全文获取类型
收费全文 | 2043篇 |
免费 | 36篇 |
国内免费 | 22篇 |
专业分类
化学 | 1336篇 |
晶体学 | 61篇 |
力学 | 26篇 |
数学 | 125篇 |
物理学 | 553篇 |
出版年
2022年 | 7篇 |
2021年 | 7篇 |
2019年 | 21篇 |
2018年 | 17篇 |
2017年 | 11篇 |
2016年 | 27篇 |
2015年 | 30篇 |
2014年 | 26篇 |
2013年 | 137篇 |
2012年 | 69篇 |
2011年 | 91篇 |
2010年 | 57篇 |
2009年 | 69篇 |
2008年 | 97篇 |
2007年 | 129篇 |
2006年 | 96篇 |
2005年 | 86篇 |
2004年 | 103篇 |
2003年 | 93篇 |
2002年 | 86篇 |
2001年 | 61篇 |
2000年 | 45篇 |
1999年 | 37篇 |
1998年 | 30篇 |
1997年 | 29篇 |
1996年 | 32篇 |
1995年 | 28篇 |
1994年 | 37篇 |
1993年 | 44篇 |
1992年 | 41篇 |
1991年 | 20篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 29篇 |
1987年 | 12篇 |
1986年 | 21篇 |
1985年 | 24篇 |
1984年 | 25篇 |
1983年 | 20篇 |
1982年 | 23篇 |
1981年 | 29篇 |
1980年 | 11篇 |
1979年 | 31篇 |
1978年 | 20篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 26篇 |
1974年 | 23篇 |
1973年 | 16篇 |
1972年 | 10篇 |
排序方式: 共有2101条查询结果,搜索用时 78 毫秒
971.
Abstract In this paper we shall solve locally in time the solutions to the Cauchy problem for first order quasilinear hyperbolic systems
of which coefficients of principal part and of lower order terms are μ- H?lder and
- H?lder continuous in time variable respectively and in Gevrey class of index s with respect to space variables under the assumption
, where ν denotes the maximal muliplicity of characteristics of systems.
Keywords: Nonlinear hyperbolic systems, Cauchy problem, Gevrey classes 相似文献
972.
The vertical absorption spectrum and photodissociation mechanism of vinyl chloride (VC) were studied by using symmetry-adapted cluster configuration interaction theory. The important vertical pi --> pi* excitation was intensively examined with various basis sets up to aug-cc-pVTZ augmented with appropriate Rydberg functions. The excitation energy for pi --> pi* transition obtained in the present study, 6.96 eV, agrees well with the experimental value, 6.7-6.9 eV. Calculated excitation energies along with the oscillator strengths clarify that the main excitation in VC is the pi --> pi* excitation. Contrary to the earlier theoretical reports, the results obtained here support that the C-Cl bond dissociation takes place through the n(Cl-)sigma(C-Cl)* state. 相似文献
973.
Fujisawa T Fukuda M Terazima M Kimura Y 《The journal of physical chemistry. A》2006,110(18):6164-6172
We investigated the solvation of several room temperature ionic liquids by Raman spectroscopy using diphenylcyclopropenone (DPCP) and phenol blue (PB) as probe molecules. We estimated acceptor numbers (AN) of room temperature ionic liquids by an empirical equation associated with the Raman band of DPCP assigned as a C=C stretching mode involving a significant C=O stretching character. According to the dependence of AN on cation and anion species, the Lewis acidity of ionic liquids is considered to come mainly from the cation charge. The frequencies and bandwidths of the C=O and C=N stretching modes of phenol blue are found to be close to those in conventional polar solvents such as methanol and dimethyl sulfoxide. The frequencies of these vibrational modes show similar dependence upon the electronic absorption band center as is observed in conventional liquid solvents. However, peculiar behavior was found in the Raman bandwidths and the excitation wavelength dependence of the C=N stretching mode in room temperature ionic liquids. Both the bandwidth of the C=N stretching mode and the extent of the excitation wavelength dependence of the Raman shift of the C=N stretching mode tend to decrease as the absorption band center decreases, in contrast to the case of conventional solvents. This anomaly is discussed in terms of the properties of room temperature ionic liquids. 相似文献
974.
Nakabayashi Y Hirosaki Y Yamauchi O 《Bioelectrochemistry (Amsterdam, Netherlands)》2006,69(2):216-222
The mediation of dipolar ruthenium(II) ammine complexes containing pyridinium ions [Ru(NH(3))(5)(L(+))](3+)(L(+): pyridinium ions) in glucose oxidation has been investigated by a voltammetric method. These ruthenium(II) complexes had appropriate redox potentials of 0.10-0.18 V vs. Ag/AgCl and high k(s) values of 5.7-17 x 10(6) M(-1) s(-1) which are the second-order rate constants for electron transfer from glucose oxidase in reduced form to [Ru(NH(3))(5)(L(+))](4+). In particular, the k(s) values for [Ru(NH(3))(5)(L(+))](3+) were greater than those of osmium(II)-polypyridine complexes possessing similar redox potentials which are most commonly used. All the dipolar ruthenium(II) complexes used in this study are therefore concluded to be useful for the electron transfer mediators of amperometric glucose sensors. 相似文献
975.
The Laser Undulator Compact X-ray source(LUCX) is a test bench for a compact high brightness X-ray generator,based on inverse Compton Scattering at KEK,which requires high intensity multi-bunch trains with low transverse emittance.A photocathode RF gun with emittance compensation solenoid is used as an electron source.Much endeavor has been made to increase the beam intensity in the multi-bunch trains.The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects,so that ... 相似文献
976.
We study the reaction cross sections (σR) and root-mean-square (RMS) radii of ^8Li and ^8B, the halo-like nuclei, with stable target ^12C, ^27Al and ^9Be within the standard optical-limit Glauber model, using densities obtained from relativistic mean-field (RMF) formalisms and other types of distributions. It is found that the experimental σR can be reproduced well at high energy. The RMS radius and Ar extracted by RMF- theory and harmonic oscillator distribution are compared. larger than those of SLi. In addition, we analyze in detail the We find that the RMS radius and Ar of SB are relationship between σR and density distribution. 相似文献
977.
Yasuo KAGAWA 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2010,86(7):667-693
ATP synthase (FoF1) consists of an ATP-driven motor (F1) and a H+-driven motor (Fo), which rotate in opposite directions. FoF1 reconstituted into a lipid membrane is capable of ATP synthesis driven by H+ flux. As the basic structures of F1 (α3β3γδε) and Fo (ab2c10) are ubiquitous, stable thermophilic FoF1 (TFoF1) has been used to elucidate molecular mechanisms, while human F1Fo (HF1Fo) has been used to study biomedical significance. Among F1s, only thermophilic F1 (TF1) can be analyzed simultaneously by reconstitution, crystallography, mutagenesis and nanotechnology for torque-driven ATP synthesis using elastic coupling mechanisms. In contrast to the single operon of TFoF1, HFoF1 is encoded by both nuclear DNA with introns and mitochondrial DNA. The regulatory mechanism, tissue specificity and physiopathology of HFoF1 were elucidated by proteomics, RNA interference, cytoplasts and transgenic mice. The ATP synthesized daily by HFoF1 is in the order of tens of kilograms, and is primarily controlled by the brain in response to fluctuations in activity. 相似文献
978.
Yasuo Iida Muthupandian Ashokkumar Toru Tuziuti Teruyuki Kozuka Kyuichi Yasui Atsuya Towata Judy Lee 《Ultrasonics sonochemistry》2010,17(2):480-486
A simple bubble population model, with emphasis on the bubble–bubble coalescence, is proposed. In this model, the bubble size distribution is simulated through the iteration of fundamental bubble population process: generation, dissolution, and coalescence. With this simple modelling, the bubble size distribution experimentally observed by the pulsed laser diffraction method and the void rate obtained by the capillary system at 443 kHz were successfully simulated. The experimental results on the bubble population growth by the repetitive pulsed sonication and the effect of pulse width on the bubble population were recreated by the numerical simulation in a semi-quantitative manner. The importance of coalescence of bubbles especially for the effect of addition of surfactant is demonstrated. By decreasing the coalescence frequency by one order of magnitude in the simulation, both the drastic decrease in the total bubble volume as well as the depression of bubble size distribution centring from a few tens of microns in water to a few microns in a dilute surfactant solution can be simultaneously derived. 相似文献
979.
Yasuo Iida Muthupandian Ashokkumar Toru Tuziuti Teruyuki Kozuka Kyuichi Yasui Atsuya Towata Judy Lee 《Ultrasonics sonochemistry》2010,17(2):473-479
To characterize the bubble populations (size and its number distribution) in a sonochemical reactor, a simple but powerful technique based on the Fraunhofer laser diffraction (LD) has been proposed. In this method, the acoustic wave disturbance to the laser probe in the sonochemical reaction field was eliminated by the temporal separation using pulsed sonication (pulsed LD). With this relatively simple strategy, the temporal development of the bubble size distribution could be evaluated by pulsed LD. A number density of bubbles was estimated by using a calibration data obtained with monosized standard particles. In addition, the effect of pulse length and a surfactant on the bubble population phenomena in a multibubble system are discussed. 相似文献
980.
Takehito Nakano Takahiro Mizukane Yasuo Nozue 《Journal of Physics and Chemistry of Solids》2010,71(4):650-653
Optical and magnetic properties are investigated for low-silica X (LSX) zeolite loaded with Na metals at various loading densities. In LSX, β-cages with the inside diameter of ∼7 Å are arrayed in a diamond structure and the supercages with that of ∼13 Å are formed among them. When the average number of guest Na atoms per β cage, n, is smaller than ∼2, optical reflectance shows a peak at ∼2.5 eV. This corresponds to the 1s-1p transition of the cluster formed in β cage. At n>2, this peak disappears and several strong peaks are seen at 1-3 eV. The oscillator strength increases with n. They can be attributed to surface-plasmon-like excitations of the Na clusters formed in supercages. At n≤10, clear absorption tails with energy gaps are observed at near IR region indicating insulating states. However, when n is increased up to ∼12, a clear Drude reflection suddenly appears in the IR region, indicating that an insulator-to-metal transition abruptly occurs. This dramatic change of the electronic state may be caused by the successive connection between adjacent clusters in supercages due to some special arrangement of Na+ ions as well as the delocalized wave function of electrons at high Na-loading density. 相似文献