全文获取类型
收费全文 | 1579篇 |
免费 | 33篇 |
国内免费 | 295篇 |
专业分类
化学 | 1590篇 |
晶体学 | 4篇 |
力学 | 60篇 |
综合类 | 4篇 |
数学 | 20篇 |
物理学 | 229篇 |
出版年
2024年 | 4篇 |
2023年 | 80篇 |
2022年 | 28篇 |
2021年 | 63篇 |
2020年 | 51篇 |
2019年 | 23篇 |
2018年 | 20篇 |
2017年 | 30篇 |
2016年 | 42篇 |
2015年 | 39篇 |
2014年 | 56篇 |
2013年 | 53篇 |
2012年 | 65篇 |
2011年 | 79篇 |
2010年 | 62篇 |
2009年 | 120篇 |
2008年 | 197篇 |
2007年 | 104篇 |
2006年 | 119篇 |
2005年 | 84篇 |
2004年 | 67篇 |
2003年 | 40篇 |
2002年 | 44篇 |
2001年 | 50篇 |
2000年 | 39篇 |
1999年 | 34篇 |
1998年 | 48篇 |
1997年 | 32篇 |
1996年 | 46篇 |
1995年 | 38篇 |
1994年 | 34篇 |
1993年 | 22篇 |
1992年 | 23篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有1907条查询结果,搜索用时 15 毫秒
1.
提出用溶胶粒子表面修饰方法,结合溶胶凝胶技术制备无机催化膜.该方法的基本原理是利用合适的金属配合物在胶粒表面的吸附作用,经溶胶凝胶过程,将活性组分结合到无机膜中.实验测定结果表明:(NiEDTA)2-,VO-3,MoO2-4,(Pd(NH3)4)2+,PdCl2-4,PtCl2-6和RhCl3-6可用来修饰AlOOH溶胶.以Pd/γAl2O3催化膜的制备为例,经三次溶胶凝胶过程,可制得无裂缺的厚度为9μm的Pd/γAl2O3催化膜,膜材料的平均孔直径为6nm,Pd被均匀地分布在膜的顶层,其平均粒径为23nm. 相似文献
2.
The synthesis of oligoethylene glycols of defined lengths possessing different end functionalities is described. The utility of these molecules towards the development of a generic membrane anchor is demonstrated. 相似文献
3.
Dielectric elastomer actuators (DEAs) have received considerable attention recently due to large voltage-induced strains, which can be over 100%. Previously, a large deformation quasi-static model that describes the out-of-plane deformations of clamped diaphragms was derived. The numerical model results compare well with quasi-static experimental results for the same configuration. With relevance to dynamic applications, the time-varying response of initially planar dielectric elastomer membranes configured for out-of-plane deformations has not been reported until now. In this paper, an experimental investigation and analysis of the dynamic response of a dielectric elastomer membrane is reported. The experiments were conducted with prestretched DEAs fabricated from 0.5 mm thick polyacrylate films and carbon grease electrodes. The experiments covered the electromechanical spectrum by investigating membrane response due to (i) a time-varying voltage input and (ii) a time-varying pressure input, resulting in a combined electromechanical loading state in both cases. For the time-varying voltage experiments, the membrane had a prestretch of three and was passively inflated to various predetermined states, and then actuated. The pole strains incurred during the inflation were as high as 25.6%, corresponding to slightly less than a hemispherical state. On actuation, the membrane would inflate further, causing a maximum additional strain of 9.5%. For the time-varying pressure experiments, the prestretched membrane was inflated and deflated mechanically while a constant voltage was applied. The membrane was cycled between various predetermined inflation states, the largest of which was nearly hemispherical, which with an applied constant voltage of 3 kV corresponded to a maximum polar strain of 28%. The results from these experiments reveal that the response of the membrane is a departure from the classical dynamic response of continuum membrane structures. The dynamic response of the membrane is that of a damped system with specific deformation shapes reminiscent of the classical membrane mode shapes but without same-phase oscillation, that is to say all parts of the system do not pass through the equilibrium configuration at the same time. Of particular interest is the ability to excite these deformations through a varying electrical load at constant mechanical pressure. 相似文献
4.
强酸性条件下 ,钯 (Ⅱ )与 5 [( 5 氯 2 吡啶 )偶氮 ] 2 ,4 二氨基甲苯 ( 5 Cl PADAT)生成紫红色螯合物 ,该螯合物可与十二烷基苯磺酸钠 (SDBS)生成离子缔合物 ,离子缔合物经 0 .3μm孔径的硝化纤维微孔滤膜富集后 ,于小体积 ( 0 .5mL)的浓硫酸中溶膜 ,用石墨炉原子吸收法 (GFAAS)测定 ,富集倍数可达 2 0 0倍 ,钯含量在 4.69× 1 0 - 1 2 ~ 7.0 9× 1 0 - 9mol/L范围内线性良好 ,检出限为 1 .78×1 0 - 1 2 mol/L。方法用于海水中痕量钯的测定。 相似文献
5.
M. Zendehdel A. Mobinikhaledi F. Hasanvand Jamshidi 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(1-2):41-44
Transition metal/Y zeolites were prepared using microwave solid state and aqueous solution ion exchange methods. The activity
of these zeolites was investigated in a conversion of acids to benzimidazoles reaction between 4-methyl-1, 2-phenylenediamine and 3-nitrobenzoic acid. The yield of these reactions increased in order of CuY < Fe2+Y < NiY < CoY < NaY < CrY < MnY < ZnY for both methods. The solid state ion-exchanged zeolites showed higher activity in comparison
to the aqueous solution exchange. Yields of products in the presence of the ZnY zeolite were of the order of 69–83%. It seems
that the Lewis sites are better sites compared to the Bronsted sites for this reaction. 相似文献
6.
Sb/ZSM-5 was obtained by solid-state reaction with the mixture of Sb2O3 and zeolite HZSM-5 under a dry nitrogen flow at 773 K. Characterization of the treated zeolite was undertaken with XRD, 27Al MAS NMR, BET, TGA and FT-IR. The results revealed that part of the antimony oxides migrated into the channels of zeolite, and decreased the Brönsted acid sites in Sb/ZSM-5 remarkably. The other part of antimony oxides together with the amorphous alumino-silicate in the products distributed on the external surface of zeolite ZSM-5 and modified it, while the framework of ZSM-5 in crystal phase was retained. The structure of occluded antimony oxide inside the channels of ZSM-5 was studied by XRD Rietveld method. The result showed that their structure can be described as a chain of non-perfect [Sb5O5(H2O)2]n5n+, which is parallel to the straight channel of ZSM-5. There is about 0.6 [Sb5O5(H2O)2]5+ unit in every cell of the ZSM-5 on an average. 相似文献
7.
8.
9.
10.
考察了中性分子电对H_2Q/Q在13X型分子筛修饰电极上的电化学行为。发现H_2Q/Q电对在修饰电极上电响应迅速,为双电子可逆反应,不受溶液温度及电极与溶液相对运动的影响,而与溶液的pH值有关。当pH≤2.0时,修饰电极对H_2Q/Q电对的氧化/还原有明显的催化作用. 相似文献