全文获取类型
收费全文 | 25944篇 |
免费 | 4367篇 |
国内免费 | 3873篇 |
专业分类
化学 | 12428篇 |
晶体学 | 226篇 |
力学 | 2621篇 |
综合类 | 269篇 |
数学 | 4924篇 |
物理学 | 13716篇 |
出版年
2024年 | 91篇 |
2023年 | 330篇 |
2022年 | 736篇 |
2021年 | 776篇 |
2020年 | 1040篇 |
2019年 | 844篇 |
2018年 | 841篇 |
2017年 | 882篇 |
2016年 | 1035篇 |
2015年 | 970篇 |
2014年 | 1389篇 |
2013年 | 2185篇 |
2012年 | 1469篇 |
2011年 | 1633篇 |
2010年 | 1414篇 |
2009年 | 1704篇 |
2008年 | 1722篇 |
2007年 | 1777篇 |
2006年 | 1741篇 |
2005年 | 1404篇 |
2004年 | 1258篇 |
2003年 | 1211篇 |
2002年 | 978篇 |
2001年 | 846篇 |
2000年 | 824篇 |
1999年 | 733篇 |
1998年 | 639篇 |
1997年 | 562篇 |
1996年 | 423篇 |
1995年 | 384篇 |
1994年 | 325篇 |
1993年 | 271篇 |
1992年 | 248篇 |
1991年 | 230篇 |
1990年 | 162篇 |
1989年 | 137篇 |
1988年 | 131篇 |
1987年 | 110篇 |
1986年 | 98篇 |
1985年 | 100篇 |
1984年 | 74篇 |
1983年 | 37篇 |
1982年 | 78篇 |
1981年 | 65篇 |
1980年 | 61篇 |
1979年 | 53篇 |
1978年 | 28篇 |
1977年 | 38篇 |
1976年 | 28篇 |
1974年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Dr. Antonio M. Rodríguez Dr. Pilar Prieto Prof. Antonio de la Hoz Prof. Ángel Díaz-Ortiz D. Raúl Martín Prof. José I. García 《ChemistryOpen》2015,4(3):308-317
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation. 相似文献
2.
Monodisperse aqueous upconverting nanoparticles (UCNPs) were covalently immobilized on aldehyde modified cellulose paper via reduction amination to develop a luminescence resonance energy transfer (LRET)-based nucleic acid hybridization assay. This first account of covalent immobilization of UCNPs on paper for a bioassay reports an optically responsive method that is sensitive, reproducible and robust. The immobilized UCNPs were decorated with oligonucleotide probes to capture HPRT1 housekeeping gene fragments, which in turn brought reporter conjugated quantum dots (QDs) in close proximity to the UCNPs for LRET. This sandwich assay could detect unlabeled oligonucleotide target, and had a limit of detection of 13 fmol and a dynamic range spanning nearly 3 orders of magnitude. The use of QDs, which are excellent LRET acceptors, demonstrated improved sensitivity, limit of detection, dynamic range and selectivity compared to similar assays that have used molecular fluorophores as acceptors. The selectivity of the assay was attributed to the decoration of the QDs with polyethylene glycol to eliminate non-specific adsorption. The kinetics of hybridization were determined to be diffusion limited and full signal development occurred within 3 min. 相似文献
3.
Synthesis,Electronic Properties and WOLED Devices of Planar Phosphorus‐Containing Polycyclic Aromatic Hydrocarbons 下载免费PDF全文
Dr. François Riobé Rózsa Szűcs Dr. Pierre‐Antoine Bouit Dr. Denis Tondelier Bernard Geffroy Fátima Aparicio Julia Buendía Prof. Luis Sánchez Prof. Régis Réau Prof. László Nyulászi Prof. Muriel Hissler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6547-6556
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs). 相似文献
4.
In view of immense importance of silylenes and the fact that their properties undergo significant changes on substitution with halogens, here, we have used B3LYP/6-311++G** level of theory to access the effects of 1–4 halogens (X = F, Cl, Br, and I) on four unprecedented sets of cyclopentasilylene-2,4-dienes; with the following formulas: SiC4H3X ( 1 X ), SiC4H2X2 ( 2 X ), SiC4HX3 ( 3 X ), and SiC4X4 ( 4 X ). In going down from F to I, the singlet (s)-triplet (t) energy gap (ΔEs-t, a possible indication of stability), and band gap (ΔEH-L) decrease while nucleophilicity (N), chemical potential (μ), and proton affinity (PA) increase. The overall order of N, μ, and PA for each X is 2 X > 1 X > 3 X > 4 X . Precedence of 2 X over 1 X is attributed to the symmetric cross conjugation in the former. The highest and lowest N are shown by 2 I and 4 F . The trend of divalent angle () for each X is 4 X > 1 X > 3 X > 2 X . The results show that in going from electron withdrawing groups (EWGs) to electron donating groups (EDGs), the ΔEs-t and ΔEH-L decrease while N, μ, and PA increase. Also, rather high N of our scrutinized silylenes may suggest new promising ligands in organometallic chemistry. 相似文献
5.
6.
7.
Rafael López 《Annals of Global Analysis and Geometry》1997,15(3):201-210
In this paper we study constant mean curvature compact surfaces with two Jordan curves in parallel planes as boundary and we investigate the point at which the surface inherits the symmetries of its boundary. 相似文献
8.
9.
具Hardy-Sobolev临界指数的奇异椭圆方程多解的存在性 总被引:1,自引:0,他引:1
运用变分方法研究了下面问题-Δpu=μupx(s)s-2u f(x,u),x∈Ω,u=0,x∈Ω,多重解的存在性,其中Ω是一个具有光滑边界的有界区域. 相似文献
10.
从点电荷的电势计算公式出发推导出了瓣形均匀带电面在其直径处的电势分布.进一步讨论了均匀带电半球面在其底面以及均匀带电球面内部和外部的电势分布. 相似文献