全文获取类型
收费全文 | 9009篇 |
免费 | 301篇 |
国内免费 | 601篇 |
专业分类
化学 | 5027篇 |
晶体学 | 50篇 |
力学 | 95篇 |
综合类 | 4篇 |
数学 | 127篇 |
物理学 | 4608篇 |
出版年
2024年 | 7篇 |
2023年 | 142篇 |
2022年 | 95篇 |
2021年 | 94篇 |
2020年 | 168篇 |
2019年 | 139篇 |
2018年 | 116篇 |
2017年 | 166篇 |
2016年 | 184篇 |
2015年 | 159篇 |
2014年 | 309篇 |
2013年 | 512篇 |
2012年 | 501篇 |
2011年 | 676篇 |
2010年 | 555篇 |
2009年 | 651篇 |
2008年 | 573篇 |
2007年 | 730篇 |
2006年 | 568篇 |
2005年 | 495篇 |
2004年 | 435篇 |
2003年 | 339篇 |
2002年 | 262篇 |
2001年 | 232篇 |
2000年 | 197篇 |
1999年 | 206篇 |
1998年 | 166篇 |
1997年 | 170篇 |
1996年 | 145篇 |
1995年 | 122篇 |
1994年 | 109篇 |
1993年 | 125篇 |
1992年 | 84篇 |
1991年 | 89篇 |
1990年 | 63篇 |
1989年 | 43篇 |
1988年 | 48篇 |
1987年 | 31篇 |
1986年 | 32篇 |
1985年 | 23篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 27篇 |
1981年 | 23篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 13篇 |
排序方式: 共有9911条查询结果,搜索用时 15 毫秒
1.
We report optical and nonlinear optical properties of CuS quantum dots and nanoparticles prepared through a nontoxic, green, one-pot synthesis method. The presence of surface states and defects in the quantum dots are evident from the luminescent behavior and enhanced nonlinear optical properties measured using the open aperture Z-scan, employing 5 ns laser pulses at 532 nm. The quantum dots exhibit large effective third order nonlinear optical coefficients with a relatively lower optical limiting threshold of 2.3 J cm−2, and the optical nonlinearity arises largely from absorption saturation and excited state absorption. Results suggest that these materials are potential candidates for designing efficient optical limiters with applications in laser safety devices. 相似文献
2.
Prof. Jen-Shyang Ni Tianliang Min Yaxi Li Menglei Zha Dr. Pengfei Zhang Prof. Chun Loong Ho Prof. Kai Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(25):10265-10271
Planar luminogens have encountered difficulties in overcoming intrinsic aggregation-caused emission quenching by intermolecular π-π stacking interactions. Although excited-state double-bond reorganization (ESDBR) can guide us on designing planar aggregation-induced emission (AIE) luminogens (AIEgens), its mechanism has yet been elucidated. Major challenges in the field include methods to efficiently restrict ESDBR and enhance AIE performance without using bulky substituents (e.g., tetraphenylethylene and triphenylamine). In this study, we rationally developed fluoro-substituent AIEgens with stronger intermolecular H-bonding interaction for restricted molecular motions and increased crystal density, leading to decreased nonradiative decay rate by one order of magnitude. The adjusted ESDBR properties also show a corresponding response to variation in viscosity. Furthermore, their aggregation-induced reactive oxygen species (ROS) generations have been discovered. The application of such planar AIEgen in treating multidrug-resistant bacteria has been demonstrated in a mouse model. The relationship between ROS generation and distinct E/Z-configurational stacking behaviors have been further understood, providing a design principle for synthesizing planar AIEgen-based photosensitizers. 相似文献
3.
Plasma-assisted flow control is of high industrial interest, but practical applications at full scale require a large surface of interaction. Nanosecond pulsed Dielectric Barrier Discharge (DBD) have demonstrated promising results of flow control, but their interacting region is limited to only a few cm2. In this paper, the conditions to extend a surface nanosecond DBD are documented. It is shown that a sliding discharge regime can fully fill an inter-electrode distance of 40 mm. This discharge regime promotes the formation of two hemispheric pressure waves originating from both air-exposed electrodes while an horizontal region of pressure gradient is also observed. 相似文献
4.
In this work the results of the statistical topometric analysis of fracture surfaces of soda-lime-silica glass with and without ionic exchange treatment are reported. In this case, the mechanism of substitution is K+-Na+. atomic force microscopy (AFM) was employed to record the topometric data from the fracture surface. The roughness exponent (ζ) and the correlation length (ξ) were calculated by the variable bandwidth method. The analysis for both glasses (subjected and non-subjected to ionic exchange) for ζ shows a value ∼0.8, this value agrees well with that reported in the literature for rapid crack propagation in a variety of materials. The correlation length shows different values for each condition. These results, along with those of microhardness indentations suggest that the self-affine correlation length is influenced by the complex interactions of the stress field of microcracks with that resulting from the collective behavior of the point defects introduced by the strengthening mechanism of ionic exchange. 相似文献
5.
原子吸收光谱法测定铝锂合金中锂 总被引:2,自引:0,他引:2
本文研究了用原子吸收光谱法在笑气-乙炔火焰中测定铝锂合金中锂的最佳条件。其电离干扰可通过加进钾进盐来控制。应用本法测定合金中 锂的含量,获得了满意结果。 相似文献
6.
7.
8.
Susana Conde Ceide 《Tetrahedron letters》2006,47(26):4415-4418
We herein report that flash heating microwave irradiation is a helpful tool in the formation of arylpyrimidines from the corresponding halopyrimidines. The palladium-catalyzed cross-coupling reactions of 2,4-di- and 2,4,5-trihalopyrimidines with phenylboronic acid under the above conditions are described. By use of the appropriate catalyst and the adequate halopyrimidine, good regioselectivity can be achieved in the 2-, 4-, or 5-positions of the heterocycle. In addition, we show that this methodology is ameneable for the stepwise preparation of mono-, di-, and triphenylpyrimidines. 相似文献
9.
Two methods for multi-element preconcentration from copper by reductive matrix precipitation are presented. In systematic investigations on the coprecipitation behaviour of Ag, Al, Au, Bi, Cd, Co, Cr, Fe, Ga, In, Mn, Mo, NJ, Pb, Sb, Se, Sn, Te and Zn during precipitation of the copper matrix as Cu2O or CuSCN, the separation parameters were optimized. By combination with a hexamethyleneammonium hexamethylenedithiocarbamate collector precipitation, a concentration of 8 elements (Cu2O precipitation) or 13 elements (CuSCN precipitation) in a small volume was achieved. The limits of detection of the procedures are, depending on the element, 0.1–5 μg g?1 for flame atomic absorption spectrometry (AAS) and 0.01–0.1 μg g?1 for graphite furnace AAS. The relative standard deviations are about 3%. The analytical performance of the procedures is compared with that of an electrolytic copper separation. 相似文献
10.
托卡马克工程试验混合堆等离子体性能的等值线图分析 总被引:3,自引:3,他引:0
盛光昭 《核聚变与等离子体物理》1989,9(1):29-36
本文简要叙述托卡马克工程试验混合堆等离子体概念设计的物理基础,对等离子体性能进行了等值线图(Plasma Operation Contour)分析。根据工程试验混合堆的要求,得出一组等离子体参数。 相似文献