全文获取类型
收费全文 | 9812篇 |
免费 | 1181篇 |
国内免费 | 2015篇 |
专业分类
化学 | 10387篇 |
晶体学 | 120篇 |
力学 | 306篇 |
综合类 | 81篇 |
数学 | 50篇 |
物理学 | 2064篇 |
出版年
2024年 | 63篇 |
2023年 | 160篇 |
2022年 | 433篇 |
2021年 | 511篇 |
2020年 | 716篇 |
2019年 | 545篇 |
2018年 | 369篇 |
2017年 | 383篇 |
2016年 | 426篇 |
2015年 | 432篇 |
2014年 | 485篇 |
2013年 | 803篇 |
2012年 | 680篇 |
2011年 | 525篇 |
2010年 | 402篇 |
2009年 | 499篇 |
2008年 | 481篇 |
2007年 | 511篇 |
2006年 | 530篇 |
2005年 | 463篇 |
2004年 | 477篇 |
2003年 | 420篇 |
2002年 | 422篇 |
2001年 | 270篇 |
2000年 | 270篇 |
1999年 | 207篇 |
1998年 | 194篇 |
1997年 | 177篇 |
1996年 | 169篇 |
1995年 | 175篇 |
1994年 | 138篇 |
1993年 | 133篇 |
1992年 | 115篇 |
1991年 | 69篇 |
1990年 | 55篇 |
1989年 | 42篇 |
1988年 | 43篇 |
1987年 | 44篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
We present a model arising from the thermal modelling of two metal casting processes. We consider an enthalpy formulation for this two‐phase Stefan problem in a time varying three‐dimensional domain and consider convective heat transfer in the liquid phase. Then, we introduce a weak formulation in a fixed domain, by means of a suitable transformation. Existence of solution is obtained by applying an abstract theorem. The proof of this theorem is done by taking an implicit discretization in time together with a regularization. By passing to the limit in the regularization parameter and in the time step, we obtain the existence of solution of the continuous problem. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
22.
Takuya Hashimoto Koichi Kitazawa Masaaki Nakabayashi Tadashi Shiraishi Youichi Suemune Takakazu Yamamoto Hideomi Koinuma 《应用有机金属化学》1991,5(4):325-330
For low-temperature deposition of oxide films relating to Bi-Sr-Ca-Cu-O superconductors, photo-absorption and -decomposition properties were examined with respect to copper and alkaline-earth ß-diketonates. It was confirmed that all ß-diketonates examined were promising as source materials for photochemical vapour deposition (photo-CVD) using a low-pressure mercury lamp, in view of their large light absorption coefficients at wavelength 254 nm. The light irradiation was effective for the formation of highly crystalline oxide films at temperatures below 600 °C. By combining two sources, Ca2CuO3 and SrCuO2 films were prepared. Photo-CVD of c-axis oriented Bi2Sr2CuOx film was achieved by the irradiation of ternary sources of Bi(C6H5)3 and strontium and copper ß-diketonates at 500 °C. 相似文献
23.
New Schiff bases of 2,4‐dihydroxybenzaldehyde with siloxane‐α,ω‐diamines having different numbers of siloxane units in the chain have been synthesized and characterized by spectroscopy, elemental and thermal analyses. These azomethines were found to form complexes readily with copper(II), nickel(II), cobalt(II), cadmium(II) and zinc(II). From IR and UV–Vis studies, the phenolic oxygen and imine nitrogen of the ligand were found to be the coordination sites. Thermogravimetric analysis (TGA) data indicate the chelates to be more stable than the corresponding ligands. The melting points increase with shortening of the siloxane segment from azomethine, as well as the result of complexation. The chelates obtained were covalently inserted in polymeric linear structures by polycondensation through the OH‐difunctionalized ligand with 1,3‐bis(carboxypropyl)tetramethyldisiloxane. Direct polycondensation, assisted either by acetic anhydride or N,N′‐dicyclohexylcarbodiimide as dehydrating agent and the complex 4‐(dimethylamino)pyridinium 4‐toluenesulfonate as catalyst, was used for the synthesis of these compound types. The structures of the polymers obtained were confirmed by IR, UV and 1H NMR. Characterization was undertaken by TGA, solubility tests and viscosity measurements. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
24.
Mooson Kwauk 《中国颗粒学报》2004,(1)
IntroductionInmaterialscience,differentmicrostructuresofthesamematerialsmayinducediversebehaviorsanddifferentcharacteristics.Westwood(1988)showed,asanexample,thatthetreatmentofaluminumsurfacewithcommercialphosphoricacidproducedmechanicallyinterlockedoxide搘hiskers?approximately10nmindiameterand400nminlength,whichmechanicallyinterlocked.Thismicro-structurecankeepsuchaconglomeratebondedoverconsiderablerangesofstressandtemperature.Inahumidatmosphere,especiallythatcontainingchlorine,however,suchox… 相似文献
25.
Using the full-potential linearized augmented plane wave (FP-LAPW) method, we have studied the effect of chemistry on the average intercalation voltage (AIV) caused by the Na ions intercalating into transition metal oxides. The effect of transition metal was systematically studied by varying M=Co, Ni and Mn in NaMO2 and fixing the α-NaFeO2 layered structure. The effect of the guest atoms into the host material is discussed in terms of the structural and electronic properties. Comparatively to Li intercalation, a significant electron transfer towards transition metal was found. This observation suggests that the transition metal contribute to the AIV determination and confirms the common assumption that intercalated electron reduces M4+ to M3+. 相似文献
26.
Ilaria Fratoddi Chiara Battocchio Alessandra L. Groia Maria V. Russo 《Journal of polymer science. Part A, Polymer chemistry》2007,45(15):3311-3329
The reactivity of square planar palladium(II) and platinum(II) complexes in trans or cis configuration, namely trans or cis‐[dichlorobis(tributylphosphine)platinum(II)] and trans‐[dichlorobis(tributylphosphine)palladium(II)] with 1,1′‐bis(ethynyl) 4,4′‐biphenyl, DEBP, leading to π‐conjugated organometallic oligomeric and polymeric metallaynes, was investigated by a systematic variation of the reaction conditions. The formation of polymers and oligomers with defined chain length [? M(PBu3)2 (C?C? C6H4? C6H4? C?C? )]n (n = 3–10 for the oligomers, n = 20–50 for the polymers) depends on the configuration of the precursor Pt(II) and Pd(II) complexes, the presence/absence of the catalyst CuI, and the reaction time. A series of model reactions monitored by XPS, GPC, and NMR 31P spectroscopy showed the route to modulate the chain growth. As expected, the nature of the transition metal (Pt or Pd) and the molecular weight of the polymers markedly influence the photophysical characteristics of the polymetallaynes, such as optical absorption and emission behavior. Polymetallaynes with nanostructured morphology could be obtained by a simple casting procedure of polymer solutions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3311–3329, 2007 相似文献
27.
Metal ion uptake properties of polystyrene-supported chelating polymer resins functionalized with (i) glycine, (ii) hydroxy
benzoic acid, (iii) Schiff base and (iv) diethanol amine have been investigated. The effects of pH, time and initial concentration
on the uptake of metal ions have been studied. The uptake of metal ion depends on pH. The resins are more selective at pH
10 for Pb(II) and Hg(II), whereas at pH 6 they are found to be Cd(II) and Cr(VI) selective. Metal ion uptake properties of
resins follow Freundlich’s equation. The resins are recyclable and are therefore employed for the removal of heavy metal pollutants
from industrial waste water. 相似文献
28.
Historical perspectives for the chemistry of diene complexes of early transition metals developed at Osaka University in the period after 1970s were reviewed briefly and personally. Preparative chemistry of this field commenced from the magnesium-diene 1:1 compounds and quickly extended to almost all the early transition metals. By the studies operated together with other researchers, unique features of these diene complexes, especially their bonding and structure, selective reactions, and catalysis performances are described. 相似文献
29.
ChujiangCai ZhigangShen MingzhuWang ShulinMa YushanXing 《中国颗粒学报》2003,1(4):156-161
This paper reports the use of a colloidal Pd^0 catalysis system to metallize the surface of precipitators separated from coal fly-ash, and metals such as Cu, Ni etc. are deposited on the precipitators surface. Alternatively, according to the characteristic surface of cenospheres, an Ag coating catalysis system is adopted to first deposit Ag on the cenospheres surface, followed, if necessary, by the deposition of other metals such as Cu, Ni, etc. on the Ag coating to produce monolayer and multilayer metal-coated cenospheres. The surface characteristics and the morphologies of the metal coatings are examined in detail with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) techniques. It can be shown that the quality of metal coatings derived from the Aa coatina catalysis system, is better than that of the colloidal Pd^0 catalysis system. 相似文献
30.