全文获取类型
收费全文 | 3658篇 |
免费 | 736篇 |
国内免费 | 309篇 |
专业分类
化学 | 3154篇 |
晶体学 | 10篇 |
力学 | 92篇 |
综合类 | 60篇 |
数学 | 686篇 |
物理学 | 701篇 |
出版年
2024年 | 3篇 |
2023年 | 38篇 |
2022年 | 114篇 |
2021年 | 121篇 |
2020年 | 182篇 |
2019年 | 115篇 |
2018年 | 123篇 |
2017年 | 122篇 |
2016年 | 217篇 |
2015年 | 210篇 |
2014年 | 261篇 |
2013年 | 317篇 |
2012年 | 272篇 |
2011年 | 257篇 |
2010年 | 191篇 |
2009年 | 226篇 |
2008年 | 234篇 |
2007年 | 276篇 |
2006年 | 215篇 |
2005年 | 194篇 |
2004年 | 178篇 |
2003年 | 171篇 |
2002年 | 101篇 |
2001年 | 83篇 |
2000年 | 77篇 |
1999年 | 62篇 |
1998年 | 56篇 |
1997年 | 57篇 |
1996年 | 47篇 |
1995年 | 33篇 |
1994年 | 19篇 |
1993年 | 18篇 |
1992年 | 12篇 |
1991年 | 18篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有4703条查询结果,搜索用时 15 毫秒
61.
Polymer colloids based on 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐α‐D ‐glucofuranose (3‐MDG) and butyl acrylate (BA) were prepared via free radical mini‐emulsion polymerization. The kinetic and colloidal features of the copolymerization were investigated. The final particle size (D) of the sugar latexes is inversely proportional to the concentration of the anionic emulsifier (sodium dodecyl sulphate, SDS) and the non‐ionic one (alkyl polyglucoside, APG). It was also found that D is independent of the concentration of either the water‐soluble initiator (potassium persulfate, KPS), or the oil‐soluble initiator (2,2′‐azobisisobutyronitrile, AIBN). The rate of mini‐emulsion polymerization is lower in comparison with the conventional emulsion polymerization under the same conditions. The polymerization rate (Rp) and the total number of particles (Np) are proportional to the 0.72th and 0.93th power of the SDS, and to the 1.40th and 2.22th of the APG concentration. Following reaction orders, 0.79/0.06 were obtained for Rp/Np versus the concentration of KPS, and 0.22/?0.01 for AIBN, respectively. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
62.
苏州荠苧总黄酮与微量元素含量的测定 总被引:1,自引:0,他引:1
采用分光光度法测定了苏州荠芋的总黄酮含量;采用了等离子发射光谱法测定了其元素含量。结果表明,苏州荠芋总黄酮的含量分别为55.31mg/g(7月采收)、65.00mg/g(8月采收);含K、Ca、Mg等多种常量元素;含Cu、Fe、Mn、Zn、Cr、Co等多种人体必需的微量元素,其中Fe含量最高;而有害重金属元素Hg未检出,Pb和AS的含量均较低(小于药典规定量)。可见8月采收的苏荠芋总黄酮含量较高,苏州荠芋含多种人体必需的微量元素,有害重金属含量低,具有较大的开发价值。 相似文献
63.
3-O-Acetyl-1,2-O-isopropylidene--D-allofuranose (2 b) was prepared from 1,2:5,6-di-O-isopropylidene--D-allofuranose (1 b). Treatment of2 b with triphenylphosphine-diethyl azodicarboxylate afforded regio- and stereospecifically the 5,6-epoxy--D-allo derivative (3). The other diastereomeric compound, 5,6-epoxy-1,2-O-isopropylidene--L-talofuranose (6) was also prepared stereoselectively from2 b
via the intermediates5 a and5 b. The epoxy sugars3 and6 were converted with lithium aluminum hydride to the corresponding 6-deoxy-1,2-O-isopropylidene--D-allofuranose (4 a) and --L-talofuranose (7 a) derivatives. Hydrolysis of4 a and7 a afforded 6-deoxy-D-allose and 6-deoxy-L-talose, respectively. The corresponding 3,5-di-O-acetyl- (4 b and7 b) and the 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) derivatives (4 c and7 c) are also described. Selective removal of the isopropylidene group and subsequent acetylation offers a convenient route to prepare sugar derivatives containing furanose ring, like8 b, as a suitable precursor for nucleoside analogs.Herrn Prof. Dr.K. Komarek mit den besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
64.
V. Climent N. García-Araez E. Herrero J. Feliu 《Russian Journal of Electrochemistry》2006,42(11):1145-1160
The electrochemical behavior of platinum single-crystal electrodes is revisited, with special emphasis on the determination
of the potential of zero charge. We show that the measure of the charge displaced during CO adsorption allows the determination
of the potential of zero total charge (PZTC). The estimation of the potential of zero free charge (PZFC) is discussed, with
different degrees of approximation. The application of this methodology to the study of the PZTC of platinum stepped surfaces
vicinal to Pt(111) reveals a marked decrease of the PZTC due to the introduction of surface steps. This effect is interpreted
as the result of the existence of markedly smaller surface potentials localized on step sites. The importance of considering
local aspects of the interface is emphasized with the use of N2O reduction as a sensitive probe to the local structure of the surface. It is proposed that the different local maxima observed
in the absolute value of the reduction current correspond to the local values of PZTC. It is shown that there is, in general,
good agreement between the overall PZTC, obtained from the CO displacement, and that calculated from the local values inferred
from the N2O reduction. Further insight is obtained with the application of the laser-induced temperature jump method. This technique
is useful to calculate the potential of maximum entropy of the double-layer formation. The resulting value of this potential
for Pt(111) is discussed in the light of the PZFC value obtained from different approaches. For stepped surfaces vicinal to
Pt(111), two local maxima in the entropy of the double layer are observed that are close to the local PZTC values estimated
from the N2O reduction. This result suggests the existence of cooperative effects in the organization of the water dipoles close to the
electrode surface.
Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 11, pp. 1275–1292.
Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22,
2005, Moscow.
The text was submitted by the authors in English. 相似文献
65.
Tianle Zhu Jiming Hao Lixin Fu Junhua Li Zhiming Liu 《Reaction Kinetics and Catalysis Letters》2005,84(1):61-67
Summary The cooperation effect of reducing species for selective reduction of NO over Ag/Al2O3 has been investigated in the presence of excess oxygen. When the combinations of propene or propane and ethanol or methanol were used as reducing agents, NO reduction took place over a wider temperature range, compared with a single hydrocarbon as reducing agent. 相似文献
66.
67.
Sorel Tchewonpi Sagu Eva Landgrber Michal Rackiewicz Gerd Huschek Harshadrai Rawel 《Molecules (Basel, Switzerland)》2020,25(24)
Sorghum is of growing interest and considered as a safe food for wheat related disorders. Besides the gluten, α-amylase/trypsin-inhibitors (ATIs) have been identified as probable candidates for these disorders. Several studies focused on wheat-ATIs although there is still a lack of data referring to the relative abundance of sorghum-ATIs. The objective of this work was therefore to contribute to the characterization of sorghum ATI profiles by targeted proteomics tools. Fifteen sorghum cultivars from different regions were investigated with raw proteins ranging from 7.9 to 17.0 g/100 g. Ammonium bicarbonate buffer in combination with urea was applied for protein extraction, with concentration from 0.588 ± 0.047 to 4.140 ± 0.066 mg/mL. Corresponding electrophoresis data showed different protein profiles. UniProtKB data base research reveals two sorghum ATIs, and P81367; both reviewed and a targeted LC–MS/MS method was developed to analyze these. Quantifier peptides ELAAVPSR ( P81368) and TYMVR ( P81367) were identified and retained as biomarkers for relative quantification. Different reducing and alkylating agents were assessed and combination of tris (2 carboxyethyl) phosphine/iodoacetamide gave the best response. Linearity was demonstrated for the quantifier peptides with standard recovery between 92.2 and 107.6%. Nine sorghum cultivars presented up to 60 times lower ATI contents as compared to wheat samples. This data suggests that sorghum can effectively be considered as a good alternative to wheat. P81368相似文献
68.
Marine organisms produce a fascinating range of structurally diverse secondary metabolites, which often possess unusual and sometimes unexpected biological activities. This structural diversity makes these marine natural products excellent molecular probes for the investigation of biochemical pathways. Recently, a number of novel and stereochemically complex macrolides, having a large macrolactone (22- to 44-membered) ring, that interact with the actin cycloskeleton have been isolated from different marine sources. Actin, like tubulin, is a major component of the cytoskeleton and has important cellular functions. Although the details of these interactions are still under investigation, these marine macrolides are becoming increasingly important as novel molecular probes to help elucidate the cellular functions of actin. Owing to their potent antitumor activities, these compounds, for example the aplyronines, also have potential for preclinical development in cancer chemotherapy. Their appealing molecular structures, with an abundance of stereochemistry, and biological significance, coupled with the extremely limited availability from the marine sources, have stimulated enormous interest in the synthesis of these compounds. This review summarizes the biological properties of these unusual marine natural products and features the recently completed total syntheses of swinholide A, scytophycin C, aplyronine A, mycalolide A--all of these being potent cytotoxic agents that target actin--and a diastereoisomer of ulapualide A. Rather than detailing each individual step of these multistep total syntheses, the different synthetic strategies, key reactions, and methods adopted for controlling the stereochemistry are compared. 相似文献
69.
70.
Suset Rodríguez-Alemn Ernesto M. Hernndez-Cooper Rolando Prez-lvarez Jos A. Otero 《Molecules (Basel, Switzerland)》2021,26(2)
Front tracking and enthalpy methods used to study phase change processes are based on a local thermal energy balance at the liquid–solid interface where mass accommodation methods are also used to account for the density change during the phase transition. Recently, it has been shown that a local thermal balance at the interface does not reproduce the thermodynamic equilibrium in adiabatic systems. Total thermal balance through the entire liquid–solid system can predict the correct thermodynamic equilibrium values of melted (solidified) mass, system size, and interface position. In this work, total thermal balance is applied to systems with isothermal–adiabatic boundary conditions to estimate the sensible and latent heat stored (released) by and salts which are used as high-temperature phase change materials. Relative percent differences between the solutions obtained with a local thermal balance at the interface and a total thermal balance for the thermal energy absorbed or released by high-temperature phase change materials are obtained. According to the total thermal balance proposed, a correction to the liquid–solid interface dynamics is introduced, which accounts for an extra amount of energy absorbed or released during the phase transition. It is shown that melting or solidification rates are modified by using a total thermal balance through the entire system. Finally, the numerical and semi-analytical methods illustrate that volume changes and the fraction of melted (solidified) solid (liquid) estimated through a local thermal balance at the interface are not invariant in adiabatic systems. The invariance of numerical and semi-analytical solutions in adiabatic systems is significantly improved through the proposed model. 相似文献