全文获取类型
收费全文 | 4273篇 |
免费 | 140篇 |
国内免费 | 34篇 |
专业分类
化学 | 2775篇 |
晶体学 | 23篇 |
力学 | 133篇 |
数学 | 583篇 |
物理学 | 933篇 |
出版年
2024年 | 6篇 |
2023年 | 28篇 |
2022年 | 112篇 |
2021年 | 148篇 |
2020年 | 108篇 |
2019年 | 156篇 |
2018年 | 141篇 |
2017年 | 130篇 |
2016年 | 188篇 |
2015年 | 140篇 |
2014年 | 177篇 |
2013年 | 239篇 |
2012年 | 312篇 |
2011年 | 337篇 |
2010年 | 186篇 |
2009年 | 196篇 |
2008年 | 284篇 |
2007年 | 251篇 |
2006年 | 232篇 |
2005年 | 208篇 |
2004年 | 171篇 |
2003年 | 112篇 |
2002年 | 110篇 |
2001年 | 51篇 |
2000年 | 46篇 |
1999年 | 40篇 |
1998年 | 48篇 |
1997年 | 46篇 |
1996年 | 41篇 |
1995年 | 26篇 |
1994年 | 7篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 21篇 |
1990年 | 4篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1972年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有4447条查询结果,搜索用时 15 毫秒
101.
102.
A. Ya. Samuilov S. V. Nesterov F. B. Balabanova Ya. D. Samuilov A. I. Konovalov 《Russian Journal of Organic Chemistry》2013,49(7):968-973
The mechanisms of the reactions of methyl isocyanate with phenol monomer and linear dimer were studied at the B3LYP/6-311++G(df,p) level of theory, and the results were compared with those obtained for the reactions with methanol associates. All the examined reactions involve asymmetric concerted transition states. The addition of phenol is electrophilic, whereas the addition of methanol is nucleophilic. The formation of H-complexes with phenol and methanol molecules increases not only electron-donating power but also gasphase acidity and basicity. 相似文献
103.
104.
Natalia A. Romanova Maria A. Fritz Dr. Kaichin Chang Dr. Nadezhda B. Tamm Dr. Alexey A. Goryunkov Prof. Lev N. Sidorov Dr. Chuanbao Chen Prof. Shangfeng Yang Prof. Erhard Kemnitz Prof. Sergey I. Troyanov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(35):11707-11716
Trifluoromethylation of a higher fullerene mixture with CF3I was performed in ampoules at 550 °C. HPLC separation followed by crystal growth and X‐ray diffraction study resulted in the structure elucidation of nine CF3 derivatives of D2d‐C84 (isomer 23). The molecular structures of C84(23)(CF3)4, C84(23)(CF3)8, C84(23)(CF3)10, C84(23)(CF3)12, two isomers of C84(23)(CF3)14, two isomers of C84(23)(CF3)16, and C84(23)(CF3)18 were discussed in terms of their addition patterns and the relative formation energies. Extensive theoretical DFT calculations were performed to identify the most stable molecular structures. It was found that the addition of CF3 groups to the C84(23) fullerene is governed by two main rules: no additions in positions of triple hexagon junctions and predominantly para additions in C6(CF3)2 hexagons on the fullerene cage. The only exception with an isolated CF3 group in C84(23)(CF3)12 is discussed in more detail. 相似文献
105.
106.
Nataliya A. Samoylova Nikita M. Belov Victor A. Brotsman Dr. Ilya N. Ioffe Dr. Natalia S. Lukonina Dr. Vitaliy Yu. Markov Dr. Adrian Ruff Alexey V. Rybalchenko Paul Schuler Olesya O. Semivrazhskaya Prof. Dr. Bernd Speiser Prof. Dr. Sergey I. Troyanov Prof. Dr. Tatiana V. Magdesieva Dr. Alexey A. Goryunkov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(52):17969-17979
Novel difluoromethylenated [70]fullerene derivatives, C70(CF2)n (n=1–3), were obtained by the reaction of C70 with sodium difluorochloroacetate. Two major products, isomeric C70(CF2) mono‐adducts with [6,6]‐open and [6,6]‐closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X‐ray analysis and high‐level spectroscopic techniques. The [6,6]‐open isomer of C70(CF2) constitutes the first homofullerene example of a non‐hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C70(CF2) isomers showed that it is substantially higher for the [6,6]‐open isomer (the 70‐electron π‐conjugated system is retained) than the [6,6]‐closed form, the latter being similar to the electron affinity of pristine C70. In situ ESR spectroelectrochemical investigation of the C70(CF2) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter‐conversion between the [6,6]‐closed and [6,6]‐open forms of a cage‐modified fullerene driven by an electrochemical one‐electron transfer. Thus, [6,6]‐closed C70(CF2) constitutes an interesting example of a redox‐switchable fullerene derivative. 相似文献
107.
Elena A. Shalamova Yeosan Lee Garam Chung Artem N. Semakin Jinho Oh Alexey Yu. Sukhorukov Dmitry E. Arkhipov Sema L. Ioffe Sergey E. Semenov 《Tetrahedron letters》2014
A general strategy for the assembly of previously unknown tris(β,β,γ-oximinoalkyl)amines from aliphatic nitro compounds and methyl vinyl ketone is described. The strategy involves N,N-bis(siloxy)enamines as key intermediates. The latter are accessible by double silylation of alkylnitro compounds. Nickel(II) and copper(II) complexes of tris(β,β,γ-oximinoalkyl)amines are prepared and structurally characterized. 相似文献
108.
Dawid Kedracki Sergey K. Filippov Nidhi Gour Helmut Schlaad Corinne Nardin 《Macromolecular rapid communications》2015,36(8):768-773
Conjugation of a hydrophobic poly(2‐oxazoline) bearing tertiary amide groups along its backbone with a short single stranded nucleotide sequence results in an amphiphilic comb/graft copolymer, which organizes in fibrils upon direct dissolution in water. Supported by circular dichroism, atomic force microscopy, transmission electron microscopy, and scattering data, fibrils are formed through inter‐ and intramolecular hydrogen bonding between hydrogen accepting amide groups along the polymer backbone and hydrogen donating nucleic acid grafts leading to the formation of hollow tubes.
109.
Sergey V. Prikhodko Diana C. Rambaldi Andrew King Elizabeth Burr Vanessa Muros Ioanna Kakoulli 《Journal of Raman spectroscopy : JRS》2015,46(7):632-635
In the past decade Surface Enhanced Raman Scattering (SERS) has emerged as a powerful technique for the analysis of artistic, historical and archaeological material culture. However, the identification of organic compounds in complex samples using SERS can be challenging owing to the complexity in optimizing the adsorption of target analytes onto the plasmonic substrate and the difficulty to identify proper areas on the sample for robust SERS analysis using optical systems. Scanning electron microscopy (SEM) interfaced with Raman spectromicroscopy (μRS) provides an ideal hyphenated system to overcome the last challenge by: (1) evaluating the nanoparticles coverage/distribution on the sample and (2) locating suitable areas for successful and reproducible SERS analysis. In this paper we demonstrate the potential of a system interfacing SEM and μRS for single fiber, extractionless analysis in the characterization of dyes from reference collections and archaeological textiles. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
110.
The paper is concerned with the finite-element analysis of natural vibrations and hydroelastic stability of two parallel plates interacting with liquid. The influence of the fluid layer thickness on the eigenfrequencies, vibration modes and hydroelastic stability boundary are estimated based on the results of numerical solution of some example problems. The numerical investigation substantiates the existence of various instability modes, the onset of which depends on the combinations of kinematic boundary conditions specified at the plate ends. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献