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921.
922.
F. Firszt K. Strzakowski A. J. Zakrzewski S. gowski H. Mczyska A. Marasek 《Crystal Research and Technology》2007,42(12):1352-1358
Zn1‐x‐yBexMnySe solid solutions were grown from the melt by the high pressure Bridgman method. Optical, luminescence, photoelectric and photothermal properties of this material were investigated. Interpretation of the piezoelectrically detected photoacoustic spectra was performed using Jackson and Amer theory. From the spectral dependence of the amplitude and phase of photoacoustic signal as well as from photoluminescence spectra the variation of energy gap with composition was determined. The values of thermal diffusivity were derived from the dependence of photoacoustic signal on modulation frequency of the laser radiation illuminating the sample. The photoluminescence‐excitation spectra and photoconductivity spectra were measured. The origin of luminescence in Zn1‐x‐yBexMnySe was discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
923.
Olivier Lagrille Jacques Taillades Laurent Boiteau Auguste Commeyras 《Journal of Physical Organic Chemistry》2007,20(4):271-284
Nitrosation of N‐carbamoylamino acids (CAA) by gaseous NO + O2, an interesting synthetic pathway to amino acid N‐carboxyanhydrides (NCA), alternative to the phosgene route, was investigated on N‐carbamoyl‐valine either in acetonitrile suspension or solventless conditions, and compared to the classical nitrosating system NaNO2 + CF3COOH (TFA), the latter being quite less efficient in terms of either rate, stoichiometric demand, or further tractability of the product. The rate and efficiency of the NO + O2 reaction mainly depends on the O2/NO ratio. Evaluation of the contribution of various nitrosating species (N2O3, N2O4, HNO2) through stoichiometric balance showed the reaction to be effected mostly by N2O3 for O2/NO ratios below 0.3, and by N2O4 for O2/NO ratios above 0.4. The relative contribution of (subsequently formed) HNO2 always remains minor. Differential scanning calorimetry (DSC) monitoring of the reaction in the solid phase by either HNO2 (from NaNO2 + TFA), gaseous N2O4 or gaseous N2O3, provides the associated rate constants (ca. 0.1, 2 and 108 s?1 at 25°C, respectively), showing that N2O3 is by far the most reactive of these nitrosating species. From the DSC measurement, the latent heat of fusion of N2O3, 2.74 kJ · mol?1 at ?105 °C is also obtained for the first time. The kinetics was investigated under solventless conditions at 0°C, by either quenching experiments or less tedious, rough calorimetric techniques. Auto‐accelerated, parabolic‐shaped kinetics was observed in the first half of the reaction course, together with substantial heat release (temperature increase of ca. 20°C within 1–2 min in a 20‐mg sample), followed by pseudo‐zero‐order kinetics after a sudden, important decrease in apparent rate. This kinetic break is possibly due to the transition between the initial solid‐gas system and a solid‐liquid‐gas system resulting from water formation. Overall rate constants increased with parameters such as the specific surface of the solid, the O2/NO ratio, or the presence of moisture (or equivalently the hydrophilicity of the involved CAA), however without precise relationship, while the last two parameters may directly correlate to the increasing acidity of the medium. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
924.
925.
Sen Han Juanjuan Feng Xiangping Ji Chunying Li Xiuqin Wang Yu Tian Min Sun 《Journal of separation science》2019,42(21):3363-3371
Nano‐molybdenum trioxide was prepared from nano‐molybdenum disulfide by simple firing in muffle furnace. Nano‐molybdenum trioxide was used as the extraction coating on the stainless steel wire. Four wires were filled in a polyetheretherketone tube to get an extraction tube. The tube was connected to the six‐port valve of a high performance liquid chromatograph, and the online analysis system was constructed. Extraction selectivity of the tube for different types of compounds, including polycyclic aromatic hydrocarbons, plasticizers, estrogens, anilines and neonicotinoids, was studied. Good enrichment ability for polycyclic aromatic hydrocarbons, but the extraction efficiency of others was not satisfactory. Using eight polycyclic aromatic hydrocarbons as the targets, an analytical method was established after optimizing main factors such as sampling volume, sampling rate, methanol content, and desorption time. The established method exhibited wide linear range to 0.016–20.00 μg/L and low limits of detection to 0.005 μg/L, and the enrichment factors can be up to 2443. The method was applied to the detection of trace polycyclic aromatic hydrocarbons in tap water and river water, and a good recovery was obtained. The tube showed good durability and chemical stability, and it still remained good extraction effect after more than 140 run. 相似文献
926.
Tianliang Hu Run Chen Qiang Wang Chiyang He Shaorong Liu 《Journal of separation science》2021,44(1):274-309
Sample pretreatment is essential for the analysis of complicated real samples due to their complex matrices and low analyte concentrations. Among all sample pretreatment methods, solid‐phase extraction is arguably the most frequently used one. However, the majority of available solid‐phase extraction adsorbents suffer from limited selectivity. Molecularly imprinted polymers are a type of tailor‐made artificial antibodies and receptors with specific recognition sites for target molecules. Using molecularly imprinted polymers instead of conventional adsorbents can greatly improve the selectivity of solid‐phase extraction, and therefore molecularly imprinted polymer‐based solid‐phase extraction has been widely applied to separation, clean up and/or preconcentration of target analytes in various kinds of real samples. In this article, after a brief introduction, the recent developments and applications of molecularly imprinted polymer‐based solid‐phase extraction for determination of different analytes in complicated real samples during the 2015‐2020 are reviewed systematically, including the solid‐phase extraction modes, molecularly imprinted adsorbent types and their preparations, and the practical applications of solid‐phase extraction to various real samples (environmental, food, biological, and pharmaceutical samples). Finally, the challenges and opportunities of using molecularly imprinted polymer‐based solid‐phase extraction for real sample analysis are discussed. 相似文献
927.
采用一步电化学法在金属 Bi板上成功制备了 Bi OCl0.5Br0.5/Bi PO4双层异质结薄膜,并通过多种表征手段对薄膜的晶型结构、元素组成及化合价、形貌和尺寸特征、吸光性能和荧光强度进行了表征。结果表明,制备得到的复合薄膜呈现出上层为梭子状的 Bi PO4颗粒层分散在下层为 Bi OCl0.5Br0.5固溶体层的双层结构。这样的双层膜排列顺序使得光生电子和空穴在不同组分之间的界面电场作用下分别向薄膜两侧流动,促进光致载流子的分离,提高了 Bi OCl0.5Br0.5/Bi PO4复合薄膜的光催化活性。活性测试结果表明,在模拟太阳光照射 120 min 后,Bi OCl0.5Br0.5/Bi PO4复合薄膜对苯酚的降解率达到了 99.97%,是相同条件下制备的 Bi OCl/Bi PO4和 Bi O... 相似文献
928.
本文采用XRD、XPS、及H_2—TPD技术对不同Cu/Co比的几个RaneyCu-Co催化剂进行了表征.并与反应醇选择性进行了关联.结果表明:RaneyCu-Co催化剂均由不同Cu/Co比的两个Cu-Co固溶体相组成,还原(H_2,563K,2h)前,表面除有Cu ̄0和Co ̄0外,尚有少量Cu ̄(+1)和显著量的Co ̄(+2)存在,还原后,Cu ̄(+1)几乎消失,Co ̄(+2)仍有一定量存在,在反应温度下(563K),CO和CO_2均能使表面Co ̄0部分氧化,且CO_2氧化能力大于CO,而合成气(H_2/CO=2)表现为还原的性质。三种气氛对Cu ̄0无明显影响。催化剂表面Cu/Co比高于体相Cu/Co比,表面Cu富集显著.RaneyCu-Co催化剂表面有四种吸氢中心:Cu(弱吸氢中心),高配位Co(弱吸氢中心),低配位Co(活化吸氢中心),及强吸氢中心;对不同催化剂,表面低配位Co中心的比例与醇选择性有一致的变化规律。基于上述结果,就CO播入中心进行了讨论。 相似文献
929.
2,2-对苯二甲硫基二乙酸与醋酸钴在低热温度下的固-固相反应张卫华*忻新泉(湖北师范学院化学系黄石435002)(南京大学配位化学国家重点实验室南京)关键词2,2-对苯二甲硫基二乙酸,醋酸钴,固-固相反应,动力学1996-08-04收稿,1997... 相似文献
930.