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41.
用经验赝势方法计算了体ZnSe以及ZnSe/GaAs单异质结系统中ZnSe外延层г、X、L等特殊对称点导带底能量随压力的变化。结果表明,同Si、Ge、GaAs等半导体材料不同,ZnSe的X点导带底具有正的压力系数,但比г点的压力系数小,这是ZnSe材料以及ZnSe基异质结构材料发生直接禁带向间接禁带的转变时所需转变压力较大的根本原因。研究了ZnSe/GaAs异质结构中晶格失配造成的应变对外延层г、X、L对称点压力系数的影响,表明这种晶格失配造成的应变可以极大地减小ZnSe外延层材料由直接禁带向间接禁带的转变压力。 相似文献
42.
43.
应用TGT法生长了直径为75mm的U:CaF2晶体,宏观上透明完整.应用公式K0=Cs/Cl计算了U在CaF2晶体中的分凝系数等于0.53.应用溶质分布一般公式Cs=K0C0(1-g)K0-1,计算U的浓度分布与测量值,数值符合说明晶体生长过程接近平衡状态.分析不同条件下生长的U: CaF2晶体的晶胞参数和吸收光谱,结果表明生长气氛决定U的价态及电荷补偿机理:无PbF2存在的条件下,U为+4价,晶体呈绿色;PbF2的加入起到氟化去氧作用,U倾向于以离子半径最接近于Ca2+的U3+存在,晶体呈红色.从晶体生长开始到结束的部位,U3+:CaF2晶体吸收光谱的峰位不变,峰强呈现与U浓度相同的增加趋势.U3+:CaF2晶体外层厚约5mm处呈黄色,含有U3+和U2+的混合价态离子,其原理是石墨坩埚的还原作用通过单质铅,使部分的U3+进一步还原成了U2+.
关键词:
铀
氟化钙晶体
分凝系数
晶胞参数 相似文献
44.
M.Hasegawa 《复旦学报(自然科学版)》2007,(5)
1 Results In the coordination system by using complexation with organic ligand, the ff emission of lanthanide(Ⅲ) (Ln(Ⅲ)) is induced the excitation energy transfer form the organic chromophore under the light-irradiation. However, there are not so much number of reports to discuss the energy relaxation mechanism in such complexes with Ln(Ⅲ). Recently, we succeeded firstly to estimate the rate constant of the energy transfer between the ligand and Ln(Ⅲ) in Pr(Ⅲ)-phenanthroline analogs[1]. Here, we will di... 相似文献
45.
V. I. Sakharov 《Fluid Dynamics》2007,42(6):1007-1016
The results of numerical simulation are presented for thermally and chemically nonequilibrium air plasma flows in a plasmatron discharge channel and underexpanded dissociated and partially ionized air jets flowing past a cylindrical model with a blunt leading edge and cooled copper surface under the experimental conditions realized in a VGU-4 100 kW induction plasmatron (Institute for Problems in Mechanics of the Russian Academy of Sciences) (see, for example, [1, 2]). The nonequilibrium excitation of the vibrational degrees of freedom of the molecules in the modal approximation and the difference between the electron and translational heavy-particle temperatures are taken into account in the calculations. The calculated data on the heat transfer and pressure at the stagnation point are compared with the results obtained within the framework of the thermally equilibrium model. Comparison with the experimental data obtained in the Institute for Problem in Mechanics of the Russian Academy of Sciences (Laboratory for interaction between plasma and radiation and materials) and kindly provided for comparison purposes gives satisfactory agreement. 相似文献
46.
Anuj Mittal Swaminathan Sivaram 《Journal of polymer science. Part A, Polymer chemistry》2005,43(21):4996-5008
A tridentate ligand, BPIEP: 2,6‐bis[1‐(2,6‐diisopropyl phenylimino) ethyl] pyridine, having central pyridine unit and two peripheral imine coordination sites was effectively employed in controlled/“living” radical polymerization of MMA at 90°C in toluene as solvent, CuIBr as catalyst, and ethyl‐2‐bromoisobutyrate (EBiB) as initiator resulting in well‐defined polymers with polydispersities Mw/Mn ≤ 1.23. The rate of polymerization follows first‐order kinetics, kapp = 3.4 × 10?5 s?1, indicating the presence of low radical concentration ([P*] ≤ 10?8) throughout the reaction. The polymerization rate attains a maximum at a ligand‐to‐metal ratio of 2:1 in toluene at 90°C. The solvent concentration (v/v, with respect to monomer) has a significant effect on the polymerization kinetics. The polymerization is faster in polar solvents like, diphenylether, and anisole, as compared to toluene. Increasing the monomer concentration in toluene resulted in a better control of polymerization. The molecular weights (Mn,SEC) increased linearly with conversion and were found to be higher than predicted molecular (Mn,Cal). However, the polydispersity remained narrow, i.e., ≤1.23. The initiator efficiency at lower monomer concentration approaches a value of 0.7 in 110 min as compared to 0.5 in 330 min at higher monomer concentration. The aging of the copper salt complexed with BPIEP had a beneficial effect and resulted in polymers with narrow polydispersitities and higher conversion. PMMA obtained at room temperature in toluene (33%, v/v) gave PDI of 1.22 (Mn = 8500) in 48 h whereas, at 50°C the PDI is 1.18 (Mn = 10,300), which is achieved in 23 h. The plot of lnkapp versus 1/T gave an apparent activation energy of polymerization as (ΔE≠app) 58.29 KJ/mol and enthalpy of equilibrium (ΔH0eq) to 28.8 KJ/mol. Reverse ATRP of MMA was successfully performed using AIBN in bulk as well as solution. The controlled nature of the polymerization reaction was established through kinetic studies and chain extension experiments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4996–5008, 2005 相似文献
47.
48.
R. Pizzoferrato L. Lagonigro T. Ziller A. Di Carlo R. Paolesse F. Mandoj A. Ricci C. Lo Sterzo 《Chemical physics》2004,300(1-3):217-225
We study the infrared emission at 1.54 μm of an organolanthanide complex, Er(III)-tetraphenylporphyrin [Er(TPP)acac], both as a result of direct optical excitation and via energy transfer from host π-conjugate polymers of type poly(arylene–ethynylene) [PAE]. In the first case, the emission of the neat complex is characterized in inert transparent materials and a value of the quantum yield at 1.54 μm φIR=4×10−4 is measured. Then, fluorescence resonance transfer is investigated in blends of Er(TPP)acac with PAEs by monitoring the quenching of the polymer fluorescence along with the enhancement of both the visible emission of the ligand and the near-infrared band of Er3+. These different procedures allow a detailed analysis of the transfer efficiency within a specific implementation of the Förster model for polymeric donors. The experimental values of the critical radius R0, ranging from 1.3 to 2.5 nm for the different blends, are in good agreement with theory for a wide interval of the physical and spectroscopic parameters. This suggests that other mechanisms for excitation transfer do not play a significant role in these materials. 相似文献
49.
50.
袁文俊 《数学物理学报(A辑)》2003,23(2):224-230
该文考虑具有控制系数 A\-0 和系数仅有有限个极点的高阶线性齐次微分方程(1.1)。得到了一个复振荡结果,该结果是J. K. Langley[11]等作者在整系数下相应结果的推广。 相似文献