全文获取类型
收费全文 | 4993篇 |
免费 | 133篇 |
国内免费 | 8篇 |
专业分类
化学 | 2906篇 |
晶体学 | 100篇 |
力学 | 171篇 |
数学 | 639篇 |
物理学 | 1318篇 |
出版年
2023年 | 41篇 |
2022年 | 68篇 |
2021年 | 80篇 |
2020年 | 89篇 |
2019年 | 79篇 |
2018年 | 56篇 |
2017年 | 50篇 |
2016年 | 130篇 |
2015年 | 131篇 |
2014年 | 117篇 |
2013年 | 191篇 |
2012年 | 233篇 |
2011年 | 286篇 |
2010年 | 171篇 |
2009年 | 148篇 |
2008年 | 197篇 |
2007年 | 183篇 |
2006年 | 211篇 |
2005年 | 171篇 |
2004年 | 156篇 |
2003年 | 155篇 |
2002年 | 123篇 |
2001年 | 81篇 |
2000年 | 104篇 |
1999年 | 62篇 |
1998年 | 53篇 |
1997年 | 53篇 |
1996年 | 70篇 |
1995年 | 58篇 |
1994年 | 50篇 |
1993年 | 64篇 |
1992年 | 58篇 |
1991年 | 52篇 |
1990年 | 49篇 |
1989年 | 54篇 |
1988年 | 57篇 |
1987年 | 57篇 |
1986年 | 50篇 |
1985年 | 45篇 |
1983年 | 50篇 |
1982年 | 37篇 |
1981年 | 61篇 |
1980年 | 43篇 |
1979年 | 58篇 |
1978年 | 61篇 |
1977年 | 45篇 |
1976年 | 51篇 |
1975年 | 33篇 |
1974年 | 35篇 |
1973年 | 37篇 |
排序方式: 共有5134条查询结果,搜索用时 0 毫秒
991.
Wagner Muniz 《PAMM》2005,5(1):689-690
We consider the inverse inhomogeneous medium scattering problem in acoustics where one tries to recover the support of anomalies in a medium by interrogating the region of interest with plane waves at fixed frequency. We discuss the validity of the Linear Sampling Method (LSM) for solving this inverse problem, and its connection to an unusual eigenvalue problem. It turns out that the existence of non-trivial solutions of the so-called interior transmission eigenvalue problem results in the failure of the LSM. We then propose a modification of the LSM that avoids these shortcomings and is numerically sound. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
992.
Abstract The behavior of a fiber laser-amplifier is considered, including the effects of mode coupling, radiation losses, and noise. In the linear regime, a competitive effect between mode coupling and losses is present, in the sense that mode coupling tends to equalize the gains of different modes, while radiation losses favor low-order modes. Thus, single-mode amplification and collective amplification are predominant, respectively, in the weak and strong coupling case. In the saturated regime a mode coupling effect is found that is independent of fiber imperfections and relies on the nonlinear nature of the process. 相似文献
993.
S. Munavalli D. K. Rohrbaugh G. W. Wagner F. R. Longo H. D. Durst 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4):781-789
Microwave catalyzed reaction of a neat mixture of styrene oxide and H-dimethylphosphonate furnished dimethyl methylphosphonate, trimethylphosphate, phenylacetaldehyde, 1-methoxy-2-phenylethanol, 1-phenylethleneglycol, cis- and trans-1,3-diphenylcyclobutanes, hydrogen 1-(2-phenylethyl)methylphosphinate, (1-phenylethyl)dimethylphosphonate, and (1-phenylethyl)dimethylphosphonate via free radical processes. 相似文献
994.
995.
Federico Moscardó Miguel Paniagua Emilio San-Fabián 《Theoretical chemistry accounts》1979,53(4):377-381
Anab initio study of the relative stability for the states2
A
1g
and2
E
g of C2H
6
+
has been carried out. The results of the Open Shell Restricted Hartree-Fock calculations lead to assign the2
A
1
g
as the ground state of the molecule in agreement with previous SCF calculations.The correlation energy associated to both states has been calculated within the correlation hole model and the results, contrary to those obtained from Configuration Interaction calculations, do not alter qualitatively the conclusions from SCF. 相似文献
996.
F. Seel G. Simon J. Schuh M. Wagner B. Wolf I. Ruppert A. B. Wieckowski 《无机化学与普通化学杂志》1986,538(7):177-190
Investigation of the Reaction of Sulfur with Sodium Nitrite in DMF, DMSO, and HMPA The mechanism of the title reaction has been elucidated by VIS/UV, IR, 15N NMR, and ESR spectrometric measurements, gas analysis, and chromatography. The course of the complex reaction and the great number of products — nitrous oxide, nitric oxide, sodium thiosulfate, sulfate, polysulfides, polythionates, nitrate — can be explained with the assumption that at first perthionitrates NaSxNO2 are formed, which are decomposed either to give dinitrogen monoxide and thiosulfate, or, react with nitrite to yield nitrate and perthionitrite NaS2NO which dissociates reversibly into sodium trisulfide(-I) and nitrogen monoxide. (The details of the two main series of competitive and consecutive reaction steps can be seen from the tabular summary at the end of the text). The characteristic colour change during the reaction from blue-Green to orange-red is due to the formation of the two coloured species: S3? (blue, λmax = 620 nm, g = 2.029) and ONSS? (red, λmax = 448 nm, δ(15N) = 334 ppm, ref. K15NO3). 相似文献
997.
J. Kempf M. Nonnenmacher H. H. Wagner 《Applied Physics A: Materials Science & Processing》1993,56(4):385-390
A sensitive interferometric technique has been applied for studying the thermal displacement of thin film heated by electron or ion beams. The steady state displacement has been measured and we discuss the dependence on material properties and film thickness showing that this method has a potential for in-situ monitoring of thin-film deposition or etching. Transient effects are studied in a thin quartz plate and the propagation velocity of thermal waves is measured.Our colleague Martin Nonnenmacher passed away May 1992. We deplore his early death deeply and acknowledge gratefully the excellent cooperation with him. 相似文献
998.
The physical, chemical and mineralogical aspects of the use of Mössbauer spectroscopy in studies of clay-based ceramics are described. Mössbauer spectra of pottery clays fired under oxidising, reducing and changing conditions are explained, and the possibilities of using Mössbauer spectra to derive information on the firing temperatures and the kiln atmosphere during firing in antiquity are discussed and illustrated by examples. 相似文献
999.
1000.