全文获取类型
收费全文 | 2733篇 |
免费 | 102篇 |
国内免费 | 7篇 |
专业分类
化学 | 2134篇 |
晶体学 | 7篇 |
力学 | 41篇 |
数学 | 388篇 |
物理学 | 272篇 |
出版年
2024年 | 2篇 |
2023年 | 25篇 |
2022年 | 79篇 |
2021年 | 95篇 |
2020年 | 71篇 |
2019年 | 76篇 |
2018年 | 37篇 |
2017年 | 42篇 |
2016年 | 109篇 |
2015年 | 96篇 |
2014年 | 103篇 |
2013年 | 167篇 |
2012年 | 197篇 |
2011年 | 202篇 |
2010年 | 154篇 |
2009年 | 113篇 |
2008年 | 171篇 |
2007年 | 150篇 |
2006年 | 136篇 |
2005年 | 137篇 |
2004年 | 130篇 |
2003年 | 102篇 |
2002年 | 99篇 |
2001年 | 34篇 |
2000年 | 41篇 |
1999年 | 31篇 |
1998年 | 25篇 |
1997年 | 26篇 |
1996年 | 30篇 |
1995年 | 22篇 |
1994年 | 22篇 |
1993年 | 19篇 |
1992年 | 21篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有2842条查询结果,搜索用时 0 毫秒
991.
Claudia Cottin 《Results in Mathematics》1993,24(3-4):211-221
When considering approximation of continuous periodic functions f: R d → R by blending-type approximants which depend on directions ξ1,…,ξν ∈ R d directional moduli of smoothness (1) are appropriate measures of smoothness of /. In this paper, we introduce equivalent directional K- functionals. As an application, we obtain a result on the degree of approximation by certain trigonometric blending functions. 相似文献
992.
Sossio Cimmino Ezio Martuscelli Clara Silvestre Maurizio Canetti Claudia De Lalla Alberto Seves 《Journal of Polymer Science.Polymer Physics》1989,27(9):1781-1794
Results of an investigation of isothermal crystallization and thermal behavior of poly(ethylene oxide)/poly(ethyl methacrylate) (PEO/PEMA) blends are reported. The blend composition and the crystallization temperature strongly influence the crystallization process from the melt and the melting temperature of PEO. The addition of PEMA to PEO causes a depression in the spherulite growth rate, in the overall kinetic crystallization constant, and in the melting temperature. Experimental data on the radial growth rate G and overall kinetic rate constant Kn are analyzed by means of the latest kinetic theory. From this analysis it emerges that the crystallization of pure PEO and PEO in the blend conforms to the regime I process of surface secondary nucleation. The depression of the melting temperature cannot be explained only in terms of a diluent effect due to the compatibility of the two components in the melt. Annealing and morphological effects, dependent on composition and time, must also be taken into account. 相似文献
993.
Daniela Goldmann Dietmar Janietz Reinhard Festag Claudia Schmidt Joachim H. Wendorff 《Liquid crystals》1996,21(5):619-623
New disc-shaped triarylamino-1,3,5-triazines were prepared by reaction of cyanuric chloride with two-fold alkoxy substituted anilines. Each of the triarylmelamines exhibits an enanti-otropic mesophase. X-ray investigations reveal the formation of columnar liquid crystalline structures with either a hexagonal or a rectangular lattice. The lattice parameters, as well as the intracolumnar ordering, depend on the length of the flexible lateral side chains. The new melamines form Langmuir monolayers at the air/water interface due to their amphiphilic nature. The monolayer organization is characterized by a side-on arrangement of the molecules. The polar central molecular parts lie flat on the water, whereas the lateral alkyl chains are oriented perpendicular to the water surface. 相似文献
994.
995.
Claudia Draxl 《Few-Body Systems》1987,2(3):N49-N49
996.
Giovanni Bagnasco Claudia Cammarano Maria Turco Serena Esposito Antonio Aronne Pasquale Pernice 《Thermochimica Acta》2008,471(1-2):51-54
Cobalt–silicon mixed oxides with Co/Si ratio of 10/90 (10Co), 20/80 (20Co) and 30/70 (30Co) were prepared by a modified sol–gel method. The materials treated in air at 400 and 600 °C were characterized by SEM and TPR/TPO techniques. TPR measurements showed that in all samples only a fraction of Co was present as Co3O4 and as amorphous silicate and was reducible by H2 within 800 °C, while a part was not reducible under TPR conditions. The fraction of Co not reducible decreased with increasing Co content. A TPO/TPR cycle gave rise to an increase of the fraction of not reducible Co. 相似文献
997.
Albrecht M Wessel C de Groot M Rissanen K Lüchow A 《Journal of the American Chemical Society》2008,130(14):4600-4601
A series of pentafluorophenyl substituted ammonium, iminium, amidinium, and phosphonium halides are presented which show extensive anion-pi interactions. Hereby, the well-known anion-donor-pi-acceptor as well as "eta6" anion-pi-complex type interactions are observed. The latter is supported by fixation of the anion on top of the aromatic system through hydrogen bonding. This arrangement was investigated by theoretical methods showing a highly attractive anion-pi interaction. In addition an eta2-type coordination of the anions to only two C-atoms of the electron-deficient ring system is described. 相似文献
998.
Swanson CH Shaikh HA Rogow DL Oliver AG Campana CF Oliver SR 《Journal of the American Chemical Society》2008,130(35):11737-11741
We have discovered a rare example of a cationically charged inorganic material. The layered structure is an example outside the extensively studied isostructural set of anionic clays/layered double hydroxides and our previously reported lead fluoride nitrate. For the present compound, the antimony oxide hydroxide layers are positively charged and are templated by anionic alkylenedisulfonate. The organic molecules are only bonded electrostatically to the layers with sulfonate oxygen to antimony distances beyond the covalent range. The material catalyzes a ketal formation reaction as a Lewis acid without the need for drying the solvent before the reaction or a nonaqueous medium such as toluene. The catalyst is heterogeneous and is completely recovered after the catalysis for reapplication. 相似文献
999.
1000.
Botek E Giribet C Ruiz de Azúa M Martín Negri R Bernik D 《The journal of physical chemistry. A》2008,112(30):6992-6998
The IPPP-CLOPPA-INDO/S method is introduced to investigate the static molecular polarizability in macromolecules. As an example of application, the polarizability of phospholipidic compounds, with and without the presence of water molecules has been estimated. The IPPP technique was employed to calculate the polarizability of the polar head and the hydrocarbon chains separately to analyze the feasibility of evaluating the total polarizability of the molecule by addition of these two projected results. INDO/S dipole moments of different fragments of the complex molecule were obtained by means of localized molecular orbitals in order to evaluate the charge transfer in the system. 相似文献