全文获取类型
收费全文 | 482篇 |
免费 | 82篇 |
国内免费 | 76篇 |
专业分类
化学 | 305篇 |
晶体学 | 1篇 |
力学 | 51篇 |
综合类 | 22篇 |
数学 | 175篇 |
物理学 | 86篇 |
出版年
2023年 | 5篇 |
2022年 | 8篇 |
2021年 | 22篇 |
2020年 | 20篇 |
2019年 | 15篇 |
2018年 | 15篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2015年 | 24篇 |
2014年 | 37篇 |
2013年 | 36篇 |
2012年 | 26篇 |
2011年 | 29篇 |
2010年 | 20篇 |
2009年 | 25篇 |
2008年 | 33篇 |
2007年 | 36篇 |
2006年 | 27篇 |
2005年 | 28篇 |
2004年 | 24篇 |
2003年 | 23篇 |
2002年 | 23篇 |
2001年 | 19篇 |
2000年 | 13篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 5篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
排序方式: 共有640条查询结果,搜索用时 250 毫秒
601.
端羟基聚丁二烯/增塑剂共混物相容性的分子动力学模拟和介观模拟 总被引:6,自引:0,他引:6
应用分子动力学(MD)和介观动力学(MesoDyn)模拟方法对固体推进剂中端羟基聚丁二烯(HTPB)与增塑剂癸二酸二辛酯(DOS)、硝化甘油(NG)的相容性进行了研究. 采用MD模拟方法在COMPASS力场下, 对纯物质、HTPB/增塑剂共混物的密度、内聚能密度、溶度参数和共混物分子间的Flory-Huggins作用参数及结合能等进行了模拟计算, 通过比较溶度参数差值(Δδ)的大小、模拟前后体系密度变化情况均可以预测HTPB与增塑剂的相容性, 结合能的分析揭示了HTPB/增塑剂共混物组分间的相互作用及本质. 将Flory-Huggins作用参数转化为MesoDyn模拟的输入参数, 采用MesoDyn模拟方法对HTPB/增塑剂共混体系的介观形貌与动力学演变过程进行了研究, 通过模拟得到的等密度图、自由能密度和有序度参数等可以判断共混体系的相容性. MD和MesoDyn模拟结果均表明: HTPB/DOS属于相容体系, 而HTPB/NG属于不相容体系, 其结论与实验结果一致. 相似文献
602.
基于中国2006~2017年的年度统计数据,运用PP与SFA组合模型,构建中国生态能源效率的静态评价模型,对中国30个省、市、自治区的生态能源效率及其影响因素进行分析,运用空间收敛方法和速度激励模型系统的分析了中国生态能源效率的时空格局演化。结果表明:城市化水平、经济开放程度、人口规模和R&D投入等与生态能源效率存在正相关关系;中国的生态能源效率空间格局具有空间分布聚集特征,但空间分布不均衡现象明显;中国的生态能源效率时间格局具有复杂波动的特点,总体趋势是先下降后再上升。 相似文献
603.
Sialic acid (N‐acetylneuraminic acid, NANA) was covalently immobilized onto the surface of a polysulfone (PSF) hollow fiber membrane. Prior to the immobilization, the surface of PSF was treated with ozone, followed by grafting with acrylic acid, and then the esterification of NANA. The surface concentration of NANA was determined by 2‐thiobarbituric acid (TBA) test. Hemocompatibility, the capability of suppressing oxidative stress, and clearance of lipopolysaccharide (LPS) from the resulting hollow fiber membrane were evaluated. The results show that by immobilizing NANA onto PSF hollow fiber, the adhesion of platelet was reduced, while both APTT and PT were little affected. Furthermore, oxidative stress was suppressed by NANA‐immobilized PSF hollow fibers. The level of LPS was also greatly reduced. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
604.
Jian Zhong Xinmian Chen Miaoran Zhang Chaoxin Xiao Lulu Cai Waleed Ali Khan Kaixuan Yu Jiayi Cui Lin He 《中国化学快报》2020,31(3):769-773
Carbon dots have unique advantages in biological applications owing to their excellent optical prope rties.However,the biosafety evaluation of carbon dots has limitations owing to cytotoxicity in vitro,and the re is little pre-safety evaluation before in vivo and clinical applications.Whether the carbon dots are or not suitable for applications in vivo,evaluation analysis can be made based on hemolysis and changes in erythrocyte morphology.In this work,a green fluorescent N,S-doped carbon dots(N,S-CDs)were obtained by hydrothermal method,tobias acid,and m-phenylenediamine as precursors.N,S-CDs not only possessed excellent dispersibility,uniform particle size,high quantum yield(37.2%)and stable photoluminescence property but also retain their photostability and stro ng fluorescence intensity in the acid/alkaline solutions,different ionic strengths(NaCl)and under 365 nm UV illumination.Moreove r,the N,S-CDs displayed low cytotoxicity and high cellular uptake efficiency in human umbilical vein endothelial cells(HUVEC)and excellent blood compatibility to the erythrocyte.It is foreseeable that N,S-CDs could be further studied as a promising biological imaging agent in vivo. 相似文献
605.
本文以醋酸锂和钛酸丁酯为原料,以冰醋酸为抑制剂,采用溶胶-凝胶法制备了晶态Li4Ti5O12负极材料。与自制的3种电解液和实验室常用的电解液分别组装成锂/钛酸锂半电池。采用恒流充放电测试、循环伏安法(CV)及交流阻抗法(EIS)对其电化学性能进行研究。研究结果发现:在以环状碳酸酯类(EC、PC)和线性碳酸酯类(MEC)为溶剂、以六氟磷酸锂(LiPF6)为电解质的电解液中添加双乙二酸硼酸锂(LiBOB),有利于提高半电池的性能,首次放电比电容达到了198mA.h.g-1,且放电比电容经多次充放电后衰减得较小。而在电解液中加入碳酸亚乙烯酯(VC),半电池的性能有所下降。Li4Ti5O12对电解液表现出较明显的兼容性。 相似文献
606.
Some Properties of the Boundary Value Problem of Linear Elasticity in Terms of Stresses 总被引:1,自引:0,他引:1
The relation between the classical formulation of linear elastic problems in displacements and the stress formulation proposed by Pobedria is studied. It is shown that if the Navier and Pobedria differential operators are elliptic then corresponding boundary value problems are equivalent. The values of parameters for which Pobedria's boundary value problem has the Fredholm property are found. The homogeneous Pobedria's system is considered as a spectral problem with Poisson's ratio as a spectral parameter. The points of the essential spectrum are found and classified. The example of solving Pobedria's system for the Lamé problem for a spherical shell is presented. 相似文献
607.
In this paper, a method of constructing displacement-based element for thick/thin plates is developed by using the technique
of generalized compatibility, and a rectangular displacement based element with 12 degrees of freedom for thick/thin plates
is presented. This method enjoys a good accuracy with simple formulation and is free of shear locking as the thickness of
the plate approaches zero.
The project supported by National Natural Science Foundation of China through Grant No. 59208075 相似文献
608.
N. M. Borodachev 《International Applied Mechanics》2005,41(3):264-271
A new solution to the three-dimensional thermoelastic problem for stresses is proposed. It satisfies the static equation and compatibility condition. The stress tensor is expressed in terms of a harmonic vector. With such a solution, the boundary conditions for some elastic bodies can be satisfied quite easily__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 3, pp. 46–54, March 2005. 相似文献
609.
The ternary blends of acrylate rubber (ACM), poly(ethyleneterephalate) (PET), and liquid crystalline polymer (LCP) were prepared by varying the amount of LCP, but fixing the ratio of ACM and PET using melt mixing procedure. The compatibility behavior of these blends was investigated with infrared spectroscopy (IR), differential scanning calorimetry (DSC), and dynamic mechanical analyzer (DMA). The IR results revealed the significant interaction between the blend components. Glass transition temperature (Tg) and melting temperature (Tm) of the blends were affected depending on the LCP weight percent in the ACM/PET, respectively. This further suggests the strong interfacial interactions between the blend components. In the presence of ACM, the nucleating effect of LCP was more pronounced for the PET. The thermogravimetric (TGA) study shows the improved thermal stability of the blends. 相似文献
610.