全文获取类型
收费全文 | 5331篇 |
免费 | 117篇 |
国内免费 | 20篇 |
专业分类
化学 | 3682篇 |
晶体学 | 69篇 |
力学 | 73篇 |
数学 | 228篇 |
物理学 | 1416篇 |
出版年
2022年 | 29篇 |
2021年 | 30篇 |
2020年 | 54篇 |
2019年 | 61篇 |
2018年 | 50篇 |
2017年 | 34篇 |
2016年 | 82篇 |
2015年 | 86篇 |
2014年 | 113篇 |
2013年 | 251篇 |
2012年 | 244篇 |
2011年 | 260篇 |
2010年 | 150篇 |
2009年 | 156篇 |
2008年 | 279篇 |
2007年 | 234篇 |
2006年 | 256篇 |
2005年 | 244篇 |
2004年 | 241篇 |
2003年 | 188篇 |
2002年 | 196篇 |
2001年 | 148篇 |
2000年 | 159篇 |
1999年 | 85篇 |
1998年 | 61篇 |
1997年 | 63篇 |
1996年 | 62篇 |
1995年 | 42篇 |
1994年 | 66篇 |
1993年 | 89篇 |
1992年 | 93篇 |
1991年 | 74篇 |
1990年 | 63篇 |
1989年 | 55篇 |
1988年 | 72篇 |
1987年 | 73篇 |
1986年 | 74篇 |
1985年 | 104篇 |
1984年 | 94篇 |
1983年 | 39篇 |
1982年 | 69篇 |
1981年 | 74篇 |
1980年 | 67篇 |
1979年 | 60篇 |
1978年 | 52篇 |
1977年 | 64篇 |
1976年 | 52篇 |
1975年 | 39篇 |
1974年 | 49篇 |
1973年 | 30篇 |
排序方式: 共有5468条查询结果,搜索用时 31 毫秒
101.
Takanari Yasui Takeshi Ohtsuka Tetsu Suzuki Shigeki Okajima Kazuya Nakayama Mitsuru Tomioka Katsuhiro Kamimura Takeo Namekata Hiroaki Minamide Hiromasa Ito 《International Journal of Infrared and Millimeter Waves》2006,27(2):199-210
A new, wide-band, high-speed and high-sensitivity THz detector has been developed. The prototype detector consists of a parabolic
cylindrical mirror, a long wire antenna and a Schottky barrier diode. Direct detection measurements have shown a stable sensitivity
of 150 ± 50 V/W for 1–2 THz without any adjustments. The long wire antenna was fixed at the focus of parabolic cylindrical
mirror then it has been realized less operation steps, easy coupling to the external THz signals and a dramatic enhancement
in the practicality of this system. The optically polished mirror and frosted surface one showed comparable sensitivities,
thus easy polishing and less cost mirror fabrication can be applied for this system. The radiation pattern showed a maximum
radiation angle of approximately 23° with its dominant main lobe, which was attributed to the wire antenna character and confirmed
good agreements with classical antenna theory. 相似文献
102.
A. Sagisaka H. Daido K. Ogura S. Orimo Y. Hayashi M. Nishiuchi M. Mori K. Matsukado A. Fukumi Z. Li S. Nakamura K. Takagaki H. Hazama M. Suzuki T. Utsumi S.V. Bulanov T. Esirkepov 《Applied physics. B, Lasers and optics》2004,78(7-8):919-922
The evolution of an Al preformed plasma produced by a prepulse was observed before and after the arrival of the main pulse by an interferometer using a femtosecond probe pulse. A central density depression due to the ponderomotive force of the main laser pulse in the preformed plasma with a 100 m scale length was clearly visible after the main pulse irradiation at an intensity of 5×1016 W/cm2. The temporal profiles of the prepulse, characterized by a cross-correlation in conjunction with a precise density profile measurement by an interferometer, contribute to the better understanding of femtosecond laser-matter interactions. PACS 52.38.-r; 52.50.Jm; 52.70.-m 相似文献
103.
Ida K Sakamoto Y Takenaga H Oyama N Itoh K Yoshinuma M Inagaki S Kobuchi T Isayama A Suzuki T Fujita T Matsunaga G Koide Y Yoshida M Ide S Kamada Y;JT- team 《Physical review letters》2008,101(5):055003
A spontaneous transition phenomena between two states of a plasma with an internal transport barrier (ITB) is observed in the steady-state phase of the magnetic shear in the negative magnetic shear plasma in the JT-60U tokamak. These two ITB states are characterized by different profiles of the second radial derivative of the ion temperature inside the ITB region (one has a weak concave shape and the other has a strong convex shape) and by different degrees of sharpness of the interfaces between the L mode and the ITB region, which is determined by the turbulence penetration into the ITB region. 相似文献
104.
105.
Dr. Wataru Suzuki Dr. Hiroaki Kotani Dr. Tomoya Ishizuka Prof. Dr. Takahiko Kojima 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(46):10480-10486
Selective two-electron reduction of dioxygen (O2) to hydrogen peroxide (H2O2) has been achieved by two saddle-distorted N,N’-dimethylated porphyrin isomers, an N21,N’22-dimethylated porphyrin ( anti -Me2P ) and an N21,N’23-dimethylated porphyrin ( syn -Me2P ) as catalysts and ferrocene derivatives as electron donors in the presence of protic acids in acetonitrile. The higher catalytic performance in an oxygen reduction reaction (ORR) was achieved by anti -Me2P with higher turnover number (TON=250 for 30 min) than that by syn -Me2P (TON=218 for 60 min). The reactive intermediates in the catalytic ORR were confirmed to be the corresponding isophlorins ( anti -Me2Iph or syn -Me2Iph ) by spectroscopic measurements. The rate-determining step in the catalytic ORRs was concluded to be proton-coupled electron-transfer reduction of O2 with isophlorins based on kinetic analysis. The ORR rate by anti -Me2Iph was accelerated by external protons, judging from the dependence of the observed initial rates on acid concentrations. In contrast, no acceleration of the ORR rate with syn -Me2Iph by external protons was observed. The different mechanisms in the O2 reduction by the two isomers should be derived from that of the arrangement of hydrogen bonding of a O2 with inner NH protons of the isophlorins. 相似文献
106.
The reflection of a pulse by multiple-dielectric layers is treated theoretically. The reflected wave is obtained by expanding the reflection coefficient of an elementary plane wave in a series, including the special case for which total reflection occurs. The pulsed waves reflected by two-dielectric slabs are considered in detail both analytically and numerically. The effect of a carrier frequency of a pulse-modulated carrier wave on the reflected wave form is also discussed. 相似文献
107.
A Necessary and Sufficient Condition for the Existence of a Heterochromatic Spanning Tree in a Graph
Kazuhiro Suzuki 《Graphs and Combinatorics》2006,22(2):261-269
We prove the following theorem. An edge-colored (not necessary to be proper) connected graph G of order n has a heterochromatic spanning tree if and only if for any r colors (1≤r≤n−2), the removal of all the edges colored with these r colors from G results in a graph having at most r+1 components, where a heterochromatic spanning tree is a spanning tree whose edges have distinct colors. 相似文献
108.
Ultrasonic longitudinal velocity and adsorption have been measured in ceramic superconductors YBa2Cu3Oy with various porosity and also in BiSrCaCu2Oy. A velocity drop of about 400 ppm was found at Tc only in the measurements on cooling. The magnitude of the velocity drop is anomalously large compared with the value expected from the thermodynamics. A hysteresis of velocity with respect to temperature was observed in all the samples studied. It is suggested that some structural change at pore size level is responsible for this phenomenon. 相似文献
109.
A. Ikegami Y. Kimura H. Suzuki T. Sato T. Tanigaki O. Kido M. Kurumada Y. Saito C. Kaito 《Surface science》2003,540(2-3):395-400
Titanium carbide formation by the solid–solid reaction on the surface of Ti nanoparticles was studied in situ using a high-resolution transmission electron microscope with a heating stage. The cross-sectional image of the Ti surface was clearly observed. Vacuum-deposited carbon covered the whole the surface of Ti nanoparticles in spite of the partly evaporation on the nanoparticle surface. The diffusion of the carbon atoms inside the Ti nanoparticles depended on the size of the nanoparticles. When the Ti nanoparticle diameter was less than 30 nm, carbon atoms diffused into the Ti nanoparticle and formed TiC. The superstructure of the Ti nanoparticles was observed, which revealed the growth process of TiC to be the diffusion of carbon atoms. For Ti nanoparticles with diameter larger than 30 nm it was observed that diffusion of Ti atoms into the carbon layer was dominant, which resulted in formation of TiC in the carbon layer at the surface of Ti nanoparticles. 相似文献
110.
Kecheng Xiao Hideo Ogawa Hideo Suzuki Yasuo Fukui 《International Journal of Infrared and Millimeter Waves》1998,19(1):15-31
A heterodyne receiver based on a 1/3 reduced height rectangular waveguide SIS mixer with two mechanical tuners has been built for astronomical observations of molecular transitions in the 230 GHz frequency band. The mixer used an untuned array (RnCj3, Rn70 ) of four Nb/AIOx/Nb tunnel junctions in series as a nonlinear mixing element. A reasonable balance between the input and output coupling efficiencies has been obtained by choosing the junction number N=4. The receiver exhibits DSB (Double Side Band) noise temperature around 50 K over a frequency range of more than 10 GHz centered at 230 GHz. The lowest system noise temperature of 38 K has been recorded at 232.5 GHz. Mainly by adjusting the subwaveguide backshort, the SSB (Single Side Band) operation with image rejection of 15 dB is obtained with the noise temperature as low as 50 K. In addition, the noise contribution from each receiver component has been studied further. The minimum SIS mixer noise temperature is estimated as 15 K, pretty close to the quantum limit v/k11 K at 230 GHz. It is believed that the receiver noise temperatures presented are the lowest yet reported for a 230 GHz receiver using untuned junctions. 相似文献