-frequency ultrasound is mainly used in medical diagnosis and in the food industry for the identification of ingredients and production line quality testing, while low-frequency ultrasounds is mainly used for extraction and separation, accelerating chemical reactions, auxiliary microbial fermentation and quality enhancement in food industry. Magnetic fields have many advantages of convenient use, such as non-toxic, nonpolluting and safe. High-intensity pulsed magnetic fields are widely used as a physical non-thermal sterilization technology in food processing, while weak magnetic fields are better at activating microorganisms and promoting their growth. Ultrasound and magnetic fields, due to their positive biological effects, have a wide range of applications in the food processing industry. This paper provides an overview of the research progress and applications of ultrasound and magnetic fields in food processing from the perspectives of their biological effects and mechanisms of action. Additionally, with the development and application of physical field technology, physical fields can now be used to provide significant technical advantages for assisting fermentation. Suitable physical fields can promote the growth of microbial cells, improve mycelial production and increase metabolic activity. Furthermore, the current status of research into the use of ultrasound and magnetic field technologies for assisting the fermentation of rare edible fungi, is discussed. 相似文献
995.
Peculiarities of shock adiabat of graphite are attributed to the graphite–diamond transformation. However only a very small
amount of diamond can be recovered from pure shocked graphite with a density approaching the theoretical value. In order to
interpret this fact, accessible data concerning the behaviour of graphite under static and dynamic load have been analysed.
An additional peculiarity of the shock adiabat of graphite has been found at 12 GPa by analysing compressibility data. It
has been attributed to shearing in the basal planes that paves the way for deformation of the planes. An isotherm of cold
compression of graphite can be constructed on the basis of the results from theoretical modelling published in the literature.
Another isotherm, fitting experimental data, has been proposed. An isotherm for graphitic boron nitride has been also proposed.
The isotherms have been used in the interpretation of the peculiarities of shock adiabats. It has been shown that the so-called
“mixed-phase” region is an apparent compressibility curve. Energy evaluations based on the isotherms have proved that the
peculiarities of the shock adiabat of graphite correspond to the formation of hexagonal instead of cubic diamond. Similarly
the formation of the wurtzite modification of BN is responsible for the peculiarities of the shock adiabat of BN. Literature data concerning the mechanism of the polymorphous transformations of graphite and BN in shock waves have been reviewed. On the basis of proposed isotherms of cold compression, the activation energy has been
appraised and an equation of kinetics proposed. The equation has been analysed by comparing results of theoretical modelling
and accessible experimental data.
Received 11 March 1993 / Accepted 15 September 1993 相似文献
996.
Zinc hydroxide fluoride (Zn(OH)F) with multiform morphologies such as flower-like particles, pumpkin-like aggregates, and hollow orange-like aggregates are prepared by a microwave-assisted ionic liquid method. During synthesis, microwave irradiation accelerates the reaction rate and shortens the reaction time. 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) or 1-2-hydroxylethyl-3-methylimidazolium tetrafluoroborate ([C2OHmim][BF4]) is used as both reactant and template. Experimental results indicate that the morphology evolution of Zn(OH)F is mainly controlled by the concentration of zinc acetate solution. A possible mechanism underlying the formation of nanostructured Zn(OH)F with diverse morphologies is proposed. Furthermore, nanoporous ZnO is obtained by the thermal decomposition of as-prepared Zn(OH)F in air, and the morphology is well retained. 相似文献
997.
采用水热法制备Bi2WO6-BiPO4异质结光催化剂.利用模拟太阳光照射下的罗丹明B降解实验评价了Bi2WO6-BiPO4复合物的光催化性能.结果表明,Bi2WO6-BiPO4光催化活性比Bi2WO6和BiPO4高得多.当Bi2WO6与BiPO4的摩尔比为1:1时复合光催化剂对罗丹明B的降解率最高.Bi2WO6-BiPO4催化活性增强主要归结为两者之间形成了有效的异质结结构,其内建电场能够促进光生载流子的分离.同时,Bi2WO6的加入增强了其对可见光的吸收.研究表明O2^· -和h^+在光催化降解过程中是主要的活性物种. 相似文献
998.
The base-catalyzed reaction between isatins and N-Boc-3-pyrrolin-2-one yields Morita–Baylis–Hillman (MBH) adducts instead of the expected aldol products in good to high yields (up to 97%). Various organic and inorganic bases are efficient catalysts for this reaction. Our study excluded the Morita–Baylis–Hillman mechanism for the formation of the MBH-type products. The MBH products are most likely formed as a result of the subsequent isomerization of the original aldol products between isatins and N-Boc-3-pyrrolin-2-one. 相似文献
999.
为了加强大学生对机械结构传动原理的掌握,本文在分析机构传动原理的基础上,提出了机构原理智能可视化平台。通过设计智能载重车、三角支架和旋转六面体平台,实现机构原理的立体化展示。基于慧鱼模型,以机械设计基础课程为例,搭建机构原理智能可视化平台。该平台在教室中可以自由行走,进行系统化展示或局部定位展示。 相似文献
1000.
刘李梅 《无锡职业技术学院学报》2005,4(3):14-17
该文通过实例摘要介绍了六十年代以来在轧钢和起重机械中,根据不同的工作性能和要求,设计和生产的典型行星齿轮减速器,以及不同的传动方式所满足的不同的机械性能的要求。 相似文献