全文获取类型
收费全文 | 52936篇 |
免费 | 10016篇 |
国内免费 | 1460篇 |
专业分类
化学 | 54817篇 |
晶体学 | 420篇 |
力学 | 735篇 |
数学 | 4218篇 |
物理学 | 4222篇 |
出版年
2023年 | 160篇 |
2022年 | 349篇 |
2021年 | 915篇 |
2020年 | 1663篇 |
2019年 | 3010篇 |
2018年 | 1371篇 |
2017年 | 990篇 |
2016年 | 3968篇 |
2015年 | 4045篇 |
2014年 | 4018篇 |
2013年 | 5138篇 |
2012年 | 4152篇 |
2011年 | 3566篇 |
2010年 | 3665篇 |
2009年 | 3606篇 |
2008年 | 3524篇 |
2007年 | 2884篇 |
2006年 | 2387篇 |
2005年 | 2495篇 |
2004年 | 2111篇 |
2003年 | 1899篇 |
2002年 | 2556篇 |
2001年 | 1560篇 |
2000年 | 1433篇 |
1999年 | 515篇 |
1998年 | 188篇 |
1997年 | 174篇 |
1996年 | 175篇 |
1995年 | 126篇 |
1994年 | 119篇 |
1993年 | 115篇 |
1992年 | 90篇 |
1991年 | 106篇 |
1990年 | 71篇 |
1989年 | 91篇 |
1988年 | 76篇 |
1987年 | 66篇 |
1986年 | 65篇 |
1985年 | 81篇 |
1984年 | 102篇 |
1983年 | 58篇 |
1982年 | 79篇 |
1981年 | 68篇 |
1980年 | 71篇 |
1979年 | 52篇 |
1978年 | 65篇 |
1977年 | 52篇 |
1976年 | 44篇 |
1975年 | 31篇 |
1963年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
63.
64.
We study spectral properties of discrete Schrödinger operators with potentials obtained via dimerization of a class of aperiodic sequences. It is shown that both the nature of the autocorrelation measure of a regular sequence and the presence of generic (full probability) singular continuous spectrum in the hull of primitive and palindromic (four block substitution) potentials are robust under dimerization. Generic results also hold for circle potentials. We illustrate these results with numerical studies of the quantum mean square displacement as a function of time. The numerical techniques provide a very fast algorithm for the time evolution of wave packets. 相似文献
65.
66.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
67.
The versatile behavior of a trihydrazidophosphoradamantane allowing the synthesis of a variety of neutral, mono- or di-cationic water-soluble molecules of potential interest for biphasic catalysis is reported. 相似文献
68.
Maria Kordaki Athanasia Balomenou 《International Journal of Computers for Mathematical Learning》2006,11(1):99-135
This study focuses on the constructions in terms of area and perimeter in equivalent triangles developed by students aged 12–15 years-old, using the tools provided by Cabri-Geometry II [Labore (1990). Cabri-Geometry (software), Université de Grenoble]. Twenty-five students participated in a learning experiment where they were asked to construct: (a) pairs of equivalent triangles “in as many ways as possible” and to study their area and their perimeter using any of the tools provided and (b) “any possible sequence of modifications of an original triangle into other equivalent ones”. As regards the concept of area and in contrast to a paper and pencil environment, Cabri provided students with different and potential opportunities in terms of: (a) means of construction, (b) control, (c) variety of representations and (d) linking representations, by exploiting its capability for continuous modifications. By exploiting these opportunities in the context of the given open tasks, students were helped by the tools provided to develop a broader view of the concept of area than the typical view they would construct in a typical paper and pencil environment. 相似文献
69.
Josep Maria Izquierdo 《TOP》2006,14(2):375-398
The paper introduces a refinement of the notion of population monotonic allocation scheme, called regular population monotonic
allocation scheme (regularpmas). This refinement is based on economic situations in which players may have to select new partners from a set of potential
players and in which there exist certain capacity constraints. A sufficient condition for the existence of a regularpmas is given. For the class of games with regularpmas, we prove that the core coincides with the Davis and Maschler and the Mas-Colell bargaining sets. 相似文献
70.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献