全文获取类型
收费全文 | 597篇 |
免费 | 42篇 |
国内免费 | 3篇 |
专业分类
化学 | 495篇 |
晶体学 | 15篇 |
力学 | 5篇 |
数学 | 32篇 |
物理学 | 95篇 |
出版年
2023年 | 8篇 |
2022年 | 6篇 |
2021年 | 17篇 |
2020年 | 21篇 |
2019年 | 22篇 |
2018年 | 16篇 |
2017年 | 11篇 |
2016年 | 23篇 |
2015年 | 18篇 |
2014年 | 23篇 |
2013年 | 40篇 |
2012年 | 60篇 |
2011年 | 61篇 |
2010年 | 30篇 |
2009年 | 28篇 |
2008年 | 38篇 |
2007年 | 36篇 |
2006年 | 34篇 |
2005年 | 25篇 |
2004年 | 21篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1995年 | 4篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 7篇 |
1972年 | 7篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 2篇 |
排序方式: 共有642条查询结果,搜索用时 62 毫秒
91.
The accelerating effect of Sc(3+) on the electron-transfer (ET) reduction of the p-benzoquinone derivative 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ) by 10,10'-dimethyl-9,9'-biacridine ((AcrH)(2)) at 233 K changes to a decelerating effect with increasing reaction temperature; the observed second-order rate constant k(et) decreases with increasing Sc(3+) concentration at high concentrations of Sc(3+) at 298 K. At 263 K the k(et) value remains constant with increasing Sc(3+) concentration. Such a remarkable difference with regard to dependence of k(et) on [Sc(3+)] between low and high temperatures results from the difference in relative activity of two ET pathways that depend on temperature, one of which affords 1:1 complex TolSQ*(-)-Sc(3+), and the other 1:2 complex TolSQ*(-)-(Sc(3+))(2) with additional binding of Sc(3+) to TolSQ*(-)-Sc(3+). The formation of TolSQ*(-)-Sc(3+) and TolSQ*(-)-(Sc(3+))(2) complexes was confirmed by EPR spectroscopy in the ET reduction of TolSQ in the presence of low and high concentrations of Sc(3+), respectively. The effects of metal ions on other ET reactions of quinones to afford 1:1 and 1:2 complexes between semiquinone radical anions and metal ions are also reported. The ET pathway affording the 1:2 complexes has smaller activation enthalpies DeltaH( not equal) and more negative activation entropies DeltaS( not equal) because of stronger binding of metal ions and more restricted geometries of the ET transition states as compared with the ET pathway to afford the 1:1 complexes. 相似文献
92.
Semiquinone radical anion of 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ(*-)) forms a strong hydrogen bond with protonated histidine (TolSQ(*-)/His x 2 H(+)), which was successfully detected by electron spin resonance. Strong hydrogen bonding between TolSQ(*-) and His x 2 H(+) results in acceleration of electron transfer (ET) from ferrocenes [R2Fc, R = C5H5, C5H4(n-Bu), C5H4Me] to TolSQ, when the one-electron reduction potential of TolSQ is largely shifted to the positive direction in the presence of His x 2 H(+). The rates of His x 2 H(+)-promoted ET from R2Fc to TolSQ exhibit deuterium kinetic isotope effects due to partial dissociation of the N-H bond in His x 2 H(+) at the transition state, when His x 2 H(+) is replaced by the deuterated compound (His x 2 D(+)-d6). The observed deuterium kinetic isotope effect (kH/kD) decreases continuously with increasing the driving force of ET to approach kH/kD = 1.0. On the other hand, His x 2 H(+) also promotes a hydride reduction of TolSQ by an NADH analogue, 9,10-dihydro-10-methylacridine (AcrH2). The hydride reduction proceeds via the one-step hydride-transfer pathway. In such a case, a large deuterium kinetic isotope effect is observed in the rate of the hydride transfer, when AcrH2 is replaced by the dideuterated compound (AcrD2). In sharp contrast to this, no deuterium kinetic isotope effect is observed, when His x 2 H(+) is replaced by His x 2 D(+)-d6. On the other hand, direct protonation of TolSQ and 9,10-phenanthrenequinone (PQ) also results in efficient reductions of TolSQH(+) and PQH(+) by AcrH2, respectively. In this case, however, the hydride-transfer reactions occur via the ET pathway, that is, ET from AcrH2 to TolSQH(+) and PQH(+) occurs in preference to direct hydride transfer from AcrH2 to TolSQH(+) and PQH(+), respectively. The AcrH2(*+) produced by the ET oxidation of AcrH2 by TolSQH(+) and PQH(+) was directly detected by using a stopped-flow technique. 相似文献
93.
Shoma Mizutani Kenta Komori Tohru Taniguchi Kenji Monde Kouji Kuramochi Kazunori Tsubaki 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(33):9705-9708
A biomimetic synthesis of naturally occurring lactams rubrobramide, flavipucine, and isoflavipucine is described. The key step is a regioselective Darzens reaction between isobutyl glyoxal and an α‐bromo‐β‐ketoamide. The construction of the core tricyclic ring system of rubrobramide was achieved by a cascade reaction in a single step from an α,β‐epoxy‐γ‐lactam. Furthermore, the absolute configuration of naturally occurring (+)‐rubrobramide was determined by vibrational circular dichroism. (±)‐Flavipucine and (±)‐isoflavipucine were synthesized from an epoxyimide, which was prepared by reaction of isobutyl glyoxal with a protected α‐bromo‐β‐ketoamide. Deprotection of the epoxyimide and formation of the pyridone ring gave (±)‐flavipucine, which was converted into (±)‐isoflavipucine by thermal isomerization. 相似文献
94.
Dynamic polymers (dynamers) based on reversible imine interactions were generated and found to respond to changes in neat/solution environment, thus displaying adaptive behavior through modification of their constitution in order to maximize the stability of their mesoscopic state as a function of conditions. 相似文献
95.
Determination of vanillin and related flavor compounds in cocoa drink by capillary electrophoresis 总被引:1,自引:0,他引:1
In the first part of this study, the stability of five terpenes (alpha-pinene, limonene, camphor, citronellol, and carvacrol) under subcritical water conditions was investigated. The stability studies were carried out at four different temperatures (100, 150, 200, and 250 degrees C) with two different heating times (30 and 300 min). When water temperature was increased, the degradation of terpenes became more serious. Prolonged exposure time to each heating temperature also caused decreased terpene stability. The terpene recoveries were determined by conducting subcritical water extraction of sand spiked with terpenes. The recoveries are typically around 70 to 80% for extractions at 100 degrees C. Terpene recoveries were decreased with increasing water temperature due to poorer stability of terpenes. After the degradation and recovery studies, basil and oregano leaves were extracted using water at both 100 and 150 degrees C. The concentrations of each individual terpene in the water extract generally ranged from trace quantity to 65 microg terpene/g herb. However, the concentration of carvacrol in the oregano-water extract at 150 degrees C was found to be as high as 4270 microg carvacrol/g oregano. 相似文献
96.
Philip Coppens Mateusz Pitak Milan Gembicky Marc Messerschmidt Stephan Scheins Jason Benedict Shin‐ichi Adachi Tokushi Sato Shunsuke Nozawa Kohei Ichiyanagi Matthieu Chollet Shin‐ya Koshihara 《Journal of synchrotron radiation》2009,16(2):226-230
A RATIO method for analysis of intensity changes in time‐resolved pump–probe Laue diffraction experiments is described. The method eliminates the need for scaling the data with a wavelength curve representing the spectral distribution of the source and removes the effect of possible anisotropic absorption. It does not require relative scaling of series of frames and removes errors due to all but very short term fluctuations in the synchrotron beam. 相似文献
97.
Kazuaki Sakoda Takashi Kuroda NaokiI keda Takaaki Mano Yoshimasa Sugimoto Tetsuyuki Ochiai Keiji Kuroda Shunsuke Ohkouchi Nobuyuki Koguchi Kiyoshi Asakawa 《中国光学快报(英文版)》2009,7(10):879-881
We fabricate photonic crystal slab microcavities embedded with GaAs quantum dots by electron beam lithography and droplet epitaxy. The Purcell effect of exciton emission of the quantum dots is confirmed by the micro photoluminescence measurement. The resonance wavelengths, widths, and polarization are consistent with numerical simulation results. 相似文献
98.
Ultrasound of 2MHz was irradiated to the emulsion prepared from canola oil and water and flocculation of the oil droplets occurred immediately. By putting the emulsion sample in a thin glass cell and setting it in bath type irradiation equipment, the progress of the separation was quantitatively monitored with the optical absorbance. The use of the cell enables visual observation of the behavior of oil droplets. Pictures show the formation of flocks of the dispersed phase and the appearance of checkered pattern consisting of flocks at a regular interval. The observation indicates that the action of radiation forces on oil droplets, which causes the flocculation. The flocks started to rise after stopping irradiation with holding their shape. The rising rate of the flocks was significantly greater than that of oil droplets in the original emulsion. Ultrasonic irradiation caused a rapid decrease in the absorbance, which expresses a progress of the separation. Effects of two major operation parameters, power and time on the separation degree were examined. The degree improved with increasing power input and irradiation time. The dataset was arranged in a plot of normalized separation degree against the input energy. The plot suggests that effective separation was attained with a lower power input and a longer irradiation time. The plot provides a guide for setting condition for the separation. 相似文献
99.
100.
Takaaki Shirai Shunsuke Satou Morihiro Saito Jun Kuwano Hidenobu Shiroishi 《Solid State Ionics》2009,180(6-8):569-574
The proton conducting 0.9MO2·0.05In2O3·1.3P2O5 (MTi, Sn, Zr) electrolytes based on a core-shell structure were synthesized by a ball milling method. The core-shell type electrolytes showed the proton conductivities ranging from a higher value than those of Nafion membranes to 10? 5 Scm? 1 at intermediate temperatures of 150–200 °C, depending on the heat-treatment conditions. The samples with high conductivity were proved to adopt a core-shell structure by SEM observation, powder XRD analysis and 31P MAS-NMR measurements. 相似文献