全文获取类型
收费全文 | 4890篇 |
免费 | 961篇 |
国内免费 | 1245篇 |
专业分类
测绘学 | 182篇 |
大气科学 | 1183篇 |
地球物理 | 1524篇 |
地质学 | 2230篇 |
海洋学 | 608篇 |
天文学 | 228篇 |
综合类 | 524篇 |
自然地理 | 617篇 |
出版年
2024年 | 19篇 |
2023年 | 88篇 |
2022年 | 209篇 |
2021年 | 273篇 |
2020年 | 174篇 |
2019年 | 260篇 |
2018年 | 287篇 |
2017年 | 244篇 |
2016年 | 292篇 |
2015年 | 238篇 |
2014年 | 329篇 |
2013年 | 262篇 |
2012年 | 292篇 |
2011年 | 295篇 |
2010年 | 295篇 |
2009年 | 270篇 |
2008年 | 273篇 |
2007年 | 246篇 |
2006年 | 223篇 |
2005年 | 185篇 |
2004年 | 145篇 |
2003年 | 179篇 |
2002年 | 150篇 |
2001年 | 129篇 |
2000年 | 161篇 |
1999年 | 191篇 |
1998年 | 193篇 |
1997年 | 171篇 |
1996年 | 152篇 |
1995年 | 168篇 |
1994年 | 134篇 |
1993年 | 136篇 |
1992年 | 95篇 |
1991年 | 57篇 |
1990年 | 51篇 |
1989年 | 51篇 |
1988年 | 44篇 |
1987年 | 42篇 |
1986年 | 26篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1958年 | 4篇 |
排序方式: 共有7096条查询结果,搜索用时 15 毫秒
501.
西南天山构造地层学初步研究 总被引:16,自引:1,他引:16
西南天山造山带可划分为伊犁中天山、中天山南缘、南天山和塔里木4个构造地层区。伊犁中天山区出露早元古代变质结晶基底及晚期地台型稳定盖层。中天山南缘区产出一套早古生代变质俯冲杂岩。南天山区早古生代为陆坡、陆棚相被动陆缘沉积,晚古生代发育洋壳建造。塔里木区北部出露中晚元古代“优地槽建造”的变质结晶基底和早震旦世后稳定盖层。 相似文献
502.
Breakage models and particle analyses have been widely used as tools for describing and interpreting various deposits and
providing parameters for assessing the particle-size distribution of the deposits. Debris flows can be seen as a two-phase
rheological fluid with a clay-fluid composition, and debris-flow deposits comprise mud, silt, sand, and boulders, with grain
sizes ranging from less than one μm to more than several meters. As a consequence, according to fractal theory, the particles
in debris-flow deposits have self-similarity in geometrical shape and scale invariance in size. In this paper, the fractal
dimensions of particles in various debris-flow deposits are calculated and corresponding fractal features are determined based
on fractal-statistical theory. The aims of the study are: to provide a quantitative grain parameter that reflects both the
grain composition and grain-size distribution in debris-flow deposits; to compare the fractal dimensions of grains in different
types of debris-flow deposits and the degree of self-organization of debris flows; as well as to discuss the geological implications
of fractal dimensions and fractal features of particles in debris-flow deposits. 相似文献
503.
504.
民和盆地上侏罗统湿型冲积扇沉积 总被引:2,自引:0,他引:2
本文通过岩相特征、粘土矿物分布、早期成岩矿物组合、微量元素等特征的综合分析,认为民和盆地上侏罗统下部为一较典型的湿型冲积扇沉积。冲积扇扇中发育河道冲刷充填和漫流沉积,而泥石流不发育。沉积层序与现代湿型冲积扇可对比。扇体中粘土岩及早期成岩矿物组合中富含高岭石,应与扇体发育时的潮湿气候和弱酸性流体的较强的淋滤有关。由粘土岩中微量元素因子分析进一步表明,该地层中富硼、钒的特征与相邻非扇相地层明显不同 相似文献
505.
506.
我国炼焦煤资源丰富,但优质炼焦煤一直处于短缺局面。根据全国已有煤质数据分析,从优质(主要考虑挥发分指标)、环保(主要考虑硫分和灰分指标)两个方面结合有害微量元素含量,将炼焦煤划分为四种类型,确定了优质环保型炼焦煤资源的评价步骤,对全国五个赋煤区优质环保型炼焦煤的资源量等级进行了统计分析。 相似文献
507.
Deep-large faults in the central continental margin of eastern China are well developed. Based on the regularity of spatial
and temporal distribution of the faults, four fault systems were divided: the Yanshan orogenic belt fault system, the Qinling-Dabie-Sulu
orogenic belt fault system, the Tanlu fault system and the East China Sea shelf basin-Okinawa trough fault system. The four
fault systems exhibit different migration behaviors. The Yanshan orogenic belt fault system deflected from an EW to a NE direction,
then to a NNE direction during the Indo-Chinese epoch-Yanshanian epoch. The thrust-nappe strength of the Qinling-Dabie orogenic
belt fault system showed the tendency that the strength was greater in the south and east, but weaker in the north and west.
This fault system faulted in the east and folded in the west from the Indo-Chinese epoch to the early Yanshanian epoch. At
the same time, the faults also had a diachronous migration from east to west from the Indo-Chinese epoch to the early Yanshanian
epoch. On the contrary, the thrust-nappe strength was greater in the north and west, weaker in the south and east during the
late Yanshanian epoch-early Himalayan epoch. The Tanlu fault system caused the basin to migrate from west to east and south
to north. The migration regularity of the East China Sea shelf basin-Okinawa trough fault system shows that the formation
age became younger in the west. The four fault systems and their migration regularities were respectively the results of four
different geodynamic backgrounds. The Yanshan orogenic belt fault system derived from the intracontinental orogeny. The Qinling-Dabie-Sulu
orogenic belt fault system derived from the collision of plates and intracontinental subduction. The Tanlu fault system derived
from the strike-slip movement and the East China Sea shelf basin-Okinawa trough fault system derived from plate subduction
and retreat of the subduction belt.
Translated from Journal of Jilin University (Earth Science Edition), 2005, 35(5): 554–563 [译自: 吉林大学学报 (地球科学版)] 相似文献
508.
福建永安坂头组植物及古气候分析 总被引:1,自引:0,他引:1
分析了福建永安盆地早白垩世坂头植物群的组成特征。共计报道该植物群化石24属52种左右,包括未定种以及存疑种21个。植物群的组成以具鳞片状叶的松柏类化石为主,苏铁类化石次之,并以本内苏铁目占绝对优势,然后是真蕨类化石,以小羽片小而质厚为特征,银杏化石及其少见,未发现被子植物。坂头组植物的组成面貌与欧洲Wealden植物群、日本外带领石植物群,以及我国南方植物区,如浙江、山东等地的早白垩世植物群比较一致,说明坂头组含化石层位年龄为早白垩世早期。坂头组大多数植物主要分布于热带或亚热带地区,具有耐干旱炎热的特点,反映了较干旱而炎热的气候特征。除此之外,还发现少量适宜生活在温凉潮湿气候环境下的植物。根据这些对气候具有指示意义的代表分子在坂头组中的数量以及分布情况,推断永安盆地早白垩世早期气候总体上比较干旱炎热,且伴随有不同程度季节性的潮湿。 相似文献
509.
Cell Size-Dependent Effects of Solar UV Radiation on Primary Production in Coastal Waters of the South China Sea 总被引:1,自引:0,他引:1
In order to examine the effects of solar ultraviolet radiation (UVR, 280–400 nm) on photosynthesis of differently cell-sized phytoplankton, natural phytoplankton assemblages from the coastal waters of the South China Sea were separated into three groups (>20, 5–20, and <5 μm) and exposed to four different solar UV spectral regimes, i.e., 280–700 nm (PAR?+?UVR), 400–700 nm (PAR), 280–400 nm (UV-A?+?B), and 315–400 nm (UV-A). In situ carbon fixation measurements revealed that microplankton (>20 μm) efficiently utilized UV-A for photosynthetic carbon fixation, with assimilation number of up to 1.01 μg C (μg chl a)?1?h?1 under 21.4 W?m?2 UV-A alone (about half of noontime irradiance at the surface), about 40 % higher than nanoplankton (5–20 μm). UV-B (280–315 nm) of 0.95 W?m?2 reduced the carbon fixation by approximately 20 and 57 % in microplankton and nanoplankton assemblages, respectively. In contrast, smaller picoplankton (<5 μm) was unable to utilize UV-A for the photosynthetic carbon fixation. In addition, only micro-sized assemblages demonstrated the UV enhancement on their primary productivity in the presence of PAR, by about 8 % under moderate intensities of solar radiation. 相似文献
510.