全文获取类型
收费全文 | 2511篇 |
免费 | 115篇 |
国内免费 | 410篇 |
专业分类
化学 | 2752篇 |
晶体学 | 60篇 |
力学 | 8篇 |
综合类 | 36篇 |
数学 | 2篇 |
物理学 | 178篇 |
出版年
2023年 | 17篇 |
2022年 | 28篇 |
2021年 | 49篇 |
2020年 | 88篇 |
2019年 | 46篇 |
2018年 | 53篇 |
2017年 | 67篇 |
2016年 | 69篇 |
2015年 | 71篇 |
2014年 | 78篇 |
2013年 | 222篇 |
2012年 | 181篇 |
2011年 | 100篇 |
2010年 | 77篇 |
2009年 | 112篇 |
2008年 | 105篇 |
2007年 | 169篇 |
2006年 | 157篇 |
2005年 | 130篇 |
2004年 | 116篇 |
2003年 | 128篇 |
2002年 | 92篇 |
2001年 | 79篇 |
2000年 | 82篇 |
1999年 | 71篇 |
1998年 | 75篇 |
1997年 | 52篇 |
1996年 | 75篇 |
1995年 | 61篇 |
1994年 | 56篇 |
1993年 | 61篇 |
1992年 | 64篇 |
1991年 | 45篇 |
1990年 | 36篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有3036条查询结果,搜索用时 15 毫秒
41.
42.
《Analytical letters》2012,45(9-10):939-962
Abstract The ET(30) scale of solvent polarity has been shown to be useful in examining many diverse analytical processes. It is based on the charge transfer absorption of 2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridinio)phenolate (referred to as ET-30 in this paper). Unfortunately, use of the ET(30) scale has been hindered by (a) the lack of a commercial source of the ET-30 dye and (b) the lack of an English language synthetic procedure. Here we discuss recent applications of the ET(30) scale to analytical techniques, as well as a simplified procedure for the synthesis of ET-30. 相似文献
43.
《Analytical letters》2012,45(18):3264-3271
Abstract A simple, precise, rapid, and low-cost conductometric method for N-acetylcysteine determination in pharmaceutical formulations is proposed. N-acetylcysteine present in pharmaceuticals containing known quantities of the drug was conductometrically titrated in aqueous solution with copper(II) sulphate using a conductometric cell coupled to an autotitrator. No interferences were observed in the presence of common components of the tablets such as sodium monophosphate, saccharine, sodium benzoate, sucrose, and fructose. Recoveries of N-acetylcysteine from various tablet dosage formulations ranging from 98.3 to 102.0% were obtained. 相似文献
44.
Claudia GargiulliGiuseppe Gattuso Anna NottiSebastiano Pappalardo Melchiorre F. Parisi 《Tetrahedron letters》2011,52(48):6460-6464
New AB-type supramolecular polymers have been prepared by acid-promoted self-assembly of an aminododecyloxy-calix[5]arene monomer precursor. The number-average degree of polymerization has been found to be dependent on the concentration of the salt monomer and on the nature of the counterion (i.e., chloride, picrate or hexafluorophosphate).Chain-length regulation experiments have been carried out, employing orthogonal chain stoppers capable of selectively interacting with a given moiety of the AB-type monomer/polymer. Competitive calix[5]arene ‘caps’ and n-butylammonium ion ‘plugs’ have been used to control the extent of self-assembly of the polymer, in turn interacting with the ammoniumdodecyloxy or with the cavity end-groups of the supramolecular calixarene assembly. These experiments, conveniently carried out at a 10 mM concentration, can be easily followed by 1H NMR spectroscopy. 相似文献
45.
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
46.
Alcohol-containing potassium organotrifluoroborates as starting reagents were prepared from their corresponding dibromobenzenes through a sequential one-pot reaction. The oxidation reactions of these substrates, which were carried out using 3.0 equiv of 8 N Jones reagent in acetone at 0 °C, provided a high yield of the desired carbonyl-functionalized compounds. In addition, the cross-coupling reactions of these organocarbonyltrifluoroborates were successfully performed in the presence of 3 mol % of Pd(PPh3)4 catalyst at 100 °C. 相似文献
47.
48.
49.
50.