全文获取类型
收费全文 | 4243篇 |
免费 | 133篇 |
国内免费 | 1篇 |
专业分类
化学 | 2213篇 |
晶体学 | 83篇 |
力学 | 195篇 |
数学 | 1093篇 |
物理学 | 793篇 |
出版年
2023年 | 30篇 |
2022年 | 42篇 |
2021年 | 58篇 |
2020年 | 83篇 |
2019年 | 109篇 |
2018年 | 167篇 |
2017年 | 150篇 |
2016年 | 201篇 |
2015年 | 155篇 |
2014年 | 206篇 |
2013年 | 614篇 |
2012年 | 225篇 |
2011年 | 250篇 |
2010年 | 225篇 |
2009年 | 178篇 |
2008年 | 194篇 |
2007年 | 178篇 |
2006年 | 145篇 |
2005年 | 120篇 |
2004年 | 117篇 |
2003年 | 83篇 |
2002年 | 64篇 |
2001年 | 53篇 |
2000年 | 46篇 |
1999年 | 50篇 |
1998年 | 39篇 |
1997年 | 39篇 |
1996年 | 37篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 19篇 |
1992年 | 16篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 19篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 30篇 |
1984年 | 19篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 28篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1975年 | 19篇 |
1974年 | 12篇 |
1973年 | 16篇 |
1968年 | 10篇 |
排序方式: 共有4377条查询结果,搜索用时 15 毫秒
1.
2.
3.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
4.
Suppose there exists a global solution u to the incompressible Navier–Stokes equations, such that . We prove that its norm goes to 0 at infinity. We next use this fact to control the norm of u, and finally we prove that such a solution is stable. To cite this article: I. Gallagher et al., C. R. Acad. Sci. Paris, Ser. I 334 (2002) 289–292. 相似文献
5.
A. Peláiz-Barranco O. García-Zaldívar F. Calderón-Piñar 《Solid State Communications》2005,133(8):515-519
The Ac behaviour of PLZT 6/80/20 ferroelectric ceramics was analyzed around and above the phase transition. Two relaxation processes are identified, showing that the so-called ‘universal relaxation law’ holds for the ceramics. A critical point in the values of the Ac conductivity, around the temperature corresponding to the maximum of the dielectric losses, is observed below the transition temperature due to the relaxor behaviour. The frequency dependence of the Ac conductivity at various temperatures and the hysteresis loops show classical relaxor behaviour with a diffuse phase transition. 相似文献
6.
The electrochemical reduction of 1-([(4-halophenyl)imino]methyl)-2-naphthols on graphite electrodes was studied using cyclic voltammetry, chronoamperometry, constant-potential coulometry and preparative constant-potential electrolysis techniques. The data revealed that the reduction on graphite was irreversible and followed an EC mechanism. The diffusion coefficients and the number of electrons transferred were determined using the chronoamperometric Cottrell slope and the ultramicro disc Pt-electrode steady-state current. The number of electrons was also determined by bulk electrolysis. The compounds were subjected to constant-potential preparative electrolysis and the electrolysis products were purified and identified by spectroscopic methods. Based on these findings, a mechanism for the electro-reduction process is proposed. 相似文献
7.
Stefan Cobzaş 《Acta Appl Math》2004,80(3):363-363
8.
We present some classical solutions to a gauge theory based on quadratically nonlinear Lie algebras without a central term. We observe that instanton-like and meron-like solutions force the internal fields to behave like solitons. 相似文献
9.
The NH,NH-dihydrocycloadduct 1 (6-chloro-9,9-dimethyl-7,8-dihydro-9H-pyrazolo[4,3-d]tetrazolo[1,5-b]-pyridazine) obtained by the cycloaddition of 2-diazopropane to 6-chlorotetrazolo[1,5-b]pyridazine, is transformed with protected or unprotected carbohydrates 2, 5, 7,9, 11, 13 and 15 in the presence of methyl acrylate ( 3 ) into the corresponding C-nucleosides 4,6,8,10,12,14 and 16 . In this one-pot synthesis two new chiral centers are formed stereoselectively, dependent on the chirality at C-atom next to aldehydo group in the carbohydrate. 相似文献
10.
Mustafa Çelebier Ertan Şahin Nilgün Ancın Nurşen Altuntaş Öztaş Selma Gül Öztaş 《应用有机金属化学》2007,21(10):viii-viii
The article referenced above was first published online on 30 August 2007 with incorrect pagination; the pagination has now been corrected online and in print. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献