全文获取类型
收费全文 | 125002篇 |
免费 | 12263篇 |
国内免费 | 13077篇 |
专业分类
化学 | 77719篇 |
晶体学 | 624篇 |
力学 | 8372篇 |
综合类 | 1981篇 |
数学 | 29268篇 |
物理学 | 32378篇 |
出版年
2023年 | 1295篇 |
2022年 | 2046篇 |
2021年 | 3702篇 |
2020年 | 3887篇 |
2019年 | 3645篇 |
2018年 | 3277篇 |
2017年 | 3789篇 |
2016年 | 4560篇 |
2015年 | 4013篇 |
2014年 | 5839篇 |
2013年 | 9449篇 |
2012年 | 7141篇 |
2011年 | 7190篇 |
2010年 | 6170篇 |
2009年 | 7636篇 |
2008年 | 8005篇 |
2007年 | 8642篇 |
2006年 | 7324篇 |
2005年 | 6210篇 |
2004年 | 5866篇 |
2003年 | 5023篇 |
2002年 | 4112篇 |
2001年 | 3425篇 |
2000年 | 2989篇 |
1999年 | 2635篇 |
1998年 | 2414篇 |
1997年 | 2112篇 |
1996年 | 1912篇 |
1995年 | 1881篇 |
1994年 | 1657篇 |
1993年 | 1498篇 |
1992年 | 1379篇 |
1991年 | 1106篇 |
1990年 | 921篇 |
1989年 | 673篇 |
1988年 | 693篇 |
1987年 | 488篇 |
1986年 | 465篇 |
1985年 | 586篇 |
1984年 | 461篇 |
1983年 | 262篇 |
1982年 | 460篇 |
1981年 | 594篇 |
1980年 | 523篇 |
1979年 | 572篇 |
1978年 | 450篇 |
1977年 | 347篇 |
1976年 | 306篇 |
1974年 | 129篇 |
1973年 | 191篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
73.
74.
Xingfei Xiang 《Journal of Mathematical Analysis and Applications》2022,505(2):125518
In bounded convex domains, the regularity of a vector field u with its , in space and the tangential component or the normal component of u over the boundary in space, is established for . As an application, we derive an estimate for solutions to a Maxwell type system with an inhomogeneous boundary condition in convex domains. In contrast to the well-posed region of r in the space for the Maxwell type system in Lipschitz domains given by Kar and Sini (2016) [16], we extend the well-posed region to be optimal. 相似文献
75.
《Discrete Mathematics》2022,345(12):113069
The toughness of a noncomplete graph G is the maximum real number t such that the ratio of to the number of components of is at least t for every cutset S of G. Determining the toughness for a given graph is NP-hard. Chvátal's toughness conjecture, stating that there exists a constant such that every graph with toughness at least is hamiltonian, is still open for general graphs. A graph is called -free if it does not contain any induced subgraph isomorphic to , the disjoint union of and two isolated vertices. In this paper, we confirm Chvátal's toughness conjecture for -free graphs by showing that every 7-tough -free graph on at least three vertices is hamiltonian. 相似文献
76.
The N–N bond is present in many important organic compounds, such as hydrazines, pyrazoles, azos, etc. Many methods based on transition metal catalyzed N–N coupling or functionalization of hydrazine have been reported for the synthesis of N–N containing organic compounds. In recent years, electrochemical dehydrogenative N–H/N–H coupling has become a powerful tool for the construction of N–N bearing organic compounds. The electrochemical methods employ electrons as traceless redox reagents instead of chemicals and produce hydrogen as the only byproduct. In this review, we summarize the recent advances in the electrochemical dehydrogenative N–H/N–H coupling reactions with focus on the mechanistic insights and synthetic applications of these transformations. 相似文献
77.
《Journal of Saudi Chemical Society》2022,26(4):101490
Biomass syngas is a form of renewable energy with very broad application prospects, and it has different combustion characteristics according to the fuel composition and processing technology of biomass syngas. The influence of combustion composition, diluent and temperature variation on combustion characteristics were studied in this paper. The FFCM-1 mechanism was used to investigate the combustion characteristics of CO/CH4/H2 under varied diluents CO2/N2 and temperature by using spherical expansion flame method and ANSYS CHEMKIN-PRO. The experimental laminar burning velocity was compared with the simulation results of FFCM-1 mechanism. The results reveal that the experimental data are in good agreement with the simulation results, which are somewhat different under the condition of rich fuel. The laminar burning velocity decreases significantly with the increase of diluent CO2/N2, with the effect of diluent CO2 being more significant. The laminar burning velocity increase dramatically with the increase of initial temperature, and the adiabatic flame temperature also decreases with the increase of diluent. The reduction caused by diluent CO2 is much larger than that caused by diluent N2. The change of initial temperature also affects the adiabatic flame temperature, but the range of variation is not as pronounced as that of diluent. Not only was the interaction between the combustion characteristics of CO/CH4/H2 under different diluents and temperature changes explored in this paper, but the influence mechanism was also revealed in depth. 相似文献
78.
79.
80.