全文获取类型
收费全文 | 256篇 |
免费 | 71篇 |
国内免费 | 9篇 |
专业分类
化学 | 160篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 32篇 |
物理学 | 117篇 |
无线电 | 25篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 13篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 19篇 |
2012年 | 26篇 |
2011年 | 23篇 |
2010年 | 11篇 |
2009年 | 8篇 |
2008年 | 12篇 |
2007年 | 10篇 |
2006年 | 12篇 |
2005年 | 9篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1996年 | 3篇 |
1994年 | 2篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1966年 | 2篇 |
1965年 | 10篇 |
1964年 | 7篇 |
1963年 | 5篇 |
1961年 | 3篇 |
1960年 | 1篇 |
1959年 | 14篇 |
1958年 | 5篇 |
1956年 | 1篇 |
1955年 | 5篇 |
1954年 | 2篇 |
排序方式: 共有336条查询结果,搜索用时 531 毫秒
91.
Yoshiharu Terui Sho‐Ichi Matsuda Shinji Ando 《Journal of Polymer Science.Polymer Physics》2005,43(15):2109-2120
Degrees of orientation of main chains and imide rings were quantitatively estimated for spin‐coated films of six kinds of aromatic polyimides (PIs) using polarized attenuated total reflection (ATR)/Fourier transform infrared (FT‐IR) spectroscopy. The degrees of chain orientation parallel to the film planes are significantly larger for the PIs having rigid structures than those having flexible structures, and the introduction of side groups decrease the degrees of chain orientation. In contrast, the rotational orientations of imide rings are almost isotropic for all PI films. Moreover, the film thickness dependences of the degrees of orientation were investigated for two kinds of rigid‐rod PIs having bulky trifluoromethyl ( CF3) side groups in their diamine moieties. The degrees of chain orientation slightly decrease as the film thickness increases, whereas the rotational orientation of imide rings is independent of the film thickness. The degrees of chain orientation on the substrate sides significantly differ from the atmospheric sides of PI films. This difference was generated during thermal imidization because of tensile stress originated from the mismatch in thermal expansion coefficients between the substrates and the PI films. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2109–2120, 2005 相似文献
92.
Dr. Masahiro Ikeshita Sho Furukawa Takahiro Ishikawa Kana Matsudaira Prof. Dr. Yoshitane Imai Prof. Dr. Takashi Tsuno 《ChemistryOpen》2022,11(4):e202100277
The relationship between the coordination geometry and photophysical properties of trans-bis[(β-iminomethyl)naphthoxy]platinum(II) was investigated both experimentally and theoretically. A series of platinum(II) complexes with differently substituted iminomethyl groups were synthesized, and their photophysical properties were examined in solution, in the crystalline, and in the PMMA film-dispersed state, respectively (PMMA=poly(methyl methacrylate)). These complexes showed structure-dependent emission spectra, in which the color of the luminescence in the crystalline state varied over a range of about 40 nm depending on the specific bowl-shaped molecular structure. The chiral complexes with (R,R)- and (S,S)-configurations were found to have structure-dependent chiroptical properties both in solution and the PMMA film-dispersed state such that the intensity of circular dichroism (CD) and circularly polarized luminescence (CPL) were enhanced with bulky cyclic substituents at the nitrogen atoms. A theoretical study using density functional theory (DFT) and time-dependent (TD)-DFT calculations revealed that the enhancement of chiroptical responses is due to the amplification of the magnetic dipole moment caused by the distortion of the square planar geometry. 相似文献
93.
Let R = K[x
1, x
2, x
3, x
4] be the polynomial ring over a field of characteristic zero. For the ideal (x1a, x2b, x3c, x4d) ì R{(x_1^a, x_2^b, x_3^c, x_4^d) \subset R}, where at least one of a, b, c and d is equal to two, we prove that its generic initial ideal with respect to the reverse lexicographic order is the almost revlex
ideal corresponding to the same Hilbert function. 相似文献
94.
95.
Dr. Masahiro Yamashina Sho Matsuno Dr. Yoshihisa Sei Prof. Dr. Munetaka Akita Dr. Michito Yoshizawa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14147-14150
The methyl group is a small substituent, usually showing relatively weak or no interactions with other functional groups and metal ions. Herein, we present the recognition of the number of methyl groups on synthetic and natural aromatic compounds (i.e., benzene and xanthine derivatives, respectively) by the 1 nm‐sized polyaromatic cavity of a coordination capsule in water. Detailed competitive encapsulation experiments as well as X‐ray crystallographic analysis revealed that multiple guest–host CH3–polyaromatic interactions in the confined nanospace are key driving forces for the high selectivity. 相似文献
96.
Kimura H Kanesaka S Kuroki S Ando I Asano A Kurosu H 《Magnetic resonance in chemistry : MRC》2005,43(3):209-216
The structure of poly(diethylsiloxane) (PDES) has been characterized using solid-state NMR of (17)O. The sample studied had a weight-average molecular weight of 2.45 x 10(5). The sample was prepared by utilizing the cationic ring-opening polymerization of (17)O-enriched hexacyclotrisiloxane. Solid-state NMR of (17)O-enriched PDES was measured on the low-temperature beta(1) phase, the high-temperature beta(2) phase, the two-phase system consisting of the liquid crystal and isotropic liquid phase and the isotropic phase. From these data, the molecular structure and dynamics of PDES in the various phases were characterized via the chemical shifts of (17)O, and electric field gradient parameters were determined from NMR and ab initio molecular orbital (MO) calculations. In addition to the solid-state NMR of (1)H, (13)C and (29)Si previously reported on these samples, knowledge of the dynamic behavior of PDES as inferred from the NMR of (17)O in the present study was enhanced significantly. Further, the potential of combining the experimental NMR of (17)O with ab initio MO calculations to characterize the dynamics of polymers containing oxygen is demonstrated. 相似文献
97.
X.R. WU M. Hirsch A. Staudt H.V. Klapdor-Kleingrothaus Cheng-Rui CHING Tso-Hsiu HO 《理论物理通讯》1993,20(4):453-460
The half-lives for 2νββ decay for all the potential Pp-emitters with A≥70 are calculated by the operator expansion method. Compared with the directly measured half-lives of 76Ge, 82Se, 100Mo and 238U the theoretical values are in excellent agreement with experimental ones. 相似文献
98.
A new method-the operator expansion method is used in neutrinoless double beta decay processes. Both the neutrino mass and mixing of right-handed leptonic current are included. It is shown that for nuclear neutrinoless double beta decay in 2n mechanism, there appear some new terms besides the terms given by the conventional treatment based on closure approximation. The ββ with a Majoron emission is also discussed. 相似文献
99.
We discuss the problem of microcausality in a model of quantized field theory. Under the assumptions that the commutator of the "in" fields satisfies the requirement of translational invariance, we show that, in the case of self-conjugate scalar particles or particles with integer spins, one can deduce the law of microcausality. 相似文献
100.