全文获取类型
收费全文 | 1277篇 |
免费 | 31篇 |
国内免费 | 9篇 |
专业分类
化学 | 807篇 |
晶体学 | 7篇 |
力学 | 88篇 |
数学 | 148篇 |
物理学 | 267篇 |
出版年
2022年 | 26篇 |
2021年 | 19篇 |
2020年 | 7篇 |
2019年 | 16篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 25篇 |
2015年 | 15篇 |
2014年 | 33篇 |
2013年 | 54篇 |
2012年 | 72篇 |
2011年 | 92篇 |
2010年 | 39篇 |
2009年 | 63篇 |
2008年 | 79篇 |
2007年 | 61篇 |
2006年 | 70篇 |
2005年 | 67篇 |
2004年 | 35篇 |
2003年 | 44篇 |
2002年 | 38篇 |
2001年 | 27篇 |
2000年 | 29篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 15篇 |
1996年 | 30篇 |
1995年 | 17篇 |
1994年 | 14篇 |
1993年 | 23篇 |
1992年 | 21篇 |
1991年 | 23篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 21篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1978年 | 7篇 |
1977年 | 24篇 |
1976年 | 11篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 5篇 |
排序方式: 共有1317条查询结果,搜索用时 0 毫秒
81.
A regular polyhedron is isomorphic to a cluster on which every face has same number of bonds and every atom has an equal number of coordinating atoms. A general strategy for generating the eigenvectors and the eigenvalues of regular polyhedra is given. Not sign analyses are also performed on the eigenvectors of regular polyhedra. The results provide us a quick way to grasp the topological feature of the electronic structure of clusters having interesting topology. 相似文献
82.
The crystal and molecular structures of three sydnone derivatives are reported. The compound 3-cyclohexylsydnone crystallizes in space group C2/c of the monoclinic system with sixteen molecules in a cell of dimensions a = 19.326 (3), b = 9.471 (2), c = 20.005 (4)Å, β = 106.85(1)°. The structure has been refined to a final value of 0.0581 for the conventional R-factor based on 2222 independent observed intensities. Form I of 3-(3-pyridyl)sydnone crystallizes in space group P2/n of the monoclinic system with eight molecules in a cell of dimensions a = 7.317(2), b = 9.283 (2), c = 20.891 (6) Å, β = 99.61(2)°. The structure has been refined to a final value of 0.0514 for the conventional R-factor based on 1208 independent observed intensities. Form II of 3-(3-pyridyl)sydnone crystallizes in space group P21/c of the monoclinic system with eight molecules in a cell of dimensions a=9.073 (2), b = 22.267 (5). c = 7.494(2)Å, β = 112.15 (2)°. The structure has been refined to a final value of 0.0462 for the conventional R-factor based on 1330 independent observed intensities. Each of the three structures contains two crystallographically independent molecules in the cell. In the case of 3-cyclohexylsydnone, one of the independent molecules exhibits disorder around the exocyclic bond at N(3). A comparison of bond lengths indicates that the (electron donating) cyclohexyl group brings about enhanced electron density in the N(3)-C(4) bond, and possibly in the N(3)-N(2) bond. All three structures studied here exhibit intermolecular hydrogen bonding involving C(4)-H(4)…O(6) interactions. Although there are no stacking interactions in the cyclohexyl derivative, there is evidence for such interactions in the 3-pyridyl derivatives. 相似文献
83.
Jwu-Ting Chen Yu-Sung Yeh Wen-Hwa Tzeng Tsang-Miao Huang Ming-Chu Cheng Geen-Hsiang Lee Yu Wang 《中国化学会会志》1991,38(6):573-580
Treatment of trans-Pt(COCOPh)(Cl)(PPh3)2 (1a) with AgBF4in THF led to the formation of a metastatic complex trans-[Pt(COCOPh)(THF)(PPh3)2](BF4) (2) which readily underwent ligand substitution to give a cationic aqua complex trans-[Pt(COCOPh)(OH2)(PPh3)2](BF4) (5a). Complex 5a has been characterized spectroscopically and crystallographically. Analogous reaction of trans-Pt(COCOOMe)(Cl)(PPh3)2 (1b) with Ag(CF3SO3) in dried CH2C12 was found first to yield a methoxyoxalyl triflato complextrans-Pt(COCOOMe)(OTf)(PPh3)2 (6). Attempts to crystallize the triflato product in CH2-cl2hexane under ambient conditions also afforded an aqua complex of the triflate salt f/wu-[Pt(COCOOMe)(OH2)(PPhj)2](CF3SO3) (5b). Complex 5a in a noncoordinating solvent such as CH2C12 or CHCl3 suffered spontaneous decarbonylation to form first cis-[Pt(COPh)(CO)(PPh3)2l(BF4) (3a) then the thermodynamically stable isomer trans-[Pt(COPh)(CO)(PPh3)2](BF4) (3b). Crystallization of complex 3b under ambient conditions resulted in an aqua benzoyl complex trans-[Pt(COPh)(OH2)(PPh3)2](BF4) (7). The replacement of the H2O ligand in complex 7 by CO was done simply by bubbling CO into the solution of 7. The single crystal structures of 5b and 7 have been determined by X-ray diffraction. The distances of the Pt-O bonds in 5a, 5b, and 7 support that the aqua ligand is a weak donor in such cationic aquaorganoplatinum(lI) complexes, in agreement with their lability to the substitution reactions. 相似文献
84.
B. K. Wagner P. E. Garrett Minfang Yeh S. W. Yates 《Journal of Radioanalytical and Nuclear Chemistry》1997,219(2):217-220
The first excited state of137Ba has been excited by the inelastic scattering of accelerator-produced neutrons. The energy of this state at 283.5 keV is not in agreement with the generally accepted value of 279.2 keV, but is in accord with other recent measurements. No evidence for a doublet of states near this energy is found. 相似文献
85.
Chemistry of Natural Compounds - A novel cyclopropanoid, 4-(2-(benzo[d][1,3]dioxol-5-yl)cyclopropoxy)-2,6-dimethoxyphenol (1) was isolated from the stems of Cinnamomum osmophloeum (Lauraceae). The... 相似文献
86.
Kai‐Hsuan Hsieh Chih‐Ying Hsu I‐Ju Hung Chih‐Ling Yeh Yau‐Hung Chen Chien‐Chung Cheng 《中国化学会会志》2021,68(1):34-38
Liposomes composed of cell‐penetrating peptide derivatives increased transport across the cell membrane. Conjugating rhodamine to a cell‐penetrating peptide increased the toxicity of rhodamine in E. coli and zebrafish embryos. A similar total protein inhibition pattern with different intensities, indicating that the interaction pathways of the rho‐KTTKS‐CONH2 monomer and liposomes were the same. It suggests that the rho‐KTTKS‐CONH2 liposomes showed higher toxicity because better transport across the cell membrane increased the effective concentration inside cells. The staining of zebrafish embryos using rho‐KTTKS‐CONH2 liposomes showed a longer retention time, suggesting that it can penetrate deeper tissues or organs in zebrafish. 相似文献
87.
A sensitive spectrophotometric method was developed for the determination of zirconium in monazite sand. The zirconium ion was previously separated from the other interfering elements by a 0.5 M thenoyltrifluoroacetone (TTA)-xylene extraction, then determined with Arsenazo III in 9 M HCl medium. Zirconium reacted with Arsenazo III to form an emeraled green coloured complex having maximum absorbance at 665 nm in 9 M HCl medium. The color was stable for at least 2 hours. Effects of time, HCl concentration, gelatine and various ions have been studied. The system confirms the Beer's law over the concentration range investigated. Optimum condition range for measurement in 1.0 cm quartz cell is 0.1–0.5 μg/ml of zirconium. The molar absorptivity is 1.51×105 liter mole?1 cm?1. The metal-ligand ratio of 1:4 was confirmed by Job's Continuous Variation method and the conditional stability constant of Zirconium-Arsenazo III Complex in 4 M HCl and 9 M HCl were also determined by this method. 相似文献
88.
Methane decomposition over metal oxides/SiO2 surface was investigated. At 1400 K obtained product distribution of this decomposition varied with metal oxide used. The effectiveness of these catalysts has been discussed in terms of activity and C2 selectivity. ThO2/SiO2 was found to be the most effective catalyst for the catalytic decomposition of methane. Positive catalytic effect of ThO2/SiO2 on the pyrolysis has also been confirmed at 1073 K. At low reaction conversions, ethane and ethylene are found as major products. Yields of ethylene and other unsaturated products are sensitively inhibited by NO impurities in the methane. A reaction mechanism has been proposed to account observed experimental results. 相似文献
89.
Prof. Chien-Wei Chu Amalia Rizki Fauziah Prof. Li-Hsien Yeh 《Angewandte Chemie (International ed. in English)》2023,62(26):e202303582
The design of ion-selective membranes is the key towards efficient reverse electrodialysis-based osmotic power conversion. The tradeoff between ion selectivity (output voltage) and ion permeability (output current) in existing porous membranes, however, limits the upgradation of power generation efficiency for practical applications. Thus, we provide the simple guidelines based on fundamentals of ion transport in nanofluidics for promoting osmotic power conversion. In addition, we discuss strategies for optimizing membrane performance through analysis of various material parameters in membrane design, such as pore size, surface charge, pore density, membrane thickness, ion pathway, pore order, and ionic diode effect. Lastly, a perspective on the future directions of membrane design to further maximize the efficiency of osmotic power conversion is outlined. 相似文献
90.
Lin CC Yeh YC Yang CY Chen CL Chen GF Chen CC Wu YC 《Journal of the American Chemical Society》2002,124(14):3508-3509
The synthesis, characterization and biological application of mannose encapsulated gold nanoparticles (m-AuNP) are reported. m-AuNP is well dispersed and very stable without aggregation in the media of broad ion strength and pH ranges. The selective binding of m-AuNP to the mannose adhesin FimH of bacterial type 1 pili is demonstrated using transmission electron microscopy. The competition assay with free mannose suggests that m-AuNP binds FimH better than free mannose does. This work demonstrates that carbohydrate attached nanoparticles can be used as an efficient affinity label and a multi-ligand carrier in a biological system. 相似文献