全文获取类型
收费全文 | 143777篇 |
免费 | 12341篇 |
国内免费 | 11543篇 |
专业分类
化学 | 48873篇 |
晶体学 | 516篇 |
力学 | 12303篇 |
综合类 | 2487篇 |
数学 | 63250篇 |
物理学 | 40232篇 |
出版年
2023年 | 1159篇 |
2022年 | 1703篇 |
2021年 | 3231篇 |
2020年 | 3175篇 |
2019年 | 3332篇 |
2018年 | 3007篇 |
2017年 | 3428篇 |
2016年 | 3878篇 |
2015年 | 3549篇 |
2014年 | 5356篇 |
2013年 | 10344篇 |
2012年 | 5998篇 |
2011年 | 7008篇 |
2010年 | 6286篇 |
2009年 | 8055篇 |
2008年 | 8778篇 |
2007年 | 9046篇 |
2006年 | 7996篇 |
2005年 | 6910篇 |
2004年 | 6151篇 |
2003年 | 6177篇 |
2002年 | 8141篇 |
2001年 | 5129篇 |
2000年 | 4574篇 |
1999年 | 4041篇 |
1998年 | 3846篇 |
1997年 | 3115篇 |
1996年 | 2788篇 |
1995年 | 2406篇 |
1994年 | 2198篇 |
1993年 | 1829篇 |
1992年 | 1694篇 |
1991年 | 1366篇 |
1990年 | 1150篇 |
1989年 | 927篇 |
1988年 | 886篇 |
1987年 | 721篇 |
1986年 | 683篇 |
1985年 | 851篇 |
1984年 | 748篇 |
1983年 | 391篇 |
1982年 | 679篇 |
1981年 | 895篇 |
1980年 | 767篇 |
1979年 | 746篇 |
1978年 | 585篇 |
1977年 | 491篇 |
1976年 | 415篇 |
1974年 | 191篇 |
1973年 | 262篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
11.
对人教版高中化学教科书新设计的“研究与实践”栏目的主题内容、功能价值进行分析,就如何充分发挥该栏目的教学功能和价值,发展学生的化学学科核心素养,提出了创设教学情境线索、开发为研究性学习课题、开发为校本选修课程、开发为STEM课程等实施策略。 相似文献
12.
13.
《Journal of Pure and Applied Algebra》2022,226(8):107024
We solve a combinatorial question concerning eigenvalues of the universal intertwining endomorphism of a subset representation. 相似文献
14.
The health monitoring has been studied to ensure integrity of design of engine structure by detection, quantification, and prediction of damages. Early detection of faults may allow the downtime of maintenance to be rescheduled, thus preventing sudden shutdown of machines. In cylinder pressure developed, vibrations and noise emissions data provide a rich source of information about condition of engines. Monitoring of vibrations and noise emissions are novel non-intrusive methodologies for which positioning of various transducers are important issue. The presented work shows applicability of these diagnosis methodologies adopted in case of diesel engines. The effects of changing various fuel injection parameters was analyzed. Scope of using non-intrusive technique has been analyzed by changing locations of microphone. Novelty of this worklies in exploring signal processing methods for various locations around the engine test set up. Various frequency ranges of contributing noise and vibration sources were identified. Time-Frequency analysis showed the onset of various cyclic. Based on the identification of various frequency bands, it is possible to device suitable filters in order to extract more information. 相似文献
15.
16.
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.
20.