全文获取类型
收费全文 | 480篇 |
免费 | 63篇 |
国内免费 | 112篇 |
专业分类
化学 | 406篇 |
晶体学 | 19篇 |
力学 | 41篇 |
综合类 | 5篇 |
数学 | 59篇 |
物理学 | 125篇 |
出版年
2023年 | 13篇 |
2022年 | 23篇 |
2021年 | 30篇 |
2020年 | 31篇 |
2019年 | 27篇 |
2018年 | 28篇 |
2017年 | 25篇 |
2016年 | 23篇 |
2015年 | 27篇 |
2014年 | 34篇 |
2013年 | 39篇 |
2012年 | 32篇 |
2011年 | 38篇 |
2010年 | 25篇 |
2009年 | 30篇 |
2008年 | 34篇 |
2007年 | 32篇 |
2006年 | 23篇 |
2005年 | 22篇 |
2004年 | 11篇 |
2003年 | 13篇 |
2002年 | 22篇 |
2001年 | 18篇 |
2000年 | 18篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有655条查询结果,搜索用时 15 毫秒
91.
设计了由超大口径前置望远系统和超大视场光谱仪组成的超大口径高光谱海洋水色仪.前置望远系统采用同轴三反光学系统结构,口径为4 m,视场为0.64°,焦距为21.6 m,波段范围为400~1 000nm.超大视场光谱仪采用改进的Offner结构,视场为240mm,光谱分辨率为10nm.探测器像元尺寸为15μm×15μm,4片探测器交错拼接实现400km幅宽.超大视场光谱仪在400~1 000nm的宽波段内,点列图半径的均方根值均小于3.9μm,静止轨道高光谱海洋水色仪全系统不同波长的MTF在33.3lp/mm处大于0.52,各项指标均满足应用要求. 相似文献
92.
Nana Sun Huayi Jiang Xiaoxu Wang Kaibin Jin 《Journal of Dispersion Science and Technology》2018,39(3):411-422
The effects of the types and contents of surfactants, alkali types and concentrations, oil-water ratios, mixing speeds, and emulsifying temperatures on the rheology of heavy oil-in-water (O/W) emulsions were studied. The experimental results showed that the apparent viscosity increased as the formulated surfactant content increased. The organic/inorganic alkali played a twofold role in the apparent viscosity of the O/W emulsion, promoting the ionization of these interfacial active components and compressing the diffused double layer, the competition of which determined whether the apparent viscosity increased or decreased. With increasing oil-water ratios, the apparent viscosity increased, whereas an increase in the emulsifying temperature resulted in a decrease of the apparent viscosity. When the mixing speed was increased from 500 to 1000?r/min, the apparent viscosity increased. However, the apparent viscosity changed minimally for mixing speeds in the range of 1000–1500?r/min. To further discuss the impacts of these factors on the emulsion rheology and pressure drop, the results of an orthogonal test were analyzed through ANOVA using SPSS software; the pressure drops in the samples were calculated using Matlab software. The results demonstrated that the effects of the oil-water ratios on emulsion viscosity and pressure drop were the most prominent. 相似文献
93.
Weihua Wang Nana Wang Ping Li Yuxiang Bu Xiaoyan Xie Rui Song 《Theoretical chemistry accounts》2008,121(1-2):21-31
The influences of thioketo substitution on the properties of uracil monomer and dimer and their interactions with Zn2+ have been systematically investigated at the B3LYP/6-311+G*level of theory. Those properties include the structural characteristics, acidities, ionization potentials, and singlet–triplet energy gaps of SU monomers and their dimers, where SU=2-thiouracil, 4-thiouracil, and 2,4-dithiouracil, respectively. Computational results suggest that thioketo substitution leads to an increase in the acidities of the N-H groups for both uracil and its dimer, where the N1–H group is still the most acidic site relative to that of N3–H group. However, the opposite behaviors are true for the ionization potentials and the singlet–triplet energy gaps of uracil monomer and its dimer, suggesting that thiouracils are more susceptible to radiation damage relative to the unsubstituted uracil. For uracil and 2-thiouracil, the corresponding triplet excited-state geometries are predicted to be highly nonplanar compared with the planar geometries of the ground state as well as 4-thiouracil and 2,4-dithiouracil upon triplet excitation. As a rule, the intermolecular H-bonds involving the sulfur atom directly have been influenced more significant than those the oxygen atom directly involved for U::U and SU::SU base pairs upon ionization and excitation. Additionally, Zn2+ binding is expected to lead to an increase in the stability of U::U and SU::SU base pairs. 相似文献
94.
95.
96.
97.
Prof. Tong-Xin Liu Xin Wang Shilu Xia Prof. Muqing Chen Mingjie Li Panting Yang Prof. Nana Ma Ziqi Hu Prof. Shangfeng Yang Prof. Guisheng Zhang Prof. Guan-Wu Wang 《Angewandte Chemie (International ed. in English)》2023,62(46):e202313074
Herein, we report divergent additions of 2,2′-diazidobiphenyls to C60 and Sc3N@Ih-C80. In stark contrast to that of the previously reported bis-azide additions, the unexpected cascade reaction leads to the dearomative formation of azafulleroids 2 fused with a 7-6-5-membered ring system in the case of C60. In contrast, the corresponding reaction with Sc3N@Ih-C80 switches to the C−H insertion pathway, thereby resulting in multiple isomers, including a carbazole-derived [6,6]-azametallofulleroid 3 and a [5,6]-azametallofulleroid 4 and an unusual 1,2,3,6-tetrahydropyrrolo[3,2-c]carbazole-derived metallofullerene 5 , whose molecular structures have been unambiguously determined by single-crystal X-ray diffraction analyses. Among them, the addition type of 5 is observed for the first time in all reported additions of azides to fullerenes. Furthermore, unexpected isomerizations from 3 to 5 and from 4 to 5 have been discovered, providing the first examples of the isomerization of an azafulleroid to a carbazole-derived fullerene rather than an aziridinofullerene. In particular, the isomerism of the [5,6]-isomer 4 to the [5,6]-isomer 5 is unprecedented in fullerene chemistry, contradicting the present understanding that isomerization generally occurs between [5,6]- and [6,6]-isomers. Control experiments have been carried out to rationalize the reaction mechanism. Furthermore, representative azafulleroids have been applied in organic solar cells, thereby resulting in improved power conversion efficiencies. 相似文献
98.
99.
Wenxing He Hong Zhang Nana Wang Xiaojun Tan Weihua Wang Ping Li 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(5):1027-1033
The cycloaddition reaction mechanisms between interstellar molecule ketenimine and unsaturated hydrocarbon (ethyne and ethylene) have been systematically investigated employing the second-order Møller-Plesset perturbation theory (MP2) method. Geometry optimizations and vibrational analyses have been performed for the stationary points on the potential energy surfaces of the system. The calculated results show that it can be produced the five-membered cyclic carbene intermediates through pericyclic reaction processes between ketenimine and ethyne (or ethylene). For the reaction between ketenimine and ethyne, through the following H-transferred processes, carbene intermediate can be isomerized to the pyrrole compounds. For the reaction between ketenimine and ethylene, carbene intermediate can be isomerized to the pyrroline compounds. The present study is helpful to understand the reactivity of nitrogenous cumulene ketenimine and the formation of prebiotic species in interstellar space. 相似文献
100.