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981.
A discrete hierarchical model with either age, size, or stage structure is derived. The resulting scalar equation for total population level is then used to study contest and scramble intra-specific competition. It is shown how equilibrium levels and resilience are related for the two different competition situations. In particular, scramble competition yields a higher population level while contest competition is more resilient if the uptake rate as a function of resource density is concave down. The conclusions are reversed if the uptake rate is concave up. 相似文献
982.
Yuan‐Jyh Lee Shiao‐Wei Kuo Wu‐Jang Huang Hung‐Yen Lee Feng‐Chih Chang 《Journal of Polymer Science.Polymer Physics》2004,42(6):1127-1136
The miscibility of a phenolic resin with polyhedral oligomeric silsesquioxane (POSS) hybrids and the specific interactions between them were investigated with Fourier transform infrared (FTIR) spectroscopy and wide‐angle X‐ray diffraction (WAXD). An analysis of the morphology and microstructure was performed with polarized optical microscopy and atomic force microscopy (AFM). The interassociation equilibrium constant between the phenolic resin and POSS (38.7) was lower than the self‐association equilibrium constant of pure phenolic (52.3) according to the Painter–Coleman association model. This result indicated that POSS was partially miscible with the phenolic resin. A polarized optical microscopy image of a phenolic/POSS hybrid material (20 wt % POSS) indicated that the crystals of POSS were arranged evenly in the phenolic matrix; the self‐assembled array of POSS crystals was also confirmed by AFM. This phenomenon was consistent with the FTIR spectroscopy and WAXD analyses. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1127–1136, 2004 相似文献
983.
Jeng‐Yueh Shieh Hann‐Jang Hwang Shih‐Peng Yang Chun‐Shan Wang 《Journal of polymer science. Part A, Polymer chemistry》2005,43(3):671-681
A 2,6‐dimethyl phenol‐dicyclopentadiene novolac (DCPDNO) was synthesized from dicyclopentadiene and 2,6‐dimethyl phenol, and the resultant DCPDNO was reacted with cyanogen bromide into 2,6‐dimethyl phenol‐dicyclopentadiene cyanate ester (DCPDCY). The structures of the novolac and cyanate ester were confirmed with Fourier transform infrared spectroscopy, elemental analysis, mass spectrometry (MS), and nuclear magnetic resonance. For the purpose of increasing the mobility of residual DCPDCY during the final stage of curing and achieving a complete reaction of cyanate groups, a small quantity of a monofunctional cyanate ester, 4‐tert‐butylphenol cyanate ester (4TPCY), was added to DCPDCY to form the cyanate ester copolymer. The synthesized DCPDCY was then cured with 4TPCY at various molar ratios. The thermal properties of the cured cyanate ester resins were studied with dynamic mechanical analysis, dielectric analysis, and thermogravimetric analysis. These data were compared with those of the commercial bisphenol A cyanate ester system. Compared with the bisphenol A cyanate ester system, the cured DCPDCY resins exhibited lower dielectric constants (2.52–2.67 at 1 GHz), dissipation factors (0.0054–0.0087 at 1 GHz), glass‐transition temperatures (261–273 °C), thermal stability (5% degradation temperature at 406–450 °C), thermal expansion coefficients (4.8–5.78 × 10?5/°C before the glass‐transition temperature), and moisture absorption (0.8–1.1%). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 671–681, 2005 相似文献
984.
Wen‐Jang Kuo Ming‐Chun Chang Tzong‐Yuan Juang Chih‐Ping Chen Chin‐Ti Chen Huey‐Ling Chang Ru‐Jong Jeng 《先进技术聚合物》2005,16(7):515-523
An organosoluble polyimide based on bipyridyl moiety and an alkoxysilane dye have been developed for second‐order non‐linear optics (NLOs). This bipyridine‐containing polyimide exhibits a glass transition temperature of 254°C and a degradation temperature of 400°C. An NLO‐active semi‐interpenetrating network (IPN) system was prepared by blending the polyimide with the alkoxysilane dye via in situ sol‐gel process of alkoxysilane. The selection of this bipyridine‐containing polyimide as the polymeric matrices provides improved solubility and thermal stability, and most importantly enhanced intermolecular interactions. No aggregation of the NLO chromophores in the polyimide matrices was observed through morphology and NLO studies. Under the limitation of chromophore degradation at elevated temperatures, the pristine poled/cured alkoxysilane dye exhibits poorer long‐term stability. By introducing the polyimide upon a silica network by the semi‐IPN system, randomization of the oriented chromophores can be effectively suppressed. Using in situ contact poling, the r33 coefficients of 2.2–17.0 pm/V were obtained for the optically clear semi‐IPN NLO materials. Excellent temporal stability (100°C) was also achieved for these semi‐IPN materials. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
985.
986.
Sampled grating DBR (SGDBR) based laser arrays were demonstrated to be feasible for realizing monolithically integrated DWDM sources. In order to ease the post-fabrication wavelength control for SGDBR laser arrays, the influence of the sampling duty cycle and the difference of reflection peak spacing is analyzed and investigated experimentally for achieving the best side-mode suppression ratio (SMSR) of a SGDBR laser array. It is found that such type of laser arrays can have good tolerance on the mirror misalignment. We demonstrated arrays with uniform wavelength combs of 32 wavelengths in 0.8 nm wavelength spacing. Both high SMSR and accurate wavelength registration are achieved for all lasers in an array. We also demonstrated 16-wavelength laser arrays of 50 GHz spacing whose wavelengths are aligned to the ITU grid with single-electrode operation. 相似文献
987.
An open-loop control scheme for minimization of residual vibrations of a flexible robot 总被引:1,自引:0,他引:1
The aim of this study is to develop a practical control scheme, called the three-step input method, whereby a flexible robot
arm is moved from one position to another with a minimum of residual vibration when the arm reaches its defined endpoint.
This work is concerned with defining a simple practical method to utilize step inputs to achieve optimum response. The optimum
response is achieved by using a self-adjusting input command function that is obtained during real-time processing. The practicality
of this control scheme is demonstrated by using an analog computer to simulate a simple flexible robot and conventional servo
controller. The experiments focus on point-to-point movement. Also, this method required little computational effort through
the intelligent use of conventional servo control technology and the robot's vibration characteristics. 相似文献
988.
Physicochemical characterization of α‐chitin, β‐chitin,and γ‐chitin separated from natural resources
Mi‐Kyeong Jang Byeong‐Gi Kong Young‐Il Jeong Chang Hyung Lee Jae‐Woon Nah 《Journal of polymer science. Part A, Polymer chemistry》2004,42(14):3423-3432
We isolated α‐chitin, β‐chitin, and γ‐chitin from natural resources by a chemical method to investigate the crystalline structure of chitin. Its characteristics were identified with Fourier transform infrared (FTIR) and solid‐state cross‐polarization/magic‐angle‐spinning (CP–MAS) 13C NMR spectrophotometers. The average molecular weights of α‐chitin, β‐chitin, and γ‐chitin, calculated with the relative viscosity, were about 701, 612, and 524 kDa, respectively. In the FTIR spectra, α‐chitin, β‐chitin, and γ‐chitin showed a doublet, a singlet, and a semidoublet at the amide I band, respectively. The solid‐state CP–MAS 13C NMR spectra revealed that α‐chitin was sharply resolved around 73 and 75 ppm and that β‐chitin had a singlet around 74 ppm. For γ‐chitin, two signals appeared around 73 and 75 ppm. From the X‐ray diffraction results, α‐chitin was observed to have four crystalline reflections at 9.6, 19.6, 21.1, and 23.7 by the crystalline structure. Also, β‐chitin was observed to have two crystalline reflections at 9.1 and 20.3 by the crystalline structure. γ‐Chitin, having an antiparallel and parallel structure, was similar in its X‐ray diffraction patterns to α‐chitin. The exothermic peaks of α‐chitin, β‐chitin, and γ‐chitin appeared at 330, 230, and 310, respectively. The thermal decomposition activation energies of α‐chitin, β‐chitin, and γ‐chitin, calculated by thermogravimetric analysis, were 60.56, 58.16, and 59.26 kJ mol?1, respectively. With the Arrhenius law, ln β was plotted against the reciprocal of the maximum decomposition temperature as a straight line; there was a large slope for large activation energies and a small slope for small activation energies. α‐Chitin with high activation energies was very temperature‐sensitive; β‐Chitin with low activation energies was relatively temperature‐insensitive. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3423–3432, 2004 相似文献
989.
Young-Lae Kim Heon-Young Lee Serk-Won Jang Seung-Joo Lee Hong-Koo Baik Young-Soo Yoon Young-Shin Park Sung-Man Lee 《Solid State Ionics》2003,160(3-4):235-240
Thin film Ni3Sn2 anodes were deposited on a Cu substrate by e-beam evaporator at room temperature. The deposited films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). They were tested as anodes for thin film rechargeable lithium batteries. These film electrodes exhibited an excellent cycle performance over 500 cycles. Ni3Sn2 films remained without undergoing any crystallographic phase change during cycling. 相似文献
990.
Yang Chiang Ling‐Sheng Jang Sung‐Lin Tsai Ming‐Kun Chen Min‐Haw Wang 《Electroanalysis》2014,26(10):2129-2137
The electrical impedance analysis of single cells can provide information on cells’ pathological condition in various environments. Cell electrical properties are affected by factors such as the location, adhesion, and size of the cell. The proposed microfluidic device captures a single cell, maintains growth conditions, and allows single‐melanoma‐cell impedance to be measured using an impedance analyzer and a function generator. The rate of impedance variation (ROIV) can be used to determine cell growth conditions. Cellular apoptosis affects cell size and membrane surface area, and thus the electrical properties of cells. At 24 h without Antrodia cinnamomea (AC) addition, ROIV was 15.23 %, 17.04 %, and 12.60 % at temperatures of 34 °C, 37 °C, and 40 °C, respectively. At 24 h and 37 °C, ROIV was 17.04 %, 40.37 %, and 45.02 % for AC concentrations of 0, 20, and 40 µL/mL, respectively. The results show that the cell impedance variation of cells cultured without AC is much lower than that of cells cultured with AC. Regarding cellular morphology, with AC addition, the cells shrank obviously after 24 h, whereas they barely shrank without AC addition. 相似文献