全文获取类型
收费全文 | 1100篇 |
免费 | 40篇 |
国内免费 | 6篇 |
专业分类
化学 | 930篇 |
晶体学 | 11篇 |
力学 | 19篇 |
数学 | 49篇 |
物理学 | 137篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 14篇 |
2020年 | 21篇 |
2019年 | 12篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 18篇 |
2015年 | 17篇 |
2014年 | 24篇 |
2013年 | 41篇 |
2012年 | 67篇 |
2011年 | 83篇 |
2010年 | 38篇 |
2009年 | 47篇 |
2008年 | 63篇 |
2007年 | 60篇 |
2006年 | 67篇 |
2005年 | 78篇 |
2004年 | 60篇 |
2003年 | 58篇 |
2002年 | 55篇 |
2001年 | 20篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1998年 | 17篇 |
1997年 | 19篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1986年 | 7篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1980年 | 20篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1966年 | 1篇 |
排序方式: 共有1146条查询结果,搜索用时 62 毫秒
991.
Kenichi Maruyama Yuji Mishima Keiji Minagawa Junko Motonaka 《Journal of Electroanalytical Chemistry》2001,510(1-2)
A transition metal complex as an electrochemical probe of a DNA sensor must have an applicable redox potential, high binding affinity and chemical stability. Some complexes with the dipyrido[3,2-a:2′,3′-c]phenazine (DPPZ) ligand have been reported to have high binding affinity for DNA. However, it was difficult to detect the targeted DNA electrochemically using these complexes because of the relatively high redox potential. In this work, a combination of bipyridine ligands with functional groups (---NH2, ---CH3 and ---COOH) and the DPPZ ligand were studied. The introduction of electron-donating groups was effective for controlling the redox potential of the DPPZ-type osmium complex. The [Os(DA-bpy)2DPPZ]2+ complex (DA-bpy; 4,4′-diamino-2,2′-bipyridine) had a lower half-wave potential (E1/2) of 147 mV (vs. Ag AgCl) and higher binding affinity with DNA {binding constant, K=3.1×107 M−1 in 10 mmol dm−3 Tris–HCl buffer with 50 mmol dm−3 NaCl (pH 7.76)} than those of other complexes. With the single stranded DNA (ssDNA) modified gold electrode, the hybridization signal (ΔI) of the [Os(DA-bpy)2DPPZ]2+ complex was linear in the concentration range of 1.0 pg ml−1–0.12 μg ml−1 for the targeted DNA with a regression coefficient of 0.999. The detection limit was 0.1 pg ml−1. 相似文献
992.
Gary J. Van Berkel Keiji G. Asano Paul D. Schnier 《Journal of the American Society for Mass Spectrometry》2001,12(7):853-862
Experiments are described that illustrate solvent oxidation, emitter electrode corrosion, and analyte oxidation in positive ion mode nano-electrospray mass spectrometry using a wire-in-a-capillary, bulk-loaded nano-electrospray emitter geometry. Time-lapsed color photography of pH and metal specific indicator solutions within operating nano-electrospray emitters, as well as temporal changes in the ions observed in the nano-electrospray mass spectra, are used to probe these reactions, judge their magnitude, and study the time dependent changes in solution composition and gas-phase ion signal brought about as a result of these electrochemical reactions. The significance of these observations for analytical applications of nano-electrospray mass spectrometry are discussed. 相似文献
993.
A tungsten trioxide (WO3) film was prepared by calcination from a precursor paste including suspended ammonium tungstate and polyethylene glycol (PEG). The ammonium tungstate suspension was yielded by an acid-base reaction of tungstic acid and an ammonium solution followed by deposition with ethanol addition. Thermogravimetric (TG) analysis showed that the TG profile of PEG is significantly influenced by deposited ammonium tungstate, suggesting that PEG is interacting strongly with deposited ammonium tungstate in the suspension paste. X-ray diffraction (XRD) data indicated that the WO3 film is crystallized by sintering over 400 °C. The scanning electron microscopic (SEM) measurement showed that the film is composed of the nano-structured WO3 platelets. The semiconductor properties of the film were examined by Mott-Schottky analysis to give flat band potential EFB=0.30 V vs. saturated calomel reference electrode (SCE) and donor carrier density ND=2.5×1022 cm−3, latter of which is higher than previous WO3 films by two orders of magnitude. The higher ND was explained by the large interfacial heterojunction area caused by the nano-platelet structure, which apparently increases capacitance per a unit electrode area. The WO3 film sintered at 550 °C produced 3.7 mA cm−2 of a photoanodic current at 1.2 V vs. SCE under illumination with a 500 W xenon lamp due to catalytic water oxidation. This photocurrent was 4.5-12.8 times higher than those for the other control WO3 films prepared by similar but different procedures. The high catalytic activity could be explained by the nano-platelet structure. The photocurrent was generated on illumination of UV and visible light below 470 nm, and the maximum incident photon-to-current conversion efficiency (IPCE) was 47% at 320 nm at 1.2 V. Technically important procedures for preparation of nano-structured platelets were discussed. 相似文献
994.
995.
Hiroko Kuritani Seiichi Imajo Keiji Shingu Masazumi Nakagawa 《Tetrahedron letters》1979,20(19):1697-1700
(+)-endo-cis-Bicyclo[3.3.0]oct-7-en-2-ol gave good optical yields in the kinetic resolution of aryl-t-butylacetic anhydrice, establishing the absolute configuration of t-butyl-α-naphthylacetic acid as (S) - (+). 相似文献
996.
997.
Naoki Oguri Akira Onishi Sigeki Uchino Keiji Nakahashi Nakamichi Yamasaki Xigao Jin 《Journal of separation science》1993,16(10):597-600
High speed hydrothermal decomposition of some chemically inert condensation polymers in alkaline solutions under near-critical pressures and temperatures has been investigated by on-line Curie-point heating–high resolution GC-MS. The technique also involves simultaneous methylation with tetramethylammonium hydroxide in a 1 mm i.d. × 20 mm sealed glass capillary. The relative standard deviation for the peak intensity (mol %) resulting from ten replicate measurements of poly(butylene terephthalate) is approximately 3%. This method requires a small amount of sample (ca. 0.1 mg) and provides simple chromatograms, greater structural information, good reproducibility, and rapid reaction (0.5–15 min) without chemical treatment. A brief overview of applications to the characterization of some condensation polymers such as aromatic polyester, polycarbonate, and aliphatic and aromatic polyamide is also described. 相似文献
998.
Keiji Matsumura Kentarou Kawaguchi Keiichi Nagai Chikashi Yamada Eizi Hirota 《Journal of Molecular Spectroscopy》1980,84(1):68-73
The v = 1 ← 0 vibration-rotation bands of the NS radical in the and electronic states were observed by using a tunable diode laser. From the least-squares analysis the band origins were determined to be 1204.2755(12) and 1204.0892(19) cm?1, respectively, for and . The rotational and centrifugal distortion constants and the internuclear distance in the X2Π electronic state were obtained as follows: Be = 0.775549(10) cm?1, De = 0.00000129(33) cm?1, and , with three standard deviations indicated in parentheses. 相似文献
999.
Degree of color constancy was measured when color memory was involved in color comparison judgment. We used the Optical Society of America (OSA) Uniform Color Scales as stimulus color samples, and chose 20 color samples as test stimuli. Four illuminants of 1700, 3000, 6500, and 30, 000 K were tested. The observer, completely adapted to a test illuminant, saw a test color sample and stored its color in his memory. After being readapted to the reference white (6500 K), he started selecting a color sample from among the 424 OSA samples which matched the test sample in his memory. We employed a memory matching method called cascade color matching, in which the number of selected color-samples was gradually reduced in four stages. In the final stage, the observer selected a color sample. The results show that, for most test colors, the distributions of selected colors in stages 1 to 4 were similar among all illuminants, and that the u’v’ chromaticity distance between a test color under 6500 K and its matched color was quite short. These indicate that good color constancy was retained in memory color comparison. 相似文献
1000.
Gary J. Van Berkel Keiji G. Asano Scott A. McLuckey 《Journal of the American Society for Mass Spectrometry》1994,5(7):689-692
The first observation of organic dications formed by multiple electron loss in electrospray mass spectra is reported. The dications of β-carotene, canthaxanthine, cobalt(II) octaethylporphyrin, and nicke(II) octaethylporphyrin were created in solution via chemical electrontransfer reactions and detected in the gas phase by electrospray ionization mass spectrometry (ES-MS) using a flow-injection experiment. The analytes were injected into a flowing solvent-oxidant stream (10 μL/min) composed of dried methylene chloride containing ≈ 0.1% by volume trifluoroacetic acid and 0.1% by volume antimony pentafluoride (SbF5). The dications created in this oxidizing solvent system were preserved for detection by rapidly transferring them from the reactive solvent-oxidant system to the gas phase, where, in the absence of the solvent system, they were “long-lived” and amenable to mass analysis. This work demonstrates means to produce ions novel to ES-MS and means to detect and study by ES-MS species that are short-lived in solution. In addition, this work shows that electrospray ionization can potentially be used to generate gas-phase dications for mass spectrometric study that are difficult to produce directly from gas-phase neutrals by other ionization techniques (e.g., M2+ from β-carotene). 相似文献