全文获取类型
收费全文 | 14474篇 |
免费 | 2322篇 |
国内免费 | 2447篇 |
专业分类
化学 | 11642篇 |
晶体学 | 199篇 |
力学 | 783篇 |
综合类 | 256篇 |
数学 | 1573篇 |
物理学 | 4790篇 |
出版年
2024年 | 40篇 |
2023年 | 205篇 |
2022年 | 431篇 |
2021年 | 438篇 |
2020年 | 523篇 |
2019年 | 623篇 |
2018年 | 455篇 |
2017年 | 479篇 |
2016年 | 703篇 |
2015年 | 778篇 |
2014年 | 843篇 |
2013年 | 1125篇 |
2012年 | 1223篇 |
2011年 | 1133篇 |
2010年 | 1044篇 |
2009年 | 897篇 |
2008年 | 1113篇 |
2007年 | 955篇 |
2006年 | 868篇 |
2005年 | 795篇 |
2004年 | 652篇 |
2003年 | 627篇 |
2002年 | 733篇 |
2001年 | 662篇 |
2000年 | 455篇 |
1999年 | 309篇 |
1998年 | 206篇 |
1997年 | 134篇 |
1996年 | 119篇 |
1995年 | 99篇 |
1994年 | 74篇 |
1993年 | 73篇 |
1992年 | 81篇 |
1991年 | 81篇 |
1990年 | 56篇 |
1989年 | 31篇 |
1988年 | 30篇 |
1987年 | 20篇 |
1986年 | 22篇 |
1985年 | 28篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1979年 | 7篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1936年 | 3篇 |
1935年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Based on the generalized Huygens–Fresnel diffraction integral and the expansion of the hard aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression of elegant Laguerre–Gaussian beams passing through a paraxial ABCD optical system with an annular aperture is derived. Meanwhile, the corresponding closed-forms for the unapertured, circular apertured or circular black screen cases are also given. The obtained results provide more convenience for studying their propagation and transformation than the usual way by using diffraction integral formula directly. Some numerical examples are given to illustrate the propagation properties of elegant Laguerre–Gaussian beams. 相似文献
62.
63.
对以本征Si及重掺杂p型和n型Si作为中间层的Fe/Si多层膜的层间耦合进行研究,并通过退火,增大Fe,Si之间的扩散,分析界面扩散对层间耦合的影响. 实验结果表明,层状结构良好的制备态的多层膜,Fe,Si之间也存在一定程度的扩散,它是影响层间耦合的 主要因素,远远超过了半导体意义上的重掺杂,使不同种类的Si作为中间层的层间耦合基本 一致.进一步还发现,在一定范围内增大Fe,Si之间的扩散,即使多层膜的层状结构已经有了相当的退化,Fe/Si多层膜的反铁磁耦合强度基本保持不变.
关键词:
Fe/Si多层膜
层间耦合
界面扩散 相似文献
64.
Shui Cao ZHENG Huo Nan LIN Di He HU 《数学学报(英文版)》2005,21(5):1137-1148
In this paper, we investigate the Hausdorff measure for level sets of N-parameter Rd-valued stable processes, and develop a means of seeking the exact Hausdorff measure function for level sets of N-parameter Rd-valued stable processes. We show that the exact Hausdorff measure function of level sets of N-parameter Rd-valued symmetric stable processes of index α is Ф(r) = r^N-d/α (log log l/r)d/α when Nα 〉 d. In addition, we obtain a sharp lower bound for the Hausdorff measure of level sets of general (N, d, α) strictly stable processes. 相似文献
65.
HaiHuiXIE XiaoYiWEI JiDongWANG MeiFangLIU RenZhouYANG 《中国化学快报》2003,14(6):588-590
A New Annonaceous acetogenin,squamostolide(1),was isolated from the seeds of Annona squamosa.Its structure was elucidated based on spectroscopic methods and comparison with known compounds.It is the first example of Annonaceous acetogenin with each of the two ends of the aliphatic chain bearing a γ-lactone.Thenew compound exhibited cytotoxic activity in vitro against bel-7402 and CNE2 human tumor cell lines. 相似文献
66.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
67.
It is well known that topology and dynamics are two major aspects to determine the function of a network. We study one of the dynamic properties of a network: trajectory convergence, i.e. how a system converges to its steady state. Using numerical and analytical methods, we show that in a logical-like dynamical model, the occurrence of convergent trajectory in a network depends mainly on the type of the fixed point and the ratio between activation and inhibition links. We analytically proof that this property is induced by the competition between two types of state transition structures in phase space: tree-like transition structure and star-like transition structure. We show that the biological networks, such as the cell cycle network in budding yeast, prefers the tree-like transition structures and suggest that this type of convergence trajectories may be universal. 相似文献
68.
报道Ar^q Ne(q=8,9,11,12)碰撞体系中多电子转移过程,得到了多组实验测量电荷交换截面数据,讨论入射离子电荷交换截面、反冲离子产生截面与入射离子电荷态、能量以及散射离子电荷态的关系,并且将实验结果与Ar^q Ar碰撞体系进行对比研究。在修正分子库仑过垒模型的基础上,对实验现象做了合理的解释。 相似文献
69.
The SmF_(2.01)was synthesized by reducing SmF_3 in H_2 stream.As it was doped inKM_gF_3 and KCaF_3.there was emission of Sm~(2+) in KMgF_3 but no emission of Sm~(2+) inKCaF_3 was observed. 相似文献
70.
Chu-Li Fu Xiang-Tuan Xiong Zhi Qian 《Journal of Mathematical Analysis and Applications》2007,331(1):472-480
In this paper a simple and convenient new regularization method for solving backward heat equation—Fourier regularization method is given. Meanwhile, some quite sharp error estimates between the approximate solution and exact solution are provided. A numerical example also shows that the method works effectively. 相似文献