全文获取类型
收费全文 | 6845篇 |
免费 | 1019篇 |
国内免费 | 1573篇 |
专业分类
测绘学 | 532篇 |
大气科学 | 772篇 |
地球物理 | 2566篇 |
地质学 | 3396篇 |
海洋学 | 822篇 |
天文学 | 281篇 |
综合类 | 299篇 |
自然地理 | 769篇 |
出版年
2024年 | 81篇 |
2023年 | 106篇 |
2022年 | 120篇 |
2021年 | 150篇 |
2020年 | 153篇 |
2019年 | 121篇 |
2018年 | 148篇 |
2017年 | 84篇 |
2016年 | 141篇 |
2015年 | 152篇 |
2014年 | 235篇 |
2013年 | 211篇 |
2012年 | 285篇 |
2011年 | 438篇 |
2010年 | 234篇 |
2009年 | 212篇 |
2008年 | 392篇 |
2007年 | 392篇 |
2006年 | 405篇 |
2005年 | 394篇 |
2004年 | 352篇 |
2003年 | 295篇 |
2002年 | 257篇 |
2001年 | 205篇 |
2000年 | 287篇 |
1999年 | 179篇 |
1998年 | 217篇 |
1997年 | 207篇 |
1996年 | 243篇 |
1995年 | 246篇 |
1994年 | 213篇 |
1993年 | 283篇 |
1992年 | 215篇 |
1991年 | 274篇 |
1990年 | 216篇 |
1989年 | 200篇 |
1988年 | 171篇 |
1987年 | 129篇 |
1986年 | 82篇 |
1985年 | 103篇 |
1984年 | 89篇 |
1983年 | 82篇 |
1982年 | 56篇 |
1981年 | 46篇 |
1980年 | 72篇 |
1979年 | 17篇 |
1964年 | 19篇 |
1959年 | 23篇 |
1958年 | 27篇 |
1957年 | 20篇 |
排序方式: 共有9437条查询结果,搜索用时 15 毫秒
31.
我们发现,长石和岩屑骨架颗粒的溶解作用(FGD)对于可溶颗粒大于10%的砂岩的储集性来说具有重要意义。据集些储集砂岩的研究,其骨架颗粒溶解孔隙度可高达70%左右,其平均孔隙度约为可见孔隙的30%。骨架颗粒溶解作用不能明显地增加储层的渗透率。但是,我们发现,骨架颗粒溶解孔隙度的发育数量是砂岩原始渗透率的函数。我们认为,页岩中的粘土及有机成熟作用为骨架颗粒溶解产生了必要的水、酸及络合剂。骨架颗粒溶解的溶剂被排驱至砂岩中,在那里长石和岩屑被溶解了,而且由此产生的溶解铝被络合,并搬运至砂岩之外。 相似文献
32.
33.
34.
引言大约在一个世纪以前人们就在世界范围内发现了金矿床和铁建造具有共同伴生组合关系。金矿床中金的来源有同生的,也有后生的。在加拿大除了由砂矿床转变而来的金矿外,大多数金矿产在岩脉、剪切带和破碎带里。可见在金矿的沉淀过程中构造因素是十分重要的。铁建造是原来的化学沉积物,它一方面作为同生金的来源,另一方面,这些硬而脆的燧石质岩石又为矿脉的形成提供了一个有利的环境。岩石的构造控制了金的 相似文献
35.
New Zealand fur seals in the Kaikoura region breed near a town with expanding tourist and fishing industries and commonly come ashore entangled in nets and plastic debris. However, the rate at which entanglement occurs was previously unknown. A decade of Department of Conservation seal callout data was analysed to determine the level of entanglement in the region and the most common debris type. Monitoring of adult female fur seals released from entanglement provided information on the potential for serious wounds to heal and survivorship of released individuals. Entanglement rates of pinnipeds in Kaikoura are some of the highest reported world-wide (average range: 0.6-2.8%) with green trawl net (42%), and plastic strapping tape (31%) together contributing the most to debris types. Nearly half of the reported entangled seals are successfully released (43%) and post-release monitoring shows that with appropriate intervention the chance of an individual surviving even with a significant entanglement wound is high. Our study demonstrates that while entanglement in the region is high, a successful intervention protocol may help reduce the potential for entanglement-related mortality in the region. 相似文献
36.
One of the major problems in the lower Jordan Valley is the increasing salinization (i.e., chloride content) of local ground water. The high levels of salinity limit the utilization of ground water for both domestic and agriculture applications. This joint collaborative study evaluates the sources and mechanisms for salinization in the Jericho area. We employ diagnostic geochemical fingerprinting methods to trace the potential sources of the salinity in (1) the deep confined subaquifer system (K2) of Lower Cenomanian age; (2) the upper subaquifer system (K1) of Upper Cenomanian and Turonian ages; and (3) the shallow aquifer system (Q) of Plio-Pleistocene ages. The chemical composition of the saline ground water from the two Cenomanian subaquifers (K1 and K2) point to a single saline source with Na/Cl approximately 0.5 and Br/Cl approximately 7 x 10(-3). This composition is similar to that of thermal hypersaline spring that are found along the western shore of the Dead Sea (e.g., En Gedi thermal spring). We suggest that the increasing salinity in both K1 and K2 subaquifers is derived from mixing with deep-seated brines that flow through the Rift fault system. The salinization rate depends on the discharge volume of the fresh meteoric water in the Cenomanian Aquifer. In contrast, the chemical composition of ground water from the Plio-Pleistocene Aquifer shows a wide range of Cl- (100-2000 mg/L), Na/Cl (0.4-1.0), Br/Cl (2-6 x 10(-3)), and SO4/Cl (0.01-0.4) ratios. These variations, together with the high SO4(2-), K+, and NO3- concentrations, suggest that the salinity in the shallow aquifer is derived from the combination of (1) upconing of deep brines as reflected by low Na/Cl and high Br/Cl ratios; (2) leaching of salts from the Lisan Formation within the Plio-Pleistocene Aquifer, as suggested by the high SO4(2-) concentrations; and (3) anthropogenic contamination of agriculture return flow and sewage effluents with distinctive high K+ (80 mg/L) and NO3- (80 mg/l) contents and low Br/Cl ratios (2 x 10(-3)). Our data demonstrates that the chemical composition of salinized ground water can be used to delineate the sources of salinity and hence to establish the conceptual model for explaining salinization processes. 相似文献
37.
Guitart C Slattery M Ankisetty S Radwan M Ross SJ Letcher RJ Reddy CM 《Marine pollution bulletin》2011,62(3):631-636
Considerable debate surrounds the sources of oxygenated polybrominated diphenyl ethers (O-PBDEs) in wildlife as to whether they are naturally produced or result from anthropogenic industrial activities. Natural radiocarbon (14C) abundance has proven to be a powerful tool to address this problem as recently biosynthesized compounds contain contemporary (i.e. modern) amounts of atmospheric radiocarbon; whereas industrial chemicals, mostly produced from fossil fuels, contain no detectable 14C. However, few compounds isolated from organisms have been analyzed for their radiocarbon content. To provide a baseline, we analyzed the 14C content of four O-PBDEs. These compounds, 6-OH-BDE47, 2′-OH-BDE68, 2′,6-diOH-BDE159, and a recently identified compound, 2′-MeO-6-OH-BDE120, were isolated from the tropical marine sponges Dysidea granulosa and Lendenfeldia dendyi. The modern radiocarbon content of their chemical structures (i.e. diphenyl ethers, C12H22O) indicates that they are naturally produced. This adds to a growing baseline on, at least, the sources of these unusual compounds. 相似文献
38.
A new methodology has been designed to identify and rank the significant environmental aspects in sea ports. The main objective of the Strategic Overview of Significant Environmental Aspects (SOSEA) is to help port managers to identify significant environmental aspects and to reinforce the awareness about them in order to prioritise work in environmental management. Developed in close collaboration with port environmental managers and tested in a set of ports, it is a user-friendly tool that can be applied in approximately half a working day. It is based on ISO 14001 vocabulary and requirements and it can be considered as the base for the implementation of any Environmental Management System for port communities. 相似文献
39.
40.
结合地震科技文献的工作实际,着重介绍了地震科技文献统计分析的主要内容指标,常用的统计分析方法及应用。 相似文献