全文获取类型
收费全文 | 897篇 |
免费 | 30篇 |
国内免费 | 179篇 |
专业分类
化学 | 1054篇 |
晶体学 | 3篇 |
力学 | 1篇 |
综合类 | 12篇 |
物理学 | 36篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 13篇 |
2019年 | 17篇 |
2018年 | 21篇 |
2017年 | 37篇 |
2016年 | 27篇 |
2015年 | 17篇 |
2014年 | 40篇 |
2013年 | 102篇 |
2012年 | 46篇 |
2011年 | 44篇 |
2010年 | 36篇 |
2009年 | 46篇 |
2008年 | 50篇 |
2007年 | 53篇 |
2006年 | 57篇 |
2005年 | 55篇 |
2004年 | 57篇 |
2003年 | 49篇 |
2002年 | 51篇 |
2001年 | 26篇 |
2000年 | 38篇 |
1999年 | 31篇 |
1998年 | 31篇 |
1997年 | 23篇 |
1996年 | 21篇 |
1995年 | 22篇 |
1994年 | 15篇 |
1993年 | 14篇 |
1992年 | 14篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 4篇 |
排序方式: 共有1106条查询结果,搜索用时 15 毫秒
61.
I. Strakova A. Strakovs M. Petrova S. Belyakov 《Chemistry of Heterocyclic Compounds》2007,43(12):1512-1518
The [3+2] cycloaddition reactions of a series of 1,3-substituted 5-diazo-6,6-dimethyl-4-oxo-4,5,6,7-tetrahydroindazoles with
maleic anhydride and dimethyl acetylenedicarboxylate gave 1′,3′-substituted 3-spiro[4,6-dioxo-4,6,3a,6a-tetrahydro-3H-furo[3,4-c]pyrazole]-5′-[6′,6′-dimethyl-4′-oxo-4′,5′,6′,7′-tetrahydroindazoles]
and 1′,3′-substituted 3-spiro[4,5-di(methoxycarbonyl)-3H-pyrazole]-5′-[6′,6′-dimethyl-4′-oxo-4′,5′,6′,7′-tetrahydroindazoles]
respectively. When heated the former eliminate nitrogen and are transformed into 1′,3′-substituted 6-spiro[2,4-dioxo-3-oxabicyclo[3.1.0]hexane]-5′-[6′,6′-dimethyl-4′-oxo-4′,5′,6′,7′-tetrahydroindazoles].
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1784–1791, December, 2007. 相似文献
62.
《Journal of polymer science. Part A, Polymer chemistry》2018,56(10):1039-1045
In this article, 10‐undecenoic acid, based on castor oil, was used a raw material for the synthesis of alternating copolymers. ω‐Unsaturated fatty esters as alkyl 10‐undecenoates were prepared by the esterification reaction of 10‐undecenoic acid with alkyl alcohol. A series of comb‐like copolymers were synthesized by free radical polymerization from maleic anhydride and alkyl 10‐undecenoates copolymers with different length of alkyl side chains in a toluene solution. These copolymers were investigated by 1H and 13C nuclear magnetic resonance, Fourier transform infrared spectroscopy, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry (DSC). The copolymers were obtained in a low molecular weight in a range 3370–12,240 g mol−1 and their structural characterization indicated the formation of alternating copolymers. DSC characterization revealed that these comb‐like copolymers showed amorphous to semicrystalline behavior by increasing the length of side chains. The bio‐based comb‐like copolymers allow for the development of new polymeric materials for several applications. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1039–1045 相似文献
63.
3-Carboxy-2-pyrazinehydroxamic acid was prepared by a one pot reaction starting from pyrazine-2,3-dicarboxylic anhydride with a high yield, and characterized by IR, Mass spectrum, 1H NMR and 13C NMR spectra and single-crystal X-ray diffraction. It crystallizes in triclinic, space group Pī with a=4.8659(10), b=7.4233(15), c=11.602(2), α=96.904(2), β=92.422(3), γ=107.454(2)°, V=395.51(14)3 , Z=2, Dc=1.689g/cm3 , F(000)=208, μ(MoKα)=0.149 mm-1 , the final R=0.0473 and wR=0.1306 for 2853 observed reflections (I>2σ (I)). A three-dimensional framework was assembled through intermolecular hydrogen bonding between water and 3-carboxy-2-pyrazine-carbohydroxamic acid molecules. 相似文献
64.
R. Hekmatshoar S. Y. S. Beheshtiha F. Soltani 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2535-2540
A series of novel 4-thioaryl-1,8-naphthalimide derivatives were synthesized using 4-chloro-1,8-naphthalic anhydrid and arylthioles as starting materials. 4-thioaryl-1,8-naphthalic anhydride was treated with different primary amines and o-phenylene diamine or 1,2-diaminoethene to produce 4-thioaryl-1,8-naphthalimides and 4-thioaryl-7 H-benzimidazo-[2,1-a]-benz-[d,c]-isoquinolin-7-one derivatives, respectively. The UV/VIS absorption properties are discussed. 相似文献
65.
Ramin Ghorbani-Vaghei Zahra Toghraei-Semiromi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1701-1707
N,N′-Diiodo-N,N′-1,2-ethanediylbis(p-toluenesulfonamide) (NIBTS) is a highly efficient catalyst for the acetylation of alcohols, phenols, amines, and thiols under solvent-free conditions. Primary, secondary, tertiary alcohols; phenols; amines; and thiols can be easily acetylated in good to excellent yields at 80 °C. 相似文献
66.
István Kapovits József Rábai Dénes Szabó Miklós Kuti 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):435-436
The reactions of possible spiro-λ4-sulfane precursor diaryl sulfoxides with dehydrating agents have been studied resulting in the formation of cyclic anhydride, spiro-λ4-sulfane, cyclic sulfonium-ylide, lactam-sulfoxide, cyclic sulfonimide and cyclic sulfilimine type of intermediates or products. The structures of the intermediates or products depend on the functional groups attached to the aryl rings at ortho positions and on the reaction conditions applied. 相似文献
67.
《高分子科学杂志,A辑:纯化学与应用化学》2013,50(5-6):451-466
A series of new poly(ether-ester-imide)s, PEEIs, was prepared from an imide dicarboxylic acid based on 1,4-diaminobutane and trimellitic anhydride. This imide dicarboxylic acid polycondensed with 1,4-dihydroxybutane formed the hard segments and poly(ethylene oxide), PEO-1000, or mixtures of PEO-1000 and poly(tetramethylene oxide), PTMO-1000, were used as soft segments. Whenever PTMO-1000 was used as comonomer, macrophase separation was observed at the end of the polycondensation. However, this macrophase separation had little influence on the mechanical properties. A poly(ether-esterimide), PEEI, containing neat PEO-1000 was characterized by dynamic mechanical thermoanalysis, stress-strain and hysteresis measurements, and by melt rheology. The mechanical properties were compared with those of an analogous PEEI containing neat PTMO-1000 and with those of a poly(ether-ester), PEE, based on poly(butylene terephthalate) hard segments and PTMO-1000. 相似文献
68.
《高分子科学杂志,A辑:纯化学与应用化学》2013,50(7):739-745
The reaction of maleic anhydride (MAH) grafted onto low density polyethylene (LDPE) in nylene solvents in the presence of benzoyl peroxide (BPO) as an initiator by microwave irradiation has been investigated. The influence of reaction conditions such as initiator content, monomer content and irradiation time have been examined. In the weight composition of xylene/LDPE/MAH/BPO=10/1/1/0.07, the grafting degree reaches 56.5 mmol MAH/100 g PE within only 8 min of microwave irradiation. The grafting reaction time of microwave irradiation shortens over 40 times than in the conventional grafting reaction. 相似文献
69.
B. Biyani A. J. Campagna D. Daruwalla C. M. Srivastava P. Ehrlich 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(3):327-339
The molecular weight distribution (MWD) of crystallizable polyphenylacetylene prepared near room temperature in the presence of ferric acetylacetonate and triethylaluminum was determined through use of fractions characterized by vapor pressure osmometry and gel permeation chromatography (GPC). The number- and weight-average molecular weights (M n and M w) are both less than the molecular weight corresponding to the maximum of the weight distribution function, which lacks a high molecular weight tail. M wandM n is less than is consistent with models allowing for chain termination characteristic of vinyl polymers. GPC elution volumes are much less than those characteristic of polystyrene of similar molecular weight, and the Mark-Houwink exponent is high (2.4 for M v 4800 to 6800). These data indicate more rodlike behavior than for polystyrene of equivalent molecular weight. The MWD and other data suggest intramolecular chain termination, possibly associated with the molecule's tendency to form paramagnetic defect states. 相似文献
70.
Ardeshir Khazaei Shahnaz Saednia Javad Saien Masoumeh Kiani Abbas Afkhami 《Supramolecular chemistry》2013,25(2):88-93
The grafting of 4-amino benzo-9-crown-3 ether to poly (styrene-alt-maleic anhydride) has been described. The covalent grafting of crown ether has led to a considerable increase in the solubility of polymer in organic solvents such as dimethyl sulphoxide, dimethylformamide and tetrahydrofuran. The highest solubility was attained in DMF and DMSO. The covalently bonded 4-benzo-9-crown-3 ether allowed the hosting of Li+. The covalently grafted crown ether to polymer was identified by infrared spectroscopy and thermogravimetric analysis methods. 相似文献