全文获取类型
收费全文 | 6758篇 |
免费 | 555篇 |
国内免费 | 371篇 |
专业分类
化学 | 4171篇 |
晶体学 | 60篇 |
力学 | 309篇 |
综合类 | 40篇 |
数学 | 929篇 |
物理学 | 2175篇 |
出版年
2023年 | 74篇 |
2022年 | 125篇 |
2021年 | 211篇 |
2020年 | 258篇 |
2019年 | 216篇 |
2018年 | 193篇 |
2017年 | 168篇 |
2016年 | 273篇 |
2015年 | 291篇 |
2014年 | 281篇 |
2013年 | 465篇 |
2012年 | 469篇 |
2011年 | 548篇 |
2010年 | 348篇 |
2009年 | 335篇 |
2008年 | 407篇 |
2007年 | 389篇 |
2006年 | 354篇 |
2005年 | 300篇 |
2004年 | 248篇 |
2003年 | 213篇 |
2002年 | 181篇 |
2001年 | 155篇 |
2000年 | 89篇 |
1999年 | 100篇 |
1998年 | 62篇 |
1997年 | 56篇 |
1996年 | 65篇 |
1995年 | 60篇 |
1994年 | 74篇 |
1993年 | 56篇 |
1992年 | 50篇 |
1991年 | 38篇 |
1990年 | 41篇 |
1989年 | 32篇 |
1988年 | 22篇 |
1987年 | 26篇 |
1986年 | 19篇 |
1985年 | 33篇 |
1984年 | 41篇 |
1983年 | 18篇 |
1982年 | 35篇 |
1981年 | 26篇 |
1980年 | 23篇 |
1979年 | 40篇 |
1978年 | 29篇 |
1977年 | 16篇 |
1976年 | 24篇 |
1975年 | 18篇 |
1974年 | 20篇 |
排序方式: 共有7684条查询结果,搜索用时 187 毫秒
101.
菲林B近红外分光光度法测定维生素C 总被引:2,自引:0,他引:2
在pH 3的三氯乙酸酸性介质中,菲林B可以定量地将还原型维生素C氧化成脱氢型维生素C,利用脱氢型维生素C在920 nm处有最大吸光度,测定其含量,建立了一种测定维生素C的新方法,并研究了影响反应的各种因素。该方法对维生素C的检出限为0.17 mg/L;线性范围为0.5~10 mg/L,对水果中维生素C含量测定的RSD<2.31%;回收率为99.7%~101.1%,比2,4-二硝基苯肼分光光度法测定结果的相对偏差<±1.6%。 相似文献
102.
Ying-Tong Di Hong-Ping He Zhi-Zhi Du Xian-Wen Yang Xiao-Jiang Hao 《Tetrahedron letters》2006,47(30):5329-5331
A novel Daphniphyllum alkaloid with a rearranged fused-hexacyclic ring system, calycilactone A, was isolated from the leaves of Daphniphyllum calycillum (Daphniphyllaceae), and the structure and relative stereochemistry of the new compound were elucidated on the basis of spectroscopic data. 相似文献
103.
De Riccardis F Di Filippo M Garrisi D Izzo I Mancin F Pasquato L Scrimin P Tecilla P 《Chemical communications (Cambridge, England)》2002,(24):3066-3067
The Na+ transporting properties of the first member of a new class of artificial ionophores, based on a C2-symmetric polyhydroxylated steroid dimer, are described. 相似文献
104.
Determination of sulfametoxazole, sulfadiazine and associated compounds in pharmaceutical preparations by capillary zone electrophoresis 总被引:3,自引:0,他引:3
Berzas Nevado JJ Castañeda Peñalvo G Guzmán Bernardo FJ 《Journal of chromatography. A》2001,918(1):205-210
A capillary zone electrophoresis method is presented to separate sulfadiazine, sulfamethoxazole, trimethoprim, bromhexine and guaiacol by using a fused-silica capillary (60.2 cm x 75 microm I.D.). The separation was carried out at 30 kV and 25 degrees C in a 15 mM phosphate buffer adjusted to pH 6.2 as electrolyte. Under these conditions, the run time was 6 min and the limits of quantification were about 1 mg/l for every component. The method was applied to pharmaceutical preparations and the results provided recoveries close to 100%. 相似文献
105.
Activation energies for the recombination of point defects generated by the /n,/ reaction in Ba (CoEDTA)2·4H2O, t-(Co(en)2(NO2)2)Cl and (Co(en)2(NO2)2) (CoEDTA)·1H2O, have been evaluated using isothermal step annealing. The reselts were interpreted in terms of compound structures. It is possible to relate the recoil atom behaviour between single complexes and the double one. 相似文献
106.
Quassinoids from Picrasma crenata 总被引:1,自引:0,他引:1
From woods of Picrasma crenata, a new stereoisomer dihydronorneoquassin was obtained together with others well knowns dihydronorneoquassin, parain, alpha-neoquassin, beta-neoquassin and quassin. The structures were determined by spectroscopic data and chemical evidence. 相似文献
107.
S Kishino Z S Di M Sugawara K Iseki K Miyazaki S Kakinoki A Homura A Kitabatake 《Journal of chromatography. A》1992,582(1-2):246-248
A rapid and simple method for the determination of alpha 1-acid glycoprotein (AAG) in serum was developed by using an anion-exchange column for clean-up of serum and a hydroxyapatite column for high-performance liquid chromatography (HPLC). A good correlation was observed between this HPLC method and the conventional radial immunodiffusion method. The method may also be used to determine the AAG concentration in the serum of experimental animals. 相似文献
108.
Cordaro M Di Donna L Grassi G Maiuolo L Mazzotti F Perri E Sindona G Tagarelli A 《European journal of mass spectrometry (Chichester, England)》2004,10(5):691-697
An evaluation of the gas-phase ion chemistry of rotenone (1) by electrospray ionisation (ESI) mass spectrometry (MS) and tandem mass spectrometry (MS2) is presented, aiming at providing tools for its determination in natural and biological matrices. The behaviour of its cycloadducts with benzonitrile-N-oxide (2) and 2,4,6-trimethylbenzonitrile-N-oxide (3) was also evaluated and the MS data thus obtained have provided evidence into the mechanism of formation of the key product ion at m/z 192 which can be considered a marker in the MS and MS2 spectra of rotenone and its derivatives. 相似文献
109.
Daniel R. Coulter Ranty H. Liang Salvador Di Stefano Jovan Moacanin Amitava Gupta 《Chemical physics letters》1982,87(6):594-598
Transient emission studies following pulse radiolysis of solid poly(1-vinyl naphthalene) show existence of excited monomers and two excimers. Quenching experiments indicate that excimers are not formed directly by recombination of ions but probably by trapping of migrating monomeric excitation in performed traps whose density is approximately one in 103. 相似文献
110.
C. M. Bertoni A. I. Shkrebtii R. Di Felice F. Finocchi 《Progress in Surface Science》1993,42(1-4):319-330
The recent application to the semiconductor surfaces of the powerful ab-initio molecular dynamics (Car-Parrinello) method [R. Car, M. Parrinello, Phys. Rev. Lett. 55, 2471 (1985)] will be reviewed. The essential features of the method will be addressed first, then we will review a number of recent studies on the properties of the clean and adsorbate covered surfaces of Si, Ge and GaAs, obtained through Car-Parrinello simulations. Finally an original application of the ab-initio molecular dynamics for the clean and hydrogenated GaAs(110) surfaces is presented. 相似文献