全文获取类型
收费全文 | 775篇 |
免费 | 15篇 |
国内免费 | 69篇 |
专业分类
化学 | 708篇 |
晶体学 | 2篇 |
力学 | 3篇 |
物理学 | 146篇 |
出版年
2024年 | 1篇 |
2023年 | 38篇 |
2022年 | 14篇 |
2021年 | 9篇 |
2020年 | 27篇 |
2019年 | 15篇 |
2018年 | 17篇 |
2017年 | 24篇 |
2016年 | 22篇 |
2015年 | 12篇 |
2014年 | 26篇 |
2013年 | 46篇 |
2012年 | 42篇 |
2011年 | 32篇 |
2010年 | 39篇 |
2009年 | 44篇 |
2008年 | 44篇 |
2007年 | 45篇 |
2006年 | 42篇 |
2005年 | 48篇 |
2004年 | 39篇 |
2003年 | 21篇 |
2002年 | 26篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 16篇 |
1998年 | 23篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 20篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1967年 | 3篇 |
排序方式: 共有859条查询结果,搜索用时 234 毫秒
101.
C. L. Kester R. O. Rye C. A. Johnson Ch. Schwartz Ch. Holmes 《Isotopes in environmental and health studies》2013,49(1):53-65
Abstract Sulfur isotopes have received little attention in ecology studies because plant and animal materials typically have low sulfur concentrations (< 1 wt.%) necessitating labor-intensive chemical extraction prior to analysis. To address the potential of direct combustion of organic material in an elemental analyzer coupled with a mass spectrometer, we compared results obtained by direct combustion to results obtained by sulfur extraction with Eschka's mixture. Direct combustion of peat and animal tissue gave reproducibility of better than 0.5‰ and on average, values are 0.8‰ higher than values obtained by Eschka extraction. Successful direct combustion of organic material appears to be a function of sample matrix and sulfur concentration. Initial results indicate that direct combustion provides fast, reliable results with minimal preparation. Pilot studies underway include defining bear diets and examining fluctuations between freshwater and brackish water in coastal environments. 相似文献
102.
激光溅射锌和镉原子与SO2分子反应的低温基质隔离红外光谱实验表明,在氩和氖的惰性基质中,形成了环式M(SO2)分子及其阴离子M(SO2)- (M=Zn, Cd).相关同位素(34SO2和S18O2)替代实验及密度泛函理论计算均证实了这一结果.此外,自然电荷布居分析表明电子从金属锌和镉的s轨道转移到了SO2配体上形成了M+(SO2)-“离子对”复合物,且该分子中的Zn-O键以及Cd-O键均表现出强的极化共价性.而Hg原子在与SO2反应中所表现出来的惰性可由其较强的相对论效应所致的6s价电子层收缩与高电离电位得以解 相似文献
103.
《应用光谱学评论》2013,48(1):71-99
Abstract High performance liquid chromatography (HPLC) has often been employed in the separation and speciation of metal containing compounds. One of the most sensitive devices used for detecting those compounds after the separation is the inductively coupled plasma (ICP). The similar flow rates for these two techniques render the coupling of the devices trivial, usually involving only a short length of capillary tubing. Upon entering the plasma, species are typically determined either via atomic emission spectrometry or mass spectrometry. HPLC-ICP devices have been employed less frequently for the determination of non-metals. This review will describe the applications of HPLC-ICP techniques to the determination of compounds containing carbon, sulfur, phosphorus, and the halogens. The instrumentation used for each application will be described, and the performance of the systems will be summarized. 相似文献
104.
105.
Xiangming He Weihua Pu Jianguo Ren Li Wang Jiulin Wang Changyin Jiang Chunrong Wan 《Ionics》2008,14(4):335-337
The charge/discharge characteristics of the sulfur composite cathodes were investigated at different temperatures and different
current densities. The composite presented the discharge capacities of 854 and 632 mAh g−1 at 60 and −20 °C, respectively, while it had the discharge capacities of 792 mAh g−1 at 25 °C. The composite presented the discharge capacities of 792 and 604 mAh g−1 at 55.6 and 667 mA g−1, respectively, at room temperature. The results showed that the sulfur composite cathodes presented good charge/discharge
characteristics between 60 and −20 °C and at a high c-rate up to 667 mA g−1. 相似文献
106.
Variously substituted 2-phenyl-1,3-dioxolanes and 2-(2-bromophenyl)-1,3-dioxolanes, prepared from the corresponding benzaldehydes, were lithiated ortho to the acetal group. Reaction of the lithio derivatives with sulfur dioxide led to the lithium sulfinate salts, which gave, upon oxidative chlorination with sulfuryl chloride, the corresponding benzenesulfonyl chlorides. Then, depending on the aromatic substitution pattern of the molecule, several protocols were elaborated for the functional group transformations leading to the target compounds. Ring closure was performed with hydrazine hydrate or acetylhydrazine, in the latter case with one-pot removal of the acetyl group. The 4-unsubstituted 2H-1,2,3-benzothiadiazine 1,1-dioxides thus obtained are potential drug candidates based on their structural similarity to biologically active phthalazinones. 相似文献
107.
In this paper, a one-step copper-catalyzed procedure for oxidative coupling of active methylene compounds including cyclic β-diketones, cyclic β-ketoesters and 5-pyrazolone with benzenethiols is described. Benzenethiols are in situ generated in the reaction mixture from aryl halides and thiourea as sulfur transfer reagent. α-Thioaryl compounds are obtained in excellent yields and in short reaction time via the process which is free from the foul smell of thiols. 相似文献
108.
Huang MD Becker-Ross H Florek S Heitmann U Okruss M Patz CD 《Analytical and bioanalytical chemistry》2008,390(1):361-367
A new method for the determination of sulfur forms in wine, i.e., free SO2, total SO2, bound SO2, total S, and sulfate, is presented. The method is based on the measurement of the carbon monosulfide (CS) molecular absorption
produced in a conventional air–acetylene flame using high-resolution continuum source absorption spectrometry. Individual
sulfur forms can be distinguished because of the different sensitivities of the corresponding CS molecular absorption. The
sensitivity of free SO2 is about three times higher than the value for bound SO2 and sulfate. The method makes use of procedures similar to those used in classic reference methods. Its performance is verified
by analyzing six wine samples. Relative standard deviations are between 5 and 13% for free SO2 and between 1 and 3% for total SO2. For the validation of the accuracy of the new method, the results are compared with those of reference methods. The agreement
of the values for total SO2 with values of the classic method is satisfactory: five out of six samples show deviations less than 16%. Due to the instability
of free SO2 in wine and the known problems of the used reference method, serious deviations of the free SO2 results are found for three samples. The evaluation of the limits of detection focuses on the value for free SO2, which is the sulfur form having by far the lowest concentration in wine. Here, the achievable limit of detection is 1.8 mg L−1.
Figure Detection of non-metal elements using continuum source flame absorption spectrometry 相似文献
109.
Shen-Ming Chen Wen-Yan Chzo R. Thangamuthu 《Journal of Solid State Electrochemistry》2008,12(11):1487-1495
Electrochemically active hybrid coatings based on cationic films, didodecyldimethylammonium bromide (DDAB), and poly(diallyldimethylammonium
chloride) (PDDAC) are prepared on electrode surface by cycling the film-covered electrode repetitively in a pH 6.5 solution
containing Fe(CN)6
3− and Ru(CN)6
4− anions. Modified electrodes exhibited stable and reversible voltammetric responses corresponding to characteristics of Fe(CN)6
3−/4− and Ru(CN)6
4−/3− redox couples. The cyclic voltammetric features of hybrid coatings resemble that of electron transfer process of surface-confined
redox couple. Electrochemical quartz crystal microbalance results show that more amounts of electroactive anionic complexes
partitioned into DDAB coating than those doped into PDDAC coating from the same doping solution. Peak potentials of hybrid
film-bound redox couples showed a negative shift compared to those at bare electrode and this shift was more pronounced in
the case of DDAB. Finally, the advantages of hybrid coatings in electrocatalysis are demonstrated with sulfur oxoanions. 相似文献
110.
Adriana González Castro José Sánchez Costa Roberta Pievo Chiara Massera Ilpo Mutikainen Urho Turpeinen Patrick Gamez Jan Reedijk Prof. Dr. 《无机化学与普通化学杂志》2008,634(14):2477-2482
A new Schiff‐base ligand having a potentially coordinating thioether group (2‐quinoline‐N‐(2′‐methylthiophenyl)methyleneimine, qmtpm ) has been prepared. The synthesis, structure, UV‐Vis and EPR studies of one copper(II) and two cobalt(II) complexes from this ligand is reported. The X‐ray structures of the CuII and CoII chlorido complexes 1 and 2 reveal the metal atoms in highly distorted square‐pyramidal environments constituted of one tridentate ligand and two anions. On the other hand, the thiocyanato CoII compound 3 exhibits a distorted trigonal‐bipyramidal structure. These structural variations are apparently due to the different counter‐ions which leads to distinct lattice interactions. The spectroscopic data obtained by EPR and UV‐Vis investigations are in agreement with the solid‐state structures of the coordination compounds. 相似文献