全文获取类型
收费全文 | 3816篇 |
免费 | 79篇 |
国内免费 | 13篇 |
专业分类
化学 | 1358篇 |
晶体学 | 35篇 |
力学 | 201篇 |
数学 | 798篇 |
物理学 | 1516篇 |
出版年
2024年 | 10篇 |
2023年 | 32篇 |
2022年 | 51篇 |
2021年 | 55篇 |
2020年 | 128篇 |
2019年 | 106篇 |
2018年 | 198篇 |
2017年 | 234篇 |
2016年 | 188篇 |
2015年 | 112篇 |
2014年 | 160篇 |
2013年 | 200篇 |
2012年 | 238篇 |
2011年 | 222篇 |
2010年 | 212篇 |
2009年 | 214篇 |
2008年 | 145篇 |
2007年 | 157篇 |
2006年 | 141篇 |
2005年 | 104篇 |
2004年 | 57篇 |
2003年 | 69篇 |
2002年 | 60篇 |
2001年 | 92篇 |
2000年 | 46篇 |
1999年 | 74篇 |
1998年 | 39篇 |
1997年 | 22篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 22篇 |
1988年 | 59篇 |
1987年 | 130篇 |
1986年 | 126篇 |
1985年 | 20篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 16篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 14篇 |
1975年 | 2篇 |
排序方式: 共有3908条查询结果,搜索用时 15 毫秒
1.
《Superlattices and Microstructures》2006,40(1):29-37
On the basis of the quasistationary state approximation, the asymptotic transfer method (ATM) was extended to calculate the energy spectra, envelope functions of carriers and dispersion relations of Ga1−xAlxAs multiple sawtooth quantum wells (MSQW) in the presence of an electric field applied along the growth direction and a magnetic field parallel to the MSQW interfaces. It turned out that the energy spectra revealed the Landau-like behavior of carriers under a magnetic field. The envelope functions of carriers displayed obvious fluctuation and the dispersion relations showed a non-parabolic shape. 相似文献
2.
3.
Mohamed Haouas Amine Harrane Mohamed Belbachir Francis Taulelle 《Journal of Polymer Science.Polymer Physics》2007,45(22):3060-3068
Results of multinuclear MAS NMR spectroscopy are reported for poly (ε‐caprolactone)/maghnite nanocomposite formation, with ε‐caprolactone in situ polymerized in the presence of maghnite, a proton exchanged montmorillonite clay. Exfoliated and intercalated materials with different maghnite loading in the range 3–15 wt % were investigated. 1H NMR evidences Brønsted acid hydroxyl groups in the silicate layers and shows that their broad signal at 7.6 ppm present in the parent clay disappears in the nanocomposite material. 27Al MAS NMR results show that beside the hexacoordinated aluminum signal, two additional peaks corresponding to two different tetrahedral Al sites are present in the clay framework. The NMR signal intensity of only one of them was found to be affected in the nanocomposites compared with the parent maghnite, suggesting that these specific aluminum sites are the reactive ones at the initial stages of the polymerization. However almost no changes occurred in the 29Si NMR spectra, confirming that the polymer grafting, as indicated earlier by atomic force microscopy, took place on the aluminum tetracoordinated sites rather than on the silicon sites. A mechanism of maghnite surface catalyzed polymerization of ε‐caprolactone was proposed, involving Brønsted and Lewis acid sites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3060–3068, 2007 相似文献
4.
《Solid State Ionics》2006,177(26-32):2481-2485
X-ray absorption spectroscopy is a prime tool in probing the local structure in condensed matter. This contribution describes some of the applications of this technique to probe the microstructure of nanocrystalline oxides. By the use of specific examples four areas will be covered, namely the effect of grain size and preparation route on microstructure, the locating of dopant sites and the chemical nature of metal/oxide catalysts. The materials involved are tin oxide, lithium niobate, titanium dioxide and copper/ceria. 相似文献
5.
《Tetrahedron: Asymmetry》2006,17(5):797-800
Several arylalkyl carbinols [1-indanol, 1-tetralol, 1-phenylethanol, 1-(1-naphthyl)ethanol, 1-(2-naphthyl)ethanol, 1-(4-methoxyphenyl)ethanol, 1-acenaphthenol] were deracemized through sequential combinations of lipase-catalyzed resolution and Mitsunobu inversion. The corresponding (R)-acetates were obtained in 72–83% yield and 89–99% ee. 相似文献
6.
《Tetrahedron: Asymmetry》2005,16(6):1183-1187
The asymmetric palladium-catalyzed benzylic reaction of 1-(2-naphthyl)ethyl acetate and its 6-methoxy substituted analogue with dimethyl malonate anion led to substitution products with up to 90% ee when the iPr-DUPHOS chiral ligand was used. 相似文献
7.
《The Journal of chemical thermodynamics》2006,38(11):1416-1421
This paper reports that new ionic liquids (ILs) have been prepared by directly mixing the chloride of group III and 1-methyl-3-pentylimidazolium chloride (PMIC) with molar ratio 1/1 under dry argon atmosphere. The densities and surface tension of these ILs were determined at temperature range of 273.15 K to 343.15 ± 0.1 K. The properties for the ionic liquids were discussed by interstice model and Glasser’s theory. 相似文献
8.
A. Markowicz N. Haselberger M. Dargie A. Tajani A. Tchantchane V. Valkovic P. R. Danesi 《Journal of Radioanalytical and Nuclear Chemistry》1996,206(2):269-277
A conventional X-ray fluorescence (XRF) method as well as total reflection XRF have been applied to the analysis of various environmental materials. Some methodological changes in order to extend the applicability range and improve the accuracy of the XRF analysis are also discussed. 相似文献
9.
《Polyhedron》2005,24(16-17):2562-2567
Molecular magnets have been recently proposed as possible building blocks for a solid-state quantum computer. In order to substantiate and develop such a proposal, one needs to identify those molecules that are best suited for the qubit encoding and manipulation. Here, we focus on a heterometallic molecular ring, namely Cr7Ni, where the substitution of one Cr3+(S = 3/2) with Ni2+(S = 1) provides an extra spin to the otherwise compensated molecule. We show that its ground state consists in an S = 1/2 doublet, energetically well separated (Δ0/kB ∼ 13 K at zero magnetic field) from the first excited multiplet. This relatively large value of Δ0, together with the reduced mixing of the subspaces corresponding to different values of the total spin S, enables a safe encoding of the |0〉 and |1〉 states with the ground-state doublet, and allows to coherently rotate the effective S = 1/2 spin, while keeping the population loss to the excited states negligible. A further, intriguing challenge is represented by the implementation of the conditional dynamics (two-qubit gates). We present here preliminary characterization of molecular “Cr7Ni-dimers”, i.e., derivatives in which two Cr7Ni rings are linked with each other by means of delocalized aromatic amines. The resulting intercluster couplings are estimated to be ⩽1 K and are expected to be permanent, i.e., not tuneable during gating, as required by the standard approach to quantum computation. We discuss a computational scheme that allows in principle to overcome this limitation. The most relevant decoherence mechanisms for Cr7Ni and possible ways to reduce their effects are discussed as well. 相似文献
10.
《Radiation Physics and Chemistry》2006,75(11):1744-1748
The electron beam ion trap has opened the door for experimental physics to perform critical tests of bound state QED in the medium-Z regime. The relatively small uncertainties associated with the theoretical predictions necessitate highly accurate experimental measurements of atomic transition energies. This work presents an overview of the issues and key concepts involved in the field. It also demonstrates several major steps taken to suppress systematic uncertainties that have limited past work and presents an error budget for current and future work. 相似文献