全文获取类型
收费全文 | 1292篇 |
免费 | 263篇 |
国内免费 | 265篇 |
专业分类
测绘学 | 354篇 |
大气科学 | 318篇 |
地球物理 | 142篇 |
地质学 | 334篇 |
海洋学 | 321篇 |
天文学 | 213篇 |
综合类 | 69篇 |
自然地理 | 69篇 |
出版年
2024年 | 19篇 |
2023年 | 52篇 |
2022年 | 74篇 |
2021年 | 82篇 |
2020年 | 55篇 |
2019年 | 61篇 |
2018年 | 54篇 |
2017年 | 52篇 |
2016年 | 52篇 |
2015年 | 61篇 |
2014年 | 68篇 |
2013年 | 69篇 |
2012年 | 66篇 |
2011年 | 76篇 |
2010年 | 78篇 |
2009年 | 81篇 |
2008年 | 75篇 |
2007年 | 54篇 |
2006年 | 55篇 |
2005年 | 61篇 |
2004年 | 60篇 |
2003年 | 57篇 |
2002年 | 44篇 |
2001年 | 39篇 |
2000年 | 34篇 |
1999年 | 22篇 |
1998年 | 23篇 |
1997年 | 45篇 |
1996年 | 27篇 |
1995年 | 36篇 |
1994年 | 25篇 |
1993年 | 24篇 |
1992年 | 26篇 |
1991年 | 26篇 |
1990年 | 32篇 |
1989年 | 27篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1985年 | 10篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有1820条查询结果,搜索用时 15 毫秒
961.
林清 《中国科学院上海天文台年刊》1995,(16):169-175
本文为中国科学院上海天文台佘山1.56米望远镜CCD的观测与处理提供了一种规范模式,并详细介绍了为配合规范化处理而编制的批处理软件CCD156的使用方法,为参加1.56米望远镜CCD观测的人员提供了方便,并为规范化数据库的建立打下基础。 相似文献
962.
韩金林 《中国天文和天体物理学报》1995,(2)
研究表明,高频射电源与低频射电源相比,前者中的类星体比例更大。3CR低频射电源(S178MHz>9Jy)中有17.8%是类星体,而在2.7GHz亮射电源样本中(S2.7GHz≥2.0Jy),有35.6%是类星体。更有趣的是,518个5GHz亮射电源中(S5GHz≥1.0Jy),至少有291个(≥56%)是类星体。因此,我们认为高频亮射电源的证认是发现类星体的有效手段。 相似文献
963.
964.
Study on Optical Properties of Unpigmented Suspended Particles,Yellow Substance and Phytoplankton Algae in Taihu Lake 总被引:1,自引:0,他引:1
The optical properties of a waterbody are subjects of research on limnological hydrooptics. The optical properties of, and parameterization methods for, three impurities in Taihu Lake, namely unpigmented suspensions, yellow substance and phytoplankton algae, are analyzed in detail in this paper dealing with the optical types of Taihu Lake waters both in winter and in summer. The results showed that : 1 ) The optical parameters of suspended particles can be calculated by the application of Mie Theory; 2) The absorption of yellow substance decreases exponentially with increasing wavelength, with the mean value of decreasing rate being about 0.014 nm^-1 ; 3) Taihu Lake waters appeared to be of type PY in winter, with suspended particles and yellow substance being the dominant light absorbers, and type CPY in summer, with suspended particles, yellow substance and phytoplankton algae being the dominant light absorbers; 4) In winter or summer, unpigmented suspension has the main effect on the scattering property of Taihu Lake waters. 相似文献
965.
966.
967.
我们对1.56米天体测量望远镜在加象场改正透镜组物和不加时,使用同样的方法作天体测量性能的检验,与墨西哥国家天文台的2.12米R-C望远镜的同类结果作了相互比较。结果表明加像场改正透镜组时能获得更好的效果。 相似文献
968.
基于水流模拟本身就是模拟模型回归求真(即实体原型)过程的认识,从模拟模型和实体原型之间的相关关系出发,应用统计学中的线性回归分析方法,通过回归系数建立了模型与原型糙率系数之间的关系式,提出了二维浅水方程模拟中糙率确定的回归系数法。数值试验表明,该方法并不依赖于糙率系数的初值,具有稳定性好、收敛速度快的特点;对磨刀门水道水流的数值模拟应用显示,该方法能有效地改善模拟计算的精度,具有较好的适应能力,简便实用,为二维浅水流动模拟计算时率定糙率系数提供了一种有效途径。 相似文献
969.
在分析固有光学参数和表观光学参数之间关系的基础上,提出一种提高悬浮物浓度的反演精度的算法。本文算法细化单位散射系数曲线的斜率s’值,并将bbp(λ)×bρ(λ)视为一个一定数值范围内的变量,其中b’bp(λ)为波长A处的悬浮物后向散射概率,bρ(λ)为悬浮物的单位散射系数。以太湖为实验区,进行了水体野外实测,获得了遥感反射率、吸收散射系数、后向散射系数、悬浮物浓度等必要参数。利用本文改进算法反演悬浮物浓度的平均相对误差绝对值为22.58%,均方根误差为13.12mg/L,均小于已有研究中将涉及的相关参数看做单一定值时,取得的平均绝对误差(44.78%)和均方根误差(31.57mg/L)。 相似文献
970.
Optical properties of estuarine dissolved organic matter isolated using cross-flow ultrafiltration 总被引:1,自引:0,他引:1
Dissolved organic matter(DOM) from freshwater, mid-salinity, and seawater endmember samples in the Jiulong River Estuary, China were fractionated using cross-flow ultrafiltration with a 10-kDa membrane. The colloidal organic matter(COM; 10 kDa–0.22 μm) retentate, low molecular weight(LMW) DOM(10 kDa) permeate, and bulk samples were analyzed using absorption spectroscopy and three-dimensional fluorescence excitation-emission-matrix spectroscopy. The UV-visible spectra of COM were very similar to those obtained for permeate and bulk samples, decreasing monotonically with increasing wavelength. Most of the chromophoric DOM(CDOM, expressed as the absorption coefficient a355) occurred in the LMW fraction, while the percentage of CDOM in the colloidal fraction was substantially higher in the freshwater endmember(13.4% of the total) than in the seawater endmember(6.8%). The bulk CDOM showed a conservative mixing behavior in the estuary, while there was removal of the COM fraction and a concurrent addition of the permeate fraction in the mid-salinity sample, implying that part of the colloidal CDOM was transformed into LMW CDOM. Two humic-like components(C1: 250, 325/402 nm; and C2: 265, 360/458 nm) and one protein-like component(C3: 275/334 nm) were identified using parallel factor analysis. The contributions of the C1, C2, and C3 components of the COM fraction to the bulk sample were 2.5%–8.7%, 4.8%–12.6%, and 7.4%–14.7%, respectively, revealing that fluorescent DOM occurred mainly in the LMW fraction in the Jiulong River Estuary. The C1 and C2 components in the retentate and permeate samples showed conservative mixing behavior, but the intensity ratio of C2/C1 was higher in the retentate than in the permeate fractions for all salinity samples, showing that the humic component was more enriched in the COM than the fulvic component. The intensity ratio of C3/(C1+C2) was much higher in the retentate than in the permeate fraction for mid-salinity and seawater samples, revealing that the protein-like component was relatively more enriched in COM than the humic-like component. The contribution of the protein-like component(C3) to the total fluorescence in the retentate increased from 14% in the freshwater endmember to 72% for the seawater endmember samples, clearly indicating the variation of dominance by the humic-like component compared to the protein-like component during the estuarine mixing process of COM. 相似文献