全文获取类型
收费全文 | 5726篇 |
免费 | 320篇 |
国内免费 | 57篇 |
专业分类
化学 | 4313篇 |
晶体学 | 23篇 |
力学 | 100篇 |
综合类 | 1篇 |
数学 | 962篇 |
物理学 | 704篇 |
出版年
2023年 | 49篇 |
2022年 | 51篇 |
2021年 | 102篇 |
2020年 | 150篇 |
2019年 | 124篇 |
2018年 | 106篇 |
2017年 | 86篇 |
2016年 | 183篇 |
2015年 | 161篇 |
2014年 | 206篇 |
2013年 | 286篇 |
2012年 | 458篇 |
2011年 | 480篇 |
2010年 | 234篇 |
2009年 | 175篇 |
2008年 | 410篇 |
2007年 | 383篇 |
2006年 | 386篇 |
2005年 | 344篇 |
2004年 | 316篇 |
2003年 | 238篇 |
2002年 | 211篇 |
2001年 | 89篇 |
2000年 | 45篇 |
1999年 | 40篇 |
1998年 | 42篇 |
1997年 | 48篇 |
1996年 | 51篇 |
1995年 | 38篇 |
1994年 | 42篇 |
1993年 | 40篇 |
1992年 | 37篇 |
1991年 | 38篇 |
1990年 | 29篇 |
1989年 | 23篇 |
1988年 | 33篇 |
1987年 | 24篇 |
1986年 | 30篇 |
1985年 | 32篇 |
1984年 | 16篇 |
1983年 | 25篇 |
1982年 | 23篇 |
1981年 | 25篇 |
1980年 | 25篇 |
1979年 | 23篇 |
1978年 | 14篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 13篇 |
排序方式: 共有6103条查询结果,搜索用时 15 毫秒
71.
There is a need to develop broadly applicable, highly sensitive detection methods for microchip CE that do not require analyte derivatization. LIF is highly sensitive but typically requires analyte derivatization. Electrochemistry provides an alternative method for direct analyte detection; however, in its most common form, direct current (DC) amperometry, it is limited to a small number of easily oxidizable or reducible analytes. Pulsed amperometric detection (PAD) is an alternative waveform that can increase the number of electrochemically detectable analytes. Increasing sensitivity for electrochemical detection (EC) and PAD requires the isolation of detection current (nA) from the separation current (muA) in a process generally referred to as current decoupling. Here, we present the development of a simple integrated decoupler to improve sensitivity and its coupling with PAD. A Pd microwire is used as the cathode for decoupling and a second Au or Pt wire is used as the working electrode for either EC or PAD. The electrode system is easy to make, requiring no clean-room facilities or specialized metallization systems. Sensitive detection of a wide range of analytes is shown to be possible using this system. Using this system we were able to achieve detection limits as low as 5 nM for dopamine, 74 nM for glutathione, and 100 nM for glucose. 相似文献
72.
In this article we give an existence theorem for localized travelling wave solutions on one-dimensional lattices with Hamiltonian $$H = \sum\limits_{n \in \mathbb{Z}} {\left( {\tfrac{1}{2}p_n^2 + V(q_{n + 1} - q_n )} \right)} ,$$ whereV(·) is the potential energy due to nearest-neighbour interactions. Until now, apart from rare integrable lattices like the Toda latticeV(φ)=ab ?1(e ?bφ+bφ?1), the only evidence for existence of such solutions has been numerical. Our result in particular recovers existence of solitary waves in the Toda lattice, establishes for the first time existence of solitary waves in the (nonintegrable) cubic and quartic latticesV(φ)= 1/2φ 2 + 1/3aφ 3,V(φ) = 1/2φ 2 + 1/4bφ 4, thereby confirming the numerical findings in [1] and shedding new light on the recurrence phenomena in these systems observed first by Fermi, Pasta and Ulam [2], and shows that contrary to widespread belief, the presence of exact solitary waves is not a peculiarity of integrable systems, but “generic” in this class of nonlinear lattices. The approach presented here is new and quite general, and should also be applicable to other forms of lattice equations: the travelling waves are sought as minimisers of a naturally associated variational problem (obtained via Hamilton's principle), and existence of minimisers is then established using modern methods in the calculus of variations (the concentration-compactness principle of P.-L. Lions [3]). 相似文献
73.
74.
Clayden J Turnbull R Helliwell M Pinto I 《Chemical communications (Cambridge, England)》2004,(21):2430-2431
Thiophene-3-carboxamides bearing allyl or benzyl substituents at nitrogen undergo dearomatising cyclisation on treatment with LDA. Rearrangements transform the dearomatised products into pyrrolinones, azepinones or partially saturated azepinothiophenes. 相似文献
75.
Reacting (−)-menthyl sulfinate with an atropisomeric but racemic aryllithium gives two atropdiastereoisomeric sulfoxides. Separation (by chromatography or crystallisation) and sulfoxide-lithium exchange of each diastereoisomer regenerates the aryllithium in enantiomerically pure form which can be quenched with a range of electrophiles with retention of stereochemical integrity. Overall the reaction sequence is a resolution but without the need for an acidic or basic substituent—a ‘traceless’ method. In certain instances, for example when the nucleophile is an ortholithiated peri-substituted 1-naphthamide, the diastereoisomeric sulfoxides may be interconverted thermally. This allows a dynamic resolution, under thermodynamic control, and hence in principle can give yields of the final products of greater than 50%. The utility of the method is demonstrated by the synthesis of a known atropisomeric phosphine ligand. 相似文献
76.
Frampton MJ Akdas H Cowley AR Rogers JE Slagle JE Fleitz PA Drobizhev M Rebane A Anderson HL 《Organic letters》2005,7(24):5365-5368
[structure: see text] A vinylene-linked porphyrin dimer, with no substituents at the beta-positions, has been synthesized by CuI/CsF promoted Stille coupling. In the crystal structure of this dimer, the C(2)H(2) bridge is twisted by 45 degrees relative to the plane of the porphyrins. The absorption, emission spectra, and electrochemistry reveal substantial porphyrin-porphyrin pi-conjugation. The triplet excited-state absorption spectrum of this dimer makes it suitable for reverse saturable absorption at 710-900 nm. 相似文献
77.
78.
Experimental and numerical results for binding Aedes aegypti densonucleosis virus (AeDNV) using anion and cation exchange membranes are presented. AeDNV particles are adsorbed by anion and cation exchange membranes providing the virus particles and membranes are oppositely charged. Q membranes which are strongly basic anion exchangers were the most effective. Dynamic and static capacities for Q membranes were found to be similar. A numerical model is proposed which assumes a log normal pore size distribution. By estimating the required parameters from static binding experiments, the model may be used to calculate the breakthrough curve for virus adsorption. 相似文献
79.
A series of hydrochalcogenido and phenylchalcogenolate complexes of zinc supported by tris(2-mercapto-1-tert-butylimidazolyl)hydroborato ligation, [Tm(Bu(t))]ZnEH (E = S, Se) and [Tm(Bu(t))]ZnEPh (E = O, S, Se, Te) have been synthesized from [Tm(Bu(t))]ZnMe; structural characterization by X-ray diffraction indicates that the variation in Zn-E bonding as a function of the chalcogen is significantly different from that in other series of metal-chalcogenolate compounds. 相似文献
80.
We present a series of conformational search calculations on the aggregation of short peptide fragments that form fibrils similar to those seen in many protein mis-folding diseases. The proteins were represented by a face-centered cubic lattice model with the conformational energies calculated using the Miyazawa-Jernigan potential. The searches were performed using algorithms based on the Metropolis Monte Carlo method, including simulated annealing and replica exchange. We also present the results of searches using the tabu search method, an algorithm that has been used for many optimization problems, but has rarely been used in protein conformational searches. The replica exchange algorithm consistently found more stable structures then the other algorithms, and was particularly effective for the octamers and larger systems. 相似文献