全文获取类型
收费全文 | 17583篇 |
免费 | 2663篇 |
国内免费 | 1708篇 |
专业分类
化学 | 12839篇 |
晶体学 | 206篇 |
力学 | 895篇 |
综合类 | 72篇 |
数学 | 1689篇 |
物理学 | 6253篇 |
出版年
2024年 | 62篇 |
2023年 | 329篇 |
2022年 | 592篇 |
2021年 | 593篇 |
2020年 | 662篇 |
2019年 | 679篇 |
2018年 | 607篇 |
2017年 | 537篇 |
2016年 | 796篇 |
2015年 | 837篇 |
2014年 | 1044篇 |
2013年 | 1336篇 |
2012年 | 1545篇 |
2011年 | 1607篇 |
2010年 | 1167篇 |
2009年 | 984篇 |
2008年 | 1189篇 |
2007年 | 1075篇 |
2006年 | 954篇 |
2005年 | 844篇 |
2004年 | 611篇 |
2003年 | 538篇 |
2002年 | 503篇 |
2001年 | 340篇 |
2000年 | 339篇 |
1999年 | 268篇 |
1998年 | 245篇 |
1997年 | 211篇 |
1996年 | 206篇 |
1995年 | 170篇 |
1994年 | 192篇 |
1993年 | 140篇 |
1992年 | 130篇 |
1991年 | 102篇 |
1990年 | 96篇 |
1989年 | 90篇 |
1988年 | 46篇 |
1987年 | 33篇 |
1986年 | 36篇 |
1985年 | 31篇 |
1984年 | 24篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1976年 | 15篇 |
1974年 | 12篇 |
1973年 | 9篇 |
1968年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
71.
The phase boundary theory and the contact rule of phase regions are compared, and some weaknesses of the latter are manifested.
The comparison between the Gupta’s method and the boundary theory method for constructing multicomponent isobaric sections
is also presented. 相似文献
72.
Y.-Q. Peng J.-H. Yang F.-P. Lu Q.-S. Yang H.-W. Xing X.-S. Li C.-A. Song 《Applied Physics A: Materials Science & Processing》2007,86(2):225-229
Based on the assumption of Gaussian energy distributions of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), analytical expressions of generalized Einstein relation in chemically doped organic semiconductor are developed, by approximation of Coulomb traps with a rectangle potential well. Numerical calculations show that traditional Einstein relations do not hold for chemically doped organic semiconductors. Similar to physical doping, the dependence of diffusion coefficient to mobility D/μ ratio on the carrier concentration has a maximum. An essential difference between chemical doping and physical doping is that, the D/μ ratio in chemically doped organic semiconductors depends not only on carrier concentration and doping concentration, but also on the applied electric field. PACS 71.20.Rv; 72.90.+y; 73.50.-h 相似文献
73.
Augustine O. Esogbue Qiang Song Donovan Young 《Mathematical Methods of Operations Research》2006,63(3):525-542
In this paper the problem of verifying the Pareto-optimality of a given solution to a dynamic multiple-criterion decision (DMCD) problem is investigated. For this purpose, some new conditions are derived for Pareto-optimality of DMCD problems. In the literature, Pareto-optimality is characterized by means of Euler-Lagrangian differential equations. There exist problems in production and inventory control to which these conditions cannot be applied directly (Song 1997). Thus, it is necessary to explore new conditions for Pareto-optimality of DMCD problems. With some mild assumptions on the objective functionals, we develop necessary and/or sufficient conditions for Pareto-optimality in the sprit of optimization theory. Both linear and non-linear cases are considered. 相似文献
74.
The single-phase diluted magnetic Fe-ion (5%) doped ZnO powders were prepared by solid-state reaction method. The powders were annealed in Ar or Ar/H2(5%) atmosphere at 1200 °C. The crystal structure, electric and magnetic properties for the Zn0.95Fe0.05O powders have been studied with X-ray diffraction (XRD) vibrating sample magnetometer, resistance and Hall measurement. All the peaks for the XRD pattern of samples belong to the hexagonal (P63mc) lattice of ZnO, and no indication of a secondary phase. The lattice parameters for the Zn0.95Fe0.05O with an annealing in Ar/H2(5%) atmosphere were a0=3.256 Å and c0=5.206 Å at room temperature. The hysteresis curve for the Zn0.95Fe0.05O at room temperature was enhanced ferromagnetic behaviour with an annealing in Ar/H2(5%) atmosphere. We give an explanation for enhanced ferromagnetic behaviour with H2 treatment by electric properties. 相似文献
75.
The crystal and molecular structure of the complex containing cobalt-carbon and iron-sulfur cluster cores, (μ-p-CH3C6H4C2S) (μ-n-C3H7S)Fe2(CO)6Co2(CO)6, has been determined by X-ray diffraction method. The crystals are triclinic, space group P&1bar;, with a — 9.139(2), b=9.610(1), c-17.183(2) Å, α = 84.36(1), β-89.45(1), γ=88.15(1)°, V-1501.0 Å3; Z=2, Dc=1.74 g/cm3. R=0.072, Rw=0.081. The results of the structure determination show a cobalt-carbon cluster core formed through the reaction of (μ-p-CH3C6H4C2S)(μ-n-C3H7S)Fe2(CO)6 with Co2(CO)8. In the cobalt-carbon cluster core, the bond length of the original C≡C lengthened to 1.324 Å which is close to the typical value of carbon-carbon double bond. The groups connecting the carbons of the cluster core are in cis position and lie on the opposite side of cobalt atoms. In this complex, the conformation of —SC3H7 is e-type, while that of —SC2C6H4CH3 is a-type. 相似文献
76.
In this paper, we analyze the manufacturing lead time in a production system with BMAP (Batch Markovian Arrival process) input and post-operation operated under the N-policy. We use the factorization principle to derive the waiting time distribution (hence the manufacturing lead time) and the mean performance measures. A numerical example is provided. 相似文献
77.
In this paper, an interior point cutting plane method (IPCPM)is applied to solve optimal power flow (OPF) problems. Comparedwith the simplex cutting plane method (SCPM), the IPCPM is simpler,and efficient because of its polynomial-time characteristic.Issues in implementing IPCPM for OPF problems are addressed,including (1) how to generate cutting planes without using thesimplex tableau, (2) how to identify the basis variables inIPCPM, and (3) how to generate mixed integer cutting planes.The calculation speed of the proposed algorithm is further enhancedby utilizing the sparsity features of the OPF formulation. Numericalsimulations on IEEE 14-300-bus test systems have shown thatthe proposed method is effective. 相似文献
78.
79.
Low-loss and rugged distal tips for CO2 laser have been proposed and fabricated based on a commercially available stainless steel (St) pipe. A method of smoothening the inner surface of the St pipe with a rough inner surface is put forward. Fabrication parameters, transmission properties, and mechanical strength of the cyclic olefin polymer-coated silver hollow St distal tip are experimentally discussed. 相似文献
80.