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41.
热辅助下的在线甲基衍生化-气相色谱法分析银杏叶中的银杏酸 总被引:2,自引:0,他引:2
采用热辅助下的在线甲基衍生化-气相色谱法测定银杏叶中的银杏酸。银杏叶样品与衍生化试剂四甲基氢氧化铵(TMAH, 25%甲醇溶液)同时进样,在300 ℃的进样口瞬间生成了银杏酸甲基衍生物,银杏叶中6种银杏酸得到很好的分离。在一定的质量浓度范围内银杏酸的线性关系良好,回归系数均大于0.9966,最低检出限范围为0.8~2.8 mg/kg。银杏叶中主要的烷基酚类物质为银杏酸C13∶0,C15∶1和C17∶1,它们的含量(用质量分数表示)分别为11.0%,36.7%和42.8%,3次平行测定的相对标准偏差(RSD)均小于3.4%(n=3)。银杏叶样品中总银杏酸的含量为4.0~10.9 mg/g。该方法无需繁琐费时的衍生化和纯化等前处理步骤,不失为银杏叶中银杏酸测定的一种快速、简便、准确的方法。 相似文献
42.
Beth Anne V. Bennett Zhongxian Cheng∗∗ Robert W. Pitz Mitchell D. Smooke 《Combustion Theory and Modelling》2013,17(3):497-527
Three axisymmetric laminar coflow diffusion flames, one of which is a nitrogen-diluted methane/air flame (the ‘base case’) and the other two of which consist of nitrogen-diluted methane vs. pure oxygen, are examined both computationally and experimentally. Computationally, the local rectangular refinement method is used to solve the fully coupled nonlinear conservation equations on solution-adaptive grids. The model includes C2 chemistry (GRI 2.11 and GRI 3.0 chemical mechanisms), detailed transport, and optically thin radiation. Because two of the flames are attached to the burner, thermal boundary conditions at the burner surface are constructed from smoothed functional fits to temperature measurements. Experimentally, Raman scattering is used to measure temperature and major species concentrations as functions of the radial coordinate at various axial positions. As compared to the base case flame, which is lifted, the two oxygen-enhanced flames are shorter, hotter, and attached to the burner. Computational and experimental flame lengths show excellent agreement, as do the maximum centreline temperatures. For each flame, radial profiles of temperature and major species also show excellent agreement between computations and experiments, when plotted at fixed values of a dimensionless axial coordinate. Computational results indicate peak NO levels in the oxygen-enhanced flames to be very high. The majority of the NO in these flames is shown to be produced via the thermal route, whereas prompt NO dominates for the base case flame. 相似文献
43.
通过6根圆形中空夹层钢管超高性能钢纤维混凝土(UHPSFRCFDST)柱爆炸破坏实验,研究了轴压、折合距离、空心率和迎爆面形状对其动态响应及损伤破坏的影响,并运用LS-DYNA软件建立了爆炸荷载作用下UHPSFRCFDST柱动态响应的有限元模型。在验证了模型有效性的基础上,运用参数化分析方法,研究了轴压比、空心率、含钢率、内层和外层钢管径厚比及其强度等关键参数对圆形UHPSFRCFDST柱抗爆性能的影响。结果表明:有限元模型能够有效地分析UHPSFRCFDST柱在爆炸荷载作用下的动态响应及损伤破坏;在小于临界轴压时,提高轴压比能够提升UHPSFRCFDST柱抗爆性能,但超过临界轴压后继续提高反而会加重其损伤破坏;减小空心率或内、外层钢管径厚比均可有效提升UHPSFRCFDST柱的抗爆性能,提高含钢率或外层钢管强度也能达到相同效果,但提高内层钢管强度对其抗爆性能的提升作用并不显著。 相似文献
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46.
在非离子表面活性剂存在下邻羧基苯基重氮氨基偶氮苯吸光光度法测定微量银 总被引:6,自引:0,他引:6
提出了一种测定微量银的吸光光度分析新方法。于硼砂-氢氧化钠缓冲溶液中(pH 10.5~11.0),在乳化剂OP存在下,Ag(Ⅰ)与邻羧基苯基重氮氨基偶氮苯(OCDAA)形成1:3稳定的红色配合物,其λ_(max)=540nm,对比度△λ=126nm,表观摩尔吸光系数ε_(540)=8.2×10~4。而在pH 10.0~10.6的相同缓冲溶液中,改用Triton X-100,且加入三乙醇胺后,配合物的λ_(max)=546nm,△λ=136nm,ε_(546)=9.9×104。两种显色体系均在Ag(Ⅰ)0~12μg/25ml范围内服从比耳定律。研究了显色反应条件和共存离子的影响。在试液中加入浓硫酸后加热处理和EDTA的掩蔽作用下,方法用于定影液的分析,六次测定的相对标准偏差为2.3%,平均回收率为98.3%。 相似文献
47.
We propose an algorithm of global multiple sequence alignment that is based on a measure of what we call information discrepancy. The algorithm follows a progressive alignment iteration strategy that makes use of what we call a function of degree of disagreement (FDOD). MSAID begins with distance calculation of pairwise sequences, based on FDOD as a numerical scoring measure. In the next step, the resulting distance matrix is used to construct a guide tree via the neighbor-joining method. The tree is then used to produce a multiple alignment. Current alignment is next used to produce a new matrix and a new tree (with FDOD scoring measure again). This iterative process continues until convergence criteria (or a stopping rule) are satisfied. MSAID was tested and compared with other prior methods by using reference alignments from BAliBASE 2.01. For the alignments with no large N/C-terminal extensions or internal insertions MSAID received the top overall average in the tests. Moreover, the results of testing indicate that MSAID performs as well as other alignment methods with an occasional tendency to perform better than these prior techniques. We, therefore, believe that MSAID is a solid and reliable method of choice, which is often (if not always) superior to other global alignment techniques. 相似文献
48.
The one-pot, palladium-catalyzed, three-component coupling of aryl bromides, internal alkynes, and environmentally friendly K4[Fe(CN)6] provides an efficient and direct method for the preparation of beta-arylalkenylnitriles. 相似文献
49.
Cobalt‐based catalyst, as a typical catalyst for volatile organic compounds (VOCs) combustion, has attracted extensive attention. However, the catalytic activity of pure Co3O4 is difficult to meet the requirements of practical application especially at low temperatures. Therefore, it is key to find an effective way to improve the catalytic performance of Co3O4. In this paper, Co3O4 is modified by engineering a combination of structural template and Ce dopant. The various characterization results verify that the template agent and the doping of appropriate Ce lead to great changes in the texture property and low temperature reducibility of Co3O4, thus resulting in superior catalytic performances of obtained mesoporous CexCoO catalysts. In particular, the best catalyst, Ce0.05CoO, achieves a toluene conversion of T90% at 238°C, which is significantly lower than many of the Co‐based catalysts reported in previous literatures. Furthermore, the toluene conversion rate maintains above 90% during 100 h at 238°C. The excellent catalytic performance of Ce0.05CoO can be attributed to its large specific surface area, uniform pore structure, good low temperature reducibility, and abundant surface oxygen species. 相似文献
50.
Xia Futing Song Zhongxian Liu Xin Liu Xi Yang Yinhua Zhang Qiulin Peng Jinhui 《Research on Chemical Intermediates》2018,44(4):2703-2717
Research on Chemical Intermediates - FeO x , MnO x and Fe–Mn–O x catalysts were prepared by the co-precipitation method and used for the selective catalytic reduction (SCR) of NO x by... 相似文献