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991.
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Contributions on the Investigation of Inorganic Nonstoichiometric Compounds. XLV. New Thermal Decomposition Products of Ln2CeMO6Cl3 – Preparation of Structure‐related (La, Tb)3.5TaO6Cl4–x The thermal decomposition (T £ 900–1050°C) of Ln2CeMO6Cl3 (M = Nb, Ta; Ln = La, Ce, Pr, Nd, Sm) leads to the formation of two mixed‐valenced phases (Ln, Ce)3.25MO6Cl3.5–x (phase ‘‘AB”︁”︁) and (Ln, Ce)3.5MO6Cl4–x (phase ‘‘BB”︁”︁) and to the formation of chlorine according to redox‐reactions between Ce4+ and Cl–. Single crystals of both phases (Ln, Ce)3.25MO6Cl3.5–x (‘‘AB”︁”︁) and (Ln, Ce)3.5MO6Cl4–x (‘‘BB”︁”︁) were obtained by chemical transport reactions using both powder of Ln2CeMO6Cl3 (phase ‘‘A”︁”︁) and powder of (Ln, Ce)3.25MO6Cl3.5–x (phase ‘‘AB”︁”︁) as starting materials and chlorine (p{Cl2; 298 K} = 1 atm) or HCl (p{HCl; 298 K} = 1 atm) as transport agent. A crystal of (La, Ce)3.25NbO6Cl3.5–x (”︁AB”︁”︁) (space group: C2/m, a = 35.288(1) Å, b = 5.418(5) Å, c = 9.522(1) Å, β = 98.95(7)°, Z = 4) was investigated by x‐ray diffraction methods, a crystal of (Pr, Ce)3.5NbO6Cl4–x (”︁BB”︁”︁) was investigated by synchrotron radiation (λ = 0.56 Å) diffraction methods. The lattice constants are a = 18.863(6) Å, b = 5.454(5) Å, c = 9.527(6) Å, β = 102.44(3)° and Z = 4. Structure determination in the space group C2/m (No. 12) let to R1 = 0.0313. Main building units are NbO6‐polyhedra with slightly distorted trigonally prismatic environment for Nb and chains of face‐sharing Cl6‐octahedra along [010]. The rare earth ions are coordinated by chlorine and oxygen atoms. These main structure features confirmed the expected relation to the starting material Ln2CeMO6Cl3 (phase ”︁A”︁”︁) and to (Ln, Ce)3.25MO6Cl3.5–x (phase ”︁AB”︁”︁). 相似文献
994.
Chinmay U. Bhatt Joseph R. Royer C. Robin Hwang Saad A. Khan 《Journal of Polymer Science.Polymer Physics》1999,37(11):1045-1056
Metallocene‐based polyolefin (MPO) foams possess a closed‐cell structure which is in contrast to the open‐celled structure of polyurethane (PU) foams. In this study, we investigate the effects of gamma‐irradiation on the mechanical behavior of MPO foams using PU foam behavior as a basis. Compressive step‐strain experiments reveal a two‐step relaxation process in MPO foams, dominated by polymer chain relaxation at short times and gas diffusion from the closed cells at longer times. On the other hand, the relaxation in PU foams is similar to fully crosslinked polymers with the relaxation modulus reaching an equilibrium value after an initial decay. The closed‐celled structure of MPO foams lends to rapid stress relaxation and low structural recoverability upon application of compressive loads. Exposure to gamma radiation induces crosslinking in MPO foams and improves their resilience and recoverability. Stress relaxation tests reveal that nonradiated MPO foams show complete relaxation and structural loss at high temperatures. In contrast, radiated MPO foams show a significant retardation in relaxation kinetics and structural stability attributed to radiation‐induced crosslinking. Dynamic rheology and solvent‐extraction studies also support the results obtained from stress‐relaxation experiments. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1045–1056, 1999 相似文献
995.
M. C. Senake Perera 《Journal of Polymer Science.Polymer Physics》1999,37(11):1141-1153
Methyl‐methacrylate‐grafted natural rubber was prepared by free radical polymerization of methyl methacrylate in natural rubber latex, and their structure and dynamics were investigated by dynamic mechanical analysis and solid‐state nuclear magnetic resonance (NMR). Samples were prepared by chemical initiation and high‐energy radiation. The changes of glass transition temperature and tan δ max with different total poly(methyl methacrylate (PMMA) content are reported. The effect of the change in composition in copolymers on tan δ peak width, tan δ max, and area under the tan δ curve are used to understand the miscibility and damping properties. Solid‐state 13C‐NMR measurements were carried out to determine several relaxation time parameters, such as rotating frame and laboratory frame proton and carbon relaxation times. Cross polarization times and carbon relaxation times were interpreted based on the changes in the molecular motion. Proton relaxation times were interpreted based on the heterogeneity of the matrix. Results confirmed phase separation and a presence of an interfacial region. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1141–1153, 1999 相似文献
996.
Ralf Flaig Tibor Koritsnszky Jan Janczak Hans-Georg Krane Wolfgang Morgenroth Peter Luger 《Angewandte Chemie (International ed. in English)》1999,38(10):1397-1400
Synchrotron radiation and CCD detection give the possibility for fast diffraction experiments, which were employed to deduce the exact charge-density distributions of some amino acids. Their topological analysis (the figure shows the negative Laplacian function of dl -serine in the plane of the carboxylate group) yields not only comparable information about intramolecular but also about weak intermolecular interactions. 相似文献
997.
Jerzy Stelmach 《Annalen der Physik》1999,8(10):837-848
We discuss the horizon problem in a universe dominated by fluid with negative pressure. We show that for generally accepted value of nonrelativistic matter energy density parameter Ωm0 < 1, the horizon problem can be solved only if the fluid influencing negative pressure (the so-called “X” component) violates the point-wise strong energy condition and if its energy density is sufficiently large (ΩX0 > 1). The calculated value of the ΩX0 parameter allowing for the solution of the horizon problem is confronted with some recent observational data. Assuming that pX/ρX < —0.6 we find that the required amount of the “X” component is not ruled out by the supernova limits. Since the value of energy density parameter Ωv0 for cosmological constant larger than 1 is excluded by gravitational lensing observations the value of the ratio pX/ρX should lie between the values —1 and —0.6 if the model has to be free of the horizon problem beeing at the same time consistent with observations. The value of ΩX0 + Ωm0 in the model is consistent with the constraints 0.2 < Ωtot < 1.5 following from cosmic microwave background observations provided that Ωm0 is low (<0.2). 相似文献
998.
999.
1000.
光学渡越辐射测量中能量分辨精度分析 总被引:4,自引:4,他引:0
基于光学渡越辐射原理的用于高能强流电子束束流参数在线测量及诊断系统,具有时间响应快、分辨率高等特点,可以测量电子束的束剖面、发散角、能量等多个参数。分析了测量系统的结构参数(包括了透镜的焦距、成像面位置、CCD像元尺寸)对电子束能量测量精度的影响,并在理论上模拟了电子束的发散角的影响。还根据系统数据的特点,阐述了数据噪声对能量测量结果精度的影响,指出了光学渡越辐射测量中电子束能量分辨精度受到多种因素的影响,需要在数据处理时考虑修正。 相似文献