全文获取类型
收费全文 | 971篇 |
免费 | 83篇 |
国内免费 | 1篇 |
专业分类
化学 | 822篇 |
晶体学 | 2篇 |
力学 | 12篇 |
数学 | 137篇 |
物理学 | 82篇 |
出版年
2023年 | 9篇 |
2022年 | 17篇 |
2021年 | 23篇 |
2020年 | 35篇 |
2019年 | 23篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 52篇 |
2015年 | 49篇 |
2014年 | 68篇 |
2013年 | 68篇 |
2012年 | 88篇 |
2011年 | 80篇 |
2010年 | 56篇 |
2009年 | 50篇 |
2008年 | 51篇 |
2007年 | 44篇 |
2006年 | 37篇 |
2005年 | 37篇 |
2004年 | 34篇 |
2003年 | 14篇 |
2002年 | 25篇 |
2001年 | 16篇 |
2000年 | 7篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1992年 | 6篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1968年 | 3篇 |
1961年 | 3篇 |
1932年 | 3篇 |
1916年 | 3篇 |
1912年 | 4篇 |
1907年 | 4篇 |
1904年 | 3篇 |
1900年 | 2篇 |
1883年 | 2篇 |
1878年 | 3篇 |
1877年 | 2篇 |
1876年 | 4篇 |
1875年 | 2篇 |
1872年 | 3篇 |
1871年 | 3篇 |
1868年 | 2篇 |
1867年 | 3篇 |
1862年 | 3篇 |
排序方式: 共有1055条查询结果,搜索用时 15 毫秒
51.
Dr. Yumei Lin Dewang Xie Prof. Dr. Werner Massa Dr. Leonhard Mayrhofer Sina Lippert Benjamin Ewers Dr. Alexey Chernikov Prof. Dr. Martin Koch Prof. Dr. Stefanie Dehnen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(27):8806-8813
In situ transformations of selenidostannate frameworks in ionic liquids (ILs) were initiated by treatment of the starting phase K2[Sn2Se5] and the consecutive reaction products by means of temperature increase and/or amine addition. Along the reaction pathway, the framework dimensionalities of the five involved selenidostannate anions develop from 3D to 1D and back, both in top‐down and bottom‐up style. Addition of ethane‐1,2‐diamine (en) led to the reversion of the 2D→1D step from 2D‐{[Sn24Se56]16?} to 1D‐{[Sn6Se14]4?}. As rationalized by DFT investigations, the 2D anion is thermodynamically favored. Photoconductivity measurements reveal that all samples show Schottky contact behavior with absolute thresholds below 10 V. One of the samples exhibits conductive states within the energy range of visible photons. 相似文献
52.
Three one‐dimensional coordination polymers, [MnCl2(4‐pyterpy)]∙2CHCl3 ( 1 ), [Mn(NO3)2(4‐pyterpy)]∙CHCl3 ( 2 ) and [Ag(NO3)(3‐pyterpy)]∙H2O ( 3 ) (4‐pyterpy = 4′‐(4‐pyridyl)‐2,2′:6′,2″‐terpyridine and 3‐pyterpy = 4′‐(3‐pyridyl)‐2,2′:6′,2″‐terpyridine) were synthesized and characterized by X‐ray diffraction. All three compounds exhibit a rare “head‐to‐tail” coordination of the multidentate ligand, but differ significantly in their polymer chain conformations. Additionally, the fluorescent properties of all three compounds were investigated and show a weak, ligand‐centered fluorescence at 416–418 nm. 相似文献
53.
54.
J. Pelzl S. Chotikaprakhan D. Dietzel B. K. Bein E. Neubauer M. Chirtoc 《The European physical journal. Special topics》2008,153(1):335-342
Thermal contact resistance between two solids is discussed with regard to its influence on the measurements of temperature
and thermo-physical parameters in micro- and nano-structures. Two important applications are considered: thin film coatings
on substrates and local measurements with a nano-probe in scanning thermal microscopy. The mechanical contact of a copper
layer on carbon is measured by adhesion strength experiments and correlated to the thermal transport across the interface
deduced from infrared radiometric measurements. A novel quantity the thermal wave contrast is introduced which takes into
account the interface resistance and modifications of the coating and substrates at the interface. With regard to scanning
thermal microscopy the contact resistance problem is discussed for 3ω-measurements in the active mode and for temperature
measurements in the passive mode. It is shown that the thermo-elastic response can offer a means to avoid the influence of
the thermal contact resistance on local temperature measurements. 相似文献
55.
I. Delgadillo-Holtfort E. Neubauer J. S. Antoniow J. Gibkes M. Chirtoc B. K. Bein J. Pelzl 《The European physical journal. Special topics》2008,153(1):147-150
Photoacoustic effect and scanning near field microscopy
have been applied to characterise the thermal properties of diamond
crystallites which were coated by a Cu film, a Cr-film and a Cr-Cu film. The
Cu-coated diamond exhibits a considerable thermal barrier at the Cu-diamond
interface which had disappeared for the crystallites with a thin bond
Cr-layer between diamond and Cu. The local inspection of the thermal
conductivity with a thermal nano-probe operated in the 3ω-mode
reveals slight local variations of the thermal conductivity of the Cr-coated
crystallite. 相似文献
56.
Thermal fluctuations of surfactant bilayers in an aqueous solution produce an effective, long-range repulsion that can lead to a continuous unbinding transition. We report on an optical interferometry study of the thermal fluctuations of multicomponent bilayers close to the unbinding transition. We find that, in contrast to the case of single-component bilayers, the thermal fluctuation spectrum of multicomponent bilayers does not agree with a continuous unbinding transition but instead indicates the proximity of an unbinding tricritical point. 相似文献
57.
Detection of myocardial viability by low-dose dobutamine Cine MR imaging 总被引:15,自引:0,他引:15
Sandstede JJ Bertsch G Beer M Kenn W Werner E Pabst T Lipke C Kretschmer S Neubauer S Hahn D 《Magnetic resonance imaging》1999,17(10):614-1443
The purpose of this work was to test the diagnostic value of dobutamine stress magnetic resonance imaging (MRI) for predicting recovery of regional myocardial contractility after revascularization. Cardiac wall motion abnormalities are due to either non-viable and/or scarred, or viable, but hibernating, myocardial tissue. Dobutamine stress leads to increased systolic wall thickening only in viable myocardium. Twenty-five patients with akinetic or dyskinetic myocardial regions were examined with a Cine FLASH-2D sequence at rest and during dobutamine stress (10 μg/kg/min). Patients were re-examined at rest 3, and in case of persisting wall motion defects, 6 months after revascularization. Criterion of viability was increasing end-systolic wall thickening during stress and/or at follow-up. Akinetic regions related either to the LAD (n = 19) or to the RCA (n = 6) were judged viable if >=50% of the affected segments improved. MR studies were completed in all subjects without arrhythmia or need for early terminations due to symptoms. Sensitivity, specificity, and positive predictive value for the prediction of myocardial viability were 61%, 90%, and 87% for the segment-related analysis, and 76%, 100%, and 100% for the patient-related analysis based on coronary artery distribution, respectively. Dobutamine stress MRI allows to predict global functional recovery of akinetic myocardial regions after revascularization with a high positive predictive value and high specificity. 相似文献
58.
59.
Melting curves of Cu and Ni were measured in the laser-heated diamond cell to 97 GPa (3800 K) and 60 GPa (2970 K), respectively. The temperatures of Cu are in good agreement with recent theoretical calculations. The Cu melting slope (dT/dP) is about 2.5 times steeper than for Ni. The present results confirm the key role d-shell electrons play in determining the temperature dependence of high pressure melting curves in transition metals that have filled or partially filled d electron bands. 相似文献
60.
Klaassen T Kasel D Harlfinger S Fuhr U 《Rapid communications in mass spectrometry : RCM》2004,18(15):1675-1680
A reliable and easy to use liquid chromatography/tandem mass spectrometry (LC/MS/MS) method without the use of sample extraction was developed for the simultaneous quantification of urinary concentrations of mephenytoin, a standard phenotyping substrate for the cytochrome P450 enzyme CYP2C19, and its phase I metabolites 4'-hydroxymephenytoin and nirvanol. Fifty microL of urine were diluted with a buffered beta-glucuronidase solution and incubated at 37 degrees C for 6 h followed by addition of methanol, containing the internal standard 4'-methoxymephenytoin. The chromatographic separation was achieved using a 100 x 3 mm, 5 micro Thermo Electron Aquasil C18 column with a gradient flow, increasing the organic fraction (acetonitrile/methanol 50:50) of the mobile phase from 10 to 90%. Quantification by triple-stage mass spectrometry (TSQ Quantum, Thermo Electron) was accomplished by negative electrospray ionization in the selected reaction monitoring mode. Linearity was observed for all substances in the concentration range 15-10 000 ng/mL. The lower limit of quantification (LLOQ) was 20 ng/mL for 4'-hydroxymephenytoin and 30 ng/mL for nirvanol and mephenytoin, respectively. Intra- and inter-day inaccuracy did not exceed 9.5% for all substances from LLOQ to 10 000 ng/mL. Intra- and inter-day precision were in the range of 0.8-10.5%. The method was validated according to international ICH and FDA guidelines and successfully applied for phenotyping of Caucasian male volunteers who received an oral dose of 50 mg mephenytoin. 相似文献