全文获取类型
收费全文 | 77854篇 |
免费 | 11813篇 |
国内免费 | 8763篇 |
专业分类
化学 | 53825篇 |
晶体学 | 881篇 |
力学 | 5105篇 |
综合类 | 657篇 |
数学 | 9496篇 |
物理学 | 28466篇 |
出版年
2024年 | 80篇 |
2023年 | 1558篇 |
2022年 | 1707篇 |
2021年 | 2413篇 |
2020年 | 2971篇 |
2019年 | 2922篇 |
2018年 | 2579篇 |
2017年 | 2343篇 |
2016年 | 3393篇 |
2015年 | 3503篇 |
2014年 | 4173篇 |
2013年 | 5543篇 |
2012年 | 6719篇 |
2011年 | 6912篇 |
2010年 | 4861篇 |
2009年 | 4732篇 |
2008年 | 4943篇 |
2007年 | 4387篇 |
2006年 | 4193篇 |
2005年 | 3673篇 |
2004年 | 2958篇 |
2003年 | 2314篇 |
2002年 | 2055篇 |
2001年 | 1879篇 |
2000年 | 1608篇 |
1999年 | 1694篇 |
1998年 | 1415篇 |
1997年 | 1197篇 |
1996年 | 1273篇 |
1995年 | 1135篇 |
1994年 | 1080篇 |
1993年 | 936篇 |
1992年 | 809篇 |
1991年 | 727篇 |
1990年 | 586篇 |
1989年 | 510篇 |
1988年 | 382篇 |
1987年 | 359篇 |
1986年 | 314篇 |
1985年 | 313篇 |
1984年 | 208篇 |
1983年 | 183篇 |
1982年 | 146篇 |
1981年 | 112篇 |
1980年 | 84篇 |
1978年 | 56篇 |
1977年 | 52篇 |
1976年 | 50篇 |
1975年 | 57篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Effective suppression of beta oscillation in Parkinsonian state via a noisy direct delayed feedback control scheme 下载免费PDF全文
This work explores the function of the noisy direct delayed feedback(NDDF)control strategy in suppressing the pathological oscillations in the basal ganglia(BG)with Parkinson’s disease(PD).Deep brain stimulation(DBS)alleviates the PD state fantastically.However,due to its unclear mechanism and open-loop characteristic,it is challenging to further improve its effects with lower energy expenditure.The noise stimulus performs competitively in alleviating the PD state theoretically,but it cannot adapt to the neural condition timely and automatically due to its open-loop control scheme.The direct delayed feedback(DDF)control strategy is able to disturb excessive synchronous effectively.Therefore,the NDDF control strategy is proposed and researched based on a BG computational model,which can reflect the intrinsic properties of the BG neurons and their connections with thalamic neurons.Simulation results show that the NDDF control strategy with optimal parameters is effective in removing the pathological beta oscillations.By comparison,we find the NDDF control strategy performs more excellent than DDF in alleviating PD state.Additionally,we define the multiple-NDDF control strategy and find that the multiple-NDDF with appropriate parameters performs better than NDDF.The obtained results contribute to the cure for PD symptoms by optimizing the noise-induced improvement of the BG dysfunction. 相似文献
72.
Nonlinear Dynamics - Nonlinear vibration isolation provides with an effective way for vibration reduction with broad band and high efficiency. This investigation focuses on the dynamic effects of a... 相似文献
73.
Zhang Ya-Li Han Rong-Sheng Chen Liang 《International Journal of Theoretical Physics》2021,60(4):1384-1398
International Journal of Theoretical Physics - In this work, we give an analytical derivation of the reduced density matrix between two qubits in a cavity field, which is described by the quantum... 相似文献
74.
The Ramanujan Journal - Inspired by the work of Lang–Trotter on the densities of primes with fixed Frobenius traces for elliptic curves defined over $${\mathbb {Q}}$$ and by the subsequent... 相似文献
75.
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
76.
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
77.
Yuan Xin Zhang Shuren Zhong Xuanmeng Yuan Hao Song Dongfan Wang Xiaoyu Yu Hanyang Guo Zijian 《中国科学:化学(英文版)》2022,65(10):1978-1984
Science China Chemistry - Oncogenic KRAS reprograms pancreatic ductal adenocarcinoma (PDAC) cells to a state that is awfully resistant to apoptosis. An alternative coping strategy is to trigger a... 相似文献
78.
79.
Science China Chemistry - 相似文献
80.
直拉硅单晶的生长过程涉及多场多相耦合与复杂的物理化学变化,其中工艺参数的波动是导致晶体直径不均匀的重要原因,如何实现工艺参数的控制以获得理想的、均匀的晶体直径具有重要的研究意义。本文分析现有控制方法存在不稳定以及控制效果不佳的问题后,提出基于贝叶斯参数优化的无模型自适应控制模型来控制硅单晶生长过程中的晶体直径。首先以坩埚上升速度与加热器的功率作为控制输入参数,晶体直径作为输出,搭建无模型自适应控制模型,并分析算法的稳定性。其次将控制模型进行仿真实验,发现硅单晶直径控制模型中不同的超参数设定会影响控制过程的迭代次数以及控制效果。最后,利用贝叶斯优化超参数的取值范围,并进行最终的仿真实验,结果表明,经贝叶斯参数优化后的控制模型计算快、迭代次数少,输出的晶体直径稳定,同时将生长工艺参数控制在实际生产要求范围内。因此,基于贝叶斯参数优化的无模型自适应控制实现了硅单晶直径均匀稳定的有效控制,具有结合工程背景的实际应用前景。 相似文献