全文获取类型
收费全文 | 2380篇 |
免费 | 81篇 |
国内免费 | 29篇 |
专业分类
化学 | 1876篇 |
晶体学 | 18篇 |
力学 | 48篇 |
数学 | 293篇 |
物理学 | 255篇 |
出版年
2023年 | 18篇 |
2022年 | 19篇 |
2021年 | 24篇 |
2020年 | 41篇 |
2019年 | 27篇 |
2018年 | 29篇 |
2017年 | 26篇 |
2016年 | 56篇 |
2015年 | 54篇 |
2014年 | 63篇 |
2013年 | 106篇 |
2012年 | 143篇 |
2011年 | 218篇 |
2010年 | 75篇 |
2009年 | 77篇 |
2008年 | 122篇 |
2007年 | 167篇 |
2006年 | 184篇 |
2005年 | 166篇 |
2004年 | 127篇 |
2003年 | 80篇 |
2002年 | 117篇 |
2001年 | 30篇 |
2000年 | 26篇 |
1999年 | 20篇 |
1998年 | 26篇 |
1997年 | 26篇 |
1996年 | 36篇 |
1995年 | 25篇 |
1994年 | 24篇 |
1993年 | 24篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 20篇 |
1988年 | 10篇 |
1987年 | 17篇 |
1985年 | 21篇 |
1984年 | 23篇 |
1983年 | 12篇 |
1982年 | 22篇 |
1981年 | 20篇 |
1980年 | 24篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1971年 | 7篇 |
排序方式: 共有2490条查询结果,搜索用时 109 毫秒
1.
Inas A. Abdallah Sherin F. Hammad Alaa Bedair Mohamed A. Abdelaziz Neil D. Danielson Ahmed H. Elshafeey Fotouh R. Mansour 《Biomedical chromatography : BMC》2022,36(6):e5365
Favipiravir is a potential antiviral medication that has been recently licensed for Covid-19 treatment. In this work, a gadolinium-based magnetic ionic liquid was prepared and used as an extractant in dispersive liquid–liquid microextraction (DLLME) of favipiravir in human plasma. The high enriching ability of DLLME allowed the determination of favipiravir in real samples using HPLC/UV with sufficient sensitivity. The effects of several variables on extraction efficiency were investigated, including type of extractant, amount of extractant, type of disperser and disperser volume. The maximum enrichment was attained using 50 mg of the Gd-magnetic ionic liquid (MIL) and 150 μl of tetrahydrofuran. The Gd-based MIL could form a supramolecular assembly in the presence of tetrahydrofuran, which enhanced the extraction efficiency of favipiravir. The developed method was validated according to US Food and Drug Administration bioanalytical method validation guidelines. The coefficient of determination was 0.9999, for a linear concentration range of 25 to 1.0 × 105 ng/ml. The percentage recovery (accuracy) varied from 99.83 to 104.2%, with RSD values (precision) ranging from 4.07 to 11.84%. The total extraction time was about 12 min and the HPLC analysis time was 5 min. The method was simple, selective and sensitive for the determination of favipiravir in real human plasma. 相似文献
2.
3.
Neil S. TrudingerXu-Jia Wang 《Journal of Functional Analysis》2002,193(1):1-23
In this paper, we continue previous investigations into the theory of Hessian measures. We extend our weak continuity result to the case of mixed k-Hessian measures associated with k-tuples of k-convex functions, on domains in Euclidean n-space, k=1,2,…,n. Applications are given to capacity, quasicontinuity, and the Dirichlet problem, with inhomogeneous terms, continuous with respect to capacity or combinations of Dirac measures. 相似文献
4.
Ethan D. Bloch 《Discrete and Computational Geometry》2006,35(2):311-328
In a 1967 paper, Banchoff stated that a certain type of polyhedral curvature,
that applies to all finite polyhedra, was zero at all vertices of an odd-dimensional polyhedral manifold; one then obtains
an elementary proof that odd-dimensional manifolds have zero Euler characteristic. In a previous paper, the author defined
a different approach to curvature for arbitrary simplicial complexes, based upon a direct generalization of the angle defect.
The generalized angle defect is not zero at the simplices of every odd-dimensional manifold. In this paper we use a sequence
based upon the Bernoulli numbers to define a variant of the angle defect for finite simplicial complexes that still satisfies
a Gauss-Bonnet-type theorem, but is also zero at any simplex of an odd-dimensional simplicial complex K (of dimension at least
3), such that χ(link(ηi, K)) = 2 for all i-simplices ηi of K, where i is an even integer such that 0 ≤ i ≤ n – 1. As a corollary, an elementary proof is given that any such simplicial
complex has Euler characteristic zero. 相似文献
5.
The N-carboethoxy precursor to (±)-tecomanine has been prepared in 11 steps from 2-methyl-1-buten-3-yne. The key step, Pauson-Khand cyclization of a methylated 5-aza-6-nonen-1-yne succeeds, but only in low yield, a consequence of the dialkyl substitution about the azaenyne framework. Nevertheless, the overall sequence to that point is one of the more efficient to be described. 相似文献
6.
7.
8.
We report the evolution of the high power THz source program at Jefferson Lab. The source is based on coherent synchrotron radiation in which short bunches of relativistic electrons radiate when traversing a dipolar magnetic field. In our first accelerator we produced 20 W of broadband THz light. Our upgraded accelerator with higher current and improved THz extraction optics will considerably enhance the output power to >100 W. In this paper we describe the source in some detail and present theoretical calculations for the upgrade. 相似文献
9.
Jacquelyn A. Carioscia Lauren Schneidewind Casey O'Brien Robert Ely Caitlin Feeser Neil Cramer Christopher N. Bowman 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5686-5696
The ability to prepare high Tg low shrinkage thiol–ene materials is attractive for applications such as coatings and dental restoratives. However, thiol and nonacrylated vinyl materials typically consist of a flexible backbone, limiting the utility of these polymers. Hence, it is of importance to synthesize and investigate thiol and vinyl materials of varying backbone chemistry and stiffness. Here, we investigate the effect of backbone chemistry and functionality of norbornene resins on polymerization kinetics and glass transition temperature (Tg) for several thiol–norbornene materials. Results indicate that Tgs as high as 94 °C are achievable in thiol–norbornene resins of appropriately controlled chemistry. Furthermore, both the backbone chemistry and the norbornene moiety are important factors in the development of high Tg materials. In particular, as much as a 70 °C increase in Tg was observed in a norbornene–thiol specimen when compared with a sample prepared using allyl ether monomer of analogous backbone chemistry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5686–5696, 2007 相似文献
10.
We show that a theorem of Shchepin and Repovš concerning the smoothness of compacta follows from the theory of semicontinuous relations. 相似文献