全文获取类型
收费全文 | 656篇 |
免费 | 15篇 |
国内免费 | 5篇 |
专业分类
化学 | 415篇 |
晶体学 | 16篇 |
力学 | 31篇 |
数学 | 46篇 |
物理学 | 168篇 |
出版年
2023年 | 6篇 |
2022年 | 30篇 |
2021年 | 32篇 |
2020年 | 23篇 |
2019年 | 25篇 |
2018年 | 22篇 |
2017年 | 22篇 |
2016年 | 27篇 |
2015年 | 17篇 |
2014年 | 31篇 |
2013年 | 56篇 |
2012年 | 30篇 |
2011年 | 53篇 |
2010年 | 30篇 |
2009年 | 20篇 |
2008年 | 16篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 2篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1970年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有676条查询结果,搜索用时 15 毫秒
11.
Mohamed M. El-Kerdawy Ali A. El-Emam Hussein I. El-Subbagh Elie Abushanab 《Monatshefte für Chemie / Chemical Monthly》1990,121(1):45-50
Summary A new series of thiophenic isosters of thioxanthones, namely: 2-substituted-4H-thieno[2,3-b][1]benzothiopyran-4-ones and 5-substituted-2-nitro-8-methyl-4H-thieno[2,3-b][1]benzothiopyran-4-ones were synthesized as potential schistosomicidal agents. The synthesized compounds were characterized by their1H-NMR data.
Synthese von substituierten 4H-Thieno[2,3-b][1]benzothiopyran-4-onen als mögliche schistosomicide Wirkstoffe
Zusammenfassung Es wurde eine neue Serie von thiophenischen Isosteren des Thioxanthons, nämlich 2-substituierte 4H-Thieno[2,3-b][1]benzothiopyran-4-one und 5-substituierte 2-Nitro-8-methyl-4H-thieno[2,3-b][1]benzothiopyran-4-one als potentielle schistosomicide Wirkstoffe synthetisiert. Die synthetisierten Verbindungen wurden mittels ihrer1H-NMR Daten charakterisiert.相似文献
12.
Summary The copper(III)-imine-oxime complexes [CuIII(Enio)]+ and [CuIII(Pre)]+ {EnioH2 =N,N-ethylene bis(isonitrosoacetylacetoneimine) and PreH2 = N,N-propylene bis (isonitrosoacetylacetoneimine)} react very rapidly with iodide. The rate law under fixed conditions for the reaction is given by the equation: –d[CuIII]/dt = (2k2[I–] + 2k3[I–]2)[CuIII] The [CuIII(Enio)]+ reaction was pH-independent whereas the [Cu (Pre)]+ reaction rate increased with increasing pH. Both the k2 and the k3 pathways are believed to involve one-electron transfer. An inner-sphere mechanism may operate in the pathway, first-order in [I–]. 相似文献
13.
A fundamental study was made on the reduction of calcium phosphate by carbon. The mechanism of reduction was presented on applying different additions. Both silica and alumina increased the extent of reduction but with variable rates. The activation energies were calculated on the basis of first-order reactions. The phases formed during reduction were investigated by X-ray analysis. 相似文献
14.
Ibnelwaleed A. Hussein M. Sayem Mozumder Sk. Asrof Ali 《European Polymer Journal》2005,41(10):2472-2482
Rheological properties of hydrophobically modified copolymer of SO2, N,N-diallyl-N-carboethoxymethylammonium chloride and the hydrophobic monomer N,N-diallyl-N-octadecylammonium chloride were studied. The influence of hydrophobe content (HP) and polymer concentration was investigated. Polymers with HP content in the range 1.5-5% were examined and the concentration was varied in the range 2-5 wt%. Both dynamic and steady-shear experiments were performed in ARES rheometer. Copolymers were observed to exhibit typical viscoelastic behavior even with low HP content. Both the dynamic viscosity, η′ and storage modulus, G′, increase with the increase of both the polymer concentration and the HP content of the system. The viscosity of the high HP content polymer showed a strong shear dependency, while G′ was a weak function of frequency and gel-like behavior was observed. The zero-shear viscosity, η0, showed a strong concentration dependency (η0 ∼ ?α; 1.1 < α < 5.9). The concentration dependency of η0 suggests that intermolecular association is dominant in the high HP content polymer. Control of the HP content and polymer concentration of this class of polymers can lead to a wide range of interesting rheological properties. 相似文献
15.
Mohamed Hilmy Elnagdi Mohamed Riffaat Hamza Elmoghayer Hassan Attia Elfaham Mohamed Mohamed Sallam Hikmat Hussein Alnima 《Journal of heterocyclic chemistry》1980,17(2):209-212
The 4-bromo-3-phenylpyrazol-5-ylhydrazonyl chlorides (Ia,b) and 1,2,4-triazol-5-ylhydrazonyl chlorides (IIa,b) were prepared via coupling of diazotized 4-bromo-3-phenyl-5-aminopyrazole (III) and 5-amino-1,2,4-triazole (IV) with α-chloro derivatives of acetylacetone and of ethyl aceto-acetate. Compounds Ia and IIa,b were utilised for the synthesis of several new heterocyclic derivatives. 相似文献
16.
17.
18.
19.
Abd El-Badih A. G. Ghattas Hassan M. Moustafa Elsayed A. A. Hassanein Bahgat R. M. Hussein 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):1469-1481
Abstract Alkylation of 4-anilino-5-phenyl-4H-1,2,4-triazole-3-thiol (1) with some halo compounds yielded the corresponding sulfides 2a–f. Some sulfides 2e,f were cyclized to give triazolothiadiazines 3 and 4. Triazolothiadiazoles 5 and 6 were prepared through the reaction of compound 1 with carbon disulfide or ethyl orthoformate, respectively. Treatment of compound 1 with ethyl chloroformate or phenyl isothiocyanate yielded triazolo-thiadiazole and triazole 9 and 10, respectively. Reaction of compound 1 with Lawesson's reagent gave triazolothiadiazaphosphole derivative 11. Also, compound 1 underwent cyclocondensation reactions with some bidentate reagents to give triazolothiazines 4, 12, and 13. Triazolo-thiazepines and triaziepine 14–16 were synthesized via the reaction of compound 1 with β-ketoesters or ethyl cyanoacetate. Tricyclic systems 19 and 20 were prepared through the reaction of compound 4 with the appropriate reagent. Some synthesized compounds were tested for antibacterial activity. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献
20.
Nabil Abdul‐kader Saleh Hussein El‐abd Saltani Fadhil Abbas Al‐Issa Al‐Sadek Gomaa Melad 《中国化学会会志》2013,60(10):1234-1240
The antimicrobial activity of thirteen newly synthesized 4‐thiazolidinones (TZONs) and four dithiolane derivatives was assessed against susceptible and resistant bacteria, including MRSA, as well as Candida albicans. The structure‐activity relationships revealed that 4‐Thiazolidinone derivatives harboring p‐chlorophenyl and dicarboxyethyl at the 2‐ethenyl and 5‐arylidine positions of the thiazolidinone ring display considerable antibacterial properties. No antifungal activity was recorded by all tested compounds against Candida albicans. The possible potentiative (synergistic) effect of the most active compounds to a few commercial antibiotics was also investigated. 相似文献