全文获取类型
收费全文 | 3778篇 |
免费 | 190篇 |
国内免费 | 96篇 |
专业分类
化学 | 2396篇 |
晶体学 | 53篇 |
力学 | 181篇 |
综合类 | 6篇 |
数学 | 765篇 |
物理学 | 663篇 |
出版年
2024年 | 7篇 |
2023年 | 60篇 |
2022年 | 107篇 |
2021年 | 121篇 |
2020年 | 140篇 |
2019年 | 130篇 |
2018年 | 123篇 |
2017年 | 88篇 |
2016年 | 159篇 |
2015年 | 123篇 |
2014年 | 154篇 |
2013年 | 302篇 |
2012年 | 255篇 |
2011年 | 290篇 |
2010年 | 190篇 |
2009年 | 168篇 |
2008年 | 225篇 |
2007年 | 207篇 |
2006年 | 188篇 |
2005年 | 190篇 |
2004年 | 144篇 |
2003年 | 127篇 |
2002年 | 113篇 |
2001年 | 67篇 |
2000年 | 35篇 |
1999年 | 43篇 |
1998年 | 34篇 |
1997年 | 33篇 |
1996年 | 22篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 16篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1973年 | 5篇 |
1940年 | 2篇 |
排序方式: 共有4064条查询结果,搜索用时 15 毫秒
101.
Ines Belhaj-Ben Romdhane Zamen Ben Romdhane Maha Bouzid Ali Gargouri Hafedh Belghith 《Applied biochemistry and biotechnology》2013,171(8):1986-2002
Waste frying oil, which not only harms people’s health but also causes environmental pollution, can be a good alternative to partially substitute petroleum diesel through transesterification reaction. This oil contained 8.8 % of free fatty acids, which cause a problem in a base-catalyzed process. In this study, synthesis of biodiesel was efficiently catalyzed by the covalently immobilized Talaromyces thermophilus lipase and allowed bioconversion yield up to 92 % after 24 h of reaction time. The optimal molar ratio was four to six parts of methanol to one part of oil with a biocatalyst loaded of 25 wt.% of oil. Further, experiments revealed that T. thermophilus lipase, immobilized by a multipoint covalent liaison onto activated chitosan via a short spacer (glutaraldehyde), was sufficiently tolerant to methanol. In fact, using the stepwise addition of methanol, no significant difference was observed from the one-step whole addition at the start of reaction. The batch biodiesel synthesis was performed in a fixed bed reactor with a lipase loaded of 10 g. The bioconversion yield of 98 % was attained after a 5-h reaction time. The bioreactor was operated successfully for almost 150 h without any changes in the initial conversion yield. Most of the chemical and physical properties of the produced biodiesel meet the European and USA standard specifications of biodiesel fuels. 相似文献
102.
Dris Ben Hmamou Rachid Salghi Abdelkader Zarrouk Hassan Zarrok Omar Benali Mohamed Errami Belkheir Hammouti 《Research on Chemical Intermediates》2013,39(7):3291-3302
The corrosion inhibition properties of horehound (Marrubium vulgare L.) extract (HE) in 1 M hydrochloric acid medium was carried out using electrochemical methods (polarization curve and electrochemical impedance spectroscopy). Experiments were performed by concentration of the inhibitor and temperature effect. The results showed variation in inhibition performance of this plant extract. The Langmuir model was tested to describe the adsorption behavior of the inhibitor on the C38 steel surface. Some thermodynamic functions of dissolution processes were also determined. 相似文献
103.
A nonlinear inequality and application to global asymptotic stability of perturbed systems 下载免费PDF全文
The goal of this work is to present a new nonlinear inequality which is used in a study of the Lyapunov uniform stability and uniform asymptotic stability of solutions to time‐varying perturbed differential equations. New sufficient conditions for global uniform asymptotic stability and/or practical stability in terms of Lyapunov‐like functions for nonlinear time‐varying systems is obtained. Our conditions are expressed as relation between the Lyapunov function and the existence of specific function which appear in our analysis through the solution of a scalar differential equation. Moreover, an example in dimensional two is given to illustrate the applicability of the main result. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
104.
105.
Amel Souibgui Anne Gaucher Jérôme Marrot Flavien Bourdreux Faouzi Aloui Béchir Ben Hassine Damien Prim 《Tetrahedron》2014
New series of acridines and phenanthrolines have been prepared from β-chlorovinyl aldehydes and various aniline derivatives allowing the installation of valuable substituents, such as ketone, nitro or amino groups at the heterocyclic core. X-ray analyses confirmed the structures of acridines and phenanthrolines as well as the presence of partially hydrogenated rings and their crucial impact on the overall shape of the acridine-based architectures. 1H NMR revealed the helical behaviour of several acridine motives. Comparison of UV data between architectures and influence of number of partially hydrogenated rings is also described. 相似文献
106.
We consider the problem of nonnegative matrix factorization where the typical objective function is altered based on geometrical arguments. A noneuclidean geometry on positive real numbers is used to describe the nonnegative entries of a nonnegative matrix, influencing the factorization model. We design an optimization procedure from a differential geometric point of view for the newly proposed model. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
107.
Menel Ben Frej Fanny d'Orlyé Gerson F. Duarte-Junior Wendell K. T. Coltro Anne Varenne 《Electrophoresis》2022,43(20):2044-2048
A low-cost and straightforward hybrid NOA (Norland optical adhesive) 81-glass microchip electrophoresis device was designed and developed for protein separation using indirect fluorescence detection. This new microchip was first characterized in terms of surface charge density via electroosmotic mobility measurement and stability over time. A systematic determination of the electroosmotic mobility (μeo) over a wide pH range (2–10) and at various ionic strengths (20–50 mM) was developed for the first time via the neutral marker approach in an original simple frontal methodology. The evolution of μeo was proved consistent with the silanol and thiol functions arising from the glass and the NOA materials, respectively. The repeatability and reproducibility of the measurements on different microchips (RSD < 14%) and within 15 days (less than 5% decrease) were successfully demonstrated. The microchip was then applied for the efficient electrophoretic separation of proteins in a zonal mode coupled with indirect fluorescence detection, which is, to our knowledge, the first proof of concept of capillary zone electrophoresis in this hybrid microsystem. 相似文献
108.
Harech Mohamed Amine Dabbebi Rawia Abouliatim Younes Elhafiane Youssef Smith Agnès Mesnaoui Mohamed Niboue Lahbib Baklouti Samir 《Journal of Thermal Analysis and Calorimetry》2022,147(10):5677-5686
Journal of Thermal Analysis and Calorimetry - The aim of the present work is to characterize the phosphate sludge from two different countries: Morocco and Tunisia, and to study the difference... 相似文献
109.
Kesler Michael S. McGuire Michael A. Conner Ben Rios Orlando Murphy Bart Carter William Henderson Hunter B. Ludtka Gerard M. Kisner Roger A. 《Journal of Thermal Analysis and Calorimetry》2022,147(13):7449-7457
Journal of Thermal Analysis and Calorimetry - A new thermal analysis technique is described that allows measurements to be performed on bulk samples at extreme heating and cooling rates and in high... 相似文献
110.
Science China Chemistry - Secrecy has received tremendous attention in modern information society. Innovative polymer-based fluorescent materials with multiple mode emission are quite desirable to... 相似文献