全文获取类型
收费全文 | 7403篇 |
免费 | 981篇 |
国内免费 | 2063篇 |
专业分类
化学 | 9512篇 |
晶体学 | 33篇 |
力学 | 52篇 |
综合类 | 59篇 |
数学 | 7篇 |
物理学 | 784篇 |
出版年
2024年 | 14篇 |
2023年 | 120篇 |
2022年 | 218篇 |
2021年 | 330篇 |
2020年 | 413篇 |
2019年 | 315篇 |
2018年 | 298篇 |
2017年 | 275篇 |
2016年 | 382篇 |
2015年 | 380篇 |
2014年 | 475篇 |
2013年 | 785篇 |
2012年 | 517篇 |
2011年 | 482篇 |
2010年 | 427篇 |
2009年 | 424篇 |
2008年 | 506篇 |
2007年 | 526篇 |
2006年 | 448篇 |
2005年 | 394篇 |
2004年 | 389篇 |
2003年 | 431篇 |
2002年 | 355篇 |
2001年 | 227篇 |
2000年 | 212篇 |
1999年 | 174篇 |
1998年 | 137篇 |
1997年 | 145篇 |
1996年 | 136篇 |
1995年 | 116篇 |
1994年 | 89篇 |
1993年 | 70篇 |
1992年 | 69篇 |
1991年 | 40篇 |
1990年 | 39篇 |
1989年 | 24篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Kh. S. Shikhaliev A. V. Falaleev G. I. Ermolova A. S. Solov'ev 《Chemistry of Heterocyclic Compounds》2002,38(2):210-212
4,6,6-Trimethyl-1,4-dihydropyrimidines have been synthesized by condensation of 2-quinazolylguanidines with mesityl oxide. The analogous reaction with benzalacetone leads to unstable 4-methyl-6-phenyl-1,4-dihydropyrimidines, which are oxidized to the corresponding 4-methyl-6-phenylpyrimidines. 相似文献
72.
Maiorova N. A. Khazova O. A. Tarasevich M. R. 《Russian Journal of Electrochemistry》2004,40(10):1060-1065
The kinetics of the hydrogen oxidation and the CO adsorption on a Pt (ultra)microelectrode is studied in a 0.5 M H2SO4 solution saturated with a mixture of gaseous H2 and CO at partial CO pressures p
CO = 10–500 ppm. The balance between rates of diffusion and adsorption of CO at different adsorption times is studied. Studied is the effect of CO impurities in H2 on steady-state polarization curves for the hydrogen ionization and nonsteady-state curves of the oxidation current decay with time at 0.02–0.05 V. Conditions under which in a certain time interval and at a certain CO concentration the slope of an I vs. t curve is proportional to p
CO are determined. The obtained dependence may be used when designing a technique for monitoring CO impurities in technical hydrogen. 相似文献
73.
I. S. Belostotskaya V. B. Vol'eva N. L. Komissarova M. O. Dekaprilevich V. N. Khrustalev A. Yu. Karmilov V. V. Ershov 《Russian Chemical Bulletin》1997,46(7):1272-1280
Oxidative transformations of 2-dialkylaminomethyl-4,6-di-tert-butylphenols depend on the nature of the oxidant, the character of the substituents at the nitrogen atom, and the medium.
A mechanism of the oxidation of these compounds is suggested. The molecular structure of the compound obtained as a result
of oxidative trimerization of 2-dimethylaminomethyl-4,6-di-tert-butylphenol was established by X-ray structural analysis.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1328–1335, July, 1997. 相似文献
74.
在二氧化钛载体中通过掺杂Ru,Mn,Ce制备了一系列用于催化湿式氧化的催化剂,利用XRD,TEM,BET等手段对催化剂进行了表征.在反应温度T=210~270℃,氧分压Po2=2.1MPa条件下,在间歇式高压反应釜中对丁二酸进行了降解实验.催化剂在反应中有很高的催化活性.催化剂在30min内对丁二酸降解的COD去除率为54.4~98.3%.Ru及Mn,Ce的氧化物对催化活性都有促进作用.建立了丁二酸催化湿式氧化的一级分段动力学模型.基于COD的一段及二段反应的活化能分别为43.74kJ/mol和54.28kJ/mol. 相似文献
75.
A. T. Soldatenkov A. V. Temesgen N. M. Kolyadina 《Chemistry of Heterocyclic Compounds》2004,40(5):537-560
Data on the oxidative transformations of heterocyclic compounds with permanganate anion are reviewed 相似文献
76.
Fearon P. K. Bigger S. W. Billingham N. C. 《Journal of Thermal Analysis and Calorimetry》2004,76(1):75-83
The oxidation of (Ti,W)C ceramics have been studied as a part of the program to investigate of properties of powder materials.
Thermogravimetry, derivative thermogravimetry (TG-DTG), and differential thermal analysis DSC have been used in the non-isothermal
study of powder oxidation (Ti,W)C in dry air atmosphere. The powder of crystalline carbide cermets with a ratio of W:Ti equals
0.3 was used in this study. The diagrams were recorded on a sample mass 3.42 mg on the Setaram apparatus in temperatures ranging
from 25 to 1000°C. Seven different heating rates were used. The analytical techniques SEM, WDX, EDX and XRD were used in the
research. The kinetics of the oxidation process was followed by the integral method by applying the Coats-Redfern's approximation.
The kinetic models of particular stages of (Ti,W)C oxidation were evaluated from the dynamic mass losses data. The values
of apparent activation energy E and the pre-exponential factor A of each stage of the oxidation were calculated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
77.
新型分子筛Ti-MMM-1的合成及其催化性能的研究 总被引:6,自引:0,他引:6
通过控制TEOS的水解,在不同时间添加与MCM-41和MFI相应的有机模板剂合成出了一种新型分子筛,Ti-MMM-1,采用XRD、FT-IR和低温N2吸附对其进行表征,并用H2O2氧化环己烷和环己醇对其催化活性进行评价.结果表明,Ti-MMM-1是一种具有MCM-41和MFI结构的两相混合的微孔/介孔材料,IR分析表明钛原子已进入分子筛骨架,并在环己烷和环己醇的氧化中表现出较好的催化活性和较高的选择性. 相似文献
78.
79.
(R)-4-Menthenone in the synthesis of optically pure sex pheromone of the peach leafminer moth (Lyonetia clerkella) 总被引:1,自引:0,他引:1
Kharisov R. Ya. Latypova E. R. Talipov R. F. Muslukhov R. R. Ishmuratov G. Yu. Tolstikov G. A. 《Russian Chemical Bulletin》2003,52(10):2267-2269
The synthesis of (14S)-methyloctadec-1-ene, sex pheromone of the peach leafminer moth (Lyonetia clerkella), is described to demonstrate a new potential of the synthetic use of (R)-4-menthenone. 相似文献
80.
ZhenshanPeng ChanglinYu TiejunCai QianDeng 《天然气化学杂志》2004,13(3):172-176
Mixed oxide catalyst Cs0.1Fe2Co6BiMnMo12Ox was prepared by the coprecipitation method.Selective oxidation of isobutene was carried out in a fixed-bed reactor over Cs0.1Fe2Co6BiMnMo12Ox.The results showed that the catalyst had high catalytic activity. Under the optimum reaction conditions(n(i-C4):n(O2)=1:2-1:4, space velocity=180 h^-1, T=360℃), the yields of methacrolein and methacrylic acid can reach 80% and 8%, respectively. The total yield of liquid products (methacrolein, methacrylic acid and acetic acid) can reach about 90%. 相似文献