全文获取类型
收费全文 | 5829篇 |
免费 | 238篇 |
国内免费 | 28篇 |
专业分类
化学 | 3895篇 |
晶体学 | 71篇 |
力学 | 174篇 |
数学 | 437篇 |
物理学 | 1518篇 |
出版年
2024年 | 4篇 |
2023年 | 30篇 |
2022年 | 68篇 |
2021年 | 154篇 |
2020年 | 104篇 |
2019年 | 106篇 |
2018年 | 86篇 |
2017年 | 94篇 |
2016年 | 151篇 |
2015年 | 170篇 |
2014年 | 220篇 |
2013年 | 379篇 |
2012年 | 425篇 |
2011年 | 459篇 |
2010年 | 294篇 |
2009年 | 245篇 |
2008年 | 427篇 |
2007年 | 364篇 |
2006年 | 375篇 |
2005年 | 308篇 |
2004年 | 288篇 |
2003年 | 237篇 |
2002年 | 234篇 |
2001年 | 168篇 |
2000年 | 111篇 |
1999年 | 95篇 |
1998年 | 54篇 |
1997年 | 29篇 |
1996年 | 45篇 |
1995年 | 56篇 |
1994年 | 34篇 |
1993年 | 38篇 |
1992年 | 29篇 |
1991年 | 15篇 |
1990年 | 31篇 |
1989年 | 29篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1985年 | 22篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有6095条查询结果,搜索用时 15 毫秒
991.
Fumio Sanda Tsuyoshi Shinjo Wonmun Choi Takeshi Endo 《Macromolecular rapid communications》2001,22(5):363-366
This article deals with the cationic and anionic depolymerization of polydithiocarbonate, which was synthesized by cationic polymerization of 5‐phenoxymethyl‐1,3‐oxathiolane‐2‐thione ( 1 ) using methyl triflate as the initiator. The cationic depolymerization of the obtained polymer was carried out in the presence of 5–20 mol‐% of methyl triflate or triflic acid catalyst in chlorobenzene at 60 °C for 96 h to afford 4‐phenoxymethyl‐1,3‐dithiolan‐2‐one ( 2 ) in 35–83% yield. The anionic depolymerization of the polymer was carried out in the presence of 5 mol‐% of triethylamine or potassium tert‐butoxide at 20 °C for 24 h to afford 2 in 85–100% yield. 相似文献
992.
The synthesis of the first lactose main‐chain copolymer was achieved by means of solution polyreaction of ethylenediaminetetraacetic acid dianhydride with D ‐lactose. The water‐soluble carboxy‐functional material based on EDTA with a high molar mass is shown to be biodegradable. The metal complexing properties of the polymer based on the liquid‐phase polymer‐based retention (LPR) method showed a strong interaction with Cr(III), Fe(III), and Sr(II) ions. 相似文献
993.
Rupasree R. Das Shashadhar Samal Seok‐Ju Choi Kurt E. Geckeler 《Macromolecular rapid communications》2001,22(11):850-854
The synthesis of a novel highly swelling, macroporous hydrogel from poly(allylamine) using 3‐chloropentan‐2,4‐dione as a crosslinker is reported. The swelling of the hydrogel was sensitive to changes in pH, temperature, and the extent of crosslinking. The dry gel exhibited a regular honeycomb network with smooth macropores. The hydrogel was inherently luminescent, and so was a metal polychelate. 相似文献
994.
995.
Alexander Steblyanko Wonmun Choi Fumio Sanda Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》2000,38(13):2375-2380
A bifunctional five‐membered cyclic carbonate was synthesized from carbon dioxide and diglycidyl terephthalate, and its polyaddition with alkyl diamines were carried out in DMF at room temperature to obtain the corresponding poly(hydroxyurethane)s with Mn s in the range of 6300–13200 in good yields. The structures of the obtained polymers were confirmed by IR and NMR spectroscopy and their glass‐transition and decomposition temperatures were observed at 3–29 °C and 182–277 °C, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2375–2380, 2000 相似文献
996.
Young Gun Ko Ung Su Choi Byeng Gil Ahn Dong June Ahn 《Journal of polymer science. Part A, Polymer chemistry》2000,38(15):2815-2823
High‐performance materials for flameproofing, phosphates (polyphosphate and ammonium phosphate) were synthesized on viscose rayon felt. This surface reaction has the advantage of a nonblooming effect and an application in thermosetting plastics. Metal complexes have the effect of reducing the amount of smoke. Therefore, in the second step, transition‐metal complexes were synthesized on the viscose rayon ammonium phosphate felt. This article focuses on the surface modification of phosphates and metal complexes on viscose rayon. All reactions were confirmed by attenuated total reflectance Fourier transform infrared and time‐of‐flight secondary ion mass spectrometry. As the concentrations of phosphoric acid and urea increased, the peak intensities of ammonium ion groups and phosphate groups greatly increased. The thermal properties of the synthesized materials were studied with thermogravimetric analysis and oxygen index testing. On the basis of the experimental results, the synthesized flame‐retardancy materials showed excellent physicochemical and thermal effects and flame retardancy. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2815–2823, 2000 相似文献
997.
998.
Polyhydroxyalkanoates (PHAs) are carbon and energy reserve material accumulated by numerous microorganisms and have been drawing much attention as biodegradable substitutes for conventional nondegradable plastics and elastomers. There are a number of different PHAs having a variety of material properties based on the different monomer composition. Poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) are now efficiently produced by bacterial fermentation at reasonable production costs. Recent advances in the production of short‐chain‐length (SCL) PHAs by bacterial fermentation are reviewed. Current status of the production of medium‐chain‐length (MCL) PHAs and SCL‐MCL‐PHA copolymers is also reviewed. 相似文献
999.
Diethylaminoethyl–chitin (DEAE–chitin) was synthesized by introducing DEAE groups onto the C(6)–OH in chitin. DEAE–chitin was N-deacetylated by heating in aqueous 10% sodium hydroxide containing sodium borohydride to prepare the diethylaminoethyl–chitosan (DEAE–chitosan). In addition, DEAE–chitin was quaternized with ethyl halide to produce triethylaminoethyl–chitin (TEAE–chitin). Their antibacterial activities were evaluated by using colony count against Staphylococcus aureus and Escherichia coli by means of shake flask method. The antibacterial activity was found to increase in order of DEAE–chitin, DEAE–chitosan, TEAE–chitin. DEAE–chitin was hydrolyzed by enzymes to investigate the effect of molecular weight on its antibacterial activities. The antibacterial activity was dependent on the structure, particularly on the molecular weight of chitin derivatives. © 1997 John Wiley & Sons, Ltd. 相似文献
1000.
Particles of semiconducting polyaniline and a copolyaniline bearing ionic substituents were synthesized. Electrorheological (ER) fluids using these particles were compared with each other with respect to their rheological properties and dielectric spectra. In the steady shear rheological experiment conducted at 3 kV/mm (DC) at 25°C, the copolymer system showed higher stress than the polyaniline system in the whole shear rate region. This result was interpreted in terms of the conductivities of the particles and their dielectric spectra. Especially, the different behavior in the high shear rate region can be related to the electrical relaxation phenomena observed in the dielectric spectra. 相似文献