全文获取类型
收费全文 | 363篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 168篇 |
力学 | 5篇 |
数学 | 85篇 |
物理学 | 113篇 |
出版年
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 10篇 |
2013年 | 7篇 |
2012年 | 10篇 |
2011年 | 13篇 |
2010年 | 5篇 |
2009年 | 11篇 |
2008年 | 17篇 |
2007年 | 9篇 |
2006年 | 16篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 9篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1972年 | 3篇 |
1970年 | 7篇 |
1969年 | 3篇 |
1966年 | 5篇 |
1962年 | 3篇 |
1886年 | 5篇 |
1883年 | 4篇 |
1873年 | 2篇 |
1870年 | 2篇 |
1869年 | 2篇 |
排序方式: 共有371条查询结果,搜索用时 15 毫秒
1.
D. De Salvador A. Coati E. Napolitani M. Berti A.V. Drigo M.S. Carroll J.C. Sturm J. Stangl G. Bauer L. Lazzarini 《Applied Physics A: Materials Science & Processing》2002,75(6):667-672
In this work we investigate the diffusion and precipitation of supersaturated substitutional carbon in 200-nm-thick SiGeC
layers buried under a silicon cap layer of 40 nm. The samples were annealed in either inert (N2) or oxidizing (O2) ambient at 850 °C for times ranging from 2 to 10 h. The silicon self-interstitial (I) flux coming from the surface under
oxidation enhances the C diffusion with respect to the N2-annealed samples. In the early stages of the oxidation process, the loss of C from the SiGeC layer by diffusion across the
layer/cap interface dominates. This phenomenon saturates after an initial period (2–4 h), which depends on the C concentration.
This saturation is due to the formation and growth of C-containing precipitates that are promoted by the I injection and act
as a sink for mobile C atoms. The influence of carbon concentration on the competition between precipitation and diffusion
is discussed.
Received: 19 October 2001 / Accepted: 19 December 2001 / Published online: 20 March 2002 / Published online: 20 March 2002 相似文献
2.
R. Sturm 《Mathematische Annalen》1873,6(3):241-263
Ohne Zusammenfassung 相似文献
3.
Rudolf Sturm 《Mathematische Annalen》1882,19(4):461-486
Ohne Zusammenfassung 相似文献
4.
5.
Reaction of N-Alkyl-bis(difluorophosphoryl)amides, RN(POF2)2, with Silylated Nucleophiles and Et2NSF3 N-Alkyl-bis(difluorophosphoryl)amides, RN(POF2)2 (R = Me, Et), react in any case with silylated nucleophiles such as Me3SiOMe and Me3SiNEt2 under cleavage of the PNP bridge forming derivatives of di- and monofluorophosphoric acid. In their reaction with Et2NSF3 (RNPF3)2 and OPF3 or PF5, resp., are obtained. The compounds F2P(O)? NR? PF4 and RN(PF4)2 postulated as intermediates are not stable. 相似文献
6.
Leuenberger M Nyfeler P Moret HP Sturm P Indermuhle A Schwander J 《Rapid communications in mass spectrometry : RCM》2000,14(16):1552-1557
A new technique for measuring CO(2) concentration in air samples, based on mass spectrometry, is described as an alternative to the common gas chromatographic method. Using a dual inlet isotope ratio mass spectrometer (IRMS), the ratio of the abundances of the m/z peaks 44 and 28 is determined. The precision of measurements (standard deviation <3 ppmv) is generally as good as the analysis with gas chromatography for small air samples (<1 ml STP of air). A major advantage of this new method is the possibility of parallel elemental and isotopic measurements of many air components. The technique is further improved by new wide mass range mass spectrometers allowing simultaneous intensity measurements of several m/z values between 28 and 44, resulting in an uncertainty of <0.5 ppm. The precision is somewhat limited by the production of N(2)O and NO(2) from N(2) and O(2) in the ion source, which accounts for about half of the signal strength at m/z 44. Copyright 2000 John Wiley & Sons, Ltd. 相似文献
7.
In this paper, we introduce a potential reduction method for harmonically convex programming. We show that, if the objective function and them constraint functions are allk-harmonically convex in the feasible set, then the number of iterations needed to find an -optimal solution is bounded by a polynomial inm, k, and log(1/). The method requires either the optimal objective value of the problem or an upper bound of the harmonic constantk as a working parameter. Moreover, we discuss the relation between the harmonic convexity condition used in this paper and some other convexity and smoothness conditions used in the literature.The authors like to thank Dr. Hans Nieuwenhuis for carefully reading this paper and the anonymous referees for the worthy suggestions. 相似文献
8.
P. Bersier und F. v. Sturm 《Fresenius' Journal of Analytical Chemistry》1966,224(1):317-332
Zusammenfassung Die Möglichkeit der gleichzeitigen Bestimmung von Niob und Zinn mit Hilfe der Polarographie wird untersucht. Es wird gefunden, daß die Bestimmung zwar nicht gleichspannungspolarographisch, wohl aber square-wave-polarographisch durchführbar ist. Zur Analyse der binären Nb-Sn-Legierungen (etwa Nb3Sn) ist 8,0±0,1 m HCl+10 Vol-% Äthylenglykol als Grundelektrolyt geeignet. In diesem Elektrolyten erscheinen die erste Reduktionswelle des Niobs, NbVIV, und die zweite Reduktionswelle des Zinns, SnIISn, gut getrennt und vermeßbar. Die Differenz der Spitzenpotentiale (E
pNbV/IV= -0.26V, E
pSnII/O= -0.46V gegen Quecksilber-Bodenelektrode) beträgt 200 mV.Die beschriebene Methode hat im Vergleich zu den bekannten nichtpolarographischen Analysenvorschriften den Vorzug, eine bis zu 100 mal kleinere Einwaage (bei vergleichbarer Reproduzierbarkeit) und einen verringerten Zeitaufwand zu erfordern.Bei Einwaagen von 2–14 mg beträgt die Genauigkeit der Niobbestimmung 1% rel., die der Zinnbestimmung 2% rel. Eine einzelne Niob-Zinn-Simultanbestimmung dauert 4 Std.
Herrn Prof. Dr. M. von Stackelberg zum 70. Geburtstag gewidmet. 相似文献
Summary The possibility of a simultaneous polarographic determination of niob and tin is investigated.It has been found that the determination cannot be carried out by direct current polarography, but square-wave polarography yields good results.8.0±0.1 M HCl+10 vol-% ethylene glycol is suitable as supporting electrolyte for the analysis of the binary Nb-Sn-alloys (Nb3Sn).In this supporting electrolyte the first reduction-wave of niobium NbVNbIV, and the second reduction wave of tin, SnIISn0, are well developed and separated. The difference of the peak potential (E pNbV/IV= -0.26V, E pSnII/O= -0.46V vs. mercury-pool electrode) is 200 mV. Compared with conventional methods the method described has the advantage of requiring smaller amounts of sample (up to 100 times smaller by weight at comparable reproducibility) with a saving of time.With sample amounts of 2 to 14 mg the accuracy of the niobium determination is 1% rel., that of the tin determination is 2% rel. One single simultaneous determination of niobium and tin takes about four hours.
Herrn Prof. Dr. M. von Stackelberg zum 70. Geburtstag gewidmet. 相似文献
9.
Seger C Sturm S Mair ME Ellmerer EP Stuppner H 《Magnetic resonance in chemistry : MRC》2005,43(6):489-491
2D NMR-derived 1H and 13C NMR signal assignments of six structurally closely related cucurbitacin derivatives are presented. The investigated 2-O-beta-D-glucopyranosylcucurbitacins I, J, K, and L were obtained from Citrullus colocynthis (L.) Schrader whereas the aglyca cucurbitacin E and I were isolated from Ecballium elaterium L. 相似文献
10.
On Chalcogenolates. 134. Studies on Esters of Haloformic Acids 2. Synthesis and Properties of Se-Alkyl Esters of Chloromonothiomonoselenoformic Acid The hitherto unknown esters RSe? CS? Cl with R ? C2H5 and nC3H7 have been prepared by reaction of thiophosgene with the corresponding alkane selenol. The compounds have been characterized with electron absorption, nuclear magnetic resonance (1H, 13C, and 77Se), infrared, and mass spectra. 相似文献