全文获取类型
收费全文 | 2534篇 |
免费 | 85篇 |
国内免费 | 11篇 |
专业分类
化学 | 1602篇 |
晶体学 | 1篇 |
力学 | 78篇 |
数学 | 505篇 |
物理学 | 444篇 |
出版年
2023年 | 17篇 |
2022年 | 33篇 |
2021年 | 38篇 |
2020年 | 49篇 |
2019年 | 46篇 |
2018年 | 33篇 |
2017年 | 39篇 |
2016年 | 71篇 |
2015年 | 51篇 |
2014年 | 82篇 |
2013年 | 120篇 |
2012年 | 154篇 |
2011年 | 207篇 |
2010年 | 130篇 |
2009年 | 104篇 |
2008年 | 157篇 |
2007年 | 182篇 |
2006年 | 144篇 |
2005年 | 112篇 |
2004年 | 105篇 |
2003年 | 92篇 |
2002年 | 79篇 |
2001年 | 31篇 |
2000年 | 33篇 |
1999年 | 30篇 |
1998年 | 31篇 |
1997年 | 33篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 16篇 |
1993年 | 21篇 |
1992年 | 26篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1974年 | 10篇 |
排序方式: 共有2630条查询结果,搜索用时 15 毫秒
901.
902.
Erik B. Hansen 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1978,29(6):977-982
In a certain method for measuring diffusion coefficients of solid materials a circular cylindrical sample of the material is clamped between annular rings and the difference in concentration between the end surfaces and the flux through the sample are measured. In order that the diffusion coefficient can be determined from these data a certain factor which depends on the geometry of the sample must be known. In this note two complementary variational principles are derived and used to obtain precise upper and lower bounds for this factor.
Zusammenfassung Bei einem Verfahren zur Messung von Diffusionskoeffizienten von Feststoffen wird eine zirkulärzylindrische Stoffprobe zwischen zwei ringförmingen Haltern eingespannt. Der Konzentrationsunterschied zwischen den Endflächen und dem Flux werden gemessen.Um bei diesem Verfahren den Koeffizient bestimmen zu können, muss ein Faktor, der von der Geometrie der Einspannungsvorrichtung abhängt, bekannt sein. In dieser Arbeit werden zwei komplementäre Variationsprinzipien hergeleitet, die dann anschliessend für die Berechnung von genauen oberen und unteren Schranken dieses Faktors angewandt werden.相似文献
903.
Eugene Brooks Geoffrey Fox Steve Otto Mohit Randeria Bill Athas Erik DeBenedictis Mike Newton Charles Seitz 《Nuclear Physics B》1983,220(4):383-400
We have calculated the mass of the 0+ glueball in SU(2) pure gauge theory in 4 dimensions, with very high statistics. The computation was done on an array of microprocessors with nearest-neighbor connections which run concurrently. We discuss, in detail, the implementation of the pure gauge algorithm for SU(2) and SU(3) and also the algorithm for calculating arbitrarily shaped Wilson loops on the array. The extension of these algorithms to the inclusion of dynamical fermions is also discussed. Finally, we present the results of our variational calculation of glueball masses which are in agreement with published results. 相似文献
904.
The Chemical shifts of the methoxyprotons in about 60 methyl esters of carboxylic acids were obtained in CCl4 and C6D6, and their dependence on constitution and solvent are discussed. It was shown that the values of a certain molecule could be assumed to be composed additively of a number of parameters which characterise the substituents. 相似文献
905.
906.
Manganese(I)‐Catalyzed C−H Activation: The Key Role of a 7‐Membered Manganacycle in H‐Transfer and Reductive Elimination
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Nasiru P. Yahaya Kate M. Appleby Magdalene Teh Conrad Wagner Erik Troschke Joshua T. W. Bray Prof. Simon B. Duckett L. Anders Hammarback Dr. Jonathan S. Ward Jessica Milani Dr. Natalie E. Pridmore Dr. Adrian C. Whitwood Dr. Jason M. Lynam Prof. Ian J. S. Fairlamb 《Angewandte Chemie (International ed. in English)》2016,55(40):12455-12459
Manganese‐catalyzed C?H bond activation chemistry is emerging as a powerful and complementary method for molecular functionalization. A highly reactive seven‐membered MnI intermediate is detected and characterized that is effective for H‐transfer or reductive elimination to deliver alkenylated or pyridinium products, respectively. The two pathways are determined at MnI by judicious choice of an electron‐deficient 2‐pyrone substrate containing a 2‐pyridyl directing group, which undergoes regioselective C?H bond activation, serving as a valuable system for probing the mechanistic features of Mn C?H bond activation chemistry. 相似文献
907.
A semi‐quantitative approach for the rapid screening and mass profiling of naphthenic acids directly in contaminated aqueous samples
下载免费PDF全文
![点击此处可从《Journal of mass spectrometry : JMS》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kyle D. Duncan Dane R. Letourneau Gregory W. Vandergrift Karl Jobst Eric Reiner Chris G. Gill Erik T. Krogh 《Journal of mass spectrometry : JMS》2016,51(1):44-52
We report the use of a direct sampling, online analytical approach for the determination of acid extractable naphthenic acids in complex aqueous samples, known as condensed phase membrane introduction mass spectrometry (CP‐MIMS). The technique employs a capillary hollow fibre semi‐permeable membrane probe configured for immersion into a pH adjusted sample. A continuously flowing methanol acceptor phase transfers naphthenic acids to an electrospray ionization source, operated in negative ion mode, whereupon they are analysed by mass spectrometry as [M–H]? ions. High‐resolution mass spectrometry is used to characterize the influence of sample pH on membrane transport of multiple components of complex naphthenic acid mixtures. We demonstrate the use of CP‐MIMS for semi‐quantitative analysis of real‐world samples using selected ion monitoring and full scan mass spectra at unit mass resolution. The technique has also been employed to continuously monitor the temporal evolution in the mass profile and concentrations of individual naphthenic acid isomer classes in heterogeneous solutions during adsorption processes. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
908.
Synthesis of Linear (Z)‐α,β‐Unsaturated Esters by Catalytic Cross‐Metathesis. The Influence of Acetonitrile
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Elsie C. Yu Brett M. Johnson Erik M. Townsend Prof. Richard R. Schrock Prof. Amir H. Hoveyda 《Angewandte Chemie (International ed. in English)》2016,55(42):13210-13214
Kinetically controlled catalytic cross‐metathesis reactions that generate (Z)‐α,β‐unsaturated esters selectively are disclosed. A key finding is that the presence of acetonitrile obviates the need for using excess amounts of a more valuable terminal alkene substrates. On the basis of X‐ray structure and spectroscopic investigations a rationale for the positive impact of acetonitrile is provided. Transformations leading to various E,Z‐dienoates are highly Z‐selective as well. Utility is highlighted by application to stereoselective synthesis of the C1–C12 fragment of biologically active natural product (?)‐laulimalide. 相似文献
909.
Haghedooren E Farkas E Kerner A Dragovic S Noszál B Hoogmartens J Adams E 《Talanta》2008,76(1):172-182
In order to study column deterioration as a result of long-term storage and/or usage in liquid chromatography analyses, 55 pairs (same batch) of different commercial reversed-phase C(18) columns were examined using an already existing column characterisation system. After initial testing, one column was stored and the other was used to analyse different pharmaceuticals. All columns were characterized by four chromatographic parameters reflecting hydrophobicity, silanol activity, metal impurity and steric selectivity at the beginning and at the end of the test. An F-value was calculated to express the change of column properties with one single number. After performing analyses, higher F-values were obtained as compared to the non-used, stored columns. Although the time during which the columns were used to perform analyses was relatively short, an obvious influence was noticed, mainly resulting from small changes in silanol activity and hydrophobicity. Most of the affected columns have no endcapping and/or no base deactivation, making them more vulnerable for degradation, resulting in higher silanol activity and faster ageing. This effect is observed less with columns equipped with polar-embedded groups and/or polar endcapping, protecting the column by blocking the silanol groups and attracting a shielding water layer. Also columns with higher coverages and bulky or long chains show more resistance towards degradation. 相似文献
910.
Palladium-catalyzed aminocarbonylations of various (hetero)aryl halides with allylamine using Mo(CO)6 as a solid, in situ CO source, were explored. Microwave-enhanced conditions proved to be highly useful in promoting the conversions in a mere 10-20 min with various (hetero)aryl iodides, bromides and chlorides. The scale-up of a microwave-enhanced aminocarbonylation to 25 mmol scale was performed successfully. 相似文献