全文获取类型
收费全文 | 2140篇 |
免费 | 212篇 |
国内免费 | 282篇 |
专业分类
测绘学 | 74篇 |
大气科学 | 164篇 |
地球物理 | 372篇 |
地质学 | 424篇 |
海洋学 | 481篇 |
天文学 | 7篇 |
综合类 | 118篇 |
自然地理 | 994篇 |
出版年
2024年 | 15篇 |
2023年 | 35篇 |
2022年 | 100篇 |
2021年 | 155篇 |
2020年 | 105篇 |
2019年 | 107篇 |
2018年 | 92篇 |
2017年 | 98篇 |
2016年 | 115篇 |
2015年 | 99篇 |
2014年 | 129篇 |
2013年 | 133篇 |
2012年 | 93篇 |
2011年 | 116篇 |
2010年 | 97篇 |
2009年 | 132篇 |
2008年 | 103篇 |
2007年 | 113篇 |
2006年 | 133篇 |
2005年 | 143篇 |
2004年 | 78篇 |
2003年 | 89篇 |
2002年 | 53篇 |
2001年 | 64篇 |
2000年 | 64篇 |
1999年 | 49篇 |
1998年 | 26篇 |
1997年 | 26篇 |
1996年 | 14篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
排序方式: 共有2634条查询结果,搜索用时 703 毫秒
991.
992.
地球生态系统的气温和水温补充机制 总被引:1,自引:0,他引:1
首次提出了地球生态系统的气温和水温补充机制,并用框图模型说明了补充机制在运行过程中的每个流程,阐明了人类对生态环境的影响过程、生态环境变化对地球生态系统的影响过程以及地球生态系统对环境变化的响应过程,解释了气温和水温的补充起因。研究结果表明,人类是引起环境变化的起源以及其变化后的结果又作用于人类,即人类排放二氧化碳引起气温和水温的上升,地球生态系统又借助其补充机制使得气温和水温下降恢复到正常的动态平衡。尽管这个补充机制带来了沙尘暴、洪水和风暴潮,但由人类引起水温和气温上升造成的灾害要比自然界中这3种灾害要深重得多。自然界的这3种灾害是局部的、短期的,而人类引起水温和气温上升的灾害却是全球的、长期的。 相似文献
993.
海洋生态系统服务的分类与计量 总被引:9,自引:0,他引:9
通过界定海洋生态系统服务的概念和内涵以及分析其组成结构、生态过程及生物多样性等服务的来源,详细描述了海洋生态系统所提供的食品供给、原材料供给、基因资源、气候调节、空气质量调节、水质净化调节、有害生物与疾病的生物调节与控制、干扰调节、精神文化服务、知识扩展服务、旅游娱乐服务、初级生产、物质循环、生物多样性和提供生境等15项服务。根据这些服务的相似作用与性质,参照千年生态系统评估的分类体系,进一步归纳为供给服务、调节服务、文化服务以及支持服务这4大基本服务类型。同时,也对各项服务的内容、表现特征和计量特征进行了描述。海洋生态系统服务不仅是海洋管理的核心内容,提高和维持海洋生态系统服务更是海洋管理的最终目标。 相似文献
994.
为了诊断运营中隧道病害的程度,需要对隧道衬砌作出系统评价.本文结合工程实际,阐述了采用地质雷达对隧道衬砌进行检测的原理及方法,采取提高检测效果的方法和技术措施,并通过典型雷达图像分析了衬砌结构完整性和衬砌厚度识别判定特征,取得了较好的检测效果,为隧道整体健康诊断提供依据. 相似文献
995.
996.
A three-dimensional coupled physical-biological model study in the spring of 1993 in the Bohai Sea of China 总被引:1,自引:1,他引:0
A three-dimensional (3-D) coupled physical and biological model was used to investigate the physical processes and their influence on the ecosystem dynamics of the Bohai Sea of China. The physical processes include M2 tide, time-varying wind forcing and river discharge. Wind records from 1 to 31 May in 1993 were selected to force the model. The biological model is based on a simple, nitrate and phosphate limited, lower trophic food web system. The simulated results showed that variation of residual currents forced by M2 tide, river discharge and time-varying wind had great impact on the distribution of phytoplankton biomass in the Laizhou Bay. High phytoplankton biomass appeared in the upwelling region. Numerical experiments based on the barotropic model and baroclinic model with no wind and water discharge were also conducted. Differences in the results by the baroclinic model and the barotropic model were significant: more patches appeared in the baroclinic model comparing with the barotropic model. And in the baroclinic model, the subsurface maximum phytoplankton biomass patches formed in the stratified water. 相似文献
997.
998.
Integrating the ecosystem service in sustainable plateau spatial planning: A case study of the Yarlung Zangbo River Basin 总被引:2,自引:2,他引:0
The Yarlung Zangbo River Basin(YZRB) is a key ecological protection area on the Qinghai–Tibet Plateau(QTP). Determination of the ecosystem service values(ESVs) can help recognize the benefits of sustainable management. It is gradually becoming the main path that constructs plateau spatial planning of integrating ecological protection, and achieves global sustainable development goals(SDGs) in China. In this paper, the spatio-temporal dynamic evolutions of the ESVs were estimated on the multiple scales of "basin, subbasin and watershed" from 1980 to 2015. The main factors influencing ESVs were explored in terms of physical geography, human activities, and climate change. It had been proposed that sustainable spatial planning including ecological protection, basin management, and regional development was urgent to set up. Our results show that the increase in wetland and forest and results in an increase of 9.4% in the ESVs. Attention should be paid to the reduction of water and grassland. Water conservation(WC), waste treatment(WT), and soil formation and conservation(SFC) are the most important ecosystem services in the YZRB. At present, the primary problem is to solve the ESVs decreasing caused by glacier melting, grassland degradation, and desertification in the upper reaches region. The middle reaches should raise the level of supply services. Regulation services should be increased in the lower reaches region on the premise of protecting vegetation. The ESVs in adjacent watersheds are interrelated and the phenomenon of "high agglomeration and low agglomeration" is obvious, existing hot-spots and cold-spots of ESVs. Additionally, when the altitude is 4500-5500 m, the temperature is 3-8°C, and the annual precipitation is 350-650 mm, ESVs could reach its maximum. A framework of sustainable plateau spatial planning could provide references to delimit the ecological protection red line, key ecological function zone, and natural resource asset accounting on the QTP. 相似文献
999.
气候变化对环境与健康的影响日益受到关注。分析了气候变化对大气环境、水环境和土壤环境的胁迫效应,阐述了气候变化对生态系统和人体健康的影响,并概述了气候变化对不同介质环境以及对生态系统与人体健康影响研究的进展。这一工作可以为今后气象与环境领域开展进一步研究提供基本框架。 相似文献
1000.
Muyingle is a new type of health food prepared from marine organisme. The mammotropic action ofMuyingte was investigated by studying its effect on mammary glands and pituitary glands of lactating miceand the survival rate of suckling mice. The results showed that the mammotropic action of Muyingle wasvery effective.The survival rates of suckling mice were 92.90% for the treated group and 0 for the controlgroup (p<0.01). The weights of mammary gland were 163±51.1mg/10g (weight of mouse)for the treatedgroup and 98.5±18.4 mg/10g for the control group (p<0.01). Histological examinations suggestal thatmammary glands from the treated group were at the secreting stages, while those from the control groupwere at the resting stages. Clinical tests also demonstrated that Muyingle was highly effective in promotinglactation and improving the quality of the puerpera's milk. The efficiency was up to 86.7%. 相似文献