全文获取类型
收费全文 | 76029篇 |
免费 | 11172篇 |
国内免费 | 2693篇 |
专业分类
化学 | 63033篇 |
晶体学 | 922篇 |
力学 | 7894篇 |
综合类 | 134篇 |
数学 | 9222篇 |
物理学 | 8689篇 |
出版年
2024年 | 17篇 |
2023年 | 159篇 |
2022年 | 320篇 |
2021年 | 544篇 |
2020年 | 971篇 |
2019年 | 2684篇 |
2018年 | 2587篇 |
2017年 | 3059篇 |
2016年 | 3382篇 |
2015年 | 5683篇 |
2014年 | 5545篇 |
2013年 | 7903篇 |
2012年 | 6150篇 |
2011年 | 5983篇 |
2010年 | 4807篇 |
2009年 | 4836篇 |
2008年 | 5141篇 |
2007年 | 4453篇 |
2006年 | 4127篇 |
2005年 | 3860篇 |
2004年 | 3288篇 |
2003年 | 2962篇 |
2002年 | 3545篇 |
2001年 | 1931篇 |
2000年 | 1784篇 |
1999年 | 921篇 |
1998年 | 399篇 |
1997年 | 386篇 |
1996年 | 342篇 |
1995年 | 292篇 |
1994年 | 259篇 |
1993年 | 223篇 |
1992年 | 220篇 |
1991年 | 174篇 |
1990年 | 146篇 |
1989年 | 122篇 |
1988年 | 119篇 |
1987年 | 74篇 |
1986年 | 77篇 |
1985年 | 90篇 |
1984年 | 86篇 |
1983年 | 44篇 |
1982年 | 85篇 |
1981年 | 35篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
7.
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
8.
David K Bisset 《国际流体数值方法杂志》2002,39(10):961-977
Turbulent flow simulation methods based on finite differences are attractive for their simplicity, flexibility and efficiency, but not always for accuracy or stability. This paper demonstrates that a good compromise is possible with the advected grid explicit (AGE) method. Starting from the same initial field as a previous spectral DNS, AGE method simulations of a planar turbulent wake were carried out as DNS, and then at three levels of reduced resolution. The latter cases were in a sense large‐eddy simulations (LES), although no specific sub‐grid‐scale model was used. Results for the two DNS methods, including variances and power spectra, were very similar, but the AGE simulation required much less computational effort. Small‐scale information was lost in the reduced resolution runs, but large‐scale mean and instantaneous properties were reproduced quite well, with further large reductions in computational effort. Quality of results becomes more sensitive to the value chosen for one of the AGE method parameters as resolution is reduced, from which it is inferred that the numerical stability procedure controlled by the parameter is acting in part as a sub‐grid‐scale model. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
9.
Let G=(V(G),E(G)) be a graph. A (n,G, λ)‐GD is a partition of the edges of λKn into subgraphs (G‐blocks), each of which is isomorphic to G. The (n,G,λ)‐GD is named as graph design for G or G‐decomposition. The large set of (n,G,λ)‐GD is denoted by (n,G,λ)‐LGD. In this work, we obtain the existence spectrum of (n,P3,λ)‐LGD. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 151–159, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10008 相似文献
10.
Several new families of c‐Bhaskar Rao designs with block size 4 are constructed. The necessary conditions for the existence of a c‐BRD (υ,4,λ) are that: (1)λmin=?λ/3 ≤ c ≤ λ and (2a) c≡λ (mod 2), if υ > 4 or (2b) c≡ λ (mod 4), if υ = 4 or (2c) c≠ λ ? 2, if υ = 5. It is proved that these conditions are necessary, and are sufficient for most pairs of c and λ; in particular, they are sufficient whenever λ?c ≠ 2 for c > 0 and whenever c ? λmin≠ 2 for c < 0. For c < 0, the necessary conditions are sufficient for υ> 101; for the classic Bhaskar Rao designs, i.e., c = 0, we show the necessary conditions are sufficient with the possible exception of 0‐BRD (υ,4,2)'s for υ≡ 4 (mod 6). © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 361–386, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10009 相似文献