全文获取类型
收费全文 | 31559篇 |
免费 | 4966篇 |
国内免费 | 3512篇 |
专业分类
化学 | 17029篇 |
晶体学 | 248篇 |
力学 | 1862篇 |
综合类 | 127篇 |
数学 | 2775篇 |
物理学 | 9694篇 |
无线电 | 8302篇 |
出版年
2024年 | 139篇 |
2023年 | 801篇 |
2022年 | 1014篇 |
2021年 | 1321篇 |
2020年 | 1221篇 |
2019年 | 1096篇 |
2018年 | 1002篇 |
2017年 | 993篇 |
2016年 | 1440篇 |
2015年 | 1443篇 |
2014年 | 1724篇 |
2013年 | 2219篇 |
2012年 | 2634篇 |
2011年 | 2681篇 |
2010年 | 1931篇 |
2009年 | 1857篇 |
2008年 | 2109篇 |
2007年 | 1756篇 |
2006年 | 1760篇 |
2005年 | 1481篇 |
2004年 | 1046篇 |
2003年 | 885篇 |
2002年 | 848篇 |
2001年 | 709篇 |
2000年 | 708篇 |
1999年 | 694篇 |
1998年 | 596篇 |
1997年 | 525篇 |
1996年 | 560篇 |
1995年 | 513篇 |
1994年 | 398篇 |
1993年 | 338篇 |
1992年 | 304篇 |
1991年 | 262篇 |
1990年 | 246篇 |
1989年 | 182篇 |
1988年 | 145篇 |
1987年 | 114篇 |
1986年 | 96篇 |
1985年 | 70篇 |
1984年 | 51篇 |
1983年 | 43篇 |
1982年 | 31篇 |
1981年 | 20篇 |
1980年 | 16篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
In this paper,we research general Defective Cion Problem under the model S,i.e,the number d of Defective cions is not fixed. For d=O,1,or 2. we get some good results. 相似文献
62.
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
63.
HL-1装置中LHCD和等离子体参数的关系 总被引:1,自引:1,他引:0
本文研究了在HL-1托卡马克的不同放电阶段的低混杂波驱动特性。给出了驱动电流及驱动效率和等离子体参数,如电子平均密度ne、等离子体电流Ip及纵向磁场的关系。也给出和分析了波驱动和入射波功率的关系。在放电平段,对正反向驱动效率进行了研究和比较。 相似文献
64.
65.
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
66.
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
67.
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
68.
69.
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
70.
介绍了采用不同材料类型的粘结膜、半固化片、所需设备和粘结材料,用于生产低到高层数的PTFE多层板的情况。 相似文献