全文获取类型
收费全文 | 8782篇 |
免费 | 1196篇 |
国内免费 | 1272篇 |
专业分类
化学 | 5416篇 |
晶体学 | 85篇 |
力学 | 1329篇 |
综合类 | 62篇 |
数学 | 499篇 |
物理学 | 3859篇 |
出版年
2024年 | 10篇 |
2023年 | 102篇 |
2022年 | 140篇 |
2021年 | 261篇 |
2020年 | 360篇 |
2019年 | 304篇 |
2018年 | 286篇 |
2017年 | 369篇 |
2016年 | 382篇 |
2015年 | 352篇 |
2014年 | 461篇 |
2013年 | 730篇 |
2012年 | 574篇 |
2011年 | 622篇 |
2010年 | 471篇 |
2009年 | 540篇 |
2008年 | 506篇 |
2007年 | 551篇 |
2006年 | 468篇 |
2005年 | 483篇 |
2004年 | 415篇 |
2003年 | 346篇 |
2002年 | 306篇 |
2001年 | 309篇 |
2000年 | 243篇 |
1999年 | 224篇 |
1998年 | 197篇 |
1997年 | 153篇 |
1996年 | 142篇 |
1995年 | 148篇 |
1994年 | 121篇 |
1993年 | 89篇 |
1992年 | 78篇 |
1991年 | 71篇 |
1990年 | 64篇 |
1989年 | 41篇 |
1988年 | 46篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 31篇 |
1984年 | 31篇 |
1983年 | 11篇 |
1982年 | 25篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 19篇 |
1978年 | 10篇 |
1977年 | 22篇 |
1976年 | 13篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
本文用XPS从Rh_4(CO)_(12)在真空条件下的脱羰过程和在氢氧中的还原过程两方面考察了一些非还原性氧化物担载Rh_4(CO)_(12)催化剂的金属载体相互作用,并把这种相互作用称为金属载体非强相互作用(non-strong metal-support interaction,缩写NSMSI).结果表明,铑与一些载体的非强相互作用的顺序是MgO>ZrO_2>γ-Al_2O_3>SiO_2-Al_2O_3≈SiO_2;Rh与载体的非强相互作用形成Rh—O键,使Rh的还原性减弱;形成M—O键是产生NSMSI效应的重要特征;这种相互作用能增加铑羰基物的稳定性,使其在真空中脱羰速率减慢.铑与非还原性氧化物载体间的非强相互作用可用酸-碱机制解释. 相似文献
93.
本文用化学吸附、原位IR、和XPS考察了钒助剂对Rh2/SiO2催化剂的H2和CO化学吸附的影响.结果表明,1)CO吸附在RhI、RhⅡ和RhⅢ中心上分别产生孪生、线式和桥式CO表面吸附物种.2)H2主要解离吸附在RhⅡ和RhⅢ中心上,但CO能优先吸附;RhI中心对H2的化学吸附能力弱,但H2和CO能共吸附在RhI中心上形成表面羰基氢化物.3)Rh2-V/SiO2催化剂在573K还原后,铑与钒助剂的强相互作用主要发生在RhⅡ和RhⅢ与钒助剂之间,H2吸附比CO吸附受到更强烈的抑制.用覆盖模型可以较好地解释钒助剂对Rh2/SiO2催化剂的H2和CO化学吸附的影响. 相似文献
94.
The solubilities of o-, m- and p-xylene in water were measured at 25.0°C up to 250, 385, and 50 MPa, respectively. The solubility increased with increasing pressure up to 120 MPa (50 MPa for p-xylene) and then decreased. The reaction volumes, Vo accompanying the dissolution at 0.1 MPa were estimated as –3.6±0.5, –3.4±0.5, and –4.1±0.5 cm3-mol–1 for o-, m-, and p-xylene, respectively, from the pressure dependences of the solubilities. The limiting partial molar volumes, of p- and o-xylene in water under high pressure were estimated from Vo and the molar volume of the xylene. The partial molar volumes decreased with increasing pressure. The reaction volume for the formation of intra-molecular pairwise hydrophobic interaction between the methyl groups, as proposed by Ben-Naim, is discussed for the Vo of p- and o-xylene at 0.1 MPa. 相似文献
95.
LiZHANG NaLI FengLinZHAO KeAnLI 《中国化学快报》2004,15(6):671-674
The interaction between heparin and neutral red was investigated by molecular spectroscopic methods. The change of all spectra suggested that positively charged neutral red had interacted with negatively charged heparin. The study of influence factors indicated that electrostatic force and hydrophobic bond might be involved in the interaction. The total binding number per disaccharide unit and intrinsic binding constant were obtained using Scatchard model. 相似文献
96.
Jerman S Podgornik A Cankar K Cadet N Skrt M Zel J Raspor P 《Journal of chromatography. A》2005,1065(1):107-113
The availability of sufficient quantities of DNA of adequate quality is crucial in polymerase chain reaction (PCR)-based methods for genetically modified food detection. In this work, the suitability of anion-exchange CIM (Convective Interaction Media; BIA Separations, Ljubljana, Slovenia) monolithic columns for isolation of DNA from food was studied. Maize and its derivates corn meal and thermally pretreated corn meal were chosen as model food. Two commercially available CIM disk columns were tested: DEAE (diethylaminoethyl) and QA (quaternary amine). Preliminary separations were performed with standard solution of salmon DNA at different pH values and different NaCl concentrations in mobile phase. DEAE groups and pH 8 were chosen for further isolations of DNA from a complex matrix-food extract. The quality and quantity of isolated DNA were tested on agarose gel electrophoresis, with UV-scanning spectrophotometry, and by amplification with real-time PCR. DNA isolated in this way was of suitable quality for further PCR analyses. The described method is also applicable for DNA isolation from processed foods with decreased DNA content. Furthermore, it is more effective and less time-consuming in comparison with the existing proposed methods for isolation of DNA from plant-derived foods. 相似文献
97.
98.
聚电解质与相反电荷表面活性剂的相互作用 总被引:2,自引:0,他引:2
通过透光度测定、电导滴定和粘度法考察了阳离子聚电解质聚苯乙烯 4 乙烯基吡啶硫酸甲酯盐与阴离子表面活性剂十二烷基硫酸钠 (SDS)的相互作用。研究表明 ,在表面活性剂未过量时 ,二者之间的静电作用占主导地位 ,并且当二者电荷总量相等时 ,生成的复合物沉淀最多 ;在表面活性剂过量后 ,复合物可部分溶解 ,溶解的原因是疏水相互作用。本文初步阐述了二者的作用机理 相似文献
99.
Dominique Dehareng Georges Dive Josette Lamotte-Brasseur Jean-Marie Ghuysen 《Theoretical chemistry accounts》1989,76(2):85-94
Summary The electrostatic interaction energy between methanol and the dyad water-imidazole has been computed numerically at three levels of approximation from 3D grids of the charge density of one partner and the electrostatic potential of the other. The minimum positions and energy values thus obtained compare well with those calculated analytically. The numerical procedure is especially interesting for the prediction of the stable conformers. 相似文献
100.
Bernards T.N.M. Huls B.G. van Bommel M.J. 《Journal of Sol-Gel Science and Technology》1997,10(2):193-202
This article describes the SmartKom Companion, one of three demonstrators developed within the SmartKom project whose goal
has been to provide an intuitive and intelligent interface for non-expert users to everyday computer-based applications in
different scenarios of use. Conceived for the SmartKom Mobile scenario, the Companion allows intuitive multimodal interaction
for drivers and pedestrians. The development of the SmartKom prototypes was constantly accompanied by Wizard-of-Oz experiments
as well as system evaluations at different stages of the project. Some usability evaluation results relative to the SmartKom
Companion will also be presented. 相似文献