全文获取类型
收费全文 | 2941篇 |
免费 | 706篇 |
国内免费 | 1187篇 |
专业分类
测绘学 | 286篇 |
大气科学 | 2293篇 |
地球物理 | 700篇 |
地质学 | 763篇 |
海洋学 | 346篇 |
天文学 | 30篇 |
综合类 | 157篇 |
自然地理 | 259篇 |
出版年
2024年 | 34篇 |
2023年 | 70篇 |
2022年 | 112篇 |
2021年 | 126篇 |
2020年 | 139篇 |
2019年 | 174篇 |
2018年 | 133篇 |
2017年 | 146篇 |
2016年 | 146篇 |
2015年 | 140篇 |
2014年 | 211篇 |
2013年 | 194篇 |
2012年 | 190篇 |
2011年 | 204篇 |
2010年 | 175篇 |
2009年 | 232篇 |
2008年 | 166篇 |
2007年 | 258篇 |
2006年 | 239篇 |
2005年 | 203篇 |
2004年 | 188篇 |
2003年 | 195篇 |
2002年 | 156篇 |
2001年 | 141篇 |
2000年 | 171篇 |
1999年 | 135篇 |
1998年 | 102篇 |
1997年 | 79篇 |
1996年 | 84篇 |
1995年 | 48篇 |
1994年 | 62篇 |
1993年 | 50篇 |
1992年 | 37篇 |
1991年 | 28篇 |
1990年 | 15篇 |
1989年 | 22篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 5篇 |
排序方式: 共有4834条查询结果,搜索用时 281 毫秒
1.
乐茂华 《广东海洋大学学报》2004,24(4):47-48
对于正整数a ,设S(a)是Smarandache函数。证明了 :方程S(1·2 ) +S(2·3) +… +S(x(x +1) ) =S(x(x +1) (x +2 ) /3)仅有正整数解x =1。 相似文献
2.
After the survey of pollution sources, a study on surface water quality assessment and forecast is given by means of grey
system method, fuzzy mathematical method and multiple-index method. Based on it, aquatic environment quality features, treatment
measures and environmental strategies of the area are proposed. The quality of aquatic environment of 5 rivers in the Tumen
River area is studied. The results show that the pollution of surface water is serious; water quality of most rivers is between
grade IV and V except the Hunchun River, being higher than grade IV standard; pollution levels of most rivers have been basically
controlled except the of Burhatong River, which is deteriorating gradually. Pollutants of the rivers are comparatively regular,
mainly are SS, COD, BOD, AR-OH, NH3-N. The main pollution trades are chemical fibre industry, pulp and paper making industry and mining industry. If the growth
rate of gross industrial product is higher than 25 percent under the encouraging-model of regional exploitation, the pollutants’
load will overtake the bearing capacity of aquatic environment. Thus some protection program against pollution must be worked
out in order to achieve the harmonious development of economy society and environment.
A project from “Studies on Earlier Stage of Regional Development” of the Chinese Academy of Sciences 相似文献
3.
We describe how a local plasma structure can be changed by a transverse shear flow using numerical simulation to investigate the disturbance process near the magnetopause. The results show that magnetic field lines are bent by transverse shear flow disturbance near the current sheet region. There are multiple bipolar structures of the normal magnetic field in the numerical simulation. We term this new feature as K-point magnetic reconnection, realistic for discussing space observations. 相似文献
4.
利用西安数字地震遥测台网记录的数字地震资料,采用P波初动半周期残差法求得1998年7月临猗5.0级地震前后不同路径的Q(品质因子)值变化,发现在地震发生前Q值为87~203,震后Q值为67~164,震前震中区附近出现明显的高Q值异常。结果表明,地震前的高Q值异常可以作为地震预测的一种手段。 相似文献
5.
A photochemical scheme which includes a detailed treatment of multiple scattering up to solar zenith angles of 96° (developed for use in a GCM) has been used to study partitioning within chemical families. Attention is drawn to the different zenith angle dependence of diffuse radiation for the two spectral regions <310 nm and >310 nm. The effect that this has on the so-called 40 km ozone problem is discussed. The importance of correctly including multiple scattering for polar ozone studies is emphasised. 相似文献
6.
Three discriminant function models are raised and cross-compared in order to distinguish geochemical patterns characteristic
for the Drava River floodplain sediments. Based on data representing total element concentrations in samples collected from
alluvium (A), terrace (T), and unconsolidated bedrock (B) at the border of a floodplain, four element clusters emerged accounting
for discrimination between the referred groups of sediments. The most prominent is contaminant/carbonate cluster characteristic
for alluvium. The other two are: silicate cluster typical for unconsolidated geological substrate (Neogene sedimentary rocks);
and naturally dispersed heavy metal cluster separating terrace from the former two groups. Models introducing depth intervals
and single profiles as grouping criteria reveal identical sediment-heavy metal matrices. The second important issue of this
paper is possibility of reclassification of samples originally assigned to one of the a priori defined groups of sediments,
based on established geochemical pattern. The mapped geological units can be reconsidered by the post hoc assignments to a
different group if geological border between alluvium and terrace or between terrace and bedrock can not be established geologically
with absolute certainty. 相似文献
7.
David P. Bacon Nash’at N. Ahmad Thomas J. Dunn Michael C. Monteith Ananthakrishna Sarma 《Natural Hazards》2008,44(3):317-327
By definition, a crisis is a situation that requires assistance to be managed. Hence, response to a crisis involves the merging
of local and non-local emergency response personnel. In this situation, it is critical that each participant: (1) know the
roles and responsibilities of each of the other participants; (2) know the capabilities of each of the participants; and (3)
have a common basis for action. For many types of natural disasters, this entails having a common operational picture of the unfolding events, including detailed information on the weather, both current and forecasted, that may impact on either
the emergency itself or on response activities. The Consequences Assessment Tool Set (CATS) is a comprehensive package of
hazard prediction models and casualty and damage assessment tools that provides a linkage between a modeled or observed effect
and the attendant consequences for populations, infrastructure, and resources, and, hence, provides the common operational
picture for emergency response. The Operational Multiscale Environment model with Grid Adaptivity (OMEGA) is an atmospheric
simulation system that links the latest methods in computational fluid dynamics and high-resolution gridding technologies
with numerical weather prediction to provide specific weather analysis and forecast capability that can be merged into the
geographic information system framework of CATS. This paper documents the problem of emergency response as an end-to-end system
and presents the integrated CATS–OMEGA system as a prototype of such a system that has been used successfully in a number
of different situations. 相似文献
8.
9.
10.