全文获取类型
收费全文 | 172篇 |
免费 | 0篇 |
专业分类
化学 | 51篇 |
晶体学 | 4篇 |
力学 | 3篇 |
数学 | 51篇 |
物理学 | 63篇 |
出版年
2020年 | 3篇 |
2013年 | 3篇 |
2012年 | 2篇 |
2011年 | 4篇 |
2008年 | 2篇 |
2007年 | 4篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 5篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1942年 | 2篇 |
1941年 | 2篇 |
1939年 | 2篇 |
1925年 | 2篇 |
1914年 | 2篇 |
1890年 | 3篇 |
1886年 | 1篇 |
1882年 | 2篇 |
1881年 | 1篇 |
1880年 | 5篇 |
1878年 | 1篇 |
1877年 | 2篇 |
1875年 | 1篇 |
1874年 | 2篇 |
1873年 | 2篇 |
1872年 | 2篇 |
1871年 | 4篇 |
1870年 | 1篇 |
1869年 | 3篇 |
排序方式: 共有172条查询结果,搜索用时 20 毫秒
31.
We consider the region of closed time-like curves (CTCs) in three-dimensional flat Lorentz space–times. The interest in this global geometrical feature goes beyond the purely mathematical one. Such space–times are lower-dimensional toy models of sourceless Einstein gravity or cosmology. In three dimensions all such space–times are known: they are quotients of Minkowski space by a suitable group of Poincaré isometries. The presence of CTCs would indicate the possibility of “time machines”, a region of space–time where an object can travel along in time and revisit the same event. Such space–times also provide a testbed for the chronology protection conjecture, which suggests that quantum back reaction would eliminate CTCs. In particular, our interest in this note will be to find the set free of CTCs for
, where
is modeled on Minkowski space and γ is a Poincaré transformation. We describe the set free of CTCs where γ is hyperbolic, parabolic, and elliptic. 相似文献
32.
D. Brill P. Beckerle C. Bormann E. Schwab Y. Shin R. Stock H. Ströbele P. Baltes C. Müntz H. Oeschler C. Sturm A. Wagner R. Barth M. Cieślak M. Dębowski E. Grosse P. Koczoń M. Mang D. Miśkowiec R. Schicker P. Senger B. Kohlmeyer F. Pühlhofer J. Speer K. Völkel W. Waluś 《Zeitschrift für Physik A Hadrons and Nuclei》1996,355(1):61-68
Midrapidity protons from209Bi+209Bi collisions were measured with the Kaon Spectrometer at SIS at incident energies of E Lab /A=400, 700 and 1000 MeV. Additionally, light fragments were analysed at 400 MeV. We have investigated the azimuthal emission pattern of the particles relative to the reaction plane as function of transverse momentum, bombarding energy and impact parameter. We observe an enhanced emission of particles perpendicular to the reaction plane at all bombarding energies. The ratio of the number of particles emitted out-of-plane/in-plane increases strongly with the particles transverse momentum. The anisotropy decreases with increasing beam energy. Composite particles show a much stronger effect than protons. 相似文献
33.
C. Müntz P. Baltes H. Oeschler C. Sartorius C. Sturm A. Wagner C. Bormann D. Brill Y. Shin J. Stein H. Ströbele W. Ahner R. Barth M. Cieślak M. Deȩbowski E. Grosse W. Henning P. Koczoń M. Mang D. Miśkowiec R. Schicker P. Senger B. Kohlmeyer H. Pöppl F. Pühlhofer J. Speer K. Völkel W. Waluś 《Zeitschrift für Physik A Hadrons and Nuclei》1997,357(4):399-409
Double differential cross sections of positively charged pions and protons have been measured in nuclear collisions of mass-symmetric systems (Ne+NaF, Ni+Ni, Au+Au, Bi+Pb) at incident energies between 0.8 and 1.8 AGeV as a function of the centrality of the reaction. Using a magnetic spectrometer pions and protons were detected with laboratory angles between 40 and 48 degrees, and with momenta up to about 1400 MeV/c. This setting allows for the study of pions and protons emitted close to midrapidity. The center-of-mass pion spectra deviate from a Boltzmann distribution. The inverse slope parameters of the high-energetic pions are smaller than those of the proton spectra and they exhibit a weaker centrality dependence. A scenario is presented where the shape of the pion spectra reflects the decay kinematics of nucleonic resonances embedded in the thermal and the collective motion of the nucleons in the reaction zone. The number of emitted pions per participating nucleon is higher for light than for heavy mass systems. For a given mass system, the total pion multiplicity increases linearly with the number of participating nucleons, whereas the multiplicity of high-energy pions increases more than linearly. This result is consistent with a scenario where the high-energy pions are produced in multiple energetic baryon-baryon collisions occurring in the high-density phase of the collision. 相似文献
34.
35.
A method is described in which gas chromatographic (GC) data obtained from cuticular hydrocarbons are treated by methods of pattern recognition. Based on a recently described sample preparation procedure, GC data are normalized to eliminate slight variations in chromatographic conditions and converted into the proper format for discriminant analysis by computer. The results of several methods of data treatment and display are discussed, based upon the chemometric system package, ARTHUR. The approach has the advantage of largely removing operator bias. 相似文献
36.
Brill D Ahner W Baltes P Barth R Bormann C Cieslak M Debowski M Grosse E Henning W Koczon P Kohlmeyer B Miskowiec D Müntz C Oeschler H Pöppl H Pühlhofer F Sartorius S Schicker R Senger P Shin Y Speer J Stein J Stiebing K Stock R Ströbele H Völkel K Wagner A Walus W 《Physical review letters》1993,71(3):336-339
37.
38.
We give an analytical formula for the steady-state distribution of queue-wait in the M/G/1 queue, where the service time for each customer is a positive integer multiple of a constant D > 0. We call this an M/{iD}/1 queue. We give numerical algorithms to calculate the distribution. In addition, in the case that the service distribution is sparse, we give revised algorithms that can compute the distribution more quickly.AMS subject classification: 60K25, 90B22 相似文献
39.
A simple, geometrical construction is given for three-dimensional spacetimes with negative cosmological constant that contain
two particles colliding head-on. Depending on parameters like particle masses and distance, the combined geometry will be
that of a particle, or of a black hole. In the black hole case the horizon is calculated. It is found that the horizon typically
starts at a point and spreads into a closed curve with corners, which propagate along spacelike caustics and disappear as
the horizon passes the particles.
相似文献
40.
Amita Gupta Alexei Yu Ganin Parmanand Sharma Vikrant Agnihotri LM Belova KV Rao Mikhail E Kozlov AA Zakhidov RH Baughman 《Pramana》2002,58(5-6):1051-1059
We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show
a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are
found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there
exists no report in literature on any BiNi compound which is magnetic. 相似文献