全文获取类型
收费全文 | 1621篇 |
免费 | 233篇 |
国内免费 | 223篇 |
专业分类
化学 | 1230篇 |
晶体学 | 11篇 |
力学 | 129篇 |
综合类 | 21篇 |
数学 | 117篇 |
物理学 | 569篇 |
出版年
2024年 | 6篇 |
2023年 | 59篇 |
2022年 | 100篇 |
2021年 | 93篇 |
2020年 | 114篇 |
2019年 | 88篇 |
2018年 | 85篇 |
2017年 | 64篇 |
2016年 | 93篇 |
2015年 | 76篇 |
2014年 | 86篇 |
2013年 | 115篇 |
2012年 | 142篇 |
2011年 | 145篇 |
2010年 | 111篇 |
2009年 | 62篇 |
2008年 | 70篇 |
2007年 | 85篇 |
2006年 | 63篇 |
2005年 | 47篇 |
2004年 | 46篇 |
2003年 | 35篇 |
2002年 | 35篇 |
2001年 | 28篇 |
2000年 | 22篇 |
1999年 | 34篇 |
1998年 | 15篇 |
1997年 | 28篇 |
1996年 | 20篇 |
1995年 | 10篇 |
1994年 | 18篇 |
1993年 | 12篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有2077条查询结果,搜索用时 15 毫秒
21.
22.
23.
Yizhao Ouyang Miao Zhan Jing Zhou Jiao Jiao Hao Hu Yoichi M. A. Yamada Pengfei Li 《中国化学》2019,37(8):807-810
A rigid C2‐symmetric chiral bipyridine ligand Z‐bpy with a triptycene‐like backbone was designed and synthesized from simple chemicals in a scalable route. Using this new ligand, copper(I) catalyzed cyclopropanation of styrenes with commercial ethyl diazoacetate produced various corresponding cyclopropanes in high yields, diastereoselectivity and enantioselectivity up to 97% ee. 相似文献
24.
Xiuxiu Wang Zong-Chang Han Wei Wei Hanshi Hu Pengfei Li Peiqing Sun Xiangzhi Liu Zhijia Lv Feng Wang Yi Cao Zijian Guo Jun Li Jing Zhao 《Chemical science》2022,13(24):7269
Metal clusters, such as iron–sulfur clusters, play key roles in sustaining life and are intimately involved in the functions of metalloproteins. Herein we report the formation and crystal structure of a planar square tetranuclear silver cluster when silver ions were mixed with human copper chaperone Atox1. Quantum chemical studies reveal that two Ag 5s1 electrons in the tetranuclear silver cluster fully occupy the one bonding molecular orbital, with the assumption that this Ag4 cluster is Ag42+, leading to extensive electron delocalization over the planar square and significant stabilization. This bonding pattern of the tetranuclear silver cluster represents an aromatic all-metal structure that follows a 4n + 2 electron counting rule (n = 0). This is the first time an all-metal aromatic silver cluster was observed in a protein.Metal clusters, such as iron–sulfur clusters, play key roles in sustaining life and are intimately involved in the functions of metalloproteins. 相似文献
25.
26.
Junfu Guo Wei Zhou Pengfei Xing Peiqing Yu Qinggong Song Ping Wu 《Solid State Communications》2012,152(11):924-928
The electronic structural, magnetic and optical properties of pure and V-doped ZnO are investigated by first-principles calculations based on the density functional theory. With the introduction of V atoms, the spin-splitting near the Fermi level leads to a net magnetic moment of the system. A significant possibility of room temperature ferromagnetism (RTFM) originated from the Ruderman–Kittel–Kassuya–Yosida (RKKY) exchange is predicted. Oxygen vacancy is positive to enhance the ferromagnetism while zinc vacancy is negative. With respect to the optical properties, the presence of V atoms was found to have an obvious influence on the transmittivity, especially in the low energy region. A slight V-doping can keep a high optical transmission and smoothly modulate the optical bandgap. 相似文献
27.
28.
Pengfei Sun Biao Deng Guohao Du He Li Weidong Sun Jiangbo Ren Tiqiao Xiao 《X射线光谱测定》2015,44(6):442-446
X‐ray fluorescence computed tomography is an emerging imaging modality that allows for the nondestructive reconstruction of the internal distribution of elements within a sample. The common use of X‐ray excitation energy (up to approximately 20 keV) has necessitated the use of l ‐shell fluorescence for heavy elements. In this study, based on high energy X‐ray at BL13W1 of the Shanghai Synchrotron Radiation Facility, we employed high‐energy excitation for tomographic imaging of the heavy metals (rare earth elements) in fish teeth from deep‐sea sediments on the micrometer scale using K‐shell X‐ray fluorescence. The virtual cross‐sectional distribution of La, Ce, Pm, Pr, Nd, and Sm were obtained, thereby providing a feasible approach for analyzing the enrichment mechanism of rare earth elements. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
29.
30.
Herein, we present three imidazo[1,2‐a]pyridin‐2(3 H)‐one derivatives that are diamagnetic in solution, but paramagnetic in the solid state, possibly owing to a stacking‐induced formation of phenoxide‐type radicals. Notably, a larger bathochromic shift of the absorption (even up to the near‐ infrared region) of these three compounds was observed in the solid state than in solution, which was attributable to the ordered columnar stacking arrangements or their single‐electron character as radicals in the solid state. Interestingly, compared to that in solution, (E)‐3‐(pyridin‐4′‐ylmethylene)imidazo[1,2‐a]pyridine 2(3 H)‐one displayed a largely red‐shifted emission (centered at 660 nm, with tailing above 800 nm) in the solid state. A larger bathochromic shift (260 nm) of the emission is an indication of better order and tight stacking in the solid state, which is brought about by the rigid and polar acceptor. These three compounds also reveal different magnetic susceptibilities at 300 K, thus implying that they possess various columnar stacking structures. Most interestingly, these three radicals exhibit unusual ferromagnetic‐to‐antiferromagnetic phase transitions, which can be attributed to anisotropic contraction and non‐uniform slippage of the columnar stacking chains. 相似文献