全文获取类型
收费全文 | 409129篇 |
免费 | 4215篇 |
国内免费 | 1366篇 |
专业分类
化学 | 221544篇 |
晶体学 | 6803篇 |
力学 | 17652篇 |
综合类 | 5篇 |
数学 | 42305篇 |
物理学 | 126401篇 |
出版年
2018年 | 3847篇 |
2017年 | 3724篇 |
2016年 | 5912篇 |
2015年 | 3885篇 |
2014年 | 6103篇 |
2013年 | 16958篇 |
2012年 | 11982篇 |
2011年 | 14911篇 |
2010年 | 10414篇 |
2009年 | 10320篇 |
2008年 | 13699篇 |
2007年 | 13821篇 |
2006年 | 13127篇 |
2005年 | 11890篇 |
2004年 | 10999篇 |
2003年 | 9829篇 |
2002年 | 9607篇 |
2001年 | 11784篇 |
2000年 | 9043篇 |
1999年 | 7123篇 |
1998年 | 5853篇 |
1997年 | 5807篇 |
1996年 | 5595篇 |
1995年 | 5137篇 |
1994年 | 5004篇 |
1993年 | 4973篇 |
1992年 | 5535篇 |
1991年 | 5554篇 |
1990年 | 5321篇 |
1989年 | 5330篇 |
1988年 | 5309篇 |
1987年 | 5255篇 |
1986年 | 4932篇 |
1985年 | 6694篇 |
1984年 | 6882篇 |
1983年 | 5559篇 |
1982年 | 5895篇 |
1981年 | 5789篇 |
1980年 | 5759篇 |
1979年 | 5937篇 |
1978年 | 6790篇 |
1977年 | 6416篇 |
1976年 | 6047篇 |
1975年 | 5582篇 |
1974年 | 5567篇 |
1973年 | 5572篇 |
1972年 | 3847篇 |
1971年 | 3206篇 |
1968年 | 3446篇 |
1967年 | 3461篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
Markus Bödenler Ludovic de Rochefort P. James Ross Nicolas Chanet Geneviève Guillot Gareth R. Davies 《Molecular physics》2019,117(7-8):832-848
ABSTRACTFast field-cycling (FFC) nuclear magnetic resonance relaxometry is a well-established method to determine the relaxation rates as a function of magnetic field strength. This so-called nuclear magnetic relaxation dispersion gives insight into the underlying molecular dynamics of a wide range of complex systems and has gained interest especially in the characterisation of biological tissues and diseases. The combination of FFC techniques with magnetic resonance imaging (MRI) offers a high potential for new types of image contrast more specific to pathological molecular dynamics. This article reviews the progress in FFC-MRI over the last decade and gives an overview of the hardware systems currently in operation. We discuss limitations and error correction strategies specific to FFC-MRI such as field stability and homogeneity, signal-to-noise ratio, eddy currents and acquisition time. We also report potential applications with impact in biology and medicine. Finally, we discuss the challenges and future applications in transferring the underlying molecular dynamics into novel types of image contrast by exploiting the dispersive properties of biological tissue or MRI contrast agents. 相似文献
132.
Dr. Felipe L. Coelho Eduarda S. Gil Dr. Paulo F. B. Gonçalves Dr. Leandra F. Campo Dr. Paulo H. Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8157-8162
In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles. 相似文献
133.
Probing the Catalytic Activity of Reduced Graphene Oxide Decorated with Au Nanoparticles Triggered by Visible Light 下载免费PDF全文
Dr. Jiale Wang Dr. Fabiane J. Trindade Caroline B. de Aquino Joana C. Pieretti Prof. Dr. Sergio H. Domingues Prof. Dr. Romulo A. Ando Prof. Dr. Pedro H. C. Camargo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9889-9894
Hybrid materials in which reduced graphene oxide (rGO) is decorated with Au nanoparticles (rGO–Au NPs) were obtained by the in situ reduction of GO and AuCl4?(aq) by ascorbic acid. On laser excitation, rGO could be oxidized as a result of the surface plasmon resonance (SPR) excitation in the Au NPs, which generates activated O2 through the transfer of SPR‐excited hot electrons to O2 molecules adsorbed from air. The SPR‐mediated catalytic oxidation of p‐aminothiophenol (PATP) to p,p′‐dimercaptoazobenzene (DMAB) was then employed as a model reaction to probe the effect of rGO as a support for Au NPs on their SPR‐mediated catalytic activities. The increased conversion of PATP to DMAB relative to individual Au NPs indicated that charge‐transfer processes from rGO to Au took place and contributed to improved SPR‐mediated activity. Since the transfer of electrons from Au to adsorbed O2 molecules is the crucial step for PATP oxidation, in addition to the SPR‐excited hot electrons of Au NPs, the transfer of electrons from rGO to Au contributed to increasing the electron density of Au above the Fermi level and thus the Au‐to‐O2 charge‐transfer process. 相似文献
134.
135.
Dr. Man-Bo Li Daniels Posevins Dr. Karl P. J. Gustafson Dr. Cheuk-Wai Tai Dr. Andrey Shchukarev Dr. Youai Qiu Dr. Jan-E. Bäckvall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(1):210-215
A highly selective and efficient oxidative carbocyclization/borylation of enallenols catalyzed by palladium immobilized on amino-functionalized siliceous mesocellular foam (Pd-AmP-MCF) was developed for diastereoselective cyclobutenol synthesis. The heterogeneous palladium catalyst can be recovered and recycled without any observed loss of activity or selectivity. The high diastereoselectivity of the reaction is proposed to originate from a directing effect of the enallenol hydroxyl group. Optically pure cyclobutenol synthesis was achieved by the heterogeneous strategy by using chiral enallenol obtained from kinetic resolution. 相似文献
136.
Tereshchenko E. D. Cherniakov S. M. Yurik R. Yu. Rietveld M. T. Häggström I. 《Radiophysics and Quantum Electronics》2020,62(10):667-676
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar... 相似文献
137.
Umie F.M. Haziz Rosenani A. Haque Shun-Ze Zhan Hassan H. Abdallah Mohd R. Razali 《应用有机金属化学》2020,34(10):e5818
The synthesis and characterizations for a series of dinuclear gold (I)-di-NHC complexes, 1–8 through the trans-metalation method of their respective silver (I)-di-NHC complexes, i–viii are reported (where NHC = N-heterocyclic carbene). The successful complexation of a series of unusual non-symmetrical and symmetrical di-NHC ligands, 3,3'-(ethane-1,2-diyl)-1-alkylbenzimidazolium-1'-butylbenzimidazolium (with alkyl = methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, benzyl) with the gold (I) ions are suggested by elemental analysis, Fourier transform-infrared, 1H- and 13C-NMR data. The 13C-NMR spectra of 1–8 show a singlet sharp peak in the range of 190.00–192.00 ppm, indicating the presence of a carbene carbon that bonded to the gold (I) ion. From single crystal X-ray diffraction data, the structure of complex 6 with the formula of [di-NHC-Au (I)]2·2PF6 is obtained [where NHC = 3,3'-(ethane-1,2-diyl)-1-hexylbenzimidazolium-1'-butylbenzimidazolium]. The photophysical study in solid state of 6 displays an intense photoluminescence with a strong emission maxima, λem = 480 nm, upon excitation at 340 nm at room temperature. Interestingly, the emission maximum at 77 K shows a structural character with a strong peak at 410 nm, a medium at 433 nm and a weak at 387 nm, accompanied by a tail band to about 500 nm. 相似文献
138.
Mathematical Notes - We prove the equivalence of a vector and a scalar equilibrium problem that naturally arise when studying the limit distribution of zeros of type I Hermite–Padé... 相似文献
139.
Lebedev V. T. Serebrov A. P. 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2020,14(1):1-5
Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques - A method for studying the magnetic dynamics of endofullerenes M@C2n (2n = 60, 70, …) and their derivatives,... 相似文献
140.