全文获取类型
收费全文 | 11516篇 |
免费 | 573篇 |
国内免费 | 195篇 |
专业分类
化学 | 6735篇 |
晶体学 | 84篇 |
力学 | 305篇 |
综合类 | 23篇 |
数学 | 2155篇 |
物理学 | 2982篇 |
出版年
2023年 | 111篇 |
2022年 | 210篇 |
2021年 | 261篇 |
2020年 | 231篇 |
2019年 | 229篇 |
2018年 | 290篇 |
2017年 | 278篇 |
2016年 | 557篇 |
2015年 | 427篇 |
2014年 | 490篇 |
2013年 | 969篇 |
2012年 | 660篇 |
2011年 | 779篇 |
2010年 | 511篇 |
2009年 | 427篇 |
2008年 | 475篇 |
2007年 | 399篇 |
2006年 | 344篇 |
2005年 | 263篇 |
2004年 | 235篇 |
2003年 | 198篇 |
2002年 | 253篇 |
2001年 | 179篇 |
2000年 | 137篇 |
1999年 | 151篇 |
1998年 | 136篇 |
1997年 | 137篇 |
1996年 | 137篇 |
1995年 | 101篇 |
1994年 | 91篇 |
1993年 | 85篇 |
1992年 | 89篇 |
1991年 | 86篇 |
1990年 | 75篇 |
1989年 | 75篇 |
1988年 | 78篇 |
1987年 | 78篇 |
1986年 | 73篇 |
1985年 | 102篇 |
1984年 | 95篇 |
1983年 | 84篇 |
1982年 | 76篇 |
1981年 | 85篇 |
1980年 | 89篇 |
1979年 | 80篇 |
1978年 | 87篇 |
1977年 | 93篇 |
1976年 | 74篇 |
1974年 | 74篇 |
1973年 | 77篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
M. Piñeiro-Iglesias M. Miñones-Vázquez E. Vázquez-Blanco S. Muniategui-Lorenzo P. López-Mahía D. Prada-Rodríguez 《Chromatographia》2002,56(7-8):483-488
Summary The aim of this work is to establish the best conditions for concentration and purification steps in the trace analysis of
aliphatic and polycyclic aromatic hydrocarbons (PAH) from atmospheric particulate matter by gas chromatography-flame ionisation
detection (GC-FID) and high performance liquid chromatography with ultraviolet and fluorescence detection (HPLC-UV-FL). The
best results for the more volatile compound were obtained with a combination of rotary evaporation and a stream of nitrogen
(near to 100% for aliphatic hydrocarbons and from 70 to 105% for PAH). Two types of solid phase extraction (SPE)cartridges
(Supelclean
tm
LC-Silica SPE tubes and Sep-Pak? Plus silica cartridges) and glass column were examined for the purification and fractionation step. Blank chromatograms of
both types of cartridges analysed by GC-FID made this study difficult, because a PSS (programmed split-splitless) injector
was employed thereby increasing the sensitivity. This problem was not observed in the HPLC-UV-FL blank chromatograms of these
cartridges. Glass columns filled with silica and alumina were chosen because no interference was found in the GC-FID blank
chromatograms and the best recoveries in the fractionation of both aliphatic hydrocarbons and PAH were achieved. This is especially
important when aliphatic hydrocarbons concentrations are lower than 1 μg mL−1. Finally, the selected conditions were applied to the analysis of hydrocarbons in real atmospheric particulate samples. 相似文献
52.
53.
54.
55.
The phase analysis of cryolite (Na3AlF6) and sodium metasilicate (Na2SiO3) was performed by thermal analysis. The eutectic system with a region of two immiscible substances at a concentration of Na2SiO3 between 42.8 and 46.3 mol‐% was identified and the eutectic temperature determined to (886±2) °C. Based on the results of mass‐loss measurements, it was assumed that the introduced Na2SiO3 reacts with Na3AlF6 due to the formation of some nonvolatile stable compounds. The stable reaction products were identified by X‐ray diffraction analysis and IR spectroscopy of the spontaneously cooled samples, which established the formation of NaF and stable amorphous aluminosilicate compounds. 相似文献
56.
A. Torrisi P. Horák J. Vacík A. Cannavò G. Ceccio J. Vaniš 《Phosphorus, sulfur, and silicon and the related elements》2020,195(11):932-935
AbstractOn the perspective to develop CuO–TiO2 MOS, multilayered Cu and Ti thin layers were alternatively deposited on silicon wafers using 25?keV Ar?+?ion beam sputtering and, subsequently, oxidized by thermal annealing in air at 400?°C for 24?h. The deposited films have variable ratios of the Cu and Ti % at. One of the main goal is to obtain such multilayers avoiding the presence of Cu–Ti–O compounds. The samples were characterized in terms of composition (by RBS and SIMS analyses) and morphology (by AFM and SEM investigations). In particular, SIMS maps allows to observe the spatial distribution and thickness of each phase of the Cu/Ti multilayers, and further to observe Cu diffusion and mixing with Ti, as well as phase separation of CuO and TiO2 in the samples. The reasons of this effect represent an open issue that has to investigated, in order to improve the MOS fabrication. 相似文献
57.
J. Málek J. šesták F. Rouquerol J. Rouquerol J. M. Criado A. Ortega 《Journal of Thermal Analysis and Calorimetry》1992,38(1-2):71-87
The applicability of both conventional Thermal Analysis (TA) and Controlled Rate Thermal Analysis (CRTA) for kinetic analysis is discussed. It is shown that TA method can give a reliable kinetic information and meaningful kinetic parameters especially for solid state transformation. On the other hand the CRTA method is more suitable for decomposition process where one or more gasses are evolved. A consistent and reliable method of kinetic analysis is proposed for both techniques. This method is illustrated to analyze the crystallization process of chalcogenide glass and the decomposition of dolomite. 相似文献
58.
I. Kúdelka P.K. Misro J. Pospíšil H. Korbanka T. Riedel G. Pfahler 《Polymer Degradation and Stability》1985,12(4):303-313
The hydroperoxide decomposing efficiencies of dioctadecylsulfide (I), dioctadecyldisulfide (IV) and dioctadecyl 3,3-thio-dipropionate (VII) have been compared at 75°C and 85°C. The formation of oxidation products from (I) and (IV) has been checked. Experimental evidence is given of the important rôle of the activation of the molecule of (IV) by the presence of two sulfidic sulfur atoms compared with the activation of the sulfur atom in (VII) by the alkoxycarbonyl group in the beta position. The explanation of the high efficiency of disulfide has been based on the formation of thiosulfinate—the key intermediate for the generation of peroxidolytic species—in the first reaction step. 相似文献
59.
The paper deals with the problem of the outpatient administration of186Re-HEDP and153Sm-EDTMP for palliative therapy of bone metastases. The subsequent 6 hours stay of the treated patients in a department of nuclear medicine appears to be in compliance with regulations proposed in the Czech Republic as well as with ICRP recommendations. 相似文献
60.
Due to the high safety risks, chemistry instructors avoid demonstrating many remarkable experiments based on the addition of a liquid to a solid. Well-known examples of such demonstrations are various pyrotechnic mixtures of potassium chlorate and sugar (sucrose), which are usually activated with a drop of concentrated sulfuric acid. Other attractive demonstrations are the addition of water to freshly prepared magnesium phosphide and addition of water to burning magnesium. In all of these demonstrations the reaction that takes place immediately is very vigorous and can be hazardous for the instructor. Because chemistry teachers and instructors usually try to avoid performing experiments that include a hazard, a number of highly attractive experiments may remain unknown to the public. Using a simple homemade device called a safety dropper, one can perform all of these experiments with complete safety, both for the audience and the demonstrator. Details for performing some of these experiments as well as for the construction of the safety dropper are given in this paper. Video clips of demonstrations are included as an aid for inexperienced instructors. 相似文献