全文获取类型
收费全文 | 10004篇 |
免费 | 1935篇 |
国内免费 | 1395篇 |
专业分类
化学 | 5435篇 |
晶体学 | 384篇 |
力学 | 952篇 |
综合类 | 144篇 |
数学 | 248篇 |
物理学 | 6171篇 |
出版年
2024年 | 14篇 |
2023年 | 64篇 |
2022年 | 215篇 |
2021年 | 293篇 |
2020年 | 261篇 |
2019年 | 247篇 |
2018年 | 287篇 |
2017年 | 396篇 |
2016年 | 470篇 |
2015年 | 367篇 |
2014年 | 502篇 |
2013年 | 917篇 |
2012年 | 710篇 |
2011年 | 661篇 |
2010年 | 605篇 |
2009年 | 644篇 |
2008年 | 585篇 |
2007年 | 685篇 |
2006年 | 608篇 |
2005年 | 553篇 |
2004年 | 524篇 |
2003年 | 456篇 |
2002年 | 390篇 |
2001年 | 332篇 |
2000年 | 343篇 |
1999年 | 330篇 |
1998年 | 251篇 |
1997年 | 213篇 |
1996年 | 197篇 |
1995年 | 163篇 |
1994年 | 142篇 |
1993年 | 161篇 |
1992年 | 131篇 |
1991年 | 78篇 |
1990年 | 72篇 |
1989年 | 69篇 |
1988年 | 89篇 |
1987年 | 51篇 |
1986年 | 43篇 |
1985年 | 28篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1982年 | 32篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1974年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Ismayadi Ismail Mansor Hashim Khamirul Amin Matori Rosidah AliasJumiah Hassan 《Journal of magnetism and magnetic materials》2011,323(11):1470-1476
Ni0.5Zn0.5Fe2O4 has been synthesized using mechanical alloying method with two variables (milling time and ball-to-powder weight ratio (BPR)) were varied in order to study its effect on the magnetic properties of the material. The effects of these two variables were studied using XRD, SEM, TEM and later by impedance analyzer with the frequency range from 1 MHz to 1.8 GHz. The results obtained however show that there are no significant trends to relate the milling time and BPR with the permeability and losses of the material studied. After being sintered at 1150 °C, all the effects of alloying process seem to diminish. 相似文献
972.
Sagar E. Shirsath R.H. KadamAnil S. Gaikwad Ali GhasemiAkimitsu Morisako 《Journal of magnetism and magnetic materials》2011,323(23):3104-3108
Sintering temperature and particle size dependent structural and magnetic properties of lithium ferrite (Li0.5Fe2.5O4) were synthesized and sintered at four different temperatures ranging from 875 to 1475 K in the step of 200 K. The sample sintered at 875 K was also treated for four different sintering times ranging from 4 to 16 h. Samples sintered at 1475 K have the cubic spinel structure with a small amount of α-Fe2O3 (hematite) and γ-Fe2O3 (maghemite). The samples sintered at≤1275 K do not show hematite and maghemite phases and the crystals form the single phase spinel structure with the cation ordering on octahedral sites. Particle size of lithium ferrite is in the range of 13-45 nm, and is depend on the sintering temperature and sintering time. The saturation magnetization increased from 45 to 76 emu/g and coercivity decreases from 151 to 139 Oe with an increase in particle size. Magnetization temperature curve recorded in ZFC and FC modes in an external magnetic field of 100 Oe. Typical blocking effects are observed below about 244 K. The dielectric constant increases with an increase in sintering temperature and particle size. 相似文献
973.
K.W. LipsøK.K. Nielsen D.V. Christensen C.R.H. BahlK. Engelbrecht L. Theil KuhnA. Smith 《Journal of magnetism and magnetic materials》2011,323(23):3027-3032
The effect of demagnetization in a stack of gadolinium plates is determined experimentally by using spatially resolved measurements of the adiabatic temperature change due to the magnetocaloric effect. The number of plates in the stack, the spacing between them and the position of the plate on which the temperature is measured are varied. The orientation of the magnetic field is also varied. The measurements are compared to a magnetostatic model previously described. The results show that the magnetocaloric effect, due to the change in the internal field, is sensitive to the stack configuration and the orientation of the applied field. This may have significant implications for the construction of a magnetic cooling device. 相似文献
974.
S.M. Masoudpanah S.A. Seyyed Ebrahimi 《Journal of magnetism and magnetic materials》2011,323(21):2643-2647
Strontium hexaferrite SrFe12O19 thin films have been synthesized at different pH, adjusted by NH4OH, on the Si (1 0 0) substrate using a spin coating sol-gel process. Fourier transform infrared spectroscopy analysis and theoretical calculations were conducted for determination and controlling metal citrates in solution precursors. X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer were applied to evaluate the composition, microstructure, crystallite size and magnetic properties of the SrFe12O19 thin films. Using the solution with pH 7, the approximately single phase strontium hexaferrite thin films with optimum physical properties can be obtained at calcination temperature of 800 °C. The SrFe12O19 thin films derived from the solution with pH 7 after calcination at 800 °C exhibited crystallite size of 42 nm and magnetic properties of Ms=267 emu/cm3 (at 10 kOe), Mr=134 emu/cm3 and Hc=4290 Oe. 相似文献
975.
F.S. Khoo L.P. Teo 《Physics letters. [Part B]》2011,703(2):199-207
We consider the finite temperature Casimir effect of a massive fermionic field confined between two parallel plates, with MIT bag boundary conditions on the plates. The background spacetime is Mp+1×Tq which has q dimensions compactified to a torus. On the compact dimensions, the field is assumed to satisfy periodicity boundary conditions with arbitrary phases. Both the high temperature and the low temperature expansions of the Casimir free energy and the force are derived explicitly. It is found that the Casimir force acting on the plates is always attractive at any temperature regardless of the boundary conditions assumed on the compact torus. The asymptotic limits of the Casimir force in the small plate separation limit are also obtained. 相似文献
976.
On spurious and corrupted multifractality: The effects of additive noise, short-term memory and periodic trends 总被引:1,自引:0,他引:1
Josef LudescherMikhail I. Bogachev Jan W. KantelhardtAicko Y. Schumann Armin Bunde 《Physica A》2011,390(13):2480-2490
We study the performance of multifractal detrended fluctuation analysis (MF-DFA) applied to long-term correlated and multifractal data records in the presence of additive white noise, short-term memory and periodicities. Such additions and disturbances that can be typically found in the observational records of various complex systems ranging from climate dynamics to physiology, network traffic, and finance. In monofractal records, we find that (i) additive white noise hardly results in spurious multifractality, but causes underestimated generalized Hurst exponents h(q) for all q values; (ii) short-range correlations lead to pronounced crossovers in the generalized fluctuation functions Fq(s) at positions that decrease with increasing moment q, thus causing significantly overestimated h(q) for small q and spurious multifractality; (iii) periodicities like seasonal trends (with standard deviations comparable with the one of the studied process) result in spurious “reversed” multifractality where h(q) increases with increasing q (except for very short time windows). We also show that in multifractal cascades moderate additions of noise, short-range memory, or periodic trends cause flawed results for h(q) with q<2, while h(q) with q>2 remains nearly unchanged. 相似文献
977.
We introduce an instantaneous and an average instantaneous cross-correlation function to detect the temporal cross-correlations between individual stocks based on the daily data of the United States and the Chinese stock markets. The memory effect of the instantaneous cross-correlations is investigated by applying the detrended fluctuation analysis (DFA), where the DFA exponents can be partly explained by the correlation function from the common sense. Long-range memory is observed for the average instantaneous cross-correlations, and persists up to a month magnitude of timescale for the United States stock market and half a month magnitude of timescale for the Chinese stock market. In addition, multifractal nature is investigated by a multifractal detrended fluctuation analysis. 相似文献
978.
Masuo Suzuki 《Physica A》2011,390(11):1904-1916
979.
980.