全文获取类型
收费全文 | 611篇 |
免费 | 10篇 |
专业分类
化学 | 318篇 |
晶体学 | 4篇 |
力学 | 36篇 |
数学 | 129篇 |
物理学 | 134篇 |
出版年
2022年 | 5篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 16篇 |
2017年 | 7篇 |
2016年 | 19篇 |
2015年 | 12篇 |
2014年 | 7篇 |
2013年 | 34篇 |
2012年 | 32篇 |
2011年 | 25篇 |
2010年 | 14篇 |
2009年 | 18篇 |
2008年 | 30篇 |
2007年 | 19篇 |
2006年 | 33篇 |
2005年 | 20篇 |
2004年 | 17篇 |
2003年 | 21篇 |
2002年 | 20篇 |
2001年 | 7篇 |
2000年 | 12篇 |
1999年 | 4篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 10篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1971年 | 4篇 |
1966年 | 3篇 |
1916年 | 2篇 |
1906年 | 2篇 |
排序方式: 共有621条查询结果,搜索用时 31 毫秒
31.
32.
The X-ray structures of c-2,t-3-di-tert-butyl-r-1-methylthiiranium 8 BF(4)(-), t-2,t-3-di-tert-butyl-r-1-methylthiiranium ion 10 BF(4)(-), and 2,3-di-tert-butyl-1-methylthiirenium 11 BF(4)(-) have been determined. The DeltaG()(298) values for the rearrangements from the cis and the trans tert-butyl groups of 8 SbCl(6)(-) to thietanium ion (two intramolecular S(N)2 displacements) and for the rearrangement of 11 SbCl(6)(-) to thietium ion (an intramolecular S(N)2-Vin displacement) are linearly correlated with the strengths of the C-S breaking bonds, suggesting that the two mechanisms are, in the absence of steric hindrance, uniquely governed by the nucleofugality of the sulfonium leaving group. 相似文献
33.
Carniti, P., Cori, L. and Ragaini, V., 1978. A Critical Analysis of the Hand and Othmer-Tobias Correlations. Fluid Phase Equilibria, 2: 39–47.The Hand (H) and Othmer-Tobias (OT) correlations are extensively analyzed on 83 aqueous and 26 non-aqueous ternary systems. Twenty solutropic systems are also included. 65% and 58% of the systems give a linear correlation coefficient greater than 0.99 for H and OT respectively.An analysis of the sensitivity to systematic or random errors demonstrates the H correlation to be highly insensitive. A remarkable insensitivity, although not completly for some systematic errors, is also demonstrated for the OT correlation. However there is sufficient proof that they are both unsuitable as a check of experimental data, even though they are used for this purpose.The relation, not necessarily linear, derived from the H correlation, log(x32/x22) vs. log(x31/x11) is useful in locating the plait point. 相似文献
34.
Porras MA Dubietis A Kucinskas E Bragheri F Degiorgio V Couairon A Faccio D Di Trapani P 《Optics letters》2005,30(24):3398-3400
We show that the angle-wavelength spectra of light filaments excited by ultrashort pulses experience a transition from X- to O-like structures when their carrier wavelengths are switched from normal to anomalous dispersion. Calculations confirm that the O-shaped conical emission follows the elliptic geometry of the nonlinear Schr?dinger equation with anomalous dispersion. 相似文献
35.
The limits posed by physics to the quantity of information that can be transmitted with a certain amount of power are investigated. The same ultimate limits are found for transmission of information encoded using matter and massless fields. 相似文献
36.
Shen M Li G Lu BZ Hossain A Roschangar F Farina V Senanayake CH 《Organic letters》2004,6(22):4129-4132
[reaction: see text] The first practical and economical process for synthesis of 2,3-disubstituted indole compounds has been developed with high regioselectivity by palladium-catalyzed indolization of 2-bromo- or chloroanilines and their derivatives with internal alkynes. 相似文献
37.
To a finitely generated profinite group G, a formal Dirichletseries PG(s)=nan/ns is associated, where an = |G:H|=n µG(H).It is proved that G is prosoluble if and only if the sequence{an}nN is multiplicative, that is, ars = aras for any pairof coprime positive integers r and s. This extends the analogousresult on the probabilistic zeta function of finite groups. 相似文献
38.
In this paper we give answers to some open questions concerninggeneration and enumeration of finite transitive permutationgroups. In [1], Bryant, Kovács and Robinson proved thatthere is a number c' such that each soluble transitive permutationgroup of degree n2 can be generated by elements, and later A. Lucchini [5] extended thisresult (with a different constant c') to finite permutationgroups containing a soluble transitive subgroup. We are nowable to prove this theorem in full generality, and this solvesthe question of bounding the number of generators of a finitetransitive permutation group in terms of its degree. The resultobtained is the following. 1991 Mathematics Subject Classification20B05, 20D60. 相似文献
39.
Giovanna Bruni Vittorio Berbenni Franco Sartor Chiara Milanese Alessandro Girella Dionigio Franchi Amedeo Marini 《Journal of Thermal Analysis and Calorimetry》2012,108(1):235-241
In this work, thermoanalytical, diffractometry, and microscopy measurements have been performed in order to characterize the
effect of high energy milling on a drug active in the migraine prophylaxis and smoke cessation. We can assert that the mechanical
treatment induces only a partial amorphisation of the solid phase, in particular it reduces the crystal order by producing
lattice defects which propagate from the surface to the bulk crystal. For this reason, the DSC is able to detect the presence
of ordered solid, while the powder X-ray diffractometry, because of its low penetration depth, does not reach the crystalline
core of the particles. 相似文献
40.
This paper concerns with a state of bending for a linear transversely isotropic plate model based on the Mindlin assumption on the displacement. By using appropriate families of line-integral measures, we are able to establish results about the spatial behaviour of transient and steady-state solutions. All the results are obtained under relaxed hypotheses on the positive definiteness of the elasticity tensor. 相似文献