全文获取类型
收费全文 | 58584篇 |
免费 | 4649篇 |
国内免费 | 6433篇 |
专业分类
化学 | 40751篇 |
晶体学 | 2779篇 |
力学 | 1048篇 |
综合类 | 729篇 |
数学 | 8083篇 |
物理学 | 16276篇 |
出版年
2023年 | 384篇 |
2022年 | 1543篇 |
2021年 | 1822篇 |
2020年 | 1273篇 |
2019年 | 1426篇 |
2018年 | 1180篇 |
2017年 | 1375篇 |
2016年 | 1762篇 |
2015年 | 1594篇 |
2014年 | 2252篇 |
2013年 | 4327篇 |
2012年 | 2658篇 |
2011年 | 2868篇 |
2010年 | 2631篇 |
2009年 | 3262篇 |
2008年 | 3451篇 |
2007年 | 3693篇 |
2006年 | 3178篇 |
2005年 | 2476篇 |
2004年 | 2393篇 |
2003年 | 2134篇 |
2002年 | 4448篇 |
2001年 | 1875篇 |
2000年 | 1447篇 |
1999年 | 1309篇 |
1998年 | 1186篇 |
1997年 | 940篇 |
1996年 | 1062篇 |
1995年 | 920篇 |
1994年 | 877篇 |
1993年 | 802篇 |
1992年 | 822篇 |
1991年 | 542篇 |
1990年 | 415篇 |
1989年 | 355篇 |
1988年 | 351篇 |
1987年 | 259篇 |
1986年 | 260篇 |
1985年 | 370篇 |
1984年 | 276篇 |
1983年 | 175篇 |
1982年 | 312篇 |
1981年 | 500篇 |
1980年 | 441篇 |
1979年 | 485篇 |
1978年 | 390篇 |
1977年 | 294篇 |
1976年 | 256篇 |
1974年 | 111篇 |
1973年 | 196篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
合成了一种新型金属杂冠醚配合物[Mn6(4-amashz)6(DMF)6]·12DMF,并用X射线衍射法对其结构进行了表征.研究了该化合物修饰金电极催化氧还原的性质,结果表明,该化合物具有平面碟状结构,对在碱性溶液中的氧有显著的催化还原作用. 相似文献
192.
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
193.
3d-metal antimonides: Fe1+x Sb, N+x Sb, Co+x Sb and the (Ni1?y Fe y )Sb solid solution have been studied by the Mössbauer effect method at 57Fe and 119Sn. It was found that the quadrupole interactions at the Fe and Sn nucleus in 3d-metal antimonides are very sensitive to the filling of different crystallographic sites with metal atoms. The metal atoms in trigonal-bipyramidal sites have a strong effect on the quadrupole splitting of 119Sn. They are nearest to anions (Sb or Sn) with the typical axial ratio of c/a = 1.25. The QS(x) dependence of 119 Sn in 3d-metal antimonides in the 0 ≤ x ≤ 0.1 concentration range can be used to determine x – the concentration of transition metal excess relative to the stoichiometric composition. 相似文献
194.
195.
Changbing Hu 《Journal of Differential Equations》2007,236(1):133-163
In this article we study the 3D Navier-Stokes equations with Navier friction boundary condition in thin domains. We prove the global existence of strong solutions to the 3D Navier-Stokes equations when the initial data and external forces are in large sets as the thickness of the domain is small. We generalize the techniques developed to study the 3D Navier-Stokes equations in thin domains, see [G. Raugel, G. Sell, Navier-Stokes equations on thin 3D domains I: Global attractors and global regularity of solutions, J. Amer. Math. Soc. 6 (1993) 503-568; G. Raugel, G. Sell, Navier-Stokes equations on thin 3D domains II: Global regularity of spatially periodic conditions, in: Nonlinear Partial Differential Equations and Their Application, College de France Seminar, vol. XI, Longman, Harlow, 1994, pp. 205-247; R. Temam, M. Ziane, Navier-Stokes equations in three-dimensional thin domains with various boundary conditions, Adv. Differential Equations 1 (1996) 499-546; R. Temam, M. Ziane, Navier-Stokes equations in thin spherical shells, in: Optimization Methods in Partial Differential Equations, in: Contemp. Math., vol. 209, Amer. Math. Soc., Providence, RI, 1996, pp. 281-314], to the Navier friction boundary condition by introducing a new average operator Mε in the thin direction according to the spectral decomposition of the Stokes operator Aε. Our analysis hinges on the refined investigation of the eigenvalue problem corresponding to the Stokes operator Aε with Navier friction boundary condition. 相似文献
196.
Hans Weber 《Order》2007,24(4):249-276
We study lattice theoretical properties of lattices of uniformities such as modularity, distributive laws and the existence
of (relative) complements. For this the concepts of permutable uniformities (see Definition 3.1) and independent uniformities
(see Definition 4.1) are important. Moreover, we show that e.g. the lattice of all lattice uniformities on a lattice L is a closed sublattice of the lattice of all uniformities on L. 相似文献
197.
Curved Ferroelectric Liquid Crystal Matrix Displays Driven by Field-Sequential-Color and Active-Matrix Techniques 总被引:1,自引:0,他引:1
Hideo Fujikake Hiroto Sato Takeshi Murashige Yoshihide Fujisaki Taiichiro Kurita Tadahiro Furukawa Fumio Sato 《Optical Review》2006,13(1):14-19
This paper describes a curved field-sequential-color matrix display using fast-response ferroelectric liquid crystal. Black
matrix and transparent electrode patterns were formed on a thin plastic substrate by a transfer method from a glass substrate.
While a composite film of liquid crystal and micro-polymers of walls and fibers was formed between the flexible substrates
by printing, laminating and curing processes of a solution of monomers and liquid crystal, the mechanical stability was enhanced
by use of multi-functional monomers to form large display panels. The image pixels of the matrix panel were driven by an active
matrix scheme using an external switch transistor array at a frequency of 180 Hz for intermittent three-primary-color backlight
illumination. The flexible A4-paper-sized color display with 24 × 16 pixels and 60 Hz field frequency was demonstrated by
illuminating it with sequential three-primary-color lights from light-emitting diodes of the backlight. Our display system
is useful in various information displays because of its freedom of setting and location. 相似文献
198.
Zhijun Yi Tingyu LiuQiren Zhang Yuanyuan Sun 《Journal of Electron Spectroscopy and Related Phenomena》2006
The electronic structures of PbWO4 crystals containing F type color centers with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Direc–Slater theory, using a numerically discrete variational (DV-Xα) method. The calculated results show that F and F+ centers have donor energy level in forbidden band. Their optical transition energy are 1.84 eV, 2.21 eV, respectively, which corresponds to the 680 nm, 550 nm absorption bands. It predicts that the 680 nm, 550 nm absorption bands originate form the F and F+ centers in PbWO4 crystals. 相似文献
199.
We study the corrections to the Clausius-Mossotti formula for the dielectric constant of a disordered system of polarizable spherical particles. Previously we have derived an exact cluster expansion for the correction terms. Here we study the three-body correction in detail. We derive an explicit expression for the integrand of the three-body cluster integral for a system of polarizable point dipoles. 相似文献
200.
A new sample business survey for agriculture, the REA survey, and a project of integration with the FADN network (RICA in
Italy) have significantly changed the production of statistical information nowadays available with reference to the agricultural
sector. On the basis of this relevant information, new economic analyses are being developed on farms’ performance, agricultural
households’ income and the Common Agricultural Policy (CAP). In this paper the authors estimate the relationship between the
levels of variables of interest and their sampling errors using models in order to improve the accessibility of the information
on estimates accuracy to the final users (agricultural analysts, policy makers).
The paper is the result of a joint research of the three authors. Sections 1–3 and 6 by Pizzoli, Sects. 4 and 5 by Rondinelli,
Sect. 7 by Filiberti, conclusions joint to the three authors. 相似文献