全文获取类型
收费全文 | 1710篇 |
免费 | 49篇 |
国内免费 | 5篇 |
专业分类
化学 | 1296篇 |
晶体学 | 12篇 |
力学 | 82篇 |
数学 | 177篇 |
物理学 | 197篇 |
出版年
2023年 | 11篇 |
2022年 | 38篇 |
2021年 | 33篇 |
2020年 | 17篇 |
2019年 | 25篇 |
2018年 | 13篇 |
2017年 | 18篇 |
2016年 | 43篇 |
2015年 | 49篇 |
2014年 | 43篇 |
2013年 | 71篇 |
2012年 | 93篇 |
2011年 | 98篇 |
2010年 | 67篇 |
2009年 | 48篇 |
2008年 | 126篇 |
2007年 | 123篇 |
2006年 | 121篇 |
2005年 | 112篇 |
2004年 | 107篇 |
2003年 | 73篇 |
2002年 | 67篇 |
2001年 | 37篇 |
2000年 | 21篇 |
1999年 | 18篇 |
1998年 | 23篇 |
1997年 | 14篇 |
1996年 | 33篇 |
1995年 | 20篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 5篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1971年 | 3篇 |
1929年 | 3篇 |
排序方式: 共有1764条查询结果,搜索用时 15 毫秒
41.
Torquato Mussini Maurizio Cicognini Paolo Longhi Sandra Rondinini Arthur K. Covington 《Analytica chimica acta》1984
Standard pH(S) values for 0.05 mol kg?1 potassium hydrogenphthalate (KHpH) reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water solvent mixtures within the temperature range 288.15–318.15 K are determined from e.m.f. measurements of the cell without transference Pt|H2|KHPh + KCl|AgCl|Ag|Pt. The consistency of the results is analysed by a recently described method of multilinear regression of the quantity p(aHγCl) as a function of both solution composition and temperature. The standard pH(S) determined can be reproduced to within ±0.01 by the equation pH(S) - 4.004 + 3.309w + 0.408z + 1.037w3 - 14.95zw2 + 27.1zw3, where w is the weight fraction of dioxane in the solvent mixture,z = (T –θ)/θ, and θ - 298.15 K. Values of the first ionization constant of phthalic acid (H2Ph; benzene-1,2-dicarboxylic acid) in the above solvent mixtures are also determined from e.m.f. measurements of the cell without transference Pt|H2|H2Ph + KHPh + KCl|AgCl|Ag|Pt. 相似文献
42.
Guldi DM Gouloumis A Vázquez P Torres T Georgakilas V Prato M 《Journal of the American Chemical Society》2005,127(16):5811-5813
Induction of self-organization between zinc phthalocyanine (ZnPc) and C60 moieties in a novel amphiphilic ZnPc-C60 salt results in uniformly nanostructured 1-D nanotubules. Their photoreactivity, in terms of ultrafast charge separation (i.e., approximately 1012 s-1) and ultraslow charge recombination (i.e., approximately 103 s-1), is remarkable. In addition, the observed ZnPc*+-C60*- lifetime of 1.4 ms implies, relative to that of the monomeric ZnPc-C60 ( approximately 3 ns), an impressive stabilization of 6 orders of magnitude. 相似文献
43.
Product distribution, total quenching rate (kT), and rate of chemical reaction (kr) with singlet oxygen have been determined for some alkyl, benzyl, α-methylbenzyl, and cumyl sulfides. Their contributions depend on the steric hindering around the sulfur atom. In protic solvents, the sulfoxide is the main product via a hydrogen-bonded persulfoxide. In apolar solvents, intramolecular α-H abstraction leads to oxidative C-S bond cleavage, with varying efficiency. The behavior of sulfides is compared to that of alkenes and amines. 相似文献
44.
Bruno P Caselli M de Gennaro G De Rienzo M Ielpo P Manigrassi D 《Annali di chimica》2002,92(9):815-824
In this paper an application of new procedures for atmospheric particulate analysis is illustrated. PM10, PAHs (benzo[a]anthracene (BaA), benzo[b]fluoranthene (BbF), benzo[j]fluoranthene (BjF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1, 2, 3-cd]pyrene (Ip), dibenzo[a, h]anthracene (DbA)) and heavy metals (Cu, Ni, Zn, Co, Mn, Cd, Fe and Pb) were investigated. PM10 determination was performed by gravimetric method, PAHs were measured by GC-MS, and heavy metals by HPIC. An air quality monitoring campaign on the territory of Bari municipality has been organised, and its results are shown. 相似文献
45.
Bernardo Masci Stefano Levi Mortera Maurizio Varrone Pierre Thury 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):o649-o651
Two compounds containing 1,3‐benzodioxin groups are reported, namely (±)‐6‐tert‐butyl‐8‐hydroxymethyl‐2‐phenyl‐4H‐1,3‐benzodioxin, C19H22O3, (I), and 2,2,2′,2′,6,6′‐hexamethyl‐8,8′‐methylenebis(4H‐1,3‐benzodioxin), C23H28O4, (II).The hydroxy groups of neighbouring molecules in (I) are hydrogen bonded to each other, giving rise to double‐row chains. The molecule in (II) adopts a `butterfly' conformation, with the O atoms in distal positions. In both compounds, the dioxin rings are in distorted half‐chair conformations. 相似文献
46.
47.
We consider an extension of the set union problem, in which dynamic weighted backtracking over sequences of unions is permitted. We present a new data structure which can support each operation inO(logn) time in the worst case. We prove that this bound is tight for pointer based algorithms. Furthermore, we design a different data structure to achieve better amortized bounds. The space complexity of both our data structures isO(n). Motivations for studying this problem arise in logic programming memory management.Work partially supported by NSF Grant CCR-88-14977, by the ESPRIT II Basic Research Actions Program of the EC under contract No. 3075 (Project ALCOM), and by the Italian MURST Project Algoritmi e Strutture di Calcolo.Partially supported by an IBM Graduate Fellowship. 相似文献
48.
49.
50.
We investigate by numerical simulations the dynamics of alignment of linear molecules in resonant pulsed laser fields and its dependence on pulse length, field strength, and molecular parameters. We propose an analytical short-time approximation for the time-dependent wave packets. We provide a theoretical basis for the occurrence of saturation in the rotational pumping. We present a formula to predict the time at which the maximum alignment occurs. We discuss the magnitude of the laser-induced alignment and we relate it to a theoretical upper limit. 相似文献