全文获取类型
收费全文 | 3094篇 |
免费 | 93篇 |
国内免费 | 11篇 |
专业分类
化学 | 2043篇 |
晶体学 | 19篇 |
力学 | 117篇 |
数学 | 418篇 |
物理学 | 601篇 |
出版年
2023年 | 24篇 |
2022年 | 68篇 |
2021年 | 113篇 |
2020年 | 99篇 |
2019年 | 67篇 |
2018年 | 56篇 |
2017年 | 48篇 |
2016年 | 135篇 |
2015年 | 105篇 |
2014年 | 91篇 |
2013年 | 167篇 |
2012年 | 205篇 |
2011年 | 241篇 |
2010年 | 147篇 |
2009年 | 105篇 |
2008年 | 189篇 |
2007年 | 203篇 |
2006年 | 187篇 |
2005年 | 156篇 |
2004年 | 162篇 |
2003年 | 116篇 |
2002年 | 91篇 |
2001年 | 44篇 |
2000年 | 22篇 |
1999年 | 17篇 |
1998年 | 16篇 |
1997年 | 26篇 |
1996年 | 27篇 |
1995年 | 19篇 |
1994年 | 19篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1991年 | 5篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有3198条查询结果,搜索用时 15 毫秒
41.
Alessandro Passera Prof. Dr. Antonio Mezzetti 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(1):193-197
The bis(carbonyl) manganese(I) complex [Mn(CO)2( 1 )]Br ( 2 ) with a chiral (NH)2P2 macrocyclic ligand ( 1 ) catalyzes the asymmetric transfer hydrogenation of polar double bonds with 2-propanol as the hydrogen source. Ketones (43 substrates) are reduced to alcohols in high yields (up to >99 %) and with excellent enantioselectivities (90–99 % ee). A stereochemical model based on attractive CH–π interactions is proposed. 相似文献
42.
43.
Alessandro Trombetta 《Rendiconti del Circolo Matematico di Palermo》2007,56(1):65-78
In [11] Sion has investigated measures and integrals having values in uniform semigroups. In this paper a result which gives
sufficient conditions for the existence of a unique product of semigroup valued measures is established. Moreover a convergence
theorem for product integrals of semigroup valued functions is proved. 相似文献
44.
In this paper, inspired by some results in linear dynamics, we will show that every dynamical system (X,f), where f is a continuous self-map on a separable metric space X, can be extended to a chaotic (in the sense of Devaney) dynamical system in an isometric way. 相似文献
45.
Leonardo Biliotti Alessandro Ghigi Peter Heinzner 《Israel Journal of Mathematics》2016,213(1):423-441
We study a compact invariant convex set E in a polar representation of a compact Lie group. Polar representations are given by the adjoint action of K on p, where K is a maximal compact subgroup of a real semisimple Lie group G with Lie algebra g = k ⊕ p. If a ? p is a maximal abelian subalgebra, then P = E ∩ a is a convex set in a. We prove that up to conjugacy the face structure of E is completely determined by that of P and that a face of E is exposed if and only if the corresponding face of P is exposed. We apply these results to the convex hull of the image of a restricted1 momentum map. 相似文献
46.
In the present work, we study the approximation of a distributed optimal control problem for a linear heat equation with model order reduction based on Proper Orthogonal Decomposition (POD-MOR). We show that snapshot location for control problems is crucial in model reduction. For the determination of the time instances (snapshot locations) we utilize an a-posteriori error control concept which is based on a reformulation of the optimality system of the underlying optimal control problem as a second order in time and fourth order in space elliptic system. Finally, we present a numerical test to illustrate our approach. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
47.
Francesca Al Francesca Miraglia Alessandro Orticoni Elda Judica Maria Cotelli Paolo Maria Rossini Fabrizio Vecchio 《Entropy (Basel, Switzerland)》2020,22(11)
Human brain, a dynamic complex system, can be studied with different approaches, including linear and nonlinear ones. One of the nonlinear approaches widely used in electroencephalographic (EEG) analyses is the entropy, the measurement of disorder in a system. The present study investigates brain networks applying approximate entropy (ApEn) measure for assessing the hemispheric EEG differences; reproducibility and stability of ApEn data across separate recording sessions were evaluated. Twenty healthy adult volunteers were submitted to eyes-closed resting EEG recordings, for 80 recordings. Significant differences in the occipital region, with higher values of entropy in the left hemisphere than in the right one, show that the hemispheres become active with different intensities according to the performed function. Besides, the present methodology proved to be reproducible and stable, when carried out on relatively brief EEG epochs but also at a 1-week distance in a group of 36 subjects. Nonlinear approaches represent an interesting probe to study the dynamics of brain networks. ApEn technique might provide more insight into the pathophysiological processes underlying age-related brain disconnection as well as for monitoring the impact of pharmacological and rehabilitation treatments. 相似文献
48.
Austen Curtin Christine Austin Alessandro Giuliani Manuel Ruiz Marín Francheska Merced-Nieves Martha M. Tllez-Rojo Robert O. Wright Manish Arora Paul Curtin 《Entropy (Basel, Switzerland)》2021,23(12)
Metabolism and physiology frequently follow non-linear rhythmic patterns which are reflected in concepts of homeostasis and circadian rhythms, yet few biomarkers are studied as dynamical systems. For instance, healthy human development depends on the assimilation and metabolism of essential elements, often accompanied by exposures to non-essential elements which may be toxic. In this study, we applied laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to reconstruct longitudinal exposure profiles of essential and non-essential elements throughout prenatal and early post-natal development. We applied cross-recurrence quantification analysis (CRQA) to characterize dynamics involved in elemental integration, and to construct a graph-theory based analysis of elemental metabolism. Our findings show how exposure to lead, a well-characterized toxicant, perturbs the metabolism of essential elements. In particular, our findings indicate that high levels of lead exposure dysregulate global aspects of metabolic network connectivity. For example, the magnitude of each element’s degree was increased in children exposed to high lead levels. Similarly, high lead exposure yielded discrete effects on specific essential elements, particularly zinc and magnesium, which showed reduced network metrics compared to other elements. In sum, this approach presents a new, systems-based perspective on the dynamics involved in elemental metabolism during critical periods of human development. 相似文献
49.
50.