全文获取类型
收费全文 | 1753篇 |
免费 | 44篇 |
国内免费 | 7篇 |
专业分类
化学 | 1367篇 |
晶体学 | 28篇 |
力学 | 20篇 |
数学 | 122篇 |
物理学 | 267篇 |
出版年
2021年 | 18篇 |
2019年 | 21篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 23篇 |
2015年 | 19篇 |
2014年 | 28篇 |
2013年 | 71篇 |
2012年 | 70篇 |
2011年 | 87篇 |
2010年 | 58篇 |
2009年 | 38篇 |
2008年 | 78篇 |
2007年 | 94篇 |
2006年 | 102篇 |
2005年 | 111篇 |
2004年 | 85篇 |
2003年 | 59篇 |
2002年 | 87篇 |
2001年 | 16篇 |
2000年 | 23篇 |
1999年 | 25篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 28篇 |
1995年 | 25篇 |
1994年 | 17篇 |
1993年 | 21篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 18篇 |
1987年 | 23篇 |
1986年 | 15篇 |
1985年 | 35篇 |
1984年 | 35篇 |
1983年 | 23篇 |
1982年 | 30篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 28篇 |
1978年 | 31篇 |
1977年 | 27篇 |
1976年 | 36篇 |
1975年 | 26篇 |
1974年 | 25篇 |
1973年 | 26篇 |
1972年 | 11篇 |
1971年 | 9篇 |
排序方式: 共有1804条查询结果,搜索用时 312 毫秒
81.
Kazuo Koyama Takashi Hirao Akira Toriba Kazuichi Hayakawa 《Biomedical chromatography : BMC》2013,27(5):583-588
The quality of starch‐containing foods may be significantly impaired by contamination with very small amounts of α‐amylase, which can enzymatically hydrolyze the starch and cause viscosity loss. Thus, for quality control, it is necessary to have an analytical method that can measure low amylase activity. We developed a sensitive analytical method for measuring the activity of α‐amylase (from Bacillus subtilis) in starch‐containing foods. The method consists of six steps: (1) crude extraction of α‐amylase by centrifugation and filtration; (2) α‐amylase purification by desalting and anion‐exchange chromatography; (3) reaction of the purified amylase with boron‐dipyrromethene (BODIPY)‐labeled substrate, which releases a fluorescent fragment upon digestion of the substrate, thus avoiding interference from starch derivatives in the sample; (4) stopping the reaction with acetonitrile; (5) reversed‐phase solid‐phase extraction of the fluorescent substrate to remove contaminating dye and impurities; and (6) separation and measurement of BODIPY fluorescence by HPLC. The proposed method could quantify α‐amylase activities as low as 10 mU/mL, which is enough to reduce the viscosity of starch‐containing foods. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
82.
Dr. Kohsuke Kawabata Prof. Dr. Kazuo Takimiya 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(63):15660-15670
Organic semiconductors with very small optical energy gaps have attracted a lot of attention for near-infrared-active optoelectronic applications. Herein, we present a series of donor-acceptor-donor (D−A−D) organic semiconductors consisting of a highly electron-deficient naphtho[1,2-b:5,6-b′]dithiophene-2,7-dione quinoidal acceptor and oligothiophene donors that show very small optical energy gaps of down to 0.72 eV in the solid state. Investigation of the physicochemical properties of the D−A−D molecules as well as theoretical calculations of their electronic structures revealed an efficient intramolecular interaction between the quinoidal acceptor and the aromatic oligothiophene donors in the D−A−D molecules; this significantly enhances the backbone resonance and thus reduces the bond length alternation along the π-conjugated backbones. Despite the very small optical energy gaps, the D−A−D molecules have low-lying frontier orbital energy levels that give rise to air-stable ambipolar carrier transport properties with hole and electron mobilities of up to 0.026 and 0.043 cm2 V−1 s−1, respectively, in field-effect transistors. 相似文献
83.
Optical Review - Increasing efficiency and productivity in the field of agriculture is important to provide sufficient food to the world’s increasing population. It is important to monitor... 相似文献
84.
Shoraku Ryu Kazuo Furihata Masanori Koda Feifei Wei Takuya Miyakawa Masaru Tanokura 《Magnetic resonance in chemistry : MRC》2016,54(3):213-221
Japanese persimmon (Diospyros kaki L.) is recognized as an outstanding source of biologically active compounds relating to many health benefits. In the present study, NMR spectroscopy provided a comprehensive metabolic overview of Japanese persimmon juice. Detailed signal assignments of Japanese persimmon juice were carried out using various 2D NMR techniques incorporated with broadband water suppression enhanced through T1 effects (BB‐WET) or WET sequences, and 26 components, including minor components, were identified. In addition, most components were quantitatively evaluated by the integration of signals using conventional 1H NMR and BB‐WET NMR. This is the first detailed analysis combined with quantitative characterization of chemical components using NMR for Japanese persimmon. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
85.
Conjugated alkenynes were prepared stereospecifically in moderate to good yields by heating haloalkenes with 1-alkynes in the presence of copper(I) iodide in hexamethylphosphoric triamide (HMPA). 相似文献
86.
The title compound was obtained from 1,3-dichloro-adamantane and some silylating reagents with Na-HMPA. 相似文献
87.
The effect of the dilution of silane and nitrogen with hydrogen on the optical properties of hydrogenated amorphous silicon-nitrogen films prepared by plasma deposition has been investigated as functions of the gas-volume ratio γ (= ([SiH4] + [N2])/([SiH4] + [N2] + [H2]) and the substrate temperature. The prepared films are characterized by the values of the deposition rate, the optical gap, the Urbach energy, the defect density, the integrated infrared absorption intensity and the refractive index, and by correlations between these parameters and the type of hydrogen- and nitrogen-bonding configurations estimated from infrared absorption spectra. The hydrogen dilution effect is discussed in terms of the above and compared with that in hydrogenated amorphous silicon reported in a previous paper by the present authors. It is pointed out that nitrogen atoms incorporated into the silicon network cause more disorder than incorporated hydrogen atoms, from the γ dependence of the Urbach energy and the integrated infrared intensities associated with the hydrogen and nitrogen bondings. 相似文献
88.
Yasuhiro Igarashi Daisuke Asano Kazuo Furihata Naoya Oku Satoshi Miyanaga Hiroaki Sakurai Ikuo Saiki 《Tetrahedron letters》2012,53(6):654-656
During the course of screening natural products for the inhibitors of tumor cell invasion, pterocidin, a linear polyketide with a δ-lactone terminus, was rediscovered from a Streptomyces strain of a marine sediment-origin. A series of J-based configuration analyses and NOESY analysis, coupled with chemical derivatization and chiral anisotropy analysis, established the absolute stereochemistry of five asymmetric centers in this compound. 相似文献
89.
90.
Fluorescence correlation spectroscopy (FCS) of colloidal nanoparticles using a near-field fiber probe was numerically simulated.
The near-wall dynamics was simulated by accounting for the anisotropic mobility of nanoparticles owing to hydrodynamic interaction
with a wall (Stokes viscous force). By comparing the simulation results with theoretical model calculations, we found that
the influence of anisotropic diffusion is insignificant in near-field FCS autocorrelation analysis. 相似文献