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991.
State‐of‐the‐Art and Progress in Method of Moments for the Model‐Based Reversible‐Deactivation Radical Polymerization 下载免费PDF全文
Reversible‐deactivation radical polymerization (RDRP) techniques have received lots of interest for the past 20 years, not only owing to their simple, mild reaction conditions and broad applicability, but also their accessibility to produce polymeric materials with well‐defined structures. Modeling is widely applied to optimize the polymerization conditions and processes. In addition, there are numerous literatures on the kinetic and reactor models for RDRP processes, which show the accessibility on polymerization kinetics insight, process optimization, and controlling over chain microstructure with predetermined molecular weight and low dispersity, copolymer composition distribution, and sequence distribution. This review highlights the facility of the method of moments in the modeling field and presents a summary of the present state‐of‐the‐art and future perspectives focusing on the model‐based RDRP processes based on the method of moments. Summary on the current status and challenges is discussed briefly.
992.
Bulk Free Radical Polymerization of Methyl Methacrylate and Vinyl Acetate: A Comparative Study 下载免费PDF全文
David Victoria‐Valenzuela Jorge Herrera‐Ordonez Gabriel Luna‐Barcenas George D. Verros Dimitris S. Achilias 《大分子反应工程》2016,10(6):577-587
The model and methodology for estimating diffusion‐controlled rate coefficients for the methyl methacrylate (MMA) polymerization system is extended to the vinyl acetate (VAc) case. Comparison of the kinetic behavior and termination rate coefficients (kt) of both monomers suggests that at low conversions the termination reaction is controlled by the chemical step, whereas at moderate and high conversions it is controlled by the diffusive step which in turn is determined by the segmental diffusion of the long radicals and not by the center of mass diffusion of short radicals. It is found that, for most of the conversion range, diffusion coefficient for VAc is lower than the one for MMA notwithstanding that ktVAc > ktMMA. An explanation of this apparent inconsistency on the base of the model results and in terms of segmental mobility is proposed.
993.
Nikoo Saveh‐Shemshaki Masoud Latifi Roohollah Bagherzadeh Mahdi Malekshahi Byranvand Naimeh Naseri Ali Dabirian 《先进技术聚合物》2016,27(3):358-365
Iron(III) oxide (hematite, Fe2O3) nanofibers, as visible light‐induced photoanode for water oxidation reaction of a water splitting process, were fabricated through electrospinning method followed by calcination treatment. The prepared samples were characterized with scanning electron microscopy, and three‐electrode galvanostat/potentiostat for evaluating their photoelectrochemical (PEC) properties. The diameter of the as‐spun fibers is about 300 nm, and calcinated fibers have diameter less than 110 nm with mesoporous structure. Optimized multilayered electrospun α‐Fe2O3 nanostructure mats showed photocurrent density of 0.53 mA/cm2 under dark and visible illumination conditions at voltage 1.23 V and constant intensity (900 mW/cm2). This photovoltaic performance of nanostructure mats makes it suitable choice for using in the PEC water splitting application as an efficient photoanode. This method, if combined with appropriate flexible conductive substrate, has the potential for producing flexible hematite solar fuel generators. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
994.
Synthesis,characterization, dielectric and rectification properties of PANI/Nd2O3:Al2O3 nanocomposites 下载免费PDF全文
Juhi Nishat Ansari Syed Khasim Ameena Parveen Omar A Al‐Hartomy Ziad Khattari Nacer Badi Aashis. S. Roy 《先进技术聚合物》2016,27(8):1064-1071
Polyaniline–Nd2O3:Al2O3 nanocomposites were prepared by in situ oxidative polymerization method using different weight percentages of oxide powders. The prepared nanocomposites were characterized by Fourier transform infrared spectroscopy and X‐ray diffraction for molecular and crystal structures. Scanning electron microscopy and transmission electron microscopy images show the tubular structure of polyaniline nanocomposite with embedded metal oxides. The electrical conductivity of the nanocomposites increases with increase in temperature as well as with concentration of Nd2O3:Al2O3 particles in polyaniline. This is because of the hopping of charge polarons and extended chain length of the nanocomposites as evidenced by the negative thermal coefficient (NTC) characteristic. A high NTC value of 2.67 was found in nanocomposites with 15 wt% of oxide particles. These nanocomposites show low dielectric constant and dielectric loss; the electrical conductivity is higher than 0.3 S/cm as confirmed by Cole–Cole plot that indicates a decrease in both grain resistance and bulk resistance of the nanocomposites. The current–voltage and capacitance–voltage measurements were also carried out. The carrier mobility μ values of pure polyaniline and nanocomposites were found to be 4.27 × 10?3 and 1.45 × 10–2 H.M?1, respectively. A significant enhancement in carrier mobility was observed in comparison with the literature. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
995.
Antibacterial poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) fibrous membranes containing quaternary ammonium salts 下载免费PDF全文
Xiaoyan Fan Maoli Yin Zhiming Jiang Nengyu Pan Xuehong Ren Tung‐Shi Huang 《先进技术聚合物》2016,27(12):1617-1624
In this study, antimicrobial membranes based on biodegradable material poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3HB‐4HB)] and quaternary ammonium salts (QASs) by two methods have been performed. Three QASs with varied alkyl chain lengths have been synthesized successfully and characterized by 1H nuclear magnetic resonance and Fourier transform infrared. The synthesized QASs were blended with P(3HB‐4HB) and electrospun into composite fibrous membranes or casted into conventional membranes. Electrospun fibrous membranes with large surface areas are a superior type of antimicrobial biomaterials, and they exhibit preferable properties than solution casting membranes. Specifically, electrospun fibrous membranes are tougher and can inactivate both Gram‐positive Staphylococcus aureus and Gram‐negative Escherichia coli O157:H7 in a contact time of 30 min, whereas the solution casting membranes cannot. The length of alkyl chain in the quaternary ammonium groups on the modified P(3HB‐4HB) membranes is able to influence the antimicrobial activity. This type of antimicrobial material may have potential applications in biomaterial field. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
996.
Theoretical investigation of the structures and spectroscopic properties of (H2O4)n (n = 1–4) clusters 下载免费PDF全文
Hong‐Dal Kim Hyun‐Il Seo Hui‐Seong Song Seung‐Joon Kim 《International journal of quantum chemistry》2016,116(19):1427-1436
Density functional theory and ab initio calculations were performed to elucidate the hydrogen interactions in (H2O4)n (n = 1–4) clusters. The optimized geometries, binding energies, and harmonic vibrational frequencies were predicted at various levels of theory. The trans conformer of the H2O4 monomer was predicted to be the most stable structure at the CCSD(T)/aug‐cc‐pVTZ level of theory. The binding energies per H2O4 monomer increased in absolute value by 9.0, 10.1, and 11.8 kcal/mol from n = 2 to n = 4 at the MP2/cc‐pVTZ level of theory (after the zero‐point vibrational energy and basis set superposition error corrections). This result implies that the intermolecular hydrogen bonds were stronger in the long‐chain clusters, that is, the formation of the longer chain in the (H2O4)n clusters was more energetically favorable. 相似文献
997.
Effect of formulation of silica‐based solution on corrosion resistance of silicate coating on hot‐dip galvanized steel 下载免费PDF全文
Shuang‐hong Zhang Gang Kong Zi‐wen Sun Chun‐shan Che Jin‐tang Lu 《Surface and interface analysis : SIA》2016,48(3):132-138
Several silica‐based solutions with 50 g/l of SiO2 were prepared from sodium silicate solutions and silica sol; the silicate conversion coatings were obtained by immersing hot‐dip galvanized steel sheets in these solutions. These solutions were characterized using high‐resolution transmission electron microscopy and 29Si nuclear magnetic resonance; the morphology of the coatings was observed by SEM and atomic force microscopy while the corrosion resistance was evaluated by electrochemical measurements as well as neutral salt spray tests. The results show that the coatings obtained from the single silica sol solution had poor adhesion and the coating obtained from the sodium silicate solution with low SiO2/Na2O molar ratio was uneven. By adding the silica sol to the silicate solution with low molar ratio, uniform coatings with better protection property were obtained. According to the results of 29Si nuclear magnetic resonance spectra, the effects of the distribution of silicate anions with various polymerization degrees in the silica‐based solutions on the microstructure and corrosion resistance of the silicate coatings are discussed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
998.
Investigation of the Catalytic Activity of a 2‐Phenylidenepyridine Palladium(II) Complex Bearing 4,5‐Dicyano‐1,3‐bis(mesityl)imidazol‐2‐ylidene in the Mizoroki‐Heck Reaction 下载免费PDF全文
The phenylidenepyridine (ppy) palladacycles [PdCl(ppy)(IMes)] ( 4 ) [IMes = 1,3‐bis(mesityl)imidazol‐2‐ylidene] and [PdCl(ppy){(CN)2IMes}] ( 6 ) [(CN)2IMes = 4,5‐dicyano‐1,3‐bis(mesityl)imidazol‐2‐ylidene] were prepared by facile two step syntheses, starting with the reaction of palladium(II) chloride with 2‐phenylpyridine followed by subsequent addition of the NHC ligand to the precatalyst precursor [PdCl(ppy)]2. Suitable crystals for the X‐ray analysis of the complexes 4 and 6 were obtained. It was shown that 6 has a shorter NHC‐palladium bond than the IMes complex 4 . The difference of the palladium carbene bond lengths based on the higher π‐acceptor strength of (CN)2IMes in comparison to IMes. Thus, (CN)2IMes should stabilize the catalytically active central palladium atom better than IMes. As a measure for the π‐acceptor strength of (CN)2IMes compared to IMes, the selone (CN)2IMes · Se ( 7 ) was prepared and characterized by 77Se‐NMR spectroscopy. The π‐acceptor strength of 7 was illuminated by the shift of its 77Se‐NMR signal. The 77Se‐NMR signal of 7 was shifted to much higher frequencies than the 77Se‐NMR signal of IMes · Se. Catalytic experiments using the Mizoroki‐Heck reaction of aryl chlorides with n‐butyl acrylate showed that 6 is the superior performer in comparison to 4 . Using complex 6 , an extensive substrate screening of 26 different aryl bromides with n‐butyl acrylate was performed. Complex 6 is a suitable precatalyst for para‐substituted aryl bromides. The catalytically active species was identified by mercury poisoning experiments to be palladium nanoparticles. 相似文献
999.
Synthesis,Structures, and Fluorescent Properties of Three Cobalt‐Based Coordination Polymers with a Rigid Tripodal Carboxylate Ligand 下载免费PDF全文
Xiao‐Bin Liu Zhen‐Yu Xiao Ao Huang Wen Wang Liang‐Liang Zhang Rong‐Ming Wang Dao‐Feng Sun 《无机化学与普通化学杂志》2016,642(1):31-35
Three cobalt(II) coordination polymers, [Co2(tatb)2(2,2′‐bipy)2 (H2O)2 · DMA · 2H2O] ( 1 ), [Co2(tatb)2(1,10‐phen)2(H2O)2 · 2H2O] ( 2 ) and [Co(tatb)(1,3‐dpp) · H2O] ( 3 ) (H3tatb = 4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)tribenzoic acid; 2,2′‐bipy = 2,2′‐bipyridyl; 1,10‐phen = 1,10‐phenanthroline; 1,3‐dpp = 1,3‐bis(pyridin‐4‐yl)propane), were synthesized solvothermally and characterized by single‐crystal and powder X‐ray diffraction (PXRD), as well as IR spectroscopy. Complexes 1 and 2 exhibit 1D double‐chain structures, which further connect into interesting 3D networks by hydrogen bond and strong π–π interactions. Complex 3 possesses 2D 44‐sql topology, which is packed parallel in an AA fashion. Moreover, thermal stability properties and photoluminescence properties of 1 , 2 and 3 were also investigated. 相似文献
1000.
Three biphenyl‐3,5‐dicarboxylic acid (H2 L ) based coordination polymers, namely, [Mn3( L )3(2,2′‐bpy)2]n ( 1 ), {[Mn( L )(phen)] · (MeOH)}n ( 2 ), and [Mn( L )(dipt)]n ( 3 ), (2,2′‐bpy = 2,2′‐bipyridine, phen = 1,10‐phenanthroline, and dipt = 2,9‐dimethyl‐1,10‐phenanthroline) were synthesized and characterized by single‐crystal X‐ray diffraction and analyses of their magnetic properties. 1 is a trinuclear manganese structure with a 2D motifs, which can join by hydrogen bond bridges to give 3D supramolecular architectures. 2 has a dinuclear center forming a 1D supramolecular ladder chain. The mononuclear complex 3 displays 1D metal‐organic chains driven by μ2‐ L linkers. Their structural differences were investigated, revealing that the influence of steric hindrance on the structures of acid‐based coordination polymers is realized through changing the N‐heterocyclic ancillaries of diverse steric hindrance. Obviously, with decreasing of the steric hindrance of the N‐donor ligand, complexes 1 – 3 show structures from 1D to 2D and mononuclear to multinuclear. Magnetic susceptibility measurements indicate that 1 and 2 have dominating antiferromagnetic couplings between metal ions, whereas compound 3 is paramagnetic. 相似文献