全文获取类型
收费全文 | 7350篇 |
免费 | 1758篇 |
国内免费 | 2473篇 |
专业分类
测绘学 | 918篇 |
大气科学 | 1063篇 |
地球物理 | 1751篇 |
地质学 | 4680篇 |
海洋学 | 1306篇 |
天文学 | 145篇 |
综合类 | 655篇 |
自然地理 | 1063篇 |
出版年
2024年 | 54篇 |
2023年 | 164篇 |
2022年 | 465篇 |
2021年 | 517篇 |
2020年 | 442篇 |
2019年 | 529篇 |
2018年 | 490篇 |
2017年 | 456篇 |
2016年 | 477篇 |
2015年 | 453篇 |
2014年 | 490篇 |
2013年 | 598篇 |
2012年 | 656篇 |
2011年 | 578篇 |
2010年 | 630篇 |
2009年 | 587篇 |
2008年 | 596篇 |
2007年 | 556篇 |
2006年 | 466篇 |
2005年 | 366篇 |
2004年 | 325篇 |
2003年 | 229篇 |
2002年 | 234篇 |
2001年 | 210篇 |
2000年 | 202篇 |
1999年 | 147篇 |
1998年 | 92篇 |
1997年 | 85篇 |
1996年 | 93篇 |
1995年 | 68篇 |
1994年 | 66篇 |
1993年 | 53篇 |
1992年 | 39篇 |
1991年 | 23篇 |
1990年 | 31篇 |
1989年 | 21篇 |
1988年 | 18篇 |
1987年 | 15篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1957年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
992.
Ming Chen Feng Yin Xiaodong Li Xiande Xie Wansheng Xiao Dayong Tan 《Meteoritics & planetary science》2013,48(5):796-805
The high‐pressure minerals of reidite and coesite have been identified in the moderately shock‐metamorphosed gneiss (shock stage II, 35–45 GPa) and the strongly shock‐metamorphosed gneiss (shock stage III, 45–55 GPa), respectively, from the polymict breccias of the Xiuyan crater, a simple impact structure 1.8 km in diameter in China. Reidite in the shock stage II gneiss displays lamellar textures developed in parental grains of zircon. The phase transformation of zircon to reidite likely corresponds to a martensitic mechanism. No coesite is found in the reidite‐bearing gneiss. The shock stage III gneiss contains abundant coesite, but no reidite is identified in the rock. Coesite occurs as acicular, dendritic, and spherulitic crystals characteristic of crystallization from shock‐produced silica melt. Zircon in the rock is mostly recrystallized. The postshock temperature in the shock stage III gneiss is too high for the preservation of reidite, whereas reidite survives in the shock stage II gneiss because of relatively low postshock temperature. Reidite does not occur together with coesite because of difference in shock‐induced temperature between the shock stage II gneiss and the shock stage III gneiss. 相似文献
993.
994.
995.
沙尘气溶胶对大气冰相过程发展的敏感性试验 总被引:8,自引:6,他引:2
利用分档云动力学模式,研究了沙尘气溶胶输送过程中在不同大气背景环境条件下对云内冰相粒子形成、发展和降水过程的影响.通过敏感性试验发现:在背景气溶胶浓度不断增加的情况下,冰相降水率以及冰相降水在总降水量中的比例逐渐减小;只有在大陆性云和污染严重的地区,含有一定比例可溶性物质的沙尘粒子提高了大气中的巨核浓度,使云中冰相降水质粒提前出现,有利于降水的形成.另一方面,当把不可溶矿物气溶胶粒子作为有效的大气冰核参与云降水形成的物理过程时,由矿物气溶胶引起的大气冰核浓度增加在一定程度上抑制云中冰相降水质粒的发展,部分抵消巨核对降水的促进作用. 相似文献
996.
青海省近45年霜冻变化特征及其对主要作物的影响 总被引:10,自引:1,他引:9
利用青海省22个地面气象站1961-2005年霜冻气候资料及日最低气温资料,对东部农业区、柴达木盆地等地的霜冻气候变化特征以及对主要作物的影响进行研究。结果表明:45年来,青海省大部分地区早(秋)霜冻初日推迟,晚(春)霜冻终日提前,无霜冻期延长。东部农业区霜冻初日推迟、终日提前的趋势最为明显,柴达木盆地次之,祁连山地区和青南高原霜冻初日推迟趋势较明显,而终日提前趋势不明显;大部分地区重霜冻频数减少,强度减弱,春霜冻期低温强度变化趋势较秋霜冻期明显;气候变暖使早霜冻危害减轻,晚霜冻危害加重。 相似文献
997.
尹仔锋 《沙漠与绿洲气象(新疆气象)》2009,3(2):59-61
总结了气候变率和近年来气候变化对20世纪欧洲植物物候的影响。针对近年来气候变化,物候学主要有两个功能:第一,它能定量揭示气候变化对自然的影响,同时实证全球气候变化存在于人们的生活中;第二,长期物候数据为20世纪温度及其变化重建提供依据。过去30~50a,温度驱动的植物物候变化最明显的是开春提早。在北半球中高纬度观测发现开春平均提早2.5d/10a。秋季各种物候变化不如春季那样明显,并且也不能与气候因子联系起来。春、夏季起始日的时空变率及其变化主要与区域和局地温度有关。本文讨论了生长季和其他物候阶段的温度响应,以及它们与北大西洋涛动(NAO)的关系。这些结果说明了气候系统中生物化学循环和陆地相互作用的主要反馈: 相似文献
998.
Attribution analyses of potential evapotranspiration changes in China since the 1960s 总被引:10,自引:0,他引:10
This paper focuses on the primary causes of changes in potential evapotranspiration (ETo) in order to comprehensively understand climate change and its impact on hydrological cycle. Based on modified Penman-Monteith model, ETo is simulated, and its changes are attributed by analyzing the sensitivity of ETo to influence meteorological variables together with their changes for 595 meteorological stations across China during the period 1961–2008. Results show the decreasing trends of ETo in the whole country and in most climate regions except the cold temperate humid region in Northeast China. For China as a whole, the decreasing trend of ETo is primarily attributed to wind speed due to its significant decreasing trend and high sensitivity. Relative humidity is the highest sensitive variable; however, it has negligible effect on ETo for its insignificant trend. The positive contribution of temperature rising to ETo is offset by the effect of wind speed and sunshine duration. In addition, primary causes to ETo changes are varied for differing climate regions. ETo changes are attributed to decreased wind speed in most climate regions mainly distributed in West China and North China, to declined sunshine duration in subtropical and tropical humid regions in South China, and to increased maximum temperature in the cold temperate humid region. 相似文献
999.
北极海冰对2008年1月乌拉尔高压异常的影响 总被引:1,自引:1,他引:0
2008年1月我国南方发生了大范围的雨雪冰冻灾害天气,造成此次灾害的一个重要原因是乌拉尔高压异常的长期维持,而作为下垫面的海洋,2007/2008冬季环北欧海海冰异常偏少。观测资料合成分析表明,乌拉尔山地区出现高压异常与巴伦支海和喀拉海的海冰偏少存在密切对应关系。利用大气环流模式试验研究了(90°W~60°E)区域海冰异常对大气的影响,模拟结果显示海冰对乌拉尔高压异常有正的贡献,线性模式诊断表明天气尺度瞬变波是海冰影响乌拉尔高压异常的一种重要机制。 相似文献
1000.
The relationship between dust weather frequency (DWF), which denotes the
number of days of dust weather events, over Beijing and the East Asian
Monsoon (EAM) was studied using DWF data for Beijing during the period
1951--2006. Results show that, during this period, the blowing-dust weather
frequency (BDWF), as well as the indices of East Asian winter monsoon (EAWM)
and East Asian summer monsoon (EASM), all decreased considerably, with a
t-test confidence level of 99%. The correlation coefficients between the
chosen EAWM index and BDWF over Beijing in winter and the following spring
were 0.34 and 0.33, respectively, with significance levels of 0.01 and 0.02,
respectively. For the chosen EASM index and BDWF, these correlation
coefficients were 0.51 and 0.45, respectively, with both at a confidence
level exceeding 99.9%. With the linear trends removed, the values (in the
same order as above) were 0.14, 0.14, -0.12, and -0.09, all not significant
at the 95% confidence level. Clearly, the EAM relates mainly to DWF over
long timescales. To a certain extent, the EAM might have some impact on DWF
by affecting the associated surface air temperature and precipitation during
the corresponding time period in sand-dust source regions at the interannual
scale. A stronger (weaker) EAWM might advance (suppress) the occurrence of
DWF, and the opposite for the EASM. 相似文献