全文获取类型
收费全文 | 1490篇 |
免费 | 132篇 |
国内免费 | 118篇 |
专业分类
化学 | 401篇 |
晶体学 | 5篇 |
力学 | 117篇 |
综合类 | 30篇 |
数学 | 915篇 |
物理学 | 272篇 |
出版年
2024年 | 1篇 |
2023年 | 45篇 |
2022年 | 60篇 |
2021年 | 85篇 |
2020年 | 140篇 |
2019年 | 147篇 |
2018年 | 147篇 |
2017年 | 135篇 |
2016年 | 113篇 |
2015年 | 95篇 |
2014年 | 127篇 |
2013年 | 184篇 |
2012年 | 167篇 |
2011年 | 39篇 |
2010年 | 21篇 |
2009年 | 28篇 |
2008年 | 42篇 |
2007年 | 16篇 |
2006年 | 12篇 |
2005年 | 17篇 |
2004年 | 12篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 12篇 |
1996年 | 4篇 |
1995年 | 16篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有1740条查询结果,搜索用时 546 毫秒
991.
Yanyong Hong 《代数通讯》2017,45(7):2821-2836
In this paper, two classes of Schrödinger-Virasoro type Lie conformal algebras TSV(a,b) and TSV(c) which are non-simple are introduced for some a, b, c∈?. Moreover, central extensions, conformal derivations and free conformal modules of rank 1 of TSV(a,b) and TSV(c) are determined. 相似文献
992.
Filippo F. Favale 《代数通讯》2017,45(7):2899-2911
Let X be the product of two projective spaces and consider the general CICY threefold Y in X with configuration matrix A. We prove the finiteness part of the analogue of the Clemens’ conjecture for such a CICY in low bidegrees. More precisely, we prove that the number of smooth rational curves on Y with low bidegree and with nondegenerate birational projection is at most finite (even in cases in which positive dimensional families of degenerate rational curves are known). 相似文献
993.
Haicheng Zhang 《代数通讯》2017,45(6):2619-2628
Let A be a finite dimensional hereditary algebra over a finite field k and 𝒫 the category consisting of finite dimensional projective (left) A-modules. In this paper, we consider the composition subalgebra of Bridgeland’s Hall algebra of the category 𝒞m(𝒫) of m-cyclic complexes for any positive integer m≥2 and determine its generating relations. 相似文献
994.
Cristián Mallol 《代数通讯》2017,45(8):3555-3586
We study the ideal of polynomial identities of a single indeterminate satisfied by all backcrossing algebras. For this we distinguish two categories according to whether or not these algebras satisfy an identity for the plenary powers. For each category, we give the generators for the vector space of identities, a condition for any object belonging to one of these two categories verify a given identity, a necessary and su?cient condition that a polynomial is an identity and we study the existence of an idempotent element. We give a method which brings the search of identities satified by the backcrossing algebras to the solution of linear systems and we illustrate this method by constructing generators of homogeneous and non homogeneous identities of degrees less than 8. 相似文献
995.
996.
In this paper, we consider a subclass of linear semi-infinite programming problems whose constraint functions are polynomials in parameters and index sets are polyhedra. Based on Handelman’s representation of positive polynomials on a polyhedron, we propose two hierarchies of LP relaxations of the considered problem which respectively provide two sequences of upper and lower bounds of the optimum. These bounds converge to the optimum under some mild assumptions. Sparsity in the LP relaxations is explored for saving computational time and avoiding numerical ill behaviors. 相似文献
997.
Angela Pinzón-Espinosa Diana Martinez-Matamoros Leonardo Castellanos Carmenza Duque Jaime Rodríguez Carlos Jiménez Freddy A. Ramos 《Tetrahedron letters》2017,58(7):634-637
Two new compounds, cereusitin A (1), the tetrapeptide cyclo-(L-phenylalanyl-trans-4-hydroxy-L-prolyl-L-leucyl-trans-4-hydroxy-L-proline and 4-(R)-hydroxysattabacin (2), along with the methyl, isopropyl, and propyl esters of p-hydroxybenzoic acid (3–5) were isolated from the organic extracts of the culture of the B. cereus RKHC-09 strain in two culture media (MOLP and B1), recovered from the sea fan Antillogorgia elisabethae (syn. Pseudopterogorgia elisabethae). Cereusitin A (1) showed mild antifungal activity against Colletotrichum gloeosporoides C26 (yam pathogen) but was inactive against Fusarium oxysporum f.sp. dianthi (carnation pathogen). The methyl and propyl esters of p-hydroxybenzoic acid (4 and 5) showed antimicrobial activity against S. aureus ATCC 33591 and S. cerevisiae, with an MIC of 2 μM. 相似文献
998.
《Tetrahedron letters》2017,58(51):4796-4798
2,2-Dimethyl-5-(triphenylphosphoranylidene)acetyl-1,3-dioxan-4,6-dione (3) is a new activated β-ketoacyl equivalent, readily prepared in quantitative yield by reaction of Meldrum’s acid with the stable ylide Ph3PCCO. Its reaction with α-amino esters affords the corresponding N-(β-ketoacyl)amino ester ylides which, when treated with aldehydes and KOtBu, undergo a simultaneous Wittig olefination cum Dieckmann cyclisation to yield the respective 3-enoyltetramic acids. 相似文献
999.
《Comptes Rendus Chimie》2015,18(1):15-22
The denitrification process occurring in wastewater treatment plants (WWTPs) is responsible for nitrous oxide (N2O) and nitric oxide (NO) emissions. These compounds indirectly lead to the global warming. In this study, we investigated the impact of the temperature on N2O and NO emissions. Experiments were achieved at PH 7 in a batch reactor with acetate as the carbon source. The nitrogen source was nitrates (NO3−) and the COD/N ratio was set to three. Results showed that NO and N2O emissions increased when the temperature decreased. NO emissions appeared only at 10 °C and 5 °C, with respectively 8% and 18% of the total denitrified nitrogen. N2O emissions increased from 13 to 40 then 82% of the total denitrified nitrogen, respectively at 20, 10 and 5 °C. Several hypotheses were suggested to explain these results: a general enzymatic slow down, enzymatic inhibitions, electron donor competition between the different enzymes and metabolic pathway alterations. 相似文献
1000.