全文获取类型
收费全文 | 345篇 |
免费 | 58篇 |
国内免费 | 362篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 124篇 |
地球物理 | 119篇 |
地质学 | 223篇 |
海洋学 | 117篇 |
天文学 | 63篇 |
综合类 | 38篇 |
自然地理 | 80篇 |
出版年
2024年 | 15篇 |
2023年 | 83篇 |
2022年 | 29篇 |
2021年 | 43篇 |
2020年 | 18篇 |
2019年 | 21篇 |
2018年 | 19篇 |
2017年 | 16篇 |
2016年 | 9篇 |
2015年 | 34篇 |
2014年 | 67篇 |
2013年 | 37篇 |
2012年 | 15篇 |
2011年 | 25篇 |
2010年 | 14篇 |
2009年 | 13篇 |
2008年 | 18篇 |
2007年 | 22篇 |
2006年 | 19篇 |
2005年 | 19篇 |
2004年 | 13篇 |
2003年 | 20篇 |
2002年 | 15篇 |
2001年 | 18篇 |
2000年 | 21篇 |
1999年 | 14篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有765条查询结果,搜索用时 285 毫秒
91.
The characteristics of the bacterial community structure in aerosols of different particle sizes over northern Chinese marginal seas and the northwestern Pacific Ocean in autumn were analyzed using high-throughput sequencing and the quantitative real-time PCR method based on 16S rRNA genes. Combined with environmental factors and air mass sources, the bacterial abundance, community diversity, composition and structural characteristics in aerosols were studied, which might provide a scientific ev... 相似文献
92.
Plants overcome environmental stress by generating metabolic pathways. Thus, it is crucial to understand the physiological mechanisms of plant responses to changing environments. Ardisia crenata var. bicolor has an important ornamental and medicinal value. To reveal the impact of elevational gradient on the habitat soil and plant physiological attributes of this species, we collected root topsoil(0–20 cm) and subsoil(20–40 cm) samples and upper leaves at the initial blooming phase, in a survey o... 相似文献
93.
The Qilian Mountains, located in the northeastern Qinghai-Tibet Plateau, is a sensitive zone of both East Asian summer monsoon(EASM)and westerly winds(WW). The evolution history and driving mechanism of the ecosystem and hydrologic cycle in this region on long-term timescales have not yet been clarified. In this study, we comprehensively study the hydrologic and ecological evolution history in the sensitive zone since the Last Glacial Maximum(LGM) by integrating surface sediments, paleoclimate r... 相似文献
94.
We present the equivalent widths of 15 extrasolar-planet hos stars.These data were based on the high-resoluton,high signal-to-noise ratio spectra obtained with the 2.16m telescope at Xinglong station.Te error in the Xinglong equivalent width is estimated by a comparison of these data with those given in previous studies of common stars. 相似文献
95.
The term"extreme environments"describes the conditions that deviate from what mesophilic cells can tolerate.These conditions are"extreme"in the eye of mankind,but they may be suitable or even essential living conditions for most microorganisms.Hyperthermophilic microorganisms form a branch at the root of the phylogenetic tree,indicating that early life originated from extreme environments similar to that of modern deep-sea hydrothermal vents,which are characterized by high-temperature and oxygen-limiting conditions.During the inevitable cooling and gradual oxidation process on Earth,microorganisms developed similar mechanisms of adaptation.By studying modern extremophiles,we may be able to decode the mysterious history of their genomic evolution and to reconstruct early life.Because life itself is a process of energy uptake to maintain a dissipative structure that is not in thermodynamic equilibrium,the energy metabolism of microorganisms determines the pathway of evolution,the structure of an ecosystem,and the physiology of cells."Following energy"is an essential approach to understand the boundaries of life and to search for life beyond Earth. 相似文献
96.
97.
Using daily temperature data from 599 Chinese weather stations during 1961–2007, the length change trends of four seasons during
the past 47 years were analyzed. Results show that throughout the region, four seasons’ lengths are: spring becomes shorter
(-0.8 d/10yrs), summer becomes longer (3.2 d/10yrs), autumn (-0.5 d/10yrs) and winter (-1.6 d/10yrs) becomes shorter. This
trend is different in spatial distribution, namely it is very obvious in northern than southern China, and also remarkable in eastern
than western China. Summer change is most obvious, but autumn has little change comparatively. This trend is highly obvious in
North, East, Central and South China. In the Southwest starting in the 21st century, summer becomes longer and winter shortens.
The trend in the Plateau region since the 1980s is that spring becomes longer and winter shortens. The average annual temperature
increased during the past 47 years, and the change of the average annual temperature precedes seasons’ length. Thus, the average
annual temperature has a certain influence on the length change of seasons. 相似文献
98.
ZHANG Dan ZHANG Yu MORAWSKA Ewa BIELAWSKI Leszek KRASINSKA Grazyna DREWNOWSKA Ma gorzata PANKAVEC Sviatlana SZYMANSKA Karolina FALANDYSZ Jerzy 《山地科学学报》2013,10(4):621-627
In the current study, we determined concentrations and transfer rates of Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, P, Rb, Sr and Zn to Brown Birch Scaber Stalks (Leccinum scabrum) mushrooms emerged in the area of Sudety Mountains (Sudetes) in Poland. Fruiting bodies and topsoil samples beneath L. scabrum were collected form the K odzka Dale. The trace elements were determined using validated method and inductively coupled plasma - atomic emission spectroscopy (ICP-AES) for final measurement. Mushrooms contained Ag, Cr, Hg, Co, Ni and Sr at < 1.0 μg/g dry weight; Ba and Pb at ~1.0 μg/g dw; Cd at < 5 μg/g dw; Cu and Mn at > 10 μg/g dw; Al and Ca at ~100 μg/g dw; Fe, Na, Rb and Zn at 100 to 500 μg/g dw, Mg at ~1,000 μg/g dw; P at ~5,000 μg/g dw and K at ~30,000 μg/g dw. Ca, Mn and Ni were nearly equally distributed between stipes and caps; stipes compared to caps were enriched in Ba, Na and Sr, while caps were enriched in Ag, Al, Cd, Co, Cr, Cu, Fe, K, P, Pb, Rb and Zn. The values of bioconcentration factor (BCF) varied highly depending on chemical element and were >1 for Ag, Cd, Cu, K, Mg, Na, P, Rb and Zn, while <1 for Al, Ba, Ca, Co, Cr, Fe, Mn, Ni, Pb and Sr. Topsoil showed elevated content of lead and mean concentration was 99 ± 32 μg/g dw, while cadmium was at 0.41 ± 0.15 and those two highly toxic to human elements occurred in edible caps of L. scabrum at 4.5 ± 2.2 and 2.9 ± 2.0 μg/g dw, respectively. 相似文献
99.
Slope aspect has significant effect on the development and distribution of montane forest,especially in arid and semiarid regions.This paper,using SPOT5 images and 1:50,000 DEM,digitally extracts and analyzes the spatial information of montane coniferous forest(mainly Qinghai spruce),and thereby explores how the upper and lower limits and the altitudinal range of coniferous forest vary and how the area of coniferous forest is related with annual insolation with all aspects in the Helan Mountains.The results show that: 1) In the eastern flank,the lower limit of coniferous forest is between 1,600 m and 2,000 m a.s.l.,and the upper limit between 2,800 m and 3,000 m a.s.l.;in the western flank,the lower limit of coniferous forest is between 2,000 m and 2,300 m a.s.l.,and the upper limit between 2,800 m and 3,100 m a.s.l.2) The altitudinal ranges of coniferous forest are 806~1,435 m,438~1,140 m for eastern flank and western flank,respectively.3) The area of coniferous forest takes on a normal distribution with aspect,and it has a close relationship with annual insolation.This distribution model developed in this paper quantitatively reveals the significant effect of slope aspect on the distribution of coniferous forest in arid and semi-arid land. 相似文献
100.
Nanoporous polystyrene fibers for oil spill cleanup 总被引:2,自引:0,他引:2
The development of oil sorbents with high sorption capacity, low cost, scalable fabrication, and high selectivity is of great significance for water environmental protection, especially for oil spillage on seawater. In this work, we report nanoporous polystyrene (PS) fibers prepared via a one-step electrospinning process used as oil sorbents for oil spill cleanup. The oleophilic-hydrophobic PS oil sorbent with highly porous structures shows a motor oil sorption capacity of 113.87 g/g, approximately 3-4 times that of natural sorbents and nonwoven polypropylene fibrous mats. Additionally, the sorbents also exhibit a relatively high sorption capacity for edible oils, such as bean oil (111.80 g/g) and sunflower seed oil (96.89 g/g). The oil sorption mechanism of the PS sorbent and the sorption kinetics were investigated. Our nanoporous material has great potential for use in wastewater treatment, oil accident remediation and environmental protection. 相似文献