全文获取类型
收费全文 | 480篇 |
免费 | 50篇 |
国内免费 | 41篇 |
专业分类
化学 | 513篇 |
晶体学 | 15篇 |
力学 | 2篇 |
综合类 | 2篇 |
物理学 | 39篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 16篇 |
2019年 | 18篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 20篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 46篇 |
2012年 | 26篇 |
2011年 | 25篇 |
2010年 | 15篇 |
2009年 | 27篇 |
2008年 | 19篇 |
2007年 | 20篇 |
2006年 | 24篇 |
2005年 | 23篇 |
2004年 | 20篇 |
2003年 | 25篇 |
2002年 | 29篇 |
2001年 | 15篇 |
2000年 | 5篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 16篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 12篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有571条查询结果,搜索用时 121 毫秒
61.
The alkylation of metalloids through the transfer of methyl groups is an important factor in the biogeochemical cycling of elements like arsenic and antimony. In the environment, many different organic and inorganic forms of these elements can therefore be found in soils, sediments or organisms. Studies that compare the ecotoxicity of these different chemical species however are rare. Therefore, this study aimed to generate toxicity data on two scarcely studied organic compounds of arsenic and antimony, as well as to compare their toxicity to the inorganic species, which are studied so far to a higher extent, in order to improve the environmental effect assessment of these elements. To this purpose, bioassays were performed in which three different aquatic organisms (the floating water plants Lemna minor and Wolffia arrhiza and the green alga Selenastrum capricornutum) were exposed to a concentration series of 3 different arsenic species (sodium arsenite — As(III), sodium arsenate — As(V), and monomethylarsonous diiodide — MMAs(III)) and three different antimony species (antimony potassium tartrate hydrate — Sb(III), potassium hexahydroxoantimonate — Sb(V), trimethylantimony(V) bromide — TMSb(V). The observed effect concentrations demonstrated that the inorganic (III)- and (V)-valent species of arsenic were clearly more toxic than the corresponding antimony species. The highest overall toxicity has been shown by MMAs(III) followed by the inorganic As(III). The highest toxicity of the three tested antimony species has been observed for TMSb(V). The observed differences in effect levels stress the importance once more that speciation must not be ignored in toxicity studies. 相似文献
62.
The title complex [K(2,2,2-crypt)]3Sb11 has been prepared by the reaction of K3Cd2Sb with Cu-C≡CH in ethylenediamine in the presence of 2,2,2-crypt, and characterized by low temperature X-ray structure analysis. The crystal is of orthorhombic system, space group C2221 with a = 15.475(3), b = 22.807(5), c = 24.834(6), V = 8765(3)3, Dc = 1.960 g/cm3, C54H108K3N6O18Sb11, Mr = 2586.01, F(000) = 4944, μ = 3.531 mm-1, Z = 4, R = 0.0442 and wR = 0.1053 for 10265 observed reflections (I > 2σ(I)). The "naked" Sb113- anion is stable due to the completely sequestered alkali metal cations through ion-ion interactions. 相似文献
63.
Humayun Ajaz Sajjad Hussain Muhammad Altaf Helen Stoeckli‐Evans Anvarhusein A. Isab Rashid Mahmood Shahnila Altaf Saeed Ahmad 《中国化学》2011,29(2):254-258
Antimony(III) complexes of thioamides [thioamides=thiourea (Tu), N,N′‐dimethylthiourea (Dmtu), tetramethylthiourea (Tmtu), imidazolidine‐2‐thione (Imt) and diazinane‐2‐thione (Diaz)] with the general formulae, Sb(thione)nCl3 (n=1, 2, 2.5, 3) were prepared and characterized by elemental analysis, IR and NMR (1H, 13C) spectroscopic methods. The spectral data of the complexes are consistent with the coordination of the thiones to antimony(III). The crystal structure of one of them, {[Sb(Imt)2Cl2]2(μ2‐Imt)}Cl2 ( 1 ), was determined by X‐ray crystallography, which shows that the complex is dinuclear consisting of two [Sb(Imt)2Cl2] units bridged by an Imt molecule. In 1 , the antimony atom is bonded to two chlorine atoms, two sulfur atoms of coordinated Imt molecules and one sulfur atom of a bridging Imt molecule. The antimony environment can be considered to be distorted octahedral with one Cl? ion weakly bound to antimony. 相似文献
64.
65.
Herewith are the two processes developed by Nitto, which produce N-containing compounds such as hydrogen cyanide and methylamines. These processes are characterized by unique selective catalysts: an Fe–Sb–O based fluid-bed catalyst for ammoxidation of methanol and a shape-selective zeolite catalyst for ammonolysis of methanol. 相似文献
66.
Hugh Rieley Daniel J. Colby Darren P. McMurray Stuart M. Reeman 《Surface science》1997,390(1-3):243-249
The effects of physisorption and two-dimensional ordering on the photochemistry of N2O4 were investigated. Ordered monolayers were prepared by adsorption of NO2 at 100 K on a water-ice surface. Irradiation with a continuous light source in the wavelength region 300–400 nm or with pulsed laser radiation at 355 nm resulted in exclusive desorption of NO2. This desorption was induced by electronic absorption directly in the adsorbate via a transition corresponding to the (
)1B2u←(
)1Ag transition in N2O4, as in the gas phase. However, the subsequent dynamics in the excited state were markedly different from the gas-phase counterpart. Time-of-flight mass spectrometry of NO2 photodesorbed at 355 nm revealed a most probable fragment translational energy of ca. 17 meV; and the angular distribution of the nascent NO2 was peaked sharply in a direction around 10° from the normal. It is apparent that, despite the weak interaction with the substrate, significant energy transfer occurs in the ordered physisorbed monolayer to yield nascent NO2 with very low translational energy and a constrained angle of escape which is consistent with a high degree of adsorbate order and alignment. 相似文献
67.
L. A. Grigoryan S. A. Avetisyan R. A. Grigoryan A. V. Mikhailova 《Russian Chemical Bulletin》1997,46(3):586-588
The fluorometric reaction of acrichin (quinacrine hydrochloride) with hexachloroantimonic acid has been studied. The formation
of a water-insoluble product has been shown. The precipitate contains equimolar quantities of acrichin and acid. The optimal
conditions of formation, extraction, and determination were found. Acrichin was used for the extraction-fluorometry determination
of nanogram amounts of antimony(v).
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 606–608, March, 1997. 相似文献
68.
Schiff base derivatives of the type Ph3Si? O? Sb(NO)Ph3 (where NO represents the donor system of a monobasic bidentate ligand) have been synthesized. These are obtained as coloured solids; they are non-electrolytes and monomeric in nature, and have been characterized by elemental analysis, IR and 1H NMR. Spectral studies suggest that silicon and antimony atoms are in tetra- and hexa-coordinated states, respectively. 相似文献
69.
本文用自制的氢化物发生装置测定了湖底泥中的Sb、Bi和Te,并探讨了各元素的测定条件。实验证明,该法灵敏度高、选择性好、操作简单、稳定性和精密度均满足要求。 相似文献
70.
Os(VIII) catalysis of oxidation of As(III)/Sb(III) by 1-equivalent oxidants like Ce(IV) and Mn(III) in acid medium is studied.
A multistep mechanism involving the intervention of the intermediate oxidation states of osmium is found to apply. Specific
rates of different steps in the mechanism are estimated and used to calculate reaction rates which are in reasonable agreement
with those of experiment. 相似文献