全文获取类型
收费全文 | 2368篇 |
免费 | 128篇 |
国内免费 | 92篇 |
专业分类
化学 | 1565篇 |
晶体学 | 23篇 |
力学 | 113篇 |
数学 | 211篇 |
物理学 | 676篇 |
出版年
2023年 | 30篇 |
2022年 | 34篇 |
2021年 | 45篇 |
2020年 | 35篇 |
2019年 | 32篇 |
2018年 | 37篇 |
2017年 | 33篇 |
2016年 | 62篇 |
2015年 | 71篇 |
2014年 | 97篇 |
2013年 | 123篇 |
2012年 | 178篇 |
2011年 | 214篇 |
2010年 | 139篇 |
2009年 | 143篇 |
2008年 | 156篇 |
2007年 | 146篇 |
2006年 | 137篇 |
2005年 | 113篇 |
2004年 | 82篇 |
2003年 | 86篇 |
2002年 | 55篇 |
2001年 | 51篇 |
2000年 | 45篇 |
1999年 | 28篇 |
1998年 | 26篇 |
1997年 | 22篇 |
1996年 | 29篇 |
1995年 | 32篇 |
1994年 | 16篇 |
1993年 | 26篇 |
1992年 | 30篇 |
1991年 | 26篇 |
1990年 | 15篇 |
1989年 | 23篇 |
1988年 | 23篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 10篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有2588条查询结果,搜索用时 15 毫秒
71.
Two fused-ring structures, 6-decyloxy-2-naphthoic acid C10ONA (3) and 6-dodecyloxyisoquinoline IS (8), were synthesized and utilized as proton donor and acceptor moieties to construct a series of simple mesogenic supramolecules. The other complementary hydrogen-bonded (H-bonded) moieties are benzoic acids, thiophenecarboxylic acid and pyridines containing different alkyl chain lengths connected by ether and ester linkages, i.e. 4-alkoxybenzoic acid C n OBA (1), terephthalic acid monoalkyl ester C n COOBA (2), 2,5-thiophenedicarboxylic acid monodecyl ester C10COOTHA (4), 4-alkoxypyridine C n OP (6) and isonicotinic acid alkyl ester C n COOP (7). Several series of simple mesogenic supramolecular dimers were constructed from 1:1 molar ratios of proton donors (C n OBA, C n COOBA, C10ONA and C10COOTHA) and proton acceptors (IS, C n OP and C n COOP), though the proton acceptor C n COOP induced phase separation in all complexes. In order to investigate their fused-ring and linking group effects on the mesogenic properties of the H-bonded complexes, analogous simple supramolecular structures are compared. Supramolecular architecture and the distinct mesomorphism of these simple H-bonded liquid crystalline materials were confirmed by polarizing optical microscopy, DSC and powder X-ray diffraction experiments. 相似文献
72.
Cheng‐Hua Lee Meng‐Rong Tsai Yen‐Tzu Chang Prof. Dr. Long‐Li Lai Dr. Kuang‐Lieh Lu Dr. Kung‐Lung Cheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10573-10579
Three unconventional dendrimers that contained rigid NH? triazine linkages and peripheral tert‐butyl moieties were prepared by using a convergent approach and characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis. Based on a thermogravimetric analysis study, these dendrimers were observed to display thermal stability at about 300 °C. The NH? triazine moiety, which possessed protonated and proton‐free nitrogen sites (like the imidazole unit), displayed the capture of polarizable CO2 molecules through hydrogen‐bond and/or dipole–quadrupole interactions. In addition, the adsorption of various amounts of CO2 and N2 at different pressures suggests that the dendritic pores, which arise from the stacking of the middle co‐planar and rim protuberant dendrimers, G n ‐N~N‐G n (n=1–3), either swell or shrink at high pressure, thus indicating that these dendrimers may have a breathing ability. 相似文献
73.
74.
Chia‐Wei Chu Xiaomin Zhai Chih Jie Lee Po‐Hao Wang Yubo Duan Din Ping Tsai Baile Zhang Yuan Luo 《Laser \u0026amp; Photonics Reviews》2015,9(4):399-404
Transformation optics, a recent geometrical design strategy of light manipulation with both ray trajectories and optical phase controlled simultaneously, promises an invisibility cloaking device that can render a macroscopic object invisible even to a scientific instrument measuring optical phase. Recent “carpet” cloaks have extended their cloaking capability to broadband frequency ranges and macroscopic scales, but they only demonstrated the recovery of ray trajectories after passing through the cloaks, while whether the optical phase would reveal their existence still remains unverified. In this paper, a phase‐preserved macroscopic visible‐light carpet cloak is demonstrated in a geometrical construction beyond two dimensions. As an extension of previous two‐dimensional (2D) macroscopic carpet cloaks, this almost‐three‐dimensional carpet cloak exhibits three‐dimensional (3D) invisibility for illumination near its center (i.e. with a limited field of view), and its ideal wide‐angle invisibility performance is preserved in multiple 2D planes intersecting in the 3D space. Optical path length is measured with a broadband pulsed‐laser interferometer, which provides unique experimental evidence on the geometrical nature of transformation optics.
75.
76.
The first principle computational screening was performed to investigate the effect of selected dopants for Li3PS4 sulfide solid electrolyte on its ionic conductivity and stability toward moisture. The results suggest that substitution P5+ using isovalent cations whose electronegativity (EN) value is closer to the value of S has more significant effects on the ionic conductivity, whereby W5+ and Sb5+ can improve most. Similarly, aliovalent cation substitutions with compensating changes in the lithium-ion concentration, particularly those with a lower oxidation state and higher EN, such as Cu2+, effectively enhance the lithium-ion conductivity in this structure. For cation dopants, it is found that ionic conductivity improvement of Li3PS4 is the synergetic effect of EN and oxidation number of the dopant as well as the material's lattice parameter change. Oxides of the considered cation dopants can also improve the ionic conductivity of the material but have much lower lithium-ion conductivity than the cases of cation dopants. However, the metal oxide dopants, particularly those derived from soft Lewis' acid cations, show a marginal improvement in moisture stability of the Li3PS4 electrolyte. The effect of halides and metal halide dopants on the lithium-ion conductivity and moisture stability of Li3PS4 electrolyte are also studied. It is found that metal halides are more effective than any other dopants in improving the ionic conductivity of Li3PS4. 相似文献
77.
Tsai I-Ting M. Merced Montero-Campillo Ibon Alkorta Jos Elguero Manuel Yez 《Molecules (Basel, Switzerland)》2021,26(11)
Intramolecular interactions are shown to be key for favoring a given structure in systems with a variety of conformers. In ortho-substituted benzene derivatives including a beryllium moiety, beryllium bonds provide very large stabilizations with respect to non-bound conformers and enthalpy differences above one hundred kJ·mol−1 are found in the most favorable cases, especially if the newly formed rings are five or six-membered heterocycles. These values are in general significantly larger than hydrogen bonds in 1,2-dihidroxybenzene. Conformers stabilized by a beryllium bond exhibit the typical features of this non-covalent interaction, such as the presence of a bond critical point according to the topology of the electron density, positive Laplacian values, significant geometrical distortions and strong interaction energies between the donor and acceptor quantified by using the Natural Bond Orbital approach. An isodesmic reaction scheme is used as a tool to measure the strength of the beryllium bond in these systems in terms of isodesmic energies (analogous to binding energies), interaction energies and deformation energies. This approach shows that a huge amount of energy is spent on deforming the donor–acceptor pairs to form the new rings. 相似文献
78.
79.
80.
Chao-Qiang Geng Da Huang Lu-Hsing Tsai 《The European Physical Journal C - Particles and Fields》2015,75(11):557
We study the CP-violation effects from two types of neutrino mass matrices with (i) \((M_\nu )_{ee}=0\), and (ii) \((M_\nu )_{ee}=(M_\nu )_{e\mu }=0\), which can be realized by the high-dimensional lepton number violating operators \(\bar{\ell }_R^c\gamma ^\mu L_L (D_\mu \Phi )\Phi ^2\) and \(\bar{\ell }_R^c l_R (D_\mu {\Phi })^2\Phi ^2\), respectively. In (i), the neutrino mass spectrum is in the normal ordering with the lightest neutrino mass within the range \(0.002\,\mathrm{eV}\lesssim m_0\lesssim 0.007\,\mathrm{eV}\). Furthermore, for a given value of \(m_0\), there are two solutions for the two Majorana phases \(\alpha _{21}\) and \(\alpha _{31}\), whereas the Dirac phase \(\delta \) is arbitrary. For (ii), the parameters of \(m_0\), \(\delta \), \(\alpha _{21}\), and \(\alpha _{31}\) can be completely determined. We calculate the CP-violating asymmetries in neutrino–antineutrino oscillations for both mass textures of (i) and (ii), which are closely related to the CP-violating Majorana phases. 相似文献