全文获取类型
收费全文 | 813篇 |
免费 | 37篇 |
国内免费 | 2篇 |
专业分类
化学 | 599篇 |
晶体学 | 8篇 |
力学 | 14篇 |
数学 | 124篇 |
物理学 | 107篇 |
出版年
2023年 | 8篇 |
2022年 | 9篇 |
2021年 | 21篇 |
2020年 | 17篇 |
2019年 | 15篇 |
2018年 | 15篇 |
2017年 | 19篇 |
2016年 | 35篇 |
2015年 | 30篇 |
2014年 | 29篇 |
2013年 | 48篇 |
2012年 | 60篇 |
2011年 | 54篇 |
2010年 | 42篇 |
2009年 | 24篇 |
2008年 | 50篇 |
2007年 | 49篇 |
2006年 | 58篇 |
2005年 | 44篇 |
2004年 | 22篇 |
2003年 | 27篇 |
2002年 | 16篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有852条查询结果,搜索用时 266 毫秒
141.
Dr. Mohammad Rahman Assoc. Prof. Haining Tian Prof. Dr. Tomas Edvinsson 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(38):16418-16433
In pursuit of inexpensive and earth abundant photocatalysts for solar hydrogen production from water, conjugated polymers have shown potential to be a viable alternative to widely used inorganic counterparts. The photocatalytic performance of polymeric photocatalysts, however, is very poor in comparison to that of inorganic photocatalysts. Most of the organic photocatalysts are active in hydrogen production only when a sacrificial electron donor (SED) is added into the solution, and their high performances often rely on presence of noble metal co-catalyst (e.g. Pt). For pursuing a carbon neutral and cost-effective green hydrogen production, unassisted hydrogen production solely from water is one of the critical requirements to translate a mere bench-top research interest into the real world applications. Although this is a generic problem for both inorganic and organic types of photocatalysts, organic photocatalysts are mostly investigated in the half-reaction, and have so far shown limited success in hydrogen production from overall water-splitting. To make progress, this article exclusively discusses critical factors that are limiting the overall water-splitting in organic photocatalysts. Additionally, we also have extended the discussion to issues related to stability, accurate reporting of the hydrogen production as well as challenges to be resolved to reach 10 % STH (solar-to-hydrogen) conversion efficiency. 相似文献
142.
The linear dichroism of the complexes of thymine and cytosine with silver(I) ions dispersed in stretched polyvinylalcohol films was measured in the infrared and in the near ultraviolet regions of the spectrum. The infrared results were helpful in establishing the orientation of the complexes in the films; they also confirmed that the site of silver binding in the case of cytosine involves the carbonyl oxygen. The ultraviolet spectra were deconvoluted into separate electronic transitions and the corresponding transition moments of silver complexes were determined. 相似文献
143.
H-bases are bases for polynomial ideals, characterized by the fact that their homogeneous leading terms are a basis for the associated homogeneous ideal. In the computation ofH-bases without term orders, an important task is to determine the orthogonal projection of a homogeneous polynomial to certain subspaces of homogeneous polynomials with respect to a given inner product. One way of doing so is to use an orthogonal basis of the subspace. In this paper, we present and study a method to efficiently compute such a basis for a particular but important inner product. 相似文献
144.
145.
146.
147.
Josep Daunis-i-Estadella Tomas Aluja-Banet Santiago Thió-Henestrosa 《Computational Statistics》2005,20(3):449-463
Conditional Multiple Correspondence Analysis (MCA), where a control variable plays the role of a partition model, allows us
to decompose global inertia into between inertia and within inertia. The problem is to assess when the conditioning variable
gives different results with respect to the unconditional analysis. In this paper, we study the asymptotic distribution function
of these inertias, which can allow us to determine whether conditioning is significant. Some simulations were performed to
corroborate the established results. 相似文献
148.
Wilson Ryan Korey Bedard Daler Baidilov Marcus Tius Tomas Hudlicky 《Tetrahedron letters》2018,59(25):2467-2469
The base-catalyzed condensation reaction between (E)-4-phenylbut-2-enal and phenylpropargyl aldehyde recently reported in the literature to provide formylcyclobutadiene was repeated under the published conditions. The product obtained was identified as (E)-5-phenyl-2-((E)-styryl)pent-2-en-4-ynal rather than the reported 2-phenyl-3-styrylcyclobutadiene-1-carboxaldehyde. The structure assignment is supported by NMR and IR data and a x-ray structure of the crystalline alcohol obtained by Luche reduction. 相似文献
149.
Lazaro J. Yamin Carlos A. Ponce Mario R. Estrada Francisco Tomas Vert 《Journal of Molecular Structure》1996,360(1-3):109-117
Ab initio molecular orbital calculations with 4-31G//4-31G, 6-31G*//4-31G and 6-31+G//4-31G basis sets have been used to examine the structure, relative energy, protonation and deprotonation of a series of seven hydroxamic acids in the gas phase. The results show that hydroxamic acids are predominantly in the E-TS form and that the most probable protonation site is the carbonyl oxygen atom, while deprotonation proceeds by loss of NH hydrogen. 相似文献
150.
Paul BJ Willis J Martinot TA Ghiviriga I Abboud KA Hudlicky T 《Journal of the American Chemical Society》2002,124(35):10416-10426
Several O-and N-linked inositols and/or aminoinositols have been prepared by iterative opening of epoxides and aziridines derived from homochiral cyclohexadiene cis-diols. The three inositols and their intermediate conduritols (conduramines) were tested against several glycosidases (alpha- and beta-glucosidase, alpha- and beta-galactosidase, alpha- and beta-mannosidase) in an assay that measured the rate of hydrolysis of p-nitrophenolglycosides rather than the concentration of p-nitrophenolate. Somewhat surprisingly, the best inhibition was seen against beta-galactosidase with several of the compounds. The inositols linked through oxygen or nitrogen were subjected to calcium binding studies performed in NMR experiments. Detailed analysis of the title compounds by NMR spectroscopy has been performed, and full assignments were made. One of the attendant benefits of the preparation of these compounds has been expressed in the design and synthesis of new salen catalysts whose effectiveness has been compared with Jacobsen's catalyst in the epoxidation of styrene. 相似文献