全文获取类型
收费全文 | 1345篇 |
免费 | 32篇 |
国内免费 | 4篇 |
专业分类
化学 | 1038篇 |
晶体学 | 7篇 |
力学 | 10篇 |
综合类 | 1篇 |
数学 | 104篇 |
物理学 | 221篇 |
出版年
2023年 | 10篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 19篇 |
2019年 | 14篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 25篇 |
2014年 | 24篇 |
2013年 | 57篇 |
2012年 | 51篇 |
2011年 | 75篇 |
2010年 | 44篇 |
2009年 | 35篇 |
2008年 | 73篇 |
2007年 | 81篇 |
2006年 | 74篇 |
2005年 | 66篇 |
2004年 | 65篇 |
2003年 | 76篇 |
2002年 | 51篇 |
2001年 | 23篇 |
2000年 | 27篇 |
1999年 | 29篇 |
1998年 | 18篇 |
1997年 | 16篇 |
1996年 | 25篇 |
1995年 | 21篇 |
1994年 | 10篇 |
1993年 | 17篇 |
1992年 | 24篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 16篇 |
1986年 | 9篇 |
1985年 | 23篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1974年 | 9篇 |
排序方式: 共有1381条查询结果,搜索用时 15 毫秒
101.
Masatoshi Miyamoto Toshio Watanabe Yoshiharu Kimura 《Macromolecular rapid communications》1997,18(10):897-902
A bicyclic pseudourea, 2,3,5,6-tetrahydroimidazo[2,1-b][1,3]oxazole ( 1 ), was isolated for the first time, and its cationic and spontaneous polymerizations were examined. Both polymerizations gave poly(1,3-imidazolidin-2-one-1,3-diylethylene) ( 2 ) in high yields. The polymer is a crystalline solid with glass transition and melting temperature of 51°C and 286°C, respectively. Thermogravimetry showed that it is stable up to 450°C under nitrogen. 相似文献
102.
Kazuhiro Watanabe Noboru Akino Tetsuo Aoyagi Noboru Ebisawa Yukio Fujiwara Atsusi Honda Takashi Inoue Takao Itoh Mikito Kawai Minoru Kazawa Junichi Koizumi Masaaki Kuriyama Kenji Miyamoto Naoki Miyamoto Kazuhiko Mogaki Yoshihiro Ohara Tokumichi Ohga Yoshikazu Okumura Hiroshi Oohara Katsumi Ohshima Fujio Satoh Kazuhiko Shimizu Syunji Takahashi Hirotsugu Usami Katsutomi Usui Masahiro Yamamoto Takeshi Yamazaki 《Radiation Physics and Chemistry》1997,49(6):631-639
A negative-ion-based neutral beam injector (N-NBI) has been constructed for JT-60U. The N-NBI is designed to inject 500 keV, 10 MW neutral beams using two ion sources, each producing a 500 keV, 22 A D− ion beam. In the preliminary experiment using one ion source, a D− ion beam of 13.5 A has been successfully accelerated with an energy of 400 keV (5.4 MW) for 0.12 s at an operating pressure of 0.22 Pa. This is the highest D− beam current and power in the world. Co-extracted electron current was effectively suppressed to the ratio of Ie/ID− < 1. The highest energy beam of 460 keV, 2.4 A, 0.44 s has also been obtained. To realize 1 MeV class NBI system for ITER (International Thermonuclear Experimental Reactor), demonstration of ampere class negative ion beam acceleration up to 1 MeV is an important mile stone. To achieve the mile stone, a prototype accelerator and a 1 MV, 1 A test facility called MeV Test Facility (MTF) were constructed. Up to now, an H− ion beam was accelerated up to the energy of 805 keV with an acceleration drain current of 150 mA for 1 s in a five stage electrostatic multi-aperture accelerator. 相似文献
103.
104.
Kyoichi Hanada Juntaro Nogami Prof. Dr. Kazunori Miyamoto Norihiko Hayase Dr. Yuki Nagashima Yusuke Tanaka Dr. Atsuya Muranaka Prof. Dr. Masanobu Uchiyama Prof. Dr. Ken Tanaka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(36):9313-9319
The enantioselective synthesis of aza[6] and [7]helicene-like molecules have been achieved by the cationic rhodium(I)/axially chiral biaryl bisphosphine complex-catalyzed intramolecular [2+2+2] cycloaddition of cyanodiynes. This protocol was successfully applied to the diastereo- and enantioselective synthesis of an S-shaped double aza[6]helicene-like molecule with a high ee value of 89 %. Although no epimerization and racemization were observed in the double carbo[6]helicene-like molecule at 80 °C, epimerization and racemization of the double aza[6]helicene-like molecule proceeded at 80 °C. This double aza[6]helicene-like molecule showed good fluorescent quantum yields and chiroptical responses under both neutral and acidic conditions. 相似文献
105.
Mitsunori Fukaya Shota Nagamine Dr. Taro Ozaki Yaping Liu Miina Ozeki Taro Matsuyama Dr. Kazunori Miyamoto Prof. Dr. Hirokazu Kawagishi Prof. Dr. Masanobu Uchiyama Prof. Dr. Hideaki Oikawa Dr. Atsushi Minami 《Angewandte Chemie (International ed. in English)》2023,62(44):e202308881
Mushroom terpenoids are biologically and chemically diverse fungal metabolites. Among them, melleolides are representative sesquiterpenoids with a characteristic protoilludane skeleton. In this study, we applied a recently established hot spot knock-in method to elucidate the biosynthetic pathway leading to 1α-hydroxymelleolide. The biosynthesis of the sesquiterpene core involves the cytochrome P450 catalyzing stepwise hydroxylation of the Δ6-protoilludene framework and a stereochemical inversion process at the C5 position catalyzed by short-chain dehydrogenase/reductase family proteins. The highlight of the biosynthesis is that the flavoprotein Mld7 catalyzes an oxidation-triggered double-bond shift accompanying dehydration and acyl-group-assisted substitution with two different nucleophiles at the C6 position to afford the Δ7-protoilludene derivatives, such as melleolide and armillarivin. The complex reaction mechanism was proposed by DFT calculations. Of particular importance is that product distribution is regulated by interaction with the cell membrane. 相似文献
106.
Ward S 《OR manager》2002,18(12):1, 12-1, 15
Employees and their work performance determine the success of any business. Permitting verbal abuse and other disruptive behaviors is bad management. Well-written policies, physician champions, strong executives, and the willingness of OR managers to try new approaches to assist the staff to develop new skill sets will help to create healthier workplaces where everyone knows words don't hurt. 相似文献
107.
108.
The memory effect upon glassification is studied in the glass-to-rubber transition of vulcanized rubber with the strain as a controlling parameter. A phenomenological model is proposed, taking the history of the temperature and the strain into account, by which the experimental results are interpreted. The data and the model demonstrate that the glassy state memorizes the time course of strain upon glassification, not as a single parameter but as the history itself. The data also show that the effect of irreversible deformation in the glassy state is beyond the scope of the present model. 相似文献
109.
A multiwavelength, multistripe tunable laser array is proposed, and its application to absorption spectroscopy is demonstrated. Laser waveguides doped with Rhodamine 6 G dye were integrated on a plastic chip, and simultaneous output at different wavelengths was obtained by use of a distributed-feedback technique. A very low threshold of 3 muJ was attained, and spectrally narrowed output (<0.1 nm) was obtained. A scheme for digital spectroscopy is also proposed based on this laser array, and absorption spectroscopy of sodium atoms without wavelength scanning is demonstrated by use of a sodium-vapor cell. 相似文献
110.
The effect of inelastic scattering on the electron reflection in multi-quantum barriers (MQBs) has been examined using the damped resonant tunnelling model for the first time. The electron reflectivity in the virtual barrier region for unstrained GalnAs/InP MQB deteriorates below 100% by about 10% for phase relaxation time of 0.22ps. We propose a strain-compensated GalnAs/GalnP MQB which not only has virtual barrier 4 times as high as that of an unstrained MQB, but whose reflectivity deterioration is reduced to less than 5% in comparison with 10% for unstrained MQB for the same phase relaxation time. We have also successfully grown a Ga0.25In0.75As (1.5% compressive) well/Ga0.25In0.75P (1.2% tensile) barrier short-period superlattice with six wells by chemical beam epitaxy, which exhibits the possibility of fabrication of the strain-compensated MQBs. 相似文献