全文获取类型
收费全文 | 909篇 |
免费 | 32篇 |
国内免费 | 3篇 |
专业分类
化学 | 555篇 |
晶体学 | 5篇 |
力学 | 11篇 |
数学 | 117篇 |
物理学 | 256篇 |
出版年
2021年 | 6篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 18篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 44篇 |
2012年 | 35篇 |
2011年 | 45篇 |
2010年 | 33篇 |
2009年 | 25篇 |
2008年 | 40篇 |
2007年 | 31篇 |
2006年 | 35篇 |
2005年 | 32篇 |
2004年 | 20篇 |
2003年 | 33篇 |
2002年 | 28篇 |
2001年 | 24篇 |
2000年 | 22篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 16篇 |
1996年 | 16篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 23篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 19篇 |
1977年 | 12篇 |
1976年 | 17篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有944条查询结果,搜索用时 15 毫秒
81.
Vogt FG Mattingly SM Gibson JM Mueller KT 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,147(1):26-35
A background-filtered version of the rotational-echo double resonance (REDOR) experiment is demonstrated. The experiment combines a traditional REDOR pulse sequence with a double-cross-polarization (DCP) sequence to select only those signals coming from spin pairs of interest. The relatively inefficient DCP sequence, which transfers polarization from (1)H to (15)N and subsequently to (13)C, is improved by the use of adiabatic passages through the (-1) sideband of the Hartmann-Hahn matching condition. The result is an efficient 2D-REDOR pulse sequence that does not require a reference experiment for removal of background signals. The data produced by the experiment are ideally suited to analysis by newly developed dipolar transform methods, such as the REDOR transform. The relevant features of the experiment are demonstrated on simple labeled amino acids. Relative efficiencies of several other potential filtering methods are also compared. Copyright 2000 Academic Press. 相似文献
82.
We report combinatorial molecular beam epitaxy synthesis and properties of a ternary epitaxial film of Co and Mn co-doped Ge grown on Ge (0 0 1) substrate. Structural effects were examined in situ by reflection high-energy electron diffraction and ex situ by microbeam X-ray diffraction techniques, and magnetic properties were probed by using magnetooptic Kerr effect. Ternary epitaxial phase diagrams have been studied for total doping concentrations up to 30 at.%, where regions of coherent epitaxy and rough disordered growth and those of near room temperature ferromagnetic ordering have been identified. 相似文献
83.
Wolfgang Scherer Prof. Dr. Christoph Hauf Dipl.‐Phys. Manuel Presnitz Dipl.‐Phys. Ernst‐Wilhelm Scheidt Dr. Georg Eickerling Dr. Volker Eyert Dr. Rolf‐Dieter Hoffmann Dr. Ute C. Rodewald Dipl.‐Ing. Adrienne Hammerschmidt Dr. Christian Vogt Dr. Rainer Pöttgen Prof. Dr. 《Angewandte Chemie (International ed. in English)》2010,49(9):1578-1582
84.
For quality tests of ceramic Bi-Pb-Sr-Ca-Cu-O superconductor materials (precursors and final products) accurate stoichiometric determinations of the metallic major components are necessary. Three methods were developed during the last decade in our group. Their properties and the results obtained are compared. The first classical analytical procedure requires to much manpower. The second combined chemical-spectrometric procedure is a routine method today, but also unsuitable for rapid tests. A new fully spectrometric procedure was recently developed using a simultaneously working Echelle spectrometer with CID detector, autosampler and a special self-made data evaluation software. The basis of this method are multi-line measurements of each analyte element, a new method of spectral line selection for main component precision determinations, multi-component calibrations, and frequent external standardizations. For this method the sum of the confidence intervals of all element determinations was less than 1%, and no systematic error was detected. 相似文献
85.
87.
88.
Nonlinear least-squares regression is a valuable tool for gaining chemical insights into complex systems. Yet, the success of nonlinear regression as measured by residual sum of squares (RSS), correlation, and reproducibility of fit parameters strongly depends on the availability of a good initial solution. Without such, iterative algorithms quickly become trapped in an unfavorable local RSS-minimum. For determining an initial solution, a high-dimensional parameter space needs to be screened, a process that is very time-consuming but can be parallelized. Another advantage of parallelization is equally important: After determining initial solutions, the used processors can be tasked to each optimize an initial guess. Even if several of these optimizations become stuck in a shallow local RSS-minimum, other processors continue and improve the regression outcome. A software package for parallel processing-based constrained nonlinear regression (RegressionLab) has been developed, implemented, and tested on a variety of hardware configurations. As proof-of-principle, microalgae to environment interactions have been studied by infrared attenuated total reflection spectroscopy. Additionally, light microscopy has been used to monitor cell production. It is shown that spectroscopic data sets with 10,000?s of data points and >1000 nonlinear model parameters as well as imaging data with 100,000s of data points and >2000 nonlinear model parameters may now be investigated by constrained nonlinear regression. Acceleration factors of up to 8.1 have been obtained which is of high practical relevance when computations take weeks on single-processor machines. Solely using parallel processing, the RSS values may be improved up to a factor of 5.5. 相似文献
89.
This review provides an overview of the most significant strategies developed in recent years for the preparation of donor-functionalized phosphinines and new developments in this field are highlighted. Selected synthetic procedures for the introduction of additional sulfur-, oxygen-, phosphorus-, and nitrogen-donor groups into the heterocyclic framework are presented. Examples of their coordination chemistry and potential applications in homogeneous catalysis and phosphorus containing molecular materials will be given. 相似文献
90.
Melinda VargováGustav Plesch Ulrich F. Vogt Miroslav ZahoranMichal Gorbár Karol Jesenák 《Applied Surface Science》2011,257(10):4678-4684
TiO2 thick films deposited on macroporous reticulated Al2O3 foams with pore size of 10 ppi and 15 ppi were prepared using dip coating from slurries of Aeroxide® P25 nanopowder and precipitated titania. All prepared films have sufficiently good adhesion to the surface of the substrate also in case of strongly cracked films. No measurable release of deposited TiO2 after repeated photocatalytic cycles was observed. The photocatalytic activity was characterized as the rate of mineralization of aqueous phenol solution under irradiation of UVA light by TOC technique. The best activity was obtained with Aeroxide® P25 coated Al2O3 foam with the pore size of 10 ppi, annealed at 600 °C. The optimal annealing temperature for preparation of films from precipitated titania could be determined at 700 °C. Films prepared by sol-gel deposition technique were considerably thinner compared to coatings made of suspensions and their photocatalytic activity was significantly smaller. 相似文献