全文获取类型
收费全文 | 1027篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
化学 | 682篇 |
晶体学 | 3篇 |
力学 | 31篇 |
数学 | 205篇 |
物理学 | 136篇 |
出版年
2023年 | 7篇 |
2022年 | 20篇 |
2021年 | 22篇 |
2020年 | 22篇 |
2019年 | 21篇 |
2018年 | 15篇 |
2017年 | 12篇 |
2016年 | 41篇 |
2015年 | 35篇 |
2014年 | 33篇 |
2013年 | 62篇 |
2012年 | 57篇 |
2011年 | 61篇 |
2010年 | 50篇 |
2009年 | 39篇 |
2008年 | 57篇 |
2007年 | 56篇 |
2006年 | 43篇 |
2005年 | 39篇 |
2004年 | 28篇 |
2003年 | 36篇 |
2002年 | 39篇 |
2001年 | 15篇 |
2000年 | 18篇 |
1999年 | 18篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 9篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 4篇 |
排序方式: 共有1057条查询结果,搜索用时 0 毫秒
31.
32.
Journal of Visualization - To enrich the three-dimensional experimental details of vortex structures in rotating Rayleigh–Bénard convection, we established a technique... 相似文献
33.
34.
Bernardo Duarte Renato Mamede Irina A. Duarte Isabel Caador Susanne E. Tanner Marisa Silva David Jacinto Teresa Cruz Vanessa F. Fonseca 《Molecules (Basel, Switzerland)》2022,27(4)
The stalked barnacle Pollicipes pollicipes is an abundant species on the very exposed rocky shore habitats of the Spanish and Portuguese coasts, constituting also an important economical resource, as a seafood item with high commercial value. Twenty-four elements were measured by untargeted total reflection X-ray fluorescence spectroscopy (TXRF) in the edible peduncle of stalked barnacles sampled in six sites along the Portuguese western coast, comprising a total of 90 individuals. The elemental profile of 90 individuals originated from several geographical sites (N = 15 per site), were analysed using several chemometric multivariate approaches (variable in importance partial least square discriminant analysis (VIP-PLS-DA), stepwise linear discriminant analysis (S-LDA), linear discriminant analysis (LDA), random forests (RF) and canonical analysis of principal components (CAP)), to evaluate the ability of each approach to trace the geographical origin of the animals collected. As a suspension feeder, this species introduces a high degree of background noise, leading to a comparatively lower classification of the chemometric approaches based on the complete elemental profile of the peduncle (canonical analysis of principal components and linear discriminant analysis). The application of variable selection approaches such as the VIP-PLS-DA and S-LDA significantly increased the classification accuracy (77.8% and 84.4%, respectively) of the samples according to their harvesting area, while reducing the number of elements needed for this classification, and thus the background noise. Moreover, the selected elements are similar to those selected by other random and non-random approaches, reinforcing the reliability of this selection. This untargeted analytical procedure also allowed to depict the degree of risk, in terms of human consumption of these animals, highlighting the geographical areas where these delicacies presented lower values for critical elements compared to the standard thresholds for human consumption. 相似文献
35.
In this paper we study the hyperstructures, saidP-hypergroupoids, (H, P*) in whichH is a set andP* is one of the hyperoperations defined as follows: ?(x, y) εH 2,xP*y=xyP orxP*y=Pxy whereP is a subset ofH. In particular we give a general formula for to express the simple hyperproducts ofn elements and then we consider some cases in which (H, P*) is feebly associative. We study, in such cases theβ-relations. 相似文献
36.
Almeida Carolane M. de Carvalho João G. M. Fujimori Mahmi França Eduardo L. Honorio-França Adenilda C. Parreira Renato L. T. Orenha Renato P. Gatto Claudia C. 《Structural chemistry》2020,31(5):2093-2103
Structural Chemistry - The current work reports the synthesis and structural investigation of three novel complexes with 2-acetyl-pyridine-N(4)-phenylthiosemicarbazone (HL1), [Ni(L1)Cl] (1),... 相似文献
37.
38.
Grosu Elena-Florentina Cârjă Gabriela Froidevaux Renato 《Research on Chemical Intermediates》2018,44(12):7731-7752
Research on Chemical Intermediates - Both photocatalytic and enzymatic degradation of phenol were studied in order to evaluate and to compare the catalytic potential of both methods. For this,... 相似文献
39.
A mean-field model of nonlinearly coupled oscillators with randomly distributed frequencies and subject to independent external white noises is analyzed in the thermodynamic limit. When the frequency distribution isbimodal, new results include subcritical spontaneous stationary synchronization of the oscillators, supercritical time-periodic synchronization, bistability, and hysteretic phenomena. Bifurcating synchronized states are asymptotically constructed near bifurcation values of the coupling strength, and theirnonlinear stability properties ascertained. 相似文献
40.
Renato Bruni 《Annals of Operations Research》2007,150(1):79-92
The paper is concerned with the problem of binary classification of data records, given an already classified training set
of records. Among the various approaches to the problem, the methodology of the logical analysis of data (LAD) is considered.
Such approach is based on discrete mathematics, with special emphasis on Boolean functions. With respect to the standard LAD
procedure, enhancements based on probability considerations are presented. In particular, the problem of the selection of
the optimal support set is formulated as a weighted set covering problem. Testable statistical hypothesis are used. Accuracy
of the modified LAD procedure is compared to that of the standard LAD procedure on datasets of the UCI repository. Encouraging
results are obtained and discussed. 相似文献