全文获取类型
收费全文 | 11427篇 |
免费 | 2204篇 |
国内免费 | 1080篇 |
专业分类
化学 | 7921篇 |
晶体学 | 79篇 |
力学 | 716篇 |
综合类 | 99篇 |
数学 | 1402篇 |
物理学 | 4494篇 |
出版年
2024年 | 39篇 |
2023年 | 236篇 |
2022年 | 414篇 |
2021年 | 455篇 |
2020年 | 544篇 |
2019年 | 444篇 |
2018年 | 419篇 |
2017年 | 367篇 |
2016年 | 570篇 |
2015年 | 607篇 |
2014年 | 690篇 |
2013年 | 878篇 |
2012年 | 1049篇 |
2011年 | 1055篇 |
2010年 | 724篇 |
2009年 | 614篇 |
2008年 | 700篇 |
2007年 | 664篇 |
2006年 | 600篇 |
2005年 | 457篇 |
2004年 | 367篇 |
2003年 | 274篇 |
2002年 | 293篇 |
2001年 | 215篇 |
2000年 | 219篇 |
1999年 | 262篇 |
1998年 | 198篇 |
1997年 | 227篇 |
1996年 | 194篇 |
1995年 | 181篇 |
1994年 | 148篇 |
1993年 | 143篇 |
1992年 | 95篇 |
1991年 | 84篇 |
1990年 | 76篇 |
1989年 | 43篇 |
1988年 | 37篇 |
1987年 | 36篇 |
1986年 | 24篇 |
1985年 | 29篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1957年 | 3篇 |
1916年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Shuang Zhao Fuquan Wu Haifeng Wang Weigang Zhong Xiuzhen Li Hengjing Tang Meng Shi Hongyan Deng 《中国光学快报(英文版)》2007,5(4)
The main refractive indices of calcite crystal are measured by the means of auto-collimation, and the thermo-optical coefficients are calculated. The coefficient expression of Sellmeier equation is obtained by solving Sellmeier equation strictly and the refractive indices of different wavelengths are calculated, which accord with experimental esultsery well. The measured main refractive indices of calcite at 488-nm wavelength are identical with the values obtained by Sellmeier equation. 相似文献
992.
Potential PDP phosphors with strong absorption around 172 nm: Rare earth doped NaLaP2O7 and NaGdP2O7
Jun Lin Yuan Jiao Wang Ding Bang Xiong Jing Tai Zhao Yi Bing Fu Chao Shu Shi 《Journal of luminescence》2007,126(2):717-722
NaLaP2O7 and NaGdP2O7 powder samples are prepared by solid-state reactions at 750 and 600 °C, respectively, and the VUV-excited luminescence properties of Ln3+ (Ln=Ce, Pr, Tb, Tm, Eu) in both diphosphates are studied. Ln3+ ions in both hosts show analogous luminescence. For Ce3+-doped samples, the five Ce3+ 5d levels can be clearly identified. As for Pr3+ and Tb3+-doped samples, strong 4f-5d absorption band around 172 nm is observed, which matches well with Xe-He excimer in plasma display panel (PDP) devices. As a result, Pr3+ can be utilized as sensitizer to absorb 172 nm VUV photon and transfer energy to appropriate activators, and Tb3+-doped NaREP2O7(RE=La, Gd) are potential 172 nm excited green PDP phosphors. For Tm3+ and Eu3+-doped samples, the Tm3+-O2− charge transfer band (CTB) is observed to be at 177 nm, but the CTB of Eu3+ is observed at abnormally low energy position, which might originate from multi-position of Eu3+ ions. The similarity in luminescence properties of Ln3+ in both hosts indicates certain structural resemblance of coordination environment of Ln3+ in the two sodium rare earth diphosphates. 相似文献
993.
Zhi-hua Xiong 《Journal of Physics and Chemistry of Solids》2007,68(8):1500-1503
We perform first-principles spin polarized calculations of the electronic structure of Ti-doped in ZnO. Ferromagnetism in Ti-doped ZnO is identified, which is in agreement with recent experimental and calculated results. A net magnetic moment of 0.715μB is found per Ti. At a Ti concentration of 12.5%, total energy calculations show that the ferromagnetic state is 68 meV lower than the antiferromagnetic state. The electronic states near Fermi energy are dominated by strong hybridization between O 2p and Ti 3d, which is just the origin of impurity band in Ti-doped ZnO and also implies that the Ti-O bond is quite covalent instead of purely ionic. Since there is no magnetic element in this compound, Ti-doped ZnO appears to be an unambiguous dilute magnetic semiconductor. 相似文献
994.
The watermiscible room temperature ionic liquid 1butyl3methylimidazolium tetrafluorob orate ([bmim] [BF4]) is a model system for studying the interactions between ionic liquid and water molecules. In this work the orientational structure of the low concentrated aqueous solution of [bmim] [BF4] at the air/liquid interface was investigated by sum frequency gener ation vibrational spectroscopy. It has been found that at very low concentrations, the butyl chain exhibited a significant gauche defect, indicating a disordered conformation; and the cation ring oriented with a fairly small tilting angle at the surface. When the concentration increased, the cation ring tended to lie flat at the surface, and the gauche defects of the butyl chain decreased due to the intermolecular chainchain interactions and the consequent more ordered interfacial molecular arrangement. Additionally, the antisymmetric stretching mode in the PPP and SPS spectra exhibited a peak shift, showing that there exists more than one kind of orientation or chemical environment for the butyl CH3 group. These results may shed new light on understanding the surface behavior of watermiscible ionic liquids as well as the imidazolium based surfactants. 相似文献
995.
996.
Zhe Zhang Li Chen Mingxiao Deng Yunyan Bai Xuesi Chen Xiabin Jing 《Journal of polymer science. Part A, Polymer chemistry》2011,49(13):2941-2951
In this article, novel smart hydrogels based on biodegradable pH sensitive poly(L ‐glutamic acid‐g‐2‐hydroxylethyl methacrylate) (PGH) chains and temperature‐sensitive hydroxypropylcellulose‐g‐acrylic acid (HPC‐g‐AA) segments were designed and synthesized. The influence of pH and temperature on the equilibrium swelling ratios of the hydrogels was discussed. The optical transmittance of the hydrogels was also changed as a function of temperature, which reflecting that the HPC‐g‐AA part of the hydrogels became hydrophobic at the temperature above the lower critical solution temperature (LCST). At the same time, the LCST of the hydrogels had a visible pH‐dependent behavior. Scanning electron microscopic analysis revealed the morphology of the hydrogels before and after enzymatic degradation. The biodegradation rate of the hydrogels was directly related to the PGH content and the pH value. The in vitro release of bovine serum albumin from the hydrogels were investigated. The release profiles indicated that both the HPC‐g‐AA and PGH contents played important roles in the drug release behaviors. These results show that the smart hydrogels seem to be of great promise in pH–temperature oral drug delivery systems. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
997.
Weiping Zhou Ping Shen Bin Zhao Peng Jiang Lijun Deng Songting Tan 《Journal of polymer science. Part A, Polymer chemistry》2011,49(12):2685-2692
Two novel low band gap conjugated copolymers containing porphyrins, thiophenes, and 2,1,3‐benzothiadiazole ( BTZ ) moieties were synthesized and applied in bulk heterojunction solar cells. The thermal, optical, electrochemical, and photovoltaic properties of the two copolymers were examined to investigate the effect of the introduction of BTZ moiety in the backbone of the porphyrin polymers. The copolymers exhibited good thermal stability and film‐forming ability. The absorption spectra indicated that the BTZ moiety has significant influence on the UV–visible region spectra of the copolymers: with increasing the molar amount of BTZ moieties in conjugated main chain, the absorption in the range of 450–700 nm is largely broadened and red‐shifted compared to the similar polymers without BTZ moiety, and the optical band gaps of copolymers were narrowed to ~1.50 eV. The photoluminescence spectra showed that there is effective charge transfer in the whole conjugated main chain. Cyclic voltammetry displayed that the band gaps were reduced effectively by the introduction of the BTZ moieties. The bulk heterojunction solar cells were fabricated based on the blend of the copolymers and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) in a 1:2 weight ratio. The maximum power conversion efficiency of 0.91% was obtained by using P2 as the electron donor under the illumination of AM 1.5, 100 mW/cm2. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
998.
Benchuan Zhu Guannan Qian Yuli Xiao Sheng Deng Meng Wang Aiguo Hu 《Journal of polymer science. Part A, Polymer chemistry》2011,49(24):5330-5338
Employing enediynes as crosslinking precursors, a novel yet efficient strategy, namely photo‐triggered Bergman cyclization, was integrated with intramolecular chain collapse to yield polymeric nanoparticles with the size regime below 20 nm. Enediyne motif was designed delicately to possess a high photo‐reactivity, with the double bond locked in a methyl benzoate ring while triple bonds substituted with phenyls. Single electron transfer‐living radical polymerization was conducted to provide linear acrylate copolymers with controlled molecular weights and narrow polydispersities. Poly(butylarylate‐co‐ 5 ) went through UV‐irradiation with a concurrent Bergman cyclization, resulting in well‐defined ultrafine polymeric nanoparticles. Results from NMR, Raman scattering, photoluminescence and UV‐vis spectra corroborated the presence of conjugative structures in the polymeric nanoparticles, indicating the occurrence of photo‐induced Bergman cyclization. A series of other acrylate‐based nanoparticles were investigated to confirm the applicability of such a unique strategy in thermal sensitive but UV‐stable polymeric structures, making photo‐Bergman cyclization a promising tool towards polymeric nanoparticles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
999.
Rui Qiao Hua Deng Karl W. Putz L. Catherine Brinson 《Journal of Polymer Science.Polymer Physics》2011,49(10):740-748
In this article, we utilize finite element modeling to investigate the effect of nanoparticle agglomeration on the glass transition temperature of polymer nanocomposites. The case of an attractive interaction between polymer and nanofiller is considered for which an interphase domain of gradient properties is developed. This model utilizes representative volume elements that are created and analyzed with varying degrees of nanoparticle clustering and length scale of interphase domain. The viscoelastic properties of the composites are studied using a statistical approach to account for variations due to the random nature of the microstructure. Results show that a monotonic increase in nanofiller clustering not only results in the loss of interphase volume but also obstructs the formation of a percolating interphase network in the nanocomposite. The combined impacts lead to a remarkable decrease of Tg enhancement of clustering nanofillers in comparison with a well‐dispersed configuration. Our simulation results provide qualitative support for experimental observations that clustering observed at high nanofiller concentrations negatively impacts the effects of the nanofiller on overall properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
1000.