全文获取类型
收费全文 | 329篇 |
免费 | 8篇 |
国内免费 | 3篇 |
专业分类
化学 | 231篇 |
晶体学 | 2篇 |
力学 | 9篇 |
数学 | 46篇 |
物理学 | 52篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 14篇 |
2020年 | 2篇 |
2019年 | 9篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 25篇 |
2012年 | 20篇 |
2011年 | 22篇 |
2010年 | 9篇 |
2009年 | 19篇 |
2008年 | 22篇 |
2007年 | 24篇 |
2006年 | 20篇 |
2005年 | 17篇 |
2004年 | 14篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1962年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有340条查询结果,搜索用时 15 毫秒
51.
Analysis of phenolic compounds in extra virgin olive oil by using reversed-phase capillary electrochromatography 总被引:1,自引:0,他引:1
In this work, the simultaneous separation of ten phenolic compounds (protocatechuic, p-coumaric, o-coumaric, vanillic, ferulic, caffeic, syringic acids, hydroxytyrosol, tyrosol and oleuropein) in extra virgin olive oils (EVOOs) by isocratic RP CEC is proposed. A CEC method was optimized in order to completely resolve all the analyzed compounds by studying several experimental parameters. The influence of the stationary phase type (C(18) and C(8) modified silica gel), buffer concentration and pH as well as the organic modifier content of the mobile phase on retention factors, selectivity and efficiency were evaluated in details. A capillary column packed with Cogent bidentate C(18) particles for 23 cm and a mobile phase composed by 100 mM ammonium formate buffer pH 3/H(2)O/ACN (5:65:30 v/v/v) allowed the baseline resolution of the compounds under study in less than 35 min setting the applied voltage and temperature at 22 kV and 20 degrees C, respectively. A study, evaluating the intra- and interday precision as well as LOD and LOQ and method linearity was developed in accordance with the analytical procedures for method validation. LODs were in the range of 0.015-2.5 microg/mL, while calibration curves showed a good linearity (r(2) >0.997). The CEC method was applied to the separation and determination of these compounds in EVOO samples after a suitable liquid-liquid extraction procedure. The mean recovery values of the studied compounds ranged between 87 and 99%. 相似文献
52.
Gas chromatographic (GC) analysis in solution and head space solid-phase microextraction (SPME)-GC analysis of a sample of crude oil gave different results. The SPME technique allowed the identification of a larger number of components than by using usual GC-mass spectrometry (MS). The method failed within the range of C14-C25 where GC-MS in solution allowed to obtain more representative results; on the contrary, SPME allowed to obtain data on the presence of volatile compounds that can not be identified in GC-MS analysis in solution. Furthermore, in the range C8-C12, SPME allowed to identify approximately 30 compounds not shown in the GC-MS analysis in solution. SPME analysis showed the presence of some alkenes not identified in GC-MS analysis in solution. SPME-GC-MS can be used in the analysis of crude oil in contaminated soil. 相似文献
53.
Vanderah DJ Walker ML Rocco MA Rubinson KA 《Langmuir : the ACS journal of surfaces and colloids》2008,24(3):826-829
Self-assembled monolayers (SAMs) of the disulfide [S(CH2CH2O)6CH3]2 ([S(EO)6]2) on Au from 95% ethanol and from 100% water are described. Spectroscopic ellipsometry and reflection-absorption infrared spectroscopy indicate that the [S(EO)6]2 films are similar to the disordered films of HS(CH2CH2O)6CH3 ((EO)6) and HS(CH2)3O(CH2CH2O)5CH3 (C3EO5) at their protein adsorption minima. The [S(EO)6]2 SAMs exhibit constant film thickness (d) of 1.2 +/- 0.2 nm over long immersion times (up to 20 days) and do not attain the highly ordered, 7/2 helical structure of the (EO)6 and C3EO5 SAMs (d = 2.0 nm). Exposure of these self-limiting [S(EO)6]2 SAMs to bovine serum albumin show high resistance to protein adsorption. 相似文献
54.
55.
Birkholz MN Dubrovina NV Jiao H Michalik D Holz J Paciello R Breit B Börner A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(20):5896-5907
Three sets of new and related chiral phospholane and phosphepine ligands have been prepared for Rh-catalyzed enantioselective hydrogenation. The size and substitution pattern of the cyclic monophosphanes were varied. More importantly, the ligands differ in the nature of the heterocyclic group linked to the trivalent phosphorus atom: 2-pyridone or 2-alkoxypyridine. In the corresponding Rh complexes, the pyridone units of two monodentate P ligands can assemble by hydrogen bonding and form chelates. In contrast, synthetic precursors bearing alkoxypyridine appendages are not able to aggregate via intramolecular hydrogen bonds. The nature of self-assembly is dependent on the nature of the P ligand and the solvent used for the hydrogenation (CH2Cl2 vs. MeOH). These features affect the rate of the reaction as well as the enantioselectivity, which varied in the range of 0-99 % ee Complexation studies and DFT calculations were performed to explain these differences. 相似文献
56.
Castelli F Sarpietro MG Rocco F Ceruti M Cattel L 《Journal of colloid and interface science》2007,313(1):363-368
The stability and bioavailability of anticancer agents, such as gemcitabine, can be increased by forming prodrugs. Gemcitabine is rapidly deaminated to the inactive metabolite (2('),2(')-difluorodeoxyuridine), thus to improve its stability a series of increasingly lipophilic gemcitabine prodrugs linked through the 4-amino group to valeroyl, lauroyl, and stearoyl acyl chains were synthesized. Studies of monolayer properties are important to improve understanding of biological phenomena involving lipid/gemcitabine or lipid/gemcitabine derivative interactions. The interfacial behavior of monolayers constituted by DMPC plus gemcitabine or lipophilic gemcitabine prodrugs at increasing molar fractions was studied at the air/water interface at temperatures below (10 degrees C) and above (37 degrees C) the lipid phase transition. The effect of the hydrophobic chain length of gemcitabine derivatives on the isotherm of pure DMPC was investigated by surface tension measurement, and the results are reported as molar fractions as a function of mean molecular area per molecule. The results show that the compounds interact with DMPC producing mixed monolayers that are subject to an expansion effect, depending on the prodrug chain length. The results give useful hints of the interaction of these prodrugs with biological membranes and increase knowledge on the incorporation site of such compounds, as a function of their lipophilicity, in a lipid carrier; they may lead to improved liposomal formulation design. 相似文献
57.
G. Fischfeld A. Affranchino A. Di Loreto C. Rocco 《Crystal Research and Technology》2004,39(10):920-925
The results obtained for the r63 electro‐optic coefficient of B‐doped and undoped KDP (KH2PO4) crystals irradiated with neutrons (including thermalized neutrons) produced by scattering of 30 Mev cyclotron protons on a target of Ta201, are presented and compared to those obtained for non‐irradiated doped and undoped crystals. The B‐doped (H3BO3, Na2B4O7 and Li2B4O7) crystals were obtained by the conventional growth method by temperature decrease with 1 wt % dopant concentration in solution. The thermal neutron flux was around ϕ = 1. 1010 n/cm2 s. Pulses of ∼15 μs long, in damped oscillatory mode (V= 8 kV, τ=1.95 μs) were used for the electro‐optic measurements. A Pockels cell, a photomultiplier, a He‐Ne laser (λ=632.8 nm, 5 mW, linearly polarized) and a Tk 720 A oscilloscope complete the experimental setup. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
58.
H.O. Di Rocco D.I. Iriarte J.A. Pomarico 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(1):19-26
In this work we make an experimental and theoretical investigation of transition probabilities (A) and lifetimes of Xe II. Eighteen Aij's corresponding to the 6p-6d array were measured using a Laser Produced Plasma (LPP) as the spectroscopic source. The ab initio (AI) and Least Square Fitting (LSF) approaches were used to calculate the atomic parameters. Relativistic corrections and
Configuration Interaction (CI) effects have been taken into account using the HFR approach described by Cowan. Whereas the
AI parameters corresponding to 6p levels are not very affected by CI effects, several of the 6d levels with J=1/2, 3/2and 5/2 making transitions to the fundamental levels 5p5
are affected by CI effects due to both, discrete nd and continuum states, modifying their lifetimes values. An extensive comparison with other measurements and calculations are made. In particular,
concerned with branching ratio and forbidden transitions.
Received 15 July 1999 相似文献
59.
60.
Dr. Gert Kiss Dr. Nihan Çelebi‐Ölçüm Dr. Rocco Moretti Prof. Dr. David Baker Prof. Dr. Dr. K. N. Houk 《Angewandte Chemie (International ed. in English)》2013,52(22):5700-5725
Recent developments in computational chemistry and biology have come together in the “inside‐out” approach to enzyme engineering. Proteins have been designed to catalyze reactions not previously accelerated in nature. Some of these proteins fold and act as catalysts, but the success rate is still low. The achievements and limitations of the current technology are highlighted and contrasted to other protein engineering techniques. On its own, computational “inside‐out” design can lead to the production of catalytically active and selective proteins, but their kinetic performances fall short of natural enzymes. When combined with directed evolution, molecular dynamics simulations, and crowd‐sourced structure‐prediction approaches, however, computational designs can be significantly improved in terms of binding, turnover, and thermal stability. 相似文献