全文获取类型
收费全文 | 34903篇 |
免费 | 5603篇 |
国内免费 | 4955篇 |
专业分类
化学 | 26019篇 |
晶体学 | 545篇 |
力学 | 2041篇 |
综合类 | 351篇 |
数学 | 3608篇 |
物理学 | 12897篇 |
出版年
2024年 | 87篇 |
2023年 | 685篇 |
2022年 | 969篇 |
2021年 | 1276篇 |
2020年 | 1438篇 |
2019年 | 1492篇 |
2018年 | 1243篇 |
2017年 | 1267篇 |
2016年 | 1627篇 |
2015年 | 1686篇 |
2014年 | 1933篇 |
2013年 | 2566篇 |
2012年 | 2962篇 |
2011年 | 3107篇 |
2010年 | 2208篇 |
2009年 | 2099篇 |
2008年 | 2331篇 |
2007年 | 2048篇 |
2006年 | 1937篇 |
2005年 | 1643篇 |
2004年 | 1365篇 |
2003年 | 1152篇 |
2002年 | 1145篇 |
2001年 | 922篇 |
2000年 | 778篇 |
1999年 | 739篇 |
1998年 | 581篇 |
1997年 | 530篇 |
1996年 | 594篇 |
1995年 | 452篇 |
1994年 | 470篇 |
1993年 | 354篇 |
1992年 | 310篇 |
1991年 | 303篇 |
1990年 | 209篇 |
1989年 | 163篇 |
1988年 | 138篇 |
1987年 | 115篇 |
1986年 | 117篇 |
1985年 | 104篇 |
1984年 | 66篇 |
1983年 | 61篇 |
1982年 | 39篇 |
1981年 | 29篇 |
1980年 | 33篇 |
1979年 | 19篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
Soliton interaction under the influence of higher-order effects 总被引:6,自引:0,他引:6
In this paper, we present exact N-soliton solution by employing simple, straightforward Darboux transformation based on the Lax pair for Hirota equation, a higher-order nonlinear Schrödinger (HNLS) equation. As examples, one- and two-soliton solutions in explicit forms are given and their properties are also analyzed. A bound solution without interaction will be theoretically predicted if one can adjust frequency shift for each soliton appropriately. Further, we obtain the approximate eigenvalues by employing two-soliton solution and discuss analytically the interaction between neighboring solitons under the influence of the higher-order effects. It is shown that the combined effects of the higher-order effects can restrain the interaction between neighboring solitons to some extent. The results are proved by directly solving HNLS equation numerically. 相似文献
73.
By using two sections of erbium doped fiber and a fiber optical reflector, a novel, highly efficient L bandamplifier is demonstrated with significantly power-conversion-efficiency enhancement and the gain increasing of as much as 13 dB. 相似文献
74.
75.
A Promising MoO_x-based Catalyst for n-Heptane Isomerization 总被引:1,自引:0,他引:1
Song Hai CHAI Xin Ping WANG* Ying Jun WANG Tian Xi CAI State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 《中国化学快报》2003,14(7)
The increasing demand for higher-octane gasoline and the regulations limiting the amount of aromatics in the fuel motivate the interest in catalytic isomerization of n-alkanes. In the last ten years, transition metal oxides or oxycarbides based on molybdenum or tungstate have attracted much attention due to their high activity and isomerization selectivity compared to the conventional bifunctional supported platinum catalyst and high resistance to sulphur and nitrogen catalyst poisons1-5. Ma… 相似文献
76.
Mo2Ni3Si/NiSi metal silicide composite coatings with a fine microstructure consisting of Mo2Ni3Si primary dendrites and the interdendritic Mo2Ni3Si/NiSi eutectics were fabricated on austenitic stainless steel AISI 321 by laser cladding process. Small amplitude reciprocating sliding wear resistance of the coatings is evaluated as functions of normal load and slip amplitude and the wear mechanisms were discussed based on worn surface morphology observations. Results showed that the Mo2Ni3Si/NiSi coatings have excellent small amplitude reciprocating sliding wear resistance. 相似文献
77.
Haibo Peng Boyu Wu Qiong Song Fei Lu Shuyun Luo 《International Journal of Infrared and Millimeter Waves》2003,24(9):1587-1596
Hybrid electrode combined coplanar waveguide (CPW) and microstrip lines in ultra-broadband electro-optic modulators. The characteristics of the modulators with hybrid electrode is like that of the modulator with the microstrip lines, in which the microstrip electrode is loaded above only one arm of Mach-Zehnder (M-Z) optical waveguide, besides the problem of microstrip line to coaxial transition and corona polarization in polymer modulators have been best solved at the same time. By using finite element method (FEM), the characteristic parameters such as half-wave voltage, modulation bandwidth characteristic impedance, effective microwave refractive index of polymer modulators with microstrip line and hybrid electrode are analysed and compared in this paper. The results present that velocity match, impendence match and lower microwave propagating loss is easily realized in modulators with hybrid electrode. 相似文献
78.
WANG Wen zhen * LIU Xin MENG Yi LIAO Dai zheng * JIANG Zong hui YAN Shi ping WANG Geng lin . Department of Chemistry Nankai University Tianjin P. R. China . State Key Laboratory of Coordination Chemistry Nanjing University Nanjijng P. R. China 《高等学校化学研究》2003,19(1)
IntroductionFive- coordinated complexes with d9- configuredcations have received much attention stereochemi-cally,spectrochemically and biologically,and havebeen comprehensively discussed[1] . Usually thereare two stable configurations for the copper( )complexes with five equal coordinating atoms:anapically elongated square pyramid( SP) and a com-pressed trigonal bipyramid( TBP) ,with an obviousenergetic preference for the latter coordination.When the ligands are rigid and provide angular d… 相似文献
79.
Ana Luísa Daniel‐da‐Silva João Carlos Moura Bordado José Miguel Martín‐Martínez 《Journal of Polymer Science.Polymer Physics》2007,45(22):3034-3045
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007 相似文献
80.