全文获取类型
收费全文 | 12326篇 |
免费 | 642篇 |
国内免费 | 216篇 |
专业分类
化学 | 6023篇 |
晶体学 | 258篇 |
力学 | 814篇 |
综合类 | 21篇 |
数学 | 1231篇 |
物理学 | 4837篇 |
出版年
2023年 | 95篇 |
2022年 | 180篇 |
2021年 | 188篇 |
2020年 | 216篇 |
2019年 | 238篇 |
2018年 | 238篇 |
2017年 | 186篇 |
2016年 | 312篇 |
2015年 | 281篇 |
2014年 | 399篇 |
2013年 | 602篇 |
2012年 | 810篇 |
2011年 | 939篇 |
2010年 | 708篇 |
2009年 | 691篇 |
2008年 | 743篇 |
2007年 | 638篇 |
2006年 | 664篇 |
2005年 | 508篇 |
2004年 | 476篇 |
2003年 | 409篇 |
2002年 | 340篇 |
2001年 | 503篇 |
2000年 | 423篇 |
1999年 | 298篇 |
1998年 | 223篇 |
1997年 | 198篇 |
1996年 | 210篇 |
1995年 | 164篇 |
1994年 | 150篇 |
1993年 | 99篇 |
1992年 | 112篇 |
1991年 | 121篇 |
1990年 | 102篇 |
1989年 | 82篇 |
1988年 | 67篇 |
1987年 | 49篇 |
1986年 | 41篇 |
1985年 | 54篇 |
1984年 | 47篇 |
1983年 | 29篇 |
1982年 | 38篇 |
1981年 | 43篇 |
1980年 | 33篇 |
1979年 | 26篇 |
1978年 | 28篇 |
1977年 | 26篇 |
1976年 | 21篇 |
1975年 | 20篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
91.
Polyethylene oxide (PEO) based polymer electrolytes with BaTiO3 as filler and Li(C2F5SO2)2N as salt have been examined in lithium polymer batteries. The aluminum disolution potential in PEO-Li(C2F5SO2)2N was estimated to be 4.1 V vs. Li/Li+ at 80 °C, which was compared to that of 3.8 V vs. Li/Li+ in PEO-Li(CF3SO2)2N. The electrical conductivity of the system was measured as a function of O/Li ratio. The highest conductivity was observed
in O/Li=8. The conductivity was 1.65×10−3 S/cm at 80 °C and 1.5×10−5 S/cm at 25 °C. The interfacial resistance of Li/polymer electrolyte/Li annealed at 80 °C for 15 days was lower than 100 Ωcm2.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001. 相似文献
92.
Iron oxide catalyst with spinel structure used for dehydrogenation of ethylbenzene is one kind of important catalyst in petrochemical industry. In this work several series of industrial catalyst were prepared with different components and different manufacturing processes. Mössbauer Spectroscopy has been used to determine the optimal components and the better manufacturing process for spinel structure formation. The results may prove useful for producing the industrial dehydrogenation catalyst with better catalytic property. 相似文献
93.
Organically modified solid-state silicates (ORMOSILS) doped with a new laser dye 1,3,5,7,8-pentamethylpyrromethene-2,6-disulfonate-BF2 complex (pyrromethene 556) have been synthesized by a sol-gel method and the compositional effects on pore characteristics, fluorescence and lasing properties have been investigated. It is found that the use of dimethylsulfoxide and γ-glycidoxypropyltrimethoxysilane could greatly change the structure properties of sol-gel derived ORMOSILS cage, and thus the fluorescence and lasing properties of the materials could improve significantly. A successful laser oscillation from this dye-doped ORMOSILS sample has been achieved upon pumping with a Q-switched frequency-doubled Nd:YAG laser at 532 nm. A slope efficiency of 54% with a useful lifetime greater than 10,000 shots has been demonstrated at a pump repetition rate of 1 Hz and a pump intensity of 1 J/cm2 by using the new ORMOSILS cage on our newly designed laser system. Our results have shown that it is possible to obtain a high-efficiency with a long-lifetime for a compact new laser device by low cost dye-doped solid-state ORMOSILS. 相似文献
94.
In this paper, according to the molecular fragment principle, a series of eight ternary luminescent lanthanide complex systems were assembled, and whose compositions were determined with elemental analysis and infrared spectrum: Ln(MA)3(L)·H2O, where Ln = Sm, Eu, Tb, Dy; HMA = α‐methylacrylic acid; L = 1,10‐phenanthroline (phen), 2,2′‐bipyridine (bipy). The photophysical properties of these functional molecular systems were studied with ultraviolet‐visible absorption spectrum, and fluorescence excitation and emission spectrum. It was found that the heterocylic compounds (phen and bipy) act as the main energy donor and luminescence sensitizer for their suitable energy match and effective energy transfer to the emission energy level of Ln3+ ions. MMA ligand was only used as the terminal structural ligand to influence the luminescence. Especially terbium complex systems show the strongest luminescence for the optimum energy match and transfer between phen (bipy) and Tb3+ ion. 相似文献
95.
Many natural products contain carbohydrate moieties that contribute to their biological activity. Manipulation of the carbohydrate domain of natural products through multiple glycosylations to identify new derivatives with novel biological activities has been a difficult and impractical process. We report a practical one‐pot enzymatic approach with regeneration of cosubstrates to synthesize analogues of vancomycin that contain an N‐alkyl glucosamine, which exhibited marked improvement in antibiotic activity against a vancomycin‐resistant strain of Enterococcus. 相似文献
96.
97.
Invex-convexlike functions and duality 总被引:4,自引:0,他引:4
P. Q. Khanh 《Journal of Optimization Theory and Applications》1995,87(1):141-165
We define a class of invex-convexlike functions, which contains all convex, pseudoconvex, invex, and convexlike functions, and prove that the Kuhn-Tucker sufficient optimality condition and the Wolfe duality hold for problems involving such functions. Applications in control theory are given.The author is grateful to Professor W. Stadler and the referees for many valuable remarks and suggestions, which have enabled him to improve considerably the paper. 相似文献
98.
Chi Kin Chau Kwang Mong Sim 《Operations Research Letters》2003,31(5):327-334
By showing that there is an upper bound for the price of anarchyρ(Γ) for a non-atomic congestion game Γ with only separable cost maps and fixed demands, Roughgarden and Tardos show that the cost of forgoing centralized control is mild. This letter shows that there is an upper bound for ρ(Γ) in Γ for fixed demands with symmetric cost maps. It also shows that there is a weaker bound for ρ(Γ) in Γ with elastic demands. 相似文献
99.
We introduce the concept of partially strictly monotone functions and apply it to construct a class of nonlinear penalty functions for a constrained optimization problem. This class of nonlinear penalty functions includes some (nonlinear) penalty functions currently used in the literature as special cases. Assuming that the perturbation function is lower semi-continuous, we prove that the sequence of optimal values of nonlinear penalty problems converges to that of the original constrained optimization problem. First-order and second-order necessary optimality conditions of nonlinear penalty problems are derived by converting the optimality of penalty problems into that of a smooth constrained vector optimization problem. This approach allows for a concise derivation of optimality conditions of nonlinear penalty problems. Finally, we prove that each limit point of the second-order stationary points of the nonlinear penalty problems is a second-order stationary point of the original constrained optimization problem. 相似文献
100.
Cory J. Hill Baohua Yang Rui Q. Yang 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):486
Mid-IR type-II interband cascade lasers were demonstrated in pulsed mode at temperatures up to 325 K and in continuous mode up to 200 K. At 80 K, the threshold current density was 8.9 A/cm2 and a continuous wave output power of 140 mW/facet was obtained. 相似文献