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131.
Jean‐Franois Lahitte Walter Kaminsky Olivera Stojkovic Frdric Peruch Pierre J. Lutz 《Macromolecular rapid communications》2004,25(10):1010-1014
Summary: ω‐Styryl‐polystyrene macromonomers were synthesized by anionic induced deactivation reactions. Their homopolymerization in the presence of a fluorinated half‐sandwich metallocene catalyst (CpTiF3/MAO) was investigated. In spite of the intrinsic lower reactivity of these macromonomers with respect to the micromolecular monomer, coordination homopolymerization was possible. The influence of several experimental parameters on the polymerization yield and degree could be demonstrated. In most cases, under identical experimental conditions, higher polymerization yields and degrees were observed with respect to the CpTiCl3/MAO catalyst.
The synthesis of p‐polystyryl‐substituted styrene derivatives by the homopolymerization of ω‐styryl‐polystyrene macromonomers in the presence of CpTiF3. 相似文献
132.
单茚钛与β-二酮钛催化苯乙烯间规聚合反应的性能 总被引:3,自引:0,他引:3
1986年Ishihara等[1]首次报道间规聚苯乙烯以来,人们对苯乙烯间规聚合的各种单茂钛类(包括单茚钛)催化剂进行了大量研究[2~5].这些单茂钛类催化剂聚合活性高,但合成复杂,催化剂总收率低.近年来,合成方法更为简便、聚合活性较高的新型非茂钛的研究开始引起人们的关注[6~8].至此苯乙烯间规聚合的催化剂大致分为两类,即单茂钛催化剂和非茂钛催化剂.这两大类催化剂的催化性能各有特点.对它们催化性能进行对比的研究报道尚不多见.我们自行设计并合成了单茚钛和β-二酮钛催化剂,对它们的催化性能进行了比较. 相似文献
133.
The mass attenuation coefficient (μ
m) of 662 keV gamma rays have been measured in the extended media of bakelite and perspex under different collimation conditions.
The increase in attenuation coefficient is seen with increase in sample thickness as well as with collimator size due to the
contribution of multiple scattered photons in the uncollided beam of 662 keV gamma rays. 相似文献
134.
Xiaoru Zhao Wenbin Wu Xuefeng Sun Xiao-Guang Li 《Physica C: Superconductivity and its Applications》1999,320(3-4):225-232
The variations of the high angle 00
peak-shape by means of X-ray l scans of the 00l fundamental reflections were investigated in detail for a highly oriented Bi2Sr2CaCu2Oy (Bi2212) crystal with sufficiently small intrinsic mosaicity and the same crystal annealed in air at 250, 300, 400, 600, and 750°C for 20 h in consequence. For the first time, we observed a new additional reflection almost overlapped original 00l fundamental reflection at annealing temperature below 400°C by X-ray diffraction measurement, which shows that there coexisted two sets of lattice periodicity in the c-direction of the annealed crystal. The new additional reflection appeared at 250°C and disappeared at 400°C. Its intensity was increased at 300°C. The measurements of the AC susceptibility, c-axis parameter and full width at half maximum (FWHM) of the 00
peaks showed that the new additional reflection was associated with the oxygen diffusion in CuO2 planes and the changes of strain field. The results provide the new experimental evidence that the structural distortion is more sensitive to the oxygen diffusion in CuO2 planes than to that in Bi–O layers. 相似文献
135.
136.
从2带正交小波基出发,探讨了2m带正交小波理论,基于该理论,提出了一种新的可精确重构子带信号的DWMT系统结构。 相似文献
137.
Jürgen Schellenberg 《Journal of polymer science. Part A, Polymer chemistry》2000,38(13):2428-2439
The syndiospecific polymerization of styrene was investigated with the fluorine‐containing half‐sandwich complexes η5‐pentamethylcyclopentadienyl titanium bis(trifluoroacetate) dimer, η5‐octahydrofluorenyl titanium tristrifluoro‐acetate, η5‐octahydrofluorenyl titanium dimethoxymonotrifluoroacetate, and η5‐octahydrofluorenyl titanium tris(pentafluorobenzoate) in comparison to known chloride and methoxide complexes in the presence of relatively low amounts of methylalumoxane and triisobutylaluminum. After the selection of effective reaction conditions for a solvent‐free polymerization, the following orders of decreasing polymerization activity of the titanium complexes can be observed: for pentamethylcyclopentadienyl compounds, Cp*Ti(OMe)3 > [Cp*Ti(OCOCF3)2]2O ≈ Cp*TiCl3, and for octahydrofluorenyl compounds, [656]Ti(OMe)3 > [656]Ti(OCOC6F5)3 > [656]Ti(OCH3)2(OCOCF3) > [656]Ti (OCOCF3)3. The [656]Ti complexes, showing the highest polymerization conversions at 70 °C and in comparison with the Cp* Ti compounds, turned out to be highly efficient catalysts for the syndiospecific styrene polymerization. The fluorine‐containing Cp* and [656]Ti complexes lead to much higher molecular weights than the chloride and methoxide compounds because of a reduction in chain‐limiting transfer reactions. The introduction of only one fluorine‐containing ligand into the coordination sphere of the metal compound is obviously sufficient for a significant increase in molecular weight. The active polymerization sites of the [656]Ti complexes with methylalumoxane and triisobutylaluminum are extremely stable during storage at room temperature in regard to their polymerization activity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2428–2439, 2000 相似文献
138.
Jonathan Masere Yuri Chekanov James R. Warren Felicia D. Stewart Rabih Al‐Kaysi Jerald K. Rasmussen John A. Pojman 《Journal of polymer science. Part A, Polymer chemistry》2000,38(21):3984-3990
Quaternary ammonium persulfates as free‐radical initiators for high‐temperature polymerization are synthesized and their shelf‐life stability investigated. These initiators do not have gaseous byproducts and are therefore ideal for frontal polymerization, a process in which polymeric materials are produced via a thermal front that propagates through the unreacted monomer/initiator solution. Quaternary ammonium persulfate initiators offer additional qualities such as high solubility in organic media and low volatility, which are desirable for frontal polymerization. The initiators are synthesized using two procedures, and the initiating efficacy of the respective products is compared to a peroxide initiator in the frontal polymerization of 1,6‐hexanediol diacrylate. Of all the quartenary ammonium persulfates synthesized, tricaprylmethylammonium (Aliquat) persulfate (APSO) is the best initiator for frontal polymerization because it is soluble in organic media, is very reactive, and does not produce volatile byproducts under decomposition. A study of the decomposition kinetics of APSO is performed, and frontal polymerization is proposed as a quicker analytical technique to assay the purity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3984–3990, 2000 相似文献
139.
Ying‐Hung So Donald L. Schmidt Matt T. Bishop Daniel R. Miller Patrick B. Smith Michael J. Radler Mindy Magyar Britton L. Kaliszewski 《Journal of polymer science. Part A, Polymer chemistry》2000,38(8):1283-1290
Upon photolysis or heating, aryl cyclic sulfonium (ACS) zwitterions polymerize by ring‐opening and loss of charge to yield nonionic polymers. These water‐soluble monomers potentially are useful for photolithography because they can be cast from and developed in water. The ACS zwitterion from bisphenol A, 1,1′‐[isopropylidenebis(6‐hydroxy‐3,1‐phenylene)] bis (tetrahydrothiophenium hydroxide) bis(inner salt) (1) is a negative‐tone, photosensitive material that after photolysis yields a crosslinked film. Unexposed regions are removed by water. The cured film has a low dielectric constant, high volume resistivity, a high degree of planarization, low residual stress, thermogravimetric stability, acceptable fracture toughness, and high hardness. These are desirable properties for a dielectric material used in microelectronic applications. However, a shortcoming of the material is its low Tg, at about 140 °C. A second ACS zwitterion, 1,1′‐[fluorenylidenebis(6‐hydroxy‐3,1‐phenylene)] bis(tetrahydrothiophenium hydroxide) bis(inner salt) (2) was prepared that yields a crosslinked polymer with a higher Tg of about 190 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1283–1290, 2000 相似文献
140.
介绍了一类新的广义勒让德有理正交函数系.建立了半直线上椭圆型问题的广义勒让德有理拟谱格式,数值结果说明了这种方法的有效性. 相似文献