全文获取类型
收费全文 | 2134篇 |
免费 | 70篇 |
国内免费 | 4篇 |
专业分类
化学 | 1728篇 |
晶体学 | 34篇 |
力学 | 30篇 |
数学 | 76篇 |
物理学 | 340篇 |
出版年
2021年 | 14篇 |
2020年 | 27篇 |
2019年 | 29篇 |
2018年 | 24篇 |
2017年 | 9篇 |
2016年 | 37篇 |
2015年 | 45篇 |
2014年 | 50篇 |
2013年 | 135篇 |
2012年 | 101篇 |
2011年 | 121篇 |
2010年 | 80篇 |
2009年 | 83篇 |
2008年 | 123篇 |
2007年 | 110篇 |
2006年 | 128篇 |
2005年 | 117篇 |
2004年 | 88篇 |
2003年 | 93篇 |
2002年 | 91篇 |
2001年 | 30篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 27篇 |
1996年 | 23篇 |
1995年 | 23篇 |
1994年 | 23篇 |
1993年 | 21篇 |
1992年 | 22篇 |
1991年 | 23篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 20篇 |
1986年 | 14篇 |
1985年 | 42篇 |
1984年 | 37篇 |
1983年 | 16篇 |
1982年 | 32篇 |
1981年 | 20篇 |
1980年 | 30篇 |
1979年 | 31篇 |
1978年 | 21篇 |
1977年 | 23篇 |
1976年 | 23篇 |
1975年 | 21篇 |
1974年 | 10篇 |
1973年 | 13篇 |
1972年 | 10篇 |
排序方式: 共有2208条查询结果,搜索用时 15 毫秒
1.
Anodic stripping voltammetry was made in AgNO3 solution, here Ag was deposited under long term potentiostatic conditions to evaluate the reduction charge, qr, and then was stripped by linear sweep voltammetry to determine the oxidation charge, qo. The charges were unbalanced, satisfying ca. qo=0.7|qr|, where other possible reduction charge such as by dioxygen and dichlorosilver were subtracted. The 30 % loss of the anodic charge can be ascribed to the negative capacitance by the potential sweep generation of Ag+. The generated Ag+ forms a dipole with a counter ion, of which orientation is the same as the direction of the externally applied electric field and opposite to the dipoles of solvent. The redox dipole decreases the conventional double layer capacitance caused by solvent dipoles, and high concentrations of Ag+ takes the capacitance to be negative values. The unbalanced charge, however, has no influence on quantitative determination of concentrations Ag+ by use of a calibration line. 相似文献
2.
Prof. James S. M. Anderson Prof. Juan I. Rodríguez Prof. Paul W. Ayers Daniel E. Trujillo-González Dr. Andreas W. Götz Prof. Jochen Autschbach Prof. Fray L. Castillo-Alvarado Prof. Koichi Yamashita 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(10):2538-2544
The topology of the molecular electron density of benzene dithiol gold cluster complex Au4−S−C6H4−S′−Au′4 changed when relativistic corrections were made and the structure was close to a minimum of the Born–Oppenheimer energy surface. Specifically, new bond paths between hydrogen atoms on the benzene ring and gold atoms appeared, indicating that there is a favorable interaction between these atoms at the relativistic level. This is consistent with the observation that gold becomes a better electron acceptor when relativistic corrections are applied. In addition to relativistic effects, here, we establish the sensitivity of molecular topology to basis sets and convergence thresholds for geometry optimization. 相似文献
3.
Takahiro Yonezawa Tatsuya Murakami Koichi Higashimine Antoine Fleurence Yoshifumi Oshima Yukiko Yamada-Takamura 《Surface and interface analysis : SIA》2019,51(1):95-99
Layered materials can be grown on various substrates through van der Waals epitaxy (vdWE) regardless of lattice mismatch. The atomistic study of the film-substrate interface in vdWE is becoming increasingly important due to their expected applications as two-dimensional (2D) materials. In this contribution, we have grown GaSe thin films on Ge(111) substrates by molecular beam epitaxy and studied the GaSe/Ge(111) interface using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Cross-sectional HAADF-STEM observations revealed that the grown layers adopt predominantly the expected wurtzite-like structure and stacking, but layers with zinc-blende-like structure, similar to Ga2Se3 but apparently different, and other layer stacking sequences, exist locally near the film-substrate interface. These results demonstrate that even in vdWE, structural changes can occur in the grown layers adjacent to the substrate, highlighting the importance of such interface for synthesizing and applying ultimately thin 2D materials. 相似文献
4.
Chikashi Shinagawa Yusuke Morikawa Shin-ichi Nishimura Hiroshi Ushiyama Atsuo Yamada Koichi Yamashita 《Journal of computational chemistry》2019,40(1):237-246
Na2FePO4F is a promising cathode material for a Na-ion battery because of its high electronic capacity and good cycle performance. In this work, first principle calculations combined with cluster expansion and the Monte Carlo method have been applied to analyze the charge and discharge processes of Na2FePO4F by examining the voltage curve and the phase diagram. As a result of the density functional theory calculation and experimental verification with structural analysis, we found that the most stable structure of Na1.5FePO4F has the P21/b11 space group, which has not been reported to date. The estimated voltage curve has two clear plateaus caused by the two-phase structure composed of P21/b11 Na1.5FePO4F and Pbcn Na2FePO4F or Na1FePO4F and separated along the c-axis direction. The phase diagram shows the stability of the phase-separated structure. Considering that Na2FePO4F has diffusion paths in the a- and c-axis directions, Na2FePO4F has both innerphase and interphase diffusion paths. We suggest that the stable two-phase structure and the diffusion paths to both the innerphase and interphases are a key for the very clear plateau. We challenge to simulate a nonequilibrium state at high rate discharge with high temperature by introducing a coordinate-dependent chemical potential. The simulation shows agreement with the experimental discharge curve on the disappearance of the two plateaus. © 2018 Wiley Periodicals, Inc. 相似文献
5.
6.
[Eu(pda)2]? and [Eu(bda)2]? (pda=1,10‐phenanthroline‐2, 9‐dicarboxylic acid; bda=2,2′ bipyridine 5,5′‐dicarboxylic acid) have an achiral D2d structure in crystals. These complexes exhibit circularly polarized luminescence (CPL) in water containing chiral amino acids. In this work, induced CPL of [Eu(pda)2]? and [Eu(bda)2]? in water solutions containing a mixture of d ‐ and l ‐ amino acids were examined. Plots of glum values of the induced CPL as a function of mol‐fraction of l ‐ and d ‐ arginine reveal that [Eu(pda)2]? favors homo‐association ([Eu(pda)2]?‐(l ‐arginine)2 or [Eu(pda)2]?‐(d ‐arginine)2) over hetero‐association {[Eu(pda)2]?‐(l ‐arginine)?(d ‐arginine)}. This suggests that association of an arginine molecule induces a structural change in [Eu(pda)2]? to promote chiral selective association to another arginine, i.e., homo‐allosteric association. On the other hand, the system of [Eu(pda)2]? with histidine favors hetero‐allosteric association over homo‐association. No allosteric effect is recognized in CPL from [Eu(bda)2]?. 相似文献
7.
Nobuyuki Otozawa Rio Hamajima Masataka Yoshioka Raito Kato Arisa Tanaka Hiroto Fukuma Toshiki Terao Kei Manabe Syuji Fujii Yoshinobu Nakamura Atsushi Takahara Tomoyasu Hirai 《Journal of polymer science. Part A, Polymer chemistry》2020,58(14):1960-1964
This study investigates the effect of ionic liquids (ILs) on the anionic polymerization of methyl methacrylate (MMA). Polymethyl methacrylate (PMMA), an isotactic polymer, is prepared by anionic polymerization at a high reaction temperature with an IL that acts as both solvent and additive. The most plausible reaction mechanism is determined using 1H NMR and Fourier-transform infrared spectroscopy. The electrostatic interaction between MMA and the IL increases the apparent steric hindrance in MMA, resulting in the isotactic PMMA. 相似文献
8.
Optical Review - The optical properties of a metal are revisited. Starting from Maxwell’s equations, a rigorous calculation on the reflection and refraction of light at the interface between... 相似文献
9.
Coronenetetraimide‐Centered Cruciform Pentamers Containing Multiporphyrin Units: Synthesis and Sequential Photoinduced Energy‐ and Electron‐Transfer Dynamics 下载免费PDF全文
Prof. Taku Hasobe Koichi Ida Dr. Hayato Sakai Prof. Kei Ohkubo Prof. Shunichi Fukuzumi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(31):11196-11205
A series of coronenetetraimide (CorTIm)‐centered cruciform pentamers containing multiporphyrin units, in which four porphyrin units are covalently linked to a CorTIm core through benzyl linkages, were designed and synthesized to investigate their structural, spectroscopic, and electrochemical properties as well as photoinduced electron‐ and energy‐transfer dynamics. These systems afforded the first synthetic case of coroneneimide derivatives covalently linked with dye molecules. The steady‐state absorption and electrochemical results indicate that a CorTIm and four porphyrin units were successfully characterized by the corresponding reference monomers. In contrast, the steady‐state fluorescence measurements demonstrated that strong fluorescence quenching relative to the corresponding monomer units was observed in these pentamers. Nanosecond laser flash photolysis measurements revealed the occurrence of intermolecular electron transfer from triplet excited state of zinc porphyrins to CorTIm. Femtosecond laser‐induced transient absorption measurements for excitation of the CorTIm unit clearly demonstrate the sequential photoinduced energy and electron transfer between CorTIm and porphyrins, that is, occurrence of the initial energy transfer from CorTIm (energy donor) to porphyrins (energy acceptor) and subsequent electron transfer from porphyrins (electron donor) to CorTIm (electron acceptor) in these pentamers, whereas only the electron‐transfer process from porphyrins to CorTIm was observed when we mainly excite porphyrin units. Finally, construction of high‐order supramolecular patterning of these pentamers was performed by utilizing self‐assembly and physical dewetting during the evaporation of solvent. 相似文献
10.
Reconstitution of Biosynthetic Machinery for the Synthesis of the Highly Elaborated Indole Diterpene Penitrem 下载免费PDF全文
Dr. Chengwei Liu Koichi Tagami Dr. Atsushi Minami Tomoyuki Matsumoto Jens Christian Frisvad Hideyuki Suzuki Jun Ishikawa Katsuya Gomi Prof. Dr. Hideaki Oikawa 《Angewandte Chemie (International ed. in English)》2015,54(19):5748-5752
Penitrem A is one of the most elaborated members of the fungal indole diterpenes. Two separate penitrem gene clusters were identified using genomic and RNA sequencing data, and 13 out of 17 transformations in the penitrem biosynthesis were elucidated by heterologous reconstitution of the relevant genes. These reactions involve 1) a prenylation‐initiated cationic cyclization to install the bicyclo[3.2.0]heptane skeleton (PtmE), 2) a two‐step P450‐catalyzed oxidative processes forming the unique tricyclic penitrem skeleton (PtmK and PtmU), and 3) five sequential oxidative transformations (PtmKULNJ). Importantly, without conventional gene disruption, reconstitution of the biosynthetic machinery provided sufficient data to determine the pathway. It was thus demonstrated that the Aspergillus oryzae reconstitution system is a powerful method for studying the biosynthesis of complex natural products. 相似文献