全文获取类型
收费全文 | 113497篇 |
免费 | 6258篇 |
国内免费 | 5666篇 |
专业分类
化学 | 51265篇 |
晶体学 | 1306篇 |
力学 | 8535篇 |
综合类 | 382篇 |
数学 | 35400篇 |
物理学 | 28533篇 |
出版年
2024年 | 78篇 |
2023年 | 681篇 |
2022年 | 1034篇 |
2021年 | 1319篇 |
2020年 | 1446篇 |
2019年 | 1460篇 |
2018年 | 11388篇 |
2017年 | 11303篇 |
2016年 | 7684篇 |
2015年 | 2668篇 |
2014年 | 2468篇 |
2013年 | 3163篇 |
2012年 | 7116篇 |
2011年 | 13879篇 |
2010年 | 8010篇 |
2009年 | 8300篇 |
2008年 | 9115篇 |
2007年 | 11030篇 |
2006年 | 2392篇 |
2005年 | 2958篇 |
2004年 | 2783篇 |
2003年 | 2994篇 |
2002年 | 2063篇 |
2001年 | 1115篇 |
2000年 | 1019篇 |
1999年 | 898篇 |
1998年 | 771篇 |
1997年 | 696篇 |
1996年 | 748篇 |
1995年 | 572篇 |
1994年 | 523篇 |
1993年 | 440篇 |
1992年 | 358篇 |
1991年 | 334篇 |
1990年 | 239篇 |
1989年 | 221篇 |
1988年 | 193篇 |
1987年 | 176篇 |
1986年 | 173篇 |
1985年 | 143篇 |
1984年 | 105篇 |
1983年 | 89篇 |
1982年 | 83篇 |
1981年 | 69篇 |
1980年 | 79篇 |
1979年 | 61篇 |
1978年 | 44篇 |
1914年 | 45篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
141.
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
142.
For ϕ a δ-subharmonic function, sharp results are obtained that connectA(r, ϕ), B(r, ϕ) andT(r, ϕ), whereA(r, ϕ)=inf|z|=r
ϕ(z),B(r, ϕ)=sup|z|=r
ϕ(z), andT(r, ϕ) is the Nevanlinna characteristics. 相似文献
143.
Lihong Wang 《Annals of the Institute of Statistical Mathematics》2004,56(2):251-264
The purpose of this paper is to investigate the asymptotic properties of the least squares estimates (L
2-estimates) and the least absolute deviation estimates (L
1-estimates) of the parameters of a nonlinear regression model subject to a set of equality and inequality restrictions, which
has a long-range dependent stationary process as its stochastic errors. Then we will compare the asymptotic relative efficiencies
of the above estimators. 相似文献
144.
145.
Jing Lin 《Tetrahedron letters》2004,45(1):103-106
Bisbinaphthyl-based macrocycles are found to carry out enantioselective fluorescent recognition of α-amino acid derivatives. It is observed that one enantiomer of a N-protected phenyl glycine can increase the fluorescence intensity of the binaphthyl fluorophores by over 4-fold but the other enantiomer does not cause much fluorescence enhancement. This highly enantioselective fluorescent response makes the binaphthyl macrocycles practically useful for the enantioselective fluorescent recognition of the amino acid substrate. 相似文献
146.
147.
148.
The vibrational dynamics of protein folding is analyzed in the framework of Tsallis statistics. We employ exact expressions
for classical harmonic oscillators by considering the unnormalized constraints. As q→1, we show that these approximations agree with the result of Gaussian network model. 相似文献
149.
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
150.