全文获取类型
收费全文 | 20522篇 |
免费 | 3178篇 |
国内免费 | 2348篇 |
专业分类
化学 | 11405篇 |
晶体学 | 163篇 |
力学 | 1152篇 |
综合类 | 64篇 |
数学 | 1658篇 |
物理学 | 6281篇 |
无线电 | 5325篇 |
出版年
2024年 | 83篇 |
2023年 | 553篇 |
2022年 | 664篇 |
2021年 | 846篇 |
2020年 | 809篇 |
2019年 | 722篇 |
2018年 | 673篇 |
2017年 | 649篇 |
2016年 | 969篇 |
2015年 | 932篇 |
2014年 | 1159篇 |
2013年 | 1435篇 |
2012年 | 1768篇 |
2011年 | 1765篇 |
2010年 | 1244篇 |
2009年 | 1196篇 |
2008年 | 1356篇 |
2007年 | 1164篇 |
2006年 | 1112篇 |
2005年 | 993篇 |
2004年 | 670篇 |
2003年 | 561篇 |
2002年 | 541篇 |
2001年 | 451篇 |
2000年 | 427篇 |
1999年 | 455篇 |
1998年 | 364篇 |
1997年 | 311篇 |
1996年 | 345篇 |
1995年 | 343篇 |
1994年 | 253篇 |
1993年 | 204篇 |
1992年 | 193篇 |
1991年 | 175篇 |
1990年 | 162篇 |
1989年 | 121篇 |
1988年 | 97篇 |
1987年 | 77篇 |
1986年 | 56篇 |
1985年 | 44篇 |
1984年 | 31篇 |
1983年 | 25篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1978年 | 2篇 |
1972年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Efficient scheduling algorithms for the slot assignment problem in a satellite-switched time-division multiple-access (SS/TDMA) system are presented. This problem is translated into a modified open-shop scheduling problem, allowing the use of known optimal algorithms. Their complexity is expressed as a function of the following parameters: the number of nonzero entries in the demand matrix, the number of uplinks, and the number of downlinks. According to the values of these parameters, the algorithm with the lowest computational complexity can be adopted. Although the computational complexity of previously published algorithms is drastically reduced, simulation results show that the results are close to previously presented solutions in terms of the assignment duration and the number of switching matrices 相似文献
22.
23.
A new method using special shape parameters has been introduced to study density behavior with synergy of lower hybrid current drive (LHCD) and ion Bernstein wave (IBW) heating in the HT-7 superconducting tokamak. During the synergy of the LHCD and IBW heating an improved confinement plasma was achieved, and the electron density was increased and peaked. 相似文献
24.
Urn模型的离散概率分布被用于构造逼近格式,具有Bernstein多项式的许多特性。本文用B网技术对Urn模型概率分布给出新的解释,指出了Urn模型B网的诸多性质,导出分布函数曲线的导数公式,构造了Urn分布的对偶基及与此相关的拟插值算子。 相似文献
25.
26.
Fine Granularity Scalability (FGS) video coding has been adopted by the MPEG-4 standard for video streaming applications. In this paper, we propose a novel FGS coding scheme, which applied adaptive leaky factors for the enhancement layer prediction to further improve the coding efficiency of FGS. A flexible method that can dynamically determine the leaky factors according to the network conditions is also presented. With the proposed method, a better trade-off between the coding efficiency and drifting reduction can be achieved, and the coding performance is further improved compared with using a fixed leaky factor. Experimental results show that the proposed method can further improve the coding efficiency over a wide range of bitrate and packet loss ratio, and still keep the original characteristics, such as fine granularity, and bandwidth adaptation. 相似文献
27.
A method has been described for the determination of arsenic species (arsenite and arsenate) by hydride generation-atomic fluorescence spectrometry (HG-AFS). The experimental conditions that influence the fluorescence intensity and the reduction of arsenic were investigated and optimized, and the influences from foreign ions and their elimination were studied. The detection limit was found to be 79.7 ng L(-1). The proposed method was applied to the determination of arsenic species in water leachate of traditional Chinese medicines with a recovery range of 91.1-109.5%. 相似文献
28.
在过去几年里,小型PCB诸如硅芯片级以及便携式移动电话的生产者和设计者们已经发现:如果要保持自己的竞争力并具备生产高密度封装板能力,就必须采用微孔技术。微孔技术的出现要求针对微孔缺陷的有效检测手段对工艺进行过程控制。本文对激光微孔的自动光学检测进行了详细介绍。 相似文献
29.
Fengping Yu Junpo He Xiaojun Wang Guangzheng Gao Yuliang Yang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(17):4013-4025
A combination of nitroxide‐mediated radical polymerization and living anionic polymerization was used to synthesize a series of well‐defined graft (co)polymers with “V‐shaped” and “Y‐shaped” branches. The polymer main chain is a copolymer of styrene and p‐chloromethylstyrene (PS‐co‐PCMS) prepared via nitroxide‐mediated radical polymerization. The V‐shaped branches were prepared through coupling reaction of polystyrene macromonomer, carrying 1,1‐diphenylethylene terminus, with polystyryllithium or polyisoprenyllithium. The Y‐shaped branches were prepared throughfurther polymerization initiated by the V‐shaped anions. The obtained branches, carrying a living anion at the middle (V‐shaped) or at the end of the third segment (Y‐shaped), were coupled in situ with pendent benzyl chloride of PS‐co‐PCMS to form the target graft (co)polymers. The purified graft (co)polymers were analyzed by size exclusion chromatography equipped with a multiangle light scattering detector and a viscometer. The result shows that the viscosities and radii of gyration of the branched polymers are remarkably smaller than those of linear polystyrene. In addition, V‐shaped product adopts a more compact conformation in dilute solution than the Y‐shaped analogy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4013–4025, 2007 相似文献
30.
Wenping Deng Gang Xu Lei Wan Anwen Liu Bo Gao Junhe Du Shuiming Hu Yang Chen 《Acta Physico》2008,24(8):1329-1334
Apparatus integrating a Fourier transform-infrared (FT-IR) spectrometer and a mid-infrared difference frequency generation (DFG) laser spectrometer was built for the study of the matrix isolation spectrum in solid molecular hydrogen. A 3-cm-long molecular hydrogen crystal was grown in a liquid-helium Dewar, and its infrared absorption spectrum in the 1-5 μm region was recorded to test the system. The W0(0) (ν=0←0, J=6←0) line around 2410 cm−1 of solid hydrogen was investigated with the DFG laser spectroscopy. High-resolution matrix isolation spectrum of CO2 co-deposited with hydrogen on a BaF2 cold plate at liquid-helium temperature was studied. 相似文献