全文获取类型
收费全文 | 68972篇 |
免费 | 12307篇 |
国内免费 | 16188篇 |
专业分类
测绘学 | 8935篇 |
大气科学 | 10604篇 |
地球物理 | 15694篇 |
地质学 | 33932篇 |
海洋学 | 8867篇 |
天文学 | 4560篇 |
综合类 | 5089篇 |
自然地理 | 9786篇 |
出版年
2024年 | 178篇 |
2023年 | 819篇 |
2022年 | 2291篇 |
2021年 | 2664篇 |
2020年 | 2815篇 |
2019年 | 3046篇 |
2018年 | 2607篇 |
2017年 | 3027篇 |
2016年 | 3137篇 |
2015年 | 3553篇 |
2014年 | 4097篇 |
2013年 | 4311篇 |
2012年 | 4416篇 |
2011年 | 4520篇 |
2010年 | 3825篇 |
2009年 | 4594篇 |
2008年 | 4578篇 |
2007年 | 4847篇 |
2006年 | 4764篇 |
2005年 | 4346篇 |
2004年 | 3871篇 |
2003年 | 3499篇 |
2002年 | 3054篇 |
2001年 | 2633篇 |
2000年 | 2593篇 |
1999年 | 2381篇 |
1998年 | 2097篇 |
1997年 | 1582篇 |
1996年 | 1362篇 |
1995年 | 1283篇 |
1994年 | 1107篇 |
1993年 | 924篇 |
1992年 | 642篇 |
1991年 | 513篇 |
1990年 | 362篇 |
1989年 | 310篇 |
1988年 | 261篇 |
1987年 | 145篇 |
1986年 | 93篇 |
1985年 | 71篇 |
1984年 | 50篇 |
1983年 | 20篇 |
1982年 | 25篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 24篇 |
1978年 | 26篇 |
1977年 | 14篇 |
1976年 | 5篇 |
1954年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
本文提出了一种把经纬度网格点上的气象要素值转化到正方形网格点上的多项式插值方案。对插值方案作了稳定性讨论和定量及定性分析。结果表明,这种插值方案方便可行,而且有广泛适用性。 相似文献
82.
介绍了MATLAB语言特点和系统建模方法的基本理论.根据南海气象数据的实际建模处理过程,给出了建模的详细步骤及其MATLAB实现过程以及MATLABTM的主要实现程序.试验讨论和结果表明利用MATLAB语言可以方便地对南海气象数据用系统建模方法进行建模和处理,MATLAB在运用系统建模法处理南海气象数据方面具有明显的优越性. 相似文献
83.
84.
Calibrating the GOCE accelerations with star sensor data and a global gravity field model 总被引:1,自引:0,他引:1
A reliable and accurate gradiometer calibration is essential for the scientific return of the gravity field and steady-state
ocean circulation explorer (GOCE) mission. This paper describes a new method for external calibration of the GOCE gradiometer
accelerations. A global gravity field model in combination with star sensor quaternions is used to compute reference differential
accelerations, which may be used to estimate various combinations of gradiometer scale factors, internal gradiometer misalignments
and misalignments between star sensor and gradiometer. In many aspects, the new method is complementary to the GOCE in-flight
calibration. In contrast to the in-flight calibration, which requires a satellite-shaking phase, the new method uses data
from the nominal measurement phases. The results of a simulation study show that gradiometer scale factors can be estimated
on a weekly basis with accuracies better than 2 × 10−3 for the ultrasensitive and 10−2 for the less sensitive axes, which is compatible with the requirements of the gravity gradient error. Based on a 58-day data
set, scale factors are found that can reduce the errors of the in-flight-calibrated measurements. The elements of the complete
inverse calibration matrix, representing both the internal gradiometer misalignments and scale factors, can be estimated with
accuracies in general better than 10−3. 相似文献
85.
Kazuo Abe 《Journal of Oceanography》2008,64(6):961-967
From August 2006 to August 2007, the concentrations of dissolved silica (Si(OH)4) were monitored in the surface water of Urasoko Bay and the mouth of the stream that runs into the bay. Urasoko Bay is located
on the northern coast of Ishigaki Island, Okinawa, Japan, which is in a subtropical area of the North Pacific Ocean and is
surrounded by a relatively poorly developed fringing reef. Added to these samples were freshwater from the upstream area and
brackish water that exudes at the beach site, which were collected from April to June 2007. Rainwater samples were also collected
during the study period. The concentration of Si(OH)4 generally decreased from upstream to the bay site, and, on clear days, Si(OH)4 data from all study sites (the bay, beach, stream mouth, and upstream) plotted against salinity fell on a single straight
line. When the influence of rainwater was, the results were scattered below the straight line, which suggests dilution by
rainwater with a much lower Si(OH)4 concentration. These findings show that offshore seawater, rainwater, and upstream freshwater regulate the concentration
of Si(OH)4 in the surface water of Urasoko Bay. 相似文献
86.
87.
We study the self-consistent, linear response of a galactic disc to vertical perturbations, as induced, say, by a tidal interaction. We calculate the self-gravitational potential corresponding to a non-axisymmetric, self-consistent density response of the disc using the Green's function method. The response potential is shown to oppose the perturbation potential because the self-gravity of the disc resists the imposed potential, and this resistance is stronger in the inner parts of a galactic disc. For the m = 1 azimuthal wavenumber, the disc response opposes the imposed perturbation up to a radius that spans a range of 4–6 disc scalelengths, so that the disc shows a net warp only beyond this region. This physically explains the well known but so far unexplained observation that warps typically set in beyond this range of radii. We show that the inclusion of a dark matter halo in the calculation only marginally changes (by ∼10 per cent) the radius for the onset of warps. For perturbations with higher azimuthal wavenumbers, the net signature of the vertical perturbations can only be seen at larger radii – for example, beyond 7 exponential disc scalelengths for m = 10 . Also, for the high- m cases, the magnitude of the negative disc response due to the disc self-gravity is much smaller. This is shown to result in corrugations of the mid-plane density, which explains the puzzling scalloping with m = 10 detected in H i in the outermost regions ∼30 kpc in the Galaxy. 相似文献
88.
GPS/LEO掩星观测的变分同化技术 总被引:6,自引:0,他引:6
在简单介绍GPS/LEO掩星探测大气的发展历史和科学意义之后,详细阐述了反演的基本原理;分析了标准反演中存在的问题,并说明一维变分同化(1DVAR)在反演方法中的重要性;给出了一维变分同化中价值函数的求解,以及各种同化因子;简单介绍了对当前气象学中普遍使用的四维变分同化(4DVAR);重点讨论了各种同化方法,以及使用各种同化因子的优缺点。最后,通过CHAMP卫星的观测实例分析,验证了GPS数据在数值天气预报(NWP)中的作用,以及相对于标准反演法一维变分对气象要素的改进。 相似文献
89.
史生才 《紫金山天文台台刊》2003,(1)
为了研制亚毫米波射电天文用超导SIS(超导 -绝缘体 -超导 )接收机 ,我们重点开展了如下研究 ,1 )Nb超导SIS结在其能隙频率附近的量子混频特性 ,及其结合高能隙超导薄膜 (NbTiN)和高电导率金属薄膜 (Al)分布结阵在 780 - 950GHz频率区间的量子混频特性 ;2 )亚毫米波超导混频器嵌入阻抗的数值和实验表征 ;3)高电流密度小面积Nb超导SIS结的制备和特性表征 ;4)一个 60 0 - 72 0GHz超导SIS混频器的研制和特性表征。本文详细介绍了相关的数值分析和实验测量结果。 相似文献
90.