全文获取类型
收费全文 | 2102篇 |
免费 | 107篇 |
国内免费 | 8篇 |
专业分类
化学 | 1518篇 |
晶体学 | 13篇 |
力学 | 64篇 |
数学 | 317篇 |
物理学 | 305篇 |
出版年
2023年 | 18篇 |
2022年 | 15篇 |
2021年 | 50篇 |
2020年 | 62篇 |
2019年 | 45篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 68篇 |
2015年 | 50篇 |
2014年 | 67篇 |
2013年 | 112篇 |
2012年 | 156篇 |
2011年 | 201篇 |
2010年 | 110篇 |
2009年 | 91篇 |
2008年 | 152篇 |
2007年 | 147篇 |
2006年 | 147篇 |
2005年 | 127篇 |
2004年 | 110篇 |
2003年 | 81篇 |
2002年 | 66篇 |
2001年 | 40篇 |
2000年 | 21篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 24篇 |
1996年 | 27篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 16篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1939年 | 3篇 |
1915年 | 4篇 |
1913年 | 3篇 |
1906年 | 2篇 |
1903年 | 2篇 |
1889年 | 3篇 |
排序方式: 共有2217条查询结果,搜索用时 15 毫秒
151.
152.
This is the fourth article of our series. Here, we study weighted norm inequalities for the Riesz transform of the Laplace–Beltrami
operator on Riemannian manifolds and of subelliptic sum of squares on Lie groups, under the doubling volume property and Gaussian
upper bounds.
相似文献
153.
154.
Repair of (6‐4) Lesions in DNA by (6‐4) Photolyase: 20 Years of Quest for the Photoreaction Mechanism 下载免费PDF全文
Exposure of DNA to ultraviolet (UV) light from the Sun or from other sources causes the formation of harmful and carcinogenic crosslinks between adjacent pyrimidine nucleobases, namely cyclobutane pyrimidine dimers and pyrimidine(6–4)pyrimidone photoproducts. Nature has developed unique flavoenzymes, called DNA photolyases, that utilize blue light, that is photons of lower energy than those of the damaging light, to repair these lesions. In this review, we focus on the chemically challenging repair of the (6–4) photoproducts by (6–4) photolyase and describe the major events along the quest for the reaction mechanisms, over the 20 years since the discovery of (6‐4) photolyase. 相似文献
155.
Philippe Zinck Andreia Valente Fanny Bonnet Ana Violante André Mortreux Marc Visseaux Simona Ilinca Rob Duchateau Pascal Roussel 《Journal of polymer science. Part A, Polymer chemistry》2010,48(4):802-814
The ability of various rare earth borohydride and chloride complexes/n‐butylethylmagnesium systems to operate styrene chain transfer polymerization in mild conditions has been assessed. Thirteen precatalysts have been considered: the rare earth trisborohydrides Ln(BH4)3(THF)x (x = 3, Ln = Nd (1), La (2), Sm (3), x = 2, Ln = Y (4), Sc (5)), the rare earth chlorides LnCl3(THF)x (x = 3, Ln = Nd (6), La (7), Sm (8), Y (9), x = 2, Ln = Sc (10)), the mixed La(BH4)2Cl(THF)2.6 (11) and the half‐lanthanidocenes Cp*Ln(BH4)2(THF)2 (Ln = Nd (12), La (13)). Six systems were found to be active precatalysts for the polymerization of styrene. 1 , 2 , and 11 led to an efficient transmetalation of the growing polystyrene chain with the simultaneous occurrence of βH elimination, whereas 7 , 12 , and 13 led to catalyzed chain growth behavior. It is noteworthy that the catalyzed chain growth obtained with 12 and 13 occurs with significant stereoselectivity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 802–814, 2010 相似文献
156.
Richard Ducray Pascal Boutron Hervé Germain Maryannick Lamorlette Mickael Maudet Georges Pasquet Iain Simpson 《Tetrahedron letters》2010,51(36):4755-4701
A two-step synthesis of 3-(2-chloropyrimidin-4-yl)imidazo[1,2-a]pyridines is presented. The late stage elaboration of the imidazopyridine through a cyclocondensation allows a rapid access to a variety of substitution patterns. The intermediate enol ethers were obtained from inexpensive reagents in a ligand-free Heck coupling. This methodology has been extended to the formation of pyrazolo[1,5-a]pyridines via a formal 1,3-dipolar cycloaddition. 相似文献
157.
Aurore Richel Pascal Laurent Bernard Wathelet Michel Paquot 《Tetrahedron letters》2010,51(10):1356-15298
Monomode microwave-assisted coupling of d-glucuronic acid with alcohols, in the presence of various impregnated acid catalysts, was successfully performed, affording in almost quantitative yields the corresponding monosubstituted β-d-glucofuranosidurono-6,3-lactones in less than 10 min at 85 °C. This study evidences the synergy of microwaves and impregnated acid catalysts as a fast and clean strategy in the field of carbohydrate chemistry. 相似文献
158.
As assemblies of graphene sheets, carbon nanotubes, and fullerenes become components of new nanotechnologies, it is important to be able to predict the structures and properties of these systems. A problem has been that the level of quantum mechanics practical for such systems (density functional theory at the PBE level) cannot describe the London dispersion forces responsible for interaction of the graphene planes (thus graphite falls apart into graphene sheets). To provide a basis for describing these London interactions, we derive the quantum mechanics based force field for carbon (QMFF-Cx) by fitting to results from density functional theory calculations at the M06-2X level, which demonstrates accuracies for a broad class of molecules at short and medium range intermolecular distances. We carried out calculations on the dehydrogenated coronene (C24) dimer, emphasizing two geometries: parallel-displaced X (close to the observed structure in graphite crystal) and PD-Y (the lowest energy transition state for sliding graphene sheets with respect to each other). A third, eclipsed geometry is calculated to be much higher in energy. The QMFF-Cx force field leads to accurate predictions of available experimental mechanical and thermodynamics data of graphite (lattice vibrations, elastic constants, Poisson ratios, lattice modes, phonon dispersion curves, specific heat, and thermal expansion). This validates the use of M06-2X as a practical method for development of new first principles based generations of QMFF force fields. 相似文献
159.
The trans-fusarinine backbone is a common feature encountered in many fungal siderophores. This monomer is notably the structural base of Nα-methyl coprogen B and dimerumic acid. Both siderophores are known to be secreted by Scedosporium apiospermum, an emerging pathogenic fungus studied for its high involvement in invasive infections of immunocompromised patients. The strategy developed here for the synthesis of the trans-fusarinine scaffold relies on the preparation of both N-hydroxyornithine and 3-anhydroxymevalonic acid subunits starting from l-ornithine and 3-butyn-1-ol, respectively. The coupling of these two building blocks led to the expected protected backbone. 相似文献
160.
Three zinc(II) nitrite coordination polymers, [Zn(4-bpdb)(NO2)2]n (1), {[Zn(3-bpdb)(NO2)]·0.5H2O}n (2) and [Zn(3-bpdh)(NO2)2]n (3), 4-bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, 3-bpdb = 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene and 3-bpdh = 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene} were prepared and characterized by elemental analyses and IR spectroscopy. Compound 3 was structurally characterized by single-crystal X-ray diffraction and is one-dimensional polymer with coordination environments of distorted octahedral, ZnN2O4. The thermal stabilities of compounds 1–3 were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). Direct calcination of the compounds 1–3 at 600 °C under air atmospheres yields different morphologies of nano-sized ZnO. 相似文献