全文获取类型
收费全文 | 1718篇 |
免费 | 255篇 |
国内免费 | 320篇 |
专业分类
测绘学 | 177篇 |
大气科学 | 53篇 |
地球物理 | 390篇 |
地质学 | 288篇 |
海洋学 | 880篇 |
天文学 | 23篇 |
综合类 | 238篇 |
自然地理 | 244篇 |
出版年
2024年 | 10篇 |
2023年 | 18篇 |
2022年 | 77篇 |
2021年 | 100篇 |
2020年 | 102篇 |
2019年 | 96篇 |
2018年 | 87篇 |
2017年 | 76篇 |
2016年 | 77篇 |
2015年 | 75篇 |
2014年 | 61篇 |
2013年 | 114篇 |
2012年 | 91篇 |
2011年 | 105篇 |
2010年 | 72篇 |
2009年 | 72篇 |
2008年 | 87篇 |
2007年 | 109篇 |
2006年 | 85篇 |
2005年 | 96篇 |
2004年 | 90篇 |
2003年 | 80篇 |
2002年 | 64篇 |
2001年 | 57篇 |
2000年 | 61篇 |
1999年 | 50篇 |
1998年 | 31篇 |
1997年 | 40篇 |
1996年 | 29篇 |
1995年 | 33篇 |
1994年 | 43篇 |
1993年 | 31篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 1篇 |
排序方式: 共有2293条查询结果,搜索用时 15 毫秒
131.
通过对一个滨海多层含水层系统的考察,该含水层系统由上、下弱透水层和介于中间的承压含水层组成,海底露头处被淤泥层覆盖.建立了描述该系统中地下水水头随潮汐波动的数学模型,并得到其解析解.该解析解与六个基本参数有关,分别是承压含水层的海潮传播参数,淤泥层的无量纲透水系数,上下弱透层与承压含水层贮水率的比率 (无量纲)和上下弱透层的无量纲越流.当这些参数取某些特殊值时,我们的解便化简为前人考虑的几种简单情形对应的解.分析表明,承压含水层中地下水水头波幅是上、下弱透水层贮水率和越流系数的减函数,是淤泥层相对透水系数的增函数;波动相位(时滞)是上、下弱透水层贮水率和越流系数的增函数,是淤泥层相对透水系数的减函数. 相似文献
132.
绿色招商与县域经济可持续发展——以河南省为例 总被引:1,自引:0,他引:1
以河南省县域经济发展为例论述了招商引资对于县域经济发展的重要性,并从可持续发展的角度对当前全民招商的现象进行了反思.在此基础上,讨论了绿色招商的内涵和主要原则,指出绿色招商和循环经济是实现县域经济可持续发展的关键所在.根据县城经济发展的特点,以河南省新郑市和义马市循环经济发展为例,从理论和实证的角度,对县域农业和工业循环经济两大体系构建进行了论述,并对县域绿色招商中应注意的问题,如市场有效性、招商载体构建、实体虚拟产业循环结合等进行了探讨. 相似文献
133.
The impact of geographical indication on the revitalisation of a regional economy: a case study of 'Boseong' green tea 总被引:1,自引:0,他引:1
Geographical indications are legal signs which identify a good as originating in a specific country or region, where the reputation of the product is attributable to its geographical roots. South Korea has operated with a geographical indication system since 1999. This research analyses the regional impacts of geographical indications using the case study of 'Boseong' green tea. The results show that geographical indication has enhanced the image of the product, leading to increased production and the stimulation of tea-related industries. We argue that geographical indication can be used as an effective policy to cope with trade liberalisation. 相似文献
134.
Determination of vertical displacements over the coastal area of Korea due to the ocean tide loading using GPS observations 总被引:2,自引:0,他引:2
This paper describes the GPS applicability for detecting the vertical displacements of ground stations caused by ocean tide loading effects. An experiment was carried out using 12 permanent GPS stations located in the coastal area of Korea using data in the period 1 July until 26 August 2003. The relative height differences were calculated from hourly DGPS data processing based on the carrier-phase observation. The power spectra of the M2 and N2 constituents of ocean tide loading were derived using the CLEAN algorithm. The differential vertical displacements generated by the ocean tide loading effect are typically 3–25 mm in coastal area of the Korea. We compared the results from GPS with those of the ocean tide models, NAO.99Jb regional model and GOT00.2, FES99 global models. The M2 (N2) amplitude differences of vertical displacements between GPS and GOT00.2 is 1.22 ± 3.61 mm (1.01 ± 1.48 mm), and that of the M2 (N2) amplitude difference between GPS and FES99 is 0.04 ± 4.64 mm (0.64 ± 1.75 mm), whereas the M2 (N2) amplitude difference between GPS and NAO.99Jb are 0.05 ± 1.03 mm (0.86 ± 1.18 mm). The highest vertical displacements at the PALM station are found for 24.5 ± 0.7 mm from GPS observation, and 22.9 mm from the regional model NAO.99Jb and 13.17 and 10.00 mm from the global models GOT00.2 and FES99, respectively. These values show that the vertical displacements derived from GPS are in good agreement with those of the regional model NAO.99Jb around Korea, more than with the global models. This result indicated that GPS is an effective tool to measure the vertical displacement caused by the ocean tide loading effect in the coastal area, and we need to use the NAO.99Jb ocean tide model rather than the global ocean tide models in and around the Korean peninsula for position determination with permanent GPS installations. This work demonstrates that vertical displacement caused by the M2 and N2 constituents of ocean tide loading can be measured by carrier-phase DGPS. 相似文献
135.
136.
The influence of Daphnia galeata×hyalina grazing and of infochemicals released by the daphnids on the colony size and growth rate of the colonial gelatinous green alga Sphaerocystis schroeteri (Chlorococcales) was investigated in laboratory batch experiments run for 96 h. High zooplankton grazing pressure was exerted by a final concentration of 100 daphnids L−1 in the Daphnia treatments. Infochemicals were obtained by filtration (0.2 μm) of water from D. galeata×hyalina cultures (200 ind. L−1 exposed for 24 h). This filtrate was added to the S. schroeteri cultures in two concentrations corresponding to 7 and 50 daphnids L−1, respectively. The growth rate of S. schroeteri was neither affected significantly by direct Daphnia grazing nor by the presence of Daphnia infochemicals, in comparison to the control. However, the portion of inedible S. schroeteri colonies (diameter>50 μm) increased under direct grazing pressure, whereas the Daphnia infochemicals did not influence the colony size significantly. We conclude that the shift in colony size by direct zooplankton grazing denotes an effective defence mechanism against size selective feeding for colonial gelatinous green algae. This effective defence in combination with unchanged growth rates of the larger colonies (under non-limiting nutrient and light conditions) falsifies the assumption of a trade-off between minimising grazing losses and maximising growth by optimising the colony size. 相似文献
137.
High-frequency (HF) radar observations of surface currents were conducted for 3 months during summer 2002 in the Keum River estuary. A comparison between HF radar-derived currents and directly measured ones form a buoy showed that the regression slope is close to 1 and the correlation coefficient greater than 0.86, with an RMS difference less than 13 cm/s which is less than 17% of the tidal current. This fairly good agreement allows us to use HF radar observation in investigating the surface flow and circulation in this tidal-current-dominant coastal-plume area. To examine the spatial variation in tidal current characteristics, as well as currents associated with non-tidal forcing, the HF radar-derived currents were separated into tidal and sub-tidal frequency currents. The overall pattern of M2-current ellipse distribution in the study area showed a counterclockwise rotation, with the offshore maximum current direction to the northeast. Eccentricity, the direction of maximum current, and the phase of net motion of the ellipse changed near the estuary mouth and near the gap of the Saemangeum reclamation tide dyke due to the complex coastal geometry and the out-flowing jet during the ebb period. 相似文献
138.
Kuniaki Abe 《Pure and Applied Geophysics》2007,164(2-3):453-463
We identified a phase representing the source length of tsunami's in the tide gauge records around Japan. This phase was observed
at tide stations, located in the direction of the long axis of the sources, for four large tsunamis: 1964 Niigata, 1968 Tokachi-oki,
1983 Nihonkaichubu, and 1993 Hokkaido-nanseioki. The phase consists of two continuous crests starting as the initial arrival
and has a time length of 15–47 minutes. This is the time required to propagate across the source area along the long axis.
Strong evidence that the phase is generated at the source is the good correlation between waveform observed at one side and
time-inversed waveform at another side. The correlation results from the instantaneous generation of the source. The source
lengths of 74–254 km were obtained under an assumption of sea depths at the sources and verified to coincide with ones within
a relative error of 15% that were previously obtained by other methods. 相似文献
139.
和田玉、玛纳斯碧玉和岫岩老玉的产地特征 总被引:7,自引:2,他引:7
本文用电子探针研究了和田玉、玛纳斯碧玉和岫岩老玉的矿物成分,结果表明和田玉的主要矿物成分是透闪石,玛纳斯碧玉是阳起石,而岫岩老玉则由透闪石和阳起石组成,并论述了它们的产地特征. 相似文献
140.