全文获取类型
收费全文 | 3837篇 |
免费 | 62篇 |
国内免费 | 20篇 |
专业分类
化学 | 2510篇 |
晶体学 | 50篇 |
力学 | 62篇 |
数学 | 239篇 |
物理学 | 1058篇 |
出版年
2022年 | 24篇 |
2021年 | 23篇 |
2020年 | 41篇 |
2019年 | 47篇 |
2018年 | 32篇 |
2017年 | 30篇 |
2016年 | 51篇 |
2015年 | 66篇 |
2014年 | 63篇 |
2013年 | 209篇 |
2012年 | 168篇 |
2011年 | 199篇 |
2010年 | 114篇 |
2009年 | 131篇 |
2008年 | 199篇 |
2007年 | 220篇 |
2006年 | 214篇 |
2005年 | 176篇 |
2004年 | 129篇 |
2003年 | 132篇 |
2002年 | 150篇 |
2001年 | 98篇 |
2000年 | 110篇 |
1999年 | 70篇 |
1998年 | 41篇 |
1997年 | 43篇 |
1996年 | 66篇 |
1995年 | 46篇 |
1994年 | 34篇 |
1993年 | 45篇 |
1992年 | 70篇 |
1991年 | 44篇 |
1990年 | 44篇 |
1989年 | 41篇 |
1988年 | 61篇 |
1987年 | 46篇 |
1986年 | 51篇 |
1985年 | 62篇 |
1984年 | 63篇 |
1983年 | 30篇 |
1982年 | 42篇 |
1981年 | 37篇 |
1980年 | 41篇 |
1979年 | 43篇 |
1978年 | 36篇 |
1977年 | 43篇 |
1976年 | 24篇 |
1975年 | 33篇 |
1974年 | 31篇 |
1973年 | 24篇 |
排序方式: 共有3919条查询结果,搜索用时 0 毫秒
41.
Masaru Yoshida Masaharu Asano Hideki Omichi Masaharu Miyajima Yasuo Takahashi Hidetoshi Yamanaka Noriyuki Yonezawa Ryoichi Katakai 《Macromolecular theory and simulations》1993,2(3):377-384
The loosely cross-linked poly(acryloyl-L -proline methyl ester) gel, which is known as one of the typical thermo-responsive gels, shows a volume transition around approximately 14°C in pure water. This volume transition is shifted to higher temperature by treatment in aqueous sodium dodecyl sulfate (SDS). The analysis of the swelling-temperature curve (frequency distribution) was performed according to a moment analysis, in which the area under the swelling-temperature curve (AUC), mean swelling transition temperature (MSTT) and variance of swelling transition temperature (VSTT) were calculated. It is shown that the apparent volume transition temperature can be estimated from MSTT and that VSTT can be used to characterize the shape of the corresponding curves. 相似文献
42.
Yasushi Takahashi 《Fortschritte der Physik》1989,37(6):443-464
The transformation of the Euler-Lagrange derivative under the point transformation is explicitly stated, and from this view point, the canonical transformation is reinvestigated. In our arguments, the canonical transformations are discussed strictly separately from the canonical equations. A proof is given that the Lagrangian can be restored after any infinitesimal canonical transformation. Some identities are obtained giving relations between canonically transformed and untransformed Lagrangians. Using the identities, the relation between the Noether charge and the generator of the canonical transformation is investigated. The chiral gauge, Galilei and scale transformations are considered as applications to field theory. 相似文献
43.
N. S. Takahashi Y. Hunyu E. Shibano N. Mochizuki S. Kurita 《Crystal Research and Technology》1993,28(5):711-716
The fabrication and characterization of double-heterostructure (DH) laser that utilizes an indium-tin oxide (Ito) transparent cladding and top contact layer. The first room-temperature lasing operation has been obtained form ITO/InGaAsP/AlGaAs DH laser diode at threshold current density of 12.1 kA/cm2. The interfacial recombination velocity of ITO/InGaAsP Interface was estimated to be 4.9 × 104 cm/s from a simple model to account for high threshold current, and optical measurements of spontaneous emission and lasing spectra from top stripe window and facet were done. 相似文献
44.
45.
An elementary method of conctructing a spinor from vectors satisfying constraint conditions is proposed. We consider orthonormal triad and tetrad as an orientable physical object and introduce parameter representations of them, in terms of the Euler angles and the pseudo-Euler angles. Having determined the transformation property of the parameters, we set up the spinor determining equation. This equation is solved. The solution (spinor) contains four arbitrary complex constants, in 3 + 1 dimensional space. Using the proposed method, we prove the spinor reconstruction theorem, i.e. the original Dirac spinor can be reconstructed from seven of the sixteen hermitian bilinear forms, except the overall phase factor (the gauge freedom of the 1st kind). The energy density of the spinor field is written in terms of currents and their space derivatives. 相似文献
46.
47.
48.
R. Minami A. Kasugai K. Takahashi N. Kobayashi Y. Mitsunaka K. Sakamoto 《International Journal of Infrared and Millimeter Waves》2006,27(1):13-24
A high efficiency launcher of quasi-optical (QO) mode converters for high power gyrotrons have been designed and tested. A
helical cut launcher radiates the RF power via its straight cut onto the first phase correcting mirror. The launchers have
been optimized for the TE31.8 mode at 170 GHz and TE22.6 mode at 110 GHz by numerically optimizing a launcher surface. The helical cut of the launcher has been optimized by taking
the taper angle into account. Further more, the amplitude of the surface perturbation have been optimized for improved focusing
in order to reduce the diffraction losses at the helical cut. Low power measurement shows a good agreement with the design.
High efficiency characteristics of the design have also been calculated on the assumption of frequency downshift due to the
thermal expansion of the cavity and stepwise frequency tuning by changing the operating mode. Besides, the possibility of
high efficiency launcher for higher mode is discussed, and these results give the prospect to high efficiency long pulse gyrotrons. 相似文献
49.
Quantum key distribution (QKD) is being studied as a way to provide unconditionally secure communications. Several experiments have shown its feasibility. However, most experiments have used a point-to-point occupied optical link. In order to use QKD for secure communications on a real network, it is preferable to be able to change parties on demand and to have quantum transmission and ordinary optical transmission share the optical network. In this work, QKD through a silica-based planar lightwave circuit (PLC) 8 × 8 non-blocking matrix switch was investigated. We found that an interferometer type switch can work even for a single-photon-level light and that a multi-user QKD network can be constructed using a silica-based PLC 8 × 8 non-blocking matrix switch. In addition, single-photon-level transmission and ordinary optical transmission can share the same 8 × 8 non-blocking matrix switch, so which shows the possibility of sending quantum signals through current optical networks. 相似文献
50.
Leonardo Puppulin Yasuhito Takahashi Wenliang Zhu Giuseppe Pezzotti 《Journal of Raman spectroscopy : JRS》2011,42(3):482-487
The complex orientation dependence in space of Raman active vibrations in the orthorhombic structure of polyethylene (PE) is discussed in terms of Raman tensor elements as intrinsic physical parameters of the lattice. Building upon the symmetry assignment of these vibrational modes, we systematically studied, from both theoretical and experimental viewpoints, the changes of polarized intensity for the Ag and the B2g + B3g vibrational modes with respect to PE molecular orientation. After explicitly expanding the Raman selection rules associated with the Ag and the B2g + B3g modes, introducing them into general expressions of the orientation distribution function, and validating them by means of a least‐square fitting procedure on experimental data, we compare here two mesostructural models for a highly crystallized and self‐aligned PE fiber structure. Stereological arguments are shown concerning the arrangement of orthorhombic fibrils in such a sample that unfold the correct values of five independent Raman tensor elements for orthorhombic PE. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献