全文获取类型
收费全文 | 173篇 |
免费 | 7篇 |
专业分类
化学 | 106篇 |
晶体学 | 5篇 |
力学 | 13篇 |
数学 | 11篇 |
物理学 | 45篇 |
出版年
2019年 | 3篇 |
2018年 | 7篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 10篇 |
2011年 | 10篇 |
2010年 | 2篇 |
2009年 | 7篇 |
2008年 | 4篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1975年 | 2篇 |
1959年 | 2篇 |
1958年 | 2篇 |
1957年 | 2篇 |
1955年 | 1篇 |
1954年 | 1篇 |
1948年 | 1篇 |
1943年 | 1篇 |
1942年 | 1篇 |
1941年 | 1篇 |
1939年 | 5篇 |
1936年 | 4篇 |
1934年 | 2篇 |
1933年 | 3篇 |
1932年 | 1篇 |
1930年 | 4篇 |
1929年 | 1篇 |
排序方式: 共有180条查询结果,搜索用时 31 毫秒
1.
High-resolution Fourier transform spectra of CH3OH have been investigated in the infrared region from 930 to 1450 cm−1 in order to map the torsion-rotation energy manifolds associated with the ν7 in-plane CH3 rock, the ν11 out-of-plane CH3 rock, and the ν6 OH bend. Upper-state term values have been determined from the assigned spectral subbands, and have been fitted to power-series expansions to obtain substate origins and effective B-values for the three modes. The substate origins have been grouped into related families according to systematic trends observed in the torsion-vibration energy map, but there are substantial differences from the traditional torsional patterns. There appears to be significant torsion-mediated spectral mixing, and a variety of “forbidden” torsional combination subbands with |Δυt|>1 have been observed, where υt denotes the torsional quantum number (equivalent to υ12). For example, coupling of the (υ6,υt)=(1,0) OH bend to nearby torsionally excited (υ7,υt)=(1,1) CH3-rock and (υ8,υt)=(1,1) CO-stretch states introduces (υ6,υt)=(1,0)←(0,1) subbands into the spectrum and makes the ν7+ν12−ν12 torsional hot band stronger than the ν7 fundamental. The results suggest a picture of strong coupling among the OH-bending, CH3-rocking, and CO-stretching modes that significantly modifies the traditional energy structure and raises interesting and provocative questions about the torsion-vibration identity of a number of the observed states. 相似文献
2.
The dispersion relation of magnetostatic waves tangentially magnetized to saturation ferrite film, with a “magnetic wall” condition (tangential component of microwave magnetic field is equal to zero) on one of the film surface and with a metal condition on the opposite surface is analyzed. The dispersion characteristics show that unidirectional magnetostatic waves appear in this structure: they can transfer energy in one direction only and fundamentally cannot transfer energy in the opposite direction. The dispersion-free propagation of magnetostatic waves also is possible in the structure in a wide frequency interval. 相似文献
3.
An ethanol process based on a gas-lift tower fermenter arrangement was used as a model system to show the strong dependence of reactor behavior on the developing chemical environment within the reactor. The reactor performance limits for realistic substrates—starch and molasses—are characterized and compared with those attainable on an ideal substrate, glucose.
相似文献4.
In this paper, we propose a theory of quantum logics which is general enough to enable us to reexamine previous work on quantum logics in the context of this theory. It is then easy to assess the differences between the different systems studied. The quantum logical systems which we incorporate are divided into two groups which we call quantum propositional logics and quantum event logics. We include the work of Kochen and Specker (partial Boolean algebras), Greechie and Gudder (orthomodular partially ordered sets), Domotar (quantum mechanical systems), and Foulis and Randall (operational logics) in quantum propositional logics; and Abbott (semi-Boolean algebras) and Foulis and Randall (manuals) in quantum event logics. In this part of the paper, we develop an axiom system for quantum propositional logics and examine the above structures in the context of this system. 相似文献
5.
We studied the vibrational dynamics of the OH-stretch oscillators of an alcohol with two vicinal OH groups using femtosecond midinfrared pump-probe spectroscopy. The absorption spectrum of pinacol (2,3-dimethyl-2,3-butanediol) in CDCl3 shows two OH-stretch peaks belonging to hydrogen bonded and free OH groups. The anharmonicities of the hydrogen-bonded and free OH-stretch vibrations are 180 and 160 cm(-1), respectively. The lifetime T1 of the OH-stretch vibration is found to be 3.5 +/- 0.4 ps for the hydrogen bonded and 7.4 +/- 0.5 ps for the free OH group. We observed sidebands in the transient spectra after excitation of the bonded OH group, which we attribute to a progression in a low-frequency hydrogen-bond mode. The sideband is redshifted 60 cm(-1) with respect to the 0 --> 1 transition. Due to the coupling between the two OH groups and the presence of the sidebands, simultaneous excitation of both OH-stretch vibrations leads to oscillations on the pump-probe signal with frequencies of 40 and 60 cm(-1). 相似文献
6.
G. Lock 《Monatshefte für Chemie / Chemical Monthly》1941,74(1):77-84
Zusammenfassung Bei der Acetylierung des Naphthalins mit Acetylchlorid und Aluminiumchlorid bei Gegenwart von Schwefelkohlenstoff wird immer ein Gemisch, von 1- und 2-Acetyl-naphthalin in einer Ausbeute von höchstens 75 % d. Th. erhalten. Der Gehalt des Ketongemisches an 1-Acetyl-naphthalin beträgt etwa 50–60%. Käufliche als '-Naphthyl-methyl-keton bezeichnete Produkte enthielten ebenfalls nur 56 bzw. 62% 1-Acetyl-naphthalin. Der Einfluß der Reaktionstemperatur und der angewendeten Aluminiumchlorid-Menge auf das Mengenverhältnis der gebildeten isomeren Ketone ist unwesentlich. Der Schmelzpunkt von 1-Acetyl-naphthalin liegt bei 10.5°. 相似文献
7.
The use of 4-nitro-1-naphthylamme as a spot test for mercuric mercury and 1-nitro-2-naph-thylamine as a specific spot test for ceric cerium have been observed In each case, the reactions appear to be suitable for general qualitative inorganic analysis The ceric cerium test was specific whereas in the case of mercuric mercury. Ce+4 was the only on of 51 tested which interfered. 相似文献
8.
9.
Lock JS May BL Clements P Lincoln SF Easton CJ 《Organic & biomolecular chemistry》2004,2(9):1381-1386
The preparation of 6(A)-deoxy-6(A)-(6-(2-(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)acetamido)hexylamino)-alpha-cyclodextrin, 3, 6(A)-deoxy-6(A)-(6-(2-(1,4,7,10,13-pentaoxa-16-azacyclooctadecan-16-yl)acetamido)hexylamino)-alpha-cyclodextrin, 4, and their beta-cyclodextrin analogues, 5 and 6, are described. (1)H (600 MHz) ROESY NMR spectra of the C(6) substituted beta-cyclodextrins, 5 and 6, are consistent with the intramolecular complexation of their azacyclopentadecanyl- and azacyclooctadecanyl(acetamido)hexylamino substituents in the beta-cyclodextrin annulus in D(2)O at pD = 8.5 whereas those of their alpha-cyclodextrin analogues, 3 and 4 are not complexed in the alpha-cyclodextrin annulus. This is attributed to the monoazacoronand components of the substituents being able to pass through the beta-cyclodextrin annulus whereas they are too large to pass through the alpha-cyclodextrin annulus. However, the substituents of 3 and 4 are intermolecularly complexed by beta-cyclodextrin to form pseudo [2]-rotaxanes. Metallocyclodextrins are formed by 5 through complexation by the monoazacoronand substituent component for which log (K/dm(3) mol(-1))= <2, 6.34 and 5.38 for Ca(2+), Zn(2+) and La(3+), respectively, in aqueous solution at 298.2 K and I= 0.10 mol dm(-3)(NEt(4)ClO(4)). 相似文献
10.