全文获取类型
收费全文 | 25055篇 |
免费 | 956篇 |
国内免费 | 1418篇 |
专业分类
化学 | 10295篇 |
晶体学 | 215篇 |
力学 | 410篇 |
综合类 | 65篇 |
数学 | 12213篇 |
物理学 | 4231篇 |
出版年
2024年 | 35篇 |
2023年 | 378篇 |
2022年 | 300篇 |
2021年 | 317篇 |
2020年 | 476篇 |
2019年 | 631篇 |
2018年 | 554篇 |
2017年 | 438篇 |
2016年 | 494篇 |
2015年 | 591篇 |
2014年 | 855篇 |
2013年 | 1682篇 |
2012年 | 953篇 |
2011年 | 1716篇 |
2010年 | 1336篇 |
2009年 | 1731篇 |
2008年 | 1912篇 |
2007年 | 1715篇 |
2006年 | 1336篇 |
2005年 | 1031篇 |
2004年 | 938篇 |
2003年 | 839篇 |
2002年 | 1121篇 |
2001年 | 569篇 |
2000年 | 543篇 |
1999年 | 574篇 |
1998年 | 445篇 |
1997年 | 366篇 |
1996年 | 439篇 |
1995年 | 422篇 |
1994年 | 361篇 |
1993年 | 285篇 |
1992年 | 273篇 |
1991年 | 207篇 |
1990年 | 180篇 |
1989年 | 191篇 |
1988年 | 129篇 |
1987年 | 133篇 |
1986年 | 106篇 |
1985年 | 143篇 |
1984年 | 119篇 |
1983年 | 64篇 |
1982年 | 107篇 |
1981年 | 103篇 |
1980年 | 52篇 |
1979年 | 43篇 |
1978年 | 34篇 |
1977年 | 45篇 |
1976年 | 35篇 |
1971年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
By combining the generalized exterior algebra of forms over a noncommutative algebra with the gauging of discrete directions and the associated Higgs fields, we consider the construction of the bosonic sector of left-right symmetric models of the form SU(2)
L
SU(2)
R
U(1). We see that within this formalism maximal use can be made of the gauge connection associated with the noncommutative graded algebra. 相似文献
92.
Reinhard Honegger 《Letters in Mathematical Physics》1993,27(3):191-203
By means of cocycle techniques in a recent paper, the global dynamics of mean field-boson couplings has been studied. Here, by restricting to the bosonic system the infinite time limit (t ) for very general initial states, one obtains time-asymptotic states on the bosonicC
*-Weyl algebra, in which one partially rediscovers the collective ordering of the infinite mean field lattice. 相似文献
93.
94.
95.
P. V. Zinin L. C. Ming I. Kudryashov N. Konishi S. K. Sharma 《Journal of Raman spectroscopy : JRS》2007,38(10):1362-1367
A direct transformation of the g‐BC3 phase to a new diamond‐like d‐BC3 phase was observed in a diamond‐anvil cell (DAC) at high temperature, 2033 ± 241 K, and high pressure, 50 GPa. Analysis of the peak positions of the d‐BC3, B4C, α‐boron, and the boron‐doped diamond leads to the conclusion that the positions of the peaks of the d‐BC3 are more similar to the peak pattern of the boron‐doped diamond rather than that of boron carbide, α‐boron. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
96.
Bermel W Bertini I Felli IC Matzapetakis M Pierattelli R Theil EC Turano P 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,188(2):301-310
Attempts are made to efficiently decouple (13)C nuclei without significant loss of coherence during the application of the decoupling package. Such attempts are based on the S(3)E spin-state selection method. A newly developed double S(3)E (DS(3)E) is particularly efficient for C(alpha) detection for proteins as large as 480 kDa. 相似文献
97.
Cr-doped mullites were prepared from single-phase precursors containing up to 9.60 wt% Cr2O3 using a sol-gel technique followed by thermal treatment. Particle induced X-ray emission spectroscopy and X-ray powder diffraction were used to characterize the samples. Mullites were orthorhombic, space group Pbam. Cr doping caused the increase of unit-cell parameters. Strongest expansion was noticed along c-axis followed by a and b (Δc/c=0.089, Δa/a=0.061, Δb/b=0.045% per mole Cr2O3). A second phase, namely θ-(Al,Cr)2O3, was revealed by XRD in the sample containing 9.60 wt% Cr2O3. The structure of mullites was refined by the Rietveld method, location of Cr3+ was performed by the EPR spectroscopy. At low chromium doping level (Cr2O3 content less than ∼5 wt%) Cr3+ ions were substituted for Al3+ in the AlO6 octahedra of the mullite structure (M1 site). For higher doping level, Cr3+ ions were additionally substituted for Al3+ in the AlO6 octahedra of the second phase [θ-(Al,Cr)2O3 at 1400 °C, or α-(Al,Cr)2O3 at 1600 °C] which segregated in the system. Substitution of Cr3+ for Al3+ on M1 site in the mullite structure resulted in increase of average distances in (M1)O6 octahedron and decrease of average distances in T*O4 tetrahedron, while average distances in TO4 tetrahedron stayed almost constant. 相似文献
98.
S. Meenakshi B.K. Godwal I. Orgzall S. Tkachev 《Journal of Physics and Chemistry of Solids》2006,67(8):1660-1667
We report the results of an X-ray diffraction study of CdAl2Se4 and of Raman studies of HgAl2Se4 and ZnAl2Se4 at room temperature, and of CdAl2S4 and CdAl2Se4 at 80 K at high pressure. The ambient pressure phase of CdAl2Se4 is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A fit of the volume pressure data to a Birch-Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at ∼9 GPa is about 10%. The analysis of the Raman data of HgAl2Se4 and ZnAl2Se4 reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order-disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl2S4 and CdAl2Se4, which shows a very weak temperature dependence of the Raman-active phonon modes. 相似文献
99.
John Greenberg 《Physics in Perspective (PIP)》2005,7(1):66-106
Nobel laureate William A. Fowler recalls his early education in physics; his part in the history of nuclear physics at the California Institute of Technology in the 1930s; parallel efforts elsewhere, particularly at Berkeley and the Department of Terrestrial Magnetism in Washington,D.C.; his contacts with J. Robert Oppenheimer; and his work with Charles C. Lauritsen and Tommy Lauritsen before and after World War II.John Greenberg received his Ph.D. degree from the University of Wisconsin and was Caltech research fellow in history from 1980–1984. The Editors were saddened to learn that he died while this interview was in press. Requests for reprints may be directed to Judith R. Goodstein, Institute Archives 015A-74, Caltech, Pasadena, CA 91125 USA; e-mail: jrg@caltech.edu. 相似文献
100.
The autoxidation of vitamin C has been studied in acetonitrile by electronic spectroscopy. Some interesting data on the role of acetonitrile in autoxidation have been obtained, perhaps for the first time. A parallelism between hydroxyl ions and CH2CN−, the ions from the self-ionization of acetonitrile, has been established. The CH2CN− anion is similar to hydroxyl anions in initiating and propagating the decomposition of ascorbic acid, at least in this system. The intermediates involved in the overall reaction in nonaqueous media have been identified by simple means.__________Published in Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 274–276, March–April, 2005. 相似文献