全文获取类型
收费全文 | 224篇 |
免费 | 10篇 |
专业分类
化学 | 172篇 |
力学 | 3篇 |
数学 | 22篇 |
物理学 | 37篇 |
出版年
2023年 | 2篇 |
2022年 | 16篇 |
2021年 | 9篇 |
2020年 | 7篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 4篇 |
2013年 | 10篇 |
2012年 | 26篇 |
2011年 | 15篇 |
2010年 | 10篇 |
2009年 | 11篇 |
2008年 | 11篇 |
2007年 | 11篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 12篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1948年 | 1篇 |
1935年 | 4篇 |
1914年 | 1篇 |
1910年 | 2篇 |
1905年 | 1篇 |
排序方式: 共有234条查询结果,搜索用时 31 毫秒
51.
Pacheco-Contreras R Dessens-Félix M Borbón-González DJ Paz-Borbón LO Johnston RL Schön JC Posada-Amarillas A 《The journal of physical chemistry. A》2012,116(21):5235-5239
The threshold method is used to explore the potential energy surface of the Pt(1)Pd(12) bimetallic cluster, defined by the Gupta semiempirical potential. A set of helical structures, which follow a Bernal tetrahelix pattern, correspond to local minima for the Pt(1)Pd(12) cluster, characterizing the region of the energy landscape where these structures are present. Both right-handed and left-handed chiral forms were discovered in our searches. Energetic and structural details of each of the tetrahelices are reported as well as the corresponding transition probabilities between these structures and with respect to the icosahedron-shaped global minimum structure via a disconnectivity graph analysis. 相似文献
52.
53.
R-matrix calculations on electron collisions with the purine bases found in DNA and RNA (i.e., adenine and guanine) are presented. Resonant anion states of these systems are identified by employing different approximation levels of ab initio theoretical methods, such as the static exchange, the static exchange plus polarization, and the close-coupling methods. The results are compared with other available calculations and experiments. All of these ab initio approximations, which we refer to as a scattering "model," give four shape resonances of (2)A' (π) symmetry within the energy range of 10 eV for both molecules. For adenine, the most sophisticated method, the close-coupling model, gives two very narrow (2)A' (σ) symmetry Feshbach-type resonances at energies above 5 eV. Quantitative results for the total elastic and electronic excitation cross sections are also presented. 相似文献
54.
Verónica Hoyos 《ZDM》2012,44(6):775-786
This paper reviews existing research on how in-service high school teachers have learned about, worked on or thought about the incorporation of mathematics technology into their teaching practices. The paper reviews different scenarios of instruction issuing from important research related to teacher professional development. Specifically, we will deal with contributions to online in-service mathematics teacher education that refer to the use of digital technologies in classroom teaching practices. The different articles reviewed belong to a range of teams of researchers from several universities and countries, and who have implemented distinct online education approaches. That work has allowed the gaining of knowledge on the specificities of using Web 2.0 tools for mathematics professional development (MPD), the function that online teacher interaction has in teacher learning, and the actual classroom conditions in which mathematics technology is incorporated into instructional practice. This paper describes and discusses the design features of those approaches emphasizing the main concepts and their underpinning theoretical frames, noting important design elements, and specific results. Finally, the paper discusses how some of these research findings are connected with emergent issues in the field of MPD. 相似文献
55.
Zusammenfassung Es wurden zwei Methoden zur Darstellung von kolloidem Quecksilber durch Reduktion von Merkurisalzen ausgearbeitet.
Der Dissoziationsgrad der angewandten Merkurisalze ist von gro?em Einflu? auf das Gelingen der Soldarstellung.
Es erwies sich, da? nur dann bei der Reduktion von Quecksilbersalzen das Metall in kolloider Form erhalten wird, wenn schon
als Zwischenprodukt ein Sol auftritt. Und zwar ist Bedingung, da? dieses Sol Teilchen enth?lt, welche, wie die von Quecksilbersol,
negativ geladen sind. Diese Bedingung wird z. B. von Merkuro-, nicht dagegen von Merkurioxydsol erfüllt. 相似文献
56.
57.
58.
59.
Darko P. A?anin Sne?ana Rajkovi? Dora Molnar-Gabor Milos? I. Djuran 《Monatshefte für Chemie / Chemical Monthly》2004,13(3):1445-1453
Hydrolytic reactions between various palladium(II) complexes of the type cis-[Pd(L)(H2O)2]2+ in which L is ethylenediamine (en), 1,2-propylenediamine (1,2-pn), isobutylenediamine (ibn), 1,2-diaminocyclohexane (1,2-dach), N-methylethylenediamine (Meen), N,N,N,N-tetramethylethylenediamine (Me4en), S-methyl L-cysteine (MeS-L-HCys), L-methionine (L-HMet), and 2,5-dithiahexane (dth) and dipeptide N-acetylated L-methionylglycine (MeCOMet-Gly) were studied by 1H NMR spectroscopy. The reactions were carried out in the pH range 2.0–2.5 and at 50°C. In all these reactions, palladium(II) complex bound to a methionine residue effects the regioselective cleavage of the amide bond involving the carboxylic group of methionine. We found that the rate of hydrolysis and mechanism of this reaction are strongly dependent from the nature of the chelate ligand L in palladium(II) complexes of the type cis-[Pd(L)(H2O)2]2+. 相似文献
60.
Lauren A. Mitchell Julie M. Stanley Liliana Espinosa De Hoyos Bradley J. Holliday 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(6):638-641
The crystal structures of 3,4,6a,7,10,10a‐hexahydro‐7,10‐epoxypyrimido[2,1‐a]isoindol‐6(2H)‐one, C11H12N2O2, and 2‐(2‐aminoethyl)‐3a,4,7,7a‐tetrahydro‐1H‐4,7‐epoxyisoindole‐1,3(2H)‐dione, C10H12N2O3, two tricyclic imides, show one and two molecules in the asymmetric unit, respectively. Intermolecular hydrogen‐bonding interactions are observed in both compounds. 相似文献