全文获取类型
收费全文 | 1569篇 |
免费 | 34篇 |
国内免费 | 3篇 |
专业分类
化学 | 991篇 |
晶体学 | 14篇 |
力学 | 15篇 |
数学 | 42篇 |
物理学 | 544篇 |
出版年
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 16篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 11篇 |
2016年 | 21篇 |
2015年 | 25篇 |
2014年 | 20篇 |
2013年 | 65篇 |
2012年 | 62篇 |
2011年 | 69篇 |
2010年 | 42篇 |
2009年 | 39篇 |
2008年 | 78篇 |
2007年 | 110篇 |
2006年 | 88篇 |
2005年 | 96篇 |
2004年 | 91篇 |
2003年 | 65篇 |
2002年 | 77篇 |
2001年 | 51篇 |
2000年 | 30篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1996年 | 25篇 |
1995年 | 13篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 17篇 |
1988年 | 18篇 |
1987年 | 9篇 |
1986年 | 16篇 |
1985年 | 28篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 28篇 |
1978年 | 23篇 |
1977年 | 23篇 |
1976年 | 15篇 |
1975年 | 9篇 |
1973年 | 10篇 |
1965年 | 7篇 |
排序方式: 共有1606条查询结果,搜索用时 15 毫秒
11.
K. Hirose M. Ejima T. Fujibayashi Y. Fujii K. Futatsukawa O. Hashimoto T. Ishikawa S. Kameoka H. Kanda F. Kato S. Kinoshita T. Kinoshita T. Kon O. Konno K. Maeda A. Matsumura Y. Miura F. Miyahara H. Miyase T. Nakabayashi S.N. Nakamura H. Nomura K. Nonaka A. Ohtani Y. Okayasu M. Oyamada A. Sasaki H. Shimizu T. Takahashi T. Tamae H. Tamura T. Terasawa H. Tsubota K. Tsukada D. Uchida M. Ukai M. Wakamatsu T. Watanabe H. Yamauchi H. Yamazaki K. Yawata 《Physics letters. [Part B]》2009
12.
Alternating polymers, poly[(disilanylene)ethynylene]s and poly[(1, 2-diethynylenedisilanylene)(1-silacyclopenta-2, 4-diene-3, 4-diyl)]s were prepared by the anionic ring-opening polymerization of 1, 2, 5, 6-tetrasilacycloocta-3, 7-diynes and 4, 5, 10-trisilacyclo[6.3.0]undeca-1(11), 8-diene-2, 6-diynes, respectively. Poly[(disilanylene)butenyne-1, 4-diyl]s were synthesized by the reaction of 1, 2-diethynyldisilanes with a catalytic amount of RhCl(PPh3)3. Photochemical and conducting properties of the polymers are described. 相似文献
13.
N. Nishida R.S. Hayano K. Nagamine T. Yamazaki J.H. Brewer D.M. Garner D.G. Fleming T. Takeuchi Y. Ishikawa 《Solid State Communications》1977,22(4):235-239
In recent positive-muon spin rotation experiment at TRIUMF on single crystal Fe, a clear temperature dependent change has been observed, for the first time, both in frequency and depolarization rates from 300 K down to 23 K. The μ+ depolarization was explained by the μ+ diffusion through inhomogeneous dipolar fields and the diffusion constant was found to obey an Arrhenius law (activation energy 17 meV) above 70 K but surprisingly deviated from this at lower temperatures, indicating quantum diffusion. We have also found that the μ+ hyperfine field has a temperature dependence slightly stronger than that of the magnetization. 相似文献
14.
Neutron scattering measurements have been made of phonons in a Fe65Ni35 crystal at several temperatures. Marked softening of the [110] acoustic shear modes and a dip in the dispersion relation are found at low temperatures. Above the magnetic ordering temperature Tc, the frequency shift is removed completely, which suggests phonon perturbation by magnetoelastic coupling. 相似文献
15.
E. V. Sampathkumaran I. Das R. Vijayaraghavan A. Hayashi Y. Ueda M. Ishikawa 《Zeitschrift für Physik B Condensed Matter》1993,92(2):191-194
The temperature dependence of the lattice constants of the alloys, RCu2Ge2 (R=Nd, Tb, Dy, Ho and Tm) shows the existence of a lattice strain due to the alignment of the 4f-electric quadrupole at low temperatures. This strain could be related to the deviation of the Néel temperatures (T
N
) from that predicted by de Gennes scaling, thereby indicating the role of the quadrupole on the magnetism. On the other hand, in PrCu2Ge2, for which the enhancement ofT
N
is the largest in thisR series, the lattice constants interestingly behave as if the 4f-quadrupole moment is almost quenched and the anomalous magnetism in this case is attributed to some degree of 4f-delocalisation. 相似文献
16.
Excitation with nanosecond-laser pulses at fluences well below the melt threshold removes Si dimers on the Si(001)-(2x1) surface and induces atomic-Si desorption through an electronic mechanism. The rate of this photoinduced reaction depends superlinearly on the excitation intensity, and is enhanced resonantly at the photon energy where the optical transition injects holes into the dimer backbond surface-band state. The results reveal the crucial role of surface holes and their nonlinear localization in the bond rupture of Si dimers on this surface. 相似文献
17.
S. Arai K. Sugita P. Ma Y. Ishikawa H. Kaetsu S. Isomura 《Applied physics. B, Lasers and optics》1989,48(5):427-435
We have been studying the practical CO2-laser-induced13C separation by a two-stage IRMPD process. The IRMPD of natural CHClF2 in the presence of Br2 mainly produced CBr2F2, which was found to be highly enriched with13C. The yield and13C-atom fraction of CBr2F2 were examined as functions of pulse number, laser line, laser fluence, total pressure, and Br2 pressure using a CO2 TEA laser with an output less than 1 J pulse–1 in order to optimize experimental conditions for13C separation. For example, we obtained CBr2F2 at a13C concentration of 55% in the irradiation of the mixture of 100-Torr CHClF2 and 10-Torr Br2 with the laser radiation at a wavenumber of 1045.02 cm–1 and at a fluence of 3.4 J cm–2. The mechanism for the IRMPD is discussed on the basis of observed results. Using 8-J pulses, we were able to obtain 1.9×10–4 g of13C-enriched CBr2F2 (13C-atom fraction, 47%) per pulse under selected conditions. It is possible to produce 90% or higher13C by the second-stage IRMPD of the CBr2F2 in the presence of oxygen. 相似文献
18.
Kazuaki Yoshimura Katsuhiko Okano Rumi Ishikawa Hidetoshi Yamamoto Michinori Sumimoto Kenji Hori 《Journal of Physical Organic Chemistry》2012,25(5):394-399
Synthesis yields of organic reactions are one of the most important factors in ranking synthesis routes created by synthesis route design systems such as Transform‐Oriented Synthesis Planning and Knowledge base‐Oriented Synthesis Planning. If it is possible to predict the yields of synthesis reactions before starting experiments, one can easily determine an order of synthesis routes for experimental works. In the present study, the reaction profiles of the Curtius rearrangement with different substituents were calculated to generate an equation predicting experimental yields of this reaction. Reactions followed by the formation of isocyanates were also analyzed to consider the relationship between reaction times and experimental yields. A partial least squares (PLS) regression was used to correlate the experimental yields with the calculated activation energies, Ea(calc), together with experimental conditions such as dielectric constants of solvents, reaction times, and reaction temperatures as explanatory variables. Although the PLS regression using all the data gave very poor results, we succeeded in making a model equation with R2 = 0.887 using a modified data set. However, there is a conflict between the predictability and the interpretability on the reaction time. This discrepancy mainly comes from unnecessarily long reaction times in the experiments for azides with calculated Ea values of less than 33 kcal mol–1. To construct a good model equation for the experimental yields of the Curtius reaction, we have to use data sets obtained from within 90 min of the reaction for the PLS regression. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
19.
A. Tsuchida K. Taguchi E. Takyo H. Yoshimi S. Kiriyama T. Okubo M. Ishikawa 《Colloid and polymer science》2000,278(9):872-877
Rate coefficients (k) in the colloidal crystallization of monodispersed silica spheres in the presence of sodium chloride are studied in microgravity
achieved by parabolic flights of an aircraft. Time-resolved reflection spectroscopy is made with a continuous circulating-type
stopped-flow cell system. The k values decrease as the salt concentration increases both at 0 and 1 G and those in microgravity are smaller than those in
normal gravity by 16% (maximum), especially in water and in the presence of a small amount of the salt lower than 2 × 10−6 mol/l. The rates in flight at 1 G are larger by 15% (maximum) compared with those at 1 G on the ground. The k values obtained at 0 G, 1 G in flight and 1 G on the ground agree excellently with each other for the suspensions with 3 × 10−6 and 4 × 10−6 mol/l sodium chloride. Disappearance of the downward diffusion of spheres and no convection of the suspensions are important
for retardation in microgravity.
Received: 20 January 2000 Accepted: 9 March 2000 相似文献
20.
T. Ishikawa S. Yamashita Y. Nakazawa A. Kawamoto M. Oguni 《Journal of Thermal Analysis and Calorimetry》2008,92(2):435-438
Thermodynamic investigation of an organic superconductor κ-(BEDT-TTF)2Ag(CN)2H2O in which the BEDT-TTF dimers are arranged in the κ-type structure in the donor layers is performed by the relaxation calorimetric
technique at low temperatures and under magnetic fields. A thermal anomaly related to the superconductive phase transition
was observed at 5 K. The existence of residual γ* in the superconductive state is about 18% of the normal state γ value, which is larger than those of κ-(BEDT-TTF)2Cu(NCS)2, and κ-(BEDT-TTF)2Cu[N(CN)2]Br salt. The lattice heat capacity reflected on the β-term in the low-temperature heat capacity was found to be affected
by the cooling rate. The disorder produced in the network structure constructed by hydrogen bond in the insulating layer is
considered to give low-energy phonon excitations reflected in the heat capacity. 相似文献