全文获取类型
收费全文 | 89976篇 |
免费 | 2390篇 |
国内免费 | 1574篇 |
专业分类
化学 | 33207篇 |
晶体学 | 922篇 |
力学 | 7287篇 |
综合类 | 92篇 |
数学 | 33109篇 |
物理学 | 19323篇 |
出版年
2023年 | 240篇 |
2022年 | 239篇 |
2021年 | 357篇 |
2020年 | 517篇 |
2019年 | 501篇 |
2018年 | 10740篇 |
2017年 | 10492篇 |
2016年 | 6650篇 |
2015年 | 1367篇 |
2014年 | 960篇 |
2013年 | 1215篇 |
2012年 | 4903篇 |
2011年 | 11574篇 |
2010年 | 6344篇 |
2009年 | 6763篇 |
2008年 | 7419篇 |
2007年 | 9508篇 |
2006年 | 933篇 |
2005年 | 1945篇 |
2004年 | 1955篇 |
2003年 | 2282篇 |
2002年 | 1370篇 |
2001年 | 566篇 |
2000年 | 537篇 |
1999年 | 401篇 |
1998年 | 386篇 |
1997年 | 309篇 |
1996年 | 362篇 |
1995年 | 293篇 |
1994年 | 246篇 |
1993年 | 210篇 |
1992年 | 149篇 |
1991年 | 172篇 |
1990年 | 149篇 |
1989年 | 121篇 |
1988年 | 115篇 |
1987年 | 104篇 |
1986年 | 103篇 |
1985年 | 96篇 |
1984年 | 71篇 |
1983年 | 51篇 |
1982年 | 64篇 |
1981年 | 57篇 |
1980年 | 53篇 |
1979年 | 51篇 |
1978年 | 44篇 |
1914年 | 45篇 |
1913年 | 41篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 176 毫秒
11.
Dr. Rong-Lin Zhong Dr. Feng-Wei Gao Dr. Hong-Liang Xu Prof. Zhong-Min Su 《Chemphyschem》2019,20(14):1879-1884
The nature of the 2e/12c bond and its conversion to a carbon-carbon single bond in phenalenyl dimers have prompted a great deal of interests recently. In this work, we theoretically investigated a series of π-stacking phenalenyl derivatives with 2e/12c bonding character by density functional theory (DFT) calculations to elucidate origin of this unusual bond conversion. Results show that bond-conversion of the phenalenyl dimer easily occurs at room-temperature both dynamically and thermodynamically. However, bond-conversion of hetero π-stacking adducts, in which the two center carbon atoms were substituted by boron and nitrogen atoms, respectively, is much more difficult, because the 2e/12c bond is stabilized by its charge transfer character. Consequently, the bond-conversion is an endothermic process, albeit with a low conversion barrier. Interestingly, Lewis acid-base interactions would be induced by substitution of the center nitrogen atom to phosphorus atom. The 2e/12c bond is further stabilized by 5.9 kcal mol−1 and its conversion is also thermodynamically unfavorable. 相似文献
12.
Zhaohui Zhang Hui Liu Qingzhu Sun Feng Shao Qingyan Pan Prof. Tao Zhuang Prof. Yingjie Zhao 《ChemistryOpen》2020,9(3):381-385
A fluorescent monolayered two-dimensional polymer (2DP) containing both tetraphenylethylene (TPE) and imine linkages is synthesized at air-water interface using the Langmuir-Blodgett method. We designed TPE-based monomers with long distances between the TPE and the imine linkages to avoid the charge transfer and therefore keep the fluorescence. A monolayered 2DP provided with more than 104 μm2 in domain size and around 0.8 nm thickness was obtained through a successive Schiff base reaction at air-water interface. The nanostructures and fluorescent property of 2DP films were characterized by optical microscopy, SEM, TEM, AFM and fluorescence spectrum. Most importantly, the tip-enhanced Raman spectroscopy (TERS) was utilized here to confirm the success of the polycondensation of monolayered 2DP. 相似文献
13.
Krishna B. N. Vamsi Bhagwan Jai Hussain Sk. Khaja Yu Jae Su 《Journal of Solid State Electrochemistry》2020,24(4):1033-1044
Journal of Solid State Electrochemistry - Hierarchical nanostructure materials have attracted significant attention due to their fascinating structural features for the application of... 相似文献
14.
15.
Yuliang Zhao 《中国科学:化学(英文版)》2018,61(12):1481-1482
正Living organisms have developed their unique strategies during the natural evolution for building hard tissues with minerals, including silica, calcium carbonate, calcium phosphate, and ferric oxide [1]. Such biomineralized materials generally have complex hierarchical structures with excellent mechanical properties. Although bioinspired approaches have led to the creation of well-defined synthetic structural materials ranging from micro to macro scales, the rational design of discrete biomimetic structures at the nanoscale remains a grand challenge. 相似文献
16.
JuHong Ge 《Nonlinear dynamics》2018,94(1):87-98
A five-neuron network model with multiple delays is proposed. This paper presents the combined effect of different delays on the dynamics of the proposed network. Pitchfork bifurcation is discussed in detail with the variation of the value of coupled weight or attenuation rate of internal neurons. By analyzing the corresponding characteristic equation, some stable criteria on delay-dependence and delay-independence are derived including multiple delays and coupled weights and the periodic oscillation arises bifurcated from the trivial equilibrium after the network loses its stability. Stable regions on delay-dependence are displayed in the two delayed parameter plane. It is shown that multiple delays can produce stability switching between resting state and periodic activity. Finally, theoretical results are justified by providing two illustrative examples. 相似文献
17.
It is shown that the countably infinite dimensional pointed vector space (the vector space equipped with a constant) over a finite field has infinitely many first order definable reducts. This implies that the countable homogeneous Boolean-algebra has infinitely many reducts. 相似文献
18.
19.
20.
Dr. Ming-Hui Sun Prof. Dr. Li-Hua Chen Shen Yu Prof. Dr. Yu Li Xian-Gang Zhou Dr. Zhi-Yi Hu Prof. Dr. Yu-Han Sun Prof. Dr. Yan Xu Prof. Dr. Bao-Lian Su 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(44):19750-19759
Zeolite Beta single crystals with intracrystalline hierarchical porosity at macro-, meso-, and micro-length scales can effectively overcome the diffusion limitations in the conversion of bulky molecules. However, the construction of large zeolite Beta single crystals with such porosity is a challenge. We report herein the synthesis of hierarchically ordered macro-mesoporous single-crystalline zeolite Beta (OMMS-Beta) with a rare micron-scale crystal size by an in situ bottom-up confined zeolite crystallization strategy. The fully interconnected intracrystalline macro-meso-microporous hierarchy and the micron-sized single-crystalline nature of OMMS-Beta lead to improved accessibility to active sites and outstanding (hydro)thermal stability. Higher catalytic performances in gas-phase and liquid-phase acid-catalyzed reactions involving bulky molecules are obtained compared to commercial Beta and nanosized Beta zeolites. The strategy has been extended to the synthesis of other zeolitic materials, including ZSM-5, TS-1, and SAPO-34. 相似文献