全文获取类型
收费全文 | 10629篇 |
免费 | 2673篇 |
国内免费 | 2034篇 |
专业分类
测绘学 | 613篇 |
大气科学 | 2415篇 |
地球物理 | 2769篇 |
地质学 | 5327篇 |
海洋学 | 1332篇 |
天文学 | 694篇 |
综合类 | 1042篇 |
自然地理 | 1144篇 |
出版年
2024年 | 179篇 |
2023年 | 250篇 |
2022年 | 435篇 |
2021年 | 500篇 |
2020年 | 459篇 |
2019年 | 461篇 |
2018年 | 479篇 |
2017年 | 478篇 |
2016年 | 588篇 |
2015年 | 465篇 |
2014年 | 613篇 |
2013年 | 561篇 |
2012年 | 534篇 |
2011年 | 536篇 |
2010年 | 635篇 |
2009年 | 536篇 |
2008年 | 530篇 |
2007年 | 505篇 |
2006年 | 380篇 |
2005年 | 384篇 |
2004年 | 300篇 |
2003年 | 309篇 |
2002年 | 285篇 |
2001年 | 336篇 |
2000年 | 346篇 |
1999年 | 545篇 |
1998年 | 483篇 |
1997年 | 437篇 |
1996年 | 452篇 |
1995年 | 388篇 |
1994年 | 321篇 |
1993年 | 312篇 |
1992年 | 261篇 |
1991年 | 202篇 |
1990年 | 164篇 |
1989年 | 130篇 |
1988年 | 136篇 |
1987年 | 69篇 |
1986年 | 63篇 |
1985年 | 50篇 |
1984年 | 36篇 |
1983年 | 27篇 |
1982年 | 38篇 |
1981年 | 32篇 |
1980年 | 22篇 |
1979年 | 20篇 |
1978年 | 7篇 |
1976年 | 9篇 |
1973年 | 5篇 |
1958年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
This study on the environmental quality of the Qingdao Cove intertidal zone sewage discharge area is based on data obtained
from the December of 1989 and 1990 macrobenthos investigations there, and uses pollution indicator species and computer aided
cladistic analysis to divide the area into a polluted area and a semipolluted area. The study showed the environmental quality
in 1990 improved over that in 1989.
Project supported by the National Natural Science Fonndation of China 相似文献
102.
Atmospheric lead(Pb) and other trace metals can transport over long distance and deposit on remote alpine ecosystems. In this work, the soil profiles, litter and dominant mosses along a large altitude were collected on Ao Mountain, Central China, to obtain the spatial distributions of Pb in these materials, decipher the possible factors controlling the distribution, and quantitatively distinguish the natural versus anthropogenic sources of Pb through the Pb isotopic tracing and biomonitoring. The results show that soil Pb concentrations(mg/kg) decreased significantly with depth, and they were markedly higher in the O(42.6± 2.7) and A(36.4 ± 2.2) horizons than in the litter(7.20 ± 1.9) and mosses(28.0 ± 3.9). The Pb enrichment in the surface soils(O and A horizons),litter and mosses existed in the relatively high altitudes, which was attributed to the influences from atmospheric wet deposition, plants, soil physicochemical properties and human activity. ThePb isotopic ratios identified the Pb sources as originating mainly from Chinese coal combustion,mining and smelting. Atmospheric Pb from southeastern, southwestern and northwestern regions could be deposited in the alpine ecosystem by long distance atmospheric transport. The anthropogenic Pb reached over 50% in the O and A horizons, and over 70% in the litter and mosses, which corresponded to the concentrations of 26.9, 17.7, 5.92 and 21.2 mg/kg, respectively. The results indicate that the mutual effects of climate and regional human activity could increase the Pb accumulation in remote alpine ecosystems. 相似文献
103.
海南省降水量的正态分布特征及正态化变换 总被引:3,自引:3,他引:3
利用海南省18个测站1966—2003年的资料,对各地月、季降水量进行正态分布检验,分析其时空分布特征,并探讨了正态分布转换的若干方法。研究表明,在0.01的信度检验下,春、夏、秋季降水基本符合正态分布,冬季仅北部和东部地区符合正态分布,月降水量的正态性也随季节而变化,且具有局地性。通过适当的数学变换,全省所有非正态分布的月降水量均可正态化。 相似文献
104.
介绍了常用全站仪基本指标的校正方法,为用户在使用全站仪过程中保证仪器的精度提供参考。 相似文献
105.
多中心空间开发战略研究——以大郑州都市区为例 总被引:1,自引:0,他引:1
通过对比分析单中心、双中心和多中心3种典型的都市区空间开发模式发现,多中心、网络化的空间开发模式已成为全球许多都市区空间发展的核心理念。以大郑州都市区为例,结合其范围界定和空间开发的现状与问题,认为,应该采取多中心空间开发模式,突破行政区划限制,向北、向南和向东3个方向积极拓展发展空间,注重与东西两翼的协同发展,加强与开封、洛阳、许昌等周边城市的空间联系,将大郑州都市区打造成为中原经济区的核心增长极、中部崛起的引领者和全国区域性中心城市。 相似文献
106.
107.
A new species of Araucaria, Araucaria beipiaoensis sp. nov., collected from the Middle Jurassic Tiaojishan Formation, southern hill of Shebudai village, near Beipiao city, western Liaoning is based on a permineralized female cone, which is ovate to elliptical in shape, about 11 cm × 7 cm × 4.5 cm in size. The cone bears rhomboid bracts that are spirally attached, texture thicker, with wings on both sides, with a detached lamina-like apex at the tip. In inner structure the ovuliferous scales are thicker and fused with bracts at the end with a ligular sulcns. There is one wingless ovule/seed per seed-scale complex embedded in the ovuliferous scale tissue, with the micropyle directed toward the cone axis. The ovules/seeds are long ovate or elliptical in shape, 1 cm long and near the base about 3 mm in diameter; the ovule/seed integuments have begun differentiation into 3 layers: the sarcotesta, sclerotesta, and endotesta. The nucellus is free from the enclosing integuments except in the chalazal region where it is fused to the inner layer (endotesta) of integument. Some ovules show cellularized nucellar tissue. Mature seeds exhibit the papery-thin wavy nucellus characteristically near to the micropyle. The embryonic tissue appears to be four cotyledons. The morphology and structure of the cone shows a close relationship to the araucarian cones of fossil and living genera but differs from any known species. The new species is distributed in the Middle Jurassic of the northern hemisphere, especially Asia, and has important significance for the evolution of the Family Araucariaceae. 相似文献
108.
基于DEM的黄河流域天文辐射空间分布 总被引:23,自引:3,他引:23
基于1 km×1 km分辨率的数字高程模型(DEM) 数据,利用建立的起伏地形下天文辐射分布式计算模型,计算了黄河流域1 km×1 km分辨率各月天文辐射的空间分布。结果表明:局部地形对黄河流域年和四季天文辐射的空间分布影响明显;在太阳高度角较低的冬季,地理和地形因子对天文辐射的影响相当强烈,山区天文辐射的空间差异大,1月份向阳山坡(偏南坡) 天文辐射可为背阴山坡(偏北坡) 的2~3倍,极端天文辐射的差异可达10倍以上;而在太阳高度角较高的夏季,天文辐射空间差异较小,7月份不同地形极端天文辐射的差异仅在16%左右;四季中,地形对天文辐射影响的程度为冬季>秋季>春季>夏季。 相似文献
109.
利用1881~2002年我国东北地区的月、季降水资料,采用历史曲线分析、功率谱分析、小波变换等方法,重点分析了松花江流域和辽河流域降水的长期变化规律。结果表明:松花江流域和辽河流域的降水都存在着明显的年代际变化,松花江流域降水以27~30年周期为主,辽河流域降水周期比松花江流域略长,大概为35~38年左右。根据降水自身演变规律及自回归方法预测的结果,估计未来5~10年,松花江流域仍将处于少雨期,辽河流域少雨期维持时间可能会稍长一些。 相似文献
110.
Xingwen Jiang Yueqing Li Song Yang Renguang Wu 《Meteorology and Atmospheric Physics》2011,113(3-4):171-180
In this study, interdecadal and interannual variations of the South Asian high (SAH) and the western Pacific subtropical high (WPSH), as well as their relationships with the summer climate over Asian and Pacific regions, are addressed. The variations of SAH and WPSH are objectively measured by the first singular value decomposition (SVD) mode of geopotential heights at the 100- and 500-hPa levels. The first SVD mode of summertime 100- and 500-hPa geopotential heights represents well the relationship between the variations of SAH and WPSH. Both SAH and WPSH exhibit large interannual variability and experienced an apparent long-term change in 1987. The WPSH intensifies and extends westward when SAH intensifies and extends eastward, and vice versa. The India?CBurma trough weakens when WPSH intensifies. The changes in SAH and WPSH at various levels are linked to broad-scale increases in tropical tropospheric temperature and geopotential height. When SAH and WPSH strengthen, monsoon flow becomes weaker over eastern Asia. In the meantime, precipitation decreases over eastern South China Sea, Philippines, the Philippine Sea and northeastern Asia, but increases over China, Korea, Japan and the ocean domain east of Japan. Similar features are mostly found on both interdecadal and interannual timescales, but are more evident on interannual timescale. 相似文献