全文获取类型
收费全文 | 475938篇 |
免费 | 14416篇 |
国内免费 | 7703篇 |
专业分类
化学 | 249091篇 |
晶体学 | 6484篇 |
力学 | 23742篇 |
综合类 | 521篇 |
数学 | 67582篇 |
物理学 | 150637篇 |
出版年
2022年 | 3443篇 |
2021年 | 3983篇 |
2020年 | 4425篇 |
2019年 | 4306篇 |
2018年 | 13046篇 |
2017年 | 13715篇 |
2016年 | 10765篇 |
2015年 | 7145篇 |
2014年 | 8101篇 |
2013年 | 18778篇 |
2012年 | 20533篇 |
2011年 | 31172篇 |
2010年 | 19355篇 |
2009年 | 19184篇 |
2008年 | 26554篇 |
2007年 | 29714篇 |
2006年 | 15634篇 |
2005年 | 21090篇 |
2004年 | 15818篇 |
2003年 | 13868篇 |
2002年 | 11549篇 |
2001年 | 11556篇 |
2000年 | 9243篇 |
1999年 | 7602篇 |
1998年 | 6190篇 |
1997年 | 5844篇 |
1996年 | 6067篇 |
1995年 | 5467篇 |
1994年 | 5146篇 |
1993年 | 4838篇 |
1992年 | 5215篇 |
1991年 | 4980篇 |
1990年 | 4604篇 |
1989年 | 4348篇 |
1988年 | 4541篇 |
1987年 | 4190篇 |
1986年 | 4015篇 |
1985年 | 5671篇 |
1984年 | 5665篇 |
1983年 | 4605篇 |
1982年 | 4944篇 |
1981年 | 4958篇 |
1980年 | 4688篇 |
1979年 | 4790篇 |
1978年 | 4807篇 |
1977年 | 4708篇 |
1976年 | 4690篇 |
1975年 | 4595篇 |
1974年 | 4430篇 |
1973年 | 4642篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
A (di)graph is supereulerian if it contains a spanning eulerian sub(di)graph. This property is a relaxation of hamiltonicity. Inspired by this analogy with hamiltonian cycles and by similar results in supereulerian graph theory, we analyze a number of sufficient Ore type conditions for a digraph to be supereulerian. Furthermore, we study the following conjecture due to Thomassé and the first author: if the arc‐connectivity of a digraph is not smaller than its independence number, then the digraph is supereulerian. As a support for this conjecture we prove it for digraphs that are semicomplete multipartite or quasitransitive and verify the analogous statement for undirected graphs. 相似文献
75.
76.
A. Lashgari S. Ghammamy R. Ramirez-Tagle G. Salgado-Moran 《Journal of Structural Chemistry》2015,56(8):1505-1513
Two new compounds of fluorine: (C2H5)4N[I2F] and (C2H5)4N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)4NF, I2 and Br2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data. 相似文献
77.
Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been deemed as clean and sustainable strategies to solve the energy crisis and environmental problems. Various catalysts have been developed to promote the process of HER and OER. Among them, two-dimensional covalent organic frameworks (2D COFs) have received great attention due to their diverse and designable structure. In this minireview, we mainly summarize the diverse linkages of 2D COFs and strategies for enhancing the catalytic performance of 2D COFs for HER and OER, such as introducing active building blocks, metal ions and tailored linkages. Furthermore, a brief outlook for the development directions of COFs in the field of HER and OER is provided, expecting to stimulate new opportunities in future research. 相似文献
78.
Yao Yuan Chen Ying Chen Jianyong Gong Yulie 《Journal of Thermal Analysis and Calorimetry》2021,144(6):2357-2367
Journal of Thermal Analysis and Calorimetry - Based on innovative design, a liquid–vapor separation plate condenser with excellent heat transfer performance is invented. It takes less time to... 相似文献
79.
Farsi R. Mohammadi M. K. Saghanezhad S. J. 《Russian Journal of Organic Chemistry》2021,57(12):2002-2009
Russian Journal of Organic Chemistry - Herein, we report the sulfonamide-functionalized covalent organic framework (COF-SO3H), prepared by condensation of melamine and terephthalaldehyde and... 相似文献
80.