全文获取类型
收费全文 | 76144篇 |
免费 | 11561篇 |
国内免费 | 8399篇 |
专业分类
化学 | 52338篇 |
晶体学 | 793篇 |
力学 | 5044篇 |
综合类 | 667篇 |
数学 | 9526篇 |
物理学 | 27736篇 |
出版年
2024年 | 61篇 |
2023年 | 1442篇 |
2022年 | 1513篇 |
2021年 | 2207篇 |
2020年 | 2766篇 |
2019年 | 2690篇 |
2018年 | 2392篇 |
2017年 | 2116篇 |
2016年 | 3318篇 |
2015年 | 3358篇 |
2014年 | 4054篇 |
2013年 | 5372篇 |
2012年 | 6497篇 |
2011年 | 6816篇 |
2010年 | 4719篇 |
2009年 | 4677篇 |
2008年 | 4977篇 |
2007年 | 4462篇 |
2006年 | 4193篇 |
2005年 | 3591篇 |
2004年 | 2931篇 |
2003年 | 2272篇 |
2002年 | 2211篇 |
2001年 | 1858篇 |
2000年 | 1632篇 |
1999年 | 1673篇 |
1998年 | 1408篇 |
1997年 | 1211篇 |
1996年 | 1276篇 |
1995年 | 1144篇 |
1994年 | 1074篇 |
1993年 | 937篇 |
1992年 | 800篇 |
1991年 | 703篇 |
1990年 | 574篇 |
1989年 | 502篇 |
1988年 | 384篇 |
1987年 | 364篇 |
1986年 | 306篇 |
1985年 | 313篇 |
1984年 | 209篇 |
1983年 | 184篇 |
1982年 | 148篇 |
1981年 | 120篇 |
1980年 | 85篇 |
1979年 | 56篇 |
1978年 | 62篇 |
1977年 | 54篇 |
1975年 | 58篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Unified convergence analysis of a second-order method of multipliers for nonlinear conic programming
Science China Mathematics - In this paper, we accomplish the unified convergence analysis of a second-order method of multipliers (i.e., a second-order augmented Lagrangian method) for solving the... 相似文献
72.
Li-Hua Su Tian-Ze Li Yun-Bao Ma Chang-An Geng Xiao-Yan Huang Xin Zhang Zhen Gao Ji-Jun Chen 《中国化学》2022,40(1):104-114
Inspired by the intriguing structures and remarkable activities of sesquiterpenoid dimers,12 new sesquiterpenoid dimers,artematrovirenolides A—D(1—4)and artematrolides S—Z(8—12),were isolated from the EtOAc fraction of Artemisia atrovirens through a bioactivity-guided approach.Their structures were elucidated by comprehensive spectroscopic data and absolute configuration was assigned based on single crystal X-ray diffraction data and ECD calculations.Structurally,all compounds are presumably formed via[4+2]cycloaddition involving three connecting model.Compounds 1—4 are four novel hetero-dimeric[4+2]Diels-Alder adducts dimerized from a rotundane-type unit and a guaiane-type monomer,and compounds 5—12 are eight new homo-dimeric[4+2]adducts derived from two guaianolide moieties.A putative biosynthetic pathway for compounds 1—4 was also proposed.Compounds 4,6,7,and 10 demonstrated moderate cytotoxicity against HepG2,SMMC-7721,and Huh7 cell lines with IC50 values ranging from 9.3 to 62.3μmol/L.Interestingly,compounds 5 and 11 manifested cytotoxicity with IC50 values of 13.6 and 12.8(HepG2),18.5 and 13.1(SMMC-7721),and 16.5 and 19.4μmol/L(Huh7),respectively,which were equivalent to the positive control,sorafenib.This investigation suggests that compounds 5 and 11 might be considered as potent antihepatoma candidates and deserve further structural modification and mechanism study. 相似文献
73.
Science China Chemistry - 相似文献
74.
Nonlinear Dynamics - Contact and friction phenomena in clearance joint adversely affect mechanical performance and may even result in chaos within the mechanism. Analysis of nonlinear... 相似文献
75.
Nonlinear Dynamics - Based on a mixed control strategy, this study addresses the finite-time stabilization with extended dissipativity for Markov jump systems (MJSs) with unreliable... 相似文献
76.
Theoretical study of (e,2e) triple differential cross sections of pyrimidine and tetrahydrofurfuryl alcohol molecules using multi-center distorted-wave method 下载免费PDF全文
We report theoretical studies of electron impact triple differential cross sections of two bio-molecules,pyrimidine and tetrahydrofurfuryl alcohol,in the coplanar asymmetric kinematic conditions with the impact energy of 250 eV and ejected electron energy of 20 eV at three scattering angles of-5°,-10°,and-15°.Present multi-center distorted-wave method well describes the experimental data,which was obtained by performing(e,2e)experiment.The calculations show that the secondary electron produced by the primary impact electron is strongly influenced by the molecular ionic multi-center potential,which must be considered when the low energy electron interacts with DNA analogues. 相似文献
77.
随着光伏行业的快速发展, 对硅单晶的品质和长晶装备的稳定性的要求也不断提高。直拉法是生产硅单晶的主要方法,通过提高单晶炉副室的高度以扩大单晶硅的生产规模。由于副室高度的大幅增加,且单晶炉提拉头质心相对于旋转轴心有一定距离,对单晶炉整体稳定性有较大影响,从而降低了单晶硅的生产质量。针对此问题,对单晶炉建立可靠的力学分析模型,采用数值仿真方法,对单晶炉整体进行动力学响应分析,计算得到副室高度增加后的单晶炉工作时中钨丝绳下端晶棒的运动规律以及最大摆动幅度,为改进设计提供依据。数值仿真分析表明提高单晶炉副室高度后,提拉头较大的质心偏心是单晶炉提拉系统发生摆动的主要原因。在此基础上提出在提拉头上添加质心调节装置,通过控制系统调节可保证提拉头质心位置在旋转轴线上以降低提拉系统的摆动。 相似文献
78.
Hu Yinlong Hua Tianyang Chen Michael Z. Q. Shi Shang Sun Yonghui 《Nonlinear dynamics》2021,105(1):99-112
Nonlinear Dynamics - In this paper, the instability of semi-active control systems caused by the utilization of semi-active inerters is analyzed. The purpose of this study is to demonstrate the... 相似文献
79.
80.
Wang Zhenya Chen Hui Yao Ligang Chen Xu Qi Xiaoli Zhang Jun 《Nonlinear dynamics》2021,106(3):2107-2130
Nonlinear Dynamics - Fault diagnosis of critical rotating machinery components is necessary to ensure safe operation. However, the commonly used rotating machinery fault diagnosis methods are... 相似文献