全文获取类型
收费全文 | 380768篇 |
免费 | 3466篇 |
国内免费 | 994篇 |
专业分类
化学 | 204508篇 |
晶体学 | 6363篇 |
力学 | 17606篇 |
综合类 | 14篇 |
数学 | 39305篇 |
物理学 | 117432篇 |
出版年
2019年 | 3552篇 |
2018年 | 4751篇 |
2017年 | 4704篇 |
2016年 | 6816篇 |
2015年 | 3837篇 |
2014年 | 6438篇 |
2013年 | 15727篇 |
2012年 | 11524篇 |
2011年 | 13931篇 |
2010年 | 10435篇 |
2009年 | 10514篇 |
2008年 | 12982篇 |
2007年 | 13038篇 |
2006年 | 11904篇 |
2005年 | 10659篇 |
2004年 | 9975篇 |
2003年 | 9087篇 |
2002年 | 8971篇 |
2001年 | 10707篇 |
2000年 | 8063篇 |
1999年 | 6262篇 |
1998年 | 5159篇 |
1997年 | 5240篇 |
1996年 | 5011篇 |
1995年 | 4536篇 |
1994年 | 4521篇 |
1993年 | 4305篇 |
1992年 | 5051篇 |
1991年 | 5065篇 |
1990年 | 4949篇 |
1989年 | 5026篇 |
1988年 | 4908篇 |
1987年 | 4929篇 |
1986年 | 4579篇 |
1985年 | 6053篇 |
1984年 | 6118篇 |
1983年 | 5121篇 |
1982年 | 5278篇 |
1981年 | 5185篇 |
1980年 | 4921篇 |
1979年 | 5407篇 |
1978年 | 5620篇 |
1977年 | 5652篇 |
1976年 | 5595篇 |
1975年 | 5286篇 |
1974年 | 5120篇 |
1973年 | 5260篇 |
1972年 | 3758篇 |
1968年 | 3367篇 |
1967年 | 3440篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
V. V. Plemenkov R. V. Ashirov O. A. Lodochnikova I. A. Litvinov R. N. Zagidullin 《Russian Journal of Organic Chemistry》2006,42(7):969-972
The Diels-Alder reaction of 1-methylcycloprop-2-ene-1-carbonitrile and coumalic acid methyl ester (methyl 2-oxo-2H-pyran-5-carboxylate) gave a 2:1 adduct with endo-syn configuration of both cyclopropane fragments, which was established by X-ray analysis. According to the 1H NMR data, the reaction involves intermediate formation of decarboxylated 1:1 adduct having a cycloheptatriene structure; its isomerization into the corresponding caradiene, followed by addition of the second dienophile molecule, was confirmed by quantum-chemical calculations. 相似文献
992.
The influence of high-temperature treatment on the properties of a styrene-containing polymer prepared from by-products of
polybutadiene production was studied. The use of the products in production of emulsion rubbers and for protecting treatment
of wood materials was examined.
Original Russian Text S.S. Nikulin, O.N. Chernykh, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 11, pp.
1900–1905. 相似文献
993.
D. N. Emel’yanov N. V. Volkova O. I. Sheronova Z. G. Chernorukova 《Russian Journal of Applied Chemistry》2006,79(8):1354-1359
The process of preservation of newspaper with aqueous solutions and dispersions of acrylic copolymers is considered from the instant of impregnation till removal of the polymeric preservative from paper. 相似文献
994.
995.
Composite optical thin-film materials have received a significant amount of interest in order to relieve the material constraints on refractive indices as well as reducing the number of layers required in optical coating design. Amongst others binary zirconia-silica composite thin films have attracted considerable attentions due to their several favorable opto-mechanical properties. In the present studies such a composite system under certain compositional mixings displayed both refractive index and band gap supremacy over pure zirconia films violating the most popular Moss rule. This unexpected evolution has several practical applications one of which can be directly employed in extending the range of tunability of the refractive index. Besides, the probing of such a novel evolution through the analysis of ellipsometric refractive index modeling and morphological correlation functions has revealed several novel as well as superior microstructural properties in the composite thin film systems. All these characterization and analysis techniques distinctly indicate a strong interrelation between the microstructural ordering and superior optical properties of the present zirconia-silica codeposited composites. 相似文献
996.
S.A. Masti A.K. Sharma P.N. Vasambekar A.S. Vaingankar 《Journal of magnetism and magnetic materials》2006
Magnetization and permeability of polycrystalline ferrites with general formula CdxMg1−xFe2−yCryO4 (x=0, 0.2, 0.4, 0.6, 0.8, 1.0; y=0, 0.05 and 0.10) were studied. Study of saturation magnetization reveals that the Neel's two-sublattice model exists upto x=0.4, for y=0, 0.05 and 0.1 and a three-sublattice model (YK-model) is predominant for x>0.4 and y=0, 0.05 and 0.10. The saturation magnetization and magnetic moment were found to decrease with the increase in Cr3+ contents, which is attributed to the dilution of B–B site interaction. Variation of initial permeability with temperature revealed the long-range ferromagnetic ordering in the compounds with x=0.4. The sample with x?0.4 and y=0, 0.05 and 0.10 showed peaking behavior near Curie temperature, which is attributed to the decrease of anisotropy constant K1 to zero. Low-frequency dispersion of initial permeability suggests domain wall displacement. Addition of Cd2+ resulted in a sharp decrease in Curie temperature. With the addition of Cr3+, initial permeability was found to decrease. 相似文献
997.
Z.G. Xiao R.J. HuH.Y. Wu G.M. JinZ.Y. Li L.M. DuanH.W. Wang B.G. ZhangS.F. Wang Z.Y. WeiH.S. Xu Y.T. ZhuS.L. Li F. FuX.H. Yuan Z.Q. Feng 《Physics letters. [Part B]》2006
The inclusive reduced velocity correlation functions of the intermediate mass fragments were measured in the reactions of 36Ar + 112,124Sn at 35 MeV/u. The anti-correlation is observed to be stronger in 36Ar + 124Sn system than that in 36Ar + 112Sn. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three body Coulomb repulsive trajectory model is employed to calculate the emission time scale of the IMFs for the two systems. The time scale is 150 fm/c in 36Ar + 112Sn and 120 fm/c in the 36Ar + 124Sn, respectively. 相似文献
998.
Methods to synthesize magnetic Fe3O4 nanoparticles and to modify the surface of particles are presented in the present investigation. Fe3O4 magnetic nanoparticles were prepared by the co-precipitation of Fe3+ and Fe2+, NH3·H2O was used as the precipitating agent to adjust the pH value, and the aging of Fe3O4 magnetic nanoparticles was accelerated by microwave (MW) irradiation. The obtained Fe3O4 magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The average size of Fe3O4 crystallites was found to be around 8–9 nm. Thereafter, the surface of Fe3O4 magnetic nanoparticles was modified by stearic acid. The resultant sample was characterized by FT-IR, scanning electron microscopy (SEM), XRD, lipophilic degree (LD) and sedimentation test. The FT-IR results indicated that a covalent bond was formed by chemical reaction between the hydroxyl groups on the surface of Fe3O4 nanoparticles and carboxyl groups of stearic acid, which changed the polarity of Fe3O4 nanoparticles. The dispersion of Fe3O4 in organic solvent was greatly improved. Effects of reaction time, reaction temperature and concentration of stearic acid on particle surface modification were investigated. In addition, Fe3O4/polystyrene (PS) nanocomposite was synthesized by adding surface modified Fe3O4 magnetic nanoparticles into styrene monomer, followed by the radical polymerization. The obtained nanocomposite was tested by thermogravimetry (TG), differential scanning calorimetry (DSC) and XRD. Results revealed that the thermal stability of PS was not significantly changed after adding Fe3O4 nanoparticles. The Fe3O4 magnetic fluid was characterized using UV–vis spectrophotometer, Gouy magnetic balance and laser particle-size analyzer. The testing results showed that the magnetic fluid had excellent stability, and had susceptibility of 4.46×10−8 and saturated magnetization of 6.56 emu/g. In addition, the mean size d (0.99) of magnetic Fe3O4 nanoparticles in the fluid was 36.19 nm. 相似文献
999.
N. Hegyvári 《Acta Mathematica Hungarica》1989,53(1-2):149-154
1000.
D. Fong J. H. Hamilton A. V. Ramayya J. K. Hwang C. Goodin K. Li J. Kormicki J. O. Rasmussen Y. X. Luo S. C. Wu I. Y. Lee A. V. Daniel G. M. Ter-Akopian G. S. Popeko A. S. Fomichev A. M. Rodin Yu. Ts. Oganessian M. Jandel J. Kliman L. Krupa J. D. Cole M. A. Stoyer R. Donangelo W. C. Ma 《Physics of Atomic Nuclei》2006,69(7):1161-1167
The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be
Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the
“hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode.
The text was submitted by the authors in English. 相似文献