全文获取类型
收费全文 | 323049篇 |
免费 | 4543篇 |
国内免费 | 1116篇 |
专业分类
化学 | 177011篇 |
晶体学 | 4472篇 |
力学 | 13162篇 |
综合类 | 8篇 |
数学 | 38226篇 |
物理学 | 95829篇 |
出版年
2020年 | 2050篇 |
2019年 | 2032篇 |
2018年 | 2015篇 |
2017年 | 1906篇 |
2016年 | 4016篇 |
2015年 | 3381篇 |
2014年 | 4610篇 |
2013年 | 14309篇 |
2012年 | 10943篇 |
2011年 | 13573篇 |
2010年 | 8448篇 |
2009年 | 8442篇 |
2008年 | 12569篇 |
2007年 | 12805篇 |
2006年 | 12450篇 |
2005年 | 11383篇 |
2004年 | 10247篇 |
2003年 | 9065篇 |
2002年 | 8930篇 |
2001年 | 10278篇 |
2000年 | 7870篇 |
1999年 | 6224篇 |
1998年 | 4998篇 |
1997年 | 4852篇 |
1996年 | 4897篇 |
1995年 | 4470篇 |
1994年 | 4230篇 |
1993年 | 4074篇 |
1992年 | 4572篇 |
1991年 | 4405篇 |
1990年 | 4135篇 |
1989年 | 3955篇 |
1988年 | 4254篇 |
1987年 | 3908篇 |
1986年 | 3784篇 |
1985年 | 5521篇 |
1984年 | 5579篇 |
1983年 | 4499篇 |
1982年 | 4910篇 |
1981年 | 4940篇 |
1980年 | 4727篇 |
1979年 | 4839篇 |
1978年 | 4846篇 |
1977年 | 4857篇 |
1976年 | 4760篇 |
1975年 | 4657篇 |
1974年 | 4478篇 |
1973年 | 4695篇 |
1972年 | 2658篇 |
1971年 | 1968篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The hydrothermal synthesis and magnetic entropy change for the perovskite manganite La0.5Ca0.3Sr0.2MnO3 have been studied. The La0.5Ca0.3Sr0.2MnO3 can be produced as phase-pure, crystalline powders in one step from solutions of metal salts in aqueous potassium hydroxide solution at a temperature of 513 K in 72 h. Scanning electron microscopy shows that the materials are made up of cuboid-shaped particles in typical dimension of 4.0×2.5×1.6 μm. Heat treatment can improve the magnetocaloric effect for the hydrothermal sample. The maximum magnetic entropy change ΔSM for the as-prepared sample is 0.88 J kg−1 K−1 at 315 K for a magnetic field change of 2.0 T. It increases to 1.52 J kg−1 K−1, near its Curie temperature (317 K) by annealing the sample at 1473 K for 6 h. The hydrothermal synthesis method is a feasible route to prepare high-quality perovskite material for magnetic refrigeration application. 相似文献
992.
J.E. Lorenzo H. Requardt 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):185-186
Eur. Phys. J. B 24, 315 (2001) Here we comment on a recently published paper on the presence of a phason contribution in the low temperature heat capacity data of the charge-density-wave compounds K0.3MoO3 and (TaSe4)2I. We have shown that the anomaly in the C
P
/
T
3
data reported by Odin et al. is straightforwardly interpreted in terms of low energy phonon modes resulting from the peculiar topology of these compounds.
Received 21 February 2002 Published online 19 July 2002 相似文献
993.
Blundell Tom L. Bolanos-Garcia Victor Chirgadze Dimitri Y. Harmer Nicholas J. Lo Thomas Pellegrini Luca Sibanda B. Lynn 《Structural chemistry》2002,13(3-4):405-412
Signaling in living systems needs to achieve high specificity, to be reversible, and to achieve high signal to noise. Signaling mediated by multiprotein systems has evolved that avoids the requirement for high-affinity binary complexes that would be difficult to reverse and which, in the overcrowded cell, would lead to excessive noise in the system. Symmetrical structures are only occasionally formed. When they are, it is principally to colocate components, for example, the tyrosyl kinases of growth factors, where dimers form. Symmetry is, however, often broken, presumably to create more sensitivity and specificity in the signaling system by assembling other components, into higher-order multiprotein systems. The binding of a single heparin to two 1:1 FGF:FGFR complexes is an example, as is the binding of a single ligase to the Xrcc4 dimer, perhaps so creating a further DNA-binding site. 相似文献
994.
The existing calculations of the nuclear matrix elements of the neutrinoless double β-decay differ by about a factor three. This uncertainty prevents quantitative interpretation of the results of experiments searching for this process. We suggest here that the observation of the neutrinoless double β-decay of several nuclei could allow to test calculations of the nuclear matrix elements through the comparison of the ratios of the calculated lifetimes with experimental data. It is shown that the ratio of the lifetimes is very sensitive to different models. 相似文献
995.
The lanthanide sulfotellurides (LS)2Te1+x (0 ≤ x < 0.50) show order-disorder phenomena. Above 450°C, they crystallize in a partially disordered structure, orthorhombic with cell parameters a, b, and c close to 4.1, 5.2, and 13.6 Å, respectively. This structure is determined from diffractometer data on a (HoS)2Te1.34 crystal (R = 0.061). It is built up along the c axis from (L4S) tetrahedra layers, separated by Te planes. Disorder and nonstoichiometry are related to the two vacant Te sites. 相似文献
996.
J. Sładkowski 《International Journal of Theoretical Physics》1991,30(4):517-520
A generalization of theG-theory defined by A. Heilet al. is presented. 相似文献
997.
J. Sładkowski 《International Journal of Theoretical Physics》1991,30(8):1075-1078
The possibility of inflation without any genuine scalar is discussed. It is suggested that drops of primordial plasma may drive inflation. The model, although naive, is consistent with observational data. 相似文献
998.
We study the superextension of the semi-infinite cohomology theory of the Virasoro Algebra. In particular, we examine the BRST complex with coefficients in the Fock Space of the RNS superstring. We prove a theorem of vanishing cohomology, and establish the unitary equivalence between a positive definite transversal space, a physical subspace and the zeroth cohomology group. The cohomology of a subcomplex is identified as the covariant equivalent of the well-known GSO subspace. An exceptional case to the vanishing theorem is discussed.Supported by NSF Grant DMS-8703581 相似文献
999.
Jan J. Dijkstra 《Topology and its Applications》2006,153(15):2948-2951
In 1988 A. Gutek proved that there exist one-point connectifications of hereditarily disconnected spaces that do not have the fixed point property. We improve on this result by constructing a one-point connectification of a totally disconnected space without the fixed point property. 相似文献
1000.
Leonard J. Prins 《Tetrahedron letters》2006,47(16):2735-2738
An efficient synthesis of ortho-substituted triphenolamines via reductive amination is reported. This approach allows access to this increasingly important class of ligands in a structurally systematic way using either commercially or easily synthesizable building blocks. 相似文献