全文获取类型
收费全文 | 1988篇 |
免费 | 103篇 |
国内免费 | 2篇 |
专业分类
化学 | 1306篇 |
晶体学 | 7篇 |
力学 | 17篇 |
数学 | 405篇 |
物理学 | 358篇 |
出版年
2023年 | 20篇 |
2022年 | 16篇 |
2021年 | 25篇 |
2020年 | 35篇 |
2019年 | 24篇 |
2018年 | 35篇 |
2017年 | 21篇 |
2016年 | 79篇 |
2015年 | 72篇 |
2014年 | 77篇 |
2013年 | 141篇 |
2012年 | 136篇 |
2011年 | 134篇 |
2010年 | 78篇 |
2009年 | 104篇 |
2008年 | 93篇 |
2007年 | 127篇 |
2006年 | 112篇 |
2005年 | 106篇 |
2004年 | 74篇 |
2003年 | 68篇 |
2002年 | 52篇 |
2001年 | 40篇 |
2000年 | 33篇 |
1999年 | 37篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 29篇 |
1994年 | 19篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 31篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有2093条查询结果,搜索用时 15 毫秒
101.
102.
Alberto García‐Peñas José M. Gómez‐Elvira Ernesto Pérez María L. Cerrada 《Journal of polymer science. Part A, Polymer chemistry》2013,51(15):3251-3259
Terpolymers based on propylene with 1‐pentene and 1‐hexene as comonomeric units are satisfactorily synthesized using a metallocene catalyst. Thus, several terpolymers are prepared with distinct overall compositions in comonomers as well as three different 1‐pentene/1‐hexene ratios at a given composition to evaluate the influence on polymerization activity, intrinsic viscosity, and microstructural details. The new trigonal δ polymorph is observed in those quenched terpolymers with a global content in comonomers of about 14 mol %, independently of the ratio between both comonomers. However, preliminary results indicate a profound influence of that ratio on the crystallization rate. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3251–3259 相似文献
103.
Numerical Algorithms - An inverse central ordering of the nodes is proposed for the Newton interpolation formula. This ordering may improve the stability for certain distributions of nodes. For... 相似文献
104.
105.
Ireneusz W. Bulik Robert Zaleśny Wojciech Bartkowiak Josep M. Luis Bernard Kirtman Gustavo E. Scuseria Aggelos Avramopoulos Heribert Reis Manthos G. Papadopoulos 《Journal of computational chemistry》2013,34(20):1775-1784
A set of exchange‐correlation functionals, including BLYP, PBE0, B3LYP, BHandHLYP, CAM‐B3LYP, LC‐BLYP, and HSE, has been used to determine static and dynamic nonresonant (nuclear relaxation) vibrational (hyper)polarizabilities for a series of all‐trans polymethineimine (PMI) oligomers containing up to eight monomer units. These functionals are assessed against reference values obtained using the Møller–Plesset second‐order perturbation theory (MP2) and CCSD methods. For the smallest oligomer, CCSD(T) calculations confirm the choice of MP2 and CCSD as appropriate for assessing the density functionals. By and large, CAM‐B3LYP is the most successful, because it is best for the nuclear relaxation contribution to the static linear polarizability, intensity‐dependent refractive index second hyperpolarizability, static second hyperpolarizability, and is close to the best for the electro‐optical Pockels effect first hyperpolarizability. However, none of the functionals perform satisfactorily for all the vibrational (hyper)polarizabilities studied. In fact, in the case of electric field‐induced second harmonic generation all of them, as well as the Hartree–Fock approximation, yield the wrong sign. We have also found that the Pople 6–31+G(d) basis set is unreliable for computing nuclear relaxation (hyper)polarizabilities of PMI oligomers due to the spurious prediction of a nonplanar equilibrium geometry. © 2013 Wiley Periodicals, Inc. 相似文献
106.
107.
Cristina García‐Simón Marc Garcia‐Borràs Dr. Laura Gómez Dr. Isaac Garcia‐Bosch Dr. Sílvia Osuna Prof. Marcel Swart Dr. Josep M. Luis Prof. Concepció Rovira Prof. Manuel Almeida Dr. Inhar Imaz Prof. Daniel Maspoch Dr. Miquel Costas Dr. Xavi Ribas 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1445-1456
The metal‐directed supramolecular synthetic approach has paved the way for the development of functional nanosized molecules. In this work, we report the preparation of the new nanocapsule 3? (CF3SO3)8 with a A4B2 tetragonal prismatic geometry, where A corresponds to the dipalladium hexaazamacrocyclic complex Pd‐1 , and B corresponds to the tetraanionic form of palladium 5,10,15,20‐tetrakis(4‐carboxyphenyl)porphyrin ( 2 ). The large void space of the inner cavity and the supramolecular affinity for guest molecules towards porphyrin‐based hosts converts this nanoscale molecular 3D structure into a good candidate for host–guest chemistry. The interaction between this nanocage and different guest molecules has been studied by means of NMR, UV/Vis, ESI‐MS, and DOSY experiments, from which highly selective molecular recognition has been found for anionic, planar‐shaped π guests with association constants (Ka) higher than 109 M ?1, in front of non‐interacting aromatic neutral or cationic substrates. DFT theoretical calculations provided insights to further understand this strong interaction. Nanocage 3? (CF3SO3)8 can not only strongly host one single molecule of M(dithiolene)2 complexes (M=Au, Pt, Pd, and Ni), but also can finely tune their optical and redox properties. The very simple synthesis of both the supramolecular cage and the building blocks represents a step forward for the development of polyfunctional supramolecular nanovessels, which offer multiple applications as sensors or nanoreactors. 相似文献
108.
Marc Garcia‐Borràs Dr. Josep M. Luis Prof. Dr. Marcel Swart Prof. Dr. Miquel Solà 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(14):4468-4479
One of the most important reactions in fullerene chemistry is the Diels–Alder (DA) reaction. In two previous experimental studies, the DA cycloaddition reactions of cyclopentadiene (Cp) and 1,2,3,4,5‐pentamethylcyclopentadiene (Cp*) with La@C2v‐C82 were investigated. The attack of Cp was proposed to occur on bond 19 , whereas that of Cp* was confirmed by X‐ray analysis to be over bond o . Moreover, the stabilities of the Cp and Cp* adducts were found to be significantly different, that is, the decomposition of La@C2v‐C82Cp was one order of magnitude faster than that of La@C2v‐C82Cp*. Herein, we computationally analyze these DA cycloadditions with two main goals: First, to compute the thermodynamics and kinetics of the cycloadditions of Cp and Cp* to different bonds of La@C2v‐C82 to assess and compare the regioselectivity of these two reactions. Second, to understand the origin of the different thermal stabilities of the La@C82Cp and La@C82Cp* adducts. Our results show that the regioselectivity of the two DA cycloadditions is the same, with preferred attack on bond o . This result corrects the previous assumption of the regioselectivity of the Cp attack that was made based only on the shape of the La@C82 singly occupied molecular orbital. In addition, we show that the higher stability of the La@C82Cp* adduct is not due to the electronic effects of the methyl groups on the Cp ring, as previously suggested, but to higher long‐range dispersion interactions in the Cp* case, which enhance the stabilization of the reactant complex, transition state, and products with respect to the separated reactants. This stabilization for the La@C82Cp* case decreases the Gibbs reaction energy, thus allowing competition between the direct and retro reactions and making dissociation more difficult. 相似文献
109.
110.