全文获取类型
收费全文 | 56907篇 |
免费 | 11705篇 |
国内免费 | 4190篇 |
专业分类
化学 | 54638篇 |
晶体学 | 588篇 |
力学 | 1755篇 |
综合类 | 231篇 |
数学 | 4430篇 |
物理学 | 11160篇 |
出版年
2024年 | 74篇 |
2023年 | 488篇 |
2022年 | 862篇 |
2021年 | 1060篇 |
2020年 | 2128篇 |
2019年 | 3435篇 |
2018年 | 1764篇 |
2017年 | 1372篇 |
2016年 | 4334篇 |
2015年 | 4547篇 |
2014年 | 4712篇 |
2013年 | 5559篇 |
2012年 | 4762篇 |
2011年 | 4048篇 |
2010年 | 4134篇 |
2009年 | 4019篇 |
2008年 | 3653篇 |
2007年 | 2863篇 |
2006年 | 2479篇 |
2005年 | 2447篇 |
2004年 | 2067篇 |
2003年 | 1878篇 |
2002年 | 2592篇 |
2001年 | 1820篇 |
2000年 | 1713篇 |
1999年 | 816篇 |
1998年 | 419篇 |
1997年 | 371篇 |
1996年 | 353篇 |
1995年 | 287篇 |
1994年 | 258篇 |
1993年 | 243篇 |
1992年 | 180篇 |
1991年 | 169篇 |
1990年 | 155篇 |
1989年 | 127篇 |
1988年 | 117篇 |
1987年 | 78篇 |
1986年 | 75篇 |
1985年 | 72篇 |
1984年 | 50篇 |
1983年 | 33篇 |
1982年 | 44篇 |
1981年 | 26篇 |
1980年 | 14篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1974年 | 8篇 |
1972年 | 7篇 |
1970年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ching Hsuan Lin Yu Ren Feng Kang Hong Dai Hou Chien Chang Tzong Yuan Juang 《Journal of polymer science. Part A, Polymer chemistry》2013,51(12):2686-2694
A phenolic OH‐containing benzoxazine ( F‐ap ), which cannot be directly synthesized from the condensation of bisphenol F, aminophenol, and formaldehyde by traditional procedures, has been successfully prepared in our alternative synthetic approach. F‐ap was prepared by three steps including (a) condensation of 4‐aminophenol and 5,5'‐methylenebis(2‐hydroxybenzaldehyde) (1) , (b) reduction of the resulting imine linkage by sodium borohydride, and (c) ring closure condensation by formaldehyde. The key starting material, (1) , was prepared from 2‐hydroxybenzaldehyde and s‐trioxane in the presence of sulfuric acid. F‐ap is structurally similar to bis(3,4‐dihydro‐2H‐3‐phenyl‐1,3‐benzoxazinyl)methane ( F‐a, a commercial benzoxazine based on bisphenol F/aniline/formaldehyde) except for two phenolic OHs. The phenolic OHs can provide reaction sites with epoxy and 1,1'‐(methylenedi‐p‐phenylene)bismaleimide (BMI). The structure–property relationships between the thermosets of F‐ap /epoxy, F‐a /epoxy, F‐ap /BMI, and F‐a /BMI were discussed. Experimental data showed that thermosets based on F‐ap /epoxy and F‐ap /BMI provided much better thermal properties than those based on F‐a /epoxy and F‐a /BMI. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2686–2694 相似文献
992.
Ryan Guterman Bradley M. Berven T. Chris Corkery Heng‐Yong Nie Mike Idacavage Elizabeth R. Gillies Paul J. Ragogna 《Journal of polymer science. Part A, Polymer chemistry》2013,51(13):2782-2792
An array of highly fluorinated polymerizable phosphonium salts (HFPPS) were synthesized from PH3 and utilized in UV‐curable formulations. Inclusion of these salts at very low loading (0.1–1 wt %) into hexanediol diacrylate (HDDA) resulted in hydrophobic surfaces. The water repellency was achieved with short C4F9 fluorocarbon appendages in the monomer as opposed to the bioaccumulative C8F17 appended polymers. The physical properties of these new monomers were also characterized. The molecular architecture of the monomers had a pronounced effect on both their physical properties along with the degree of hydrophobicity imparted in the polymer. Salts utilizing the bis(trifluoromethylsulfonyl)imide anion displayed excellent compatibility with HDDA, while the chloride salts were insoluble. Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) confirmed the presence of the HFPPS at the surface of the polymer coating. For the first time this demonstrates how these salts may be used to functionalize the surface of a UV‐cured film with ionic species. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2782–2792 相似文献
993.
Joseph W. Rumer Sheng‐Yao Dai Matthew Levick Laure Biniek David J. Procter Iain McCulloch 《Journal of polymer science. Part A, Polymer chemistry》2013,51(6):1285-1291
Two novel dihydropyrroloindoledione (DPID)‐based copolymers have been synthesized in a two directional approach and characterized (gel permeation chromatography (GPC), ultraviolet‐visible (UV–vis), cyclic voltammetry, and computational models). These planar, broad absorption copolymers show promise for use in organic electronics, with deep energy levels and low bandgaps. The two‐directional Knoevenagel condensation used demonstrates the versatility of DPID as a useful yet underexploited conjugated unit. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
994.
Feng Xu Shu‐Zhen Zheng Yan‐Ling Luo 《Journal of polymer science. Part A, Polymer chemistry》2013,51(20):4429-4439
Thermosensitive polylactide‐block‐poly(N‐isopropylacrylamide) (t‐PLA‐b‐PNIPAAm) tri‐armed star block copolymers were synthesized by atom transfer radical polymerization (ATRP) of monomer NIPAAm using t‐PLA‐Cl as macroinitiator. The synthesis of t‐PLA‐Cl was accomplished by esterification of star polylactides (t‐PLA) with 2‐chloropropionyl chloride using trimethylolpropane as a center molecule. FT‐IR, 1H NMR, and GPC analyses confirmed that the t‐PLA‐b‐PNIPAAm star block copolymers had well‐defined structure and controlled molecular weights. The block copolymers could form core‐shell micelle nanoparticles due to their hydrophilic‐hydrophobic trait in aqueous media, and the critical micelle concentrations (CMC) were from 6.7 to 32.9 mg L?1, depending on the system composition. The as‐prepared micelle nanoparticles showed reversible phase changes in transmittance with temperature: transparent below low critical solution temperature (LCST) and opaque above the LCST. Transmission electron microscopy (TEM) observations revealed that the micelle nanoparticles were spherical in shape with core‐shell structure. The hydrodynamic diameters of the micelle nanoparticles depended on copolymer compositions, micelle concentrations and media. MTT assays were conducted to evaluate cytotoxicity of the camptothecin‐loaded copolymer micelles. Camptothecin drug release studies showed that the copolymer micelles exhibited thermo‐triggered targeting drug release behavior, and thus had potential application values in drug controlled delivery. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4429–4439 相似文献
995.
Gholam‐Reza Nejabat Mehdi Nekoomanesh Hassan Arabi Hamid Salehi‐Mobarakeh Gholam‐Hossein Zohuri Mojtaba Omidvar Stephen A. Miller 《Journal of polymer science. Part A, Polymer chemistry》2013,51(3):724-731
Various elastomeric polypropylenes (PPs) are synthesized through homogeneous propylene polymerization with metallocene catalyst (2‐PhInd)2ZrCl2 in the presence of different cocatalyst mixtures: triethylaluminum (TEA)/methylaluminoxane (MAO) or triisobutylaluminum (TIBA)/MAO in the range of AlAlR3/AlMAO = 0.0–0.9. The cocatalyst formulation impacts the resultant polymer microstructure and the thermal and dynamic mechanical properties of the produced PPs. 13C NMR analysis of the polymers reveals essentially atactic PP, with mmmm = 7.9%, when AlAlR3/AlMAO = 0.0. The mmmm pentad content is maximized when AlAlR3/AlMAO = 0.8; for TIBA, mmmm = 23.5%; and for TEA, mmmm = 17.6%. Differential scanning calorimetry analysis and dynamic mechanical thermal analysis corroborate these findings. Specifically, Tm, ΔHm, and Tg are essentially maximized under these conditions, and the minimum damping is observed for AlAlR3/AlMAO = 0.6–0.8. 1H NMR analysis of the mixtures of catalyst and cocatalysts (without monomer) shows very minor differences for [Zr]:AlAlR3 in the range of 1:1–1:5. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
996.
Alberto García‐Peñas José M. Gómez‐Elvira Ernesto Pérez María L. Cerrada 《Journal of polymer science. Part A, Polymer chemistry》2013,51(15):3251-3259
Terpolymers based on propylene with 1‐pentene and 1‐hexene as comonomeric units are satisfactorily synthesized using a metallocene catalyst. Thus, several terpolymers are prepared with distinct overall compositions in comonomers as well as three different 1‐pentene/1‐hexene ratios at a given composition to evaluate the influence on polymerization activity, intrinsic viscosity, and microstructural details. The new trigonal δ polymorph is observed in those quenched terpolymers with a global content in comonomers of about 14 mol %, independently of the ratio between both comonomers. However, preliminary results indicate a profound influence of that ratio on the crystallization rate. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3251–3259 相似文献
997.
Eliézer Fernando de Oliveira Alexandre Camilo‐Jr Luiz Carlos da Silva‐Filho Francisco Carlos Lavarda 《Journal of Polymer Science.Polymer Physics》2013,51(10):842-846
The widespread use of poly(3‐hexylthiophene) (P3HT) in the active layers of organic solar cells indicates that it possesses chemical stability and solubility suitable for such an application. However, it would be desirable to have a material that can maintain these properties but with a smaller bandgap, which would lead to more efficient energy harvesting of the solar spectrum. Fifteen P3HT derivatives were studied using the Density Functional Theory. The conclusion is that it is possible to obtain compounds with significantly smaller bandgaps and with solubility and stability similar to that of P3HT, mostly through the binding of oxygen atoms or conjugated organic groups to the thiophenic ring. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys., 2013 相似文献
998.
Musammir Khan Yakai Feng Dazhi Yang Wei Zhou Hong Tian Ying Han Li Zhang Wenjie Yuan Jin Zhang Jintang Guo Wencheng Zhang 《Journal of polymer science. Part A, Polymer chemistry》2013,51(15):3166-3176
The synthetic polycations are ideal candidates as antimicrobial agents, because they resemble natural antimicrobial peptides, but to render hemocompatibility to these materials is a great challenge. Herein, we used 2‐(tert‐butyl‐aminoethyl) methacrylate (TBAEMA), to synthesize its homopolymer and pegylated random and diblock copolymers with polyethyleneglycol methacrylate (PEGMA, Mn = 360 Da) by single‐electron transfer–living radical polymerization (SET‐LRP). In the second step, the secondary amino groups in the precursor polymers were quaternized with iodomethane and bromohexane, to obtain three series of quaternized polymers. The antimicrobial properties of these quaternized polymers were evaluated against Escherichia coli (E. coli), by studying the minimum inhibitory concentrations (MICs) which ranged between 32 and 200 mg L?1 and showed higher values for the quaternized random than the diblock copolymers. In addition to, we have also demonstrated the grafting of these polycations onto polycarbonate urethane film surfaces, which showed good killing efficacy against E. coli. Furthermore, the hemolysis of these materials was investigated against human red blood cells, which indicated that except the quaternized homopolymers that showed highest hemolysis, all other amphiphilic polycations exhibited very low hemolytic activity. Therefore, our designed materials with controlled structures and functionality, synthesized from cheaply available resources could serve as useful agents in the field of biomedicines and implantable materials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3166–3176 相似文献
999.
Yves Leterrier Jérémy Thivolle Fabiane Oliveira Jan‐Anders Månson Lorenz Gubler Hicham Ben youcef Lukas Bonorand Günther Scherer 《Journal of Polymer Science.Polymer Physics》2013,51(15):1139-1148
The influence of temperature and moisture activity on the viscoelastic behavior of fluorinated membranes for fuel cell applications was investigated. Uncrosslinked and crosslinked ethylene tetrafluoroethylene (ETFE)‐based proton‐conducting membranes were prepared by radiation grafting and subsequent sulfonation and their behavior was compared with ETFE base film and commercial Nafion® NR212 membrane. Uniaxial tensile tests and stress relaxation tests at controlled temperature and relative humidity (RH) were carried out at 30 and 50 °C for 10% < RH < 90%. Grafted films were stiffer and exhibited stronger strain hardening when compared with ETFE. Similarly, both uncrosslinked and crosslinked membranes were stiffer and stronger than Nafion®. Yield stress was found to decrease and moisture sensitivity to increase on sulfonation. The viscoelastic relaxation of the grafted films was found to obey a power‐law behavior with exponent equal to ?0.04 ± 0.01, a factor of almost 2 lower than ETFE, weakly influenced by moisture and temperature. Moreover, the grafted films presented a higher hygrothermal stability when compared with their membranes counterparts. In the case of membranes, a power‐law behavior at RH < 60% was also observed. However, a markedly different behavior was evident at RH > 60%, with an almost single relaxation time exponential. An exponential decrease of relaxation time with RH from 60 s to 10 s was obtained at RH ≥ 70% and 30 °C. The general behavior of grafted films observed at 30 °C was also obtained at 50 °C. However, an anomalous result was noticed for the membranes, with a higher modulus at 50 °C when compared with 30 °C. This behavior was explained by solvation of the sulfonic acid groups by water absorption creating hydrogen bonding within the clusters. A viscoelastic phase diagram was elaborated to map critical conditions (temperature and RH) for transitions in time‐dependent behavior, from power‐law scaling to exponential scaling. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1139–1148 相似文献
1000.
Xinyu Wei Weiyin Gu Le Li Xiaobo Shen Jung‐Keun Kim Thomas P. Russell 《Journal of Polymer Science.Polymer Physics》2013,51(1):78-85
We reported the synthesis and morphology of a novel alkyne‐functionalized diblock copolymer (di‐BCP) poly(methyl methacrylate‐random‐propargyl methacrylate)‐block‐poly(4‐bromostyrene). The di‐BCPs were synthesized by atom transfer radical polymerization and postpolymerization deprotection, with good control over molecular weight and polydispersity index. Microphase separation in bulk di‐BCPs was confirmed by thermal analysis, small‐angle X‐ray scattering, and transmission electron microscopy. Microphase‐separated morphologies were also observed in thin films, and the orientation of the microdomains can be conveniently controlled by annealing under different solvents. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献