全文获取类型
收费全文 | 6604篇 |
免费 | 337篇 |
国内免费 | 65篇 |
专业分类
化学 | 4492篇 |
晶体学 | 69篇 |
力学 | 264篇 |
综合类 | 2篇 |
数学 | 746篇 |
物理学 | 1433篇 |
出版年
2024年 | 38篇 |
2023年 | 83篇 |
2022年 | 149篇 |
2021年 | 438篇 |
2020年 | 303篇 |
2019年 | 279篇 |
2018年 | 296篇 |
2017年 | 234篇 |
2016年 | 336篇 |
2015年 | 265篇 |
2014年 | 294篇 |
2013年 | 545篇 |
2012年 | 439篇 |
2011年 | 489篇 |
2010年 | 285篇 |
2009年 | 253篇 |
2008年 | 270篇 |
2007年 | 285篇 |
2006年 | 205篇 |
2005年 | 187篇 |
2004年 | 115篇 |
2003年 | 111篇 |
2002年 | 99篇 |
2001年 | 87篇 |
2000年 | 63篇 |
1999年 | 65篇 |
1998年 | 35篇 |
1997年 | 31篇 |
1996年 | 52篇 |
1995年 | 47篇 |
1994年 | 29篇 |
1993年 | 36篇 |
1992年 | 37篇 |
1991年 | 45篇 |
1990年 | 18篇 |
1989年 | 28篇 |
1988年 | 33篇 |
1987年 | 30篇 |
1986年 | 28篇 |
1985年 | 41篇 |
1984年 | 26篇 |
1983年 | 24篇 |
1982年 | 24篇 |
1981年 | 15篇 |
1980年 | 28篇 |
1979年 | 25篇 |
1978年 | 29篇 |
1977年 | 29篇 |
1976年 | 22篇 |
1973年 | 12篇 |
排序方式: 共有7006条查询结果,搜索用时 375 毫秒
1.
Saqib Kamal Arif I. Inamdar Kuan-Ru Chiou Batjargal Sainbileg Muhammad Usman Jenq-Wei Chen Tzuoo-Tsair Luo Michitoshi Hayashi Chen-Hsiung Hung Wen-Feng Liaw Kuang-Lieh Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(30):e202103905
The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH2) and electron-withdrawing (R=NO2) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L1)(L2)]n ( 1 ) and [Zn(L1)(L3)]n ( 2 ) [L1=2-(2-pyridyl) benzimidazole (Pbim), L2=5-aminoisophthalate (Aip), and L3=5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH2 and NO2 substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO2 and NH2. Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties. 相似文献
2.
3.
Journal of Thermal Analysis and Calorimetry - This article considers viscoelastic effects on the enhancement of transportation of heat in thin-film flow when the relaxation time phenomenon is... 相似文献
4.
5.
6.
ABSTRACTDirect bandgap semiconductors are very essential to fulfil the demand for the advancement in optoelectronic devices. Therefore it is important to predict new potential candidates having such unique features. In current work, Sr3X2 (X=N, P, As, Sb and Bi) compounds have been reported for the first time by well trusted FP-APW+lo method. For the better prediction of the energy band gap, mBJ is used alongwith routine generalised gradient approximation (GGA). The results show small and direct energy band gaps at Γ-Γ symmetry points with magnitude in the range from 0.62?eV (Sr3P2) to zero energy band gap (Sr3Bi2). In partial density of state Sr-d state and X-p state are contributed in the band structure. The compounds show mostly covalent bonding nature. The frequecy dependent optical properties in the linear optical range are also investigated. 相似文献
7.
In this paper we study the Cauchy problem of the incompressible fractional Navier-Stokes equations in critical variable exponent Fourier-Besov-Morrey space F Ns(·)p(·),h(·),q(R3)with s(·)=4-2α-3/p(·).We prove global well-posedness result with small initial data belonging to FN4-2α-3/p(·)p(·),h(·)q(R3).The result of this paper extends some recent work. 相似文献
8.
Mohammad Azam Saud I. Al-Resayes Agata Trzesowska-Kruszynska Rafal Kruszynski S.F. Adil N.K. Lokanath 《Journal of Saudi Chemical Society》2019,23(5):636-641
A new derivative of dioxouranium(VI) salen complex, [UO2(L)(pyridine)], where [L = N,N′-Bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-propanediamine] is synthesized and characterized by elemental analysis (C, H, N), FT-IR, ESI-MS spectrometry, UV/Vis, fluorescence, 1H and 13C NMR spectroscopy and thermal gravimetric (TG) study. Furthermore, the single crystal X-ray diffraction measurements of the complex were carried out at 100 and 273 K. The crystal structure measurements revealed that the complex has distorted pentagonal bipyramidal geometry with uranium atom located at the centre and bonded to two phenoxy oxygen and two azomethine nitrogen in tetradenate fashion and one nitrogen from pyridine making it seven coordinated. In addition, the photoluminescence property of the complex was also recorded. 相似文献
9.
10.