全文获取类型
收费全文 | 21544篇 |
免费 | 1740篇 |
国内免费 | 1121篇 |
专业分类
化学 | 9688篇 |
晶体学 | 316篇 |
力学 | 1201篇 |
综合类 | 48篇 |
数学 | 2012篇 |
物理学 | 7198篇 |
综合类 | 3942篇 |
出版年
2024年 | 59篇 |
2023年 | 242篇 |
2022年 | 468篇 |
2021年 | 489篇 |
2020年 | 454篇 |
2019年 | 445篇 |
2018年 | 472篇 |
2017年 | 405篇 |
2016年 | 583篇 |
2015年 | 601篇 |
2014年 | 831篇 |
2013年 | 1181篇 |
2012年 | 1495篇 |
2011年 | 1569篇 |
2010年 | 1179篇 |
2009年 | 1159篇 |
2008年 | 1261篇 |
2007年 | 1118篇 |
2006年 | 1103篇 |
2005年 | 880篇 |
2004年 | 822篇 |
2003年 | 667篇 |
2002年 | 650篇 |
2001年 | 826篇 |
2000年 | 654篇 |
1999年 | 616篇 |
1998年 | 473篇 |
1997年 | 460篇 |
1996年 | 461篇 |
1995年 | 356篇 |
1994年 | 337篇 |
1993年 | 263篇 |
1992年 | 231篇 |
1991年 | 234篇 |
1990年 | 217篇 |
1989年 | 173篇 |
1988年 | 155篇 |
1987年 | 89篇 |
1986年 | 79篇 |
1985年 | 78篇 |
1984年 | 60篇 |
1983年 | 41篇 |
1982年 | 44篇 |
1981年 | 43篇 |
1980年 | 43篇 |
1979年 | 32篇 |
1978年 | 47篇 |
1977年 | 30篇 |
1976年 | 31篇 |
1974年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
The Hawking radiation of Dirac particles in an arbitrarily rectilinearly accelerating Kinnersley black hole with electromagnetic charge and cosmological constant is investigated by using the generalized tortoise coordinate transformation. Both the location and the temperature of the event horizon depend on the time and the polar angle. The Hawking thermal radiation spectrum of Dirac particles is also derived. 相似文献
63.
本文研究了在不同pH值下吐温—80.Tritonx—100.SLS三种表面活性剂四—(对-三甲铵苯基)卟啉Soret带的影响。 相似文献
64.
The blends composed of polyamide 6 (PA6) and polyamide 66 (PA66) were obtained using two different preparation methods, one of which was the melt‐mixing through a twin‐screw extruder and the subsequent injection molding; and the other, the in situ blending through anionic polymerization of ε‐caprolactam in the presence of PA66. For the former, there existed a remarkable improvement in toughness but a drastic drop in strength and modulus; however, for the latter, a reverse but less significant trend of mechanical properties change appeared. Various characterizations were conducted, including the analyses of crystalline morphology, crystallographic form, and crystallization and melting behaviors using polarized optical microscopy (POM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC), respectively; observation of morphology of fractured surface with scanning electron microscope (SEM); measurement of glass transition through dynamic mechanical analysis (DMA); and the intermolecular interaction as well as the interchange reaction between the two components by Fourier transform infrared spectrometry (FT‐IR) and 13C solution NMR. The presence and absence of interchange reaction was verified for the in situ and melt‐mixed blends, respectively. It is believed that the transreaction resulted in a drop in glass transition temperature (Tg) for the in situ blends, contrary to an increase of Tg with increasing PA66 content for the melt‐mixed ones. And the two kinds of fabrication methods led to significant differences in the crystallographic form, spherulite size and crystalline content and perfection as well. Accordingly, it is attempted to explain the reasons for the opposite trends of changes in the mechanical properties for these two blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1176–1186, 2007 相似文献
65.
All-optical wavelength conversion of 10-Gb/s signal based on four-wave mixing is experimentally demonstrated in a 30-m-long dispersion-flattened microstructure fiber with small positive dispersion. For an average pump power of 26 dBm, the conversion efficiency was around -19.5 dB with the fluctuation less than ±1.4 dB, covering a conversion bandwidth of 20 nm. The eye diagram of the converted signal shows good eye opening. 相似文献
66.
A. I. Golovashkin G. N. Izmaïlov G. V. Kuleshova T. Q. Khánh A. M. Tskhovrebov L. N. Zherikhina 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):243-249
A scheme of magnetic calorimeter for registration of rare events
characterized by small energy release (cosmic rays, WIMPs, solitary X-ray
quanta) is proposed. The calorimeter is brought to operation by adiabatic
demagnetization, and its magnetic response is measured by a quantum
interferometer (SQUID, A. Barone and G. Paterno, Physics and applications of Josephson Effect). Special consideration is given to the specific
features of calorimeter operation in the ferromagnetic transition region.
The trigger registration of ultrasmall energy release by a ferromagnetic
system in the metastable state is described. 相似文献
67.
Q.J. Zhu 《Journal of Mathematical Analysis and Applications》2007,326(1):708-720
Investment systems are studied using a framework that emphasize their profiles (the cumulative probability distribution on all the possible percentage gains of trades) and their log return functions (the expected average return per trade in logarithmic scale as a function of the investment size in terms of the percentage of the available capital). The efficiency index for an investment system, defined as the maximum of the log return function, is proposed as a measure to compare investment systems for their intrinsic merit. This efficiency index can be viewed as a generalization of Shannon's information rate for a communication channel. Applications are illustrated. 相似文献
68.
We propose general variational inclusion problems which are slightly different from corresponding problems considered in several recent papers in the literature and show that they are advantageous. Sufficient conditions for the solution existence are established. As applications we derive consequences for several special cases of variational inclusion problems, quasioptimization problems, equilibrium problems and implicit variational inequalities and show that they improve the results of some recent existing papers. 相似文献
69.
Natural convections in conjugated single and double enclosures 总被引:7,自引:0,他引:7
The natural convection in single and double conjugated enclosures are numerically investigated. The single and double enclosures are formed by low conductance walls with finite thickness. The outside vertical surfaces of the conducting walls are of the third kind of boundary condition while the top and bottom outside surfaces are adiabatic. The problem studied is characterized by a dominant horizontal temperature gradient and the thermal boundary conditions at the cavity surfaces can not be specified in priori. Numerical results reveal the characteristics in such kind of enclosures and show the importance of the thermal boundary conditions on the natural convection in enclosures. It is also found that the natural convections in the conjugated double enclosures are basically the same, with a major difference in their fluid temperature levels. 相似文献
70.