全文获取类型
收费全文 | 238449篇 |
免费 | 2030篇 |
国内免费 | 622篇 |
专业分类
化学 | 123941篇 |
晶体学 | 4088篇 |
力学 | 10180篇 |
综合类 | 9篇 |
数学 | 27142篇 |
物理学 | 75741篇 |
出版年
2021年 | 1986篇 |
2020年 | 2227篇 |
2019年 | 2540篇 |
2018年 | 3407篇 |
2017年 | 3558篇 |
2016年 | 5076篇 |
2015年 | 2773篇 |
2014年 | 4626篇 |
2013年 | 10528篇 |
2012年 | 8250篇 |
2011年 | 9669篇 |
2010年 | 7279篇 |
2009年 | 7291篇 |
2008年 | 9107篇 |
2007年 | 8886篇 |
2006年 | 8460篇 |
2005年 | 7604篇 |
2004年 | 7078篇 |
2003年 | 6364篇 |
2002年 | 6246篇 |
2001年 | 7083篇 |
2000年 | 5278篇 |
1999年 | 4051篇 |
1998年 | 3484篇 |
1997年 | 3295篇 |
1996年 | 3019篇 |
1995年 | 2836篇 |
1994年 | 2794篇 |
1993年 | 2701篇 |
1992年 | 3055篇 |
1991年 | 3045篇 |
1990年 | 2935篇 |
1989年 | 2877篇 |
1988年 | 2806篇 |
1987年 | 2763篇 |
1986年 | 2616篇 |
1985年 | 3371篇 |
1984年 | 3506篇 |
1983年 | 3078篇 |
1982年 | 3198篇 |
1981年 | 2925篇 |
1980年 | 2890篇 |
1979年 | 3061篇 |
1978年 | 3207篇 |
1977年 | 3167篇 |
1976年 | 3134篇 |
1975年 | 3032篇 |
1974年 | 2996篇 |
1973年 | 3141篇 |
1972年 | 2127篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
S. V. Zvezdina M. B. Berezin B. D. Berezin 《Russian Journal of Inorganic Chemistry》2007,52(8):1269-1273
The metal-exchange reaction of cadmium deuteroporphyrin (CdDP) and cadmium gematoporphyrin (CdGP) with cobalt chloride in acetonitrile is studied spectrophotometrically. The stoichiometry of the metal-exchange reaction is determined. The results are compared with the exchange reaction of cadmium mesoporphyrin and cadmium protoporphyrin with cobalt acetate in acetonitrile. Substituents in the 2,4-positions of cadmium complexes of protoporphyrins are shown to influence the rate of the metal-exchange reaction. The increasing order of the rates of the metal-exchange reaction between protoporphyrins and cobalt chloride in acetonitrile is established. 相似文献
912.
M. P. Evstigneev V. V. Khomich D. B. Davies 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(5):741-746
The self-association of an antitumor antibiotic, daunomycin (DAU), in various buffer solutions, including water-salt solutions, phosphate buffer, HEPES, and TRIS, was studied by 1D and 2D 1H NMR spectroscopy at 500 MHz. The two-dimensional NOESY spectra and the concentration and temperature dependences of the chemical shifts of antibiotic protons in the solvents studied showed that the self-association parameters of DAU were independent of the type of buffer solutions. The most probable two spatial structures of the dimer of DAU in solution were constructed by the method of molecular mechanics. The mutual orientation of the chromophores was parallel in one structure and antiparallel in the other. 相似文献
913.
A. V. Zaikina E. I. Yarmukhamedova Yu. I. Puzin A. A. Fatykhov Yu. B. Monakov 《Polymer Science Series A》2006,48(5):457-461
The specific features of free-radical polymerization of methyl methacrylate in the presence of a new initiating system, benzoyl peroxide-N,N-dimethyl-N-(methylferrocenyl)amine, are studied. Mutual influence of the ferrocene and amino groups on the kinetic parameters of polymerization and on the microstructure of the resulting polymers is revealed. The polymer formed in the presence of this initiating system is shown to have a predominantly syndiotactic structure. 相似文献
914.
L.A. Leites A.V. Zabula S.S. Bukalov A.A. Korlyukov P.S. Koroteev O.S. Maslennikova M.P. Egorov O.M. Nefedov 《Journal of Molecular Structure》2005,750(1-3):116-122
Vibrational (Raman and IR) spectra of the 1:1 complexes of dihalogermylene and dihalostannylene with 1,4-dioxane and PPh3 have been reported, the structures of the complexes Cl2Ge·C4H8O2 and Cl2Ge·PPh3 updated using high-resolution X-ray method. Quantum-chemistry calculations of the geometry and normal mode frequencies and eigenvectors were carried out for some of the complexes. The results show that in the structure of the polymeric solid complexes of X2M with 1,4-dioxane, intermolecular coordination XM plays a prominent role, whereas the corresponding complexes with PPh3 are monomeric. In the vibrational spectra of all the complexes, an inversion of symmetric and antisymmetric stretching νXM (X=Cl, Br; M=Ge, Sn) frequencies, found for ‘free’ X2MII particles, still persists, suggesting that the X2M moieties preserve their specifity as carbene analogues also in the complexes. 相似文献
915.
K. A. Gulyamova B. Kh. Rozmukhamedova K. D. Davranov 《Chemistry of Natural Compounds》1994,30(5):622-624
Two forms of lipases (A and B) have been isolated from the fungusMucor miehei UzLT-3 and purified to the homogeneous state, and molecular masses of 43 and 40 kDa have been established for them from the
results of disk electrophoresis and gel filtration. The isoelectric points of the lipases are 4.7 for form A and 4.9 for form
B.
Institute of Microbiology, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax 41 71 29. Translated from Khimiya
Prirodnykh Soedinenii, No. 5, pp. 673–676, September–October, 1994. 相似文献
916.
Preparation and crystal structure of the La2Ni12P5 and isotypic ternary lanthanoid—Nickel phosphides
Yu. B. Kuz'ma V. S. Babizhet'sky S. I. Chykhrij S. V. Oryshchyn V. K. Pecharsky 《无机化学与普通化学杂志》1993,619(3):587-592
The new ternary phosphide La2Ni12P5 has been prepared by direct arc melting of the components as pure metals and red phosphorus. The crystal structure has been determined using X-ray single crystal diffraction data. The compound exhibits a new type of crystal structure, P21/m with lattice parameters a = 10.911(3), b = 3.696(2), c = 13.174(4) Å, β = 108.02(2)°, V = 505,2(6) Å3, Z = 2. Atomic parameters least squares refinement of 116 independent variables (anisotropic approximation for thermal vibrations) employed 1 284 independent Io(hkl); RF = 0.0278 and RW = 0.0287. The crystal structure is characterized by trigonal prismatic arrangement of phosphorus atoms stacking variant of infinite (with phosphorus centered) columns built by metal trigonal prisms ‖ [010]. Two or three such columns are connected through common edges (lanthanum atoms). The compounds RE2Ni12P5 (where RE = Ce, Pr, Nd and Eu) display the same with La2Ni12P5 crystal structure. Lattice parameters of these compounds have been refined using powder diffraction data. 相似文献
917.
Martin B. Hocking David T. Syme David E. Axelson Kirk H. Michaelian 《Journal of polymer science. Part A, Polymer chemistry》1990,28(11):2969-2982
The comonomer required, p-maleimidobenzoic acid (MBA) was first prepared in good yield by refinements of published methods. p-Carboxysuccinanilic acid (CSA), and p-succinimidobenzoic acid (SBA), were also prepared to provide models useful for IR and NMR for spectroscopic assignments of the new copolymers. Polymerization of MBA with acrylamide in glacial acetic acid at 60°C gave copolymers with estimated viscosity average molecular weights of 60,000 to 90,000. Yields and viscosity average molecular weights decreased as the MBA to acrylamide monomer feed ratio was increased. The rate of incorporation of MBA into the copolymer rose from 7 to 23% when the mole ratio in the feed was raised from 5 to 20%. Decreasing the initiator concentration increased molecular weights by less than predicted and reduced the yield of copolymer for any given feed ratio of MBA to acrylamide. In all cases about 30–40% of the MBA units in the purified copolymers were hydrolyzed. A change to dimethyl sulfoxide solvent gave good, and poor yields of copolymer at 5 and 10 mol % MBA, respectively, and no copolymer at 20 mol % MBA. Viscosity average molecular weights of the copolymer products prepared in DMSO were somewhat lower than obtained for the copolymers prepared in acetic acid. Polymerization in a DMSO-water mixture gave a negligible yield of polymeric product. Instead, only hydrolysates of MBA precipitated when the coloured polymerization solutions were added to methanol. 相似文献
918.
B. Robrieux G. Desrousseaux A. Renou M. Gillet 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,12(1-4):27-29
In this paper, we show that it is possible to deduce the actual morphology of small particle condensed onto an insulator by combining the granularity analysis from electron micrographs and the electrical sheet conductance of the deposit on its substrate. Assuming the particles are truncated ellipsoids, we determine the excentricity and the contact angle with the substrate for Au on amorphous carbon and MgO substrates. 相似文献
919.
Diffusion of organic vapors at low concentrations in glassy PVC, polystyrene, and PMMA 总被引:1,自引:0,他引:1
Diffusion coefficients of various C1 to C6 organic vapors, at concentrations 0.5 wt. percent, have been determined by gravimetric sorption rate measurements on emulsion and suspension-polymerized powder samples of PVC, polystyrene, and PMMA. Fickian diffusion kinetics were observed at the lowest concentrations, with a second-stage, relaxation-controlled sorption appearing at higher concentrations. In conjunction with published data for diffusivities of fixed gases in these polymers, the results indicate that diffusivity decreases exponentially, and that diffusion activation energy (ED) increases linearly, with increasing diameter of “spherical” penetrant molecules (e.g., the noble gases, CH4, SF6, CCl4, and neopentane). Much of the observed scatter in these correlations is attributable to uncertainty in the molecular diameters. For C4 and larger n-alkanes and other elongated or flattened molecules, diffusivities are higher, and ED lower, than for spherical molecules of similar molar volume. This finding suggests that anisometric molecules are oriented and move along their long axes during diffusion through the glassy polymer matrix. Correlations of diffusivities with molecular dimensions suggests that transport of anisometric molecules is governed by a diameter smaller than the mean (equivalent sphere) diameter but larger than the minimum dimension of their extended-chain conformation. Among the three polymers studied, diffusivity of each penetrant, at a given temperature, decreases in the order polystyrene> PVC ≥ PMMA. 相似文献
920.
Panasyugin A. S. Golikova N. B. Il'inykh N. P. Strukova O. V. 《Russian Journal of Applied Chemistry》2002,75(6):1029-1031
Sorption of 137Cs on NaX zeolite modified with Cu2[Fe(CN)6] was studied under dynamic conditions. 相似文献