全文获取类型
收费全文 | 80531篇 |
免费 | 737篇 |
国内免费 | 633篇 |
专业分类
化学 | 25999篇 |
晶体学 | 826篇 |
力学 | 6826篇 |
综合类 | 8篇 |
数学 | 32313篇 |
物理学 | 15929篇 |
出版年
2023年 | 42篇 |
2022年 | 49篇 |
2021年 | 86篇 |
2020年 | 114篇 |
2019年 | 110篇 |
2018年 | 10500篇 |
2017年 | 10322篇 |
2016年 | 6173篇 |
2015年 | 987篇 |
2014年 | 426篇 |
2013年 | 561篇 |
2012年 | 4015篇 |
2011年 | 10725篇 |
2010年 | 5768篇 |
2009年 | 6169篇 |
2008年 | 6748篇 |
2007年 | 8906篇 |
2006年 | 342篇 |
2005年 | 1425篇 |
2004年 | 1603篇 |
2003年 | 2072篇 |
2002年 | 1068篇 |
2001年 | 320篇 |
2000年 | 347篇 |
1999年 | 201篇 |
1998年 | 232篇 |
1997年 | 178篇 |
1996年 | 240篇 |
1995年 | 144篇 |
1994年 | 111篇 |
1993年 | 128篇 |
1992年 | 76篇 |
1991年 | 86篇 |
1990年 | 63篇 |
1989年 | 87篇 |
1988年 | 73篇 |
1987年 | 66篇 |
1986年 | 78篇 |
1985年 | 62篇 |
1984年 | 55篇 |
1983年 | 38篇 |
1982年 | 46篇 |
1981年 | 39篇 |
1980年 | 46篇 |
1979年 | 46篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40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 15 毫秒
1.
Ya-Shan Huang Yuan Xue Prof. Alvaro Muñoz-Castro Prof. Dr. Ivan A. Popov Prof. Dr. Zhong-Ming Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(62):e202202192
During the past two decades, single-atom-centered medium-sized germanium clusters [M@Gen] (M=transition metals, n>12) have been extensively explored, both from theoretical perspectives and experimental gas-phase syntheses. However, the actual structural arrangements of the Ge13 and Ge14 endohedral cages are still ambiguous and have long remained an unresolved problem for experimental implementation. In this work, we successfully synthesize 13-/14-vertex Ge clusters [Nb@Ge13]3− ( 1 ) and [Nb@Ge14]3− ( 2 ), which are structurally characterized and exhibit unprecedented topologies, neither classical deltahedra nor 3-connected polyhedral structures. Theoretical analysis indicates that the major stabilization of the Ge backbones arises due to the substantial interaction of Ge 4p-AOs with the endohedral Nb 4d-AOs through three/four-center two-electron bonds with an enhanced electron density accumulated over the shortest Nb−Ge13 contact in 1 . Low occupancies of the direct two-center two-electron (2c–2e) Nb−Ge and Ge−Ge σ bonds point to a considerable degree of electron delocalization over the Ge cages revealing their electron deficiency. 相似文献
2.
Nonlinear Dynamics - In order to solve the constrained-input problem and reduce the computing resources, a novel event-triggered optimal control method is proposed for a class of discrete-time... 相似文献
3.
Muše Ante Jurić Zdeslav Račić Nikola Radica Gojmir 《Journal of Thermal Analysis and Calorimetry》2020,141(1):337-350
Journal of Thermal Analysis and Calorimetry - The main energy source in marine industry is fossil fuel. Diesel engines are main power supply in sea transport at present times and will also be in... 相似文献
4.
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
5.
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
6.
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
7.
8.
Dr. Jie Shen Dr. Jingrong Fan Ruijuan Ye Dr. Ning Li Prof. Yuguang Mu Dr. Huaqiang Zeng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13430-13436
Synthetic strategies that enable rapid construction of covalent organic nanotubes with an angstrom-scale tubular pore remain scarcely reported. Reported here is a remarkably simple and mild one-pot polymerization protocol, employing POCl3 as the polymerization agent. This protocol efficiently generates polypyridine amide foldamer-based covalent organic nanotubes with a 2.8 nm length at a yield of 50 %. Trapping single-file water chains in the 2.8 Å tubular cavity, rich in hydrogen-bond donors and acceptors, these tubular polypyridine ensembles rapidly and selectively transport water at a rate of 1.6×109 H2O⋅S−1⋅channel−1 and protons at a speed as fast as gramicidin A, with a high rejection of ions. 相似文献
9.
10.
Zinovy Reichstein 《Archiv der Mathematik》2018,111(5):449-455
We use a recent advance in birational geometry to prove new lower bounds on the essential dimension of some finite groups. 相似文献