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981.
地表覆盖是地理国情监测的重要对象,为地理国情分析评价模型提供了可靠的数据源.高效的地表覆盖数据检索方法是挖掘地表覆盖数据潜在价值的前提.由于地表覆盖数据体量庞大、更新频繁,要素分布密集且不均匀,传统的空间检索方法出现了扩展困难、检索能力不足等问题.提出了一种基于HBase与静态多级格网索引的地表覆盖数据空间检索方法,针对地表覆盖数据特征设计了基于HBase的静态多级格网索引,利用MapReduce实现索引并行构建,通过多级过滤的方式,提高了地表覆盖空间范围的查询效率.实验表明,该方法能快速完成大规模、密集分布的地表覆盖数据的空间索引构建,提升空间检索性能,并具有良好的扩展性,可为其他海量空间矢量数据的检索提供借鉴. 相似文献
982.
983.
984.
It is well recognized that frost formation on heat exchanger surfaces seriously affects the performance of a refrigeration system. Consequently, defrosting is essential, yet it is only effective when both analytical tools and comprehensive experimental data on frost formation are available. In air conditioning units, frost formation most commonly takes place in the entrance region of the heat exchanger. Therefore, in this study, an experimental investigation was undertaken to characterize the effect of environmental conditions on the frost growth occurring on a vertical plate in the hydrodynamically and thermally developing region. Several experiments were performed while four environmental parameters, inlet air temperature, inlet air humidity, air velocity and cooling surface temperature, were varied. The thickness, mass, and density of the frost layer were determined from the measured data and empirical correlations were reduced from dimensionless parameters. 相似文献
985.
结构健康监测中的损伤检测技术研究进展 总被引:35,自引:0,他引:35
对结构健康监测研究中的结构损伤检测方法及其特点进行了介绍.从基于结构模态分析的方法和基于结构动态试验信号处理的方法两方面,阐述了结构健康监测中的损伤检测方法及其最新研究进展.基于结构模态分析的结构损伤检测方法是针对整个结构的检测,使用的模态都限于低阶模态范围内,所检测的结构应容易建立有限元模型,便于进行响应预测.基于结构动态试验信号处理的损伤检测方法通常是针对结构局部构件的损伤检测,不需要对结构进行有限元建模,而直接从测试的动态响应信号中提取表征结构损伤的特征参数.文中提出了对比性损伤检测方法和非对比性损伤检测方法的概念,并对结构损伤检测中常用的信息传感与处理技术进行了论述,指出了结构损伤检测研究中应该考虑的传感器布置问题.提出了将损伤信息的主动检测与被动检测相结合进行损伤程度判断和剩余寿命估计等问题是有待进一步深入研究的课题. 相似文献
986.
As failures of rolling bearings lead to major failures in rotating machines, recent vibration-based rolling bearing fault diagnosis techniques are focused on obtaining useful fault features from the huge collection of raw data. However, too many features reduce the classification accuracy and increase the computation time. This paper proposes an effective feature selection technique based on intrinsic dimension estimation of compressively sampled vibration signals. First, compressive sampling (CS) is used to get compressed measurements from the collected raw vibration signals. Then, a global dimension estimator, the geodesic minimal spanning tree (GMST), is employed to compute the minimal number of features needed to represent efficiently the compressively sampled signals. Finally, a feature selection process, combining the stochastic proximity embedding (SPE) and the neighbourhood component analysis (NCA), is used to select fewer features for bearing fault diagnosis. With regression analysis-based predictive modelling technique and the multinomial logistic regression (MLR) classifier, the selected features are assessed in two case studies of rolling bearings vibration signals under different working loads. The experimental results demonstrate that the proposed method can successfully select fewer features, with which the MLR-based trained model achieves high classification accuracy and significantly reduced computation times compared to published research. 相似文献
987.
988.
Javier D. Breccia Nelson Torto Lo Gorton Faustino Siñeriz Rajni Hatti-Kaul 《Applied biochemistry and biotechnology》1998,69(1):31-40
A thermostable xylanase purified from a strain of Bacillus amyloliquefaciens MIR 32 was characterized with respect to its
substrate specificity and mode of hydrolytic action. The enzyme was highly specific for xylans as substrate and displayed
no activity toward other polysaccharides, including cellulose. The enzyme exhibited Km and Vmax of 4.5 mg/mL and 0.58 mmol/min/mg, respectively, with birchwood xylan as the substrate. Microdialysis sampling with anion
exchange chromatography and integrated pulsed electrochemical detection were used for rapid on-line monitoring of products
during hydrolysis of oat spelt and bagasse xylan, and xylooligosaccharides. Xylobiose and xylotriose were the main end products.
Xylotetraose was the smallest oligosaccharide to be acted on by the xylanase. The product pattern confirmed that the enzyme
was an endoxylanase. 相似文献
989.
Different experimental approaches have been suggested in the last few decades to determine metal species in complex matrices of unknown composition as environmental waters. The methods are mainly focused on the determination of single species or groups of species.The more recent developments in trace elements speciation are reviewed focusing on methods for labile and free metal determination.Electrochemical procedures with low detection limit as anodic stripping voltammetry (ASV) and the competing ligand exchange with adsorption cathodic stripping voltammetry (CLE-AdCSV) have been widely employed in metal distribution studies in natural waters. Other electrochemical methods such as stripping chronopotentiometry and AGNES seem to be promising to evaluate the free metal concentration at the low levels of environmental samples. Separation techniques based on ion exchange (IE) and complexing resins (CR), and micro separation methods as the Donnan membrane technique (DMT), diffusive gradients in thin-film gels (DGT) and the permeation liquid membrane (PLM), are among the non-electrochemical methods largely used in this field and reviewed in the text. Under appropriate conditions such techniques make possible the evaluation of free metal ion concentration. 相似文献
990.
便携式气相色谱-质谱仪测定空气中挥发性有机污染物的准确性 总被引:4,自引:0,他引:4
便携式气相色谱-质谱仪(便携式GC-MS)能同时对多组分复杂有机物进行定性定量分析,在环境监测尤其是事故现场应急监测中发挥越来越重要的作用。本文比较了便携式GC-MS与EPATO-14A方法分析测定环境空气中低浓度挥发性有机物(VOCs)的性能,并探讨了利用定量环(loop环)模式测定高浓度VOCs的准确度。结果表明,采用内标标准曲线定量,HAPSITE便携式GC-MS测定空气中VOCs的检出限与EPATO-14A方法相当,准确度和精密度略低,但均符合环境监测分析的要求。利用loop环可对大部分10-6级的高浓度VOCs样品进行较为准确的测定,在突发性环境污染事故中可以得到基本准确的结果。 相似文献