全文获取类型
收费全文 | 403047篇 |
免费 | 4438篇 |
国内免费 | 1414篇 |
专业分类
化学 | 214623篇 |
晶体学 | 6814篇 |
力学 | 17705篇 |
综合类 | 6篇 |
数学 | 43010篇 |
物理学 | 126741篇 |
出版年
2018年 | 3934篇 |
2017年 | 3795篇 |
2016年 | 6045篇 |
2015年 | 4001篇 |
2014年 | 6237篇 |
2013年 | 17144篇 |
2012年 | 12301篇 |
2011年 | 15238篇 |
2010年 | 10569篇 |
2009年 | 10435篇 |
2008年 | 13960篇 |
2007年 | 14067篇 |
2006年 | 13371篇 |
2005年 | 12116篇 |
2004年 | 11222篇 |
2003年 | 9984篇 |
2002年 | 9754篇 |
2001年 | 11840篇 |
2000年 | 9065篇 |
1999年 | 7132篇 |
1998年 | 5874篇 |
1997年 | 5839篇 |
1996年 | 5623篇 |
1995年 | 5153篇 |
1994年 | 5024篇 |
1993年 | 4990篇 |
1992年 | 5551篇 |
1991年 | 5574篇 |
1990年 | 5329篇 |
1989年 | 5309篇 |
1988年 | 5264篇 |
1987年 | 5188篇 |
1986年 | 4886篇 |
1985年 | 6585篇 |
1984年 | 6790篇 |
1983年 | 5557篇 |
1982年 | 5828篇 |
1981年 | 5743篇 |
1980年 | 5572篇 |
1979年 | 5808篇 |
1978年 | 6141篇 |
1977年 | 5889篇 |
1976年 | 5916篇 |
1975年 | 5508篇 |
1974年 | 5510篇 |
1973年 | 5527篇 |
1972年 | 3776篇 |
1971年 | 3152篇 |
1968年 | 3335篇 |
1967年 | 3346篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
941.
942.
The theory of dielectric space-charge polarization losses describes well both the model of an inhomogeneous dielectric [1]
and the polarization resulting from mosaic blocks of alkali-halide crystals [2]. The Debye frequency dependences ε*(ω) and
tan δ(ω) with non-Arrhenius relaxation time are calculated in the first approximation of perturbation theory [3, 4] with the
use of a nonlinear system of the Fokker-Planck and Poisson equations for the interlayer polarization with allowance for tunnel
transitions of relaxation oscillators. For the Maxwell mechanism of space-charge relaxation, tan δ(ω) also has the Debye form
[5]. It should be noted that in studies cited above the electric field was considered uniform, and the nonlinearity of the
initial system of equations was not investigated. This paper removes these restrictions and elaborates a theory of relaxation
mechanism.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 28–34, November, 2006. 相似文献
943.
A. P. Avdeenko S. A. Konovalova O. N. Ludchenko 《Russian Journal of Organic Chemistry》2006,42(5):683-688
Reactions of halogens with N-arylsulfonyl-1,4-benzoquinone monoimines occur with the formation of a halogenonium ion that either transforms into a carbocation where the first halogen atom adds to the carbon in the ortho-position relative to the carbonyl carbon, or the halogenonium ion adds directly the second halogen atom. 相似文献
944.
A model for the flow of a fluid through a channel with parallel plates is investigated. The channel is narrow, so that the lubrication approximation may be applied. The channel walls are maintained at a constant temperature. Shear heating effects are included and the fluid viscosity decreases exponentially with temperature. When the flow is driven solely by shear stress or imposed velocity at the top, analytical progress is possible. When pressure gradient also drives the flow the problem is solved numerically. 相似文献
945.
In this paper we propose a general integration scheme for a Multi-Criteria Decision Making model of the Multi-Attribute Utility
Theory in Constraint Programming. We introduce the Choquet integral as a general aggregation function for multi-criteria optimization
problems and define the Choquet global constraint that propagates this function during the Branch-and-Bound search. Finally the benefits of the propagation
of the Choquet constraint are evaluated on the examination timetabling problem. 相似文献
946.
S.N. Abdulmadjid M.M. Suliyanti K.H. Kurniawan T.J. Lie M. Pardede R. Hedwig K. Kagawa M.O. Tjia 《Applied physics. B, Lasers and optics》2006,82(1):161-166
We report in this paper the results of an experimental study on hydrogen analysis of solid samples in high pressure helium
ambient gas employing the basic scheme of laser induced breakdown spectroscopy (LIBS). It is shown that the metastable excited
state of helium atom can be utilized to induce delayed excitation of the ablated hydrogen atoms, and thereby avoid the Stark
broadening effect as well as overcoming the undesirable mismatch effect, which are responsible for inefficient excitation
respectively. It is further demonstrated that for samples of high boiling-point materials such as zircaloy, successful hydrogen
analysis can be achieved by a newly introduced double excitation technique employing single laser realized in a modified configuration
of the conventional LIBS method.
PACS 51-52 相似文献
947.
We consider three one-dimensional quantum, charged and spinless particles interacting through delta potentials. We derive
sufficient conditions which guarantee the existence of at least one bound state. 相似文献
948.
Y. Oner O. Kamer Joseph H. Ross Jr. 《Journal of magnetism and magnetic materials》2006,300(2):373-381
We report resistivity and magnetization measurements on an amorphous Ni74Mn24Pt2 thin film in the temperature range of 3–300 K. Two significant features are apparent in both the magnetic susceptibility and electrical resistivity. A low-temperature (low-T) anomaly is observed at about 40 K, where a cusp appears in the resistivity, while a concomitant step-like increase in zero-field-cooled (ZFC) magnetization (M) appears with increasing temperature. The low-T anomaly is attributed to a crossover from a pure re-entrant spin-glass within individual domains to a mixed ferro-spin-glass regime at lower temperatures. By contrast, the high-temperature (high-T) anomaly, signaled by the appearance of hysteresis below 250 K, corresponds to the freezing of transverse spins in individual domains acting independently. Between the low-T and high-T anomalies a small but discernable magnetic hysteresis is observed for warming vs. cooling in the field-cooled (FC) case. This behavior clearly indicates the presence of domain structure in the sample, while the disappearance of this hysteresis at lower temperatures indicates the complete freezing of the spin orientation of these domains. According to these results, we have divided the magnetic state of this sample into three regions: at temperatures above 250 K, the sample behaves like a soft ferromagnet, exhibiting M vs. H loops with very small hysteresis (less than 5 Oe). As the temperature is lowered into the intermediate region (the range 40–250 K), spins become frozen randomly and progressively within the individual domains. These domains behave independently, rather than as a cooperative behavior of the sample. Weak irreversibility sets in, indicating the onset of transverse spin freezing within the domains. At temperatures below 40 K, the M vs. H loops exhibit larger hysteresis, for both the ZFC and FC cases, as in a pure spin-glass. We have also demonstrated giant noise in the resistivity at temperatures just below 250 K. Such noise can originate from fluctuations of the domains near the film surface because of competing effective bulk and surface anisotropy fields. The large observed amplitude may be explained by means of a large ferromagnetic anisotropy in the resistivity due to the large spin–orbit effect seen in NiMn systems. Finally, the low-T peak in the resistivity has been analyzed using Fisher and Langer's expression based on the Friedel Model proposed for critical transitions in transition metals (s–d systems). The fitted results are in satisfactory agreement with the predictions of this model. 相似文献
949.
950.