全文获取类型
收费全文 | 5809篇 |
免费 | 580篇 |
国内免费 | 393篇 |
专业分类
化学 | 2394篇 |
晶体学 | 35篇 |
力学 | 898篇 |
综合类 | 4篇 |
数学 | 1128篇 |
物理学 | 2323篇 |
出版年
2024年 | 5篇 |
2023年 | 219篇 |
2022年 | 193篇 |
2021年 | 236篇 |
2020年 | 301篇 |
2019年 | 164篇 |
2018年 | 212篇 |
2017年 | 288篇 |
2016年 | 223篇 |
2015年 | 286篇 |
2014年 | 364篇 |
2013年 | 429篇 |
2012年 | 448篇 |
2011年 | 467篇 |
2010年 | 401篇 |
2009年 | 418篇 |
2008年 | 413篇 |
2007年 | 321篇 |
2006年 | 297篇 |
2005年 | 194篇 |
2004年 | 130篇 |
2003年 | 117篇 |
2002年 | 119篇 |
2001年 | 125篇 |
2000年 | 56篇 |
1999年 | 92篇 |
1998年 | 61篇 |
1997年 | 40篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 13篇 |
1993年 | 22篇 |
1992年 | 21篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1971年 | 7篇 |
排序方式: 共有6782条查询结果,搜索用时 93 毫秒
51.
论文针对中密度聚乙烯材料(MDPE),采用平板试样进行了I型疲劳裂纹扩展和单次过载下裂纹扩展试验.发现与金属材料类似,单次拉伸过载对聚乙烯(PE)的疲劳裂纹扩展有明显的迟滞作用,降低了裂纹扩展速率.试验还通过变载荷刻线法获取疲劳裂纹扩展前缘的实际形貌和变化规律,对常规变载荷刻线方法进行了调整和验证,其修正方法对高分子材料的疲劳裂纹扩展前缘刻线具有较好的效果.通过观察发现含楔形塑性区的裂尖钝化是裂纹迟滞的主要原因.过载引入的塑性区内残余应力对裂纹迟滞也起了重要作用.论文利用Dugdale模型计算了塑性区尺寸,使用基于残余应力的Wheeler模型对过载迟滞进行了很好的拟合. 相似文献
52.
53.
Cheng Sheng Dr. Zheng Ling Dr. Tanveer Ahmad Prof. Dr. Fang Xie Prof. Dr. Wanbin Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(23):e202200128
Regioselective [3+3] annulation of alkynyl ketimines with α-cyano ketones for the synthesis of polysubstituted 4H-pyran derivatives with a quaternary CF3-containing center has been realized by using Cu(OAc)2 as the catalyst. The novel strategy tolerates a wide range of α-CF3 alkynyl ketimines and α-cyano ketones with both aryl and alkyl substitutents. A preliminary asymmetric synthesis of chiral product 3 has been attempted by using copper and chiral thiourea as the cocatalyst with excellent yields (86-99 %) and good enantioselectivities (71–78 % ee). Furthermore, product 3 aa could be obtained on a gram-scale reaction with 75 % yield and 99 % ee after recrystallization. Several products were also transformed readily. Control experiments indicate that the reaction involves a process with a base-catalyzed or chiral thiourea-catalyzed Mannich-type reaction followed by a highly regioselective copper-catalyzed ring-closing reaction on the alkynyl moiety in a 6-endo-dig fashion. 相似文献
54.
The Random Batch Method proposed in our previous work(Jin et al.J Comput Phys,2020)is not only a numerical method for interacting particle systems and its mean-field limit,but also can be viewed as a model of the particle system in which particles interact,at discrete time,with randomly selected mini-batch of particles.In this paper,we investigate the mean-field limit of this model as the number of particles N→∞.Unlike the classical mean field limit for interacting particle systems where the law of large numbers plays the role and the chaos is propagated to later times,the mean field limit now does not rely on the law of large numbers and the chaos is imposed at every discrete time.Despite this,we will not only justify this mean-field limit(discrete in time)but will also show that the limit,as the discrete time intervalτ→0,approaches to the solution of a nonlinear Fokker-Planck equation arising as the mean-field limit of the original interacting particle system in the Wasserstein distance. 相似文献
55.
56.
Transport in Porous Media - This paper numerically investigates the heat transfer performance of thermally developing non-Darcy forced convection in a fluid-saturated porous medium tube under... 相似文献
57.
59.
We developed a novel method to assemble TiO2 nanorods conjugated with CdS quantum dots by L-cysteine molecular linker for type II semiconducting hybrid structure. The XRD patterns indicate that the CdS quantum dots perform the cubic phase structure, and TEM images show that CdS quantum dots are well dispersed on the surfaces of anatase TiO2 nanorods with little agglomeration. The UV-vis absorption spectra reveal the bandgap alignment in type II configuration between CdS QDs and TiO2 nanorods. 相似文献
60.