全文获取类型
收费全文 | 1383篇 |
免费 | 55篇 |
国内免费 | 3篇 |
专业分类
化学 | 1158篇 |
晶体学 | 10篇 |
力学 | 18篇 |
数学 | 109篇 |
物理学 | 146篇 |
出版年
2023年 | 24篇 |
2022年 | 25篇 |
2021年 | 36篇 |
2020年 | 41篇 |
2019年 | 33篇 |
2018年 | 18篇 |
2017年 | 15篇 |
2016年 | 43篇 |
2015年 | 42篇 |
2014年 | 43篇 |
2013年 | 60篇 |
2012年 | 106篇 |
2011年 | 130篇 |
2010年 | 65篇 |
2009年 | 54篇 |
2008年 | 103篇 |
2007年 | 98篇 |
2006年 | 83篇 |
2005年 | 94篇 |
2004年 | 76篇 |
2003年 | 72篇 |
2002年 | 49篇 |
2001年 | 14篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1971年 | 1篇 |
1965年 | 1篇 |
1881年 | 1篇 |
1876年 | 1篇 |
排序方式: 共有1441条查询结果,搜索用时 9 毫秒
221.
Density functional modelling of silicate and aluminosilicate dimerisation solution chemistry 总被引:1,自引:0,他引:1
White CE Provis JL Kearley GJ Riley DP van Deventer JS 《Dalton transactions (Cambridge, England : 2003)》2011,40(6):1348-1355
Common throughout sol-gel chemistry, including zeolite synthesis, aluminosilicate glass formation and geopolymerisation, is the process of inorganic oxide polymerisation and deprotonation. In this investigation, some of the fundamental reactions occurring during zeolite synthesis and geopolymerisation at high pH are investigated using density functional theory (DFT), and are compared with: (i) existing values reported in the literature, and (ii) new and previously published DFT-derived data for similar silicate reactions at near-neutral pH. From the results it is seen that the energetics of deprotonation and dimerisation reactions depend greatly on the pH value, and these results correlate well with existing experimental values and trends. Hence, this investigation exemplifies that an accurate replication of the solution environment is crucial for obtaining useful theoretical results for species dissolved in non-ideal environments. 相似文献
222.
Fey N Ridgway BM Jover J McMullin CL Harvey JN 《Dalton transactions (Cambridge, England : 2003)》2011,40(42):11184-11191
The association and dissociation of ligands plays a vital role in determining the reactivity of organometallic catalysts. Computational studies with density functional theory often fail to reproduce experimental metal-ligand bond energies, but recently functionals which better capture dispersion effects have been developed. Here we explore their application and discuss future challenges for computational studies of organometallic catalysis. 相似文献
223.
Bedford RB Chang YN Haddow MF McMullin CL 《Dalton transactions (Cambridge, England : 2003)》2011,40(35):9042-9050
The reactions of a range of chiral resorcinol monophosphite ligands with [PdCl(2)(NCMe)(2)] was investigated in order to establish whether the meta-hydroxyl function was involved in the orthometallation processes. These ligands underwent facile orthopalladation at room temperature in the presence of Et(3)N, whilst the equivalent hydroxyl-free analogues needed more forcing conditions to induce orthometallation. When the hydroxyl function was replaced by a similar sized methyl group no orthometallation occurred, even on heating. Furthermore the hydroxyl group influences both the structure and isomerism in the resultant palladacycles via hydrogen bonding to adjacent chloride ligands. Similarly, the hydroxyl function leads to higher enantiocontrol in the asymmetric allylation of benzaldehyde with allyl tributyltin. Representative examples of the ligands and the palladium complexes obtained were characterised by single crystal X-ray diffraction. 相似文献
224.
Ball V Nguyen I Haupt M Oehr C Arnoult C Toniazzo V Ruch D 《Journal of colloid and interface science》2011,364(2):359-365
Dopamine-melanin films produced through the oxidation of dopamine in the presence of oxygen as an oxidant allow to reduce silver ions onto silver particles as already described in the paper by Lee et al. (H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Science 318 (2007) 426.). This reduction process has to occur through the oxidation of moieties present in the melanin film. This investigation shows that the free radicals present in the pseudomelanin film, quantified by means of electron spin resonance spectroscopy (ESR) for the first time, are not used in the transformation of Ag(+) cations to deposit silver. The ESR signal is hardly affected by the deposition of silver particles. On the other hand, X-ray photoelectron spectroscopy shows a small increase in the density of quinone groups and a small decrease of catechol groups on the surface of the film during the deposition of silver. This suggests that the deposited pseudomelanin films contain a significant fraction of catechol groups able to trigger reduction processes of metallic cations. These silver nanoparticles remain adherent to the melanin films and allow for a quantitative killing of Escherichia coli over a broad range of bacterial dilutions. However, the presence of the bacteria induces a release of the nanoparticles. The pseudomelanin films cannot be reused again for a silver ion reduction step. Nevertheless, the easy preparation of the pseudomelanin-silver composite and its effective one shot bacterial killing activity renders the strategy presented in this paper attractive. Some fundamental questions about redox process allowed by the pseudomelanin films will also be asked. 相似文献
225.
The enantioselective synthesis of three structurally distinct classes of lignan from a single, aza-Claisen-derived, chiral morpholine amide is reported. The class of lignan formed is dependent on the substitution pattern in the aryl rings and choice of protecting group on a key benzylic hydroxyl group. The methodology has been used to asymmetrically synthesize and determine the absolute stereochemistry of lignans (+)-cyclogalgravin 3, (-)-pycnanthulignene A 4, (-)-pycnanthulignene B 5, and (-)-kadangustin J 8. 相似文献
226.
An electrochemical route for the fabrication of zinc, titanium and silicon nanowires from ionic liquid (IL) based plating solutions is presented. Thanks to the large potential window of IL and good solubility of the corresponding anhydrous chloride salts, the presented method proceeds by a kinetically controlled electrochemical decoration of step-edges at highly oriented pyrolytic graphite surface. Resulting rather crystalline nanowires are more than a few hundreds of μm long while their diameter can be controlled in the 10 to 100 nm range by the electrolysis duration. 相似文献
227.
Mathematische Zeitschrift - We show that if the base frequency is Diophantine, then the Lyapunov exponent of a $$C^{k}$$ quasi-periodic $$SL(2,{\mathbb {R}})$$ cocycle is... 相似文献
228.
Wipawee Nittayananta Aornrutai Promsong Claire Levy Florian Hladik Nithinart Chaitaveep Suwipa Ungphaiboon Supinya Tewtrakul Surada Satthakarn 《Molecules (Basel, Switzerland)》2022,27(22)
Objectives: Ellagic acid (EA) has a wide range of biological effects. The purpose of this study was to investigate the in vitro effects of EA on HIV-1 replication, viral enzyme activity and cytokine secretion by infected cells. Methods: The anti-HIV-1 activity of EA in solution was determined in vitro using the infection of TZM-bl cells by the nano luciferase-secreting R5-tropic JRCSF strain of HIV-1, which allows for the quantification of viral growth by measuring nano luciferase in the culture supernatants. The effect of EA on the cytokine secretion of TZM-bl cells was determined by a multiplexed bead array after 48 h of HIV-1 exposure. The antiviral effect of EA in the gel formulation (Ellagel), as would be used for vaginal application, was investigated by the inhibition of infection of UC87.CD4.CCR5 cells with R5-tropic pBaLEnv-recombinant HIV-1. Results: EA in solutions of up to 100 µM was not toxic to TZM-bl cells. EA added either 1 h before or 4 h after HIV-1 exposure suppressed the replication of R5-tropic HIV-1 in TZM-bl cells in a dose-dependent manner, with up to 69% inhibition at 50 µM. EA-containing solutions also exhibited a dose-dependent inhibitory effect on HIV-1 replication in U87 cells. When EA was formulated as a gel, Ellagel containing 25 µM and 50 µM EA inhibited HIV-1 replication in U87 cells by 56% and 84%, respectively. In assays of specific HIV-1 enzyme activity, Ellagel inhibited HIV-1 integrase but not protease. EA did not significantly modulate cytokine secretion. Conclusions: We conclude that EA either in solution or in a gel form inhibits HIV infection without adverse effects on target cells. Thus, gel containing EA can be tested as a new microbicide against HIV infection. 相似文献
229.
230.
Francesco Valentini Pierluigi Veltri Andr Mangeney 《Journal of computational physics》2005,210(2):730-751
We present a numerical algorithm for the solution of the Vlasov–Poisson system of equations, in the magnetized case. The numerical integration is performed using the well-known “splitting” method in the electrostatic approximation, coupled with a finite difference upwind scheme; finally the algorithm provides second order accuracy in space and time. The cylindrical geometry is used in the velocity space, in order to describe the rotation of the particles around the direction of the external uniform magnetic field.Using polar coordinates, the integration of the Vlasov equation is very simplified in the velocity space with respect to the cartesian geometry, because the rotation in the velocity cartesian space corresponds to a translation along the azimuthal angle in the cylindrical reference frame. The scheme is intrinsically symplectic and significatively simpler to implement, with respect to a cartesian one. The numerical integration is shown in detail and several conservation tests are presented, in order to control the numerical accuracy of the code and the time evolution of the entropy, strictly related to the filamentation problem for a kinetic model, is discussed. 相似文献