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141.
The title compounds were synthesized from RE, REX3, and Ge under an Ar atmosphere at 1200-1370 K. Y2GeI2 and Gd2GeI2 crystallize in space group Rm with lattice constants a = 4.2135(3) and 4.2527(1) A and c = 31.480(2) and 31.657(1) A, respectively. Gd2GeBr2 crystallizes in two modifications, the 1T-type (space group Pm1; a = 4.1668(2) A, c = 9.8173(6) A) and the 3R-type (space group Rm; a = 4.1442(9) A, c = 29.487(7) A). The structural motifs of RE2GeX2 compounds are Ge-centered slightly distorted RE6 octahedra connected via their common edges and extending in the a and b directions. The resulting close-packed double layers are separated by halogen atoms. The electrical resistivity measurements revealed semiconductor behavior for Y2GeI2 and Gd2GeI2 and a metal-semiconductor transition for 1T-Gd2GeBr2. Magnetic susceptibility and heat capacity measurements show long-range magnetic ordering for Gd2GeI2 and 1T-Gd2GeBr2 at approximately 15 and approximately 13 K, respectively. 相似文献
142.
Boyko V Richter S Burchard W Arndt KF 《Langmuir : the ACS journal of surfaces and colloids》2007,23(2):776-784
Microgels are highly swollen colloids built up of flexible cross-linked chains. We studied the static and dynamic light scattering (LS) behavior of thermosensitive microgels based on N-vinylcaprolactam and N-vinylpyrrolidone prepared by precipitation copolymerization in H2O (CP-1) and D2O (CP-2). Striking differences in behavior were observed in the two solvents. In both cases the angular dependence of static LS could reasonably well be described by a soft sphere model (J. Polym. Sci., Polym. Phys. Ed. 1982, 20, 157) with small deviations at large qRg. At temperatures larger than the collapse temperatures, the CP-1 sample in water started to aggregate whereas the CP-2 sample in D2O showed no association and developed the expected change toward hard sphere behavior. Dynamic LS permitted the determination of internal or segmental mobility. A remarkable shift toward large qRg was found for CP-1 compared to the behavior of linear chains. The dynamic behavior is clearly displayed in a plot of Gamma*(q) = (Gamma1(q)/q3)(eta0/kT), with Gamma1(q) the first cumulant of the field time correlation function and the common meaning of the other parameters. A long range of hard sphere behavior indicated the suppression of internal modes, but at large qRg the swollen microgel CP-1 in water displayed internal motions with a spectrum similar to that of Zimm relaxations. No internal mobility could be detected with the CP-2 sample in D2O. The behavior is in agreement with observations in the literature. The differences in the two similar solvents were attributed to the poorer solvent quality of D2O. 相似文献
143.
144.
145.
Haoqing Hou Arndt Reuning Joachim H. Wendorff Andreas Greiner 《Macromolecular bioscience》2001,1(1):45-48
Butyric esters (BuPC) of hydroxypropylcellulose (HPC) with different degrees of substitution (DS) were obtained by the reaction of (2‐hydroxypropyl)cellulose with butyryl chloride. Blends of these BuPCs were obtained from ternary solutions by removal of the common solvent. The blends displayed thermotropic cholesteric mesophases and showed iridescent colors at ambient temperatures depending on the blend composition. The spectroscopic analysis of the blends showed systematic variations of the reflection colors with variations of the ratio of the blend components between the reflection colors of the pure blend components covering the range from 453–938 nm corresponding to pitch heights from 308–640 nm. 相似文献
146.
Structure, Twinning, and Properties of Ce4Br3C4 The new compound Ce4Br3C4 can be prepared from Ce metal, CeBr3 and C (3 : 3 : 2) at 1020 °C. It crystallizes in P 1 with a = 422.7(1) pm, b = 1103.4(3) pm, c = 1126.8(2) pm, α = 77.15(3)°, β = 90.13(2)° and γ = 84.42(3)°. The crystals are characteristically twinned, the twin law being (1 0 0, 1/2 –1 0, 0 0 –1). The crystal structure contains puckered layers of edge sharing Ce6C2 octahedra. The mean C–C distance in the C2 units is 133(5) pm. Ce4Br3C4 has at room temperature a specific resistivity of 100 mΩ cm and an effective magnetic moment of 2.55(3) μB (Ce3+). 相似文献
147.
Anke Spannenberg Markus Oberthür Henrik Noss Annegret Tillack Perdita Arndt Rhett Kempe 《Angewandte Chemie (International ed. in English)》1998,37(15):2079-2082
The reaction of a neodymium “ate” complex and an electron-rich transition metal chloride by salt elimination is an efficient method for synthesizing heterobinuclear compounds which contain a lanthanide and a Group 9 or 10 metal [Eq. (1), H2Ap=2-amino-4-methylpyridine]. The use of bisaminopyridinato ligands allows extremely short distances between Rh or Pd and Nd. 相似文献
148.
The effect of metal substitution in La2C2Br2 by Lu (non-magnetic) and Ce (magnetic), respectively, on Tc was studied. The Lu substitution affects Tc, which decreases moderately with increasing amount of Lu. However Ce substitution affects Tc drastically, such that only 10% Ce substitution makes superconductivity disappear. 相似文献
149.
Y16I19C8B4 – a Yttrium Boride Carbide Halide Containing B2C4 Units The new compound Y16I19C8B4 was prepared from Y, YI3, C and B at 1050–1150 °C. The structure of a twinned crystal was determined by means of X-ray diffraction (space group P 1¯, a = 12.311(2) Å, b = 13.996(3) Å, c = 19.695(3) Å, α = 74.96(2)°, β = 89.51(2)°, γ = 67.03(2)°, Z = 2). Y16I19C8B4 is a semiconductor and contains nearly planar B2C4 units which are located in cages built up by 12 yttrium atoms. Assuming (B2C4)12–, these units can be regarded as isoelectronic with B2F4. The yttrium cages are connected via faces to form rods, which are surrounded by iodine atoms. Bridging iodine atoms connect the rods so that layers are formed. The characteristic twinning observed can be understood from the geometry of the crystal structure. 相似文献
150.
Load balancing on parallel computers aims at equilibrating some initial load which is different from one processor to another. We consider only nearest neighbour algorithms: in each step a processor communicates only with its direct neighbours. Load balancing algorithms can be divided into two classes: diffusion and dimension exchange. Whereas the first is appropriate for the so‐called all‐port‐model where a processor can send tokens to all its neighbours at a time, the latter is useful for the one‐port‐model. Both kinds of algorithms can be viewed as methods for solving certain singular linear systems. Since a few years there exist finite diffusion algorithms which have the property that they compute l2‐minimal flows. In this paper a new finite dimension exchange method will be presented that is based on edge‐colourings of the underlying graph. It is usually faster and more stable than its diffusion counterpart. The flows computed by the new method are not minimal but it can be shown that they are bounded. Our analysis is based on techniques from numerical linear algebra. 相似文献