全文获取类型
收费全文 | 718篇 |
免费 | 186篇 |
国内免费 | 176篇 |
专业分类
测绘学 | 34篇 |
大气科学 | 207篇 |
地球物理 | 134篇 |
地质学 | 387篇 |
海洋学 | 97篇 |
天文学 | 14篇 |
综合类 | 90篇 |
自然地理 | 117篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 38篇 |
2021年 | 34篇 |
2020年 | 38篇 |
2019年 | 43篇 |
2018年 | 48篇 |
2017年 | 50篇 |
2016年 | 53篇 |
2015年 | 46篇 |
2014年 | 51篇 |
2013年 | 50篇 |
2012年 | 41篇 |
2011年 | 52篇 |
2010年 | 48篇 |
2009年 | 67篇 |
2008年 | 54篇 |
2007年 | 35篇 |
2006年 | 36篇 |
2005年 | 30篇 |
2004年 | 14篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 26篇 |
1998年 | 23篇 |
1997年 | 25篇 |
1996年 | 20篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 16篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有1080条查询结果,搜索用时 93 毫秒
101.
102.
为了廓清异地保护条件下孑遗濒危植物四合木(Tetraena mongolica)的气候生物学特征、光合生理生态适应性及生境适宜性,应用1971—2011年的地面气象资料进行了不同试验区的气候生物图解与分析,测定了四合木及其伴生种白刺(Nitraria tangutorum)的叶片气体交换参数及光合效率。结果表明:①四合木自然分布区(内蒙古乌海地区)与异地保护区的气候生物学特征存在明显分异;②当年种植的四合木实生苗的生长量大小依次为:乌海四合木核心区实生苗鄂尔多斯实生苗阿拉善实生苗;③自然条件下,5个处理的净光合速率(Pn)依次为阿拉善移植的四合木成株(24.05±1.68μmol·m-2·s-1)乌海客土栽培的四合木(19.97±1.05μmol·m-2·s-1)乌海栽培的四合木实生苗(18.96±1.04μmol·m-2·s-1)鄂尔多斯栽培的四合木实生苗(16.64±0.92μmol·m-2·s-1)阿拉善栽培的四合木实生苗(16.48±0.13μmol·m-2·s-1);异地保护试验区栽培的四合木实生苗的Pn没有明显差异(p≥0.05),即原生境条件下栽培的四合木实生苗的Pn较高。同时,异地保护栽培四合木实生苗中,鄂尔多斯栽培的四合木实生苗的Pn阿拉善栽培的四合木实生苗。从四合木光合作用特征中的Pn、蒸腾速率、气孔导度和胞间CO2浓度、气候生物学特征和生长量等综合研究结果可以推断,从原生境区东移的实生苗迁地保护,使四合木具有更高的生理生态适宜性和环境适应性。 相似文献
103.
Palaeoflood hydrology study is a leading subject in global change study. Through field investigation in the upper reaches of Hanjiang River, palaeoflood slackwater deposits(SWD) were found in the bedrock gorges of the Yunxi reach. The results of field observation, laboratory analysis including particle-size distribution and magnetic susceptibility, and comparison with modern flood deposits, the SWD were identified as the most typical Holocene palaeoflood deposits of the Hanjiang River. By using stratigraphic correlation and OSL dating method, the palaeoflood event was dated to be 3200–2800 a BP at the turn from the middle to late Holocene. According to the palaeoflood peak stage and hydraulic parameters, the peak discharges of the palaeoflood were reconstructed as 48,830–51,710 m3/s by using the slope-area method. At same time, the flood peak discharges of 1983, 2005 and 2010 severe floods were reconstructed with the same method and hydraulic parameters in the same cross section. The error between the reconstructed and gauged discharges was 1.99%–4.21%. This showed that the reconstructed palaeoflood peak discharges were reliable. The flood peak discharge-frequency relationship at 10,000-year time scale was established by a combination of the gauged flood, historical flood and palaeoflood hydrological data. These results are very important for hydraulic engineering and flood mitigation on the Hanjiang River. 相似文献
104.
Accurate rainfall distribution is difficult to acquire based on limited meteorological stations, especially in remote areas like high mountains and deserts. The Hexi Corridor and its adjacent regions (including the Qilian Mountains and the Alxa Plateau) are typical districts where there are only 30 available rain gauges. Tropical Rainfall Measuring Mission (TRMM) data provide a possible solution. After precision analysis of monthly 0.25 degree resolution TRMM 3B43 data from 1998 to 2012, we find that the correlations between TRMM 3B43 estimates and rain gauge precipitation are significant overall and in each station around the Hexi Corridor; however, the biases of annual precipitation differ in different stations and are seriously overestimated in most of the sites. Thus, Inverse Distance Weighting (IDW) interpolation method was used to rectify TRMM data based on the difference between TRMM 3B43 estimates and rain gauge observations. The results show that rectified TRMM data present more details than rain gauges in remote areas where there are few stations, alt- hough they show high coherence of distribution. Precipitation decreases from southeast to northwest on an annual and seasonal scale. There are three rainfall centers (〉500 mm) including Menyuan, Qilian and Toson Lake, and two low rain- fall centers (〈50 mm) including Dunhuang and Ejin Banner. Meanwhile, precipitation in most of the study area presents an increasing trend; especially in northern Qilian Mountains (〉5 mm/a), Badain Jaran Desert (〉2 mm/a), Toson Lake (〉20 mm/a) and Qingtu Lake (〉20 ram/a) which shows a significant increasing trend, while precipitation in Hala Lake (〈-2 mm/a) and Tengger Desert (〈-3 mm/a) demonstrates a decreasing trend. 相似文献
105.
The annual life cycle of the brown seaweed Undaria pinnatifi da(Harvey)Suringer comprises a macroscopic diploid sporophyte stage and a microscopic haploid gametophyte stage.In 2011,an unusual zoospore-derived monoecious gametophyte isolate(designated as line 10-5-3)of U.pinnatifi da was observed.To understand this phenomenon,a comprehensive screening of eighty-two previously identifi ed male gametophyte cultures,isolated from three randomly selected cultivars(lines 10,7,and 5)was performed.Thirty-six of the isolates developed both antheridia and oogonia on the same fi lamentous fragment in a standard gametogenesis test(SGT: 18°C,60 μmol photons/(m 2·s)).Selfi ng of the monoecious gametophyte or crossing it with a normal male gametophyte both gave rise to morphologically normal sporophytic offspring.However,crossing resulted in a much higher fertilization rate(89.7%).The hybrid and selfed sporophytic offspring were grown to maturity in fl ow tanks at an ambient temperature of 10–18°C over a period of 69 days.Active zoospores were released from both types of mature sporophylls.The majority of these developed into male gametophytes,while 15%–20% developed into the observed monoecious structures on the same fi lament.Using PCR amplifi cation it was found that all the monoecious gametophyte isolates and the sporophytic offspring resulting from the selfi ng and crossing lacked the femalelinked microsatellite sequence(a part of the locus Up-AC-2A8,GenBank accession No.AY738602.1),indicating their male nature.U.pinnatifi da is an invasive species in some regions and the implications of the above fi ndings for this species in nature are briefl y discussed. 相似文献
106.
107.
提高月预报业务水平的动力相似集合方法 总被引:3,自引:0,他引:3
针对基于大气环流模式的月预报问题,提出了一种能有效减小预报误差并提高预报技巧的动力相似集合预报新方法。该方法着眼于动力模式与统计经验的内在结合,在模式积分过程中通过提取大气环流历史相似性信息,对模式误差进行参数化处理,形成多个时变的相似强迫量来扰动生成预报的集合成员。将这一集合新方法应用到中国国家气候中心业务大气环流模式(BCC AGCM1.0),一组10 a准业务环境下回报试验结果显示,相比于业务集合预报,动力相似集合预报方法能有效改进模式对于大气环流的纬向平均、超长波和长波预报,从而有效提高了月平均环流预报技巧(几乎达到业务可用标准)和逐日环流预报技巧,并显著降低了预报误差,合理增加集合离散度,使二者配置关系得以改善,有望在业务预报中应用。 相似文献
108.
Xiongqing Zhang Yuancai Lei Yong Pang Xianzhao Liu Jinzeng Wang 《Climatic change》2014,124(1-2):179-190
Tree mortality in response to climate change induced drought has emerged as a global concern. Small changes of tree mortality rates can profoundly affect forest structure, composition, dynamics and ecosystem services such as carbon sequestration. Our analyses of longitudinal data from natural stands (82 plots) in Beijing showed that tree mortality rates have increased significantly over the two decades from 1986 to 2006. In contrast, recruitment rates decreased significantly over this period. The increase in overall mortality rates resulted from an increase in tree deaths dominantly attributed to changes in temperature and precipitation resulting in drier conditions across latitudes, elevations, tree species, and tree sizes. In addition, the results showed that mortality rates of Chinese pine (Pinus tabuliformis) (β 1 ?=?0.0874) as a result of climate change induce drought were much smaller than oak (Quercus) (β 1 ?=?0.1583). 相似文献
109.
A‐Juan Pang Sheng‐Rong Li M. Santosh Qing‐Yu Yang Bao‐Jian Jia Cheng‐Dong Yang 《Geological Journal》2014,49(1):52-68
The Jilongshan skarn Cu–Au deposit is located at the Jiurui ore cluster region in the southwestern part of the Middle–Lower Yangtze River valley metallogenic belt. The region is characterized by NW‐, NNW‐ and EW‐trending faults and the mineralization occurs at the contact of lower Triassic carbonate rocks and Jurassic granodiorite porphyry intrusions. The intrusives are characterized by SiO2, K2O, and Na2O concentrations ranging from 61.66 to 67.8 wt.%, 3.29 to 5.65 wt.%, and 2.83 to 3.9 wt.%, respectively. Their A/CNK (A/CNK = n(Al2O3)/[n(CaO) + n(Na2O) + n(K2O)]) ratio, δEu, and δCe vary from 0.77 to 1.17, 0.86 to 1, and 0.88 to 0.96, respectively. The rocks show enrichment in light rare earth elements ((La/Yb)N = 7.61–12.94) and large ion lithophile elements (LILE), and depletion in high field strength elements (HFSE), such as Zr, Ti. They also display a peraluminous, high‐K calc‐alkaline signature typical of intrusives associated with skarn and porphyry Cu–Au–Mo polymetallic deposits. Laser ablation inductively coupled plasma spectrometry (LA‐ICP‐MS) zircon U–Pb age indicates that the granodiorite porphyry formed at 151.75 ± 0.70 Ma. A few inherited zircons with older ages (677 ± 10 Ma, 848 ± 11 Ma, 2645 ± 38 Ma, and 3411 ± 36 Ma) suggest the existence of an Archaean basement beneath the Middle–Lower Yangtze River region. The temperature of crystallization of the porphyry estimated from zircon thermometer ranges from 744.3 °C to 751.5 °C, and 634.04 °C to 823.8 °C. Molybdenite Re–Os dating shows that the Jilongshan deposit formed at 150.79 ± 0.82 Ma. The metallogeny and magmatism are correlated to mantle–crust interaction, associated with the subduction of the Pacific Plate from the east. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
110.
地热是主要地球物理场之一,地热能是地球的本土能源。李四光在20世纪60年代开创了我国地热科学。到90年代,学科体系基本建立。在过去20年里,我国地热研究得到了进一步深化和拓展。本文从大地热流、岩石圈热结构、地热系统、油气盆地地热、矿山地热、天然气水合物以及气候变化等方面回顾地热研究代表性的创新进展,并对深层地热、海洋地热、环境地热等研究方向作了展望。本文认为,过去20年我国地热研究成果丰硕,国际影响力得到提高,未来发展势头强劲。在经历了由浅入深,从今到古的成长之后,地热研究还将不断拓展领域,为我国地球科学,特别是能源与环境安全做出更大贡献。 相似文献