全文获取类型
收费全文 | 1676篇 |
免费 | 20篇 |
国内免费 | 7篇 |
专业分类
化学 | 1266篇 |
晶体学 | 11篇 |
力学 | 54篇 |
数学 | 156篇 |
物理学 | 216篇 |
出版年
2023年 | 11篇 |
2022年 | 21篇 |
2021年 | 24篇 |
2020年 | 22篇 |
2019年 | 26篇 |
2018年 | 21篇 |
2017年 | 13篇 |
2016年 | 18篇 |
2015年 | 17篇 |
2014年 | 27篇 |
2013年 | 87篇 |
2012年 | 67篇 |
2011年 | 73篇 |
2010年 | 46篇 |
2009年 | 46篇 |
2008年 | 106篇 |
2007年 | 89篇 |
2006年 | 88篇 |
2005年 | 87篇 |
2004年 | 91篇 |
2003年 | 74篇 |
2002年 | 49篇 |
2001年 | 17篇 |
1999年 | 16篇 |
1998年 | 16篇 |
1997年 | 15篇 |
1996年 | 27篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 26篇 |
1992年 | 22篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 40篇 |
1984年 | 29篇 |
1983年 | 20篇 |
1982年 | 29篇 |
1981年 | 17篇 |
1980年 | 30篇 |
1979年 | 18篇 |
1978年 | 23篇 |
1977年 | 15篇 |
1976年 | 18篇 |
1975年 | 21篇 |
1974年 | 27篇 |
1973年 | 14篇 |
排序方式: 共有1703条查询结果,搜索用时 15 毫秒
81.
The structural rules which govern the epitaxial crystallisation of polymers - and especially polyolefins - on organic substrates are established. Illustrative examples involve isotactic and syndiotactic polypropylenes and poly( l-butene). Investigation of the film structure by electron microscopy, electron diffraction and atomic force microscopy reveals some unprecedented features, including in particular the selection of the contact plane according to the chirality of its constituent helices, and direct observation of both right and left hands of polyolefin helices. 相似文献
82.
83.
Françoise Maugé Jean-Paul Gallas Jean-Claude Lavalley Guido Busca Gianguido Ramis Vincenzo Lorenzelli 《Mikrochimica acta》1988,95(1-6):57-61
In the far IR region at low molybdenum loadings, Mo-SiO2 catalysts present a pseudomolybdate or a polymolybdate species, while bulk-like MoO3 appears at loadings close to the geometrical monolayer coverage. W-SiO2 and V-SiO2 spectra show bands close to those observed on the corresponding bulk oxides.In the case of TiO2, Al2O3, ZrO2 supported catalysts, a band is observed near 1000 cm–1 which is assigned to the Mo=O stretching vibration of coordinatively unsaturated Mo
n+ ions showing a stronger interaction with the support than one observed on silica. 相似文献
84.
Noncovalent complexes of DNA and Hoechst 33258 were investigated by ESI-FT/ICR MS in various activation modes (collision-induced dissociation (CID), sustained off-resonance irradiation collision-induced dissociation (SORI-CID), infrared multiphoton dissociation (IRMPD) and electron detachment dissociation (EDD)). The binding selectivity of Hoechst 33258 was confirmed by the comparative study of its noncovalent association with different DNA sequences. The CID spectra of [ds + HO - 5H](5-) obtained with a linear hexapole ion trap resulted in unzipping of the strands. This outcome is a clue to the drug-binding mode, shading light on the localization of the binding sites of Hoechst 33258 to the DNA sequence. The IRMPD and SORI-CID experiments mainly gave DNA backbone cleavages and internal fragment ions. From this result, information on the localization of the binding sites of Hoechst 33258 in the DNA sequence was obtained. No sodium cationization was observed on the DNA sequence ions although they were present on fragmentation of the duplex, indicating that the backbone cleavages were generated from the single strand associated with the Hoechst 33258 where the number of alkali cation is restricted. Under electron detachment (ED) conditions, multiple EDs were achieved for the [ds + HO - 5H](5-) ion without any significant dissociation. The presence of drug appears to enhance the stability of the multiply charged system. It was proposed that the studied noncovalent complex involved the formation of zwitterions and consequently strong salt-bridge interactions between DNA and drug. 相似文献
85.
范宇航 孙丽萍 霍丽华 赵辉 Jean-Marc Bassat Aline Rougier Sbastien Fourcade Jean-Claude Grenier 《无机化学学报》2013,29(18)
采用EDTA-柠檬酸法合成了中温固体氧化物燃料电池阴极材料Sr1.5La0.5Mn1-xCoxO4(SLMCOx),并利用粉末X射线衍射(XRD)、X射线光电子能谱(XPS)以及电化学交流阻抗谱(EIS)进行表征。结果表明,该材料与Ce0.9Gd0.1O1.95(CGO)在1 200℃烧结12 h不发生化学反应。随着Co掺入量的增加,氧化物中Mn3+和Co2+含量增多,晶格氧含量降低,晶格畸变率增大。交流阻抗谱(EIS)测试结果显示,钴的掺杂明显降低电极的极化电阻,其中Sr1.5La0.5Mn0.7Co0.3O4阴极在700℃空气中的极化电阻为0.62 Ω·cm2,明显小于Sr1.5La0.5MnO4阴极在750℃的极化电阻(1.5 Ω·cm2),表明钴掺杂的Sr1.5La0.5Mn1-xCoxO4是一种潜在的IT-SOFC阴极材料。 相似文献
86.
Saurabh Bhatia Rashita Makkar Tapan Behl Aayush Sehgal Sukhbir Singh Mahesh Rachamalla Vasudevan Mani Muhammad Shahid Iqbal Simona Gabriela Bungau 《Molecules (Basel, Switzerland)》2022,27(5)
Marine drugs are abundant in number, comprise of a diverse range of structures with corresponding mechanisms of action, and hold promise for the discovery of new and better treatment approaches for the management of several chronic diseases. There are huge reserves of natural marine biological compounds, as 70 percent of the Earth is covered with oceans, indicating a diversity of chemical entities on the planet. The marine ecosystems are a rich source of bioactive products and have been explored for lead drug molecules that have proven to be novel therapeutic targets. Over the last 70 years, many structurally diverse drug products and their secondary metabolites have been isolated from marine sources. The drugs obtained from marine sources have displayed an exceptional potential in the management of a wide array of diseases, ranging from acute to chronic conditions. A beneficial role of marine drugs in human health has been recently proposed. The current review highlights various marine drugs and their compounds and role in the management of chronic diseases such as cancer, diabetes, neurodegenerative diseases, and cardiovascular disorders, which has led to the development of new drug treatment approaches. 相似文献
87.
88.
Jean-Claude Petit 《Accreditation and quality assurance》1999,4(11):458-462
An appropriate Quality approach in fundamental research should have its roots in the very principles of the "scientific method".
Quality and fundamental research could thus reconcile at the condition, on the one hand, that Quality practioners understand
and take into account the reality of the "science in action" and, on the other hand, that scientists improve their awareness
of the new deal which is being made between science, technology and society as well as of the actual issues of Quality. A
modern Quality approach, well adapted to this specific activity, should help both scientists, decision-makers and the public
face the issues concerning the role of science in society in the future. In this context, I specify a number of practical
proposals concerning, in particular, the adaptation of the requirements of the quality approach to the type of research, the
distinction between the three major steps of a research programme (i.e. quality of the objective, the process and the results)
and the encouragement of experience feedback.
Received: 8 March 1998 / Accepted: 8 December 1998 相似文献
89.
K. Andersen O. P. Anderson T. Miller N. S. Mani T. F. Baumann M. Anderson W. E. Broderick D. M. Eichhorn D. Goldberg W. Jarrell S. J. Lange S. Lee H. Nie M. Sabat J. W. Sibert C. Stern B. M. Hoffman S. Baum L. S. Beall A. S. Cook Q. J. Mccubbin A. Garrido Montalban M. S. Rodriguez-Morgade A. J. P. White D. B. G. Williams D. J. Williams A. G. M. Barrett H. Hope M. M. Olmstead 《Journal of heterocyclic chemistry》1998,35(5):1013-1042
90.