全文获取类型
收费全文 | 49049篇 |
免费 | 7795篇 |
国内免费 | 5533篇 |
专业分类
化学 | 26097篇 |
晶体学 | 519篇 |
力学 | 2468篇 |
综合类 | 285篇 |
数学 | 4427篇 |
物理学 | 15169篇 |
无线电 | 13412篇 |
出版年
2024年 | 238篇 |
2023年 | 1191篇 |
2022年 | 1472篇 |
2021年 | 1799篇 |
2020年 | 1874篇 |
2019年 | 1720篇 |
2018年 | 1513篇 |
2017年 | 1483篇 |
2016年 | 2077篇 |
2015年 | 2258篇 |
2014年 | 2674篇 |
2013年 | 3292篇 |
2012年 | 4017篇 |
2011年 | 4090篇 |
2010年 | 2910篇 |
2009年 | 3033篇 |
2008年 | 3201篇 |
2007年 | 2891篇 |
2006年 | 2809篇 |
2005年 | 2213篇 |
2004年 | 1691篇 |
2003年 | 1502篇 |
2002年 | 1394篇 |
2001年 | 1177篇 |
2000年 | 1165篇 |
1999年 | 1121篇 |
1998年 | 1018篇 |
1997年 | 903篇 |
1996年 | 923篇 |
1995年 | 809篇 |
1994年 | 689篇 |
1993年 | 537篇 |
1992年 | 557篇 |
1991年 | 419篇 |
1990年 | 348篇 |
1989年 | 279篇 |
1988年 | 237篇 |
1987年 | 188篇 |
1986年 | 176篇 |
1985年 | 162篇 |
1984年 | 112篇 |
1983年 | 74篇 |
1982年 | 68篇 |
1981年 | 39篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1959年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Xu Mengtao Li Changyou Sun Yang Yang Tianzhi Zhang Hongzhuang Liu Zhendong Liu Haiyang Li Zhenyuan Zhang Yimin 《Nonlinear dynamics》2021,105(4):3061-3092
Nonlinear Dynamics - Investigation of the dynamic characteristics of linear guideway is essential for enhancing structural performance of machine tools. However, few mechanical models are... 相似文献
12.
Interactions of the vector breathers for the coupled Hirota system with $$4\times 4$$ 4 × 4 Lax pair
Nonlinear Dynamics - In this paper, we investigate the interactions of the vector breathers for the coupled Hirota system with $$4\times 4$$ Lax pair. Firstly, we give the first-order breather... 相似文献
13.
Dr. Yong-Sheng Wei Dr. Liming Sun Miao Wang Dr. Jinhua Hong Dr. Lianli Zou Hongwen Liu Dr. Yu Wang Dr. Mei Zhang Dr. Zheng Liu Prof. Yinwei Li Prof. Satoshi Horike Prof. Kazu Suenaga Prof. Qiang Xu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(37):16147-16156
Understanding the thermal aggregation behavior of metal atoms is important for the synthesis of supported metal clusters. Here, derived from a metal–organic framework encapsulating a trinuclear FeIII2FeII complex (denoted as Fe3) within the channels, a well-defined nitrogen-doped carbon layer is fabricated as an ideal support for stabilizing the generated iron nanoclusters. Atomic replacement of FeII by other metal(II) ions (e.g., ZnII/CoII) via synthesizing isostructural trinuclear-complex precursors (Fe2Zn/Fe2Co), namely the “heteroatom modulator approach”, is inhibiting the aggregation of Fe atoms toward nanoclusters with formation of a stable iron dimer in an optimal metal–nitrogen moiety, clearly identified by direct transmission electron microscopy and X-ray absorption fine structure analysis. The supported iron dimer, serving as cooperative metal–metal site, acts as efficient oxygen evolution catalyst. Our findings offer an atomic insight to guide the future design of ultrasmall metal clusters bearing outstanding catalytic capabilities. 相似文献
14.
Ruirui Xu Kun Wang Haoying Liu Prof. Dr. Weijun Tang Dr. Huaming Sun Prof. Dr. Dong Xue Prof. Dr. Jianliang Xiao Prof. Dr. Chao Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(49):22143-22148
A ruthenium-catalyzed formal anti-Markovnikov hydroamination of allylic alcohols for the synthesis of chiral γ-amino alcohols is presented. Proceeding via an asymmetric hydrogen-borrowing process, the catalysis allows racemic secondary allylic alcohols to react with various amines, affording enantiomerically enriched chiral γ-amino alcohols with broad substrate scope and excellent enantioselectivities (68 examples, up to >99 % ee). 相似文献
15.
16.
The existing analytical average bit error rate (ABER) expression of conventional generalised spatial modulation (CGSM) does not agree well with the Monte Carlo simulation results in the low signal‐to‐noise ratio (SNR) region. Hence, the first contribution of this paper is to derive a new and easy way to evaluate analytical ABER expression that improves the validation of the simulation results at low SNRs. Secondly, a novel system termed CGSM with enhanced spectral efficiency (CGSM‐ESE) is presented. This system is realised by applying a rotation angle to one of the two active transmit antennas. As a result, the overall spectral efficiency is increased by 1 bit/s/Hz when compared with the equivalent CGSM system. In order to validate the simulation results of CGSM‐ESE, the third contribution is to derive an analytical ABER expression. Finally, to improve the ABER performance of CGSM‐ESE, three link adaptation algorithms are developed. By assuming full knowledge of the channel at the receiver, the proposed algorithms select a subset of channel gain vector (CGV) pairs based on the Euclidean distance between all CGV pairs, CGV splitting, CGV amplitudes, or a combination of these. 相似文献
17.
18.
19.
20.