全文获取类型
收费全文 | 59909篇 |
免费 | 5470篇 |
国内免费 | 3646篇 |
专业分类
化学 | 24999篇 |
晶体学 | 341篇 |
力学 | 7223篇 |
综合类 | 887篇 |
数学 | 15695篇 |
物理学 | 19880篇 |
出版年
2024年 | 85篇 |
2023年 | 495篇 |
2022年 | 1086篇 |
2021年 | 1870篇 |
2020年 | 1358篇 |
2019年 | 1300篇 |
2018年 | 1094篇 |
2017年 | 1301篇 |
2016年 | 1599篇 |
2015年 | 1581篇 |
2014年 | 2363篇 |
2013年 | 3985篇 |
2012年 | 2566篇 |
2011年 | 3070篇 |
2010年 | 2780篇 |
2009年 | 3430篇 |
2008年 | 3535篇 |
2007年 | 3598篇 |
2006年 | 2995篇 |
2005年 | 2269篇 |
2004年 | 2168篇 |
2003年 | 2097篇 |
2002年 | 4494篇 |
2001年 | 2104篇 |
2000年 | 1556篇 |
1999年 | 1368篇 |
1998年 | 1303篇 |
1997年 | 1009篇 |
1996年 | 991篇 |
1995年 | 848篇 |
1994年 | 787篇 |
1993年 | 775篇 |
1992年 | 776篇 |
1991年 | 533篇 |
1990年 | 486篇 |
1989年 | 406篇 |
1988年 | 372篇 |
1987年 | 293篇 |
1986年 | 285篇 |
1985年 | 399篇 |
1984年 | 310篇 |
1983年 | 199篇 |
1982年 | 338篇 |
1981年 | 503篇 |
1980年 | 452篇 |
1979年 | 481篇 |
1978年 | 386篇 |
1977年 | 289篇 |
1976年 | 246篇 |
1973年 | 153篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
1.
2.
4.
5.
6.
In this work, a vanillin complex is immobilized onto MCM-41 and characterized by FT-IR, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, and BET techniques. This supported Schiff base complex was found to be an efficient and recoverable catalyst for the chemoselective oxidation of sulfides into sulfoxides and thiols into their corresponding disulfides (using hydrogen peroxide as a green oxidant) and also a suitable catalyst for the preparation of 2,3-dihydroquinazolin-4(1H)-one derivatives in water at 90°C. Using this protocol, we show that a variety of disulfides, sulfoxides, and 2,3-dihydroquinazolin-4(1H)-one derivatives can be synthesized in green conditions. The catalyst can be recovered and recycled for further reactions without appreciable loss of catalytic performance. 相似文献
7.
G. Peruginelli 《代数通讯》2018,46(11):4724-4738
We classify the maximal subrings of the ring of n×n matrices over a finite field, and show that these subrings may be divided into three types. We also describe all of the maximal subrings of a finite semisimple ring, and categorize them into two classes. As an application of these results, we calculate the covering number of a finite semisimple ring. 相似文献
8.
Knowledge of the vibrational properties of nanoparticles is of fundamental interest since it is a signature of their morphology, and it can be utilized to characterize their physical properties. In addition, the vibration characteristics of the nanoparticles coupled with surrounding media and subjected to magnetic field are of recent interest. This paper develops an analytical approach to study the radial breathing-mode frequency of elastically confined spherical nanoparticles subjected to magnetic field. Based on Maxwell's equations, the nonlocal differential equation of radial motion is derived in terms of radial displacement and Lorentz's force. Bessel functions are used to obtain a frequency equation. The model is justified by a good agreement between the results given by the present model and available experimental and atomic simulation data. Furthermore, the model is used to elucidate the effect of nanoparticle size, the magnetic field and the stiffness of the elastic medium on the radial breathing-mode frequencies of several nanoparticles. Our results reveal that the effects of the magnetic field and the elastic medium are significant for nanoparticle with small size. 相似文献
9.
就标准厚度卡片在霍尔传感器的定标方面的应用作了有益的探讨。在纵向测量微小长度时,霍尔片处于磁场边缘位置,其对磁场的梯度更大,即灵敏度更高,且靠中心位置的线性更好。 相似文献
10.
Thalia Tsiaka Panagiotis Zoumpoulakis Vassilia J. Sinanoglou Constantinos Makris Georgios A. Heropoulos Antony C. Calokerinos 《Analytica chimica acta》2015
High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE. 相似文献