全文获取类型
收费全文 | 342篇 |
免费 | 18篇 |
国内免费 | 7篇 |
专业分类
化学 | 237篇 |
力学 | 5篇 |
数学 | 66篇 |
物理学 | 59篇 |
出版年
2024年 | 1篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 15篇 |
2014年 | 11篇 |
2013年 | 13篇 |
2012年 | 24篇 |
2011年 | 33篇 |
2010年 | 8篇 |
2009年 | 16篇 |
2008年 | 23篇 |
2007年 | 20篇 |
2006年 | 26篇 |
2005年 | 12篇 |
2004年 | 11篇 |
2003年 | 13篇 |
2002年 | 14篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有367条查询结果,搜索用时 0 毫秒
111.
Danny Birmingham 《General Relativity and Gravitation》1996,28(1):87-96
We study the form of topology changing amplitudes within the Regge calculus approach to four-dimensional gravity. The four-dimensional simplicial complex is chosen to be a cone over the disjoint union of a number of topologically distinct lens spaces. By restricting attention to a simplicial minisuperspace, the analytic properties of the Regge action can be identified explicitly. The classical extrema and convergent steepest descent contours defining these amplitudes are determined, and a factorization property is established. In the cases studied, we find ground state wave functions which predict Lorentzian oscillatory behaviour in the late universe. 相似文献
112.
Photonic crystal fiber based evanescent-wave sensor for detection of biomolecules in aqueous solutions 总被引:5,自引:0,他引:5
Jensen JB Pedersen LH Hoiby PE Nielsen LB Hansen TP Folkenberg JR Riishede J Noordegraaf D Nielsen K Carlsen A Bjarklev A 《Optics letters》2004,29(17):1974-1976
We demonstrate highly efficient evanescent-wave detection of fluorophore-labeled biomolecules in aqueous solutions positioned in the air holes of the microstructured part of a photonic crystal fiber. The air-suspended silica structures located between three neighboring air holes in the cladding crystal guide light with a large fraction of the optical field penetrating into the sample even at wavelengths in the visible range. An effective interaction length of several centimeters is obtained when a sample volume of less than 1 microL is used. 相似文献
113.
Kelvin K. Ogilvie Gholam H. Hakimelahi Zbigniew A. Proba Danny P.C. McGee 《Tetrahedron letters》1982,23(19):1997-2000
Procedure have been developed which allow for the selective derivatization of arabinonucleosides at the 5′? or 2′? and 5′? or 3′? and 5′? positions. 相似文献
114.
Laurence E. Strong Danny J. Blubaugh Christopher R. Cavalli 《Journal of solution chemistry》1981,10(11):811-830
Precise conductance measurements are reported for four xylic acids, 2,3-2,5-2,6 and 3,5-dimethylbenzoics. Limiting molar conductances ΛO and pK a obtained from a Fuoss type analysis, are reported for each of these acids at five degree intervals covering the range from 0° to 100°C. The ΛO values for each acid are described by a polynomial in the Celsius temperature. The pK a were smoothed as a function of the Kelvin temperature T with an equation of the form: $$pK_{\text{a}} = A{\text{ }} + {\text{ }}B/T{\text{ }} + {\text{ }}C{\text{ }}logT{\text{ }} + {\text{ }}DT$$ where the term linear in T was required only for the 2,3-acid. Standard enthalpy, entropy, and heat capacity changes were calculated by suitable differentiation of this equation. Walden products were calculated for the four anions at each of the temperatures and are compared with earlier data for the toluate and the benzoate ions. Those acids with ortho groups undergo a large decrease in enthalpy on ionization and are substantially more acidic than benzoic acid. These effects are especially large for 2,6-dimethylbenzoic acid. A methyl group in the meta position lowers acidity slightly both in m-toluic and in 2,5-dimethylbenzoic acid. However, 2,3-dimethylbenzoic acid is more acidic than o-toluic. 相似文献
115.
In this paper, we present a direct approach for routing a shortest rectilinear path between two points among a set of rectilinear obstacles in a two-layer interconnection model that is used for VLSI routing applications. The previously best known direct approach for this problem takes O(nlog2n) time and O(nlogn) space, where n is the total number of obstacle edges. By using integer data structures and an implicit graph representation scheme (i.e., a generalization of the distance table method), we improve the time bound to O(nlog3/2n) while still maintaining the O(nlogn) space bound. Comparing with the indirect approach for this problem, our algorithm is simpler to implement and is probably faster for a quite large range of input sizes. 相似文献
116.
117.
118.
119.
Frederik Beaujean Christoph Bobeth Danny van Dyk 《The European Physical Journal C - Particles and Fields》2014,74(6):1-18
The available data on \(|\Delta B| = |\Delta S| = 1\) decays are in good agreement with the Standard Model when permitting subleading power corrections of about \(15\,\%\) at large hadronic recoil. Constraining new-physics effects in \(\mathcal {C}_{7}^{\mathrm {}}\) , \(\mathcal {C}_{9}^{\mathrm {}}\) , \(\mathcal {C}_{10}^{\mathrm {}}\) , the data still demand the same size of power corrections as in the Standard Model. In the presence of chirality-flipped operators, all but one of the power corrections reduce substantially. The Bayes factors are in favor of the Standard Model. Using new lattice inputs for \(B\rightarrow K^*\) form factors and under our minimal prior assumption for the power corrections, the favor shifts toward models with chirality-flipped operators. We use the data to further constrain the hadronic form factors in \(B\rightarrow K\) and \(B\rightarrow K^*\) transitions. 相似文献
120.
Dr. Bo Peng Dr. Danny Geerdink Dr. Christophe Farès Prof. Dr. Nuno Maulide 《Angewandte Chemie (International ed. in English)》2014,53(21):5462-5466
A new approach for the fully chemoselective α‐arylation of amides is presented. By means of electrophilic amide activation, aryl groups can be regioselectively introduced α‐ to amides, even in the presence of esters and alkyl ketones. Mechanistic studies reveal key reaction intermediates and emphasize a remarkably subtle base effect in this transformation. 相似文献