全文获取类型
收费全文 | 184319篇 |
免费 | 38527篇 |
国内免费 | 27319篇 |
专业分类
化学 | 123112篇 |
晶体学 | 2078篇 |
力学 | 12377篇 |
综合类 | 841篇 |
数学 | 22622篇 |
物理学 | 89135篇 |
出版年
2024年 | 615篇 |
2023年 | 2911篇 |
2022年 | 3940篇 |
2021年 | 4392篇 |
2020年 | 5439篇 |
2019年 | 5518篇 |
2018年 | 4966篇 |
2017年 | 5132篇 |
2016年 | 7322篇 |
2015年 | 7218篇 |
2014年 | 8245篇 |
2013年 | 11940篇 |
2012年 | 13798篇 |
2011年 | 15574篇 |
2010年 | 15501篇 |
2009年 | 15444篇 |
2008年 | 10125篇 |
2007年 | 8984篇 |
2006年 | 8271篇 |
2005年 | 7474篇 |
2004年 | 7111篇 |
2003年 | 5736篇 |
2002年 | 5360篇 |
2001年 | 5302篇 |
2000年 | 4320篇 |
1999年 | 4785篇 |
1998年 | 4083篇 |
1997年 | 3889篇 |
1996年 | 4264篇 |
1995年 | 4280篇 |
1994年 | 4191篇 |
1993年 | 3973篇 |
1992年 | 3492篇 |
1991年 | 3035篇 |
1990年 | 2531篇 |
1989年 | 2464篇 |
1988年 | 2271篇 |
1987年 | 1519篇 |
1986年 | 1577篇 |
1985年 | 1204篇 |
1984年 | 1192篇 |
1983年 | 527篇 |
1982年 | 1013篇 |
1981年 | 822篇 |
1980年 | 823篇 |
1979年 | 550篇 |
1978年 | 549篇 |
1977年 | 656篇 |
1976年 | 1062篇 |
1972年 | 546篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
单匝线圈在辐向磁场中的受力情况,很多教师都用纯数学方法(微元法)推导出其有效长度为线圈周长.文章用音频电流通过方形线圈,依次增加磁铁的个数让学生感觉音量的变化,并进一步合理外推出同样的结论.不仅能让学生体会基于实验合理外推这一科学的研究方法,还能让学生对扬声器的工作原理有清晰的认识. 相似文献
22.
Jiraya Kiriratnikom Xun Zhang Xiaohan Cao Bo Chu Chengjian Zhang Xinghong Zhang 《Journal of polymer science. Part A, Polymer chemistry》2022,60(15):2262-2268
Facile construction of sulfur-rich polymers using readily available raw chemicals is an area aggressively pursued but challenging. Herein we use common feedstocks of ethylene oxide (EO), propylene oxide (PO), and carbonyl sulfide (COS) to synthesize copoly(thioether)s which are traditionally produced from unpleasant and difficult to store episulfides. In this protocol, the EO/COS coupling selectively generates a pure poly(ethylene sulfide) (PES) with melting temperature (Tm) values up to 172°C and high yields up to 98%. The EO/PO/COS terpolymerization leads to the incorporation of soft poly(propylene sulfide) (PPS) and hard PES segments together, affording a random PES-co-PPS copoly(thioether) with the complete consumption of EO and PO. Additionally, by simply varying the EO/PO feeding ratio, the obtained copoly(thioether)s possess tunable thermal properties, Tm values in the range of 76–144°C, and excellent solubility. These copolymerizations are conducted in one-pot/one-step at industrially favored reaction temperatures of 100–120°C using catalysts of common organic bases, suggesting a facile and practical manner. Especially, the copoly(thioether) exhibits high refractive indices up to 1.68 owing to its high sulfur content, suggesting a broad application prospect in optical materials. 相似文献
23.
Journal of Visualization - Forecast calibration methods based on historical similar atmospheric state are effective means weather forecast accuracy. Conventional approaches search similar forecasts... 相似文献
24.
International Journal of Theoretical Physics - The thermal entanglement in the two-qubit Ising spin chain in the presence of the Dzyaloshinski-Moriya(DM) anisotropic antisymmetric interaction in a... 相似文献
25.
26.
Journal of Optimization Theory and Applications - We distinguish two kinds of piecewise linear functions and provide an interesting representation for a piecewise linear function between two normed... 相似文献
27.
Li Y. Shi W. H. Dong L. M. Xu S. X. Huang H. J. Yin J. R. 《Journal of Applied Spectroscopy》2022,89(3):534-541
Journal of Applied Spectroscopy - Sr3B2O6:Dy3+, Eu3+ single-matrix white-light-emitting materials are prepared using the high-temperature solid-state method. The microstructure, emission spectrum,... 相似文献
28.
Dr. Ruijuan Yao Prof. Di Liu Dr. Huihui Wan Dr. Yongqiang Mei Jiahui Wang Dr. Rui Cai Dr. Huimin Zhang Dr. Yuzhen Zhao Dr. Zemin He 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(71):e202202269
By linking the carbazole unit to the nitrogen atom of acridone through phenyl or pyridyl, two compounds, named 10-(4-(9H-carbazol-9-yl)phenyl)acridin-9(10H)-one (AC-Ph-Cz) and 10-(5-(9H-carbazol-9-yl)pyridin-2-yl)acridin-9(10H)-one (AC-Py-Cz) were designed and synthesized. These two materials, characterized with highly twisted and rigid structure, good thermal stability, and balanced carrier-transporting properties, were employed as host materials for green phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes (OLEDs). The carbazole group, despite its small contribution to the highest occupied molecular orbitals (HOMOs) of these two materials, plays an essential role as an intramolecular host in energy delivering and improving the hole transporting ability of these two hosts. The incorporation of the electron-deficient pyridyl group as a linking group slightly improves the electron transporting capability of AC-Py-Cz. The green phosphorescent OLED (PhOLED) based on AC-Py-Cz exhibited excellent device performance with a turn-on voltage of 2.5 V, a maximum power efficiency and an external quantum efficiency (ηext) of 89.8 lm W−1 and 25.2 %, respectively, benefitting from the better charge-balancing ability of AC-Py-Cz host due to the presence of the pyridyl bridge. More importantly, all the devices based on these two hosts showed low efficiency roll-off at high brightness due to the suppressed non-radiative transition in the emitting layer. In particular, the AC-Py-Cz-hosted green PhOLED exhibited an efficiency roll-off of 1.6 % from the maximum next at a high brightness of 1000 cd m−2 and a roll-off of 15.9 % at an extremely high brightness of 10000 cd m−2. This study manifests that acridone-based host materials have great potential in fabricating OLEDs with low efficiency roll-off. 相似文献
29.
Liu Jingze Fei Qingguo Wu Shaoqing Tang Zhenhuan Zhang Dahai 《Nonlinear dynamics》2021,106(3):1869-1890
Nonlinear Dynamics - Rolling bearing and squeeze film damper will introduce structural nonlinearity into the dynamic model of aeroengine. Rubbing will occur due to the clearance reduction design of... 相似文献
30.
Yi-Tong Xu Tian-Yang Zhang Zheng Li Xiang-Nan Liu Yuan-Cheng Zhu Wei-Wei Zhao Hong-Yuan Chen Jing-Juan Xu 《Electroanalysis》2022,34(6):947-955
Photoelectrochemical (PEC) cytosensors, a combination of the PEC process and the living-cell assay, have emerged as a powerful tool in the analytical and biological science. This mini review provides a brief introduction of this arena and summaries the key steps about the development of PEC cytosensors with representative examples, followed by future prospects based on our own opinions. 相似文献