全文获取类型
收费全文 | 10039篇 |
免费 | 777篇 |
国内免费 | 1915篇 |
专业分类
化学 | 11303篇 |
晶体学 | 76篇 |
力学 | 62篇 |
综合类 | 81篇 |
数学 | 10篇 |
物理学 | 1199篇 |
出版年
2024年 | 35篇 |
2023年 | 173篇 |
2022年 | 353篇 |
2021年 | 366篇 |
2020年 | 340篇 |
2019年 | 343篇 |
2018年 | 275篇 |
2017年 | 317篇 |
2016年 | 390篇 |
2015年 | 356篇 |
2014年 | 368篇 |
2013年 | 697篇 |
2012年 | 741篇 |
2011年 | 562篇 |
2010年 | 513篇 |
2009年 | 610篇 |
2008年 | 619篇 |
2007年 | 711篇 |
2006年 | 609篇 |
2005年 | 616篇 |
2004年 | 566篇 |
2003年 | 457篇 |
2002年 | 355篇 |
2001年 | 271篇 |
2000年 | 269篇 |
1999年 | 258篇 |
1998年 | 230篇 |
1997年 | 215篇 |
1996年 | 179篇 |
1995年 | 182篇 |
1994年 | 128篇 |
1993年 | 133篇 |
1992年 | 115篇 |
1991年 | 98篇 |
1990年 | 57篇 |
1989年 | 47篇 |
1988年 | 46篇 |
1987年 | 20篇 |
1986年 | 26篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The parameters that affect the shape of the band profiles of acido‐basic compounds under moderately overloaded conditions (sample size less than 500 nmol for a conventional column) in RPLC are discussed. Only analytes that have a single pKa are considered. In the buffer mobile phase used for their elution, their dissociation may, under certain conditions, cause a significant pH perturbation during the passage of the band. Two consecutive injections (3.3 and 10 μL) of each one of three sample solutions (0.5, 5, and 50 mM) of ten compounds were injected on five C18‐bonded packing materials, including the 5 μm Xterra‐C18 (121 Å), 5 μm Gemini‐C18 (110 Å), 5 μm Luna‐C18(2) (93 Å), 3.5 μm Extend‐C18 (80 Å), and 2.7 μm Halo‐C18 (90 Å). The mobile phase was an aqueous solution of methanol buffered at a constant WWpH of 6, with a phosphate buffer. The total concentration of the phosphate groups was constant at 50 mM. The methanol concentration was adjusted to keep all the retention factors between 1 and 10. The compounds injected were phenol, caffeine, 3‐phenyl 1‐propanol, 2‐phenyl butyric acid, amphetamine, aniline, benzylamine, p‐toluidine, procainamidium chloride, and propranololium chloride. Depending on the relative values of the analyte pKa and the buffer solution pH, these analytes elute as the neutral, the cationic, or the anionic species. The influence of structural parameters such as the charge, the size, and the hydrophobicity of the analytes on the shape of its overloaded band profile is discussed. Simple but general rules predict these shapes. An original adsorption model is proposed that accounts for the unusual peak shapes observed when the analyte is partially dissociated in the buffer solution during its elution. 相似文献
22.
Ivan Horvath Viera Luptakova 《Journal of inclusion phenomena and macrocyclic chemistry》1991,11(3):257-265
Benzothiazolium compounds exhibit pronounced antimicrobial activities and stimulation effects on plant growth. When applied to fields they can pollute soil colloids. In contact with the soil they can potentially interact with a clay fraction giving rise to clay organocomplexes. Model intercalation complexes were prepared using monoionic montmorillonite and a variety of water-soluble benzothia zolium salts. It was found that the adsorption into the silicate interlayer space proceeds via a cation exchange process. Substantial differences were observed in the extent of the reaction between non-substituted andN-substituted species. The sulphur atoms present in the benzothiazolium molecules repel the surface oxygen atom: this is considered to be the factor responsible for prevention of insertion of the guest cations perpendicular to the layers. 相似文献
23.
Influence of boric acid on the electrochemical deposition of Ni 总被引:1,自引:0,他引:1
M. Šupicová R. Rozik L. Trnková R. Oriňáková M. Gálová 《Journal of Solid State Electrochemistry》2006,10(2):61-68
The electrolytic deposition of Ni onto a paraffin-impregnated graphite electrode from supporting chloride electrolyte (0.5 mol dm−3 NaCl) adjusted to the required pH using dilute HCl is investigated. The effect of electrolyte composition on the Ni electrodeposition
is studied using linear sweep voltammetry in the cathodic region. An elimination voltammetry procedure was applied to evaluate
the polarization curves. The aim of this work was to deduce the mechanism of Ni reduction in the chloride bath as well as
the influence of boric acid on this. Positively-charged NiCl+ ions were found to be the electroactive particles in the Ni reduction mechanism. The strong competition between the NiCl+, Cl− and H+ ions for active sites at the electrode is discussed. Kinetically-controlled adsorption/desorption processes of various species
were also confirmed using elimination voltammetry with a linear scan. The evolution of gaseous hydrogen, catalyzed by the
freshly-deposited Ni, accompanies the electrodeposition process. The presence of boric acid at a sufficiently high concentration
inhibits the deposition of Ni and, at the same time, improves the morphology and brightness, as well as the adhesion of the
deposited Ni.
Elimination voltammetry with a linear scan is an efficient way to evaluate current–potential curves that reflect the electrodeposition
of one-component Ni coatings. By eliminating selected currents, additional interesting and useful information can be obtained
from voltammetric data. 相似文献
24.
The viscosities of aqueous solutions of gelatin at different temperatures were carefully measured in a common glass‐capillary Ubbelohde viscometer at dilute to extremely dilute concentrations. The adsorption effect that occurred in the viscosity measurements was theoretically analyzed and discussed. A theory based on Langmuir isotherms could adequately describe the existing data. Some structural information was obtained by the use of an iterative fitting procedure to treat the reduced viscosity data, which disclosed that individual gelatin chains underwent a coil‐to‐helix transition as the solution cooled from 40 to 15 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1804–1812, 2006 相似文献
25.
《Electroanalysis》2006,18(10):947-954
In this work, for the first time a fast continuous cyclic voltammetry was used as a highly sensitive detection method for Penicillin G in a flow‐injection system. A special computer‐based numerical calculation method (using Fast Fourier Transformation) is introduced here for enhancing the analyte signal and noise reduction. During the measurements, the potential waveform (consists of potential steps for cleaning, stripping and potential ramp) was continuously applied on an Au disk microelectrode (with a radius 12.5 μm in radius). The stripping time was less than 200 ms. Effects of rest potential, sweep rate, and delay time on the sensitivity of the method were investigated. The limit of detection of the method was 1.0 × 10?11 M. The detection limit of the method is 660 times lower than the most sensitive reported method. The relative standard deviation of the method at 1.0×10?7 M of Penicillin G was 2.7% for 10 runs. 相似文献
26.
In this paper, a model of the motional nonlinear heterogeneous catalysis process is discussed using the characteristic line method, the analytical results of elution profile are obtained and the formula which determines the parameters of reaction rate and adsorption isotherm through the motional measurement data under the nonlinear condition is given. 相似文献
27.
以碳酸锶为甲烷吸附活化的模型催化剂,用切换变应答、CH4(CO2)-TPD等技术,对甲烷的吸附、碱性对催化剂性能的影响进行了研究,结果表明,甲烷在碳酸锶上的活化显示出明显的酸碱活化机理特征,瞬变应答及TPD结果均证明,甲烷在碳酸锶表面有较强的吸附,其脱附温度约310℃,关联结果表明,甲烷转化率及C2烃收率与催化剂表面SrO碱性中心浓度有非常一致的顺变关系,因此催化剂表面的酸碱中心可能是甲烷的选择活 相似文献
28.
29.
乙酰丙酮稀土四苯基卟啉配合物的电化学研究 总被引:5,自引:0,他引:5
本文指出我国环境保护产业发展中存在的问题,论述了“入关“对我国环境保护产业的影响及应采取的经济和税收政策。 相似文献
30.
膨润土对结晶紫的吸附 总被引:5,自引:0,他引:5
用分光光度、显微电泳和x-射线衍射等方法研究了膨润土对结晶紫的吸附;实验表明,钙型膨润土在吸收结晶紫溶液时,加入钠盐可明显改善吸附效果。 相似文献