全文获取类型
收费全文 | 1061篇 |
免费 | 61篇 |
国内免费 | 26篇 |
专业分类
化学 | 677篇 |
晶体学 | 22篇 |
力学 | 45篇 |
综合类 | 1篇 |
数学 | 180篇 |
物理学 | 223篇 |
出版年
2023年 | 14篇 |
2022年 | 28篇 |
2021年 | 18篇 |
2020年 | 29篇 |
2019年 | 27篇 |
2018年 | 33篇 |
2017年 | 37篇 |
2016年 | 43篇 |
2015年 | 37篇 |
2014年 | 52篇 |
2013年 | 94篇 |
2012年 | 92篇 |
2011年 | 77篇 |
2010年 | 55篇 |
2009年 | 36篇 |
2008年 | 49篇 |
2007年 | 62篇 |
2006年 | 49篇 |
2005年 | 40篇 |
2004年 | 42篇 |
2003年 | 29篇 |
2002年 | 24篇 |
2001年 | 6篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 18篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1968年 | 1篇 |
1937年 | 2篇 |
排序方式: 共有1148条查询结果,搜索用时 15 毫秒
991.
Catalytic Cyclization of o‐Alkynyl Phenethylamines via Osmacyclopropene Intermediates: Direct Access to Dopaminergic 3‐Benzazepines
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Andrea Álvarez‐Pérez Dr. Carlos González‐Rodríguez Dr. Cristina García‐Yebra Dr. Jesús A. Varela Dr. Enrique Oñate Prof. Miguel A. Esteruelas Prof. Carlos Saá 《Angewandte Chemie (International ed. in English)》2015,54(45):13357-13361
A novel osmium‐catalyzed cyclization of o‐alkynyl phenethylamines to give 3‐benzazepines is reported. The procedure allows the straightforward preparation of a broad range of dopaminergic 3‐benzazepine derivatives. Mechanistic investigations revealed that the process takes place via osmacyclopropene intermediates, which were isolated and characterized by X‐ray crystallography. 相似文献
992.
Dr. Joshua R. Biller Dr. Mark Tseitlin Dr. Deborah G. Mitchell Zhelin Yu Laura A. Buchanan Dr. Hanan Elajaili Dr. Gerald M. Rosen Dr. Joseph P. Y. Kao Dr. Sandra S. Eaton Gareth R. Eaton 《Chemphyschem》2015,16(3):528-531
Radicals, including hydroxyl, superoxide, and nitric oxide, play key signaling roles in vivo. Reaction of these free radicals with a spin trap affords more stable paramagnetic nitroxides, but concentrations in vivo still are so low that detection by electron paramagnetic resonance (EPR) is challenging. Three innovative enabling technologies have been combined to substantially improve sensitivity for imaging spin‐trapped radicals at 250 MHz. 1) Spin‐trapped adducts of BMPO have lifetimes that are long enough to make imaging by EPR at 250 MHz feasible. 2) The signal‐to‐noise ratio of rapid‐scan EPR is substantially higher than for conventional continuous‐wave EPR. 3) An improved algorithm permits image reconstruction with a spectral dimension that encompasses the full 50 G spectrum of the BMPO–OH spin adduct without requiring the wide sweeps that would be needed for filtered backprojection. A 2D spectral–spatial image is shown for a phantom containing ca. 5 μM BMPO–OH. 相似文献
993.
Alissa Wiengarten Julian A. Lloyd Dr. Knud Seufert Dr. Joachim Reichert Dr. Willi Auwärter Runyuan Han Dr. David A. Duncan Dr. Francesco Allegretti Dr. Sybille Fischer Dr. Seung Cheol Oh Dr. Özge Sağlam Li Jiang Dr. Saranyan Vijayaraghavan Dr. David Écija Dr. Anthoula C. Papageorgiou Prof. Dr. Johannes V. Barth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(35):12285-12290
Selectivity in chemical reactions is a major objective in industrial processes to minimize spurious byproducts and to save scarce resources. In homogeneous catalysis the most important factor which determines selectivity is structural symmetry. However, a transfer of the symmetry concept to heterogeneous catalysis still requires a detailed comprehension of the underlying processes. Here, we investigate a ring‐closing reaction in surface‐confined meso‐substituted porphyrin molecules by scanning tunneling microscopy, temperature‐programmed desorption, and computational modeling. The identification of reaction intermediates enables us to analyze the reaction pathway and to conclude that the symmetry of the porphyrin core is of pivotal importance regarding product yields. 相似文献
994.
Frontispiece: Reversible Mechanical Interlocking of D‐Shaped Molecular Karabiners bearing Coordination‐Bond Loaded Gates: Route to Self‐Assembled [2]Catenanes
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
995.
Frédéric Jamin Moulay Saı̈d El Youssoufi Christian Saix 《Comptes Rendus Mecanique》2004,332(2):153-159
A study of temperature influence on the yield surface for one unsaturated soil at constant suction is presented. Mechanical consolidation tests are realized at different temperatures on clayey silty sand. A specific triaxial apparatus for unsaturated soils with temperatures included between 30 °C and 60 °C is used. Experimental results show without ambiguity a thermo-extensive nature of the yield surface. The physical interpretation proposed calls for microscopic considerations on the menisci capillary evolution according to temperature and suction. To cite this article: F. Jamin et al., C. R. Mecanique 332 (2004). 相似文献
996.
Modeling the Dynamics and Kinematics of a Telescopic Rotary Crane by the Bond Graph Method: Part II 总被引:1,自引:0,他引:1
Simulation of a rotary telescopic crane for which a detailed nonlinearbond graph model has been established in Part I of this study, isrealized utilizing experimental actual system for geometrical anddynamical parameters. With the intention of comparing the real system andthe model and of verifying the sufficiency of the model accuracy,various scenarios are defined corresponding to different loading andoperating conditions. Of the scenarios defined, impulse response, timeresponse and static response are used to experimentally gather such system parameters and variables as damping coefficient, cylinderdisplacements, and stiffness of the telescopic boom, respectively.Following, the simulation for two dissimilar scenarios which are staticresponse and impulse response is undergone and results are presented. 相似文献
997.
In ([11]), we have studied quadratic Leibniz algebras that are Leibniz algebras endowed with symmetric, nondegenerate, and associative (or invariant) bilinear forms. The nonanticommutativity of the Leibniz product gives rise to other types of invariance for a bilinear form defined on a Leibniz algebra: the left invariance, the right invariance. In this article, we study the structure of Leibniz algebras endowed with nondegenerate, symmetric, and left (resp. right) invariant bilinear forms. In particular, the existence of such a bilinear form on a Leibniz algebra 𝔏 gives rise to a new algebra structure ☆ on the underlying vector space 𝔏. In this article, we study this new algebra, and we give information on the structure of this type of algebras by using some extensions introduced in [11]. In particular, we improve the results obtained in [22]. 相似文献
998.
999.
Mohamed Saïdi 《Mathematische Annalen》1998,312(4):625-639
1000.
S. Sa e Sant'Anna E. A. Evangelista R. B. Alves D. S. Raslan 《Chemistry of Natural Compounds》2005,41(4):385-387
Among a wide variety of synthetic routes to pterocarpan prototypes, a mild approach uses a reaction known as Heck oxyarylation.
This method involves a reaction between 2H-chromenes and 2-chloromercuriophenols in the presence of Li2PdCl4.
__________
Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 311–312, July–August, 2005. 相似文献