全文获取类型
收费全文 | 2784篇 |
免费 | 56篇 |
国内免费 | 13篇 |
专业分类
化学 | 1683篇 |
晶体学 | 24篇 |
力学 | 82篇 |
数学 | 387篇 |
物理学 | 677篇 |
出版年
2022年 | 23篇 |
2021年 | 29篇 |
2020年 | 30篇 |
2019年 | 28篇 |
2018年 | 30篇 |
2017年 | 27篇 |
2016年 | 45篇 |
2015年 | 46篇 |
2014年 | 50篇 |
2013年 | 138篇 |
2012年 | 117篇 |
2011年 | 118篇 |
2010年 | 73篇 |
2009年 | 69篇 |
2008年 | 105篇 |
2007年 | 129篇 |
2006年 | 110篇 |
2005年 | 111篇 |
2004年 | 74篇 |
2003年 | 73篇 |
2002年 | 73篇 |
2001年 | 61篇 |
2000年 | 71篇 |
1999年 | 51篇 |
1998年 | 41篇 |
1997年 | 44篇 |
1996年 | 30篇 |
1995年 | 43篇 |
1994年 | 39篇 |
1993年 | 32篇 |
1992年 | 26篇 |
1991年 | 38篇 |
1990年 | 30篇 |
1989年 | 36篇 |
1988年 | 23篇 |
1987年 | 34篇 |
1986年 | 32篇 |
1985年 | 37篇 |
1984年 | 41篇 |
1983年 | 28篇 |
1982年 | 29篇 |
1980年 | 24篇 |
1979年 | 31篇 |
1978年 | 26篇 |
1977年 | 27篇 |
1975年 | 29篇 |
1973年 | 24篇 |
1968年 | 32篇 |
1967年 | 56篇 |
1966年 | 61篇 |
排序方式: 共有2853条查询结果,搜索用时 31 毫秒
1.
Karen Beatriz Méndez-Rodríguez Nicté Figueroa-Vega César Arturo Ilizaliturri-Hernandez Mónica Cardona-Alvarado Jaime Antonio Borjas-García Carlos Kornhauser Juan Manuel Malacara Rogelio Flores-Ramírez Francisco Javier Pérez-Vázquez 《Biomedical chromatography : BMC》2020,34(12):e4956
Metabolomics is a potential tool for the discovery of new biomarkers in the early diagnosis of diseases. An ultra-fast gas chromatography system equipped to an electronic nose detector (FGC eNose) was used to identify the metabolomic profile of Volatile Organic Compounds (VOCs) in type 2 diabetes (T2D) urine from Mexican population. A cross-sectional, comparative, and clinical study with translational approach was performed. We recruited twenty T2D patients and twenty-one healthy subjects. Urine samples were taken and analyzed by FGC eNose. Eighty-eight compounds were identified through Kovats's indexes. A natural variation of 30% between the metabolites, expressed by study groups, was observed in Principal Component 1 and 2 with a significant difference (p < 0.001). The model, performed through a Canonical Analysis of Principal coordinated (CAP), allowed a correct classification of 84.6% between healthy and T2D patients, with a 15.4% error. The metabolites 2-propenal, 2-propanol, butane- 2,3-dione and 2-methylpropanal, were increased in patients with T2D, and they were strongly correlated with discrimination between clinically healthy people and T2D patients. This study identified metabolites in urine through FGC eNose that can be used as biomarkers in the identification of T2D patients. However, more studies are needed for its implementation in clinical practice. 相似文献
2.
3.
Let A be a symmetric matrix of size n×n with entries in some (commutative) field K. We study the possibility of decomposing A into two blocks by conjugation by an orthogonal matrix T∈Matn(K). We say that A is absolutely indecomposable if it is indecomposable over every extension of the base field. If K is formally real then every symmetric matrix A diagonalizes orthogonally over the real closure of K. Assume that K is a not formally real and of level s. We prove that in Matn(K) there exist symmetric, absolutely indecomposable matrices iff n is congruent to 0, 1 or −1 modulo 2s. 相似文献
4.
Jaime Keller 《International Journal of Theoretical Physics》1991,30(2):137-184
From the definition of spinors as the minimal left (right) modules of multivectors (that is, of vectors and their outer products), we can construct a unified mathematical approach for the study of matter and its interaction fields, which are either defined as fields in the geometrical spacetime or considered as generators of the physical spacetime. It is also shown how matter and interaction fields can be represented either by spinor fields or by multivector fields, both types of fields carrying the same information as the traditional corresponding spinors, vectors, or tensors. Geometry is more transparent in one representation (multivector form), and physics is more obvious in the spinor representation. Our theory provides a unified and totally self-consistent representation of quarks (barions), leptons, and all their known interactions. 相似文献
5.
Antonio Uris Jose Maria Bravo Jaime Llinares Hermelando Estelles 《Applied Acoustics》2004,65(4):421-430
In this paper the influence on sound reduction index of the length and the depth of sound leaks at the perimeter of lightweight partitions was examined. It was shown that the most important decrease on sound reduction index is caused by the first slit between lightweight partition and one of the structural members. When the length of the slit is increased, the decrease on sound reduction index is less significative. Calculated results show the same effects as measured ones. 相似文献
6.
Keller Teichmann Hans Pfeiffer W. Langenbeck A. Reid Heinrich Menzel Th. Höpner W. Mühlsteph M. Ulmann Geib R. E. Liesegang 《Colloid and polymer science》1939,87(1):100-104
Ohne Zusammenfassung 相似文献
7.
The effect of viscous dissipation on the development of the boundary layer flow from a cold vertical surface embedded in a Darcian porous medium is investigated. It is found that the flow evolves gradually from the classical Cheng–Minkowycz form to the recently discovered asymptotic dissipation profile which is a parallel flow. 相似文献
8.
9.
10.
Each convex planar set K has a perimeter C, a minimum width E, an area A, and a diameter D. The set of points (E,C, A1/2, D) corresponding to
all such sets is shown to occupy a cone in the non-negative orthant of R4with its vertex at the origin. Its three-dimensional cross section S in the
plane D = 1 is investigated. S lies in a rectangular parallelepiped in R3. Results of Lebesgue, Kubota, Fukasawa, Sholander, and Hemmi are used to
determine some of the boundary surfaces of S, and new results are given for the other boundary surfaces. From knowledge of S, all inequalities among
E, C ,A, and D can be found. 相似文献