全文获取类型
收费全文 | 15327篇 |
免费 | 2503篇 |
国内免费 | 2914篇 |
专业分类
测绘学 | 3217篇 |
大气科学 | 1369篇 |
地球物理 | 2284篇 |
地质学 | 8188篇 |
海洋学 | 1934篇 |
天文学 | 390篇 |
综合类 | 1206篇 |
自然地理 | 2156篇 |
出版年
2024年 | 93篇 |
2023年 | 272篇 |
2022年 | 605篇 |
2021年 | 702篇 |
2020年 | 666篇 |
2019年 | 727篇 |
2018年 | 574篇 |
2017年 | 752篇 |
2016年 | 778篇 |
2015年 | 761篇 |
2014年 | 938篇 |
2013年 | 1002篇 |
2012年 | 926篇 |
2011年 | 965篇 |
2010年 | 797篇 |
2009年 | 904篇 |
2008年 | 938篇 |
2007年 | 956篇 |
2006年 | 994篇 |
2005年 | 884篇 |
2004年 | 826篇 |
2003年 | 632篇 |
2002年 | 657篇 |
2001年 | 534篇 |
2000年 | 475篇 |
1999年 | 405篇 |
1998年 | 373篇 |
1997年 | 295篇 |
1996年 | 253篇 |
1995年 | 205篇 |
1994年 | 191篇 |
1993年 | 166篇 |
1992年 | 122篇 |
1991年 | 105篇 |
1990年 | 77篇 |
1989年 | 46篇 |
1988年 | 49篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1954年 | 3篇 |
1900年 | 3篇 |
1897年 | 1篇 |
1880年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
青岛浮山野生花卉种质资源 总被引:2,自引:0,他引:2
本文简要叙述了青岛浮山野生花卉的种类、生长环境、园林用途及开花结果日期,为把这些野生花生花卉引进城市园林提供科学依据。 相似文献
102.
以 CG2 0潜山为例 ,从建立地质模型入手 ,包括地层模型、构造模型、储集模型、储盖组合模型、速度模型等 ,认识到各套地层分布和储层物性的差异均与地震响应密切相关 ,因此可以利用地震波的信息 ,预测潜山储层的发育及分布情况。在对 CG2 0潜山进行精细全三维构造解释的基础上 ,探讨性地应用了测井约束反演、吸收系数、相干分析及三维模式识别等技术 ,对潜山储层进行了预测 ,从而提高了潜山勘探的效益 ,并为类似断阶型潜山带的勘探提供了成功的经验 ,具有一定的指导意义。 相似文献
103.
Marco Ortiz 《Marine Ecology》2002,23(1):1-9
Abstract. The current article describes statistical power analysis as an efficient strategy for the estimation of the optimum sample size. The principle aim is constructively to criticise and enrich the results presented by Mouillot et al. (1999) , who estimate the optimum sample size for evaluating possible perturbations. The authors did not make any reference to statistical power analysis, even though their objective clearly went beyond a simple stock evaluation to assess management strategies in a particular marine ecosystem. Surprisingly, they proposed (a priori) an ANOVA design to test a hypothesis considering both space and temporal scales. However, the authors did not cover important topics related with power analysis and the precautionary principle, both used into environment impact assessment programmes for marine ecosystems. Based on their results and on statistical power analysis, it is demonstrated that the variability (dispersion statistics), a key factor they used to estimate the sample size, is less relevant than the magnitude of perturbation (effect size). Therefore, a greater effort must be devoted to estimate the effect size of a particular phenomenon rather than a desired variability. 相似文献
104.
Moo Hee Kang Hyun-Chul Han Hyesu Yun Gee Soo Kong Kyong O. Kim Youn Soo Lee 《Marine Geophysical Researches》2007,28(3):257-269
A seamount chain with an approximately WNW trend is observed in the northeastern Ulleung Basin. It has been argued that these
seamounts, including two islands called Ulleung and Dok islands, were formed by a hotspot process or by ridge related volcanism.
Many geological and geophysical studies have been done for all the seamounts and islands in the chain except Anyongbok Seamount,
which is close to the proposed spreading ridge. We first report morphological characteristics, sediment distribution patterns,
and the crustal thickness of Anyongbok Seamount using multibeam bathymetry data, seismic reflection profiles, and 3D gravity
modeling. The morphology of Anyongbok Seamount shows a cone shaped feature and is characterized by the development of many
flank cones and flank rift zones. The estimated surface volume is about 60 km3, and implies that the seamount is smaller than the other seamounts in the chain. No sediments have been observed on the seamount
except the lower slope, which is covered by more than 1,000 m of strata. The crustal structure obtained from a 3D gravity
modeling (GFR = 3.11, SD 3.82 = mGal) suggests that the seamount was formed around the boundary of the Ulleung Plateau and
the Ulleung Basin, and the estimated crustal thickness is about 20 km, which is a little thicker than other nearby seamounts
distributed along the northeastern boundary of the Ulleung Basin. This significant crustal thickness also implies that Anyongbok
Seamount might not be related to ridge volcanism. 相似文献
105.
107.
2000年夏季莱州湾生态环境要素的分布特征 总被引:1,自引:0,他引:1
论文依据 2 0 0 0年夏季 8月 2 9日至 9月 2日莱州湾的 1次综合性生态环境调查资料 ,给出了表、中、底 3层的平均温度、盐度、主要营养盐浓度及其比例和叶绿素 a浓度 ,分析了莱州湾的温盐结构、主要营养盐和叶绿素 a的分布特征。由于莱州湾的水深较浅 ,各要素的垂直分布都比较均匀。生态环境要素的水平分布表现为小清河口为高温、低盐、高营养盐和高叶绿素 a浓度区 ,小清河口东测的湾顶区域为高温、高盐、相对低的营养盐和叶绿素 a浓度区。此次观测到的盐度较 1997年以前有明显升高。莱州湾各层平均的 N/ P和 Si/ N分别为 16.73和 1.67,都比 1998~ 1999年渤海中部的值大 ,但 N/ P比 1992 ,1995和 1996年莱州湾的 N/ P明显偏低。叶绿素 a浓度与硅酸盐浓度之间有较好的相关关系 (α=0 .0 1) ,表、中、底 3层叶绿素 a浓度同硅酸盐浓度的线性相关系数分别为 :0 .5 4 ,0 .68和 0 .67 相似文献
108.
109.
南海东北部末次冰期以来的沉积环境演变 总被引:1,自引:0,他引:1
利用南海东北部上陆坡处所取的D孔柱样进行硅藻分析,结合粒度与碎屑矿物分析结果,探讨该海域末次冰期以来沉积环境演变过程.结果表明:粒度与硅藻分析结果较为吻合,共同显示D孔柱样可分为上下两层.上表层(0~2 cm)的砂质沉积层为冰后期海进过程改造的晚更新世残留沉积层,即变余沉积;下层(2~130 cm)主要是末次冰期形成的浅海沉积.整个柱样可反映出海洋同位素MIS 4期海退至MIS 3期海进与MIS 2期海退至冰后期海进的沉积变化韵律. 相似文献
110.
Jonathan M. Bull Martin Gutowski Justin K. Dix Timothy J. Henstock Peter Hogarth Timothy G. Leighton Paul R. White 《Marine Geophysical Researches》2005,26(2-4):157-169
Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1–24 kHz) to produce
decimetre vertical resolution cross-sections of the sub-seabed. Here the design and development of the first true 3D Chirp
system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and
precise positioning of sources and receivers. Full 3D numerical modelling of the combined source and receiver directivity
was completed to determine optimal source and receiver geometries. The design incorporates four source transducers (1.5–13 kHz)
that can be arranged into different configurations, including Maltese Cross, a square and two separated pairs. The receive
array comprises 240 hydrophones in 60 groups whose group-centres are separated by 25 cm in both horizontal directions, with
each hydrophone group containing four individual elements and a pre-amplifier.
After careful consideration, it was concluded that the only way to determine with sufficient accuracy the source–receiver
geometry, was to fix the sources and receivers within a rigid array. Positional information for the array is given by a Real
Time Kinematic GPS and attitude system incorporating four antennas to give position, heading, pitch and roll. It is shown
that this system offers vertical positioning accuracy with a root-mean-square (rms) error less than 2.6 cm, while the horizontal
positioning rms error was less than 2.0 cm. The system is configured so that the Chirp source signature can be chosen by software
aboard the acquisition vessel.
The complete system is described and initial navigational and seismic data results are presented. These data demonstrate that
the approach of using fixed source-receiver geometry combined with RTK navigation can provide complete 3D imaging of the sub-surface. 相似文献