全文获取类型
收费全文 | 179591篇 |
免费 | 7221篇 |
国内免费 | 5820篇 |
专业分类
化学 | 82963篇 |
晶体学 | 2134篇 |
力学 | 12509篇 |
综合类 | 433篇 |
数学 | 44035篇 |
物理学 | 50558篇 |
出版年
2023年 | 867篇 |
2022年 | 1411篇 |
2021年 | 2120篇 |
2020年 | 2694篇 |
2019年 | 2834篇 |
2018年 | 13253篇 |
2017年 | 13013篇 |
2016年 | 9739篇 |
2015年 | 3598篇 |
2014年 | 4192篇 |
2013年 | 5780篇 |
2012年 | 9358篇 |
2011年 | 16250篇 |
2010年 | 10245篇 |
2009年 | 10546篇 |
2008年 | 11307篇 |
2007年 | 13133篇 |
2006年 | 4288篇 |
2005年 | 4911篇 |
2004年 | 4717篇 |
2003年 | 4818篇 |
2002年 | 3836篇 |
2001年 | 2867篇 |
2000年 | 2296篇 |
1999年 | 1765篇 |
1998年 | 1732篇 |
1997年 | 1470篇 |
1996年 | 1480篇 |
1995年 | 1202篇 |
1994年 | 1246篇 |
1993年 | 1202篇 |
1992年 | 1125篇 |
1991年 | 1195篇 |
1990年 | 1181篇 |
1989年 | 1099篇 |
1988年 | 978篇 |
1987年 | 976篇 |
1986年 | 940篇 |
1985年 | 970篇 |
1984年 | 963篇 |
1983年 | 868篇 |
1982年 | 848篇 |
1979年 | 855篇 |
1978年 | 853篇 |
1977年 | 831篇 |
1976年 | 937篇 |
1975年 | 832篇 |
1974年 | 859篇 |
1973年 | 873篇 |
1972年 | 771篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Rotating detonation combustors (RDC) are at the forefront of pressure gain combustion (PGC) research. The simplicity in design and the ease of assembly makes it a promising technology that could be integrated into existing combustor architectures. This is, however, coupled with the considerable complexities of the detonation-based flow field, and the associated modes and coupling mechanisms. The current paper is an overview of the research done at the University of Cincinnati to address some of the challenges and questions pertaining to the physics of RDC operation. Issues such as combustor geometry, injection schemes and mixing, varied reactants behavior and modes of RDC operation are discussed. The effects of pressurization of the combustor, along with other detonation enhancement strategies are also deliberated upon. When appropriate, parallels are drawn to the phenomena of high frequency combustion instabilities to address the similarities in observations between the two fields. 相似文献
72.
73.
74.
Yuliang Zhao 《中国科学:化学(英文版)》2018,61(12):1481-1482
正Living organisms have developed their unique strategies during the natural evolution for building hard tissues with minerals, including silica, calcium carbonate, calcium phosphate, and ferric oxide [1]. Such biomineralized materials generally have complex hierarchical structures with excellent mechanical properties. Although bioinspired approaches have led to the creation of well-defined synthetic structural materials ranging from micro to macro scales, the rational design of discrete biomimetic structures at the nanoscale remains a grand challenge. 相似文献
75.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant. 相似文献
76.
Lin Hui-Min Mu Chao Li Ao Liu Xu-Feng Li Yu-Long Jiang Zhong-Qing Wu Hong-Ke 《Transition Metal Chemistry》2019,44(5):491-498
Transition Metal Chemistry - In this paper, four diiron toluene-3,4-dithiolate complexes with phosphine ligands were synthesized and characterized. Treatment of complex... 相似文献
77.
In this paper, we study the explicit expansion of the first order Melnikov function near a double homoclinic loop passing through a nilpotent saddle of order m in a near-Hamiltonian system. For any positive integer , we derive the formulas of the coefficients in the expansion, which can be used to study the limit cycle bifurcations for near-Hamiltonian systems. In particular, for , we use the coefficients to consider the limit cycle bifurcations of general near-Hamiltonian systems and give the existence conditions for 10, 11, 13, 15 and 16 (11, 13 and 16, respectively) limit cycles in the case that the homoclinic loop is of cuspidal type (smooth type, respectively) and their distributions. As an application, we consider a near-Hamiltonian system with a nilpotent saddle of order 2 and obtain the lower bounds of the maximal number of limit cycles. 相似文献
78.
Dr. Weixin Zou Lixia Xu Yu Pu Haojie Cai Xiaoqian Wei Yidan Luo Dr. Lulu Li Prof. Dr. Bin Gao Prof. Dr. Haiqin Wan Prof. Dr. Lin Dong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(19):5058-5064
Bimetallic AgPd nanoparticles have been synthesized before, but the interfacial electronic effects of AgPd on the photocatalytic performance have been investigated less. In this work, the results of hydrogen evolution suggest that the bimetallic AgPd/g-C3N4 sample has superior activity to Ag/g-C3N4 and Pd/g-C3N4 photocatalysts. The UV/Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, CO adsorption diffuse reflectance FTIR spectroscopy, and FTIR results demonstrate that in the AgPd/g-C3N4, the surface electronic structures of Pd and Ag are changed, which is beneficial for faster photogenerated electron transfer and greater H2O molecule adsorption. In situ ESR spectra suggest that, under visible light irradiation, there is more H2O dissociation to radical species on the AgPd/g-C3N4 photocatalyst. Furthermore, DFT calculations confirm the interfacial electronic effects of AgPd/g-C3N4, that is, Pdδ−⋅⋅⋅Agδ+, and the activation energy of H2O molecule dissociation on AgPd/g-C3N4 is the lowest, which is the main contributor to the enhanced photocatalytic H2 evolution. 相似文献
79.
80.
In this paper, the existence and multiplicity of positive solutions is established for Schrödinger‐Poisson system of the form where 0 ∈ Ω is a smooth bounded domain in , , and λ > 0 is a real parameter. Combining with the variational method and Nehari manifold method, two positive solutions of the system are obtained. 相似文献