全文获取类型
收费全文 | 1326篇 |
免费 | 27篇 |
国内免费 | 9篇 |
专业分类
化学 | 967篇 |
晶体学 | 11篇 |
力学 | 23篇 |
数学 | 62篇 |
物理学 | 299篇 |
出版年
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2018年 | 10篇 |
2016年 | 16篇 |
2015年 | 30篇 |
2014年 | 21篇 |
2013年 | 56篇 |
2012年 | 46篇 |
2011年 | 48篇 |
2010年 | 47篇 |
2009年 | 28篇 |
2008年 | 67篇 |
2007年 | 63篇 |
2006年 | 48篇 |
2005年 | 51篇 |
2004年 | 45篇 |
2003年 | 48篇 |
2002年 | 43篇 |
2001年 | 30篇 |
2000年 | 42篇 |
1999年 | 17篇 |
1998年 | 9篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1993年 | 9篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 29篇 |
1988年 | 26篇 |
1987年 | 14篇 |
1986年 | 19篇 |
1985年 | 43篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 23篇 |
1981年 | 30篇 |
1980年 | 22篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 23篇 |
1976年 | 30篇 |
1975年 | 31篇 |
1974年 | 19篇 |
1973年 | 11篇 |
1969年 | 6篇 |
1967年 | 5篇 |
排序方式: 共有1362条查询结果,搜索用时 15 毫秒
101.
The smallness is proved of étale fundamental groups for arithmetic schemes. This is a higher dimensional analogue of the Hermite-Minkowski theorem. We also refer to the case of varieties over finite fields. As an application, we prove certain finiteness results of representations of the fundamental groups over algebraically closed fields. 相似文献
102.
We extend Geiger’s size-biased tree method to the multitype case to give another proof of Zubkov’s result that the asymptotic relative generation distribution of the closest common ancestor of the multitype Galton–Watson branching process conditioned on non-extinction is uniform. 相似文献
103.
Garuda Fujii Toshiro Matsumoto Toru Takahashi Tsuyoshi Ueta 《Applied Physics A: Materials Science & Processing》2012,107(1):35-42
In a random system composed of dielectric materials, laser action is expected to occur from the light localization caused
by multiple scattering and interference effect. The wavelengths at which the laser oscillation occurs in random media depend
on the mean free path of continuous scattering. Since the mean free path of continuous scattering is dependent on the filling
factor, it is important to investigate systematically the effect of the filling factor for the laser action. In the present
study, we calculate the Poynting vectors of the light emitted from two-dimensional random media consisting of dielectric rods
with population inversion modeled by the negative imaginary part of relative permittivity. The spectra of the radiated Poynting
vectors from the two-dimensional random media are shown for several different filling factors and for various values of population
inversion. We try to find laser generation which occurs at low population inversion and discuss about the threshold of laser
action occurring in dielectric structures with different filling factors. We also study the spacial distribution of the electric
field amplitude in several frequency regions where light strongly amplifies. 相似文献
104.
Hiroyuki Sasaki Akinori Tanaka Tazumi Nagasawa Shoji Suzuki Toshiro Nagase 《Solid State Communications》2004,129(2):91-95
We have carried out an angle-resolved photoemission study for CoSi2 nanofilms grown on the Si(111)-7×7 substrates. The surface of CoSi2(111) nanofilm changes from the bulk-truncated surface to the surface with additional Si-bilayer by annealing at higher temperature above 825 K. The angle-resolved photoemission spectra of the CoSi2 nanofilm annealed at 853 K show the spectral features originated from the surface resonance state on the CoSi2 surface terminated by Si-bilayer. From the detailed photoemission study, we discuss the surface electronic structure in CoSi2(111) nanofilms grown on Si(111) substrates. 相似文献
105.
S. Tanabete Y. Nakagawa T. Okamoto M. Haraguchi T. Isu G. Shinomiya 《Applied Physics A: Materials Science & Processing》2013,112(3):605-611
Many researching efforts have been reported to seek various fundamental LC resonance structures, recently. But still the Split Ring Resonator (SRR) is the most famous and major fundamental LC-resonance structure used in the metamaterial. We employed SRR structure as the fundamental LC-resonance mechanism to fabricate photonic crystal with periodic arrangement of two different metamaterial areas composed from SRR arrays on the dielectric substrate. We developed Photonic Metamaterial Crystal (PMC) to realize the more advanced and versatile functions of the metamaterial by 1 dimensional or 2 dimensional periodic arranging of two metamaterial sections which have different dispersion properties due to the different size of SRR structures each other. In this paper, we report the fabrication process, estimation of PMC properties and some possible future application prospects, for instance the PMC waveguide structures and nonlinear properties of PMC observed as selective LC-resonant properties in Raman mapping analysis of PMC. These are quite interesting characters of PMC and the attractive applications as the PMC devices. 相似文献
106.
Mitsuru Musha Yosuke Tamura Ken’ichi Nakagawa Ken-ichi Ueda 《Optics Communications》2007,272(1):211-216
We have developed a practical and precise frequency measurement system at 1.5 μm telecommunication band. An electro-optic-modulator based optical frequency comb is phase-locked to a dither-free acetylene-stabilized laser to realize an optical frequency comb with frequency uncertainty of 10 kHz (5 × 10−11) and the linewidth of 15 kHz. The present frequency comb can be also used as an optical frequency reference grid defined by ITU-T (International Telecommunication Union, Telecommunication Standardization Sector). Using the present frequency measurement system, we have demonstrated the first optical frequency measurement of 12C16O overtone absorption lines around 1.56 μm with the uncertainty of lower than 900 kHz. 相似文献
107.
Hiroaki Nitani Masato Yuya Takahiro Ono Takashi Nakagawa Satoshi Seino Kenji Okitsu Yoshiteru Mizukoshi Shuichi Emura Takao A. Yamamoto 《Journal of nanoparticle research》2006,8(6):951-958
A sample of Au–Pd bimetallic nanoparticles supported on γ-Fe2O3 was synthesized in a sonochemically one-pot process. The structural analyses of the synthesized sample were performed by the techniques of X-ray Absorption Fine Structure (XAFS), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and UV–vis spectrometry. Results indicated that the synthesized sample formed a core-shell structure in which a gold core was surrounded by a thin palladium shell. The reaction rate constant for the hydrogenation of cyclohexene of the present sample showed higher value than that of Pd nanoparticles supported on γ-Fe2O3 and core-shell structured Au–Pd nanoparticles supported on SiO2. The present sample is a promising catalyst material which has a high catalytic activity. 相似文献
108.
We study the size dependence of the nonlinear response of weakly confined excitons for the size region beyond the long wavelength approximation regime. The observed degenerate-four-wave mixing signal of GaAs thin layers exhibits an anomalous size dependence, where the signal is resonantly enhanced at a particular thickness region. The theoretical analysis elucidates that this enhancement is due to the size-resonant enhancement of the internal field with a spatial structure relevant to the nondipole-type excitonic state. These results establish the formerly proposed new type of size dependence of nonlinear response due to the nonlocality induced double resonance. 相似文献
109.
Hiroaki Inoue Yuji Arai Tsunao Kishida Masaharu Shin-Ya Ryu Terauchi Shuji Nakagawa Masazumi Saito Shinji Tsuchida Atsuo Inoue Toshiharu Shirai Hiroyoshi Fujiwara Osam Mazda Toshikazu Kubo 《Ultrasonics》2014
The goal of this feasibility study was to examine whether sonoporation assisted transduction of siRNA could be used to ameliorate arthritis locally. If successful, such approach could provide an alternative treatment for the patients that have or gradually develop adverse response to chemical drugs. Tumor necrosis factor alpha (TNF-α) produced by synovial fibroblasts has an important role in the pathology of rheumatoid arthritis, inducing inflammation and bone destruction. In this study, we injected a mixture of microbubbles and siRNA targeting TNF-α (siTNF) into the articular joints of rats, and transduced siTNF into synovial tissue by exposure to a collimated ultrasound beam, applied through a probe 6 mm in diameter with an input frequency of 3.0 MHz, an output intensity of 2.0 W/cm2 (spatial average temporary peak; SATP), a pulse duty ratio of 50%, and a duration of 1 min. Sonoporation increased skin temperature from 26.8 °C to 27.3 °C, but there were no adverse effect such as burns. The mean level of TNF-α expression in siTNF-treated knee joints was 55% of those in controls. Delivery of siTNF into the knee joints every 3 days (i.e., 7, 10, 13, and 16 days after immunization) by in vivo sonoporation significantly reduced paw swelling on days 20–23 after immunization. Radiographic scores in the siTNF group were 56% of those in the CIA group and 61% of those in the siNeg group. Histological examination showed that the number of TNF-α positive cells was significantly lower in areas of pannus invasion into the ankle joints of siTNF- than of siNeg-treated rats. These results indicate that transduction of siTNF into articular synovium using sonoporation may be an effective local therapy for arthritis. 相似文献
110.
Immel S Nakagawa T Lindner HJ Lichtenthaler FW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(18):3366-3371
Periodate oxidation of alpha-cyclodextrin followed by borohydride reduction readily provided an octadeca-hydroxymethyl-substituted 30-crown-12 polyacetal 1, its 30-membered macrocycle being composed of six meso-butanetetrol/glycolaldehyde acetal units, which is, consequently, optically inactive. Its solid-state molecular geometry emerged from the X-ray structural analysis of the well-crystallizing octadeca-acetate 2, which revealed the undulated macrocycle to be molded into three loops with a unique order of succession of the -CHR-CHR-O-CHR-O- units: alternating gauche- and anti-conformations of the meso-butanetetrol portions and consecutive disposition of the glycolaldehyde-acetoxymethyl groups above and below the mean-plane of the macrocycle. In solution, however, as evidenced by 1H- and 13C-NMR spectra, the macrocycle is highly flexible at ambient and higher temperatures, its mobility becoming distinctly restricted only below -20 degrees C. 相似文献