全文获取类型
| 收费全文 | 1983篇 |
| 免费 | 536篇 |
| 国内免费 | 1090篇 |
专业分类
| 测绘学 | 133篇 |
| 大气科学 | 2055篇 |
| 地球物理 | 322篇 |
| 地质学 | 583篇 |
| 海洋学 | 244篇 |
| 天文学 | 14篇 |
| 综合类 | 106篇 |
| 自然地理 | 152篇 |
出版年
| 2024年 | 18篇 |
| 2023年 | 40篇 |
| 2022年 | 71篇 |
| 2021年 | 94篇 |
| 2020年 | 102篇 |
| 2019年 | 124篇 |
| 2018年 | 102篇 |
| 2017年 | 97篇 |
| 2016年 | 98篇 |
| 2015年 | 93篇 |
| 2014年 | 160篇 |
| 2013年 | 129篇 |
| 2012年 | 153篇 |
| 2011年 | 140篇 |
| 2010年 | 147篇 |
| 2009年 | 167篇 |
| 2008年 | 113篇 |
| 2007年 | 199篇 |
| 2006年 | 201篇 |
| 2005年 | 176篇 |
| 2004年 | 160篇 |
| 2003年 | 178篇 |
| 2002年 | 127篇 |
| 2001年 | 116篇 |
| 2000年 | 133篇 |
| 1999年 | 104篇 |
| 1998年 | 80篇 |
| 1997年 | 64篇 |
| 1996年 | 58篇 |
| 1995年 | 40篇 |
| 1994年 | 48篇 |
| 1993年 | 21篇 |
| 1992年 | 21篇 |
| 1991年 | 12篇 |
| 1990年 | 5篇 |
| 1989年 | 6篇 |
| 1988年 | 4篇 |
| 1987年 | 4篇 |
| 1986年 | 3篇 |
| 1982年 | 1篇 |
排序方式： 共有3609条查询结果，搜索用时 31 毫秒
1.
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
2.
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
3.
Evolution of sedimentary systems at large temporal and spatial scales cannot be scaled down to laboratory dimensions by conventional hydraulic Froude scaling. Therefore, many researchers question the validity of experiments aiming to simulate this evolution. Yet, it has been shown that laboratory experiments yield stratigraphic responses to allocyclic forcing that are remarkably similar to those in real‐world prototypes, hinting at scale independency with strong dependence on boundary conditions but weak dependence on the actual sediment transport dynamics. This paper addresses the dilemma by contrasting sediment transport rules that apply in the laboratory with those that apply in real‐world geological systems. It is demonstrated that the generation of two‐dimensional stratigraphy in a flume can be simulated numerically by the non‐linear diffusion equation. Sediment transport theory is used to demonstrate that only suspension‐dominated meandering rivers should be simulated with linear diffusion. With increasing grain‐size (coarse sand to gravel) and shallowness of river systems, the prediction of long‐term transport must be simulated by non‐linear, slope‐dependent diffusion to allow for increasing transport rates and thus change in stratigraphic style. To point out these differences in stratigraphic style, three stages in infill of accommodation have been defined here: (i) a start‐up stage, when the system is prograding to base level (e.g. the shelf edge) with no sediment flux beyond the base‐level point; (ii) a fill‐up stage, when the system is further aggrading while progressively more sediment is bypassing base level with the progression of the infill; and (iii) a keep‐up stage, when more than 90% of the input is bypassing the base level and less than 10% is used for filling the accommodation. By plotting the rate of change in flux for various degrees of non‐linearity (varying the exponent in the diffusion equation) it was found that the error between model and real‐world prototype is largest for the suspension‐dominated prototypes, although never more than 30% and only at the beginning of the fill‐up stage. The error reduces to only 10% for the non‐linear sandy‐gravelly and gravelly systems. These results are very encouraging and open up ways to calibrate numerical models of sedimentary system evolution by such experiments. 相似文献
4.
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
5.
6.
7.
8.
9.
10.
本文探讨东海区近海强风预报模式，首先介绍建立预报模式的思路和步骤，及使用说明，为了验证强风预报模式和判别条件，用１９８６、１９８７上日本传真天气图进行试报，准确和基本准确度为９１．１％，并给出了１９８９、１９９５年随船试验预报结果，准确和基本准确率为９０％以上。 相似文献