全文获取类型
收费全文 | 5080篇 |
免费 | 518篇 |
国内免费 | 992篇 |
专业分类
测绘学 | 439篇 |
大气科学 | 528篇 |
地球物理 | 1531篇 |
地质学 | 2452篇 |
海洋学 | 700篇 |
天文学 | 154篇 |
综合类 | 344篇 |
自然地理 | 442篇 |
出版年
2024年 | 43篇 |
2023年 | 76篇 |
2022年 | 89篇 |
2021年 | 116篇 |
2020年 | 74篇 |
2019年 | 99篇 |
2018年 | 134篇 |
2017年 | 76篇 |
2016年 | 107篇 |
2015年 | 88篇 |
2014年 | 199篇 |
2013年 | 140篇 |
2012年 | 176篇 |
2011年 | 260篇 |
2010年 | 165篇 |
2009年 | 167篇 |
2008年 | 263篇 |
2007年 | 245篇 |
2006年 | 302篇 |
2005年 | 292篇 |
2004年 | 236篇 |
2003年 | 208篇 |
2002年 | 191篇 |
2001年 | 123篇 |
2000年 | 206篇 |
1999年 | 150篇 |
1998年 | 162篇 |
1997年 | 217篇 |
1996年 | 150篇 |
1995年 | 173篇 |
1994年 | 170篇 |
1993年 | 192篇 |
1992年 | 149篇 |
1991年 | 183篇 |
1990年 | 121篇 |
1989年 | 121篇 |
1988年 | 98篇 |
1987年 | 81篇 |
1986年 | 47篇 |
1985年 | 79篇 |
1984年 | 61篇 |
1983年 | 58篇 |
1982年 | 41篇 |
1981年 | 33篇 |
1980年 | 42篇 |
1965年 | 12篇 |
1964年 | 18篇 |
1959年 | 15篇 |
1958年 | 24篇 |
1957年 | 15篇 |
排序方式: 共有6590条查询结果,搜索用时 484 毫秒
981.
分析了东寨港海水、表层沉积物和生物体中重金属Cu、Zn、Pb、Cd、Hg、类金属As的含量及分布特征,并运用单因子指数法、地积累指数法评价了该调查区重金属污染程度。结果表明:东寨港海水中除Pb的含量符合二类海水标准外,其余含量均符合一类海水标准,且远低于渔业水质标准限值;表层沉积物中典型重金属元素含量都符合海洋沉积物质量一类标准,基本属于无污染区;本区湿地沉积物中的重金属含量比岛内及周边区典型红树林湿地略偏高;红树林及暗滩沉积物中重金属比东寨港水底沉积物重金属含量高,表明河口湾潮滩上的红树林区可能是重金属元素的富集区,东寨港目前可能受到了陆源污染的影响;生物体中重金属含量均符合一类标准,符合无公害水产品的要求。 相似文献
982.
为了提升天气雷达对弱气象目标的发现能力,扩展系统观测的动态范围,可以从改善雷达回波的输出信噪比方面来考虑.从信号处理算法层面寻求改善天气雷达回波的输出信噪比的方法,提出运用小波变换的方法来达到这个目的.首先介绍了小波消噪的基本原理,再结合具体雷达系统参数,进行了相关的算法模拟,其结果表明,在符合高斯谱特征分布的模拟回波在不同信噪比(-20~10dB)设定条件下,运用小波变换的去噪方法可以使其信号的输出信噪比提高大约5~11dB,为天气雷达探测更多的弱气象目标提供了有利条件. 相似文献
983.
本文以SOA开放式架构与OGC标准规范,提出了极地海冰-海洋参数遥感反演模型分布式共享服务体系。服务体系以"模型服务"为核心,探讨了模型服务接口和模型服务的互操作问题。为了简化极地海冰-海洋参数遥感反演模型的分布式共享过程,提出了极地海冰-海洋参数遥感反演模型共享服务平台的概念。共享服务平台处于模型与模型应用客户端之间,可以实现两者之间的数据转化和功能协同,以及实现模型算法与其他功能的分离,使模型开发者可以专注于模型算法的设计和实现。最后,以海冰密集度遥感反演模型和冰间湖识别模型为例,实现了极地海冰-海洋参数遥感反演模型分布式共享方法。 相似文献
984.
文章根据新一轮重要矿产资源利用现状调查成果,通过查明的资源储量的数量、类型、结构、品质、空间分布等数据,对广西锡矿资源禀赋特征进行分析,对勘查及开发利用现状及资源保障能力进行研究。锡矿是广西的优势矿产,查明的资源储量位列全国第二,具有规模大、品位高、分布高度集中、可集中开发的优势,利用程度高,但保有资源储量下降过快,资源后备基地明显不足,按照矿山设计产能估算广西锡矿资源静态保障年限为24年,迫切需要加大锡矿资源地质勘查力度,实施更严格的总量控制指标、调整贸易税率等政策和措施,对广西锡矿资源的开发和保护进行控制和管理,同时加强矽卡岩型难选冶锡矿、低品位锡矿的利用研究,以提高共伴生矿产综合利用率。 相似文献
985.
The membrane interface probe (MIP) is widely used to characterize the subsurface distribution of volatile organic compounds (VOCs). One problem that arises during MIP application is that disproportionately high MIP signals are obtained after passing source zones which contain mobile or residual phases. This serious problem occurs because of a carry-over effect, in particular caused by compound-specific retention times in the conventional unheated transfer line, commonly used during such an investigation. The objective of this study was to perform a qualitative methodical field evaluation of the carry-over effect of a conventional MIP system with a conventional unheated transfer line. This was achieved by coupling a mobile mass spectrometer to the MIP device. Results obtained were then further compared with those achieved using a laser induced fluorescence (LIF) system. Because of this coupling, time- and depth-dependent signals for different substances became known. Field evaluation data obtained showed complex superpositions of compounds with MIP system results. As a result of this superposition, MIP signals from the saturated zone beneath the source zone (zone with free and/or residual phase) are blurred and are therefore not representative of particular depths. However, utilizing multidirectional probing alongside conventional MIP probing (forwards and backwards), it was possible to detect the upper and lower phase boundary of the source zone. These MIP results correlated excellently with the LIF results. An important conclusion that can be drawn from the field investigation is that coupling a mobile mass spectrometer to the MIP system enables advanced MIP signal interpretation to be successfully achieved. 相似文献
986.
Assessment of the effects of a marine urban outfall discharge on caged mussels using chemical and biomarker analysis 总被引:1,自引:0,他引:1
de los Ríos A Juanes JA Ortiz-Zarragoitia M López de Alda M Barceló D Cajaraville MP 《Marine pollution bulletin》2012,64(3):563-573
To assess the presence of endocrine disruptors in treated marine outfall discharges and their possible effects, mussels (Mytilus galloprovincialis) were caged in the environmental mixing zone of the outfall of the Santander sanitation system and in one control area. After 30, 60 and 90 days, samples were collected to perform chemical analyses (metals, anionic surfactants, alkylphenols, bisphenol A, phthalates and estrogenic hormones), biomarkers of general stress (lysosomal membrane stability-LMS, histopathology) and biomarkers of endocrine disruption (vitellogenin-like proteins and gonad index). There were no significant differences between outfall and control sites on contaminant levels, except for 4-tert-octylphenol which was higher in the outfall site. Bacteriological counts were higher in the outfall area. No relevant differences in biomarkers were detected between treated and control mussels. A significant reduction in LMS occurred in both groups after 90 days caging, indicating a stress situation possibly related to caging or to post-spawning reproductive state. 相似文献
987.
Macrobenthic community structure in the northern Saudi waters of the Gulf, 14 years after the 1991 oil spill 总被引:1,自引:0,他引:1
Joydas TV Qurban MA Al-Suwailem A Krishnakumar PK Nazeer Z Cali NA 《Marine pollution bulletin》2012,64(2):325-335
The 1991 Gulf oil spill heavily impacted the coastal areas of the Saudi waters of the Arabian Gulf and recent studies have indicated that even 15 years after the incident, macrobenthos had not completely recovered in the sheltered bays in the affected region such as, Manifa Bay. This study investigates the community conditions of macrobenthos in the open waters in one of the impacted areas, Al-Khafji waters, about 14 years after the spill. Diversity measures and community structure analyses indicate a healthy status of polychaete communities. The BOPA index reveals that oil sensitive amphipods were recolonized in the study area. This confirms that the benthic communities of the oil spill impacted area had taken only <14 years to recover in the open waters of the impacted areas. The study also reveals the existence of three distinct polychaete communities along the depth and sediment gradients. 相似文献
988.
Cantarero S Camino-Sánchez FJ Zafra-Gómez A Ballesteros O Navalón A Vílchez JL Verge C Reis MS Saraiva PM 《Marine pollution bulletin》2012,64(3):587-594
The contamination of aquatic environments has become the focus of increasing regulation and public concern due to their potential and unknown negative effects on the ecosystems. The present work develops a monitoring and statistical study, based on the analysis of variance test (ANOVA) and the multivariable analysis, both for insoluble soap and LAS in order to compare the behavior of different anionic surfactants in this environmental compartment. First, a novel and successfully validated methodology to analyze insoluble soap in these samples is developed. The matrix effect and the comparison of different extraction techniques were also performed. The optimized analytical methodologies were applied to 48 representative samples collected from the Almeria Coast (Spain) and then a statistical analysis to correlate anionic surfactant concentration and several variables associated with marine sediment samples was also developed. The results obtained showed relevant conclusions related to the environmental behavior of anionic surfactants in marine sediments. 相似文献
989.
Carroll C Waters D Vardy S Silburn DM Attard S Thorburn PJ Davis AM Halpin N Schmidt M Wilson B Clark A 《Marine pollution bulletin》2012,65(4-9):136-149
Targets for improvements in water quality entering the Great Barrier Reef (GBR) have been set through the Reef Water Quality Protection Plan (Reef Plan). To measure and report on progress towards the targets set a program has been established that combines monitoring and modelling at paddock through to catchment and reef scales; the Paddock to Reef Integrated Monitoring, Modelling and Reporting Program (Paddock to Reef Program). This program aims to provide evidence of links between land management activities, water quality and reef health. Five lines of evidence are used: the effectiveness of management practices to improve water quality; the prevalence of management practice adoption and change in catchment indicators; long-term monitoring of catchment water quality; paddock & catchment modelling to provide a relative assessment of progress towards meeting targets; and finally marine monitoring of GBR water quality and reef ecosystem health. This paper outlines the first four lines of evidence. 相似文献
990.
Muñoz-Barbosa A Gutiérrez-Galindo EA Daesslé LW Orozco-Borbón MV Segovia-Zavala JA 《Marine pollution bulletin》2012,64(2):405-409
In 1992 and 2004, heavy metals concentrations were measured in surficial sediments from Todos Santos Bay, located in Ensenada, Baja California, Mexico. The aim was to search for relationships between metal enrichment factors and a biological adverse effects index. Unlike Ni, the elements Cd, Cu and Zn showed significant correlations (p<0.05) between enrichment factors and the biological adverse effects index. Cu showed a 0.74:1 relationship, which means that any enrichment above 0.74 could represent biological adverse effects. On the other hand, Cd and Zn enrichments must be >5.5 and >1.5, respectively, in order for the sediments to be considered toxic. In general, data showed that most of the metal concentrations in Todos Santos Bay sediments could not cause adverse effects to biota. Only Ensenada's harbor and the zone next to a dredging dumping site showed metal enrichments that could be toxic. 相似文献