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281.
Pei‐Chun Kuo Ya‐Ching Chang Chuh‐Yung Chen Chieh‐Tsung Lo 《Journal of Polymer Science.Polymer Physics》2015,53(3):192-202
The isothermal crystallization of poly(l ‐lactide) (PLLA) in blends with poly(butylene oxalate) (PBOX) is investigated by time‐resolved small‐angle X‐ray scattering, differential scanning calorimetry, and optical microscopy. We focus on the temperatures at which only PLLA crystallizes while PBOX is amorphous. It is obtained that the addition of PBOX causes a reduction of the melting temperature of PLLA. The lamellar thickness of PLLA crystals decreases whereas the amorphous layer thickness increases with blend composition, suggesting the occurrence of the interlamellar incorporation upon the addition of PBOX. The crystal growth rate and morphology of PLLA/PBOX blends are analyzed by polarized optical microscopy. The spherulite growth rate of PLLA is found to increase with the addition of PBOX. Analysis of the isothermal crystallization in terms of the Lauritzen and Hoffman equation give the reduction of the fold surface free energy upon the addition of PBOX in PLLA, indicating that the mobility of the PLLA chains is significantly improved due to the presence of PBOX. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 192–202 相似文献
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分别采用1,4-(双乙氧基硅烷)苯(1,4-BTEB)和1,2-三乙氧基硅基乙烷(1,2-BTESE)作为有机硅源,正硅酸乙酯(TEOS)为无机硅源,钛酸四丁酯(TBOT)为钛源,以Pluronic EO20PO70EO20(P123)为模板剂在酸性环境下水热合成制备了Ti掺杂的有机-无机有序介孔有机硅材料Ti-SBA-15-ben和Ti-SBA-15-et.同时,在合成过程中加入H2O2作为配合剂调节钛源水解速度,制备得到Ti-SBA-15-ben-H和Ti-SBA-15-et-H.采用FT-IR、DR UV-Vis、N2物理吸附、XRD、TG-DSC、TEM等方法对制备的样品进行了表征.结果表明:合成过程中加入H2O2制备的苯基桥连有机硅杂化材料具有较好的疏水性能,其骨架中活性4价位钛含量高,结构有序性最好.在以叔丁基过氧化氢(TBHP)为氧源的环己烯氧化反应中对制备的催化材料进行了对比评价,结果表明:Ti-SBA-15-ben-H表现出最高的催化活性,其催化的反应以环氧化产物为主,环己烯的转化率为26.9%,环氧选择性为32.8%,T i-SBA-15-et催化的反应以烯丙位氧化产物2-环己烯-1-酮为主,环己烯的转化率为8.5%,2-环己烯-1-酮选择性为41.2%. 相似文献
285.
以热解氧化石墨烯材料为碳基底,分别使用有机氮源和无机氮源对其进行氮掺杂处理,制备了一系列氮掺杂石墨烯材料.采用透射电子显微镜、扫描电子显微镜、拉曼光谱和X射线光电子能谱等表征方法考察了氮掺杂石墨烯的生长机理.结果表明,随着制备过程中退火温度的改变,氮掺杂石墨烯中不同氮物种的含量有显著差别.这种差异是由不同氮物种化学环境的差异所导致的.所制备的含氮石墨烯材料对乙苯选择性氧化制苯乙酮反应均表现出优良的催化活性.其中,石墨氮的含量对于提高苯乙酮收率起到至关重要的作用.此外,通过氧化剂控制活化的方法可以消除过多的结构缺陷和过量氮掺杂对催化反应的不利影响,有效提升氮掺杂石墨烯的催化活性. 相似文献
286.
Xingxun Liu Hongxin Ma Long Yu Ling Chen Zhen Tong Pei Chen 《Journal of Thermal Analysis and Calorimetry》2014,115(1):659-665
Thermal oxidation degradation of high-amylose (80 %) cornstarch has been studied using thermogravimetry analyser coupled to Fourier transform infrared spectroscopy (TG-FTIR). The linear structure of amylose provides a modal material to understand how the starch microstructure affects on the decomposition mechanisms. Kinetics of the thermal oxidation has been studied using different methods. It is found that the thermal oxidation degradation is more complex than thermal degradation, thermal oxidation degradation kinetics of the starch can be interpreted in terms of multi-step degradation mechanism, the activation energies obtain from Flynn–Wall–Ozawa (F–W–O) method and modified Coats–Redfern method are in good agreement. TG-FTIR and FTIR results confirm that the thermal oxidation mechanism of starch is a process containing long chain scission and glowing combustion. 相似文献
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Chiral Separations in Normal‐phase Liquid Chromatography: Updating a Screening Strategy with a Chlorine‐containing Polysaccharide‐based Selector 下载免费PDF全文
Jie Zhou Shanshan Chen Pei Luo Chong Sun Lingchang Meng Qiuzheng Du Fang Sun 《中国化学会会志》2015,62(12):1059-1067
The screening conditions of an existing column and mobile phase selection strategy for chiral compounds in normal‐phase high performance liquid chromatography (NP‐HPLC) were tested for their applicability on Chiralpak IC, which is a chiral stationary phase (CSP) made by immobilising cellulosic tris (3,5‐dichlorophenyl‐carbamate) on silica gel. In this study, the applicability of the optimization steps of the existing separation strategy was examined using 36 compounds representing the three possible resolution situations that occur after screening. The cumulative number of separated compounds is 27 (75.0 %), and the cumulative number of baseline separated compounds is 19 (52.8 %). 相似文献
289.
A Highly Efficient Chirality Switchable Synthesis of Dihydropyran‐Fused Benzofurans by Fine‐Tuning the Phenolic Proton of β‐Isocupreidine (β‐ICD) Catalyst with Methyl 下载免费PDF全文
Feng Wang Chen Yang Dr. Xiao‐Song Xue Prof. Dr. Xin Li Jin‐Pei Cheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(29):10443-10449
A highly enantioselective β‐isocupreidine (β‐ICD) catalyzed synthesis of dihydropyran‐fused benzofurans through [4+2] cycloaddition of allenoates and benzofuranone alkenes was developed. Switchable chirality inversion of cycloaddition products was achieved by replacing the phenolic proton of the catalyst with a methyl, demonstrating an amazing effect of minimal structural variation on inverting enantioselectivity. DFT calculations were utilized to elucidate the origin of the observed phenomena. Computation also provided a clue for a rational design in which the multi‐hydrogen bond with the alcohol additive was found to improve the enantioselectivity of the cycloaddition. Finally, the substrate scope was examined, in which a number of functionalized dihydropyran‐fused benzofurans could be obtained in high yields (up to 97 %) with very good regio‐ (>20:1) and enantioselectivities (up to 98:2 e.r.). 相似文献
290.
Postfunctionalization of BN‐Embedded Polycyclic Aromatic Compounds for Fine‐Tuning of Their Molecular Properties 下载免费PDF全文
Dr. Xiao‐Ye Wang Dong‐Chu Yang Fang‐Dong Zhuang Jia‐Jie Liu Dr. Jie‐Yu Wang Prof. Jian Pei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(24):8867-8873
New BN‐embedded, thiophene‐fused, polycyclic aromatic compounds with planar geometry were designed and synthesized. The molecules showed excellent stability and chemical robustness. Postfunctionalization on this skeleton was demonstrated with a series of electrophilic bromination, palladium‐catalyzed cross‐coupling, and Knoevenagel condensation reactions. The π skeleton remained intact during these late‐stage transformations. The optical and electronic properties have been well tuned through incorporation of electron‐rich and ‐deficient groups on the backbone. This work shows the great advantage of the postfunctionalization strategy on BN‐containing polycyclic aromatic compounds for fast diversification and materials screening. 相似文献