全文获取类型
收费全文 | 185514篇 |
免费 | 16783篇 |
国内免费 | 14063篇 |
专业分类
化学 | 69082篇 |
晶体学 | 2484篇 |
力学 | 14904篇 |
综合类 | 2175篇 |
数学 | 53880篇 |
物理学 | 73835篇 |
出版年
2023年 | 1181篇 |
2022年 | 1902篇 |
2021年 | 3768篇 |
2020年 | 3631篇 |
2019年 | 3698篇 |
2018年 | 3475篇 |
2017年 | 3765篇 |
2016年 | 4214篇 |
2015年 | 3418篇 |
2014年 | 5672篇 |
2013年 | 9945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 | 3470篇 |
1995年 | 3702篇 |
1994年 | 3646篇 |
1993年 | 2891篇 |
1992年 | 2399篇 |
1991年 | 1798篇 |
1990年 | 1509篇 |
1989年 | 1238篇 |
1988年 | 1188篇 |
1987年 | 993篇 |
1986年 | 737篇 |
1985年 | 1560篇 |
1984年 | 1174篇 |
1983年 | 812篇 |
1982年 | 1117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 15 毫秒
11.
12.
13.
14.
15.
将有机物2,5-二溴对苯二甲酸(H2L1)和2,2′-联吡啶(L2)作为双配体,使用溶剂热法和七水合硫酸锌(ZnSO4·7H2O)、六水合硝酸钴(Co(NO3)2·6H2O)分别反应,得到配合物[Zn(L1)(L2)(H2O)]n(1)和配合物[Co(L1)(L2)(H2O)]n(2)。采用单晶X射线衍射、元素分析、红外光谱、紫外光谱、荧光光谱、热重分析等测试方法对这两种物质进行分析研究。单晶测试结果表明配合物1是单斜晶系,以Zn2+配位连接L2-1与L2形成一维链状结构,各条链在分子间氢键和π…π共轭作用下有规律地堆叠形成三维网络结构。配合物2是三斜晶系,Co1离子和Co1i离子由H2L1上的羧酸氧原子O4和O4i连接,形成双齿螯合的配位结构单元,以Co2+配位连接 L2-1和L2形成二维网格结构,各层在O—H…O分子间氢键和范德瓦耳斯力作用下有规律的堆叠形成三维网络结构。配合物1和2均含有芳香杂环、羧基杂环和氮杂环,具有良好的荧光性质和热稳定性,最大发射波长分别为345 nm和333 nm。 相似文献
16.
We propose a conjecture on the relative twist formula of l-adic sheaves, which can be viewed as a generalization of Kato—Saito's conjecture. We verify this conjecture under some transversal assumptions. We also define a relative cohomological characteristic class and prove that its formation is compatible with proper push-forward. A conjectural relation is also given between the relative twist formula and the relative cohomological characteristic class. 相似文献
17.
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
18.
19.
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
20.