全文获取类型
收费全文 | 80577篇 |
免费 | 437篇 |
国内免费 | 393篇 |
专业分类
化学 | 25920篇 |
晶体学 | 812篇 |
力学 | 6782篇 |
数学 | 32451篇 |
物理学 | 15442篇 |
出版年
2018年 | 10450篇 |
2017年 | 10270篇 |
2016年 | 6115篇 |
2015年 | 904篇 |
2014年 | 354篇 |
2013年 | 487篇 |
2012年 | 3902篇 |
2011年 | 10632篇 |
2010年 | 5720篇 |
2009年 | 6108篇 |
2008年 | 6729篇 |
2007年 | 8876篇 |
2006年 | 381篇 |
2005年 | 1438篇 |
2004年 | 1665篇 |
2003年 | 2080篇 |
2002年 | 1109篇 |
2001年 | 277篇 |
2000年 | 326篇 |
1999年 | 184篇 |
1998年 | 224篇 |
1997年 | 181篇 |
1996年 | 242篇 |
1995年 | 154篇 |
1994年 | 111篇 |
1993年 | 138篇 |
1992年 | 87篇 |
1991年 | 91篇 |
1990年 | 83篇 |
1989年 | 92篇 |
1988年 | 86篇 |
1987年 | 83篇 |
1986年 | 82篇 |
1985年 | 85篇 |
1984年 | 86篇 |
1983年 | 70篇 |
1982年 | 70篇 |
1981年 | 71篇 |
1980年 | 82篇 |
1979年 | 69篇 |
1978年 | 58篇 |
1977年 | 48篇 |
1976年 | 37篇 |
1975年 | 39篇 |
1973年 | 48篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Quantum theory accepts the point-like indivisible (classical) character of a particle as a mere product of a measuring process, or what has become known as a collapse. Following the notion of empty waves, which accepts the particle as a real existent entity without regard to the measurement process, we propose an experiment that may shed some light on the reality of the particle and the consequences of that reality. 相似文献
902.
John Doyle 《The Journal of the Operational Research Society》1994,45(2):203-213
Following a critique of existing algorithms, an algorithm is presented which will re-organize a 2-way data table to bring like rows together, and like columns together. Extensions of the method are described, and justified, to accommodate distances measured in modular arithmetic, and with bipolar columns/rows, as in repertory grid analysis. One value of the algorithms is that the user can see relationships in the tables without the data in the cells themselves ever having been transformed. Thus, users will continue to feel they own their data. 相似文献
903.
This paper deals with the GI x /G/c queueing system in a steady state. We refine a diffusion approximation method incorporating the constraint of traffic conservation for general queueing systems. An approximate expression for the distribution of the number of customers is obtained. Numerical results are presented to show that the refined model provides improved performance. 相似文献
904.
Arcadiy V. Krasheninnikov Konstantin E. Kon’kov Leonid A. Openov Vladimir F. Elesin 《Czechoslovak Journal of Physics》1996,46(3):1197-1198
The effect of ion irradiation on the superconducting transition temperatureT c and resistivityρ ab (T) of YBa2Cu3O7-x films with different oxygen content (initial temperatureT c0≈90 K and 60 K) is studied experimentally. The dependenciesT c /T c0 on residual resistivityρ o are obtained in very wide range 0.2<T c /T c0 <1 andρ o μΩ·cm. The critical values ofρ o , corresponding to the vanishing of superconductivity, are found to be an order of magnitude larger then those predicted by theory ford-wave pairing. At 0.5÷0.6<T c /T c0<1 the experimental data are in close agreement with theoretical dependencies, obtained for the anisotropics-wave superconductor within the BCS-framework. 相似文献
905.
N. E. Hussey J. R. Cooper Chen Changkang J. W. Hodby 《Czechoslovak Journal of Physics》1996,46(3):1201-1202
Low-field magnetizationM(H) measurements can be used to probe the nature of the screening currents and the interlayer coupling in high-T c cuprates. Here we compare theM(H) behaviour of single crystals of Bi2Sr2CaCu2O8 and fully oxygenated and oxygen reduced YBa2Cu3O7??. In YBa2Cu3O7, theM(H) behaviour is consistent with anisotropic 3D superconductivity whilst in Bi2Sr2CaCu2O8, the surface screening currents are strongly affected by the presence of vortices, implying that the CuO2 planes are coupled via a weak Josephson interaction. In oxygen-deficient YBa2Cu3O6.7 (T c =63K), theM(H) behaviour at low temperatures is similar to that found for Bi2Sr2CaCu2O8, implying that the removal of oxygen from the chains has resulted in a dimensional crossover of the superconducting state in YBa2Cu3O7??. As the temperature approachesT c , the 3D behaviour is eventually restored as thec-axis coherence length ξ c becomes comparable with the interlayer spacingd. 相似文献
906.
Tshakane Tshepe Johan F. Prins Michael J. R. Hoch 《Czechoslovak Journal of Physics》1996,46(5):2439-2440
We have investigated low-temperature electrical transport mechanisms in the surface layer of a type IIa diamond which has been heavily implanted with boron-ions at low temperatures and then annealed at high temperatures. The boron atoms occupy substitutional sites giving rise to a heavily doped wide-bandgap semiconductor. The dc-conductivity results suggest that for the maximum boron doping that has been achieved, the diamond sample is close to the insulator-metal transition. A model to account for the observed increase in activated boron centres with ion dose is presented. On the insulating side of the transition, the data are interpreted in terms of variable-range hopping laws. 相似文献
907.
Katsunori Wakabayashi Mitsutaka Fujita Koichi Kusakabe Kyoka Nakada 《Czechoslovak Journal of Physics》1996,46(4):1865-1866
Anoble mechanism of spin polarization is proposed for finite graphite sheet with edge. For graphite ribbon with zigzag edge, there appear peculiar ‘edge states’. These localized states comprise nearly flat band at the Fermi level, which easily causes magnetic instability. Magnetic structure is suggested from Hartree-Fock analysis of the Hubbard model, where huge magnetic moments are induced at around both of edges by weak HubbardU and are coupled antiferromagnetically with each other. 相似文献
908.
LetK be an algebraically closed field withp:=char (K)>0 andX a bielliptic curve over Spec(K) with genus≥6 and such that the canonical model ofX is ordinary. In this paper we determine all the possible gap sequences of Weierstrass points on such curves. 相似文献
909.
Ron M. Roth 《Designs, Codes and Cryptography》1996,9(2):177-191
Codes
of length 2
m
over {1, -1} are defined as null spaces of certain submatrices of Hadamard matrices. It is shown that the codewords of
all have an rth order spectral null at zero frequency. Establishing the connection between
and the parity-check matrix of Reed-Muller codes, the minimum distance of
is obtained along with upper bounds on the redundancy of
. An efficient algorithm is presented for encoding unconstrained binary sequences into
. 相似文献
910.
Gur Mosheiov 《The Journal of the Operational Research Society》1996,47(9):1184-1191
We study a problem of scheduling deteriorating jobs, i.e. jobs whose processing times are an increasing function of their starting times. We consider the case of a single machine and linear job-independent deterioration. The objective is to minimize the sum of weighted completion times, with weights proportional to the basic processing times. The optimal schedule is shown to be Λ-shaped, i.e. the sequence of the basic processing times has a single local maximum. Moreover, we show that the problem is solved in O(N log N) time. In the last section we test heuristics for the case of general weights. 相似文献