全文获取类型
收费全文 | 4569篇 |
免费 | 957篇 |
国内免费 | 1218篇 |
专业分类
测绘学 | 461篇 |
大气科学 | 802篇 |
地球物理 | 955篇 |
地质学 | 2639篇 |
海洋学 | 628篇 |
天文学 | 157篇 |
综合类 | 462篇 |
自然地理 | 640篇 |
出版年
2024年 | 35篇 |
2023年 | 110篇 |
2022年 | 301篇 |
2021年 | 305篇 |
2020年 | 260篇 |
2019年 | 283篇 |
2018年 | 312篇 |
2017年 | 279篇 |
2016年 | 292篇 |
2015年 | 263篇 |
2014年 | 273篇 |
2013年 | 283篇 |
2012年 | 232篇 |
2011年 | 257篇 |
2010年 | 264篇 |
2009年 | 238篇 |
2008年 | 218篇 |
2007年 | 214篇 |
2006年 | 149篇 |
2005年 | 157篇 |
2004年 | 155篇 |
2003年 | 184篇 |
2002年 | 307篇 |
2001年 | 240篇 |
2000年 | 208篇 |
1999年 | 202篇 |
1998年 | 120篇 |
1997年 | 87篇 |
1996年 | 78篇 |
1995年 | 77篇 |
1994年 | 76篇 |
1993年 | 60篇 |
1992年 | 56篇 |
1991年 | 31篇 |
1990年 | 31篇 |
1989年 | 17篇 |
1988年 | 16篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 1篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1958年 | 4篇 |
1957年 | 1篇 |
1954年 | 5篇 |
排序方式: 共有6744条查询结果,搜索用时 687 毫秒
611.
降雪深度预报是北方地区冬季气象服务的重点和难点,新降雪密度估算是降雪深度预报的关键技术。本文回顾了新降雪密度估算中需要着重考虑的气象要素,并对国内外广泛使用的几类新降雪密度估算方法进行了详细的介绍和对比,在此基础上,评述几种估算方法的特点、局限性以及它们之间的承接联系,并对未来新降雪密度估算的发展方向进行了展望。主要结论为:(1)温度、风速、湿度的垂直分布及太阳辐射、降水量是影响新降雪密度的重要气象要素。(2)目前被广泛应用的新降雪密度估算方法有设为常数法、建立公式法、后处理诊断法和基于微物理过程法等四类,四种方法各具特点和局限性,且存在着上下承接关系。(3)较为科学的后处理诊断法和基于微物理过程法有着各自的相对优势也有着难以克服的不足,未来新降雪密度的估算需要在这两种方法的相互促进、共同提高中逐步发展。 相似文献
612.
利用江西省93个国家气象观测站降水量资料,对2014年ECMWF集合预报降水统计量进行逐6 h和24 h晴雨检验、降水分级检验及区域性暴雨检验。结果表明:1)10%、25%、Mode、融合、最小值在晴雨预报准确率方面较控制预报更有参考价值。2)对于全年降水分级检验,10%、25%、Mode、融合、最小值这5个统计量在小雨的预报方面较控制预报更有参考价值;中位数、概率对中雨的ETS评分要略高于控制预报;90%、75%、概率对大雨预报比控制预报好。对于暴雨预报,最大值、90%、融合比控制预报好;融合、最大值对大暴雨落区的指示意义不大,但对大暴雨量级降水的可能性可以供预报员参考。3)对于区域性暴雨预报,90%、融合、最大值的预报技巧比控制预报高,最大值虽然空报较严重,但对降水量级有一定的指示意义。集合预报各统计量对于强降水过程爆发或发展阶段的预报效果不如降水过程成熟期或末期好。 相似文献
613.
Fen-Fei Wang Jian-Jun Liu Chun-Lai Li Xin Ren Ling-Li Mu Wei Yan Wen-Rui Wang Jing-Tao Xiao Xu Tan Xiao-Xia Zhang Xiao-Duan Zou Xing-Ye Gao 《中国天文和天体物理学报》2014,(12)
The establishment of a lunar control network is one of the core tasks in selenodesy, in which defining an absolute control point on the Moon is the most important step. However, up to now, the number of absolute control points has been very sparse. These absolute control points have mainly been lunar laser ranging retroreflectors, whose geographical location can be observed by observations on Earth and also identified in high resolution lunar satellite images. The Chang'e-3(CE-3) probe successfully landed on the Moon, and its geographical location has been monitored by an observing station on Earth. Since its positional accuracy is expected to reach the meter level, the CE-3 landing site can become a new high precision absolute control point. We use a sequence of images taken from the landing camera, as well as satellite images taken by CE-1 and CE-2, to identify the location of the CE-3 lander. With its geographical location known, the CE-3 landing site can be established as a new absolute control point, which will effectively expand the current area of the lunar absolute control network by 22%, and can greatly facilitate future research in the field of lunar surveying and mapping, as well as selenodesy. 相似文献
614.
1 INTRODUCTION Magnetotactic bacteria are able to respond and orient along the direction of terrestrial or artificial magnetic field, a behavior referred to as magneto- taxis. In the majority of magnetotactic bacteria, the magnetosomes are 25–120 nm in d… 相似文献
615.
616.
肖洪生 《广东海洋大学学报》1995,(2)
本文阐述了国标图纸分片输出的意义与方法;通过举例,AutoCAD用户能够容易地掌握使用本文中所述的分片输出方法,用小幅面图形输出设备绘制大幅面的工程技术图纸。 相似文献
617.
Hui Zhao Jing-Xiu Wang Jun Zhang Chi-Jie Xiao National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(5):443-447
Employing the Poincare index of isolated null-points in a vector field, we worked out a mathematical method of searching for 3D null-points in coronal magnetic fields. After introducing the relevant differential topology, we test the method by using the analytical model of Brown & Priest. The location of null-point identified by our method coincides precisely with the analytical solution. Finally we apply the method to the 3D coronal magnetic fields reconstructed from an observed MDI magnetogram of a super-active region (NOAA 10488). We find that the 3D null-point seems to be a key element in the magnetic topology associated with flare occurrence. 相似文献
618.
619.
620.
PostlarvalPenaeus orientalis kishinouye were simultaneously sampled at three fixed stations near the mouth of the Dagu River estuary in northwestern Jiaozhou
Bay, China, at hourly intervals over a 49-h period in mid-June, 1984. The purpose of this sampling was to investigate the
prawn’s recruitment into estuaries from coastal areas.
The abundance of the postlarvae varied considerably between stations and time, but they tended to concentrate at the surface.
Maximum entropy spectral analysis was first applied in the study of prawn recruitment and it revealed that variations in abundance
involved a pronounced 12.4 hr cycle. It was concluded that natural tidal cycles had a strong influence on the changes of postlarval
abundance, in contrast with the minor effects of diet and other environmental cycles. A tidally varying cross-river gradient
of postlarval density was found. During flood tides the postlarvae were more abundant in the axis of the channel than over
the banks. The opposite held true during ebb tides. Mechanisms of the postlarval recruitment are discussed in terms of alternating
movements of the postlarvae between the banks and the channels in response to tidal cycles.
Contribution No. 1485 from the Institute of Oceanology, Academia Sinica 相似文献