全文获取类型
收费全文 | 3043篇 |
免费 | 543篇 |
国内免费 | 635篇 |
专业分类
测绘学 | 252篇 |
大气科学 | 578篇 |
地球物理 | 707篇 |
地质学 | 1466篇 |
海洋学 | 358篇 |
天文学 | 101篇 |
综合类 | 280篇 |
自然地理 | 479篇 |
出版年
2024年 | 13篇 |
2023年 | 51篇 |
2022年 | 135篇 |
2021年 | 184篇 |
2020年 | 134篇 |
2019年 | 161篇 |
2018年 | 129篇 |
2017年 | 151篇 |
2016年 | 169篇 |
2015年 | 148篇 |
2014年 | 173篇 |
2013年 | 199篇 |
2012年 | 184篇 |
2011年 | 212篇 |
2010年 | 207篇 |
2009年 | 177篇 |
2008年 | 197篇 |
2007年 | 196篇 |
2006年 | 142篇 |
2005年 | 114篇 |
2004年 | 92篇 |
2003年 | 74篇 |
2002年 | 73篇 |
2001年 | 59篇 |
2000年 | 66篇 |
1999年 | 109篇 |
1998年 | 83篇 |
1997年 | 107篇 |
1996年 | 74篇 |
1995年 | 79篇 |
1994年 | 54篇 |
1993年 | 59篇 |
1992年 | 59篇 |
1991年 | 43篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有4221条查询结果,搜索用时 257 毫秒
861.
862.
863.
机器学习模型(Machine Learning,ML)的不可解释性给其在气象业务中的应用带来了挑战。模型解释和可视化是解决这一问题的有效途径。文中将SHAP值应用于天气预报ML模型解释,研究了江西省暖季暴雨模型的预报因子对预报结果的影响。分别选取2016—2020年、2021—2022年4—9月ECWMF(European Centre for Medium-Range Weather Forecasts)高分辨率数值模式物理量及国家站降水观测数据进行XGBoost 建模与模型解释。结果表明,全局重要性排名前4位依次是总降水(重要性42.70%)、850 hPa比湿(重要性11.17%)、925 hPa相对湿度(重要性10.44%)、500 hPa相对湿度(重要性 9.16%)。个例分析表明,命中个例中高重要性物理因子在暴雨区的 SHAP 值较大,漏报(空报)个例在漏报(空报)区域高重要性物理因子的SHAP值偏小(偏大)。SHAP值从全局和局部可定量给出ML模型有物理意义的解释,解释结果与天气学原理和业务经验较一致,有利于ML在气象业务中的深入应用。 相似文献
864.
为建立一个较严密、系统的常见变质岩石的岩相学分类,采用既反映岩石结构构造特征又蕴含岩石基本组成的变质岩组构组分作为岩石分类的一级分类指标,以岩石结构、构造和组构组分的成分依次作为二、三和四级指标,划分了归属于造山区域变质岩、接触热变质岩、断层动力变质岩、蚀变交代变质岩和混合岩这5个大类变质成因的基本岩石.如岩石的地质产状已知,可用对应于地质产状的成因类型变质岩替换组构组分,升级为一级分类指标,然后用同样程序进行划分.本分类方案中,造山区域变质岩与接触热变质岩因具有相同组构组分,因此,大部分基本岩石名称相同,但可借助其地质产状和一些特征变质矿物的特殊显微构造的有无将它们区分开来.本分类方案的分类效果优于国内外现有的岩相学分类方案. 相似文献
865.
Gang-Hai Huang Yuan-Zhen Xu Xiong-Wei Yi Ming Xia Yu-Yong Jiao Shu Zhang 《国际地质力学数值与分析法杂志》2020,44(9):1301-1314
The efficiency of solving equations plays an important role in implicit-scheme discontinuous deformation analysis (DDA). A systematic investigation of six iterative methods, namely, symmetric successive over relaxation (SSOR), Jacobi (J), conjugate gradient (CG), and three preconditioned CG methods (ie, J-PCG, block J-PCG [BJ-PCG], and SSOR-PCG), for solving equations in three-dimensional sphere DDA (SDDA) is conducted in this paper. Firstly, simultaneous equations of the SDDA and iterative formats of the six solvers are presented. Secondly, serial and OpenMP-based parallel computing numerical tests are done on a 16-core PC, the result of which shows that (a) for serial computing, the efficiency of the solvers is in this order: SSOR-PCG > BJ-PCG > J-PCG > SSOR>J > CG, while for parallel computing, BJ-PCG is the best solver; and (b) CG is not only the most sensitive to the ill-condition of the equations but also the most time consuming under both serial and parallel computing. Thirdly, to estimate the effects of equation solvers acting on SDDA computations, an application example with 10 000 spheres and 200 000 calculation steps is simulated on this 16-core PC using serial and parallel computing. The result shows that SSOR-PCG is about six times faster than CG for serial computing, while BJ-PCG is about four times faster than CG for parallel computing. On the other hand, the whole computation time using BJ-PCG for parallel computing is 3.37 hours (ie, 0.061 s per step), which is about 36 times faster than CG for serial computing. Finally, some suggestions are given based on this investigation result. 相似文献
866.
Tidal current ridges, widely distributed geomorphological phenomena over the continental shelf of the world, are studied.
They are formed by tidal current and the trend of their sand bodies runs parallel to the direction of tidal current. There
are two types of the plane shapes: the parallel and the fingered. Conditions of forming tidal current ridges are the velocities
of tidal current ranging from 1 to 3.5 knots and the supply of abundant sediments. Tidal current ridges often develop in following
morphological locations: the bays, estuaries, the mouths of channels, as well as the offshore area with strong tidal current.
Tidal current ridges occur generally at a water depth of less than 35 metres.
The sediments of tidal current ridges are mainly composed of sand. The grain size of the sediments is uniform and well sorted.
The characteristics of grain size of the sand imply that their formation mechanism is similar to that of river sand, that
is, both of them are the result of flow movements in a trongth channel controlled by boundary. There is however difference
between them that the river sand is formed by one-way flow movement while the tidal current sand by two-way movement. There
are two saltation populations in the log-probability curves of tidal current sand, the sorting of first saltation population
is better than the second one, and having positive skewness, which differs from beach sand. In the C-M grain size pattern
tidal current sand is most found in graded suspension segment.
The continental shelves of the Yellow Sea, the East China Sea and the South China Sea have favourable conditions for developing
tidal current ridges in massive scale and special shape, such as the tidal current ridges in the offshore of Jiangsu, the
Gulf of Korea, the shoal of Liaodong, the east and west mouths of the channel of Qiongzhou, Jiaozhou Bay, the shoal of Taiwan,
Lingdingyang, the north branch of Changjiang estuary. The studies of them are of vital significance in shipping, fishing,
submarine engineering, military installations, oil and gas explorations, as well as in scientific research.
This paper was published in Chinese inOceanologia et Limnologia Sinica
14 (3): 286–296. 相似文献
867.
介绍一种用于人卫激光测距仪的望远镜转台跟踪控制和数据处理系统。该系统具有卫星轨道计算、跟踪控制测量、数据采集和跟踪误差可实时修正以及跟踪状态在计算机屏幕实时显示等多种功能,使我国SLR网的观测水平跃上一个新的台阶。 相似文献
868.
本文统计了1990年1月至8月S.G,D〔15〕发表的8800MHz太阳射电辐射事件、Hα耀斑和软X射线事件。8800MHz射电事件与耀斑相关率达83.1%,文章还给出了云南天文台米波射电事件与Hα耀斑的统计相关结果,并于Boulder的结果作了比较,详细分折了它们之间的关系。 相似文献
869.
Song Jingjing Xia Xiangao Zhang Xiaoling Che Huizheng Li Xiaojing 《Theoretical and Applied Climatology》2018,131(3-4):1019-1041
Theoretical and Applied Climatology - A weekly cycle of surface particulate matter (PM) characterized by smaller values during weekends and larger values during weekdays was reported in eastern... 相似文献
870.
利用0.5°×0.5°的ECWMF再分析资料,常规气象资料以及西南区域数值预报模式模拟等资料,应用天气分析和诊断方法,对2016年2月21日川西高原中东部的极端暴雪天气过程进行系统分析。结果表明:500hPa贝加尔湖横槽旋转南下使得冷空气并入川西高原中部的低槽中,其与西南暖湿气流交汇产生的锋生以及西南急流存在是此次暴雪天气产生的重要原因;随着副高的北进,此次强降雪开始之前有来自于孟加拉湾和南海的两支水汽输送,西南低空急流稳定维持为此次暴雪提供了充足的水汽。MPV2在此次暴雪过程中起到了重要作用;强降雪主要发生在SVD(Slantwise Vorticity Development)强烈发展的时段内,暴雪落区与SVD发展最强烈的区域重合;西南区域数值预报模式提前6h对此次暴雪的形势场和物理量场都做出了较为准确的预报,其中垂直速度和水汽条件预报与实况最吻合,但降水预报的量级较实况偏弱一个量级,强降水落区比强度预报更准确。 相似文献