全文获取类型
收费全文 | 499篇 |
免费 | 25篇 |
国内免费 | 12篇 |
专业分类
化学 | 394篇 |
晶体学 | 4篇 |
力学 | 13篇 |
数学 | 59篇 |
物理学 | 66篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 18篇 |
2021年 | 15篇 |
2020年 | 29篇 |
2019年 | 19篇 |
2018年 | 28篇 |
2017年 | 16篇 |
2016年 | 21篇 |
2015年 | 26篇 |
2014年 | 29篇 |
2013年 | 59篇 |
2012年 | 28篇 |
2011年 | 31篇 |
2010年 | 32篇 |
2009年 | 24篇 |
2008年 | 32篇 |
2007年 | 18篇 |
2006年 | 20篇 |
2005年 | 24篇 |
2004年 | 14篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有536条查询结果,搜索用时 656 毫秒
141.
Given a projective surface and a generic projection to the plane,the braid monodromy factorization(and thus,the braid monodromy type)of the complement of its branch curve is one of the most important topological invariants,stable on deformations.From this factorization,one can compute the fundamental group of the complement of the branch curve,either in C~2 or in CP~2.In this article,we show that these groups,for the Hirzebruch surface F_1,(a,b),are almost-solvable.That is, they are an extension of a solvable group,which strengthen the conjecture on degeneratable surfaces. 相似文献
142.
A simple, efficient, and general method has been developed for the one-pot synthesis of α-aminophosphonic esters in water using β-cyclodextrin as an efficient catalyst. α-Aminophosphonic esters were obtained in good yields (45-82%) and purity under mild conditions by the reaction of diethyl phosphite with a mixture of aldehyde and amine in water at reflux. 相似文献
143.
Given a projective surface and a generic projection to the plane, the braid monodromy factorization (and thus, the braid monodromy
type) of the complement of its branch curve is one of the most important topological invariants, stable on deformations. From
this factorization, one can compute the fundamental group of the complement of the branch curve, either in ℂ2 or in ℂℙ2. In this article, we show that these groups, for the Hirzebruch surface F
1,(a,b), are almost-solvable. That is, they are an extension of a solvable group, which strengthen the conjecture on degeneratable
surfaces.
This work was supported by the Emmy Noether Institute Fellowship (by the Minerva Foundation of Germany) and Israel Science
Foundation (Grant No. 8008/02-3) 相似文献
144.
145.
In this paper, the behavior of a fractional order Van der Pol-like oscillator is investigated using a describing function method. A parametric function for the boundary between oscillatory and nonoscillatory regions of this system is extracted. The analytical results are evaluated by numerical simulations which demonstrate sufficient reliability of the proposed analyzing method. 相似文献
146.
Nishiwaki N Nishida D Ohnishi T Hidaka F Shimizu S Tamura M Hori K Tohda Y Ariga M 《The Journal of organic chemistry》2003,68(22):8650-8656
The acyl group of an alpha-aryl-beta-keto ester was readily transferred to N-, O-, and S-nucleophiles. The transacylation from arylated diethyl 3-oxoglutarate to amines led to unsymmetrical malonic acid amide esters in high yields. The present reaction proceeded under mild conditions without formation of detectable byproducts. Only simple experimental manipulations were required. This reaction was also found to be sensitive to steric factors, which enabled the chemoselective monoacylation of diamines and amino alcohols without any modifications such as protection. 相似文献
147.
One-photon mass-analyzed threshold ionization (MATI) spectrum of CH2BrI was obtained using coherent vacuum-ultraviolet radiation generated by four-wave difference-frequency mixing in Kr. Unlike CH2ClI investigated previously, a very extensive bending (Br-C-I) progression was observed. Vibrational frequencies of CH2BrI+ were measured from the spectra and the vibrational assignments were made by utilizing frequencies calculated by the density-functional-theory (DFT) method using relativistic effective core potentials with and without the spin-orbit terms. A noticeable spin-orbit effect on the vibrational frequencies was observed from the DFT calculations, even though its influence was not so dramatic as in CH2ClI+. A simple explanation based on the bonding characteristics of the molecular orbitals involved in the ionization is presented to account for the above differences between the MATI spectra of CH2BrI and CH2ClI. The 0-0 band of the CH2BrI spectrum could be identified through the use of combined data from calculations and experiments. The adiabatic ionization energy determined from the position of this band was 9.5944+/-0.0006 eV, which was significantly smaller than the vertical ionization energy reported previously. 相似文献
148.
Lavinia L. Ruta Ileana C. Farcasanu Mihaela Bacalum Mina Rileanu Arpad Mihai Rostas Constantin Daniliuc Mariana Carmen Chifiriuc Luminia Mruescu Marcela Popa Mihaela Badea Emilia Elena Iorgulescu Rodica Olar 《Molecules (Basel, Switzerland)》2021,26(22)
Novel complexes of type [Cu(N-N)(dmtp)2(OH2)](ClO4)2·dmtp ((1) N-N: 2,2′-bipyridine; (2) L: 1,10-phenantroline and dmtp: 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine) were designed in order to obtain biologically active compounds. Complexes were characterized as mononuclear species that crystallized in the space group P-1 of the triclinic system with a square pyramidal geometry around the copper (II). In addition to the antiproliferative effect on murine melanoma B16 cells, complex (1) exhibited low toxicity on normal BJ cells and did not affect membrane integrity. Complex (2) proved to be a more potent antimicrobial in comparison with (1), but both compounds were more active in comparison with dmtp—both against planktonic cells and biofilms. A stronger antimicrobial and antibiofilm effect was noticed against the Gram-positive strains, including methicillin-resistant Staphylococcus aureus (MRSA). Both electron paramagnetic resonance (EPR) and Saccharomyces cerevisiae studies indicated that the complexes were scavengers rather than reactive oxygen species promoters. Their DNA intercalating capacity was evidenced by modifications in both absorption and fluorescence spectra. Furthermore, both complexes exhibited nuclease-like activity, which increased in the presence of hydrogen peroxide. 相似文献
149.
Sattar R. Majeed Mina A. Amin Fawzy A. Attaby Marta E. Alberto Ahmed A. Soliman 《Molecules (Basel, Switzerland)》2022,27(3)
Three new palladium complexes ([Pd(DABA)Cl2], [Pd(CPDA)Cl2], and [Pd(HZPY)Cl2]) bearing dinitrogen ligands (DABA: 3,4-diaminobenzoic acid; CPDA: 4-chloro–o-phenylenediamine; HZPY: 2-hydraziniopyridine) were synthesized, characterized, and tested against breast cancer (MCF-7), prostate carcinoma cell line (PC3) and liver carcinoma cell line (HEPG2). [Pd(DABA)Cl2] complex exhibited the highest inhibition percentage, lying between 68–71%. The hydrolysis mechanism of each palladium complex, the key step preceding the binding to the biological target, as well as their photophysical properties were explored by means of DFT and TDDFT computations. Results indicate a faster hydrolysis process for the Pd(DABA)Cl2 complex. The computed activation energies for the first and second hydrolysis processes suggest that all the compounds could reach DNA in their monohydrated form. 相似文献
150.
My Hang V. Huynh Jennifer Smyth Modi Wetzler Brendan Mort Paul K. Gong Laura M. Witham Donald L. Jameson David K. Geiger Joanne M. Lasker Mina Charepoo Michelle Gornikiewicz Jose M. Cintron Gretchen Imahori Roberto R. Sanchez Amy C. Marschilok Lynn M. Krajkowski David G. Churchill Melvyn Rowen Churchill Kenneth J. Takeuchi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2001,113(23):4601-4605