全文获取类型
收费全文 | 350553篇 |
免费 | 10090篇 |
国内免费 | 5408篇 |
专业分类
化学 | 195779篇 |
晶体学 | 4916篇 |
力学 | 15429篇 |
综合类 | 292篇 |
数学 | 40593篇 |
物理学 | 109042篇 |
出版年
2021年 | 3033篇 |
2020年 | 3435篇 |
2019年 | 3342篇 |
2018年 | 3197篇 |
2017年 | 3023篇 |
2016年 | 5580篇 |
2015年 | 4960篇 |
2014年 | 6515篇 |
2013年 | 16591篇 |
2012年 | 13848篇 |
2011年 | 16578篇 |
2010年 | 10469篇 |
2009年 | 10425篇 |
2008年 | 14701篇 |
2007年 | 14685篇 |
2006年 | 14220篇 |
2005年 | 12716篇 |
2004年 | 11279篇 |
2003年 | 9913篇 |
2002年 | 9666篇 |
2001年 | 10839篇 |
2000年 | 8498篇 |
1999年 | 6879篇 |
1998年 | 5578篇 |
1997年 | 5379篇 |
1996年 | 5432篇 |
1995年 | 4964篇 |
1994年 | 4636篇 |
1993年 | 4358篇 |
1992年 | 4837篇 |
1991年 | 4608篇 |
1990年 | 4300篇 |
1989年 | 4059篇 |
1988年 | 4320篇 |
1987年 | 3949篇 |
1986年 | 3827篇 |
1985年 | 5465篇 |
1984年 | 5492篇 |
1983年 | 4447篇 |
1982年 | 4810篇 |
1981年 | 4828篇 |
1980年 | 4561篇 |
1979年 | 4673篇 |
1978年 | 4665篇 |
1977年 | 4646篇 |
1976年 | 4597篇 |
1975年 | 4508篇 |
1974年 | 4356篇 |
1973年 | 4524篇 |
1972年 | 2569篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
A practical Sonogashira alkynylation protocol for the preparation of 8-alkynylated adenosines and guanosines has been developed. Protection of the sugar hydroxyl substituents is not required; protection hinders the purification of these products. A preliminary fluorescent study is reported, which shows that the presence of a substituent on the phenylene ring influences the fluorescent properties considerably, an outcome that could be utilized in biological applications. 相似文献
62.
科学与完美是不是一致的?科学家们是否有权使用完美这个词?至少,对于物理学家和数学家来说答案是肯定的“是”.2002年,温伯格(Steven Weinberg)写道:“近代物理学的一些重要方程式是科学知识的永久部分,甚至比它们较早出现的美丽大教堂还要经久不衰.”1960年代,狄拉克(Paul A.M.Dirac)有句名言:“完整的方程式之完美较之它们适合实验结果更为重要.”1965年诺贝尔物理学奖获得者费因曼(Richard P.Feynman)也坚信他提出的一项理论,即使该理论显得与实验数据有矛盾.1957年,他写道:“理论是优雅和完美的,重大事件是短暂的闪光.” 相似文献
63.
We present the design and study of waveguide structures based on porous silicon where the light confinement is not due to the usual total reflection effect but to the use of photonic crystals (PCs) as confining walls. These PC are omnidirectional mirrors (OMs), consisting of the periodic repetition of two porous silicon layers with different refractive indices and thicknesses. They reflect the radiation for all angles of incidence within a frequency range called the omnidirectional band gap (OBG). We have followed the PC formalism to investigate the properties of the OM as a multimode waveguide: the number of modes within the band gap, their field spatial distribution and their confinement as a function of the frequency and the core thickness. 相似文献
64.
V. Edon M.C. Hugon B. Agius L. Miotti C. Radtke F. Tatsch J.J. Ganem I. Trimaille I.J.R. Baumvol 《Applied Physics A: Materials Science & Processing》2006,83(2):289-293
The influence of processing parameters on the electrical characteristics of RuO2/LaAlO3/Si metal-oxide-semiconductor structures was investigated. In particular, the sputtering regime during deposition of LaAlO3 on Si and the atmosphere used in the post-deposition annealing step were addressed by determining capacitance-voltage and
gate current-voltage characteristics. These results were correlated with compositional information obtained by Rutherford
backscattering spectrometry and nuclear reaction analysis. A post-deposition annealing step in oxygen at 600 °C resulted in
better electrical characteristics of the final structure as compared to the same treatment performed in nitrogen. This result
is explained by oxygen ability to heal oxygen vacancies in the LaAlO3 film, especially at the dielectric/semiconductor interface region. A thermalized sputtering regime during deposition of LaAlO3 on Si leads to capacitors with electrical characteristics superior to those deposited in ballistic regime.
PACS 77.84.Dy; 81.15.Cd; 81.40.Gh; 73.40.Qv; 82.80.Yc 相似文献
65.
Benjamin J. K. Evans Susan M. Scott Antony C. Searle 《General Relativity and Gravitation》2002,34(10):1675-1684
We have developed a new tool for numerical work in General Relativity: GRworkbench. We discuss how GRworkbench's implementation of a numerically-amenable analogue to Differential Geometry facilitates the development of robust and chart-independent numerical algorithms. We consider, as an example, geodesic tracing on two charts covering the exterior Schwarzschild space-time. 相似文献
66.
In this paper, the dimension of the spaces of bivariate spline with degree less that 2r and smoothness order r on the Morgan-Scott triangulation is considered. The concept of the instability degree in the dimension of spaces of bivariate spline is presented. The results in the paper make us conjecture the instability degree in the dimension of spaces of bivariate spline is infinity. 相似文献
67.
68.
The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method. 相似文献
69.
70.
Michael K. Kinyon Kenneth Kunen J. D. Phillips 《Proceedings of the American Mathematical Society》2002,130(3):619-624
An A-loop is a loop in which every inner mapping is an automorphism. A problem which had been open since 1956 is settled by showing that every diassociative A-loop is Moufang.