全文获取类型
收费全文 | 460篇 |
免费 | 28篇 |
专业分类
化学 | 363篇 |
晶体学 | 5篇 |
力学 | 8篇 |
数学 | 21篇 |
物理学 | 91篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 8篇 |
2017年 | 3篇 |
2016年 | 22篇 |
2015年 | 12篇 |
2014年 | 22篇 |
2013年 | 36篇 |
2012年 | 32篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 25篇 |
2008年 | 25篇 |
2007年 | 23篇 |
2006年 | 32篇 |
2005年 | 18篇 |
2004年 | 28篇 |
2003年 | 14篇 |
2002年 | 9篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1998年 | 4篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1970年 | 1篇 |
1966年 | 3篇 |
排序方式: 共有488条查询结果,搜索用时 31 毫秒
41.
42.
43.
The spin torque and zeta force, which govern spin dynamics, are studied by using monoatoms in their steady states. We find nonzero local spin torque in transition metal atoms, which is in balance with the counter torque, the zeta force. We show that d-orbital electrons have a crucial effect on these torques. Nonzero local chirality density in transition metal atoms is also found, though the electron mass has the effect to wash out nonzero chirality density. Distribution patterns of the chirality density are the same for Sc–Ni atoms, though the electron density distributions are different. 相似文献
44.
We have investigated the values of the Rashba spin-orbit coupling constant alpha in In(0.52)Al(0.48)As/In(0.53)Ga(0.47)As/In(0.52)Al(0.48)As quantum wells using the weak antilocalization (WAL) analysis as a function of the structural inversion asymmetry (SIA) of the quantum wells. We have found that the deduced alpha values have a strong correlation with the degree of SIA of the quantum wells as predicted theoretically. The good agreement between the theoretical and experimental values of alpha suggests that our WAL approach for deducing alpha values provides a useful tool in designing future spintronics devices that utilize the Rashba spin-orbit coupling. 相似文献
45.
We propose an electronic spin-filter device that uses a nonmagnetic triple barrier resonant tunneling diode (TB-RTD). This device combines the spin-split resonant tunneling levels induced by the Rashba spin-orbit interaction and the spin blockade phenomena between two regions separated by the middle barrier in the TB-RTD. Detailed calculations using the InAlAs/InGaAs material system reveal that a splitting of a peak should be observed in the I-V curve of this device as a result of the spin-filtering effect. The filtering efficiency exceeds 99.9% at the peak positions in the I-V curve. 相似文献
46.
Measurement Accuracy in Phase-Shifting Point Diffraction Interferometer with Two Optical Fibers 总被引:1,自引:0,他引:1
Toshiaki Matsuura Satoru Okagaki Takaaki Nakamura Yasushi Oshikane Haruyuki Inoue Motohiro Nakano Toshihiko Kataoka 《Optical Review》2007,14(6):401-405
A phase-shifting point diffraction interferometer (PS/PDI) with point sources of two single mode optical fibers has been developed,
which will be appropriate for the surface figure measurement of large aperture optics on a sub-nanometer scale. To reduce
the measurement error factors, a fiber optic plate (FOP) is used as a projection plane for interference pattern. Errors caused
by imperfection of optical alignment, such as position of point sources and tilt of FOP, are minimized by analyzing the measured
phase data with an original method. Measurement accuracy in the PS/ PDI is estimated with the interference pattern produced
by the two optical fiber sources. If inhomogeneity of the FOP and a systematic error of the PS/PDI are eliminated, the measurement
accuracy of the present system is estimated to be less than 4nm P-V and 0.7nm rms, respectively, at a measurement wavelength
of 632.8 nm. 相似文献
47.
Toshinobu Kanai Hiroki Ishibashi. Yoshikazu Hayashi Kunio Oka Takaaki Dohmaru Tatsuo Ogawa Shoji Furukawa Robert West 《Journal of Polymer Science.Polymer Physics》2001,39(11):1085-1092
The thermochromic behavior of poly(di‐n‐octylsilane) {[Si(C8H17)2]n; PDOS} was studied by ultraviolet (UV) absorption, differential scanning calorimetry, and X‐ray diffraction measurements. The structure of PDOS in the low‐temperature phase strongly depended on not only the temperature but also the rate of cooling, that is, the thermal history. Temperature‐dependent UV absorption spectra were highly dependent on thermal hysteresis. Cooled rapidly (10 K/min), PDOS showed two absorption peaks at 3.32 and 3.51 eV in low‐temperature‐ordered phases, whereas a single absorption peak at 3.32 eV became predominant with slow cooling (0.3 K/min). The appearance of the two peaks at low temperatures suggested that a mixture of different conformations was introduced by rapid cooling. A fiber diffraction pattern measured at 240 K after rapid cooling also showed evidence of the existence of novel conformation. A temperature‐dependent powder X‐ray diffraction pattern changed significantly between 270 and 280 K. Rapid cooling reduced the intensity of the X‐ray diffraction peak in this temperature region. This intensity change was explained by the conformational mixture in the polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1085–1092, 2001 相似文献
48.
Takaaki Horaguchi Eietsu Hasegawa Takahachi Shimizu Kiyoshi Tanemura Tsuneo Suzuki 《Journal of heterocyclic chemistry》1989,26(2):365-369
Cyclohepta[cd]benzofuran 2 was synthesized by heating (5-oxo-5H-benzocyclohepten-4-yloxy)acetic acid 16 with sodium acetate in acetic anhydride or by photocyclization of 16 in acetonitrile. Several reactions of cyclohepta[cd]benzofuran 2 were examined. Protonation of 2 with trifluoroacetic acid occurred at the 2-position to give a tropylium ion 17 . Catalytic hydrogenation of 2 with palladium on charcoal proceeded smoothly to give tetrahydrocyclohepta[cd]benzofuran 18 . The Diels-Alder reaction of 2 with tetracyano-ethylene produced an adduct 19 . Formylation of 2 with phosphorus oxychloride and dimethylformamide occurred easily at the 2-position to afford compound 20 . Cyclohepta[cd]benzofuran 2 has both properties of heptafulvene and benzofuran. 相似文献
49.
Takaaki Horaguchi Kazuhiro Miyazawa Eietsu Hasegawa Takahachi Shimizu Tsuneo Suzuki Kiyoshi Tanemura 《Journal of heterocyclic chemistry》1990,27(4):941-948
A variety of 2,5-dioxacyclohepta[jkl]-as-indacenes 5, 7–14 were synthesized as a new heterocycle by the treatment of diethyl (5,9-dioxobenzocyclohepten-1,4-diyloxy)diacetates 4a-e with potassium hydroxide or sodium hydride in dioxane. The mechanism of furan-ring formation from 4a-e was discussed. 相似文献
50.
Yoshida K Fujikawa T Watanabe Y 《The Journal of the Acoustical Society of America》2011,130(1):135-144
The direction of the secondary Bjerknes force between a free bubble and an attached bubble was experimentally investigated. The behavior of the two bubbles in an ultrasonic standing wave of 27 kHz was observed using an imaging system with a high-speed video camera. It was demonstrated experimentally that the direction of the force reversed at a specific separation distance between the two bubbles, which was defined as the threshold distance. The threshold distance changed with the radius of the attached bubble. In addition, a theoretical calculation was performed using a previously derived model that coupled the vibrations of two free bubbles [Ida, Phys. Lett. A 297, 210-217 (2002)]. The experiment data for the threshold distance qualitatively agreed with the theoretical predictions, except when the separation distance was very small. Then, it was discovered that the free bubble became trapped near the attached bubble when the separation distance between the two bubbles was very small. This indicated that a stable equilibrium point for the separation distance exists that cannot be predicted by the theoretical model. 相似文献