全文获取类型
收费全文 | 199篇 |
免费 | 3篇 |
专业分类
化学 | 140篇 |
晶体学 | 8篇 |
数学 | 32篇 |
物理学 | 22篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 1篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 1篇 |
2014年 | 11篇 |
2013年 | 8篇 |
2012年 | 14篇 |
2011年 | 10篇 |
2010年 | 14篇 |
2009年 | 9篇 |
2008年 | 15篇 |
2007年 | 6篇 |
2006年 | 10篇 |
2005年 | 16篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1993年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1977年 | 2篇 |
排序方式: 共有202条查询结果,搜索用时 203 毫秒
121.
Cecilia Saiz Valentina Villamil Mariano M. González Ma. Agustina Rossi Lorena Martínez Leopoldo Suescun Alejandro J. Vila Graciela Mahler 《Tetrahedron: Asymmetry》2017,28(1):110-117
The synthesis of new oxazolidinylthiazolidines bicycles, oxygen analogues of bisthiazolidines, also known as metallo-β-lactamase inhibitors is described. The reaction of β-aminoalcohols and 2,5-dihydroxy-1,4-dithiane led to oxazolidinylthiazolidines and/or dithioazabicycles as the main products. The distribution pattern depends mainly on the aminoalcohol substituents. In a one-pot reaction, four new bonds are formed in good yields and with high atom efficiency. When the oxazolidinylthiazolidines are formed, two stereogenic centres are generated with high enantiospecificity. The reaction mechanism is discussed based on crystallographic data and interconversion studies. Two oxazolidinylthiazolidines were evaluated as inhibitors of the potent lactamase NDM-1 and compound 4f displayed competitive inhibition with Ki = 1.6 ± 0.6 μM. 相似文献
122.
123.
124.
The adsorption of isocyanate (? NCO) species on Cu(100) was studied using the density functional theory (DFT) and the periodic slab model. The calculations indicate that at low and intermediate coverages NCO adsorbs preferentially on bridge and hollow sites. Work function and dipole moment changes show a significant negative charge transfer from Cu to NCO. The resulting charged NCO species interact repulsively among themselves being these dipole–dipole interactions particularly intensive when they are adsorbed in adjacent sites. Consequently, isocyanates tend to be separated from each other generating the vacant sites required for the dissociation to N and CO. This condition for NCO dissociation has been suggested in the past from experimental observations. A comparison was also performed with the NCO adsorption on Pd(100). In particular, the calculated minimal energy barrier for NCO dissociation was found to be higher on Cu(100) than on Pd(100) in accord with the well known higher NCO stability on Cu(100). 相似文献
125.
Baptista L Pfeifer R da Silva EC Arbilla G 《The journal of physical chemistry. A》2011,115(40):10911-10919
Using density functional methods, the initial reaction steps of limonene ozonolysis have been investigated with a focus on primary ozonide formation and its decomposition to Criegee intermediates and carbonyl compounds. The ozonide formation is highly exothermic, and the decomposition channels have similar free energies of activation, ΔG(?), indicating that there is no primary pathway for ozonide decomposition. Assuming that ozonide formation is the rate limiting step, the theoretical rate coefficient, k = 1.6 × 10(-16) molecule(-1) cm(3) s(-1), evaluated at the CCSD(T)/6-31G(d,p)//BHandHLYP/cc-pvdz level and 298.15 K for d-limonene is in good agreement with the experimental value, k(exp) = 3.3 × 10(-16) molecule(-1) cm(3) s(-1). The theoretical Arrhenius expression is also in good agreement with experimental results. 相似文献
126.
The preparation of new diblock copolypeptide hydrogels derived from homologs of l ‐methionine, that is, l ‐homomethionine and l ‐6‐(methylthio)‐l ‐norleucine is described. Compared to l ‐methionine residues, use of l ‐methionine homologs allow improved copolymerization with l ‐leucine residues to give well‐defined block copolypeptides. These copolypeptides are subsequently modified using robust thioether alkylation reactions employing a variety of functional epoxides, which yield samples capable of forming transparent, self‐healing hydrogels in water. The facile variation of different functional epoxides for postpolymerization modification is found to allow predictable functionalization and tuning of hydrogel properties by the modification of simple precursors. 相似文献
127.
Bessone V Pizarro MD Izaguirre MF Biancardi ME Furno G Baumgartner N Rodriguez JV Quintana AB 《Cryo letters》2011,32(1):69-80
Human cardiac valve allografts (HVAs) suffer injuries during the cryopreservation period. Here, we described structural, ultrastructural and functional damages suffered by HVAs after an increment of their cryostorage temperature (100 degree C). Two experimental groups of pulmonary and aortic HVAs were compared: cryopreserved (HVAcryo) and cryopreserved with temperature changes (HVAΔT). Transmission electron microscopy (TEM) was used to analyze valve fibroblasts and extracellular matrix morphology. Total collagen amount was estimated using two different methods and fibroblast viability was assessed measuring their oxygen consumption rate. Porcine heart grafts valves were used to set the techniques. Disorganized collagen network was seen in HVAΔT by TEM. Fibroblasts showed damages in the cellular membrane and many secretor vesicles. Mitochondria and chromatin were also altered. HVAΔT had less amount of collagen and fibroblasts showed an oxygen consumption rate markedly diminished compared to HVAcryo. The increment of 100 degree C suffered by HVAs caused damages that made them unsuitable for clinical purposes. 相似文献
128.
We apply residuated structures associated with fuzzy logic to develop certain aspects of information processing in quantum computing from a logical perspective. For this purpose, we introduce an axiomatic system whose natural interpretation is the irreversible quantum Poincaré structure. 相似文献
129.
Graciela D. Venera Claudia Machalinski Hugo Zum’arraga Mirtha J. Biscoglio Jim’enez de Bonino 《Applied biochemistry and biotechnology》1997,68(3):207-216
Further characterization of an aspartyl protease fromMucor bacilliformis with milk-clotting activity was performed. An extinction coefficient, ε278 cm = 1.61 mL/mg/cm, a molecular mass of 35,400 Da and a pI of 5.2 were determined. Proteolytic activity and kinetic parameters
were evaluated by using the hexapeptide Leu-Ser-pNO2-Phe-Nle-Ala-Leu-OMe as the substrate. The effect of pH and temperature on peptide cleavage, as well as protease heat stability,
was determined. Such properties, taken as a whole, indicate that theM. bacilliformis protease can be considered a potential substitute for bovine chymosin in cheese manufacture. 相似文献
130.
Luis Anchordoqui Graciela Birman Santiago Perez Bergliaffa Héctor Vucetich 《General Relativity and Gravitation》1996,28(6):701-706
Cosmological solutions of Einstein equation for a 5-dimensional space time, in the case of a dust-filled universe, are presented. With these solutions we are able to test a hypothetical relation between the rest mass of a particle and the 5th dimension. Comparison with experiment strongly refutes the implied dependence of the rest mass on the cosmological time. 相似文献