全文获取类型
收费全文 | 453490篇 |
免费 | 5825篇 |
国内免费 | 1530篇 |
专业分类
化学 | 221250篇 |
晶体学 | 6597篇 |
力学 | 15674篇 |
综合类 | 15篇 |
数学 | 41501篇 |
物理学 | 114914篇 |
无线电 | 60894篇 |
出版年
2019年 | 3668篇 |
2018年 | 4073篇 |
2017年 | 4115篇 |
2016年 | 6825篇 |
2015年 | 4641篇 |
2014年 | 7007篇 |
2013年 | 18608篇 |
2012年 | 13391篇 |
2011年 | 16495篇 |
2010年 | 11464篇 |
2009年 | 11851篇 |
2008年 | 16036篇 |
2007年 | 16586篇 |
2006年 | 15972篇 |
2005年 | 14715篇 |
2004年 | 13343篇 |
2003年 | 12216篇 |
2002年 | 11780篇 |
2001年 | 13189篇 |
2000年 | 10558篇 |
1999年 | 8618篇 |
1998年 | 7301篇 |
1997年 | 7270篇 |
1996年 | 7162篇 |
1995年 | 6644篇 |
1994年 | 6414篇 |
1993年 | 6114篇 |
1992年 | 7095篇 |
1991年 | 6898篇 |
1990年 | 6555篇 |
1989年 | 6424篇 |
1988年 | 6296篇 |
1987年 | 5697篇 |
1986年 | 5405篇 |
1985年 | 6976篇 |
1984年 | 7038篇 |
1983年 | 5744篇 |
1982年 | 5992篇 |
1981年 | 5996篇 |
1980年 | 5662篇 |
1979年 | 5903篇 |
1978年 | 6140篇 |
1977年 | 5997篇 |
1976年 | 5778篇 |
1975年 | 5364篇 |
1974年 | 5273篇 |
1973年 | 5267篇 |
1972年 | 3539篇 |
1968年 | 3603篇 |
1967年 | 3625篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
961.
Experimental data is presented for the interaction between a propagating flame and a simple vortex flow field structure generated
in the wake of solid obstacles. The interaction between gas movement and obstacles creates vortex shedding forming a simple
flow field recirculation. The presence of the simple turbulent structure within the gas mixture curls the flame front increasing
curvature and enhancing burning rate. A novel twin camera Particle Image Velocimetry, PIV, was employed to characterise the
flow field recirculation and the interaction with the flame front. The technique allowed the quantification of the flame/vortex
interaction. The twin camera technique provides data to define the spatial variation of both the velocity of the flow field
and flame front. Experimentally obtained values of local flame displacement speed and flame stretch rate are presented for
simple flame/vortex interactions. 相似文献
962.
Tunable properties of light propagation in photonic crystal fibers filled with liquid crystals, called photonic liquid crystal
fibers (PLCFs) are presented. The propagation properties of PLCFs strongly depend on contrast between refractive indices of
the solid core (pure silica glass) and liquid crystals (LCs) filing the holes of the fiber. Due to relatively strong thermo-optical
effect, we can change the refractive index of the LC by changing its temperature. Numerical analysis of light propagation
in PLCF, based on two simulation methods, such as finite difference (FD) and multipole method (MM) is presented. The numerical
results obtained are in good agreement with our earlier experimental results presented elsewhere [1]. 相似文献
963.
Steady state temperature distribution in a model Czochralski crucible has been mapped by liquid crystal thermography (LCT).
The crucible is a water-filled glass beaker. Water is used as the test fluid because of ease of experimentation, as well as
the availability of correct thermo-physical properties. In addition, the Prandtl number of water matches those of molten oxides.
A copper cylinder whose diameter is smaller than that of the beaker is placed centrally at the water surface. Convection patterns
are set up by applying constant temperature difference between the crucible wall and the cylinder surface, in the temperature
range of the liquid crystals. The cylinder is given a fixed rotation, thus creating mixed convection conditions in the test
fluid. The LCT images recorded in the present study clearly reveal convective rolls, and the interaction of buoyancy-driven
convection in the crucible with cylinder rotation. The resulting temperature distributions match numerical simulation quite
well. The pure buoyancy and pure rotation experiments result in axisymmetric temperature fields, while in mixed convection,
the field is unsteady and three dimensional. 相似文献
964.
N. F. Morozov Yu. K. Startsev Yu. V. Sud’enkov A. A. Suslikov G. A. Baranov A. A. Belyaev 《Technical Physics》2006,51(7):872-877
The radiation hardness and mechanical strength of single-and two-phase glasses are studied for the case when nanosecond laser pulses (λ= 1.06 μm, τ0.5 ≈ 12.5 ns) are focused inside the material. Laser interferometry is applied to measure the displacement of the free surface, find optical breakage thresholds, and carry out the fractographic analysis of damaged regions. It is shown that breakdown channels and damage regions develop in a nonlinear manner according to optical breakdown mechanisms, changing each other with an increase in the laser energy. The strength of the two-phase glass is found to be more than four times that of the single-phase glass, although their elastic properties differ insignificantly. Such a considerable difference in the hardness of these materials with chemically similar constitutents is attributed to the presence of the double-lattice nanometer-scale structure of the two-phase glass. 相似文献
965.
We present a simplified computational scheme in order to calculate the effects of electron correlations on the energy bands of diamond and silicon. By adopting a quasiparticle picture we compute first the relaxation and polarization effects around an electron set into a conduction-band Wannier orbital. This is done by allowing the valence orbitals to relax within a self-consistent field (SCF) calculation. The diagonal matrix element of the Hamiltonian leads to a shift of the center of gravity of the conduction band while the off-diagonal matrix elements result in a small reduction of the conduction-electron bandwidth. This calculation is supplemented by the computation of the loss of ground-state correlations due to the blocked Wannier orbital into which the added electron has been placed. The same procedure applies to the removal of an electron, i.e., to the valence bands. But the latter have been calculated previously in some detail and previous results are used to estimate the energy gap in the two materials. The numerical data reported here show that the methods works, in principle, but that some extension of the scheme is also necessary to obtain fully satisfactory results.Dedicated to J.-P. Malrieu on the occasion of his 60th birthday 相似文献
966.
P. K. Sazonov G. A. Artamkina I. P. Beletskaya 《Russian Journal of Organic Chemistry》2006,42(3):438-447
The nucleophilic aromatic and vinyl substitution using diaza-18-crown-6 as nucleophile afforded a number of its N,N’-diaryl-[aryl = 2,4-(NO2)2C6H3, 4-C5F4N, 4-CF3C6F4] and N,N’-dialkenyl-substituted derivatives [alkenyl = PhC(O)CH=CH, MeOCOCH=CH, (EtO2C)2C=C(Ph), etc.]. Arylation of diaza-18-crown-6 with nonactivated aryl bromides, such as 4-Me2NC6H4Br, 4-MeOC6H4Br, C6H5Br, and 4-CF3C6H4Br, was effected under catalysis by palladium complexes. N,N’-Diaryldiaza-18-crowns-6 having electron-acceptor substituents in the aromatic rings turned out to be incapable of forming complexes with metal cations, while their analogs containing electron-donor para-methoxy and para-dimethylamino groups gave complexes with barium perchlorate. 相似文献
967.
陈永静 朱胜江 J.H.Hamilton A.V.Ramayya J.K.Hwang Y.X.Luo J.O.Rasmussen 车兴来 丁怀博 李明亮 《中国物理 C》2006,30(8):740-744
通过测量252Cf自发裂变所产生的瞬发γ射线, 对146Ce核的高自旋结构进行了重新研究, 结果更新了以前报道的能级纲图, 把八级形变集体带扩展到更高的自旋, 并且重新构建了可能的准γ带结构. 此外, 用反射不对称壳模型(RASM)对146Ce核的八级形变带进行了计算, 低自旋处的计算结果与实验数据符合得很好. 相似文献
968.
969.
YoungJu Choie Olav K. Richter 《Proceedings of the American Mathematical Society》2007,135(8):2309-2315
We determine a class of functions spanned by theta series of higher degree. We give two applications: A simple proof of the inversion formula of such theta series and a classification of skew-holomorphic Jacobi forms.
970.
B. D. Kabulov K. A. Akhundzhanov F. U. Yunusov O. A. Shpigun S. S. Negmatov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(3):354-356
The hydrolytic polycondensation of tetraethoxysilane in the presence of various polymers (polyacrylonitrile, polycaproamide, and chitosan) as templates was performed with the use of the sol-gel technology to obtain nanohybrid composite polymer-silica sorbents-nanofractals. 相似文献