全文获取类型
收费全文 | 1702篇 |
免费 | 63篇 |
国内免费 | 26篇 |
专业分类
化学 | 1068篇 |
晶体学 | 7篇 |
力学 | 61篇 |
数学 | 256篇 |
物理学 | 399篇 |
出版年
2023年 | 14篇 |
2022年 | 20篇 |
2021年 | 25篇 |
2020年 | 45篇 |
2019年 | 30篇 |
2018年 | 22篇 |
2017年 | 15篇 |
2016年 | 36篇 |
2015年 | 29篇 |
2014年 | 47篇 |
2013年 | 72篇 |
2012年 | 115篇 |
2011年 | 118篇 |
2010年 | 69篇 |
2009年 | 59篇 |
2008年 | 118篇 |
2007年 | 78篇 |
2006年 | 91篇 |
2005年 | 96篇 |
2004年 | 71篇 |
2003年 | 60篇 |
2002年 | 60篇 |
2001年 | 43篇 |
2000年 | 40篇 |
1999年 | 20篇 |
1998年 | 17篇 |
1997年 | 9篇 |
1996年 | 23篇 |
1995年 | 14篇 |
1994年 | 24篇 |
1993年 | 26篇 |
1992年 | 19篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1984年 | 26篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 19篇 |
1976年 | 12篇 |
1974年 | 12篇 |
1973年 | 10篇 |
排序方式: 共有1791条查询结果,搜索用时 546 毫秒
261.
The reprecipitation method was applied to Coumarin 6. A concentrated solution of the dye in acetone was mixed at room temperature with a large volume of water, and microcrystals rapidly appeared in the medium. Their size and shape were visualized by fluorescence microscopy, as well as by transmission electron microscopy. The absorption and fluorescence properties were studied on the suspensions and compared with those of the dissolved dye. This study is aimed at clarifying the influence of the reprecipitation process upon the fluorescence properties of the dye in the solid state. 相似文献
262.
Lam CS 《Physical review letters》2008,101(12):121602
We argue that the best way to determine horizontal symmetry is from neutrino mixing and proceed to show that the only finite group capable of yielding the tribimaximal mixing for all Yukawa couplings is S4, or any group containing it. The method used is largely group theoretical, but it can be implemented by dynamical schemes in which the Higgs expectation values introduced to break S4 spontaneously are uniquely determined up to an unknown scale for each. 相似文献
263.
We have experimentally demonstrated how two beams of light separated by an octave in frequency can become entangled after their interaction in a chi;{(2)} nonlinear medium. The entangler was a nonlinear optical resonator that was strongly driven by coherent light at the fundamental and second-harmonic wavelengths. An interconversion between the fields created quantum correlations in the amplitude and phase quadratures, which were measured by two independent homodyne detectors. Analysis of the resulting correlation matrix revealed a wave function inseparability of 0.74(1)<1, thereby satisfying the criterion of entanglement. 相似文献
264.
We present a simple quantum memory scheme that allows for the storage of a light field in an ensemble of two-level atoms. The technique is analogous to the NMR gradient echo for which the imprinting and recalling of the input field are performed by controlling a linearly varying broadening. Our protocol is perfectly efficient in the limit of high optical depths and the output pulse is emitted in the forward direction. We provide a numerical analysis of the protocol together with an experiment performed in a solid state system. In close agreement with our model, the experiment shows a total efficiency of up to 15%, and a recall efficiency of 26%. We suggest simple realizable improvements for the experiment to surpass the no-cloning limit. 相似文献
265.
266.
Dr. Haoxuan Li Haifei Wen Dr. Zhijun Zhang Dr. Nan Song Prof. Ryan T. K. Kwok Prof. Jacky W. Y. Lam Prof. Lei Wang Prof. Dong Wang Prof. Ben Zhong Tang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20551-20555
Using reverse thinking of the aggregation-induced emission (AIE) principle, we demonstrate an ingenious and universal protocol for amplifying molecular motions to boost photothermal efficiency of fibers. Core–shell nanofibers having the olive oil solution of AIE-active molecules as the core surrounded by PVDF-HFP shell were constructed by coaxial electrospinning. The molecularly dissolved state of AIE-active molecules allows them to freely rotate and/or vibrate in nanofibers upon photoexcitation and thus significantly elevates the proportion of non-radiative energy dissipation, affording impressive heat-generating efficiency. Photothermal evaluation shows that the core–shell nanofibers with excellent durability can reach up to 22.36 % of photothermal conversion efficiency, which is 26-fold as the non-core–shell counterpart. Such a core–shell fiber can be used for photothermal textiles and solar steam generation induced by natural sunlight with green and carbon-zero emission. 相似文献
267.
Aggregation‐Induced‐Emission‐Active Macrocycle Exhibiting Analogous Triply and Singly Twisted Möbius Topologies
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Engui Zhao Luming Meng Christian Schütt Jacky W. Y. Lam Herman H. Y. Sung Prof. Dr. Ian D. Williams Prof. Xuhui Huang Prof. Rainer Herges Prof. Ben Zhong Tang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(33):11707-11711
Molecules with Möbius topology have drawn increasing attention from scientists in a variety of fields, such as organic chemistry, inorganic chemistry, and material science. However, synthetic difficulties and the lack of functionality impede their fundamental understanding and practical applications. Here, we report the facile synthesis of an aggregation‐induced‐emission (AIE)‐active macrocycle (TPE‐ET) and investigate its analogous triply and singly twisted Möbius topologies. Because of the twisted and flexible nature of the tetraphenylethene units, the macrocycle adjusts its conformations so as to accommodate different guest molecules in its crystals. Moreover, theoretical studies including topological and electronic calculations reveal the energetically favorable interconversion process between triply and singly twisted topologies. 相似文献
268.
The critical dimension necessary for a flame to propagate in suspensions of fuel particles in oxidiser is studied analytically and numerically. Two types of models are considered: First, a continuum model, wherein the individual particulate sources are not resolved and the heat release is assumed spatially uniform, is solved via conventional finite difference techniques. Second, a discrete source model, wherein the heat diffusion from individual sources is modelled via superposition of the Green's function of each source, is employed to examine the influence of the random, discrete nature of the media. Heat transfer to cold, isothermal walls and to a layer of inert gas surrounding the reactive medium are considered as the loss mechanisms. Both cylindrical and rectangular (slab) geometries of the reactive medium are considered, and the flame speed is measured as a function of the diameter and thickness of the domains, respectively. In the continuum model with inert gas confinement, a universal scaling of critical diameter to critical thickness near 2:1 is found. In the discrete source model, as the time scale of heat release of the sources is made small compared to the interparticle diffusion time, the geometric scaling between cylinders and slabs exhibits values greater than 2:1. The ability of the flame in the discrete regime to propagate in thinner slabs than predicted by continuum scaling is attributed to the flame being able to exploit local fluctuations in concentration across the slab to sustain propagation. As the heat release time of the sources is increased, the discrete source model reverts back to results consistent with the continuum model. Implications of these results for experiments are discussed. 相似文献
269.
Letters in Mathematical Physics - Let L be an even (positive definite) lattice and $$g\in O(L)$$. In this article, we prove that the orbifold vertex operator algebra $$V_{L}^{{\hat{g}}}$$ has... 相似文献
270.