全文获取类型
收费全文 | 186481篇 |
免费 | 16851篇 |
国内免费 | 14066篇 |
专业分类
化学 | 69965篇 |
晶体学 | 2484篇 |
力学 | 14934篇 |
综合类 | 2175篇 |
数学 | 53886篇 |
物理学 | 73954篇 |
出版年
2023年 | 1181篇 |
2022年 | 2384篇 |
2021年 | 3768篇 |
2020年 | 3630篇 |
2019年 | 3723篇 |
2018年 | 3475篇 |
2017年 | 3765篇 |
2016年 | 4214篇 |
2015年 | 3418篇 |
2014年 | 5672篇 |
2013年 | 9947篇 |
2012年 | 6531篇 |
2011年 | 7659篇 |
2010年 | 7523篇 |
2009年 | 13157篇 |
2008年 | 14205篇 |
2007年 | 12912篇 |
2006年 | 11224篇 |
2005年 | 8762篇 |
2004年 | 8239篇 |
2003年 | 7833篇 |
2002年 | 10614篇 |
2001年 | 6792篇 |
2000年 | 6162篇 |
1999年 | 5717篇 |
1998年 | 4987篇 |
1997年 | 3819篇 |
1996年 | 3499篇 |
1995年 | 3754篇 |
1994年 | 3697篇 |
1993年 | 2943篇 |
1992年 | 2458篇 |
1991年 | 1830篇 |
1990年 | 1555篇 |
1989年 | 1290篇 |
1988年 | 1230篇 |
1987年 | 1006篇 |
1986年 | 750篇 |
1985年 | 1577篇 |
1984年 | 1185篇 |
1983年 | 833篇 |
1982年 | 1131篇 |
1981年 | 1222篇 |
1980年 | 1066篇 |
1979年 | 965篇 |
1978年 | 851篇 |
1977年 | 739篇 |
1976年 | 670篇 |
1974年 | 401篇 |
1973年 | 561篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
11.
12.
13.
14.
Pattern transition and regulation in a subthalamopallidal network under electromagnetic effect 下载免费PDF全文
Although the significant roles of magnetic induction and electromagnetic radiation in the neural system have been widely studied, their influence on Parkinson's disease (PD) has yet to be well explored. By virtue of the magnetic flux variable, this paper studies the transition of firing patterns induced by magnetic induction and the regulation effect of external magnetic radiation on the firing activities of the subthalamopallidal network in basal ganglia. We find: (i) The network reproduces five typical waveforms corresponding to the severity of symptoms: weak cluster, episodic, continuous cluster, episodic, and continuous wave. (ii) Magnetic induction is a double-edged sword for the treatment of PD. Although the increase of magnetic coefficient may lead the physiological firing activity to transfer to pathological firing activity, it also can regulate the pathological intensity firing activity with excessive β-band power transferring to the physiological firing pattern with weak β-band power. (iii) External magnetic radiation could inhibit continuous tremulous firing and β-band power of subthalamic nucleus (STN), which means the severity of symptoms weakened. Especially, the bi-parameter plane of the regulation region shows that a short pulse period of magnetic radiation and a medium level of pulse percentage can well regulate pathological oscillation. This work helps to understand the firing activity of the subthalamopallidal network under electromagnetic effect. It may also provide insights into the mechanisms behind the electromagnetic therapy of PD-related firing activity. 相似文献
15.
16.
Kai Cheng Xiao-Shuai Zhang Jie An Cheng Li Ruo-Yun Zhang Run Ye Prof. Dr. Bang-Jiao Ye Prof. Dr. Bo Liu Prof. Dr. Yuan-Di Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(31):7553-7560
Given their superior penetration depths, photosensitizers with longer absorption wavelengths present broader application prospects in photodynamic therapy (PDT). Herein, Ag2S quantum dots were discovered, for the first time, to be capable of killing tumor cells through the photodynamic route by near-infrared light irradiation, which means relatively less excitation of the probe compared with traditional photosensitizers absorbing short wavelengths. On modification with polydopamine (PDA), PDA-Ag2S was obtained, which showed outstanding capacity for inducing reactive oxygen species (increased by 1.69 times). With the addition of PDA, Ag2S had more opportunities to react with surrounding O2, which was demonstrated by typical triplet electron spin resonance (ESR) analysis. Furthermore, the PDT effects of Ag2S and PDA-Ag2S achieved at longer wavelengths were almost identical to the effects produced at 660 nm, which was proved by studies in vitro. PDA-Ag2S showed distinctly better therapeutic effects than Ag2S in experiments in vivo, which further validated the enhanced regulatory effect of PDA. Altogether, a new photosensitizer with longer absorption wavelength was developed by using the hitherto-unexplored photodynamic function of Ag2S quantum dots, which extended and enhanced the regulatory effect originating from PDA. 相似文献
17.
18.
In this work, a vanillin complex is immobilized onto MCM-41 and characterized by FT-IR, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, and BET techniques. This supported Schiff base complex was found to be an efficient and recoverable catalyst for the chemoselective oxidation of sulfides into sulfoxides and thiols into their corresponding disulfides (using hydrogen peroxide as a green oxidant) and also a suitable catalyst for the preparation of 2,3-dihydroquinazolin-4(1H)-one derivatives in water at 90°C. Using this protocol, we show that a variety of disulfides, sulfoxides, and 2,3-dihydroquinazolin-4(1H)-one derivatives can be synthesized in green conditions. The catalyst can be recovered and recycled for further reactions without appreciable loss of catalytic performance. 相似文献
19.
20.
We consider concentrated vorticities for the Euler equation on a smooth domain in the form of supported on well-separated vortical domains , , of small diameters . A conformal mapping framework is set up to study this free boundary problem with being part of unknowns. For any given vorticities and small , through a perturbation approach, we obtain such piecewise constant steady vortex patches as well as piecewise smooth Lipschitz steady vorticities, both concentrated near non-degenerate critical configurations of the Kirchhoff–Routh Hamiltonian function. When vortex patch evolution is considered as the boundary dynamics of , through an invariant subspace decomposition, it is also proved that the spectral/linear stability of such steady vortex patches is largely determined by that of the 2N-dimensional linearized point vortex dynamics, while the motion is highly oscillatory in the 2N-codim directions corresponding to the vortical domain shapes. 相似文献