全文获取类型
收费全文 | 1206篇 |
免费 | 28篇 |
专业分类
化学 | 661篇 |
晶体学 | 10篇 |
力学 | 42篇 |
数学 | 86篇 |
物理学 | 435篇 |
出版年
2022年 | 9篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 15篇 |
2018年 | 9篇 |
2016年 | 16篇 |
2015年 | 17篇 |
2014年 | 21篇 |
2013年 | 54篇 |
2012年 | 44篇 |
2011年 | 55篇 |
2010年 | 38篇 |
2009年 | 28篇 |
2008年 | 55篇 |
2007年 | 61篇 |
2006年 | 64篇 |
2005年 | 45篇 |
2004年 | 46篇 |
2003年 | 34篇 |
2002年 | 29篇 |
2001年 | 31篇 |
2000年 | 25篇 |
1999年 | 13篇 |
1998年 | 8篇 |
1997年 | 19篇 |
1996年 | 10篇 |
1995年 | 22篇 |
1994年 | 29篇 |
1993年 | 34篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 22篇 |
1977年 | 14篇 |
1976年 | 25篇 |
1975年 | 14篇 |
1974年 | 19篇 |
1973年 | 11篇 |
1972年 | 10篇 |
排序方式: 共有1234条查询结果,搜索用时 15 毫秒
61.
Anne‐Catherine Bédard Prof. Dr. Shawn K. Collins 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(6):2108-2113
The aggregation properties of poly(ethylene glycol) (PEG) can be exploited in organic synthesis to control dilution effects. Through the use of solvent mixtures containing PEG400/MeOH, macrocyclization by Glaser–Hay coupling can be conducted at high concentrations. The origin of the selectivity has been studied by using surface tension measurements, UV spectroscopy, and chemical tagging and demonstrates the dependence of the yield and selectivity on the aggregation of PEG400 and its ability to preferentially solubilize organic substrates, resulting in a phase separation from the catalyst system. 相似文献
62.
Tuning Thiophene with Phosphorus: Synthesis and Electronic Properties of Benzobisthiaphospholes 下载免费PDF全文
Yunyan Qiu Joshua C. Worch Danielle N. Chirdon Aman Kaur Andrew B. Maurer Samuel Amsterdam Christopher R. Collins Prof. Tomislav Pintauer Prof. David Yaron Prof. Stefan Bernhard Prof. Kevin J. T. Noonan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7746-7751
1,4‐Dimercapto‐2,5‐diphosphinobenzene and 3,6‐bis(hexyloxy)‐1,4‐dimercapto‐2,5‐diphosphinobenzene were synthesized and combined with various acid chlorides to obtain a series of benzobisthiaphospholes. Electrochemical and photophysical properties of the substituted benzobisthiaphospholes have been evaluated, and the observed reductions are more facile than the related benzothiaphospholes and 2,6‐diphenylbenzobisthiazole. A benzobisthiaphosphole with C6H4‐p‐CN substituents was reduced at E1/2=?1.08 V (vs. saturated calomel electrode (SCE)). X‐ray diffraction data for several of these phosphorus heterocycles has been obtained, and DFT calculations at the B3LYP level have been performed. 相似文献
63.
The triple phase boundary transfer of anions from the aqueous into an organic phase can be driven electrochemically here with the tetraphenylporphyrinato‐Mn(III/II) (or TPPMn) redox system in 4‐(3‐phenylpropyl)‐pyridine) (or PPP). Anions investigated are perchlorate, chloride, fluoride, and bicarbonate. The bicarbonate and fluoride transfer processes are shown to be chemically more complex compared to the perchlorate and chloride cases with UV‐vis‐spectroelectrochemical measurements indicating a combination of HCO3?/CO32? transfer processes and association of fluoride with TPPMn(III)+, respectively. In situ spectroelectrochemistry is developed for ion‐transfer voltammetry into sub‐microliter organic phase regions on mesoporous ITO conducting film electrodes. 相似文献
64.
65.
66.
In this paper we design and implement rigorous algorithms for computing symbolic dynamics for piecewise-monotone-continuous maps of the interval. The algorithms are based on computing forwards and backwards approximations of the boundary, discontinuity and critical points. We explain how to handle the discontinuities in the symbolic dynamics which occur when the computed partition element boundaries are not disjoint. The method is applied to compute the symbolic dynamics and entropy bounds for the return map of the singular limit of a switching system with hysteresis and the forced Van der Pol equation. 相似文献
67.
Bradley K Jhi SH Collins PG Hone J Cohen ML Louie SG Zettl A 《Physical review letters》2000,85(20):4361-4364
The thermoelectric power (TEP) of single-walled carbon nanotubes (SWNTs) is extremely sensitive to gas exposure history. Samples exposed to air or oxygen have an always positive TEP, suggestive of holelike carriers. However, at fixed temperature the TEP crosses zero and becomes progressively more negative as the SWNTs are stripped of oxygen. The time constant for oxygen adsorption/desorption is strongly temperature dependent and ranges from seconds to many days, leading to apparently "variable" TEP for a given sample at a given temperature. The saturated TEP can be accounted for within a model of strong oxygen doping of the semiconducting nanotubes. 相似文献
68.
Osipov GV Collins JJ 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(1):54-57
Here we propose mechanisms for suppressing non-steady-state motions--propagating pulses, spiral waves, spiral-wave chaos--in excitable media. Our approach is based on two points: (1) excitable media are multistable; and (2) traveling waves in excitable media can be separated into fast and slow motions, which can be considered independently. We show that weak impulses can be used to change the values of the slow variable at the front and back of a traveling wave, which leads to wave front and wave back velocities that are different from each other. This effect can destabilize the traveling wave, resulting in a transition to the rest state. 相似文献
69.
Edmund J Collins 《The Journal of the Operational Research Society》2015,66(10):1595-1604
We introduce a class of models for multidimensional control problems that we call skip-free Markov decision processes on trees. We describe and analyse an algorithm applicable to Markov decision processes of this type that are skip-free in the negative direction. Starting with the finite average cost case, we show that the algorithm combines the advantages of both value iteration and policy iteration—it is guaranteed to converge to an optimal policy and optimal value function after a finite number of iterations but the computational effort required for each iteration step is comparable with that for value iteration. We show that the algorithm can also be used to solve discounted cost models and continuous-time models, and that a suitably modified algorithm can be used to solve communicating models. 相似文献
70.
Collins Okon Edet Francisco Cleiton E. Lima Carlos Alberto S. Almeida Norshamsuri Ali Muhammad Asjad 《Entropy (Basel, Switzerland)》2022,24(8)
We investigate quantum information by a theoretical measurement approach of an Aharanov–Bohm (AB) ring with Yukawa interaction in curved space with disclination. We obtained the so-called Shannon entropy through the eigenfunctions of the system. The quantum states considered come from Schrödinger theory with the AB field in the background of curved space. With this entropy, we can explore the quantum information at the position space and reciprocal space. Furthermore, we discussed how the magnetic field, the AB flux, and the topological defect influence the quantum states and the information entropy. 相似文献