全文获取类型
收费全文 | 24705篇 |
免费 | 4439篇 |
国内免费 | 3981篇 |
专业分类
化学 | 19594篇 |
晶体学 | 338篇 |
力学 | 1270篇 |
综合类 | 348篇 |
数学 | 2950篇 |
物理学 | 8625篇 |
出版年
2024年 | 49篇 |
2023年 | 409篇 |
2022年 | 682篇 |
2021年 | 778篇 |
2020年 | 951篇 |
2019年 | 1038篇 |
2018年 | 860篇 |
2017年 | 803篇 |
2016年 | 1256篇 |
2015年 | 1354篇 |
2014年 | 1448篇 |
2013年 | 1891篇 |
2012年 | 2174篇 |
2011年 | 2308篇 |
2010年 | 1686篇 |
2009年 | 1679篇 |
2008年 | 1799篇 |
2007年 | 1543篇 |
2006年 | 1461篇 |
2005年 | 1358篇 |
2004年 | 1127篇 |
2003年 | 984篇 |
2002年 | 1116篇 |
2001年 | 862篇 |
2000年 | 676篇 |
1999年 | 538篇 |
1998年 | 373篇 |
1997年 | 307篇 |
1996年 | 294篇 |
1995年 | 251篇 |
1994年 | 201篇 |
1993年 | 169篇 |
1992年 | 126篇 |
1991年 | 107篇 |
1990年 | 81篇 |
1989年 | 65篇 |
1988年 | 49篇 |
1987年 | 43篇 |
1986年 | 36篇 |
1985年 | 29篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 9篇 |
1981年 | 21篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1975年 | 8篇 |
1974年 | 9篇 |
1973年 | 6篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
为提高煤与瓦斯突出矿井瓦斯抽放效果,建立了3个一级指标、14个二级指标的突出矿井瓦斯抽放限制影响因素评价指标体系,利用AHP和熵权法分别确定指标因子主、客观权重.通过实地调研分析和反馈验证了AHP-熵权法的可行性和正确性,利用加权平均法确定评价模型的综合权重.研究表明:封孔方式、钻孔半径、抽放时间、煤体裂隙发育程度和抽放负压是目前影响煤矿瓦斯抽放效果的主控因素. 相似文献
3.
Let p ∈ [1, ∞), q ∈ [1, ∞), α∈ R, and s be a non-negative integer. Inspired by the space JNp introduced by John and Nirenberg(1961) and the space B introduced by Bourgain et al.(2015), we introduce a special John-Nirenberg-Campanato space JNcon(p,q,s) over Rn or a given cube of R;with finite side length via congruent subcubes, which are of some amalgam features. The limit space of such spaces as p →∞ is just the Campanato space which coincides with the space BMO(the space of functions with bounded mean oscillations)when α = 0. Moreover, a vanishing subspace of this new space is introduced, and its equivalent characterization is established as well, which is a counterpart of the known characterization for the classical space VMO(the space of functions with vanishing mean oscillations) over Rn or a given cube of Rn with finite side length.Furthermore, some VMO-H1-BMO-type results for this new space are also obtained, which are based on the aforementioned vanishing subspaces and the Hardy-type space defined via congruent cubes in this article. The geometrical properties of both the Euclidean space via its dyadic system and congruent cubes play a key role in the proofs of all these results. 相似文献
4.
Zeng Qing-Wei Wen Zhuo-Yu Fu Jun-Feng Zhou Nan-Run 《International Journal of Theoretical Physics》2021,60(9):3306-3333
International Journal of Theoretical Physics - A new quantum watermark algorithm is presented by combining maximum pixel difference partitioning with the least significant bit substitution... 相似文献
5.
The Ramanujan Journal - We calculate the dimensions of the spaces of invariant vectors under the Klingen congruence subgroup of level $${\mathfrak {p}}^2$$ for all irreducible, admissible... 相似文献
6.
Nonlinear Dynamics - With an increasing number of people sharing feelings and opinions online, the online platforms have become one of the most important channels for public opinion dissemination.... 相似文献
7.
Yi Han Zibo Xue Dr. Guangwu Li Dr. Yanwei Gu Dr. Yong Ni Dr. Shaoqiang Dong Prof. Chunyan Chi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9111-9116
Incorporation of a non-hexagonal ring into a nanographene framework can lead to new electronic properties. During the attempted synthesis of naphthalene-bridged double [6]helicene and heptagon-containing nanographene by the Scholl reaction, an unexpected azulene-embedded nanographene and its triflyloxylated product were obtained, as confirmed by X-ray crystallographic analysis and 2D NMR spectroscopy. A 5/7/7/5 ring-fused substructure containing two formal azulene units is formed, but only one of them shows an azulene-like electronic structure. The formation of this unique structure is explained by arenium ion mediated 1,2-phenyl migration and a naphthalene to azulene rearrangement reaction according to an in-silico study. This report represents the first experimental example of the thermodynamically unfavorable naphthalene to azulene rearrangement and may lead to new azulene-based molecular materials. 相似文献
8.
9.
10.