全文获取类型
收费全文 | 5513篇 |
免费 | 338篇 |
国内免费 | 36篇 |
专业分类
化学 | 3782篇 |
晶体学 | 65篇 |
力学 | 206篇 |
数学 | 886篇 |
物理学 | 948篇 |
出版年
2023年 | 43篇 |
2022年 | 193篇 |
2021年 | 168篇 |
2020年 | 116篇 |
2019年 | 200篇 |
2018年 | 170篇 |
2017年 | 117篇 |
2016年 | 276篇 |
2015年 | 170篇 |
2014年 | 283篇 |
2013年 | 573篇 |
2012年 | 326篇 |
2011年 | 338篇 |
2010年 | 242篇 |
2009年 | 232篇 |
2008年 | 246篇 |
2007年 | 237篇 |
2006年 | 226篇 |
2005年 | 182篇 |
2004年 | 170篇 |
2003年 | 146篇 |
2002年 | 194篇 |
2001年 | 77篇 |
2000年 | 117篇 |
1999年 | 66篇 |
1998年 | 48篇 |
1997年 | 48篇 |
1996年 | 43篇 |
1995年 | 44篇 |
1994年 | 38篇 |
1993年 | 38篇 |
1992年 | 33篇 |
1991年 | 28篇 |
1990年 | 16篇 |
1989年 | 34篇 |
1988年 | 37篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 31篇 |
1984年 | 28篇 |
1983年 | 23篇 |
1982年 | 27篇 |
1981年 | 27篇 |
1980年 | 17篇 |
1979年 | 21篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1974年 | 9篇 |
排序方式: 共有5887条查询结果,搜索用时 46 毫秒
971.
Mohamed I. Hegab Nasser A. Hassan Emad M. El‐Telbani Ibrahim S. Ahmed Farag Farouk M. E. Abdel‐Megeid 《Heteroatom Chemistry》2003,14(3):223-228
Hydrazones 12a–c and ketazines 13a–c were prepared by the reaction of ketones 11a–c with hydrazine hydrate depending on the temperature and the reaction time. Some ketone (aryl)hydrazone derivatives 14a,c,e reacted with thionyl chloride to afford the chlorothiadiazoline derivatives 15a–c . Surprisingly, the chlorine atom in the latter compounds was found to undergo smooth nucleophilic substitution, and by boiling these compounds in absolute ethanol gave the corresponding ethoxythiadiazoline derivatives 16a–c . The structure of the ethoxythiadiazoline 16b was confirmed by single crystal X‐ray determination. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:223–228, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10125 相似文献
972.
Mahmoud G. Metwally Abdelaziz H. Benhawy Reda M. Khalifa Rasha M. El Nashar Marek Trojanowicz 《Molecules (Basel, Switzerland)》2021,26(21)
The increase of the global population and shortage of renewable water resources urges the development of possible remedies to improve the quality and reusability of waste and contaminated water supplies. Different water pollutants, such as heavy metals, dyes, pesticides, endocrine disrupting compounds (EDCs), and pharmaceuticals, are produced through continuous technical and industrial developments that are emerging with the increasing population. Molecularly imprinted polymers (MIPs) represent a class of synthetic receptors that can be produced from different types of polymerization reactions between a target template and functional monomer(s), having functional groups specifically interacting with the template; such interactions can be tailored according to the purpose of designing the polymer and based on the nature of the target compounds. The removal of the template using suitable knocking out agents renders a recognition cavity that can specifically rebind to the target template which is the main mechanism of the applicability of MIPs in electrochemical sensors and as solid phase extraction sorbents. MIPs have unique properties in terms of stability, selectivity, and resistance to acids and bases besides being of low cost and simple to prepare; thus, they are excellent materials to be used for water analysis. The current review represents the different applications of MIPs in the past five years for the detection of different classes of water and wastewater contaminants and possible approaches for future applications. 相似文献
973.
A k‐star is the graph K1,k. We prove a general theorem about k‐star factorizations of Cayley graphs. This is used to give necessary and sufficient conditions for the existence of k‐star factorizations of any power (Kq)s of a complete graph with prime power order q, products C × C ×··· × C of k cycles of arbitrary lengths, and any power (Cr)s of a cycle of arbitrary length. © 2001 John Wiley & Sons, Inc. J Graph Theory 36: 59–66, 2001 相似文献
974.
Alaa S. Abd‐El‐Aziz Erin K. Todd Tarek H. Afifi 《Macromolecular rapid communications》2002,23(2):113-117
This communication is focused on the controlled design of star‐shaped aromatic ethers with pendent cyclopentadienyliron moieties. A trimetallic core was prepared, which was then reacted with a number of oligomeric ether complexes to give star‐shaped polymers with six, nine, twelve and fifteen pendent cationic cyclopentadienyliron moieties. Cyclic voltammetric studies showed reduction of the iron centers between –0.99 and –1.41 V. Thermogravimetric analysis showed that loss of the metallic moieties occurred between 225 and 284°C. 相似文献
975.
Polymer‐solvent compounds can be formed from homogeneous solutions obtained at high temperature but also by solvent diffusion at the solid interface of a bulk polymer at room temperature. This phenomenon we call “physical” corrosion as it modifies the surface structure without chemical change. Here we report preliminary experiments indicating that the thermodynamics seems to be little dependent upon the path used while the morphology is. 相似文献
976.
Nilufar Z. Mamadalieva Fadia S. Youssef Hidayat Hussain Gokhan Zengin Adriano Mollica Nawal M. Al Musayeib Mohamed L. Ashour Bernhard Westermann Ludger A. Wessjohann 《Molecules (Basel, Switzerland)》2021,26(21)
The antioxidant and enzyme inhibitory potential of fifteen cycloartane-type triterpenes’ potentials were investigated using different assays. In the phosphomolybdenum method, cycloalpioside D (6) (4.05 mmol TEs/g) showed the highest activity. In 1,1-diphenyl-2-picrylhydrazyl (DPPH*) radical and 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) cation radical scavenging assays, cycloorbicoside A-7-monoacetate (2) (5.03 mg TE/g) and cycloorbicoside B (10) (10.60 mg TE/g) displayed the highest activities, respectively. Oleanolic acid (14) (51.45 mg TE/g) and 3-O-β-d-xylopyranoside-(23R,24S)-16β,23;16α,24-diepoxycycloart-25(26)-en-3β,7β-diol 7-monoacetate (4) (13.25 mg TE/g) revealed the highest reducing power in cupric ion-reducing activity (CUPRAC) and ferric-reducing antioxidant power (FRAP) assays, respectively. In metal-chelating activity on ferrous ions, compound 2 displayed the highest activity estimated by 41.00 mg EDTAE/g (EDTA equivalents/g). The tested triterpenes showed promising AChE and BChE inhibitory potential with 3-O-β-d-xylopyranoside-(23R,24S)-16β,23;16α,24-diepoxycycloart-25(26)-en-3β,7β-diol 2′,3′,4′,7-tetraacetate (3), exhibiting the highest inhibitory activity as estimated from 5.64 and 5.19 mg GALAE/g (galantamine equivalent/g), respectively. Compound 2 displayed the most potent tyrosinase inhibitory activity (113.24 mg KAE/g (mg kojic acid equivalent/g)). Regarding α-amylase and α-glucosidase inhibition, 3-O-β-d-xylopyranoside-(23R,24S)-16β,23;16α,24-diepoxycycloart-25(26)-en-3β,7β-diol (5) (0.55 mmol ACAE/g) and compound 3 (25.18 mmol ACAE/g) exerted the highest activities, respectively. In silico studies focused on compounds 2, 6, and 7 as inhibitors of tyrosinase revealed that compound 2 displayed a good ranking score (−7.069 kcal/mole) and also that the ΔG free-binding energy was the highest among the three selected compounds. From the ADMET/TOPKAT prediction, it can be concluded that compounds 4 and 5 displayed the best pharmacokinetic and pharmacodynamic behavior, with considerable activity in most of the examined assays. 相似文献
977.
The reaction of 2‐amino‐3‐cyano‐4,5,6,7‐tetrahydrobenzo[b]thiophene ( 1 ) with diethyl malonate ( 2 ) gave two products: 3 and 4 . The reactivity of 3 toward a variety of chemical reagents was studied to give azoles, azines, and their fused derivatives. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:168–175, 2001 相似文献
978.
Giuseppe Vasapollo Antonio Scarpa Giuseppe Mele Ludovico Ronzini Bassam El Ali 《应用有机金属化学》2000,14(11):739-743
Palladium acetate [Pd(OAc)2] and 1,4‐bis(diphenylphosphino)butane (dppb) catalyse regioselective cyclocarbonylation of bisallyl derivatives of bisphenols affording seven‐membered ring bislactones in good yields. Double cyclocarbonylation reactions carried out using different conditions afforded bislactones with two different ring sizes (7–6 and 7–5‐membered). Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
979.
In this work, an approach for finding the solution of coupled semi‐linear diffusion equations for initial value problems is presented. The formal exact solution is found and the Picard iteration is constructed. It is shown that the constructed sequence of solutions converges uniformly for some classes of initial value problems. The problem of dispersion of an oxygen demanding pollutant released into a uniform flow is studied. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
980.
For a positive integer d, the usual d‐dimensional cube Qd is defined to be the graph (K2)d, the Cartesian product of d copies of K2. We define the generalized cube Q(Kk, d) to be the graph (Kk)d for positive integers d and k. We investigate the decomposition of the complete multipartite graph K into factors that are vertex‐disjoint unions of generalized cubes Q(Kk, di), where k is a power of a prime, n and j are positive integers with j ≤ n, and the di may be different in different factors. We also use these results to partially settle a problem of Kotzig on Qd‐factorizations of Kn. © 2000 John Wiley & Sons, Inc. J Graph Theory 33: 144–150, 2000 相似文献