全文获取类型
收费全文 | 51570篇 |
免费 | 944篇 |
国内免费 | 284篇 |
专业分类
化学 | 25535篇 |
晶体学 | 473篇 |
力学 | 1783篇 |
综合类 | 12篇 |
数学 | 12883篇 |
物理学 | 12112篇 |
出版年
2023年 | 155篇 |
2022年 | 146篇 |
2021年 | 330篇 |
2020年 | 385篇 |
2019年 | 378篇 |
2018年 | 1665篇 |
2017年 | 1879篇 |
2016年 | 1602篇 |
2015年 | 1248篇 |
2014年 | 1227篇 |
2013年 | 2230篇 |
2012年 | 4495篇 |
2011年 | 3720篇 |
2010年 | 2643篇 |
2009年 | 2301篇 |
2008年 | 1869篇 |
2007年 | 1914篇 |
2006年 | 1750篇 |
2005年 | 5431篇 |
2004年 | 4807篇 |
2003年 | 3015篇 |
2002年 | 1131篇 |
2001年 | 770篇 |
2000年 | 554篇 |
1999年 | 501篇 |
1998年 | 346篇 |
1997年 | 296篇 |
1996年 | 344篇 |
1995年 | 251篇 |
1994年 | 279篇 |
1993年 | 224篇 |
1992年 | 365篇 |
1991年 | 343篇 |
1990年 | 313篇 |
1989年 | 270篇 |
1988年 | 247篇 |
1987年 | 203篇 |
1986年 | 185篇 |
1985年 | 263篇 |
1984年 | 252篇 |
1983年 | 165篇 |
1982年 | 160篇 |
1981年 | 173篇 |
1980年 | 162篇 |
1979年 | 144篇 |
1978年 | 128篇 |
1977年 | 126篇 |
1976年 | 160篇 |
1975年 | 126篇 |
1973年 | 121篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Micha? Chmielewski 《Tetrahedron letters》2004,45(31):6007-6010
Comparison of the anion binding properties of a series of uncharged macrocyclic tetraamides reveal significant effects of the receptor's size on the strength of its anion complexes. This study allowed for estimation of the optimal size of a macroring for complexation of common anions. 相似文献
52.
53.
A. Baeza M. Fernández M. Herranz F. Legarda C. Miró A. Salas 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(2):321-326
We studied the effectiveness of potable water treatment processes that consist of the stages of coagulation-flocculation-decantation,
using iron-based coagulants, in eliminating gamma-emitting man-made radioisotopes of cesium, strontium, and americium from
two natural waters with different degrees of mineralization. The resulting decontamination was found to depend on the chemical
behavior of each of the radionuclides considered, on the pH at which the process of coagulation is carried out, and on the
concentration of the other stable cations present.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
54.
Tadeusz Biedro Przemysaw Kubisa 《Journal of polymer science. Part A, Polymer chemistry》2004,42(13):3230-3235
The cationic polymerization of styrene in a neutral ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate, with a 1‐phenetyl chloride/TiCl4 initiating system is reported. The polymerization proceeds to a high conversion, but an analysis of the matrix‐assisted laser desorption/ionization time‐of‐flight spectra of the polymers indicates that chain transfer is significant, leading to a lack of control over the molecular weight and molecular weight distribution. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3230–3235, 2004 相似文献
55.
JPC – Journal of Planar Chromatography – Modern TLC - Flavonoid glycosides are much more polar than their aglycones and the two groups of compounds are difficult to separate by planar... 相似文献
56.
Sándor G?r?g 《Analytical sciences》2004,20(5):767-782
The development during the last 15 years and the state-of-the-art in the analysis of bulk steroid hormone drugs and hormone-like structures and pharmaceutical formulations made thereof are summarized. Other steroids (sterols, bile acids, cardiac glycosides, vitamins D) as well as biological-clinical aspects and pharmacokinetic and metabolic studies are excluded from this review. The state-of-the-art is summarized based on comparisons of monographs in the latest editions of the European Pharmacopoeia, United States Pharmacopoeia and the Japanese Pharmacopoeia. This is followed by sections dealing with new developments in the methodology for the fields of spectroscopic and spectrophotometric, chromatographic, electrophoretic and hyphenated techniques as well electroanalytical methods. The review is terminated by two problem-oriented sections: examples on impurity and degradation profiling as well as enantiomeric analysis. 相似文献
57.
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
58.
A sequential injection methodology for the spectrophotometric determination of calcium, magnesium and alkalinity in water samples is proposed. A single manifold is used for the determination of the three analytes, and the same protocol sequence allows the sequential determination of calcium and magnesium (the sum corresponds to the water hardness). The determination of both metals is based on their reaction with cresolphtalein complexone; mutual interference is minimized by using 8-hydroxyquinoline for the determination of calcium and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) for the determination of magnesium. Alkalinity determination is based on a reaction with acetic acid, and corresponding color change of Bromcresol Green. Working ranges of 0.5 - 5 mg dm(-3) for Ca, 0.5 - 10 mg dm(-3) for Mg, and 10 - 100 mg HCO3- dm(-3), for alkalinity have been achieved. The results for water samples were comparable to those of the reference methods and to a certified reference water sample. RSDs lower than 5% were obtained, a low reagent consumption and a reduced volume of effluent have been accomplished. The determination rate for calcium and magnesium is 80 h(-1), corresponding to 40 h(-1) per element, while 65 determinations of alkalinity per hour could be carried out. 相似文献
59.
JingXiaWANG ChengYouKAN DeShanLIU 《中国化学快报》2004,15(10):1161-1163
Two novel polymerizable dyes with anthraquinone residue have been prepared, and their structures were characterized by FTIR, ^1HNMR and EA. 相似文献
60.