全文获取类型
收费全文 | 819篇 |
免费 | 36篇 |
专业分类
化学 | 684篇 |
晶体学 | 4篇 |
力学 | 17篇 |
数学 | 71篇 |
物理学 | 79篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 63篇 |
2021年 | 51篇 |
2020年 | 30篇 |
2019年 | 57篇 |
2018年 | 37篇 |
2017年 | 33篇 |
2016年 | 37篇 |
2015年 | 37篇 |
2014年 | 24篇 |
2013年 | 55篇 |
2012年 | 61篇 |
2011年 | 56篇 |
2010年 | 47篇 |
2009年 | 31篇 |
2008年 | 51篇 |
2007年 | 31篇 |
2006年 | 38篇 |
2005年 | 30篇 |
2004年 | 12篇 |
2003年 | 19篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有855条查询结果,搜索用时 15 毫秒
101.
Functionalization of the diaminodibenzocrown ethers with 2H-[1]benzopyrane and 3H-naphtho[2,1-b]pyrane units by Buchwald-Hartwig C-N coupling was developed. It is demonstrated that the novel molecule possesses photochromic properties that can be modified by the complex formation process. 相似文献
102.
Yuliya A. Volkova Ekaterina M. Budynina Tamara S. Kuznetsova Nikolai S. Zefirov 《Tetrahedron》2008,64(16):3548-3553
A novel approach to acyclic alkyldinitronitronates using nucleophilic opening of epoxides with the trinitromethyl anion is presented. The scope and limitations of this synthetic procedure are presented. A series of highly functionalized 3,3-dinitroisoxazolidines were synthesized as mixtures of diastereomers. 相似文献
103.
Ekaterina V. Matveeva 《Tetrahedron letters》2008,49(42):6129-6133
Water as a solvent significantly accelerates the addition of various amines to diethyl vinylphosphonate to yield β-aminophosphonates without any catalyst compared to known procedures for such aza-Michael reactions. The products are obtained in quantitative yields and high purity over short reaction times. Using a reactant ratio (vinylphosphonate/amine) of 2:1 resulted in double phosphorylation of primary amines. 相似文献
104.
105.
Bogdan Kurtev Ekaterina Simova Maya Victorova Nikolina Berova Stefanka Christoskova 《Monatshefte für Chemie / Chemical Monthly》1981,112(5):669-673
Diphenylhalonium salts were used in stereospecific N-phenylation of racemic and optically active 3-amino-2,3-diphenyl-1-propanols leading to 3-anilino-2,3-diphenyl-1-propanols. The absolute configurations of the latter and of genetically related compounds were established.
Stereochemische Korrelation von diastereomeren 3-Amino- mit 3-Arylaminosäuren bzw. ihrer Derivate durch stereospezifische N-Phenylierung mit DiphenylhaloniumsalzenKurze Mitteilung
Zusammenfassung Durch stereospezifische N-Phenylierung mit Hilfe von Diphenylhaloniumsalzen werden racemische sowie optische aktive 3-Amino-2,3-diphenyl-1-propanole in die entsprechenden 3-Anilino-2,3-diphenyl-1-propanole übergeführt. Auf Grund dieser Umwandlung wird die absolute Konfiguration der Aminoalkohole und davon abgeleiteter Derivate ermittelt.相似文献
106.
107.
Ekaterina A. Ilyina Carla Cirillo Carmine Attanasio 《Physica C: Superconductivity and its Applications》2010,470(19):877-879
Current–voltage (I–V) characteristics and critical current density, Jc, for the onset of vortex motion were measured at different magnetic fields, H, and temperatures, T, in a superconducting (S)/ferromagnetic (F) bilayer and in a single Nb film. We choose Nb as a superconductor and a weak ferromagnetic alloy, Pd1−xNix with x = 16, as F. We found that Jc was smaller for the S/F bilayer with respect to the single Nb film. The result was related to the reduced value of the superconducting order parameter in the bilayer. 相似文献
108.
Alexander Serbin Ekaterina Karaseva Vladimir Tsvetkov Olga Alikhanova Igor Rodionov 《Macromolecular Symposia》2010,296(1):466-477
Self assembly of viral biopolymers to nano-complexes forming virions during virus delivery from infected cell and reverse disintegration to virus entry into new cells play a crucial role in viral life cycle and in viral diseases. Therefore artificial instruments for selective counter intervention into these processes are dramatically required for the high effective antiviral protection. Hybrid macromolecular systems (HMS) rationally integrating heterogeneous structure-functional factors for selective recognition - inhibition of viruses (nano-objects) without detriment for cells (micro-objects) can become a molecular basis for cardinal progress in this area. Here we discuss approaches to design and current experimental results of synthesis, and antiviral selectivity evaluations of the HMS, based on combinations of polyelectrolyte-grafted components constructed on principles of mimicry and/or complementarity to viral targets or virus-sensitive cell receptors. Particularly, the HMS generations strongly inhibiting the human immunodeficiency virus (HIV) were created as platform to novel drug development against HIV/AIDS and other sexually transmitted infections. 相似文献
109.
Within the data envelopment analysis context, problems of discrimination between efficient and inefficient decision-making units often arise, particularly if there are a relatively large number of variables with respect to observations. This paper applies Monte Carlo simulation to generalize and compare two discrimination improving methods; principal component analysis applied to data envelopment analysis (PCA–DEA) and variable reduction based on partial covariance (VR). Performance criteria are based on the percentage of observations incorrectly classified; efficient decision-making units mistakenly defined as inefficient and inefficient units defined as efficient. A trade-off was observed with both methods improving discrimination by reducing the probability of the latter error at the expense of a small increase in the probability of the former error. A comparison of the methodologies demonstrates that PCA–DEA provides a more powerful tool than VR with consistently more accurate results. PCA–DEA is applied to all basic DEA models and guidelines for its application are presented in order to minimize misclassification and prove particularly useful when analyzing relatively small datasets, removing the need for additional preference information. 相似文献
110.
Kristopher G. Urie Ekaterina Pletneva Harry B. Gray Jay R. Winkler 《Molecular physics》2013,111(2):301-313
A geometrical model has been developed to study the unfolding of iso-1 cytochrome c. The model draws on the crystallographic data reported for this protein. These data were used to calculate the distance between specific residues in the folded state, and in a sequence of extended states defined by n?=?3, 5, 7, 9, 11, 13, and 15 residue units. Exact calculations carried out for each of the 103 residues in the polypeptide chain demonstrate that different regions of the chain have different unfolding histories. Regions where there is a persistence of compact structures can be identified, and this geometrical characterization is fully consistent with analyses of time-resolved fluorescence energy-transfer (TrFET) data using dansyl-derivatized cysteine side-chain probes at positions 39, 50, 66, 85, and 99. The calculations were carried out assuming that different regions of the polypeptide chain unfold synchronously. To test this assumption, lattice Monte Carlo simulations were performed to study systematically the possible importance of asynchronicity. Calculations show that small departures from synchronous dynamics can arise if displacements of residues in the main body of the chain are much more sluggish than near-terminal residues. 相似文献