全文获取类型
收费全文 | 674篇 |
免费 | 6篇 |
国内免费 | 6篇 |
专业分类
化学 | 373篇 |
晶体学 | 5篇 |
力学 | 18篇 |
数学 | 146篇 |
物理学 | 144篇 |
出版年
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 41篇 |
2012年 | 34篇 |
2011年 | 30篇 |
2010年 | 13篇 |
2009年 | 21篇 |
2008年 | 23篇 |
2007年 | 34篇 |
2006年 | 28篇 |
2005年 | 12篇 |
2004年 | 22篇 |
2003年 | 22篇 |
2002年 | 14篇 |
2001年 | 19篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1995年 | 11篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1970年 | 7篇 |
1969年 | 9篇 |
1967年 | 4篇 |
1966年 | 4篇 |
排序方式: 共有686条查询结果,搜索用时 15 毫秒
41.
42.
Results and new theory are presented for the uncoated and coated facet reflectivity of a shallowly buried waveguide, taking account of the diffracting corner present at the air–semiconductor interface. The corner effects are shown to be most significant in the case of coated facets. The analysis also predicts the asymmetry introduced into the radiation pattern. 相似文献
43.
44.
Rotich A. Benson Nader M. A. Mohamed Mohamed Soliman Mohammed Hassan Mohsen A. Abou Mandour 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(1):23-27
Rapid determination of gross alpha and beta emitters in urine by liquid scintillation counting is discussed. This method is based on direct addition of urine into scintillation cocktail. 241Am, 239Pu and 90Sr were selected as model radionuclides. The LSA Hidex 300 SL equipped with Triple-Double-Coincidence-Ratio technique was used for sample measurement. The work focused on optimizing the LSC cocktail to urine volume ratio with respect to the model radionuclides. The overall efficiencies for 241Am, 239Pu and 90Sr were greater than 92 %; therefore, this method would be suitable for rapid determination of gross alpha/beta activity. 相似文献
45.
In this paper, we present a primal-dual interior-point method for solving nonlinear programming problems. It employs a Levenberg-Marquardt (LM) perturbation to the Karush-Kuhn-Tucker (KKT) matrix to handle indefinite Hessians and a line search to obtain sufficient descent at each iteration. We show that the LM perturbation is equivalent to replacing the Newton step by a cubic regularization step with an appropriately chosen regularization parameter. This equivalence allows us to use the favorable theoretical results of Griewank (The modification of Newton’s method for unconstrained optimization by bounding cubic terms, 1981), Nesterov and Polyak (Math. Program., Ser. A 108:177–205, 2006), Cartis et al. (Math. Program., Ser. A 127:245–295, 2011; Math. Program., Ser. A 130:295–319, 2011), but its application at every iteration of the algorithm, as proposed by these papers, is computationally expensive. We propose a hybrid method: use a Newton direction with a line search on iterations with positive definite Hessians and a cubic step, found using a sufficiently large LM perturbation to guarantee a steplength of 1, otherwise. Numerical results are provided on a large library of problems to illustrate the robustness and efficiency of the proposed approach on both unconstrained and constrained problems. 相似文献
46.
47.
Jiawang Zhou Ljiljana Stojanovi Andrey A. Berezin Tommaso Battisti Abigail Gill Benson M. Kariuki Davide Bonifazi Rachel Crespo-Otero Michael R. Wasielewski Yi-Lin Wu 《Chemical science》2021,12(2):767
Development of purely organic materials displaying room-temperature phosphorescence (RTP) will expand the toolbox of inorganic phosphors for imaging, sensing or display applications. While molecular solids were found to suppress non-radiative energy dissipation and make the RTP process kinetically favourable, such an effect should be enhanced by the presence of multivalent directional non-covalent interactions. Here we report phosphorescence of a series of fast triplet-forming tetraethyl naphthalene-1,4,5,8-tetracarboxylates. Various numbers of bromo substituents were introduced to modulate intermolecular halogen-bonding interactions. Bright RTP with quantum yields up to 20% was observed when the molecule is surrounded by a Br⋯O halogen-bonded network. Spectroscopic and computational analyses revealed that judicious heavy-atom positioning suppresses non-radiative relaxation and enhances intersystem crossing at the same time. The latter effect was found to be facilitated by the orbital angular momentum change, in addition to the conventional heavy-atom effect. Our results suggest the potential of multivalent non-covalent interactions for excited-state conformation and electronic control.The number and position of halogen substituents in purely organic π–π* chromophores critically affect the efficiency of phosphorescence. 相似文献
48.
In this note we show that various branch and bound methods for solving continuous global optimization problems can be readily adapted to the discrete case. As an illustration, we present an algorithm for minimizing a concave function over the integers contained in a compact polyhedron. Computational experience with this algorithm is reported. 相似文献
49.
Nataliya Sakhnenko Alexander Nerukh Trevor Benson Phillip Sewell 《Optical and Quantum Electronics》2007,39(10-11):825-836
The resolvent method approach is proposed for analytically solving the time domain Volterra integral equation (TDVIE) which describes the electromagnetic fields in 2-D cylindrical structures with time changes in the permittivity. It is shown that the approach allows investigation of the electromagnetic field transformation due to an abrupt time change in dielectric permittivity inside a circular cylinder as well as the construction of the Green’s function for an initial-boundary value problem. Key mechanisms of electromagnetic field transformation are investigated and a qualitative distinction of the processes is shown that depends on an initial field configuration. 相似文献
50.