全文获取类型
收费全文 | 421841篇 |
免费 | 4789篇 |
国内免费 | 1304篇 |
专业分类
化学 | 210418篇 |
晶体学 | 6039篇 |
力学 | 19692篇 |
综合类 | 19篇 |
数学 | 61679篇 |
物理学 | 130087篇 |
出版年
2020年 | 2181篇 |
2019年 | 2172篇 |
2018年 | 11188篇 |
2017年 | 12057篇 |
2016年 | 8314篇 |
2015年 | 4545篇 |
2014年 | 4986篇 |
2013年 | 14861篇 |
2012年 | 15627篇 |
2011年 | 26301篇 |
2010年 | 15975篇 |
2009年 | 15826篇 |
2008年 | 23109篇 |
2007年 | 26610篇 |
2006年 | 12670篇 |
2005年 | 18476篇 |
2004年 | 13761篇 |
2003年 | 12364篇 |
2002年 | 10237篇 |
2001年 | 10410篇 |
2000年 | 8140篇 |
1999年 | 6309篇 |
1998年 | 5070篇 |
1997年 | 4877篇 |
1996年 | 5049篇 |
1995年 | 4563篇 |
1994年 | 4298篇 |
1993年 | 4109篇 |
1992年 | 4609篇 |
1991年 | 4437篇 |
1990年 | 4168篇 |
1989年 | 3983篇 |
1988年 | 4278篇 |
1987年 | 3951篇 |
1986年 | 3813篇 |
1985年 | 5501篇 |
1984年 | 5594篇 |
1983年 | 4525篇 |
1982年 | 4915篇 |
1981年 | 4950篇 |
1980年 | 4703篇 |
1979年 | 4836篇 |
1978年 | 4838篇 |
1977年 | 4728篇 |
1976年 | 4724篇 |
1975年 | 4640篇 |
1974年 | 4469篇 |
1973年 | 4655篇 |
1972年 | 2647篇 |
1971年 | 1923篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
The periodic precipitation pattern formation in gelatinous media is interpreted as a moving boundary problem. The time law,
spacing law and width law are revisited on the basis of the new scenario. The explicit dependence of the geometric structure
on the initial concentrations of the reactants is derived. Matalon—Packter law, which relates the spacing coefficient with
the initial concentrations is reformulated removing many ambiguities and impractical parameters. Experimental results are
discussed to establish the significance of moving boundary concept in the diffusion controlled pattern forming systems 相似文献
902.
I. A. Stefanova 《Acoustical Physics》2003,49(2):203-206
Empirical approximating formulas describing the most important psychophysiological properties of the human auditory analyzer are derived. 相似文献
903.
In this paper a predictive control strategy is applied to a periodic-review dynamic inventory system with deteriorating items.
Given the current inventory level, we determine the optimal production rates to be implemented at the beginning of each of
the following periods over the control horizon. The effectiveness of this approach is the use of future information of the
inventory target level and the desired production rate, which are available, along the fixed horizon. The deterioration coefficient
may be known or unknown and both cases are considered. In the case where it is unknown, the self-tuning predictive control
is applied. The proposed control algorithms are illustrated by simulations. 相似文献
904.
The rotational spectra of three low-energy conformers of thiodiglycol (TDG) (HOCH2CH2SCH2CH2OH) have been measured in a molecular beam using a pulsed-nozzle Fourier-transform microwave spectrometer. To determine the likely conformational structures with ab initio approach, conformational structures of 2-(ethylthio)ethanol (HOEES) (CH3CH2SCH2CH2OH) were used as starting points together with the consideration of possible intramolecular hydrogen bonding in TDG. Three lower-energy conformers have been found for TDG at the MP2=Full/6311G** level and ab initio results agree nicely with experimentally determined rotational constants. In addition, Stark measurements were performed for two of the three conformers for dipole moment determinations, adding to our confidence of the conformational structure matches between experimental observations and ab initio calculations. Of the three lower-energy conformers, one displays a compact folded-like structure with strong hydrogen bonding between the two hydroxyl groups and the central sulfide atom. Two other conformers have relatively open chain-like structures with hydrogen bonding between each of the hydroxyl groups to the central sulfur atom, of which one has pure b-type dipole moment according to the ab initio results. 相似文献
905.
Positions and intensities for 453 spectral lines in 12 rovibrational bands of 12C16O2 have been determined between 3700 and 3750 cm−1. At three temperatures (294, 500, and 698 K) eight spectra have been recorded at a pressure around 5 mbar and for an absorption path of about 190 cm−1 using a Bomen DA3 Fourier transform spectrometer (4 × 10−3 cm−1 resolution). Some of the measured positions and intensities can be compared with recent experimental results that validate the experimental set-up and the data analysis procedure. The results are also compared with the values listed in the HITRAN 2000 database. If the agreement is generally good, discrepancies are observed for three hot bands. 相似文献
906.
Christian J. Bordé Claus Lämmerzahl Ernst M. Rasel 《General Relativity and Gravitation》2004,36(10):2193-2196
907.
A. V. Burenin 《Optics and Spectroscopy》2004,97(6):867-875
A noninvariant geometrical group characterizing the internal dynamics of the tetrahydrofuran molecule C4H8O with allowance for the clearly pronounced pseudorotation effect is constructed. On this basis, some qualitative features of the energy spectrum of the molecule following from the analysis of high-resolution spectroscopic data are explained. 相似文献
908.
The kinetics of decay of a phase hologram in a semiconductor CdF2 crystal with bistable In centers is studied. Kinetic constants of the hologram decay are found, and the potential relief of the bistable center is plotted. The resolving power of the crystal is evaluated and recording of a transparency is demonstrated. 相似文献
909.
The cross section of absorption of electromagnetic radiation by an inhomogeneous spherical particle is calculated. The general case of an arbitrary value of the ratio of the particle radius to the radius of the dielectric core is considered. The condition of diffuse reflection of electrons from the inner and outer surfaces of the metal layer of the particle is taken as the boundary condition of the problem. The limiting cases are considered and the results obtained are discussed. 相似文献
910.
Computer processing of electronic absorption spectra of rare-earth elements in inorganic laser media
Algorithms and program modules are developed for calculation of the Judd-Ofelt parameters on modern computers. These programs can be used to perform numerical analysis of the energy absorption by rareearth ions in laser media. 相似文献