全文获取类型
收费全文 | 5936篇 |
免费 | 145篇 |
国内免费 | 23篇 |
专业分类
化学 | 3786篇 |
晶体学 | 41篇 |
力学 | 105篇 |
数学 | 739篇 |
物理学 | 1433篇 |
出版年
2021年 | 36篇 |
2020年 | 66篇 |
2019年 | 71篇 |
2018年 | 53篇 |
2017年 | 44篇 |
2016年 | 105篇 |
2015年 | 85篇 |
2014年 | 130篇 |
2013年 | 283篇 |
2012年 | 235篇 |
2011年 | 253篇 |
2010年 | 179篇 |
2009年 | 163篇 |
2008年 | 270篇 |
2007年 | 247篇 |
2006年 | 254篇 |
2005年 | 239篇 |
2004年 | 199篇 |
2003年 | 159篇 |
2002年 | 157篇 |
2001年 | 113篇 |
2000年 | 112篇 |
1999年 | 68篇 |
1998年 | 83篇 |
1997年 | 85篇 |
1996年 | 101篇 |
1995年 | 90篇 |
1994年 | 91篇 |
1993年 | 108篇 |
1992年 | 101篇 |
1991年 | 88篇 |
1990年 | 75篇 |
1989年 | 74篇 |
1988年 | 81篇 |
1987年 | 82篇 |
1986年 | 91篇 |
1985年 | 91篇 |
1984年 | 100篇 |
1983年 | 63篇 |
1982年 | 51篇 |
1981年 | 65篇 |
1980年 | 79篇 |
1979年 | 57篇 |
1978年 | 68篇 |
1977年 | 75篇 |
1976年 | 64篇 |
1975年 | 54篇 |
1974年 | 43篇 |
1973年 | 57篇 |
1970年 | 37篇 |
排序方式: 共有6104条查询结果,搜索用时 31 毫秒
1.
Reza Kordnezhadian Bing-Yu Li Armir Zogu Dr. Joachim Demaerel Prof. Dr. Wim M. De Borggraeve Dr. Ermal Ismalaj 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201491
Pentafluorosulfanyl (SF5)-containing compounds and corresponding analogs are a highly valuable class of fluorine-containing building blocks owing to their unique properties. The reason for that is the set of peculiar and tremendously beneficial characteristics they can impart on molecules once introduced onto them. Despite this, their application in distinct scientific fields remains modest, given the extremely harsh reaction conditions needed to access such compounds. The recent synthetic approaches via S−F, and C−SF5 bond formation as well as the use of SF5-containing building blocks embody a “stairway-to-heaven” loophole in the synthesis of otherwise-inaccessible chemical scaffolds only a few years ago. Herein, we report and evaluate the properties of the SF5 group and analogs, by summarizing synthetic methodologies available to access them as well as following applications in material science and medicinal chemistry since 2015. 相似文献
2.
3.
4.
We discuss an error estimation procedure for the global error of collocation schemes applied to solve singular boundary value problems with a singularity of the first kind. This a posteriori estimate of the global error was proposed by Stetter in 1978 and is based on the idea of Defect Correction, originally due to Zadunaisky. Here, we present a new, carefully designed modification of this error estimate which not only results in less computational work but also appears to perform satisfactorily for singular problems. We give a full analytical justification for the asymptotical correctness of the error estimate when it is applied to a general nonlinear regular problem. For the singular case, we are presently only able to provide computational evidence for the full convergence order, the related analysis is still work in progress. This global estimate is the basis for a grid selection routine in which the grid is modified with the aim to equidistribute the global error. This procedure yields meshes suitable for an efficient numerical solution. Most importantly, we observe that the grid is refined in a way reflecting only the behavior of the solution and remains unaffected by the unsmooth direction field close to the singular point. 相似文献
5.
Summary We present an approximation method of a space-homogeneous transport equation which we prove is convergent. The method is very promising for numerical computation. Comparison of a numerical computation with an exact solution is given for the Master equation. 相似文献
6.
7.
Nuclear Magnetic Resonance (NMR) was used to investigate the extrusion behaviour of PTFE pastes in a ram extruder. By means
of 1H-NMR imaging (MRI) it is possible to determine the local proton density and therefore, the local fluid concentration. The
19F-MRI provides the local solid concentration. Thus the local saturation and the local porosity can be calculated with the
information of the local fluid and solid concentration. Furthermore displacement profiles can be derived from NMR images by
means of correlation techniques without any preparation or marking of the pastes.
Received: 8 May 2000 Accepted: 1 May 2001 相似文献
8.
Matrix extensions and eigenvalue completions, the generic case 总被引:2,自引:0,他引:2
William Helton Joachim Rosenthal Xiaochang Wang 《Transactions of the American Mathematical Society》1997,349(8):3401-3408
In this paper we provide new necessary and sufficient conditions for the so-called eigenvalue completion problem.
9.
10.