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排序方式: 共有484条查询结果,搜索用时 46 毫秒
461.
利用正交拟群的特点, 克服Edon80的弱点, 设计了称为Double40的二进制加法同步流密码算法. 它基于一对8阶相互正交的自正交拟群, 使得Johansson和Hell的密钥恢复攻击对Double40无法奏效. 相似文献
462.
将超声辅助碱液分解杂质与溶剂萃取相结合,采用气相色谱-电子捕获检测(GC-ECD)建立了一种快速高效净化、萃取海洋沉积物中8种常见多溴联苯醚(PBDEs)的分析方法。样品在2.00 mol/L NaOH甲醇溶液中超声30 min,经正己烷萃取、单层硅胶净化、正己烷洗脱、旋蒸浓缩后定容至100 μL,采用GC-ECD分析。结果表明,PBDEs各单体的加标回收率为63.6%~110.3%,相对标准偏差(RSD)为1.7%~15.5%(n=5);十溴联苯醚(BDE-209)的检出限为0.097 ng/g,其他7种单体的检出限为0.002~0.011 ng/g(信噪比为3)。该方法的准确度和精密度较高,稳定性和回收率良好,可满足沉积物中PBDEs的分析要求。利用建立的方法测定了渤海表层沉积物中PBDEs的含量,8种PBDEs总含量在1.566~6.760 ng/g之间,其中BDE-209的含量为1.461~6.438 ng/g,总体呈现出由近岸向远岸递减的趋势,表明人为活动、表层冲刷和陆地河流的输入对渤海地区PBDEs的含量有重要影响。 相似文献
463.
Yuan D Petersen C Rynd M Mainquist J Meyer A Isbell JJ 《Journal of chromatography. A》2005,1092(2):228-234
Following purification, the fractions of purified samples typically are analyzed to determine the relative purities of each fraction. We report a novel technique for performing post-purification analysis immediately after each preparative LC/MS run. The Single Pass Compound Purification and Analysis System (SPACPASS) samples and stores a representative aliquot from the fraction while it is being collected. Demonstrated for '1:1' fraction collections, this method of fraction purity assessment streamlined sample processing by reducing post-purification sample handling. For 97% of the collected fractions, this technique provided relative purities to within +/-5% when compared with more traditional post-purification analysis. 相似文献
464.
The utility of 29Si NMR spectroscopy has been demonstrated on sediment-like materials in the quantitative and qualitative determination of polyorganosiloxanes (silicones) in selected environmental samples. This technique is highly selective for polydimethylsiloxanes (PDMS) and is non-destructive to the sample. Also, specific identification of polyorganosiloxanes in sediment is possible, in contrast to previous methods which provided only quantitative information while consuming the sample. The detection limit for a 9 h experiment is approximately 45 ppm. 相似文献
465.
S. Pedersen-Bjergaard S. I. Semb J. Vedde E. M. Brevik T. Greibrokk 《Chromatographia》1996,43(1-2):44-52
Summary Electron capture detection (ECD), low- and highresolution mass spectrometry (LR- and HRMS), and atomic emission detection (AED) were compared for the gas chromatographic (GC) detection of polychlorinated biphenyls (PCBs) present in highly contaminated marine sediments. With ECD, LRMS, and even HRMS, detection was seriously disturbed by the complex matrix of the sediments, whereas AED in the chlorine-selective mode provided excellent PCB profiles without interferences. In addition, GC-AED provided congener independent responses, which enabled accurate quantitation of all PCBs based on a single calibration curve. However, because GC-AED was less sensitive than the other techniques studied, preparation of relatively large amounts of sample (10–20 g dry sediment) was required for most analyses. 相似文献
466.
467.
The methylation of tin(II) chloride by methyl iodide in porewater and formation of monomethyltin as the only methyltin product are described. A factorial experiment tested the effects of concentrations of tin(II), methyl iodide, and oxygen on monomethyltin yields. The experiments gave 0.18 to 12.8 % yield. Analysis of variance (ANOVA) calculations showed that all three variables were significant at the 95 % level. Comparison of yields in aqueous 23 g kg?1 sodium chloride solutions to those in porewater and to those containing fulvic acid, salicylic acid, and EDTA showed that only fulvic acid significantly reduced yields. Reasons for this observation are discussed and the findings in the model system are related to methylation of tin compounds in sediments. 相似文献
468.
Marta Ewelina Kobusińska Maria Witt Leszek Łęczyński 《International journal of environmental analytical chemistry》2018,98(5):453-476
This study comprises optimisation of sample preparation and HPLC analytical procedure for the determination of a personal care product ingredient, triclosan (TCS), in marine sediments. The testing of several varying pre-treatment parameters confirmed that ultrasonic extraction is an effective method for the isolation of TCS from marine sediments, and that the choice of extraction solvent appeared to be of major importance. The selection of the mobile-phase composition and the absorption wavelength was made for the high-performance liquid chromatography analysis step. Based on the validated method, a preliminary assessment of the benthic ecosystem quality with regards to TCS contamination has been demonstrated in the southern Baltic Sea – a semi-enclosed sea, characterised by poor water exchange, thus particularly susceptible to anthropopression. TCS has been identified and quantified in situ in marine bottom sediments, sediment dwelling isopod – Saduria entomon L. and estimated in silico in pore waters based on the equilibrium partition theory in order to assess the potential exposure and uptake from the aqueous phase. TCS concentrations identified in the bottom sediments of the Gdansk Basin, as the natural habitat for studied S.entomon L., appear to be threatening to the benthic environment. Particularly when considering S. entomon L. as a major nutrition source for cod (Gadus morhua) undergoing the feminisation process, since the recent studies prove TCS to have a potential to induce critical alterations in the endocrine system of marine ichthyofauna. 相似文献
469.
超椭圆柱设计表面能够减小线圈与目标的距离,提高空间利用率,扩大成像区域的有效范围.提出利用流函数法及柱面的可展性在超椭圆柱面上设计核磁共振成像系统中的梯度线圈.根据Biot-Savart定律建立磁场强度与流函数的表达式,采用最小二乘法和Tikhonov正则化方法构造了双目标设计函数.利用柱面的可展性提高了基于分片离散流函数计算电磁场的数值精度,通过L-曲线方法实现了正则参数的合理选取.通过引入适当的流函数边界约束条件,把梯度线圈的优化问题转化为适定线性方程组的直接求解问题.通过数值算例验证了超椭圆柱面展开求解方法的正确性.优化结果显示,在满足线性度误差小于5%的设计约束下,该方法在设计超椭圆柱面线圈驱动电流分布的同时有效控制了梯度线圈的能耗. 相似文献
470.