全文获取类型
收费全文 | 323篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
化学 | 212篇 |
晶体学 | 1篇 |
力学 | 12篇 |
数学 | 6篇 |
物理学 | 98篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 7篇 |
2014年 | 18篇 |
2013年 | 27篇 |
2012年 | 13篇 |
2011年 | 22篇 |
2010年 | 12篇 |
2009年 | 9篇 |
2008年 | 12篇 |
2007年 | 10篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 9篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有329条查询结果,搜索用时 15 毫秒
171.
Schiff bases are the most widely used versatile ligands, able to coordinate many elements and to stabilize them in various oxidation states. Recently, this class of compounds has been employed as models for biological systems, and in control of stereochemistry in six-coordinate transition metal complexes. Recently, the chemistry of organotin(IV) complexes of Schiff bases has also stemmed from their antitumour, antimicrobial, antinematicidal, anti-insecticidal and anti-inflammatory activities. Furthermore, organotin(IV) complexes of Schiff bases present a wide variety of interesting structural possibilities. Both aliphatic and aromatic Schiff bases in their neutral and deprotonated forms have been used to yield adducts and chelates with variable stoichiometry and different modes of coordination. This critical review (>155 references) focuses upon the chemistry and biological applications of organotin(IV) complexes of Schiff bases reported in the past 15 years. Thermal behavior of these complexes is also discussed. 相似文献
172.
Joshi R Poonam Saini R Guleria S Babu GD Kumari M Gulati A 《Natural product communications》2011,6(8):1155-1158
Volatile flavour components of tea flowers (Camellia sinensis) were isolated by two methods viz. simultaneous distillation extraction (SDE), supercritical fluid extraction (SFE), analyzed by GC and GC/MS and compared with headspace analysis (HS). The composition of the volatile components extracted by the three methods differed considerably. In SFE, phenylethanol (14.7%), linalool (7.9%), (E)-linalool oxide furanoid (3.5%), epoxy linalool (1.6%), geraniol (2.3%) and hotrienol (1.5%) were major components. m-Xylene (2.6%), (E)-linalool oxide pyranoid (5.4%), p-myrcene (5.2%), alpha-cadinol (4.3%) and methyl palmitate (2.9%) were major compounds isolated by SDE. 3-hexenol (2.1%) (E)-4,8-dimethyl-1,3,7-nonatriene (20.9%) and linalool (35.1%) are major components in headspace analysis. Acetophenone and pheromone germacrene D is detected in tea flowers by all the methods studied. Floral, fresh and fruity odour of tea flowers is retained by SFE as there is very little loss of heat sensitive volatiles in SFE. The flavour isolated from SFE has superior quality compared to SDE. 相似文献
173.
Sunil K. Jangra Neeti Saini J. S. Yadav Dimple Sharma V. K. Sharma 《Journal of solution chemistry》2011,40(6):1055-1066
Excess molar volumes, V123EV_{123}^{\mathrm{E}}, of 1,3-dioxolane or 1,4-dioxane (1) + aniline (2) + benzene or toluene (3) ternary mixtures have been determined over the
entire mole fraction range at 308.15 K. V123EV_{123}^{\mathrm{E}} data have been fitted to the Redlich-Kister equation to evaluate ternary adjustable parameters and standard deviations. The
observed V123EV_{123}^{\mathrm{E}} data have been analyzed in terms of (i) Graph theory, (ii) Prigogine-Flory-Patterson theory, and (iii) Sanchez and Lacombe
theory. It has been observed that V123EV_{123}^{\mathrm{E}} values predicted by Graph theory compare well with the corresponding experimental values. 相似文献
174.
Abstract Radiolytic oxidation of Pu(VI) to Pu(VII) in 1M NaOH solution has been investigated in presence of K2S2O8. The radiolytic yield of Pu(VII), G[Pu(VTI)], has been found to depend both on the concentrations of Pu(VI) and K2 S2O8., The maximum value of G [Pu(VII)] =4.0 has been obtained in solution containing 5.1 × 10?4 M Pu(VI) and 7. 0 × 10?2 M K2S2O8. 相似文献
175.
G. Campi D. Di Castro G. Bianconi S. Agrestini N.L. Saini H. Oyanagi 《Phase Transitions》2013,86(7-8):927-933
Here we report the evidence of a disorder-to-order photo-induced phase transition (PIPT) under X-ray (h x = 12.4 keV) illumination in oxygen doped La 2 CuO 4 + i . The commensurate striped polaron crystalline phase is induced by the irradiation of X-rays in a cuprate perovskite at hole doping i ¨ 1/8 and high Cu-O micro-strain, k >7%. The nucleation of long range crystalline phases of holes on the oxygen 2 p x,y orbitals in the CuO 2 plane associated with pseudo Jahn Teller local lattice distortions (LLD) is favored by mobile counter-ions (interstitial oxygen ions in the La 2 O 2 layer) in the temperature range 200-350 K. The PIPT appears beyond a threshold dose of 10 17 photons/cm 2 at 220 K and a power law of the polaron crystal growth is observed as a function of the X-ray illumination dose. 相似文献
176.
Computing Eigen value equation and modal dispersion characteristics of an elliptical Bragg waveguide
Using the method of separation of variables in the elliptical coordinate system, a recursive formula for the electromagnetic fields in a new type of Bragg waveguide having elliptical core cross section with multilayered cladding is derived. The eigen equation is written in the form of Mathieu and the modified Mathieu functions and a dispersion relation is obtained for various modes supported by the proposed Bragg waveguide. The cutoff frequencies for several lower order even-odd modes have been calculated and their propagation characteristics are plotted. The results show that the dispersion curves are discontinuous and modes can exist only in particular wavelength bands. The effects of elliptical eccentricity on the mode cutoff values and mode transmission are addressed. Finally, the modal birefringence in the said waveguide is also estimated. 相似文献
177.
Gaurav Saini Landon A. Wiest David Herbert Katherine N. Biggs Andrew Dadson Michael A. Vail Matthew R. Linford 《Journal of chromatography. A》2009,1216(16):3587-3593
In spite of advances in solid-phase extraction (SPE) technology there are certain disadvantages to current SPE silica-based, column packings. The pH range over which extraction can occur is limited and each column is generally only used once. New diamond-based reversed SPE phases (C18, C8, and perfluorinated) were developed in our laboratories. Studies were done which show that these phases do not have the same limitations as traditional silica-based stationary phases. The synthesis and properties of these diamond-based phases are presented, and the stability, percent recovery, and column capacity are given for the C18 phase. 相似文献
178.
A quantum mechanical theory of the rate of excitation energy transfer from a fluorescent dye molecule to the surface plasmonic modes of a spherical metal nanoparticle is presented. The theory predicts the distance dependence of the transfer rate to vary as 1/d(sigma), with sigma=3-4 at intermediate distances, in partial agreement with the recent experimental results. F?rster's 1/d(6) dependence is recovered at large separations. The predicted rate exhibits nontrivial nanoparticle size dependence, ultimately going over to an asymptotic, a(3) size dependence. Unlike in conventional fluorescence resonance energy transfer, the orientational factor is found to vary between 1 and 4. 相似文献
179.
Summary: Two novel conjugated isomeric hexathiophenes 6T1 and 6T2 bearing 5-methyl-2-thienyl substituents have been synthesized by Suzuki coupling and oxidative dimerization method. These isomers were characterized by 1H NMR, 13C NMR, elemental and mass analysis. The two hexamers show good solubility in common solvents and show almost identical UV-vis absorption spectra in solution with a maximum cantered at 387 nm. These materials bearing thienyl substituents in the sidechain are anticipated to provide better charge transport in devices and hold promise for use in organic field effect transistors. 相似文献
180.
Jianlin Xu Haibo Tan Yuchan Chen Saini Li Heng Guo Zilei Huang Haohua Li Xiaoxia Gao Hongxin Liu Weimin Zhang 《中国化学快报》2019,30(2):439-442
Lithocarpinols A(1) and B(2), a pair of tenellone diastereoisomers with novel fused skeleton were isolated from the deep-sea derived fungus Phomopsis lithocarpus FS508. Their structures were elucidated by comprehensive spectroscopic analyses, X-ray diffraction and quantum molecular calculation. Their plausible biogenetic pathway featured an intriguing carbonyl-ene cyclization. Lithocarpinol A exhibited moderate inhibitory effect against HepG-2 and A549 tumor cell lines with IC_(50) values of 9.4 μmol/L and10.9 μmol/L,respectively. 相似文献