全文获取类型
收费全文 | 164902篇 |
免费 | 26003篇 |
国内免费 | 19292篇 |
专业分类
化学 | 114080篇 |
晶体学 | 1911篇 |
力学 | 9892篇 |
综合类 | 1268篇 |
数学 | 20636篇 |
物理学 | 62410篇 |
出版年
2024年 | 532篇 |
2023年 | 3056篇 |
2022年 | 5599篇 |
2021年 | 5973篇 |
2020年 | 6345篇 |
2019年 | 6147篇 |
2018年 | 5685篇 |
2017年 | 5323篇 |
2016年 | 7809篇 |
2015年 | 7752篇 |
2014年 | 9502篇 |
2013年 | 12350篇 |
2012年 | 14479篇 |
2011年 | 14821篇 |
2010年 | 10279篇 |
2009年 | 9925篇 |
2008年 | 10587篇 |
2007年 | 9463篇 |
2006年 | 8853篇 |
2005年 | 7359篇 |
2004年 | 5836篇 |
2003年 | 4777篇 |
2002年 | 4721篇 |
2001年 | 3915篇 |
2000年 | 3186篇 |
1999年 | 3474篇 |
1998年 | 2867篇 |
1997年 | 2579篇 |
1996年 | 2616篇 |
1995年 | 2277篇 |
1994年 | 2081篇 |
1993年 | 1634篇 |
1992年 | 1506篇 |
1991年 | 1336篇 |
1990年 | 1117篇 |
1989年 | 856篇 |
1988年 | 660篇 |
1987年 | 552篇 |
1986年 | 569篇 |
1985年 | 428篇 |
1984年 | 301篇 |
1983年 | 262篇 |
1982年 | 207篇 |
1981年 | 138篇 |
1980年 | 101篇 |
1979年 | 57篇 |
1978年 | 37篇 |
1977年 | 34篇 |
1976年 | 34篇 |
1975年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Mao‐Chuan Yuan Ping‐I Shih Chen‐Han Chien Ching‐Fong Shu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(14):2925-2937
We have synthesized a blue‐light‐emitting polyfluorene (PF) derivative ( PF‐CBZ‐OXD ) that presents bulky hole‐transporting carbazole and electron‐transporting oxadiazole pendent groups functionalized at the C‐9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF‐CBZ‐OXD and its analogue PF‐TPA‐OXD with a red‐light‐emitting iridium phosphor for use as components of phosphorescent red‐light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF‐CBZ‐OXD , in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007 相似文献
52.
Li Yingle Huang Jiying Gong Shuohong 《International Journal of Infrared and Millimeter Waves》2003,24(6):953-961
The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references. 相似文献
53.
学生学习知识,一般来说,是从生动的具体的直观开始的,生动的直观能使学生获得关于事物生动而具体的感性认识。但是,感性认识并没有揭露事物的本质,人们对事物本质的认识要通过一系列的抽象来完成。 相似文献
54.
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
55.
56.
Liuman Ou Guilie Luo Yiping Li 《Journal of Mathematical Analysis and Applications》2003,283(2):534-548
In this paper, we consider an autonomous predator-prey Lotka-Volterra system in which individuals in the population may belong to one of two classes: the immatures and the matures, the age to maturity is represented by a time delay. By using eigenvalue analysis, principal term analyze method, reduction to absurdity, and iterative method, we obtain some simple conditions for global asymptotic stability of the unique positive equilibrium point. Moreover, a condition that the prey population in the system get extinction and the predator population in the system get permanence will be obtained. Meanwhile the theorems extend the corresponding conclusions in which there have no two stage structures. 相似文献
57.
Nickel complexes 1–4 ligated with 2,9-disubstituted-1,10-phenanthroline were synthesized and characterized by FT-IR spectra and elemental analysis.
The molecular structure of complex 2 was confirmed by X-ray crystal diffraction analysis. Activated with methylaluminoxane (MAO), those complexes showed moderate
activities for ethylene oligomerization.
Published in Kinetika i Kataliz, 2007, Vol. 48, No. 5, pp. 710–714.
This article was submitted by the authors in English. 相似文献
58.
Herein we report a new method to collect a qualified infrared spectrum of a solute in solution by two solvent cells with different thickness during background single-beam spectrum scanning. By collecting the background spectrum with two cells (two stages), we successfully achieved accurate solvent compensation between a sample and a reference, namely, the solvent amounts in the sample and background measurements could become congruent. Therefore, the solvent bands were thoroughly suppressed in the infrared spectrum and a qualified spectrum of the solute was obtained. 相似文献
59.
J. Song H. Jiang Z.J. Liu D.Y. Khang Y. Huang J.A. Rogers C. Lu C.G. Koh 《International Journal of Solids and Structures》2008,45(10):3107-3121
A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically. 相似文献
60.
Anti-BZ-Structure in Effect Algebras 总被引:1,自引:0,他引:1
The definitions of sharply approximating effect algebras, anti-BZ-effect algebras, central approximating effect algebras, and S-anti-BZ-effect algebras are given, the relationships between sharply approximating effect algebras and anti-BZ-effect algebras, between central approximating effect algebras and anti-BZ-effect algebras are established, and the set of anti-BZ-sharp elements in S-anti-BZ-effect algebras is proved to be an orthomodular lattice. 相似文献