全文获取类型
收费全文 | 1598篇 |
免费 | 57篇 |
国内免费 | 16篇 |
专业分类
化学 | 1202篇 |
晶体学 | 35篇 |
力学 | 19篇 |
数学 | 84篇 |
物理学 | 331篇 |
出版年
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 21篇 |
2019年 | 23篇 |
2018年 | 18篇 |
2017年 | 8篇 |
2016年 | 35篇 |
2015年 | 42篇 |
2014年 | 30篇 |
2013年 | 67篇 |
2012年 | 83篇 |
2011年 | 114篇 |
2010年 | 58篇 |
2009年 | 51篇 |
2008年 | 83篇 |
2007年 | 80篇 |
2006年 | 86篇 |
2005年 | 78篇 |
2004年 | 86篇 |
2003年 | 68篇 |
2002年 | 66篇 |
2001年 | 54篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 27篇 |
1997年 | 15篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 27篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有1671条查询结果,搜索用时 31 毫秒
951.
Dicyanoanthracene-sensitized photolysis of aryldiazomethanes affords stilbenes with cis/trans ratios of ~3 via free radical cations; anodic oxidation gives similar results but via radical cations adsorbed on electrode surface. 相似文献
952.
953.
Saito S Thorwart M Tanaka H Ueda M Nakano H Semba K Takayanagi H 《Physical review letters》2004,93(3):037001
We have observed multiphoton transitions between two macroscopic quantum-mechanical superposition states formed by two opposite circulating currents in a superconducting loop with three Josephson junctions. Resonant peaks and dips of up to three-photon transitions were observed in spectroscopic measurements when the system was irradiated with a strong rf-photon field. The widths of the multiphoton absorption dips are shown to scale with the Bessel functions in agreement with theoretical predictions derived from the Bloch equation or from a spin-boson model. 相似文献
954.
Ahn MH Aoki S Ashie Y Bhang H Boyd S Casper D Choi JH Fukuda S Fukuda Y Gran R Hara T Hasegawa M Hasegawa T Hayashi K Hayato Y Hill J Ichikawa AK Ikeda A Inagaki T Ishida T Ishii T Ishitsuka M Itow Y Iwashita T Jang HI Jang JS Jeon EJ Joo KK Jung CK Kajita T Kameda J Kaneyuki K Kato I Kearns E Kibayashi A Kielczewska D Kim BJ Kim CO Kim JY Kim SB Kobayashi K Kobayashi T Koshio Y Kropp WR Learned JG Lim SH Lim IT Maesaka H Maruyama T Matsuno S Mauger C Mcgrew C Minamino A Mine S Miura M Miyano K 《Physical review letters》2004,93(5):051801
We present a search for electron neutrino appearance from accelerator-produced muon neutrinos in the K2K long-baseline neutrino experiment. One candidate event is found in the data corresponding to an exposure of 4.8 x 10(19) protons on target. The expected background in the absence of neutrino oscillations is estimated to be 2.4+/-0.6 events and is dominated by misidentification of events from neutral current pi(0) production. We exclude the nu(micro) to nu(e) oscillations at 90% C.L. for the effective mixing angle in the 2-flavor approximation of sin((2)2theta(microe)( approximately 1/2sin((2)2theta(13))>0.15 at Deltam(2)(microe)=2.8 x 10(-3) eV(2), the best-fit value of the nu(micro) disappearance analysis in K2K. The most stringent limit of sin((2)2theta(microe)<0.09 is obtained at Deltam(2)(microe)=6 x 10(-3) eV(2). 相似文献
955.
Single crystals of NaCoO2 have been successfully synthesized for the first time by a flux method at 1323 K. A single-crystal X-ray diffraction study confirmed the trigonal space group and the lattice parameters , . The crystal structure has been refined to the conventional values R=1.9% and wR=2.1% for 309 independent observed reflections. The electron density distribution of NaCoO2 has been studied by the maximum entropy method (MEM) using single-crystal X-ray diffraction data obtained at 298 K. From the results of the MEM analysis, the strong covalent bonding was clearly observed between Co and O atoms, while no bonding was observed around Na atoms. We also calculated the electron density of NaCoO2 by first principles calculations. The electron density obtained experimentally is in good agreement with the theoretical one. 相似文献
956.
Furukawa Ryudai Tanaka Yasunori Nagase Y. Nakano Y. Ishijima T. Sueyasu S. Watanabe S. Nakamura K. 《Plasma Chemistry and Plasma Processing》2022,42(3):435-463
Plasma Chemistry and Plasma Processing - The influences of upper-coil and lower-coil current modulation of tandem-type modulated induction thermal plasma (tandem-MITP) were studied for silicon... 相似文献
957.
The characteristics of tonal noise and the variations of flow structure around NACA0018 airfoil in a uniform flow are studied by means of simultaneous measurement of noise and velocity field by particle-image velocimetry to understand the generation mechanism of tonal noise. Measurements are made on the noise characteristics, the phase-averaged velocity field with respect to the noise signal, and the cross-correlation contour of velocity fluctuations and noise signal. These experimental results indicate that the tonal noise is generated from the periodic vortex structure on the pressure surface of the airfoil near the trailing edge of the airfoil. It is found that the vortex structure is highly correlated with the noise signal, which indicates the presence of noise-source distribution on the pressure surface. The vorticity distribution on the pressure surface breaks down near the trailing edge of the airfoil and forms a staggered vortex street in the wake of the airfoil. 相似文献
958.
Three‐dimensional reference interaction site model self‐consistent field analysis of solvent and substituent effects on the absorption spectra of Brooker's merocyanine
下载免费PDF全文
![点击此处可从《Journal of computational chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yuichi Tanaka Norio Yoshida Haruyuki Nakano 《Journal of computational chemistry》2015,36(22):1655-1663
Solvent and substituent effects on the absorption spectra of Brooker's merocyanine (BM) are investigated using the three‐dimensional reference interaction site model self‐consistent field method and time‐dependent density functional theory. The π–π* excitation energies are computed for BM and its derivative 2,6‐di‐tert‐butyl (di‐t‐Bu) BM. The behaviors of the computed excitation energies with increasing solvent polarity are in good agreement with those of the corresponding experimental measurements. In addition, analysis of the solute–solvent interaction energies and spatial distribution functions reveals that the effects of the solvent on the absorption spectra are reduced by the steric hindrance of the t‐Bu groups. Furthermore, from the difference in the solute–solvent interaction energies of BM and di‐t‐Bu BM, it is shown that the effect of the t‐Bu substituents on the absorption spectrum is greater in high‐polarity solvents. © 2015 Wiley Periodicals, Inc. 相似文献
959.
Development of spin‐dependent relativistic open‐shell Hartree–Fock theory with time‐reversal symmetry (I): The unrestricted approach
下载免费PDF全文
![点击此处可从《International journal of quantum chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An open‐shell Hartree–Fock (HF) theory for spin‐dependent, two‐component relativistic calculations, termed the Kramers‐unrestricted HF (KUHF) method, is developed. The present KUHF method, which is formulated as a relativistic counterpart of nonrelativistic UHF, is based on quaternion algebra and partly uses time‐reversal symmetry. The fundamental characteristics of KUHF are discussed in this study. From numerical assessments, it was revealed that KUHF gives a corresponding solution to nonrelativistic UHF; furthermore, KUHF properly describes spin‐orbit interactions. In addition, KUHF can improve the self‐consistent field convergence behavior in spin‐dependent calculations, for example, for f‐block elements. 相似文献
960.
Dr. Shunpei Nobusue Hirokazu Miyoshi Dr. Akihiro Shimizu Dr. Ichiro Hisaki Kotaro Fukuda Prof. Masayoshi Nakano Prof. Yoshito Tobe 《Angewandte Chemie (International ed. in English)》2015,54(7):2090-2094
A tetramesityl derivative of hitherto unknown tetracyclopenta[def,jkl,pqr,vwx]tetraphenylene (TCPTP), which is a potential tetraradicaloid hydrocarbon, was synthesized. Theoretical calculations based on spin‐flip time‐dependent density functional theory predict that the closed‐shell D2h form of TCPTP is more stable than the open‐shell D4h form with its slightly tetraradical character. The tetramesityl derivative (Mes)4‐TCPTP exhibits remarkable antiaromaticity as a result of the peripheral 20‐π‐electron circuit, which causes an absorption maximum at a long wavelength and a small HOMO–LUMO gap. In solution, (Mes)4‐TCPTP most likely adopts rapidly equilibrating D2h structures that interconvert via the D4h transition state. X‐ray crystallographic analysis showed (Mes)4‐TCPTP as an approximate D2h structure. 相似文献