全文获取类型
收费全文 | 4388篇 |
免费 | 174篇 |
国内免费 | 13篇 |
专业分类
化学 | 3606篇 |
晶体学 | 14篇 |
力学 | 43篇 |
数学 | 391篇 |
物理学 | 521篇 |
出版年
2023年 | 19篇 |
2022年 | 45篇 |
2021年 | 108篇 |
2020年 | 69篇 |
2019年 | 77篇 |
2018年 | 60篇 |
2017年 | 57篇 |
2016年 | 116篇 |
2015年 | 132篇 |
2014年 | 127篇 |
2013年 | 262篇 |
2012年 | 292篇 |
2011年 | 324篇 |
2010年 | 186篇 |
2009年 | 197篇 |
2008年 | 259篇 |
2007年 | 271篇 |
2006年 | 305篇 |
2005年 | 302篇 |
2004年 | 223篇 |
2003年 | 187篇 |
2002年 | 163篇 |
2001年 | 71篇 |
2000年 | 58篇 |
1999年 | 51篇 |
1998年 | 36篇 |
1997年 | 39篇 |
1996年 | 44篇 |
1995年 | 39篇 |
1994年 | 34篇 |
1993年 | 39篇 |
1992年 | 37篇 |
1991年 | 29篇 |
1990年 | 32篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 24篇 |
1986年 | 24篇 |
1985年 | 34篇 |
1984年 | 27篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1970年 | 5篇 |
排序方式: 共有4575条查询结果,搜索用时 15 毫秒
1.
2.
(S)-2-[2-(p-Tolylsulfinyl)phenyl]acetaldehyde reacts with different O-silylated ketenethioacetals in the presence of Yb(OTf)3 yielding β-hydroxythioesters in high yields and diastereoselectivities. The obtained compounds were readily transformed into β-hydroxyacids and their corresponding diols. These Mukaiyama aldol reactions are a direct evidence of the ability of the sulfinyl group to control 1,5- and 1,6-asymmetric induction processes. 相似文献
3.
Rhodium catalysts have been prepared on palygorskite and montmorillonite (clay) supports by reduction with hydrogen (1 atmosphere) at room temperature of a cationic organometallic rhodium compound anchored to the support. The activity of these catalysts for the hydrogenation of liquid-phase 1-hexene remains constant with increase of prehydrogenation time and with re-use for several runs. No rhodium leaching is observed. 相似文献
4.
An efficient way of obtaining travelling waves in a periodic fluid system is described and tested. We search for steady states in a reference frame travelling at the wave phase velocity using a first‐order pseudospectral semi‐implicit time scheme adapted to carry out the Newton's iterations. The method is compared to a standard Newton–Raphson solver and is shown to be highly efficient in performing this task, even when high‐resolution grids are used. This method is well suited to three‐dimensional calculations in cylindrical or spherical geometries. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
5.
6.
Neutral Community Theory: How Stochasticity and Dispersal-Limitation Can Explain Species Coexistence
Neutral community theory explains biodiversity, i.e. the coexistence of several species, as the result of a stochastic balance
between immigration and extinction on a local level, and between speciation and extinction on a regional level. The most popular
model, presented by Hubbell in 2001, has seen many analytical developments in recent years, which can be used in model analysis,
model testing and model comparison. We review these developments here, and present alternative derivations and shine previously
unnoticed lights on them. 相似文献
7.
Standard ODE methods such as linear multistep methods encounter difficulties when applied to differential-algebraic equations (DAEs) of index greater than 1. In particular, previous results for index 2 DAEs have practically ruled out the use of all explicit methods and of implicit multistep methods other than backward difference formulas (BDFs) because of stability considerations. In this paper we embed known results for semi-explicit index 1 and 2 DAEs in a more comprehensive theory based on compound multistep and one-leg discretizations. This explains and characterizes the necessary requirements that a method must fulfill in order to be applicable to semi-explicit DAEs. Thus we conclude that the most useful discretizations are those that avoid discretization of the constraint. A freer use of e.g. explicit methods for the non-stiff differential part of the DAE is then possible.Dedicated to Germund Dahlquist on the occasion of his 70th birthdayThis author thanks the Centro de Estadística y Software Matemático de la Universidad Simón Bolivar (CESMa) for permitting her free use of its research facilities.Partial support by the Swedish Research Council for Engineering Sciences TFR under contract no. 222/91-405. 相似文献
8.
B. G. Konopelchenko L. Martínez Alonso E. Medina 《Theoretical and Mathematical Physics》2007,151(3):820-830
Based on the Lenard relations, we completely classify integrable deformations of general algebraic curves. We construct the
general solution of the Lenard relation from the invariance condition with respect to an element of the Galois group of the
curve. We give some examples and also some associated conservation laws.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 151, No. 3, pp. 458–469, June, 2007. 相似文献
9.
Ilda Abe Rafael E. de Ges Jos L. Fabris Hypolito J. Kalinowski Mrcia Müller Meire C. Fugihara Rosane Falate Barbara W. Diesel Ricardo C. Kamikawachi Carmen L. Barbosa 《Optics and Lasers in Engineering》2003,39(5-6):537-548
In this work, we report production and modelling of both Bragg gratings and rocking filters in high birefringence fibre optics. Bragg gratings are produced by UV (257.0 nm) external interferometric exposition of a frequency-doubled Ar+ ion laser, whereas for rocking filters formation the visible Ar+ ion laser lines in 488.0 and 514.5 nm are used in an internal method. The spectral characteristics due to the birefringence properties are studied through numerical methods and experimental techniques. The spectral responsivity of the structures under temperature changes and stress application is presented. 相似文献
10.
Marta Gimnez-Pedrs Ali Aghmiz Carmen Claver Anna M. Masdeu-Bult Denis Sinou 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):157-163
High linear alkenes (1-octene and 1-decene) have been hydroformylated using water-soluble rhodium complexes associated with sulfonated diphosphines in the presence of ionic surfactants or methanol. In all cases, the hydroformylation activities were higher than in experiments without additives. The selectivity in aldehydes was higher when we used cetyltrimethylammonium hydrogensulfate (CTAHSO4) as the surfactant or methanol as the co-solvent. 相似文献