全文获取类型
收费全文 | 1349篇 |
免费 | 265篇 |
国内免费 | 143篇 |
专业分类
化学 | 915篇 |
晶体学 | 9篇 |
力学 | 135篇 |
综合类 | 27篇 |
数学 | 173篇 |
物理学 | 498篇 |
出版年
2024年 | 1篇 |
2023年 | 36篇 |
2022年 | 42篇 |
2021年 | 37篇 |
2020年 | 66篇 |
2019年 | 56篇 |
2018年 | 35篇 |
2017年 | 37篇 |
2016年 | 63篇 |
2015年 | 65篇 |
2014年 | 74篇 |
2013年 | 97篇 |
2012年 | 130篇 |
2011年 | 119篇 |
2010年 | 93篇 |
2009年 | 93篇 |
2008年 | 93篇 |
2007年 | 77篇 |
2006年 | 87篇 |
2005年 | 45篇 |
2004年 | 54篇 |
2003年 | 40篇 |
2002年 | 31篇 |
2001年 | 19篇 |
2000年 | 22篇 |
1999年 | 14篇 |
1998年 | 24篇 |
1997年 | 19篇 |
1996年 | 23篇 |
1995年 | 20篇 |
1994年 | 10篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有1757条查询结果,搜索用时 31 毫秒
61.
Recently, a polynomial-based (k, n) steganography and authenticated image sharing (SAIS) scheme was proposed to share a secret image into n stego-images. At the same time, one can reconstruct a secret image with any k or more than k stego-images, but one cannot obtain any information about the secret from fewer than k stego-images. The beauty of a (k, n)-SAIS scheme is that it provides the threshold property (i.e., k is the threshold value), the steganography (i.e., stego-images look like cover images), and authentication (i.e., detection of manipulated stego-images). All existing SAIS schemes require parity bits for authentication. In this paper, we present a novel approach without needing parity bits. In addition, our (k, n)-SAIS scheme provides better visual quality and has higher detection ratio with respect to all previous (k, n)-SAIS schemes. 相似文献
62.
63.
Yue Ren He Wang Jiangjiang Liu Zhiping Zhang Morgan N. McLuckey Zheng Ouyang 《Chromatographia》2013,76(19-20):1339-1346
Paper spray has been developed as a fast sampling ionization method for direct analysis of raw biological and chemical samples using mass spectrometry (MS). Quantitation of therapeutic drugs in blood samples at high accuracy has also been achieved using paper spray MS without traditional sample preparation or chromatographic separation. The paper spray ionization is a process integrated with a fast extraction of the analyte from the raw sample by a solvent, the transport of the extracted analytes on the paper, and a spray ionization at the tip of the paper substrate with a high voltage applied. In this study, the influence on the analytical performance by the solvent–substrate systems and the selection of the elution methods was investigated. The protein hemoglobin could be observed from fresh blood samples on silanized paper or from dried blood spots on silica-coated paper. The on-paper separation of the chemicals during the paper spray was characterized through the analysis of a mixture of the methyl violet 2B and methylene blue. The mode of applying the spray solvent was found to have a significant impact on the separation. The results in this study led to a better understanding of the analyte elution, on-paper separation, as well as the ionization processes of the paper spray. This study also helps in establishing a guideline for optimizing the analytical performance of paper spray for direct analysis of target analytes using mass spectrometry. 相似文献
64.
65.
66.
67.
Zhang Jiaqing Zhang Bosi Li Wenjie Ouyang Benhong Fan Minghao Wang Haoming 《Journal of Thermal Analysis and Calorimetry》2020,140(6):2749-2756
Journal of Thermal Analysis and Calorimetry - The burning process and typical fire parameters of power-cable silicon ointment were explored experimentally using a cone calorimeter, and the effects... 相似文献
68.
Yuebin Lian Wenjuan Yang Chufeng Zhang Hao Sun Zhao Deng Wenjie Xu Li Song Zhongwen Ouyang Zhenxing Wang Jun Guo Yang Peng 《Angewandte Chemie (International ed. in English)》2020,59(1):286-294
Reversible oxygen conversion is important for various green energy technologies. Herein we synthesize a series of bimetallic coordination polymers by varying the Ni/Co ratio and using HITP (HITP=2,3,6,7,10,11‐hexaiminotriphenylene) as the ligand, to interrogate the role of metal centres in modulating the activity of the oxygen reduction reaction (ORR). Co3HITP2 and Ni3HITP2 are compared. Unpaired 3d electrons in Co3HITP2 result in less coplanarity but more radical character. Thus, despite of a reduced crystallinity and conductivity, the best ORR activity, comparable to 20 % Pt/C, is obtained for Co3HITP2, showing the 3d orbital configuration of the metal centre promotes ORR. Experimental and DFT studies show a transition of ORR pathway from four‐electron for Co3HITP2 to two‐electron for Ni3HITP2. Rechargeable zinc–air batteries using Co3HITP2 as the air cathode catalyst demonstrate excellent energy efficiency and stability. 相似文献
69.
Wenjuan Ma Guangzhe Yao Xuhua Huang Qi Jia Jiayuan Shen Yanxu Chang Huizi Ouyang Jun He 《Journal of separation science》2020,43(5):865-876
We investigated crude Aster tataricus, vinegar‐processed Aster tataricus, honey‐processed Aster tataricus, and steamed Aster tataricus as a case study and developed a comprehensive strategy integrating quantitative analysis and chemical pattern recognition methods for the evaluation and differentiation of Aster tataricus from different regions, as well as related processed products. In the study, 15 batches of raw Aster tataricus collected from seven provinces were analyzed. A sensitive and rapid ultra‐high performance liquid chromatography with tandem mass spectrometry method for simultaneous determination of 15 compounds was established to evaluate the quality of raw and processed Aster tataricus. Furthermore, multivariate statistical techniques were applied to compare the differences among Aster tataricus samples. As a result, the herbs collected from seven provinces were divided into two categories, and chlorogenic acid was the most important component distinguishing between the regions. Moreover, all of the raw and processed samples were classified by partial least squares discriminant analysis based on the 15 analyzed compounds. Results showed that raw Aster tataricus, vinegar‐processed Aster tataricus, honey‐processed Aster tataricus, and steamed Aster tataricus were clustered in four different areas. Shionone, chlorogenic acid and kaempferol were the significant constituents differentiating the raw and differently processed Aster tataricus samples. 相似文献
70.
Tai-ran Wang Jian-cong Li Wu Shu Su-lei Hu Run-hai Ouyang Wei-xue Li 《化学物理学报(中文版)》2020,33(6):703-711
Over the last few years, machine learning is gradually becoming an essential approach for the investigation of heterogeneous catalysis. As one of the important catalysts, binary alloys have attracted extensive attention for the screening of bifunctional catalysts. Here we present a holistic framework for machine learning approach to rapidly predict adsorption energies on the surfaces of metals and binary alloys. We evaluate different machine-learning methods to understand their applicability to the problem and combine a tree-ensemble method with a compressed-sensing method to construct decision trees for about 60000 adsorption data. Compared to linear scaling relations, our approach enables to make more accurate predictions lowering predictive root-mean-square error by a factor of two and more general to predict adsorption energies of various adsorbates on thousands of binary alloys surfaces, thus paving the way for the discovery of novel bimetallic catalysts. 相似文献