全文获取类型
收费全文 | 1914篇 |
免费 | 58篇 |
国内免费 | 11篇 |
专业分类
化学 | 1561篇 |
晶体学 | 31篇 |
力学 | 29篇 |
数学 | 73篇 |
物理学 | 289篇 |
出版年
2023年 | 10篇 |
2022年 | 21篇 |
2021年 | 19篇 |
2020年 | 25篇 |
2019年 | 30篇 |
2018年 | 20篇 |
2016年 | 31篇 |
2015年 | 34篇 |
2014年 | 43篇 |
2013年 | 118篇 |
2012年 | 90篇 |
2011年 | 103篇 |
2010年 | 77篇 |
2009年 | 70篇 |
2008年 | 117篇 |
2007年 | 94篇 |
2006年 | 117篇 |
2005年 | 97篇 |
2004年 | 88篇 |
2003年 | 84篇 |
2002年 | 112篇 |
2001年 | 29篇 |
2000年 | 21篇 |
1999年 | 31篇 |
1998年 | 19篇 |
1997年 | 26篇 |
1996年 | 26篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 28篇 |
1981年 | 20篇 |
1980年 | 27篇 |
1979年 | 22篇 |
1978年 | 17篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1975年 | 15篇 |
1973年 | 12篇 |
1972年 | 8篇 |
排序方式: 共有1983条查询结果,搜索用时 15 毫秒
981.
Koichi Sakamaki Joji Ohshita Atsutaka Kunai Hidenobu Nakao Akira Adachi Koichi Okita 《应用有机金属化学》2001,15(7):604-612
We have synthesized novel σ–π conjugated polymers with an alternating organosilanylene and π‐electron system, intending to utilize them for hole‐transporting materials of electroluminescent (EL) devices. 3,6‐Di(lithioethynyl)carbazoles were co‐polymerized with organodichlorosilanes to give the corresponding polymers with molecular weights of MW = 2000–5000. Another type of polymer with a thienylene unit was also synthesized by the nickel‐catalyzed reaction of the di‐Grignard reagent of 1,2‐bis[2‐(5‐bromothienyl)]tetraethyldisilane with 3,6‐dibromocarbazole, the molecular weight being Mn = 3100. The EL devices with a double‐layer system composed of tris(8‐quinolinolato)aluminum(III) and the present polymers as the emitting‐electron‐transporting and hole‐transporting layers, respectively, emit green EL with a maximum intensity of the order of 103 cd m?2. Of these, the device with the thienylene–carbazole polymers exhibited the highest luminance of 1480 cd m?2. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
982.
We report atomic scale flattening of surfaces of microstructures formed on Si wafers by furnace annealing. To avoid thermal deformation of the fabricated structures, advantage was taken of hydrogen annealing, which enables us to decrease the relaxation rate of Si surfaces due to surface hydrogenation. We examined cross-sectional shape and sidewall morphology of 3 μm deep trenches on Si(0 0 1) substrates after annealing at 1000 °C under various H2 pressures of 40-760 Torr. We successfully formed Si trenches with flat surfaces composed of terraces and steps while preserving the designed trench profile by increasing H2 pressure to 760 Torr. 相似文献
983.
984.
985.
This paper applies the SDP (semidefinite programming)relaxation originally developed for a 0-1 integer program to ageneral nonconvex QP (quadratic program) having a linear objective functionand quadratic inequality constraints, and presents some fundamental characterizations of the SDP relaxation including its equivalence to arelaxation using convex-quadratic valid inequalities for the feasible regionof the QP. 相似文献
986.
Hiroki Sakurai Noboru Ebihara Eiji Osawa Makoto Takahashi Masanori Fujinami Koichi Oguma 《Analytical sciences》2006,22(3):357-362
A nanodiamond with a mean particle size of 4 nm, which was prepared by the detonation of a nanodiamond, has been characterized and used as a collector for tungstate in water samples. An aqueous solution of nanodiamond was found to be stable over the pH range from 3 to 10. Coagulation of the nanodiamond could be brought about by adding an electrolyte solution. The adsorption characteristics of nanodiamond have been elucidated to be attributable to amino groups on its surface by the elemental-analysis data and the zeta potential measured in weak acid media. The unique adsorption properties of the nanodiamond for oxoacid anions were applied to a selective preconcentration method for tungstate in water samples. An appropriate amount of nanodiamond was added to a sample solution at pH 5 and a calcium chloride solution was added to aggregate nanodiamond. The sample solution was then allowed to stand for 2 h and centrifuged. The nanodiamond was transferred onto a membrane filter, washed with a diluted calcium chloride solution and treated in advance of an ICP-AES measurement by either of the following procedures: (a) redispersion of the nanodiamond into dilute nitric acid with an ultrasonic washer and (b) ashing of the membrane filter and the coagulated nanodiamond at 700 degrees C, followed by a treatment of the ash with hydrochloric and tartaric acids. The average recovery of tungstate from 100-ml artificial river-water was found to be 99% at the 0.25 ppm level with an RSD of 2.2% (n = 3). The concentration factor at present is 10. 相似文献
987.
It is known that a doubly periodic guided-mode resonant grating (GMRG) filter has a broad angular selectivity with a narrow spectral bandwidth. This means that the doubly periodic GMRG filter operates for small beam diameter and grating area. This report describes the wave localization in the doubly periodic GMRG filter. We investigated the spread area of light waves in the waveguide layer and the accumulation of field energy by numerical simulation using the finite differential time domain (FDTD) method. Simulation results showed that, in the case of a doubly periodic GMRG filter with a Q factor of 600, the field energy is spread over an area 5 um in width, which corresponds to the expected value from the angular tolerance. And the magnitude of the field energy in the waveguide layer was Q factor times greater than the incident energy. On the other hand, a singly periodic GMRG filter with the same Q factor spread the field energy over an area 72 urn in width. This filter does not work for a small size structure or a small diameter light beam. 相似文献
988.
Numerical study on three-dimensional C-J detonation waves: detailed propagating mechanism and existence of OH radical 总被引:1,自引:0,他引:1
Keitaro Eto Nobuyuki Tsuboi A. Koichi Hayashi 《Proceedings of the Combustion Institute》2005,30(2):1907-1913
An unsteady three-dimensional simulation is performed for a hydrogen/air C–J detonation in a rectangular tube, where a detailed chemical reaction model is used to reveal the C–J detonation structure. In this simulation, detailed propagating detonation structures for a diagonal mode are described in three-dimensions. The detonation front structures, the line of triple points, and the strong explosions at the corners of the rectangular tube are revealed by using a three-dimensional numerical visualization. From the spatial isosurface profiles of H2 mass fraction, it is confirmed that the triple point lines have a role of “shutter” to generate unburned gas pockets and become of a ring shape behind the detonation front due to its explosion. The explosion process and its influence on an induction delay are observed by visualizing the spatial isosurface profiles of OH mass fraction. Moreover, a high “peninsula-shaped” OH mass fraction area, which has been experimentally reported, is reproduced on the side wall of the rectangular tube. 相似文献
989.
Koichi Kuroda Kaoru Yoshida Mieko Yoshimura Yoko Endo Hideki Wanibuchi Shoji Fukushima Ginji Endo 《应用有机金属化学》2005,19(2):221-225
Arsenic is a carcinogen in humans. However, neither the mechanism of action nor the ultimate chemical form of arsenic which causes cancer has been clearly defined. Dimethylarsinous acid is detected in the urine of individuals who ingest arsenic‐polluted drinking water. The cytogenetic study in V79 cells using iododimethylarsine, which is easily hydrolyzed to dimethylarsinous acid in water, revealed that dimethylarsinous acid was very cytotoxic (50% growth inhibition concentration; 1.1 ± 0.14 µM ), and either induced aneuploids or a high rate of tetraploids (73% at 2.5 µM ). Dimethylarsinous acid caused mitotic arrest, since the mitotic index at toxic dose (5 µM ) was 13.9%, significantly higher than the control (2.7%). Dimethylarsinous acid significantly increased sister chromatid exchange (SCE) and chromosomal aberrations, most of which were chromatid gaps and chromatid breaks. The cytotoxicity and the activity of dimethylarsinous acid in inducing chromosomal aberration or SCE was as effective as arsenite, but the activity was much lower than that of mitomycin C, which was used as a positive control. The most potent effects of dimethylarsinous acid on the cells were induction of aneuploids, tetraploids and c‐mitosis. Our results suggest that toxicity of dimethylarsinous acid is strongly related to the disturbance of the normal cell cycle. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
990.
Effect of Water Vapor on Benzene Decomposition Using a Nonthermal-Discharge Plasma Reactor 总被引:4,自引:0,他引:4
Ogata Atsushi Shintani Noboru Yamanouchi Kazushi Mizuno Koichi Kushiyama Satoshi Yamamoto Toshiaki 《Plasma Chemistry and Plasma Processing》2000,20(4):453-467
The effect of water vapor on benzene decomposition in air was investigatedusing a nonthermal-discharge plasma reactor packed with ferroelectricmaterials. The conversion of benzene was found to decrease with an increaseof water concentration. On the other hand, the selectivity to CO2 in thedecomposition products increased with an increase of water concentration. Acomparison between the benzene conversion to CO and CO2 suggested that COformation was suppressed by water to a greater extent than was CO2formation. N2O formation also decreased with an increase of waterconcentration. These results suggest that the activity of oxygen speciesresponsible for the formation of CO and N2O is reduced by water. 相似文献