全文获取类型
收费全文 | 8648篇 |
免费 | 257篇 |
国内免费 | 62篇 |
专业分类
化学 | 5836篇 |
晶体学 | 85篇 |
力学 | 250篇 |
综合类 | 1篇 |
数学 | 1323篇 |
物理学 | 1472篇 |
出版年
2022年 | 69篇 |
2021年 | 82篇 |
2020年 | 155篇 |
2019年 | 113篇 |
2018年 | 85篇 |
2017年 | 96篇 |
2016年 | 187篇 |
2015年 | 157篇 |
2014年 | 195篇 |
2013年 | 402篇 |
2012年 | 457篇 |
2011年 | 558篇 |
2010年 | 283篇 |
2009年 | 226篇 |
2008年 | 494篇 |
2007年 | 460篇 |
2006年 | 446篇 |
2005年 | 454篇 |
2004年 | 431篇 |
2003年 | 291篇 |
2002年 | 308篇 |
2001年 | 89篇 |
2000年 | 88篇 |
1999年 | 68篇 |
1998年 | 83篇 |
1997年 | 100篇 |
1996年 | 141篇 |
1995年 | 88篇 |
1994年 | 69篇 |
1993年 | 98篇 |
1992年 | 71篇 |
1991年 | 88篇 |
1990年 | 78篇 |
1989年 | 63篇 |
1988年 | 72篇 |
1987年 | 63篇 |
1986年 | 57篇 |
1985年 | 114篇 |
1984年 | 136篇 |
1983年 | 95篇 |
1982年 | 116篇 |
1981年 | 111篇 |
1980年 | 95篇 |
1979年 | 82篇 |
1978年 | 109篇 |
1977年 | 96篇 |
1976年 | 84篇 |
1975年 | 67篇 |
1974年 | 69篇 |
1973年 | 61篇 |
排序方式: 共有8967条查询结果,搜索用时 78 毫秒
991.
Erik D. Demaine Martin L. Demaine Vi Hart John Iacono Stefan Langerman Joseph O��Rourke 《Graphs and Combinatorics》2011,27(3):363-376
We construct the first two continuous bloomings of all convex polyhedra. First, the source unfolding can be continuously bloomed. Second, any unfolding of a convex polyhedron can be refined (further cut, by a linear number of cuts) to have a continuous blooming. 相似文献
992.
Convex and concave relaxations are used extensively in global optimization algorithms. Among the various techniques available
for generating relaxations of a given function, McCormick’s relaxations are attractive due to the recursive nature of their
definition, which affords wide applicability and easy implementation computationally. Furthermore, these relaxations are typically
stronger than those resulting from convexification or linearization procedures. This article leverages the recursive nature
of McCormick’s relaxations to define a generalized form which both affords a new framework within which to analyze the properties
of McCormick’s relaxations, and extends the applicability of McCormick’s technique to challenging open problems in global
optimization. Specifically, relaxations of the parametric solutions of ordinary differential equations are considered in detail,
and prospects for relaxations of the parametric solutions of nonlinear algebraic equations are discussed. For the case of
ODEs, a complete computational procedure for evaluating convex and concave relaxations of the parametric solutions is described.
Through McCormick’s composition rule, these relaxations may be used to construct relaxations for very general optimal control
problems. 相似文献
993.
A robust route to 2,4-disubstituted pyrrole heterocycles relying upon a cascade reaction is reported. The reaction benefits from operational simplicity: it is air and moisture tolerant and is performed at ambient temperature. Control over the reaction conditions provides ready access to isopyrroles, 2,3,4-trisubstituted pyrroles, and 3-substituted pyrollidin-2-ones. 相似文献
994.
Salandria KJ Arico JW Calhoun AK McLaughlin LW 《Journal of the American Chemical Society》2011,133(6):1766-1768
We describe here the synthesis and properties of A-T rich DNA containing covalently bound water mimics located in the DNA minor groove. 相似文献
995.
Kumarasamy E Jesuraj JL Omlid JN Ugrinov A Sivaguru J 《Journal of the American Chemical Society》2011,133(43):17106-17109
Nonbiaryl axially chiral 2-pyridones were synthesized and employed for light-induced electrocyclic 4π ring closure leading to bicyclo-β-lactam photoproducts in solution. The enantioselectivity in the photoproducts varied from 22 to 95% depending on the reaction temperature and the ability of the axially chiral chromophore to form intramolecular and/or intermolecular H-bonds with the solvent. On the basis of the differential activation parameters, entropic control of the enantiospecificity was observed for 2-pyridones lacking the ability to form H-bonds. Conversely, enthalpy played a significant role for 2-pyridones having the ability to form H-bonds. 相似文献
996.
The Ph(4)P(+) salt of the tetrahedral complex [Co(SPh)(4)](2-), possessing an S = (3)/(2) ground state with an axial zero-field splitting of D = -70 cm(-1), displays single-molecule magnet behavior in the absence of an applied magnetic field. At very low temperatures, ac magnetic susceptibility data show the magnetic relaxation time, τ, to be temperature-independent, while above 2.5 K thermally activated Arrhenius behavior is apparent with U(eff) = 21(1) cm(-1) and τ(0) = 1.0(3) × 10(-7) s. Under an applied field of 1 kOe, τ more closely approximates Arrhenius behavior over the entire temperature range. Upon dilution of the complex within a matrix of the isomorphous compound (Ph(4)P)(2)[Zn(SPh)(4)], ac susceptibility data reveal the molecular nature of the slow magnetic relaxation and indicate that the quantum tunneling pathway observed at low temperatures is likely mediated by intermolecular dipolar interactions. 相似文献
997.
Coppage R Slocik JM Briggs BD Frenkel AI Heinz H Naik RR Knecht MR 《Journal of the American Chemical Society》2011,133(32):12346-12349
The ability to control the size, shape, composition, and activity of nanomaterials presents a formidable challenge. Peptide approaches represent new avenues to achieve such control at the synthetic level; however, the critical interactions at the bio/nano interface that direct such precision remain poorly understood. Here we present evidence to suggest that materials-directing peptides bind at specific time points during Pd nanoparticle (NP) growth, dictated by material crystallinity. As such surfaces are presented, rapid peptide binding occurs, resulting in the stabilization and size control of single-crystal NPs. Such specificity suggests that peptides could be engineered to direct the structure of nanomaterials at the atomic level, thus enhancing their activity. 相似文献
998.
He F Wang W Chen W Xu T Darling SB Strzalka J Liu Y Yu L 《Journal of the American Chemical Society》2011,133(10):3284-3287
A series of semiconducting copolymers (PTAT-x) containing extended π-conjugated tetrathienoanthracene units have been synthesized. It was shown that the extended conjugation system enhanced the π-π stacking in the polymer/PC(61)BM blend films and facilitated the charge transport in heterojunction solar cell devices. After structural fine-tuning, the polymer with bulky 2-butyloctyl side chains (PTAT-3) exhibited a PCE of 5.6% when it was blended with PC(61)BM. 相似文献
999.
Moran J Smith AG Carris RM Johnson JS Krische MJ 《Journal of the American Chemical Society》2011,133(46):18618-18621
The coupling of carbonyl electrophiles at the donor position of donor-acceptor cyclopropanes is described, representing an inversion of polarity with respect to conventional reactivity modes displayed by these reagents. Specifically, upon exposure of donor-acceptor cyclopropanes to alcohols in the presence of a cyclometalated iridium catalyst modified by (S)-BINAP, catalytic C-C coupling occurs, providing enantiomerically enriched products of carbonyl allylation. Identical products are obtained upon isopropanol-mediated transfer hydrogenation of donor-acceptor cyclopropanes in the presence of aldehydes. The reaction products are directly transformed to cis-4,5-disubstituted δ-lactones. 相似文献
1000.
An electrochemical genosensor in which signal amplification is achieved using p-aminophenol (p-AP) redox cycling by nicotinamide adenine dinucleotide (NADH) is presented. An immobilized thiolated capture probe is combined with a sandwich-type hybridization assay, using biotin as a tracer in the detection probe, and streptavidin-alkaline phosphatase as reporter enzyme. The phosphatase liberates the electrochemical mediator p-AP from its electrically inactive phosphate derivative. This generated p-AP is electrooxidized at an Au electrode modified self-assembled monolayer to p-quinone imine (p-QI). In the presence of NADH, p-QI is reduced back to p-AP, which can be re-oxidized on the electrode and produce amplified signal. A detection limit of 1 pM DNA target is offered by this simple one-electrode, one-enzyme format redox cycling strategy. The redox cycling design is applied successfully to the monitoring of the 16S rRNA of E. coli pathogenic bacteria, and provides a detection limit of 250 CFU μL−1. 相似文献