全文获取类型
收费全文 | 2174篇 |
免费 | 357篇 |
国内免费 | 667篇 |
专业分类
测绘学 | 213篇 |
大气科学 | 333篇 |
地球物理 | 386篇 |
地质学 | 1470篇 |
海洋学 | 245篇 |
天文学 | 125篇 |
综合类 | 169篇 |
自然地理 | 257篇 |
出版年
2024年 | 23篇 |
2023年 | 64篇 |
2022年 | 78篇 |
2021年 | 121篇 |
2020年 | 113篇 |
2019年 | 121篇 |
2018年 | 82篇 |
2017年 | 86篇 |
2016年 | 117篇 |
2015年 | 102篇 |
2014年 | 129篇 |
2013年 | 123篇 |
2012年 | 124篇 |
2011年 | 134篇 |
2010年 | 112篇 |
2009年 | 123篇 |
2008年 | 130篇 |
2007年 | 144篇 |
2006年 | 131篇 |
2005年 | 122篇 |
2004年 | 117篇 |
2003年 | 98篇 |
2002年 | 98篇 |
2001年 | 88篇 |
2000年 | 93篇 |
1999年 | 79篇 |
1998年 | 62篇 |
1997年 | 56篇 |
1996年 | 60篇 |
1995年 | 47篇 |
1994年 | 37篇 |
1993年 | 32篇 |
1992年 | 36篇 |
1991年 | 29篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 20篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有3198条查询结果,搜索用时 11 毫秒
1.
2.
Temperature data from 18 measurement series obtained during logging of the Oseberg field in the northern North Sea are presented. Because the measurement series are taken at approximately the same depth, they should give identical temperatures after depth correction, and are suitable for assessing the performance of different models used to determine virgin rock temperatures from well log information.We have used this data set to test the properties of the different models given by Shen and Beck (1986). Although these models were built to simulate closely the thermal recovery of a well and are unbiased, the uncertainties in the temperature estimates when applied to real data are found to be no less than those from simpler (biased) models. This fact confirms the conclusion of Hermanrud (1989a) who showed that physical factors other than those presently accounted for significantly influence the thermal recovery of a borehole. 相似文献
3.
There is a growing concern with the impact of marine operations on the environment. This requires reducing fuel consumption and vessel pollution during operation. On-board computers and satellite communications will enable the operator to reduce fuel consumption and NOX emissions during vessel operations.This paper presents the results of a study on this problem and how such an on-board system could be implemented to reduce fuel consumption and engine NOX emissions. 相似文献
4.
5.
6.
7.
利用卫星遥感资料对南海北部陆架海洋表层温度锋的分析 总被引:4,自引:0,他引:4
利用7年(1993~1999)月平均的SST卫星遥感资料,分析了南海北部陆架区域海洋表层温度锋在一年中的逐月变化特征,表明南海北部陆架海洋表层温度锋存在明显的季节内变化。结合风场的卫星遥感资料,分析了东北季风对南海北部陆架温度锋的影响,表明东北季风风速的增加有利于温度锋强度的增强。通过对黑潮南海流套入侵较强的1999年2月与流套入侵较弱的1998年2月的SST卫星遥感资料的对比分析,考察了黑潮南海流套的入侵对南海北部陆架温度锋的影响,结果表明黑潮流套的较强入侵能够增加陆架温度锋的强度,对温度锋的走向也会产生一定的影响。 相似文献
8.
Taeko Shinonaga Helmuth Aigner Dilani Klose Peter Spinder Heinz Fröschl David Donohue 《Geostandards and Geoanalytical Research》2008,32(1):93-101
The recommended concentrations of 239Pu, 240Pu and 239+240Pu in reference material IAEA‐315 (marine sediment) were estimated by three analytical methods: isotope dilution thermal ionisation mass spectrometry (TIMS), isotope dilution inductively coupled plasma‐mass spectrometry (ICP‐MS) and alpha spectrometry. The determination of 239Pu and 240Pu (239+240Pu by alpha spectrometry) was carried out with samples from randomly selected bottles using each method. Plutonium‐238 was also measured by alpha spectrometry. A plutonium‐242 reference material was used as a spike for the quantitative analysis. The influence of 242Pu in the samples was therefore calculated; however, this contribution was less than the range of uncertainty and did not influence the final results. The obtained data were statistically analysed using variance component analysis and paired comparison. The combined standard uncertainties from “method/measurement”, “bottle” and “sub‐sample” were in the order of 3 to 6%. The main contributions to the uncertainty were from the material heterogeneity and from systematic differences between methods. Based on this study with twenty‐seven analyses using 10–14 g sample mass, concentrations of (38 ± 3) Bq kg?1, (28 ± 3) Bq kg?1 and (66 ± 4) Bq kg?1 are proposed as recommended values for 239Pu, 240Pu and 239+240Pu, respectively, and (9.5 ± 0.4) Bq kg?1 for 238Pu as an information value in reference material IAEA‐315. In mass concentration units, these amount to (16.4 ± 1.2) ng kg?1, (3.3 ± 0.4) ng kg?1 and (0.015 ± 0.003) ng kg?1 for 239Pu, 240Pu and 238Pu, respectively. The certified reference materials NIST 4350B and NIST 4354 were also analysed by TIMS for quality assurance of the method used in this study. 相似文献
9.
J. B. W. Day 《Environmental Geology》1996,27(2):77-78
Predictably, in a country such as Britain, with its preponderance of consolidated, sedimentary, mainly fissure-flow aquifers, there is a very large number of springs, many of which are, or have been, used for public supply. Migratory springs are a feature of the British (Ur. Cretaceous) Chalk, the most important British aquifer. The Chalk's low specific yield and high capillary moisture retention together give rise to very considerable fluctuations (more than 33 m in some areas) of the unconfined water table. Along the gentle dip slopes of the Chalk (North and South Downs of southern and southeastern England) springs may migrate laterally for several miles, giving rise to seasonal streams locally known as bournes or lavants. However, springs such as at Duncton, West Sussex, at the base of the much steeper scarp slopes of the Chalk, form point sources, the flows from which tend to be relatively steady; such springs commonly supply and are the original reason for the existence of many of the small towns and villages which nestle along the bases of the chalk scarps of Sussex and Kent.Where the Chalk forms coastal cliffs, a number of springs break out at the base of the cliff between high and low tide levels; there are major chalk coastal springs, for instance, at St. Margaret's Bay (Kent) and at Arish Mells, east of Lulworth Cove, Dorset. Such springs are not used for direct supply (their salinity is usually too high) but are indicators of the presence of local reserves of groundwater for possible future development. 相似文献
10.
Controls on low-pressure anatexis 总被引:2,自引:0,他引:2
Low-pressure anatexis, whereby rocks melt in place after passing through the andalusite stability field, develops under more restricted conditions than does low-pressure metamorphism. Our thermal modelling and review of published work indicate that the following mechanisms, operating alone, may induce anatexis in typical pelitic rocks without inducing wholesale melting in the lower crust: (i) magmatic advection by pervasive flow; (ii) crustal-scale detachment faulting; and (iii) the presence of a high heat-producing layer. Of these, only magmatic advection by pervasive flow and crustal-scale detachment faulting have been shown quantitatively to provide sufficient heat to cause widespread melting. Combinations of the above mechanisms with pluton-scale magmatic advection, shear heating, removal of the lithospheric mantle, or with each other provide additional means of developing suitable high temperatures at shallow crustal levels to generate low-pressure anatexis. 相似文献