全文获取类型
收费全文 | 2789篇 |
免费 | 542篇 |
国内免费 | 290篇 |
专业分类
化学 | 2217篇 |
晶体学 | 37篇 |
力学 | 154篇 |
综合类 | 14篇 |
数学 | 238篇 |
物理学 | 961篇 |
出版年
2024年 | 5篇 |
2023年 | 61篇 |
2022年 | 93篇 |
2021年 | 111篇 |
2020年 | 153篇 |
2019年 | 152篇 |
2018年 | 135篇 |
2017年 | 116篇 |
2016年 | 168篇 |
2015年 | 171篇 |
2014年 | 171篇 |
2013年 | 255篇 |
2012年 | 271篇 |
2011年 | 280篇 |
2010年 | 171篇 |
2009年 | 142篇 |
2008年 | 206篇 |
2007年 | 145篇 |
2006年 | 140篇 |
2005年 | 102篇 |
2004年 | 88篇 |
2003年 | 75篇 |
2002年 | 58篇 |
2001年 | 47篇 |
2000年 | 39篇 |
1999年 | 45篇 |
1998年 | 27篇 |
1997年 | 21篇 |
1996年 | 28篇 |
1995年 | 22篇 |
1994年 | 25篇 |
1993年 | 14篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 20篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有3621条查询结果,搜索用时 31 毫秒
991.
多虑平类化合物在溶液体系中可能存在着构象交换过程,在其核磁共振图谱中出现的谱线展宽(包峰)或缺失现象增加了化合物结构解析的难度,甚至产生误导。该文以多虑平类化合物11-[(3-二甲基氨基)亚丙基]-6,11-二氢二苯并[b,e]氧杂-2-甲醛为样本,通过改变实验条件证明该化合物在几种溶液体系中均存在着构象交换。实验表明升温可以改善这类化合物的核磁共振测试效果,在80℃下获取的谱图信号清晰完整,信号展宽和缺失现象得到有效抑制。利用升温条件下获取的谱图,顺利实现了对11-[(3-二甲基氨基)亚丙基]-6,11-二氢二苯并[b,e]氧杂-2-甲醛的结构解析。 相似文献
992.
993.
A nanofiber metal–organic framework filter, a polyacrylonitrile (PAN) nanofiber membrane composite with an iron/2-amino-terephthalic acid-based metal–organic framework (MIL101(Fe)-NH2), was prepared by one-step electrospinning. MIL101(Fe)-NH2 was combined into the polymer nanofibers in situ. PAN-MIL101(Fe)-NH2 composite nanofiber membranes (NFMs) were prepared from a homogeneous spinning stock containing MIL101(Fe)-NH2 prebody fluid and PAN. Crystallization of MIL101(Fe)-NH2 and solidification of the polymer occurred simultaneously during electrospinning. The PAN-MIL101(Fe)-NH2 composite NFM showed that MIL101(Fe)-NH2 was uniformly distributed throughout the nanofiber and was used to adsorb and separate acidic organic ionic dyes from the aqueous solution. The results of Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis showed that MIL101(Fe)-NH2 crystals were effectively bonded in the PAN nanofiber matrix, and the crystallinity of MIL101(Fe)-NH2 crystals remained good, while the distribution was uniform. Owing to the synergistic effect of PAN and the MIL101(Fe)-NH2 crystal, the PAN-MIL101(Fe)-NH2 composite NFM showed a fast adsorption rate for acidic ionic dyes. This study provides a reference for the rapid separation and purification of organic ionic dyes from wastewater. 相似文献
994.
Yang Li Wei Huang Dejiang Zhao Lu Wang Zhiqiang Jiao Qingyu Huang Peng Wang Mengna Sun Guangcai Yuan 《Molecules (Basel, Switzerland)》2022,27(6)
In the last few decades, organic solar cells (OSCs) have drawn broad interest owing to their advantages such as being low cost, flexible, semitransparent, non-toxic, and ideal for roll-to-roll large-scale processing. Significant advances have been made in the field of OSCs containing high-performance active layer materials, electrodes, and interlayers, as well as novel device structures. Particularly, the innovation of active layer materials, including novel acceptors and donors, has contributed significantly to the power conversion efficiency (PCE) improvement in OSCs. In this review, high-performance acceptors, containing fullerene derivatives, small molecular, and polymeric non-fullerene acceptors (NFAs), are discussed in detail. Meanwhile, highly efficient donor materials designed for fullerene- and NFA-based OSCs are also presented. Additionally, motivated by the incessant developments of donor and acceptor materials, recent advances in the field of ternary and tandem OSCs are reviewed as well. 相似文献
995.
提出一种新的诊断飞秒脉冲振幅与位相的高精度测量方法.该方法发展了传统的SPIDER方法,保留了原方法对脉冲信息可以实时、有效和全面地测取的优点,并能克服其不能测量脉宽较大或位相信息复杂的脉冲的缺点.在新方法中和频后的脉冲对没有相对延时,形成无干涉条纹的剪切干涉图.在调节一个小量延时于某些特定值,可去掉剪切干涉图的歧义性.给出数值模拟结果,证明此方法无需经过傅里叶变换滤波,可直接由干涉图唯一地提取出脉冲的振幅与位相信息.
关键词:
光谱位相相干直接电场重构法
飞秒脉冲测量
超快信息光学 相似文献
996.
D. Zhang P. Wang X. Jiao C. Min G. Yuan Y. Deng H. Ming L. Zhang W. Liu 《Applied physics. B, Lasers and optics》2006,85(1):139-143
Optical polarization properties of aluminum, gold and aluminum/gold subwavelength metallic gratings (SWMGs) are investigated numerically in the visible light band. Their performance as polarizing beam splitters are simulated with RCWA for varied metallic materials, grating depth and incident angle. Metallic waveguide theory is applied to explain the performance difference between Au and Al grating. A new type of Al/Au bimetallic is also investigated numerically for potential applications. PACS 42.79.Dj; 42.81.Gs; 73.20.Mf 相似文献
997.
We give a good characterization of the permutation polynomials in two variables over Z/p2Z. 相似文献
998.
Based on the D6d-symmetrical C24H24 fullerene, its derivatives, which have been exohedrally functionalized by replacing one of its H atoms with –CH2OH, –CONH2, –COOH, and –COH, have been firstly calculated using the hybrid DFT-B3LYP functional in conjunction with 6-31G(d) basis sets. Present calculations show that the C24H23(COOH) is the most stable under the values of ΔH and De. The calculated HOMO–LUMO energy gaps of the derivatives with –CH2OH and –COOH groups are same as in the case of the not functionalized C24H24 cluster. In addition, the C24H23(CONH2) displays the largest dipole moment (3.32 D), and the vertical electron affinities of the functionalized derivatives are all very higher. These can promote new development in the fields of the bio-medical applications. 相似文献
999.
1000.
This paper presents an algorithm for finding a global minimum of a multimodal, multivariate and nondifferentiable function. The algorithm is a modification to the new version of the Price’s algorithm given in Brachetti et al. [J. Global Optim. 10, 165–184 (1997)]. Its distinguishing features include: (1) The number-theoretic method is applied to generate the initial population so that the points in the initial population are uniformly scattered, and therefore the algorithm could explore uniformly the region of interest at the initial iteration; (2) The simplified quadratic approximation with the three best points is employed to improve the local search ability and the accuracy of the minimum function value, and to reduce greatly the computational overhead of the algorithm. Two sets of experiments are carried out to illustrate the efficiency of the number-theoretic method and the simplified quadratic model separately. The proposed algorithm has also been compared with the original one by solving a wide set of benchmark problems. Numerical results show that the proposed algorithm requires a smaller number of function evaluations and, in many cases, yields a smaller or more accurate minimum function value. The algorithm can also be used to deal with the medium size optimization problems. 相似文献