全文获取类型
收费全文 | 220604篇 |
免费 | 33091篇 |
国内免费 | 22408篇 |
专业分类
化学 | 113952篇 |
晶体学 | 1831篇 |
力学 | 11510篇 |
综合类 | 978篇 |
数学 | 21014篇 |
物理学 | 66301篇 |
无线电 | 60517篇 |
出版年
2024年 | 491篇 |
2023年 | 4840篇 |
2022年 | 5429篇 |
2021年 | 7854篇 |
2020年 | 8195篇 |
2019年 | 7481篇 |
2018年 | 6602篇 |
2017年 | 6441篇 |
2016年 | 9330篇 |
2015年 | 9610篇 |
2014年 | 11800篇 |
2013年 | 15276篇 |
2012年 | 18406篇 |
2011年 | 18914篇 |
2010年 | 13429篇 |
2009年 | 13422篇 |
2008年 | 14348篇 |
2007年 | 12937篇 |
2006年 | 12260篇 |
2005年 | 10560篇 |
2004年 | 7423篇 |
2003年 | 6250篇 |
2002年 | 5633篇 |
2001年 | 4798篇 |
2000年 | 4552篇 |
1999年 | 5188篇 |
1998年 | 4552篇 |
1997年 | 4084篇 |
1996年 | 4248篇 |
1995年 | 3534篇 |
1994年 | 3273篇 |
1993年 | 2693篇 |
1992年 | 2476篇 |
1991年 | 2111篇 |
1990年 | 1625篇 |
1989年 | 1184篇 |
1988年 | 950篇 |
1987年 | 741篇 |
1986年 | 726篇 |
1985年 | 616篇 |
1984年 | 427篇 |
1983年 | 308篇 |
1982年 | 263篇 |
1981年 | 175篇 |
1980年 | 128篇 |
1979年 | 66篇 |
1978年 | 40篇 |
1976年 | 42篇 |
1974年 | 50篇 |
1957年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
191.
192.
193.
194.
Floquet engineering appears as a new protocol for designing topological states of matter,and features anomalous edge modes pinned at quasi-energy π/T with vanished topological index.We propose how to predict the anomalous edge modes via the bulk Hamiltonian in frequency space,and use Zak phase to quantitatively index the topological properties.The above methods are clarified by the example of time periodic Kitaev chain with chemical potential of harmonic driving and pulse driving,and topological phase transitions are manifested at different driving frequencies. 相似文献
195.
In this paper,we investigate the non-autonomous Hamilton-Jacobi equation ■ where H is 1-periodic with respect to t and M is a compact Riemannian manifold without boundary.We obtain the viscosity solution denoted by T_(t_0)~tφ(x) and show T_(t_0)~tφ(x) converges uniformly to a time-periodic viscosity solution u~*(x,t) of ?_tu+H(t,x,?_xu,u)=0. 相似文献
196.
DFT mechanistic study of the H2‐assisted chain transfer copolymerization of propylene and p‐methylstyrene catalyzed by zirconocene complex 下载免费PDF全文
Cheng‐Gen Zhang Shu‐Yuan Yu Liaoyun Zhang Huayi Li Zhi‐Xiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2015,53(4):576-585
DFT computations have been performed to investigate the mechanism of H2‐assisted chain transfer strategy to functionalize polypropylene via Zr‐catalyzed copolymerization of propylene and p‐methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2‐insertion over 2,1‐insertion both kinetically and thermodynamically, explaining the observed 1,2‐insertion regioselectivity for propylene insertion. (ii) The 2,1‐inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2‐insertion. The observation of 2,1‐insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H2 can react with the deactivated [Zr]?pMS?PPn facilely, which displace functionalized pMS?PPn chain and regenerate [Zr]? H active catalyst to continue copolymerization. The effects of counterions are also discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 576–585 相似文献
197.
Zhang Kailun Wu Hongjuan Wang Tian Yao Meng Xie Jixing Jiao Yunhong 《Journal of Thermal Analysis and Calorimetry》2021,145(6):3067-3075
Journal of Thermal Analysis and Calorimetry - A phosphazene-based flame retardant (PBFA) was synthesized by hexachlorocyclotriphosphazene and N-aminoethylpiperazine. To improve the flame retardancy... 相似文献
198.
Rong Yin Jihui Zhang Xudong Shang 《Mathematical Methods in the Applied Sciences》2020,43(15):8736-8752
This paper is dedicated to studying the following Schrödinger–Poisson system Under some different assumptions on functions V(x), K(x), a(x) and f(u), by using the variational approach, we establish the existence of positive ground state solutions. 相似文献
199.
200.
Shi-Tao Han Hong-Ying Duan Lan-Yun Chen Dr. Tian-Guang Zhan Dr. Li-Juan Liu Li-Chun Kong Prof. Kang-Da Zhang 《化学:亚洲杂志》2021,16(23):3886-3889
A photo-switchable hetero-complementary quadruple H-bonding array, which consists of an azobenzene-derived ureidopyrimidinone (UPy) module ( Azo-UPy ) and a nonphotoactive diamidonaphthyridine (DAN) derivative ( Napy-1 ), is constructed based on a reversible photo-locking approach. Upon UV (390 nm)/Vis (460 nm) light irradiations, photo-switchable quadruple H-bonded dimerization between Azo-UPy and Napy-1 can be achieved with exhibiting 4.8×104-fold differences in binding strength (ON/OFF ratios). Furthermore, smart polymeric gels with unique photo-controlled macroscopic self-assembly behavior can be fabricated by introducing such quadruple H-bonding array as photo-regulable noncovalent interfacial connections. 相似文献