全文获取类型
收费全文 | 1411篇 |
免费 | 55篇 |
国内免费 | 46篇 |
专业分类
化学 | 1031篇 |
晶体学 | 11篇 |
力学 | 79篇 |
数学 | 119篇 |
物理学 | 272篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 42篇 |
2021年 | 45篇 |
2020年 | 58篇 |
2019年 | 59篇 |
2018年 | 82篇 |
2017年 | 53篇 |
2016年 | 83篇 |
2015年 | 66篇 |
2014年 | 90篇 |
2013年 | 208篇 |
2012年 | 98篇 |
2011年 | 93篇 |
2010年 | 73篇 |
2009年 | 66篇 |
2008年 | 75篇 |
2007年 | 66篇 |
2006年 | 43篇 |
2005年 | 27篇 |
2004年 | 26篇 |
2003年 | 12篇 |
2002年 | 29篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1978年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有1512条查询结果,搜索用时 15 毫秒
31.
Hamid Reza Shaterian Asghar Hosseinian Majid Ghashang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):3136-3144
Herein, we describe a green procedure for the one-pot preparation of 1,8-dioxo-octahydroxanthene derivatives by condensation of dimedone and substituted benzaldehydes in the presence of FeCl 3 -SiO 2 as an efficient and heterogeneous catalyst under microwave irradiation and thermal conditions. This method has the advantages of high yields, cleaner reactions, efficient and cost-effective method, simple methodology, short reaction times, easy workup, and greener conditions. 相似文献
32.
Hossein A. Oskooie Azam Ranjbaran Majid M. Heravi Mitra Ghassemzadeh 《Phosphorus, sulfur, and silicon and the related elements》2013,188(9):1711-1714
Reduction of aromatic nitro compounds to amine with hydroiodic acid was revisited. Under microwave irradiation on solid support the reduction proceeded efficiently and rapidly. 相似文献
33.
Majid M. Heravi Hossein A. Oskooie Pegah Kazemian Fatemeh Drikvand Mitra Ghassemzadeh 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2341-2344
Cerium ammonium nitrate (CAN) adsorbed on HNO 3 /silica gel is a mild reagent for selective oxidation of benzylic alcohols to the corresponding aldehydes under microwave irradiation in solventless system. 相似文献
34.
Mehdi Mousavi-Kamazani Masoud Salavati-Niasari Majid Ramezani 《Journal of Cluster Science》2013,24(3):927-934
This study reports on the synthesis of Cu2S nanoparticles via an ultrasonic method by employing Na2SO3 as a reducing agent. Morphology, structure, and composition of the obtained products were characterized by X-ray diffraction, energy dispersive X-ray analysis, scanning electron microscope and photoluminescence spectroscopy. The effects of time and power of irradiation were studied. 相似文献
35.
Owing to the versatile applications in different areas including biology, natural compounds, dyes, and fluorescent materials, the synthesis of 2-pyridone compounds is an important research field and has attracted a great deal of attention. In this review, 2-pyridones new synthetic methods are classified to tree classes including reactions based on pyridine rings, cyclization, and cycloaddition reactions. 相似文献
36.
A new composite electrode has been fabricated based on coating multi‐walled carbon nanotubes (MWCNTs) and n‐octylpyridinum hexafluorophosphate (OPPF6) ionic liquid composite on a glassy carbon (GC) electrode (OPPF6‐MWCNTs/GCE). This electrode shows very attractive electrochemical performances for electrooxidation of risperidone (RIS) compared to conventional electrodes using carbon and mineral oil, notably improved sensitivity and stability. The oxidation peak potentials in cyclic voltammogram of RIS on the OPPF6‐MWCNTs/GCE was occurred around 230 mV vs. SCE at Britton–Robinson (B–R) buffer (pH 4.0) at scan rate of 100 mV s?1. The electrochemical parameters such as diffusion coefficient (D), charge transfer coefficient (α) and the electron transfer rate constant (k/s) were determined using cyclic voltammetry. Under the optimized conditions, the peak current was linear to risperidone concentration over the concentration range of 10–200 nM with sensitivity of 0.016 μA/nM?1 using differential pulse voltammetry. The detection limit was 6.54 nM (S/N = 3). The electrode also displayed good selectivity and repeatability. In the presence of clozapine (CLZ) the response of RIS kept almost unchanged. Thus this electrode could find application in the determination of RIS in some real samples. The analytical performance of the OPPF6‐MWCNTs/GCE was demonstrated for the determination of RIS in human serum and pharmaceutical samples. 相似文献
37.
Majid Haji Hosseini Peyman Asaadi Mohammad Rezaee Mohammad Reza Rezaei Mohammad Reza Pourjavid Masoud Arabieh Ahmad Amrollah Abhari 《Chromatographia》2013,76(23-24):1779-1784
This work proposes a new, rapid and simple homogeneous liquid–liquid microextraction via flotation assistance technique for the analysis of six organochlorine pesticides in water samples. A special extraction cell was used to facilitate collection of the low-density solvent extract. No centrifugation was required in this procedure. Determination was carried using gas chromatography–mass spectrometry. The water sample solution was then added into the extraction cell containing appropriate mixture of extract and homogeneous solvents. In the first step, a homogeneous solution and then with the continuation of water sample injection, a cloudy solution was formed. Using air flotation, the organic solution was collected at the conical part of the designed cell. The optimized levels of effective parameters were found based on response surface methodology approach. Applying the optimized conditions to the system understudy, the limits of detection of all target analytes were obtained in the range of 1.4–7 ng mL?1, while the precisions were found to be in the range of 11.08–14.87 (RSD, n = 3). The linearity of the method lay in the range of 10–150 ng mL?1 with the coefficients of correlation (r 2 ) ranging from 0.998 to 0.999. 相似文献
38.
Hassan Keypour Ahmad Ali Dehghani-Firouzabadi Majid Rezaeivala Sadegh Salehzadeh 《合成通讯》2013,43(7):1136-1142
A new Schiff base cryptand (L) has been prepared via [2 + 2] condensation of 1,3,5-tris(2-formylphenoxymethyl)benzene (1) with 1,3,5-tris(aminomethyl)benzene trishydrochloride (2) in the presence of Ba(II) ion. The analytical data show that the Ba(II) cation is not retained by the product. Thus it seems that the role of the Ba(II) ion is to organize the transition state preceding the formation of the cryptand. 相似文献
39.
Majid M. Heravi Vahideh Rasmi Fatemeh F. Bamoharram Sodeh Sadjadi Lida Fotouhi Samahe Sadjadi 《合成通讯》2013,43(22):4109-4116
Silica-supported Preyssler nanoparticles appear to be a new and efficient solid acid catalyst for an economical, and environmentally benign one-pot synthesis of 3-substituted phthalides. 相似文献
40.
An efficient and convenient conversion of aldoximes and ketoximes to the corresponding carbonyl compounds with tetrameric DABCO–bromine complex is reported. 相似文献