全文获取类型
收费全文 | 55142篇 |
免费 | 4761篇 |
国内免费 | 10436篇 |
专业分类
化学 | 54708篇 |
晶体学 | 1581篇 |
力学 | 818篇 |
综合类 | 453篇 |
数学 | 2096篇 |
物理学 | 10683篇 |
出版年
2024年 | 75篇 |
2023年 | 566篇 |
2022年 | 1186篇 |
2021年 | 1549篇 |
2020年 | 1781篇 |
2019年 | 1776篇 |
2018年 | 1507篇 |
2017年 | 1995篇 |
2016年 | 2125篇 |
2015年 | 1969篇 |
2014年 | 2477篇 |
2013年 | 4868篇 |
2012年 | 3544篇 |
2011年 | 3609篇 |
2010年 | 3086篇 |
2009年 | 3573篇 |
2008年 | 3694篇 |
2007年 | 3822篇 |
2006年 | 3556篇 |
2005年 | 3330篇 |
2004年 | 2996篇 |
2003年 | 2436篇 |
2002年 | 2091篇 |
2001年 | 1671篇 |
2000年 | 1599篇 |
1999年 | 1304篇 |
1998年 | 1087篇 |
1997年 | 1031篇 |
1996年 | 906篇 |
1995年 | 885篇 |
1994年 | 779篇 |
1993年 | 666篇 |
1992年 | 568篇 |
1991年 | 405篇 |
1990年 | 286篇 |
1989年 | 296篇 |
1988年 | 235篇 |
1987年 | 152篇 |
1986年 | 131篇 |
1985年 | 113篇 |
1984年 | 104篇 |
1983年 | 61篇 |
1982年 | 84篇 |
1981年 | 70篇 |
1980年 | 69篇 |
1979年 | 60篇 |
1978年 | 53篇 |
1977年 | 32篇 |
1976年 | 18篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The composite comprised of zinc oxide quantum dots and poly(amic acid) (PAAc) was prepared and studied by X-rays diffraction, X-ray photoelectron spectroscopy, light scattering, UV absorbance and UV fluorescence. The UV absorbance of the ZnO/PAAc composite was found to be much larger than that of its components taken separately. The fluorescence of the ZnO/PAAc composite was found to be shifted to longer wavelengthes in comparison with pure ZnO. The presence of the dopant dodecylbenzenesulfonic acid was found to affect the observed fluorescence. 相似文献
72.
《Fiber and Integrated Optics》2007,26(6):335-342
A fiber-optic chemical sensor (FOCS) for detection of nitrogen dioxide (NO2) molecules is reported. The FOCS presents an optropode structure because of the transmission properties of the sensitive material. The NO2 FOCS is activated by using the semiconductor polymer: regioregular head-to-tail poly(3-octylthiophene-2,5-diyl). The operation wavelength of the sensor is 543.5 nm such that a simple LED and detector can be used for the design of this device. The sensor response decreases after each exposure, demonstrating the reduction in sensitivity as well as irreversibility lower than 5%. However, its properties such as rapid response, high selectivity, high sensitivity (0.43 ± 0.01 muW/ppm), hygroscopic properties, and its operation at room temperature make this kind of FOCS a good alternative for NO2 toxic gas detection. 相似文献
73.
The title compound (C2H7NO·C7H4N2O6) has been obtained by the reaction of etha- nolamine with 3,5-dinitrobenzoic acid in deionized water at room temperature. The crystal crystal- lizes in orthorhombic, space group P212121 with a = 6.048(2), b = 9.146(3), c = 21.955(7)(A), C9H11N3O7, Mr = 273.21, Z = 4, V = 1214.3(7)(A)3, Dc = 1.494 g/cm3, F(000) = 568, μ(MoKα) = 0.131 mm-1, R1 = 0.0338 and wR2 = 0.0497. The new organic adduct is composed of one ethanolamine and one 3,5-dinitrobenzoic acid, which are linked up by O-H…O and N-H…O types of hydrogen bonds to form a nine-membered ring and an eleven-membered ring, extending into a one-dimensional network structure. 相似文献
74.
Resistivity-temperature characteristics of sol gel YBa2Cu3Oy samples synthesized in flowing oxygen atmosphere
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The relationship of resistivity versus synthesizing temperature of sol gel YBa_2Cu_3O_y samples was studied when prepared under flowing oxygen conditions. A set of high-temperature ρ-T curves was obtained for the whole process. After the sample finished the test measuring, its resistivity was ρ_{300}=9.83×10^{-3 }Ω·cm at room temperature. The ρ-T curve also showed that the orthorhombic-tetragonal phase transformation of sol-gel YBa_2Cu_3O_y sample occurred at 581℃ for the sample in the rising temperature process, but at 613℃ in the cooling process, lower than that of the samples made by using the conventional powder metallurgy methods. 相似文献
75.
A highly efficient substitution of the vinyl fluoride of perfluoroketene dithioacetals was achieved using trimethylsilylacetate to give 2-perfluoroalkyl succinic acid derivatives and 2-trifluoromethyl succinimides. This chain process was initiated by a catalytic amount of fluoride salt, whereas reaction failed with the corresponding lithium enolate. 相似文献
76.
Reaction of acetylene dicarboxaldehyde monoacetal with substituted Meldrum’s acid leads good yields in 2-pyranones-4-carboxaldehydes substituted in position 3. 相似文献
77.
A simple, efficient and highly chemoselective method for tetrahydropyranylation of alcohols and phenols has been developed by their reaction with 3,4-dihydro-2H-pyran at room temperature in the presence of a catalytic amount of polystyrene supported AlCl3. The method is also highly selective for monoprotection of symmetrical diols. 相似文献
78.
Grindstone Chemistry--a greatly evolved version of Toda’s method of grinding solids together for solvent-free chemical reactions--has been described and its usefulness illustrated by the successful application of this technique to a simplified process for conducting the multi-component Biginelli reaction for the synthesis of physiologically active tetrahydropyrimidinones. 相似文献
79.
R. Bairava Ganesh Hitoshi Matsuo Takahiro Kawamura Yoshihiro Kangawa Koji Arafune Yoshio Ohshita Masafumi Yamaguchi Koichi Kakimoto 《Journal of Crystal Growth》2008,310(11):2697-2701
Multicrystalline silicon was grown by unidirectional solidification method using the accelerated crucible rotation technique. The application of the accelerated crucible rotation technique in unidirectional solidification method induced growth striations across the axial direction of the grown crystal. This striation pattern was observed from carbon concentration distribution, obtained by using Fourier transform infrared spectroscopy. The generated striation pattern was found to be weak and discontinuous. Some striations were absent, probably due to back melting, caused during each crucible rotation. From the growth striations and applied time period in crucible rotation, the growth rate was estimated by using Fourier transformation analysis. 相似文献
80.
Zavarzin I. V. Smirnova N. G. Chernoburova E. I. Yarovenko V. N. Krayushkin M. M. 《Russian Chemical Bulletin》2004,53(6):1257-1260
A method for syntheses of previously unknown derivatives of thieno[2,3-d]pyrimidines and quinazolines from monothiooxamides was proposed. 相似文献