全文获取类型
收费全文 | 2658篇 |
免费 | 89篇 |
国内免费 | 17篇 |
专业分类
化学 | 1517篇 |
晶体学 | 27篇 |
力学 | 150篇 |
数学 | 327篇 |
物理学 | 743篇 |
出版年
2023年 | 7篇 |
2022年 | 17篇 |
2021年 | 54篇 |
2020年 | 41篇 |
2019年 | 45篇 |
2018年 | 20篇 |
2017年 | 25篇 |
2016年 | 51篇 |
2015年 | 67篇 |
2014年 | 90篇 |
2013年 | 139篇 |
2012年 | 175篇 |
2011年 | 201篇 |
2010年 | 125篇 |
2009年 | 112篇 |
2008年 | 197篇 |
2007年 | 137篇 |
2006年 | 152篇 |
2005年 | 131篇 |
2004年 | 108篇 |
2003年 | 82篇 |
2002年 | 91篇 |
2001年 | 66篇 |
2000年 | 66篇 |
1999年 | 39篇 |
1998年 | 35篇 |
1997年 | 22篇 |
1996年 | 42篇 |
1995年 | 36篇 |
1994年 | 35篇 |
1993年 | 40篇 |
1992年 | 30篇 |
1991年 | 36篇 |
1990年 | 22篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1974年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有2764条查询结果,搜索用时 31 毫秒
891.
Multi-casting autoregression (MCAR, for short) is suggested as a natural extension of the bifurcating autoregressive (BAR) model (cf. [Cowan, R., Staudte, R.G., 1986. The bifurcating autoregression model in cell lineage studies. Biometrics 42, 769–783]) in order to analyze multi-splitting tree-structured data. Pathwise stationarity of the MCAR model is discussed. Least squares estimation for the autoregressive parameter is considered and relevant limiting distribution is derived, in particular, for the pathwise explosive case. These results can be regarded as generalizations of those for standard stationary and explosive AR(1) time series. A simulation study is conducted to illustrate our results. 相似文献
892.
A new reinforced concrete model, in which the reinforcement steel is assumed as smeared / layered in concrete, is established and installed into a currently used finite element code for nonlinear analysis. It performs the nonlinear behaviors of both concrete and the reinforcement steel. The results of examples are in good agreement with the experimental data. 相似文献
893.
This paper deals with methods of constructing new BIB designs from known designs. First, we provide a method of finding trades on a given BIB design so that new designs with the same parameters ν, b, k can be constructed. Second, we point out that the method of combining designs mentioned in [9] is particularly useful for constructing designs based on ν = 2k, k even, when designs based on ν = 2k ? 1 are available. By utilizing the above methods with the aid of Table I in [4], we have constructed a table of 53 BIB designs based on V = 8 and k = 4 with support sizes except for . BIB designs with ν = 8, k = 4 and are shown to be nonexistent. 相似文献
894.
In mean-partition problems the goal is to partition a finite set of elements, each associated with a d-vector, into p disjoint parts so as to optimize an objective, which depends on the averages of the vectors that are assigned to each of the parts. Each partition is then associated with a d × p matrix whose columns are the corresponding averages and a useful approach in studying the problem is to explore the mean-partition polytope, defined as the convex hull of the set of matrices associated with feasible partitions. 相似文献
895.
The effect of the antiferromagnetic IrMn thickness upon the magnetic properties of CoFe/Pt/CoFe/[IrMn(tIrMn)] multilayers is studied. An oscillatory interlayer coupling (IEC) has been shown in pinned CoFe/Pt(tPt)/CoFe/IrMn multilayers with perpendicular anisotropy. The period of oscillation corresponds to about 2 monolayers of Pt. The oscillatory behavior of IEC depends on the nonmagnetic metallic Pt thickness and is thought to be related to the antiferromagnetic ordering induced by the IrMn layer. From the extraordinary Hall voltage amplitude (EHA) curves as function of IrMn thickness, we report that the oscillation dependence of IEC for the [CoFe/Pt/CoFe] multilayer system induced by IrMn with spacer-layer thickness is a important features of perpendicular exchange biased system. 相似文献
896.
H. Bhang S. Ajimura K. Aoki A. Banu T. Fukuda O. Hashimoto J. I. Hwang S. Kameoka B. H. Kang E. H. Kim J. H. Kim M. Kim T. Maruta Y. Miura Y. Miyake T. Nagae M. Nakamura S. N. Nakamura H. Noumi S. Okada Y. Okayasu H. Outa H. Park P. K. Saha Y. Sato M. Sekimoto S. Shin T. Takahashi H. Tamura K. Tanida A. Toyota K. Tsukada T. Watanabe H. J. Yim 《The European Physical Journal A - Hadrons and Nuclei》2007,33(3):259-263
Recent exclusive coincidence measurements of non-mesonic weak decays (NMWD) reported for the ratio of the partial decay width
of neutron-induced-to-proton-induced NMWD, Γn/Γp , values of 0.45±0.11±0.03 and 0.51±0.13±0.04 for 5lam and 12
Λ
C , respectively. These observations agree well with the improved theoretical Γn/Γp ratios which are in the range of 0.3-0.7. It appears that the long-standing discrepancy between the experimental and theoretical
values of Γn/Γp has finally been solved. However, when compared to the results of intra-nuclear cascade (INC) calculations, the observed
numbers of both single nucleons and coincident nucleon pairs are strongly quenched. The quenching of the proton yield observed
previously has been interpreted as an increase of the Γn/Γp ratio. On the other hand, significant contributions from the two-nucleon-induced three-body process ΛNN → nNN are predicted. Indeed, the angular correlation of the emitted nucleon pairs in the NMWD of 12
Λ
C showed not only decay events in back-to-back kinematics, but also events with non-back-to-back kinematics. In this paper
we show that the difficulties to extract the correct Γn/Γp ratio from the proton spectra is related to the three-body weak-interaction process which strongly quenches the nucleon yields. 相似文献
897.
M. W. Lee M. F. Tai H. J. Lee H. L. Hwang H. -C. I. Kao 《Physica C: Superconductivity and its Applications》1994,230(3-4):292-296
We report that the diamagnetism of as-grown YBa2Cu3O7−δ powders can be enhanced by treatment with RF-generated hydrogen plasma. The field-cooling susceptibility at 5 K is found to increase by up to 24%. The enhancement is reproducible for all five samples studied. The lattice parameter c decreases after hydrogenation. For a sample treated for the shortest period, its pinning potential,obtained from magnetic relaxation measurements, is reduced following H-treatment. 相似文献
898.
In this paper the behavior of general fuzzy acceptor over a commutative cl-semigroup
is considered, and the properties of ε-equivalence relation are investigated. From these results, we can apply for pattern recognition of deformed images, or for enhancement of distorted patterns. 相似文献
899.
Three series of ferroelectric liquid crystals containing a (2S)-2-(6-(4-hydroxybiphenyl-4'-carbonyloxy)-2'-naphthyl)propionate mesogenic group and oligo(oxyethylene) spacers were synthesized. These obtained liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC), optical polarized microscopy (POM), and X-ray powder diffraction measurements. Some of these materials containing four phenyl rings of ester cores (i.e. -Ph-Ph-COO-naph-) and chiral heptyl tail exhibited a rich mesomorphic behaviour, a blue phase (BP), a cholesteric phase (Ch), a smectic A (SA), a twist grain boundary A (TGBA), and a chiral smectic C (SC*) phase. Another series containing four phenyl rings of ester cores and chiral butyl and pentyl chain tails revealed only a SA phase and a SC* phase. Moreover, a crystal E phase was observed in the short spacer chain (n = 0 or 1) homologues of three series of compounds. Also, the mesomorphism properties were discussed as a function of spacer units, numbers of aromatic rings of core, and different terminal asymmetric moieties. 相似文献
900.
J. H. Lee In-Woo Chang S. J. Byun T. K. Hong K. Rhie W. Y. Lee Kyung-Ho Shin Chanyong Hwang S. S. Lee B. C. Lee 《Journal of magnetism and magnetic materials》2002,240(1-3):137-139
An unusually large enhancement of TMR at 77 K was observed in double barrier tunnel junctions (DBTJ). This is explained with extended Julliere's model which yields a twice larger TMR value. When the spin coherence length is much smaller at higher temperature, DBTJ is shown to work as a series of two single barrier tunnel junctions. 相似文献