全文获取类型
收费全文 | 6616篇 |
免费 | 437篇 |
国内免费 | 390篇 |
专业分类
化学 | 951篇 |
晶体学 | 24篇 |
力学 | 2222篇 |
综合类 | 18篇 |
数学 | 2727篇 |
物理学 | 1501篇 |
出版年
2024年 | 11篇 |
2023年 | 85篇 |
2022年 | 109篇 |
2021年 | 119篇 |
2020年 | 235篇 |
2019年 | 139篇 |
2018年 | 161篇 |
2017年 | 176篇 |
2016年 | 235篇 |
2015年 | 237篇 |
2014年 | 404篇 |
2013年 | 712篇 |
2012年 | 275篇 |
2011年 | 461篇 |
2010年 | 402篇 |
2009年 | 489篇 |
2008年 | 455篇 |
2007年 | 386篇 |
2006年 | 326篇 |
2005年 | 246篇 |
2004年 | 234篇 |
2003年 | 181篇 |
2002年 | 165篇 |
2001年 | 123篇 |
2000年 | 96篇 |
1999年 | 110篇 |
1998年 | 109篇 |
1997年 | 91篇 |
1996年 | 57篇 |
1995年 | 52篇 |
1994年 | 67篇 |
1993年 | 77篇 |
1992年 | 68篇 |
1991年 | 65篇 |
1990年 | 49篇 |
1989年 | 40篇 |
1988年 | 26篇 |
1987年 | 36篇 |
1986年 | 14篇 |
1985年 | 33篇 |
1984年 | 33篇 |
1983年 | 20篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1970年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有7443条查询结果,搜索用时 31 毫秒
1.
2.
4.
5.
6.
Over the past two decades, advanced materials with hollow interiors have received significant attention in materials research owing to their great application potential across a vast number of technological fields. Though with great difficulty, multi-shelled hollow metal–organic frameworks (MSHMs) have also been successfully synthesized in recent years. Herein, a rational shell-by-shell soft-templating protocol has been devised to fabricate highly uniform multi-shelled hollow cobalt-imidazole-based MOF (ZIF-67). For the first time, it has become possible to endow mesoporosity to this new type of functional material (i.e., mesoporous MOFs). When used as carrier materials in catalytic reactions, in principle, these mesoporous MSHMs with high surface area not only improve the dispersity of metal nanoparticles (NPs), but also efficiently facilitate the mass diffusion of the reactions, resulting in enhanced catalyst activity. Moreover, the obtained MSHMs/M nanocomposites serve as base-metal bifunctional catalysts for one-pot oxidation-Knoevenagel condensation cascade reaction, in which the MSHMs itself serves as a pristine active catalyst in addition to its role of catalyst support. The results demonstrate that excellent multifunctional catalysts can be achieved via preparing intrinsically microporous bulk MOFs into extrinsically mesoporous MSHMs which possess many structural merits that conventional bulk MOFs do not have. 相似文献
7.
FINITE GROUPS WHOSE AUTOMORPHISM GROUP HAS ORDER CUBEFREE 总被引:3,自引:0,他引:3
Li Shirong 《数学年刊B辑(英文版)》1997,18(3):301-308
FINITEGROUPSWHOSEAUTOMORPHISMGROUPHASORDERCUBEFREELISHIRONGAbstractLetGdenoteafinitegroup.Itisshownthatif|Aut(G)|iscubefre... 相似文献
8.
一类非线性Schr(o)dinger方程的守恒差分法与Fourier谱方法 总被引:1,自引:0,他引:1
考察了一类带导数项的非线性Schrodinger方程的周期边值问题,提出了一种守恒的差分格式,在空间方向上采用Fourier谱方法,证明了格式的稳定性和收敛性.数值试验得到了与理论分析一致的结果. 相似文献
9.
Gauss periods give an exponentiation algorithm that is fast for many finite fields but slow for many other fields. The current paper presents a different method for construction of elements that yield a fast exponentiation algorithm for finite fields where the Gauss period method is slow or does not work. The basic idea is to use elements of low multiplicative order and search for primitive elements that are binomial or trinomial of these elements. Computational experiments indicate that such primitive elements exist, and it is shown that they can be exponentiated fast. 相似文献
10.
The influence of pulse duration on the stress levels in ablation of ceramics: A finite element study
A. Vila Verde 《Applied Surface Science》2006,252(13):4511-4515
We present a finite element model to investigate the dynamic thermal and mechanical response of ceramic materials to pulsed infrared radiation. The model was applied to the specific problem of determining the influence of the pulse duration on the stress levels reached in human dental enamel irradiated by a CO2 laser at 10.6 μm with pulse durations between 0.1 and 100 μs and sub-ablative fluence. Our results indicate that short pulses with durations much larger than the characteristic acoustic relaxation time of the material can still cause high stress transients at the irradiated site, and indicate that pulse durations of the order of 10 μs may be more adequate both for enamel surface modification and for ablation than pulse durations up to 1 μs. The model presented here can easily be modified to investigate the dynamic response of ceramic materials to mid-infrared radiation and help determine optimal pulse durations for specific procedures. 相似文献