全文获取类型
收费全文 | 2861篇 |
免费 | 295篇 |
国内免费 | 313篇 |
专业分类
化学 | 2172篇 |
晶体学 | 9篇 |
力学 | 214篇 |
综合类 | 47篇 |
数学 | 124篇 |
物理学 | 903篇 |
出版年
2024年 | 10篇 |
2023年 | 52篇 |
2022年 | 125篇 |
2021年 | 101篇 |
2020年 | 109篇 |
2019年 | 72篇 |
2018年 | 73篇 |
2017年 | 163篇 |
2016年 | 188篇 |
2015年 | 185篇 |
2014年 | 176篇 |
2013年 | 237篇 |
2012年 | 166篇 |
2011年 | 167篇 |
2010年 | 160篇 |
2009年 | 147篇 |
2008年 | 141篇 |
2007年 | 153篇 |
2006年 | 161篇 |
2005年 | 108篇 |
2004年 | 119篇 |
2003年 | 98篇 |
2002年 | 77篇 |
2001年 | 59篇 |
2000年 | 63篇 |
1999年 | 57篇 |
1998年 | 45篇 |
1997年 | 36篇 |
1996年 | 30篇 |
1995年 | 23篇 |
1994年 | 26篇 |
1993年 | 24篇 |
1992年 | 12篇 |
1991年 | 17篇 |
1990年 | 18篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有3469条查询结果,搜索用时 31 毫秒
991.
Christian Capezza Antonio Lepore Alessandra Menafoglio Biagio Palumbo Simone Vantini 《商业与工业应用随机模型》2020,36(3):477-500
To respond to the compelling air pollution programs, shipping companies are nowadays setting‐up on their fleets modern multisensor systems that stream massive amounts of observational data, which can be considered as varying over a continuous domain. Motivated by this context, a novel procedure is proposed, which extends classical multivariate techniques to the monitoring of multivariate functional data and a scalar quality characteristic related to them. The proposed procedure is shown to be also applicable in real time and is illustrated by means of a real‐case study in the maritime field on the continuous monitoring of operating conditions (ie, the multivariate functional data) and total CO2 emissions (ie, the scalar quality characteristic) at each voyage of a cruise ship. The real‐time monitoring is particularly helpful for promptly supporting managerial decision making by indicating if and when an anomaly occurs during the navigation. 相似文献
992.
J. Knorr 《Isotopes in environmental and health studies》2013,49(8):310-314
Ein neuartiges Verfahren und eine Meβanordnung zu kontinuierlichen, berūhrungslosen und zerstörungsfreien Durchmesser-kontrolle werden beschrieben. Als Meβgut kommen strangförmige Gebilde, wie Kabel, Drāhte oder Rohre, in Betracht. Strahlenquelle und Detektor sind so angeordnet, daβwert ein Maβ für die Querschnittsflāche des Prüflings senkrecht zur Abzugsrichtung ist. Dadurch kann z. B. bei der Kabelfertigung der Ummantelungsprozeβ nicht nur fūr Leiter mit kreisförmigem Querschnitt, sondern auch für solche mit elliptischem oder kreissektorförmigen Querschnitt ūberwacht werden. Positions-änderungen des Meβgutes relativ zur Meβstrecke haben keinen Einfluβ auf den Meβwert. Mit dem beschriebenen Funktionsmuster können Durchmesseründerungen von 0,02 mm für Material mit kreisförmigem Querschnitt im Durchmesserberich 3 bis 20 mm nachgewiesen werden. 相似文献
993.
Nikolaos Stamatis Vassilios Triantafyllidis Dimitra Hela 《International journal of environmental analytical chemistry》2013,93(15):1602-1619
The occurrence of eight pharmaceutical compounds (PhCs), two metabolites and caffeine was investigated in River Acheloos, located in Western Greece, during a twelve-month monitoring period (March 2007–February 2008). Solid-phase extraction (SPE) was used for the extraction and pre-concentration of the target pollutants and gas chromatography mass spectrometry (GC–MS) for the detection and quantification. Recoveries were determined between 74.0–100.4% for distilled water and 72.6–95.1% for the river water, whereas the relative standard deviation was less than 9.4% for distilled water and 8% for the river water, respectively. The limits of detection ranged between 1–40 ng L?1. Two pharmaceuticals (paracetamol and carbamazepine), caffeine and the metabolite (salicylic acid), have been detected in all the analysed samples. Maximum concentration levels determined in river samples reached 305 ng L?1 recorded for paracetamol. The concentrations of target compounds were significantly higher in the samples collected at the sampling station situated after the wastewater treatment plant (WWTP) of Agrinio City compared to the samples collected in upper and lower parts of the river. Seasonal variations were attributed mainly to river flow variations and removal percentages by WWTP. Risk quotient method for median environmental concentrations revealed minimal to median risk with the exception of triclosan, ibuprofen and diclofenac, which presented high risk when maximum environmental concentrations were used. 相似文献
994.
J. I. Baumbach D. Berger J. W. Leonhardt D. Klockow 《International journal of environmental analytical chemistry》2013,93(1-4):189-193
Abstract Ion mobility spectrometry is a technique for generating ions at atmospheric pressure via ion-molecule reactions, and for analysing them in an ion drift tube. The time required for the ions to traverse the length of the drift tube is mainly a function of the mass and the charge of the ions. Besides, ion shape and polarizability also affect the drift time. Ion mobility spectrometry does not allow structural identification and quantification of unknown substances in mixtures. However, under certain boundary conditions it provides selective fingerprints of the substances to be observed, and operates at the ppbv concentration level and the millisecond time scale. Through further miniaturization of a recently developed instrument of this type an ion mobility sensor is to be constructed. This sensor includes drift channel, operating shutter, collecting electrode, electronic data acquisition and translation board. The sensor makes possible to obtain real-time ion mobility spectra. We present and discuss the concept of a small ion mobility spectrometer, its operation principle and first results on the way towards its further miniaturization. 相似文献
995.
Abstract: This article reviews the most recent applications of Raman spectroscopy (RS) in tissue engineering and regenerative medicine (TERM). Raman spectroscopy can potentially alleviate the current lack of capabilities to capture important biological data beyond the standard metabolite and pH indicators in tissue bioreactors. Key process components in bioreactors that are important to evaluate cellular integrity and functionality of tissue-engineered constructs include cells, scaffolds, and proteins. A number of studies are discussed to highlight the capability of RS in noninvasive, nondestructive, and label-free in situ analysis. Protein detection is emphasized due to the urgent need for faster and cheaper techniques. The extensiveness of protein detection studies and the inadequacy of current technology formulate the basis for detailing relevant methods seeking to improve the detection limit, specificity, or multiplexing performance of RS. We argue that RS has great promise to solve the key problem in tissue bioprocessing, namely, inadequate monitoring capabilities that handicap TERM from rising to prevalence in clinical practice. 相似文献
996.
This review covers the concepts of photonic crystal (PhC) and its usage for the sensing of environmental pollutants. PhCs are composed of periodic and ordered nanostructures which can manipulate the diffraction or reflection of light propagation through the structures. If the light spectra locate in the visible range, the color of materials can be observed by naked eye. The optical properties of PhCs are determined by the lattice constant of the crystal or by the refractive index contrast between the colloids and the surrounding medium. Based on these features, responsive PhCs can be designed to detect the environmental pollutants. In this review, we primarily described the photonic crystals for the sensing of volatile organic compounds (VOCs), organophosphates (OPs), heavy metal ions and endocrine disrupting chemicals (EDCs), and these sensors exhibited excellent sensitivity and are promising for the on-site monitoring of pollutants. 相似文献
997.
通过改变基于宽范围粒径谱仪的温度控制方法,研究温度变化对气溶胶浓度的影响和作用.本文首先对宽范围粒径谱仪进样系统温度控制方法进行改进,即采用钽管加热器及不加热切换的温度控制方法来改变宽范围粒径谱仪进样部分温度,使用改进后的系统测量室内外大气气溶胶,对不同温度下大气气溶胶的浓度分布情况进行讨论与分析.结果表明室外粒子数浓度分布的峰值与室内粒子浓度分布的峰值相比,室内空气中粒子数浓度峰值明显要小,即室外大气中的粒径大的粒子更多.证实了宽范围粒径谱仪适用于大气气溶胶的检测,在环境检测中有广泛的应用前景. 相似文献
998.
Vera Yu. Mishina Irina V. Abrashina Andrei T. Teleshev Larisa K. Vasyanina Eduard E. Nifant'ev 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2425-2434
Interaction between the equimolecular amounts of glycols (diatomic phenols) and phosphorous acid triamides in diglyme or without solvent gives phosphorus-bearing polyamidophosphites. The structure of these compounds was studied by NMR spectroscopy, and it was shown that a partial disproportionation of amidophosphite fragments into phosphite ones can occur in the course of their synthesis. The chemical properties of the obtained compounds are being studied. First rhodium complexes with polyamidophosphite ligands were obtained. These complexes are shown to be more active hydrogenation catalysts than the corresponding low-molecular complexes. 1 相似文献
999.
M. M. El-Dessouky 《Isotopes in environmental and health studies》2013,49(8):404-405
The publication shows the radiological measurements of rain water, cress, and milk before and after Chernobyl nuclear power accident. The measurements showed that Egyptian environment was affected by the accident, but the increase of radioactive contamination was small and below the permissible. The paper suggests methodological procedures for measuring the growth activity in the studied materials. It offers also a simplified diagram for automatic national radiological monitoring station to measure the environmental background radiation by a routine way for detection any increase of radioactivity rapidly. This station enables the responsibles to take rapid and optimum decisions in time to lessen the environmental radiological contamination. 相似文献
1000.
为探究不同场地条件下远场地震动强度指标与结构最大响应的相关性问题,本文从K-NET和KiK-net台网强震记录中选取震级7级以上、断层距大于200 km的地震动记录1 328条,首先选用28个地震动强度指标进行了远场地震动强度指标与结构最大响应的总体相关性分析.然后,分别选取典型加速度类地震动强度指标、典型速度类地震动强度指标和典型位移类地震动强度指标进行了场地条件对结构最大响应相关性的影响分析.结果表明:(1) 加速度类地震动强度指标的相关系数随单自由度(SDOF)体系周期增大逐渐减小,与自振周期结构T≤1 s的低自振周期结构响应具有明显的相关性;速度类地震动强度指标的相关系数在T=2~5 s具有较大值,说明这一类指标与中长周期结构的响应具有明显相关性;当T>3~5 s时,典型位移类地震动强度指标的相关系数逐渐增大进入峰值区段,并保持较大的相关系数值,因此可以采用这一类指标表征长周期结构响应.(2) 对于加速度类地震动强度指标,Ⅰ、Ⅱ、Ⅲ类场地的相关系数随自振周期变化曲线走势较接近,Ⅳ类场地的相关系数值总体上要大于其它三类场地的相关系数.对于速度类地震动强度指标,在短周期区域,相关系数大小呈现Ⅰ<Ⅱ<Ⅲ<Ⅳ的特点;当T>2 s后,四类场地的相关系数随自振周期变化曲线趋势逐渐接近.对于位移类地震动强度指标,当T>3 s后,Ⅰ类场地和Ⅱ类场地的相关系数随自振周期变化曲线逐渐趋于一致,而Ⅲ类场地和Ⅳ类场地的相关系数随自振周期变化曲线也逐渐趋于一致. 相似文献