全文获取类型
收费全文 | 60736篇 |
免费 | 10319篇 |
国内免费 | 8066篇 |
专业分类
化学 | 43690篇 |
晶体学 | 886篇 |
力学 | 3624篇 |
综合类 | 569篇 |
数学 | 7262篇 |
物理学 | 23090篇 |
出版年
2024年 | 60篇 |
2023年 | 1145篇 |
2022年 | 1393篇 |
2021年 | 1944篇 |
2020年 | 2374篇 |
2019年 | 2356篇 |
2018年 | 2042篇 |
2017年 | 2024篇 |
2016年 | 2846篇 |
2015年 | 2826篇 |
2014年 | 3554篇 |
2013年 | 4476篇 |
2012年 | 5388篇 |
2011年 | 5733篇 |
2010年 | 4113篇 |
2009年 | 3985篇 |
2008年 | 4292篇 |
2007年 | 3897篇 |
2006年 | 3698篇 |
2005年 | 2903篇 |
2004年 | 2253篇 |
2003年 | 1851篇 |
2002年 | 1733篇 |
2001年 | 1449篇 |
2000年 | 1397篇 |
1999年 | 1276篇 |
1998年 | 1055篇 |
1997年 | 955篇 |
1996年 | 904篇 |
1995年 | 840篇 |
1994年 | 750篇 |
1993年 | 581篇 |
1992年 | 558篇 |
1991年 | 448篇 |
1990年 | 412篇 |
1989年 | 315篇 |
1988年 | 269篇 |
1987年 | 221篇 |
1986年 | 209篇 |
1985年 | 199篇 |
1984年 | 121篇 |
1983年 | 87篇 |
1982年 | 77篇 |
1981年 | 42篇 |
1980年 | 22篇 |
1979年 | 18篇 |
1977年 | 4篇 |
1971年 | 4篇 |
1957年 | 7篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Dr. Si-Yong Qin Yan Jiang Dr. Han Sun Han Liu Prof. Ai-Qing Zhang Prof. Xinxiang Lei 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(39):17245-17251
Residual dipolar coupling (RDC), a robust anisotropic NMR parameter for structural elucidation of organic molecules, is only accessible in an anisotropic environment. Herein, we introduce a novel alignment medium based on the molecular self-assembly of oligopeptide amphiphile (OPA). This medium is compatible with different intermediate and polar solvent systems, such as CD3OD, [D6]DMSO, and D2O. The preparation of the OPA-based medium is simple and rapid, while only very weak background signals were observed from OPAs. Furthermore, we show that the purity of OPA has only a minor influence on the quality of the RDC data. These advantages allow RDC measurements of organic molecules with different polarities and solubilities with high efficiency and accuracy. 相似文献
92.
Single-crystalline gallium nitride nanobelts have been synthesized through the reaction of gallium vapor with flowing ammonia using nickel as a catalyst. The as-synthesized products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected-area electron diffraction (SAED). XRD and SAED results revealed that the products are pure, single-crystalline GaN with hexagonal structure. The widths and thickness of the nanobelts ranged from 80 to 200 nm, and 10 to 30 nm, respectively. The lengths were up to several tens of micrometers. The nanobelts had smooth surface with no amorphous sheath, and a sharp-tip end. The growth mechanism of nanobelts was discussed. 相似文献
93.
94.
We prove the existence of global smooth solutions near a given steady state of the hydrodynamic model of the semiconductors
in a bounded domain with physical boundary conditions. The steady state and the doping profile are permitted to be of large
variation but the initial velocity must be small. Two cases are considered. In the first one the problem is three-dimensional,
the boundary conditions are insulating and the steady state velocity vanishes. In the second one, the problem is one-dimensional,
the boundary is of contact type and the steady state velocity does not vanish. 相似文献
95.
Bijian Lan Chunming Liu Xiang Yin Hua Zhang Wei Xu Zhongyi Hua 《Frontiers of Chemistry in China》2006,1(3):296-299
Organic materials of D-π-A type MR-X (MR-1: p-dimethylaminophenylethenetrica-rbonitrile and MR-2: p-diphenylaminophenylethene tricarbonitrile) were designed and synthesized. The device with a sandwich structure shows good
rectificative phenomena. The highest rectification ratio 10000 was achieved in device Cu/MR-1/Ag, and about 100 in other device
M/MR-X/M (M: Cu, Ag). It has been found that rectificative phenomena exist only in the atmosphere-liquid interface region
by means of liquid adsorption, and electric field could help form the oriented molecular film.
__________
Translated from Journal of Fudan University (Natural Science), 2005, 44(4) (in Chinese) 相似文献
96.
电路过渡过程所列方程是微分方程,本文中采用的是方框图模型分析法,即将微分方程的复杂示解分解成最基本的加(减)、乘(除)、积分(微分)、增益等运算,采用VB设计用户界面产进行计算,并给出了一算例。 相似文献
97.
98.
WANG Zhong HONG Haitao XIAO Hai SUN Changku MENG Yan YE Shenghua 《Chinese Journal of Lasers》1997,6(5):435-440
1.IntroductionAbsolutedistancemeasurementisfarfromanewtopic.However,itisstillafieldstimulatinggreatinterestsnowadaysduetoitSimportantroleinmanufacturingandassembly['J.SincethegreatsuccessachievedbyMichelsonandBenoitwhentheyfirstdevelopedaninterferometertodeterminethestandardmeterintermsofthemonochromaticredcadmiumline,theopticinterferometerhasbeenprovedtobeoneofthemostpreciseandefficientwayindisplacementmeasurementbecauseofitshighdiscriminationandsimplestructure.However,thetraditionalinterfe… 相似文献
99.
100.
玻璃陶瓷材料中Tm3+离子红外到蓝色上转换发光 总被引:4,自引:0,他引:4
系统研究了PbF2+GeO2+WO3ⅩⅣTmF3玻璃陶瓷材料中,在近红外光(1.06μm)激发下,Tm3+离子的发光特性.实验中观测到Tm3+离子的两组峰值位置分别在20920cm-1和22173cm-1的蓝色上转换发光,并证实这两组上转换发光分别与吸收三个和四个光子有关,同时建立了上转换发光的模型.为了选择最佳掺杂浓度,详细地测量了Tm3+离子峰值为20920cm-1的蓝色上转换发光强度与TmF3浓度的关系. 相似文献