全文获取类型
收费全文 | 2443篇 |
免费 | 422篇 |
国内免费 | 283篇 |
专业分类
化学 | 1839篇 |
晶体学 | 32篇 |
力学 | 201篇 |
综合类 | 7篇 |
数学 | 304篇 |
物理学 | 765篇 |
出版年
2024年 | 5篇 |
2023年 | 59篇 |
2022年 | 64篇 |
2021年 | 93篇 |
2020年 | 124篇 |
2019年 | 80篇 |
2018年 | 104篇 |
2017年 | 89篇 |
2016年 | 121篇 |
2015年 | 150篇 |
2014年 | 147篇 |
2013年 | 196篇 |
2012年 | 198篇 |
2011年 | 229篇 |
2010年 | 145篇 |
2009年 | 131篇 |
2008年 | 154篇 |
2007年 | 142篇 |
2006年 | 123篇 |
2005年 | 99篇 |
2004年 | 74篇 |
2003年 | 70篇 |
2002年 | 89篇 |
2001年 | 67篇 |
2000年 | 52篇 |
1999年 | 50篇 |
1998年 | 49篇 |
1997年 | 40篇 |
1996年 | 35篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 15篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1964年 | 1篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有3148条查询结果,搜索用时 78 毫秒
91.
Periodic Solutions of Third-order Differential Equations with Finite Delay in Vector-valued Functional Spaces 下载免费PDF全文
In this paper, we study the well-posedness of the third-order differential equation with finite delay(P_3): αu'"(t) + u"(t) = Au(t) + Bu'(t) + Fut +f(t)(t ∈ T := [0,2π]) with periodic boundary conditions u(0) = u(2π), u'(0) = u"(2π),u"(0)=u"(2π) in periodic Lebesgue-Bochner spaces Lp(T;X) and periodic Besov spaces B_(p,q)~s(T;X), where A and B are closed linear operators on a Banach space X satisfying D(A) ∩ D(B) ≠ {0}, α≠ 0 is a fixed constant and F is a bounded linear operator from Lp([-2π, 0]; X)(resp. Bp,qs([-2π, 0]; X)) into X, ut is given by ut(s) = u(t + s) when s ∈ [-2π,0]. Necessary and sufficient conditions for the Lp-well-posedness(resp. B_(p,q)~s-well-posedness)of(P_3) are given in the above two function spaces. We also give concrete examples that our abstract results may be applied. 相似文献
92.
Dr. Hong Shang Yu Gu Prof. Yingbin Wang Dr. Zicheng Zuo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(24):5434-5440
Nonuniform nucleation is one of the major reasons for the dendric growth of metallic lithium, which leads to intractable problems in the efficiency, reversibility, and safety in Li-based batteries. To improve the deposition of metallic Li on Cu substrates, herein, a freestanding current collector (NGDY@CuNW) is formed by coating pyridinic nitrogen-doped graphdiyne (NGDY) nanofilms on 3D Cu nanowires (CuNWs). Theoretical predictions reveal that the introduction of nitrogen atoms in the 2D GDY can enhance the binding energy between the Li atom and GDY, therefore improving the lithiophilicity on the surface for uniform lithium nucleation and deposition. Accordingly, the deposited metallic Li on the NGDY@CuNW electrode exhibits a dendrite-free morphology, resulting in significant improvements in terms of the reversibility with a high coulombic efficiency (CE) and a long lifespan at high current density. Our research provides an efficient method to control the surface property of Cu, which also will be instructive for other metal batteries. 相似文献
93.
Manikandan Muthu Judy Gopal Shang Xiao Min Sechul Chun 《Applied biochemistry and biotechnology》2016,180(4):780-790
The feasibility of utilizing the antimicrobial activity of naturally available teas was studied. Eleven teas including 2 green teas and 9 other traditional Korean mixed teas were tested for their antimicrobial properties. Antibacterial and antifungal properties were assessed. The results showed that green teas possessed significant antifungal and antibacterial properties, while most of the mixed teas showed some amount of antifungal activity and almost insignificant antibacterial properties. Confocal microscopic imaging revealed mycelial damage as well as attack on sporophores rather than spores/spore germination to be the reason behind the antifungal activity. EGCG was identified as the crucial catechin for antimicrobial activity. The study confirmed that green tea had a clear edge over the traditional mixed teas when it comes to antimicrobial activity. 相似文献
94.
Jilei Wang Bing Wu Shang Li Yaning He 《Journal of polymer science. Part A, Polymer chemistry》2017,55(15):2450-2457
Using atom transfer radical polymerization (ATRP) and macromolecular azo coupling reaction, both o‐nitrobenzyl (ONB) group and azobenzene group were efficiently incorporated into the center of the amphiphilic diblock copolymer chain. The prepared diblock copolymer was well characterized by UV–vis, 1H NMR, and GPC methods. Self‐assembly of the amphiphilic copolymer in selected solvents can result in uniform self‐assembly aggregates. In the presence of external stimuli [upconversion nanoparticles (UCNPs)/NIR light or enzyme], the amphiphilic diblock copolymer chain could be broken by the cleavage of ONB or azobenzene group, which would lead to the disruption of the self‐assembly aggregates. This photo‐ and enzyme‐triggered disruption process was proved by using transmission electron microscopy (TEM) and GPC method. Fluorescence emission spectra measurements indicated that the release of Nile red, a hydrophobic dye, encapsulated by the self‐assembly aggregates, could be successfully realized under the NIR light and enzyme stimuli. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2450–2457 相似文献
95.
96.
97.
Highly efficient AgNO3‐catalyzed approach to 2‐(benzo[d]azol‐2‐yl)phenols from salicylaldehydes with 2‐aminothiophenol, 2‐aminophenol and benzene‐1,2‐diamine 下载免费PDF全文
A new, convenient and efficient AgNO3‐catalyzed strategy for the preparation of 2‐(benzo[d]azol‐2‐yl)phenol derivatives in good to excellent yields (63–98%) is described. The reaction proceeds via condensation/intramolecular nucleophilic addition/oxidation process between substituted salicylaldehydes and 2‐aminothiophenol, 2‐aminophenol or benzene‐1,2‐diamine under mild reaction conditions. Notably, this reaction utilizes cheap AgNO3 as a readily available and low‐cost benign oxidant at low catalyst loadings with excellent functional group tolerance. 相似文献
98.
99.
Dr. Zhen Lei Zong‐Jie Guan Dr. Xiao‐Li Pei Shang‐Fu Yuan Xian‐Kai Wan Jin‐Yuan Zhang Prof.Dr. Quan‐Ming Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(32):11156-11160
A red–near‐IR dual‐emissive nanocluster with the composition [Au10Ag2(2‐py?C≡C)3(dppy)6](BF4)5 ( 1 ; 2‐py?C≡C is 2‐pyridylethynyl, dppy=2‐pyridyldiphenylphosphine) has been synthesized. Single‐crystal X‐ray structural analysis reveals that 1 has a trigonal bipyramidal Au10Ag2 core that contains a planar Au4(2‐py?C≡C)3 unit sandwiched by two Au3Ag(dppy)3 motifs. Cluster 1 shows intense red–NIR dual emission in solution. The visible emission originates from metal‐to‐ligand charge transfer (MLCT) from silver atoms to phosphine ligands in the Au3Ag(dppy)3 motifs, and the intense NIR emission is associated with the participation of 2‐pyridylethynyl in the frontier orbitals of the cluster, which is confirmed by a time‐dependent density functional theory (TD‐DFT) calculation. 相似文献
100.
考虑一类带有非线性阻尼项和源项的四阶波动方程的初边值问题.通过结合Galerkin逼近,势井方法和单调紧致方法,在最少的先验估计下获得了整体解的存在性.此外,在初始能量为负的情况下,证明了存在有限时间内爆破的解. 相似文献