全文获取类型
收费全文 | 3174篇 |
免费 | 564篇 |
国内免费 | 468篇 |
专业分类
化学 | 2517篇 |
晶体学 | 45篇 |
力学 | 162篇 |
综合类 | 21篇 |
数学 | 360篇 |
物理学 | 1101篇 |
出版年
2024年 | 10篇 |
2023年 | 64篇 |
2022年 | 117篇 |
2021年 | 129篇 |
2020年 | 152篇 |
2019年 | 146篇 |
2018年 | 113篇 |
2017年 | 125篇 |
2016年 | 184篇 |
2015年 | 185篇 |
2014年 | 202篇 |
2013年 | 279篇 |
2012年 | 276篇 |
2011年 | 251篇 |
2010年 | 226篇 |
2009年 | 171篇 |
2008年 | 207篇 |
2007年 | 153篇 |
2006年 | 163篇 |
2005年 | 167篇 |
2004年 | 133篇 |
2003年 | 92篇 |
2002年 | 106篇 |
2001年 | 119篇 |
2000年 | 72篇 |
1999年 | 78篇 |
1998年 | 40篇 |
1997年 | 36篇 |
1996年 | 27篇 |
1995年 | 24篇 |
1994年 | 25篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 22篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有4206条查询结果,搜索用时 15 毫秒
991.
Back Cover: Elastic and Wearable Wire‐Shaped Lithium‐Ion Battery with High Electrochemical Performance (Angew. Chem. Int. Ed. 30/2014) 下载免费PDF全文
992.
Poly(3-hexylthiophene) (PBHT) was used in a solid-state dye-sensitized solar cell (S-DSC) with a broad- absorption metal-free organic dye sensitizer 1,2,4,5-benzenetetracarboxylic acid (BzTCA). Under full- sunlight irradiation (AM 1.5 G, 100 mW/cm2 ), an overall conversion efficiency of 3.21% was achieved, which represents one of the highest efficiencies reported in an S-DSC. Our results indicate that the P3HT polymer is a promising material as both a hole conductor and an assistant sensitizer in the fabrication of solid-state DSCs. 相似文献
993.
Discriminative model over bag-of-visual-words representation significantly improves the accuracy of object detection under clutter. However, it encounters bottleneck because of completely ignoring geometric constraint between features. On the contrary, to detect object accurately explicit shape model heavily relies on geometric information of the object, which as a result lacks of discriminative power. In this paper, we present a discriminative shape model to make use of the advantages of the two models based on the insight that the two models are essentially complementary. Discriminative model provides discriminative power, while shape model encodes geometry. The cost function that we used to distinguish objects considers both the detection maps of the discriminative model and the result of shape matching. In this cost function, we adopt a novel way to deal with multi-scale detection maps. We show that this cost function has very strong discriminative power, which makes learning a discriminative threshold for full object detection possible. For shape model, we also present a scheme for learning a good shape model from noisy images. Experiments on UIUC Car and Weizmann–Shotton horses show state-of-the-art performance of our model. 相似文献
994.
Most of the existing color image watermarking schemes was designed to mark grayscale images or use the color components, which ignore the significant correlation between different color channels. Recently, several approaches were developed to process the color channels intrinsically, but they always cannot counterattack geometric distortions. It is a challenging work to design a robust color image watermarking scheme against geometrical distortions. In this paper, we propose a geometric correction based robust color image watermarking approach using quaternion Exponent moments (QEMs). The novelty of our approach is that (1) the QEMs are derived to deal with the color images in a holistic manner, and (2) the QEMs are exploited for estimating the geometric distortions parameters in order to permit watermark extraction. Experimental results confirm the validity of our approach and its higher robustness against geometrical distortions compared to alternative watermarking methods in the literature. 相似文献
995.
996.
Wen-Zuo Li Quan-Zhen Cao Yu-Wei Pei Ran Li Hong-Jie Zhu Qing-Zhong Li Jian-Bo Cheng 《Structural chemistry》2012,23(3):867-871
The germylenoid H2GeFBeF was studied by using the DFT B3LYP and QCISD methods in gas phase and in benzene, diethylether, tetrahydrofuran, acetone, and dimethyl sulphoxide solvents. Geometry optimization calculations indicated that H2GeFBeF has three equilibrium configurations, in which the p-complex structure is the lowest in energy and is the most stable structure. The solvent effect on the geometries, energies, and isomerization reactions were discussed. For the stablest structure, the infrared spectrum was simulated. 相似文献
997.
998.
Dr. Cheng‐Kui Pei Yu Jiang Yin Wei Prof. Dr. Min Shi 《Angewandte Chemie (International ed. in English)》2012,51(45):11328-11332
999.
Cuixiang Pei Kazuyuki Demachi Haitao Zhu Tetsuo Fukuchi Kazuyoshi Koyama Mitsuru Uesaka 《Optics & Laser Technology》2012,44(4):860-865
A numerical model based on the finite element method (FEM) is developed for crack inspection using laser-induced ultrasonic waves with the shadow method. Before the simulation, the numerical code is verified by comparing the directivity patterns of ultrasonic waves with the experiment. The use of thermo-elastically generated ultrasonic waves for crack detection and evaluation with the shadow method is investigated by simulation. The simulation is validated by comparing with the experiment. 相似文献
1000.
Xiao-Jiang Zhou Xue-Song Li Ying Shen Gang Pei Jun-Feng Wang Yong-Xian Cheng 《Chemistry of Natural Compounds》2012,48(3):419-422
Investigations on the EtOH extract of Cucumis sativus roots led to the isolation of 15 compounds (1–15). Their structures were identified using spectroscopic methods. Among these compounds, compound 1, stigmasta-8(14),22-diene-7α-methoxy-3β-ol, is a new steroid, and 2, 4–15 were isolated from this plant for the first time. 相似文献