全文获取类型
收费全文 | 26874篇 |
免费 | 5161篇 |
国内免费 | 7412篇 |
专业分类
化学 | 19882篇 |
晶体学 | 867篇 |
力学 | 1977篇 |
综合类 | 976篇 |
数学 | 3949篇 |
物理学 | 11796篇 |
出版年
2024年 | 41篇 |
2023年 | 260篇 |
2022年 | 778篇 |
2021年 | 800篇 |
2020年 | 853篇 |
2019年 | 962篇 |
2018年 | 881篇 |
2017年 | 1111篇 |
2016年 | 1070篇 |
2015年 | 1389篇 |
2014年 | 1559篇 |
2013年 | 2080篇 |
2012年 | 2179篇 |
2011年 | 2336篇 |
2010年 | 2143篇 |
2009年 | 2270篇 |
2008年 | 2452篇 |
2007年 | 2222篇 |
2006年 | 2177篇 |
2005年 | 1919篇 |
2004年 | 1528篇 |
2003年 | 1162篇 |
2002年 | 1253篇 |
2001年 | 1170篇 |
2000年 | 1132篇 |
1999年 | 752篇 |
1998年 | 427篇 |
1997年 | 308篇 |
1996年 | 275篇 |
1995年 | 267篇 |
1994年 | 217篇 |
1993年 | 227篇 |
1992年 | 191篇 |
1991年 | 143篇 |
1990年 | 124篇 |
1989年 | 123篇 |
1988年 | 115篇 |
1987年 | 110篇 |
1986年 | 78篇 |
1985年 | 56篇 |
1984年 | 65篇 |
1983年 | 61篇 |
1982年 | 38篇 |
1981年 | 34篇 |
1980年 | 43篇 |
1979年 | 23篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1959年 | 6篇 |
1936年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
Importing intramolecular hydrogen bond in phosphorescent transition metal complexes has been considered one of the excellent approaches to improve the electroluminescence performance of organic light-emitting diodes in real applications. However, the relationships between such H-bond structure and phosphorescent properties have not been theoretically revealed yet. In this study, two types of intramolecular hydrogen bonds are introduced into the two classes of traditional materials, that is, Pt(II) and Ir(III) complexes ( 1a and 2a ) to completely elucidate their influence on the structures and properties by comparing with the original phosphors ( 1b and 2b ) using density functional theory/time-dependent density functional theory for the first time. A comprehensive analysis of the geometric structures, molecular orbitals, and luminescence properties (including phosphorescence emission wavelengths and radiative and nonradiative decay processes) has been carried out. Our theoretical model highlights that complexes 1a and 2a embedded with H-bonds significantly promote the phosphorescence emission band blue-shifted and restrict molecular deformations compared with the corresponding 1b and 2b , which can provide helpful guidance to regulate and design several aspects of highly efficient blue phosphorescent emitters. 相似文献
942.
943.
Given a planar continuum Gaussian free field h𝒰 in a domain 𝒰 with Dirichlet boundary condition and any δ > 0, we let be a real-valued smooth Gaussian process where is the average of h𝒰 along a circle of radius δ with center v. For γ > 0, we study the Liouville first-passage percolation (in scale δ), i.e., the shortest path distance in 𝒰 where the weight of each path P is given by . We show that the distance between two typical points is for all sufficiently small but fixed γ > 0 and some constant c* > 0. In addition, we obtain similar upper bounds on the Liouville first-passage percolation for discrete Gaussian free fields, as well as the Liouville graph distance, which roughly speaking is the minimal number of euclidean balls with comparable Liouville quantum gravity measure whose union contains a continuous path between two endpoints. Our results contradict some reasonable interpretations of Watabiki's prediction (1993) on the random distance of Liouville quantum gravity at high temperatures.© 2019 Wiley Periodicals, Inc. 相似文献
944.
Jian Wang Jinjin Zhou Yu Xu Bingqi Zhu Huiyi Li 《Rapid communications in mass spectrometry : RCM》2019,33(17):1410-1419
945.
Na-Na Jiang Shu-Zong Du Yan-Song Ye Hui Yan Xing-Wei Yang Jian Yang Yin Nian Gang Xu 《Tetrahedron letters》2019,60(45):151220
Hyphenone A (1), a new type of bicyclic polyprenylated acylphloroglucinols (BPAPs) featured with an unprecedented 3,3-diisoprenylated 1,3,5-trione core, were characterized from the roots of Hypericum henryi together with two new congeners (hyphenones B–C, 2–3) and five known biosynthetic related PPAPs. Biogenetically, 1 should be derived from a novel 3,3,5,5-tetraisoprenylated MPAPs precursor. Their structures were elucidated by comprehensive spectroscopic data and X-ray diffraction. Moreover, 1–3 were identified as the first PPAPs type Cav3.1 T-type calcium channel (TTCC) inhibitors, with IC50 values of 7.07, 6.19, and 5.47 μM, respectively. 相似文献
946.
Teng GUO Zhen PENG Hui ZHU Li XU Jun-Guo DONG Zheng-Xu HUANG Ping CHENG Zhen ZHOU 《分析化学》2019,47(1):13-22
Ion funnel is a new-style ion guider which can reduce spatial divergence and energy dispersity of the transmission ions by using radio frequency (RF) electric field to confine the ions radially and the direct current (DC) axial electric field to move the ions toward the exit, and thus it can greatly increase the ion transmission efficiency and improve the sensitivity of the mass spectrometry. Since ion funnel was invented in 1997, it has attracted a close attention of mass spectrometry scientists all over the world. Ion funnel has been used in various kinds of mass spectrometry, and built a bridge with high efficiency ion transmission between low vacuum ionization source and high vacuum mass analyzer. In this paper, the principle, technology development, and application progress of ion funnel are reviewed, and the future prospects are prospected. 相似文献
947.
空间填充设计在计算机试验中应用十分广泛,当拟合回归模型时,正交的空间填充设计保证了因子效应估计的独立性.基于广义正交设计,文章给出了构造二阶正交拉丁超立方体设计和列正交设计的方法,新构造的设计不仅满足任意两列之间相互正交,还能保证每一列与任一列元素平方组成的列以及任两列元素相乘组成的列都正交.当某些正交的空间填充设计不存在时,具有较小相关系数的近似正交设计可作为替代设计使用.设计构造的灵活性为计算机试验在实践中的广泛应用提供了必要的支持. 相似文献
948.
Yunyun Wang Yajun Jian Ya Wu Huaming Sun Guofang Zhang Weiqiang Zhang Ziwei Gao 《应用有机金属化学》2019,33(7)
Bifunctional catalysts bearing two catalytic sites, Lewis acidic organometallic titanocene and Brønsted acidic COOH, have been assembled in situ from Cp2TiCl2 with carboxylic acid ligands, showing high catalytic activity over an intramolecular Mannich reaction towards synthesis of 2‐aryl‐2,3‐dihydroquinolin‐4(1H)‐ones. The determination of the bifunctional catalyst Cp2Ti(C8H4NO6)2 was elucidated by single X‐ray HR‐MS and investigation of catalytic behavior. In particular, masking the Brønsted acidic COOH catalytic site with dormant COOMe lowered the reaction yield greatly, indicating that two catalytic sites work together to maintain high catalytic efficiency. 相似文献
949.
Wang Jing-Xian Liu Nan Wang Chen Xu Jian 《International Journal of Theoretical Physics》2019,58(8):2654-2663
International Journal of Theoretical Physics - Quantum secure communication is the key development object of current communication technology. There are many branches, among which the most... 相似文献
950.