全文获取类型
收费全文 | 30466篇 |
免费 | 5439篇 |
国内免费 | 4169篇 |
专业分类
化学 | 22904篇 |
晶体学 | 484篇 |
力学 | 1567篇 |
综合类 | 292篇 |
数学 | 3376篇 |
物理学 | 11451篇 |
出版年
2024年 | 61篇 |
2023年 | 581篇 |
2022年 | 720篇 |
2021年 | 1041篇 |
2020年 | 1215篇 |
2019年 | 1241篇 |
2018年 | 1168篇 |
2017年 | 1063篇 |
2016年 | 1521篇 |
2015年 | 1494篇 |
2014年 | 1820篇 |
2013年 | 2408篇 |
2012年 | 2814篇 |
2011年 | 2961篇 |
2010年 | 2159篇 |
2009年 | 2019篇 |
2008年 | 2209篇 |
2007年 | 1950篇 |
2006年 | 1744篇 |
2005年 | 1463篇 |
2004年 | 1127篇 |
2003年 | 865篇 |
2002年 | 929篇 |
2001年 | 762篇 |
2000年 | 602篇 |
1999年 | 615篇 |
1998年 | 429篇 |
1997年 | 398篇 |
1996年 | 390篇 |
1995年 | 323篇 |
1994年 | 288篇 |
1993年 | 259篇 |
1992年 | 184篇 |
1991年 | 200篇 |
1990年 | 154篇 |
1989年 | 120篇 |
1988年 | 104篇 |
1987年 | 92篇 |
1986年 | 79篇 |
1985年 | 70篇 |
1984年 | 66篇 |
1983年 | 40篇 |
1982年 | 42篇 |
1981年 | 26篇 |
1980年 | 29篇 |
1979年 | 17篇 |
1978年 | 18篇 |
1976年 | 21篇 |
1975年 | 18篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
ZHONG Hui WAN Mingxi JIANG Yifeng WANG Supin 《声学学报:英文版》2006,25(2):104-115
The present study was to investigate the differential imaging method for detecting HIFU (High Intensity Focused Ultrasound)-induced lesions and the estimation of variation of attenuation for lesion evaluation with log spectral difference algorithm. Experiment results of bovine muscle and liver in vitro were acquired. Several algorithms for lesion detection - Absolute Difference (AD), Sum Absolute Differences (SAD) and Sum Squared Differences (SSD) - were analyzed with several window sizes and threshold values. Then three attenuation parameters were compared to evaluate the degree of tissue damage. It was found that variation of the mean attenuation △α was an effective parameter to evaluate lesions. 相似文献
52.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime. 相似文献
53.
54.
基于同步辐射加速器的康普顿背散射γ射线源(Ⅰ)产生MeV量级γ光子的数值计算 总被引:1,自引:0,他引:1
提出在筹建的上海同步辐射装置上建造一条MeV量级γ射线束及应用站,采用μm波长的红外(或远红外)激光与储存环中3.5GeV电子束进行康普顿背散射,从而获得能区为1—25MeV的康普顿背散射γ光子束,该光子束具有高强度、高极化度(线和圆极化)、准单色、方向性好的优点,可以广泛地应用于核物理和核天体物理基础研究及相关的应用研究领域.介绍了康普顿背散射的基本原理,并结合储存环参数给出了光子束性能的数值计算结果. 相似文献
55.
Hongbo Zhang Rui Wang Kaixin Chen Han Yang Daming Zhang Maobin Yi Guoquan Wang Zhenchang Ma 《Optics & Laser Technology》2002,34(4):283-286
A new method, based on zero point of longitudinal electric field, was used to determine the spatial resolution of external electro-optic (EO) probing equipment. Considering the diffraction of Gauss beam, the result of external EO probing was simulated which was in accordance with the experiment. A spatial resolution <1 μm was demonstrated initially in our equipment using 650 nm laser diode as probe beam and semi-insulating GaP as probe tip. 相似文献
56.
57.
58.
Ching Sum Hui Lillian Sze Man Lam Chun Yin Wai Kin Chan Aleksandra B. Djurii 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1708-1715
Polyurethanes incorporated with rhenium diimine complexes were synthesized. The polymers exhibited interesting morphologies and solution properties. Results from gel permeation chromatography suggested the formation of polymer aggregates in solutions. The polymers could act as probes for metal ions. The addition of metal ions to polymer solutions led to significant changes in the electronic absorption properties of the polymer solutions. This was attributed to the interactions between the polyether moieties and metal ions. The metal complexes could also act as efficient photosensitizers. After doping with charge‐transport viologens, the photoconductivity of the polymers was greatly enhanced. The experimental quantum efficiency was simulated with Onsager's theory. The thermalization distances and the primary yields were typically 12–14 Å and 10?3, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1708–1715, 2003 相似文献
59.
60.
In mononuclear HgI2[(C5H4N)3N], mercury is tetrahedrally coordinated by two nitrogen atoms of a tris(2‐pyridyl)amine ligand and two iodides. The coordination moieties are connected by weak intermolecular Hg(II)···I interactions to give a one‐dimensional structure. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献