全文获取类型
收费全文 | 655篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
化学 | 440篇 |
晶体学 | 8篇 |
力学 | 20篇 |
数学 | 106篇 |
物理学 | 108篇 |
出版年
2023年 | 3篇 |
2022年 | 14篇 |
2021年 | 28篇 |
2020年 | 19篇 |
2019年 | 15篇 |
2018年 | 16篇 |
2017年 | 14篇 |
2016年 | 33篇 |
2015年 | 20篇 |
2014年 | 26篇 |
2013年 | 50篇 |
2012年 | 40篇 |
2011年 | 59篇 |
2010年 | 35篇 |
2009年 | 21篇 |
2008年 | 43篇 |
2007年 | 33篇 |
2006年 | 31篇 |
2005年 | 21篇 |
2004年 | 14篇 |
2003年 | 20篇 |
2002年 | 21篇 |
2001年 | 15篇 |
2000年 | 17篇 |
1999年 | 7篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1975年 | 3篇 |
1966年 | 1篇 |
排序方式: 共有682条查询结果,搜索用时 156 毫秒
81.
We establish lower bounds on the matching number of graphs of given odd regularity d and odd girth g, which are sharp for many values of d and g. For d=g=5, we characterize all extremal graphs. 相似文献
82.
This paper considers a special but broad class of convex programming problems whose feasible region is a simple compact convex set intersected with the inverse image of a closed convex cone under an affine transformation. It studies the computational complexity of quadratic penalty based methods for solving the above class of problems. An iteration of these methods, which is simply an iteration of Nesterov’s optimal method (or one of its variants) for approximately solving a smooth penalization subproblem, consists of one or two projections onto the simple convex set. Iteration-complexity bounds expressed in terms of the latter type of iterations are derived for two quadratic penalty based variants, namely: one which applies the quadratic penalty method directly to the original problem and another one which applies the latter method to a perturbation of the original problem obtained by adding a small quadratic term to its objective function. 相似文献
83.
84.
Transparent SiO2:Li2O:Nb2O5 glass doped with Tm3+ has been prepared by the sol–gel method, and heat-treated in air (HT) at temperatures between 500 and 800 °C. X-ray diffraction (XRD) patterns and Raman spectroscopy show SiO2 and LiNbO3 phases in samples HT above 650 °C, and a NbTmO4 phase for T > 750 °C. The XRD SEM analysis show increasing particle size and number with the increase of HT temperature. Intra-4f12 transitions due to Tm3+ ion dispersed in the matrix are observed in samples with T > 650 °C. The luminescence is dominated by the 1G4 → 3F4 (~650 nm), 1D2 → 3F3 (~780 nm), 3H4 → 3H6 (~800 nm), 3H5 → 3H6 (~1200 nm) and 3H4 → 3F4 (~1500 nm) transitions under resonant excitation to the ion levels. 相似文献
85.
Melissa D'Ascenzio Kathryn M. Pugh Rebecca Konietzny Georgina Berridge Cynthia Tallant Shaima Hashem Octovia Monteiro Jason R. Thomas Markus Schirle Stefan Knapp Brian Marsden Oleg Fedorov Chas Bountra Benedikt M. Kessler Paul E. Brennan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(4):1019-1024
86.
87.
Diego Fontana de Andrade Louise Jank Vitor Breda Rego Roberto Minozzo Marcus Vinícius Burgel Sfoggia Álvaro Bavaresco Fabiano Barreto 《Biomedical chromatography : BMC》2020,34(9):e4873
Saponins from Quillaja saponaria have been commonly used as immunomodulatory adjuvants in foot-and-mouth disease vaccines (FMDVs). However, due to the lack of consensus over the possible exacerbation of local inflammatory responses in cattle and its economic impacts, their use has been discouraged by Brazilian authorities. A qualitative method intended to determine the presence of saponins from Q. saponaria bark extracts in FMDVs was developed and validated. Instrumental analysis was performed using an liquid chromatography (LC) coupled to a quadrupole–time-of-flight–mass spectrometry (TOF-MS) system. The method was validated according to the International Conference on Harmonization Harmonized Tripartite Guideline Q2 (R1) and Brazilian Ministry of Agriculture, Livestock and Food Supply Analytical Quality Assurance Guidelines. Validation parameters were determined and considered suitable to the established criteria. The validated method has been applied in routine analysis in the National Agricultural Laboratory at Rio Grande do Sul (LANAGRO-RS). All results obtained were in agreement with the vaccine's composition described by the manufacturer. The method is easy and adequate for analysis in routine laboratories. To the best of the authors' knowledge, this is the first report of a method which intends to investigate the presence of saponins from Q. saponaria bark extracts in veterinary vaccines. 相似文献
88.
Juan Manuel Cornejo Luiz F. Monteiro Hanamantagouda P. Sankappanavar Ignacio D. Viglizzo 《Mathematical Logic Quarterly》2020,66(4):409-417
We determine the number of non-isomorphic semi-Heyting algebras on an n-element chain, where n is a positive integer, using a recursive method. We then prove that the numbers obtained agree with those determined in [1]. We apply the formula to calculate the number of non-isomorphic semi-Heyting chains of a given size in some important subvarieties of the variety of semi-Heyting algebras that were introduced in [5]. We further exploit this recursive method to calculate the numbers of non-isomorphic semi-Heyting chains with n elements such that removing the mth element () we are left with a subalgebra. We also solve a related problem posed in [1] of determining the number of ways a semi-Heyting chain with elements can be extended to a n element semi-Heyting chain by adding a new element in the mth place. Finally we combine these results by finding a second way to calculate the numbers that provides some extra information. 相似文献
89.
90.
Ana Carolina de C. Correia Tamyris F. Ferreira Italo Rossi R. Martins Cibério L. Macêdo Fabio de S. Monteiro Vicente Carlos O. Costa 《Natural product research》2015,29(10):980-984
Xylopia langsdorfiana A. St.-Hil. &Tul. (Annonaceae) is popularly known in the northeast of Brazil as ‘pimenteira da terra’, and an essential oil (XL-OE) was extracted from its leaves. Since Xylopia species are cited in folk medicine and diterpenes from X. langsdorfiana have spasmolytic activity, this study aimed to investigate a possible spasmolytic action of XL-OE on smooth muscle models. XL-OE (243 and 729 μg/mL) showed low pharmacologic efficacy on guinea pig trachea and rat aorta and uterus. However, in guinea pig ileum, XL-OE (27–729 μg/mL) inhibited carbachol or histamine-induced phasic contractions (1 μM) in a significant and concentration-dependent manner. In addition, XL-OE (81 μg/mL) reduced fluorescence intensity in ileal myocytes stimulated by histamine, indicating a decrease in cytosolic calcium concentration, which could explain the spasmolytic activity. Thus, XL-OE proved to be a promising natural product to be used in gastrointestinal diseases acting by modulating the cytosolic calcium concentration. 相似文献