全文获取类型
收费全文 | 34969篇 |
免费 | 697篇 |
国内免费 | 313篇 |
专业分类
测绘学 | 893篇 |
大气科学 | 2770篇 |
地球物理 | 7085篇 |
地质学 | 12733篇 |
海洋学 | 3072篇 |
天文学 | 7013篇 |
综合类 | 86篇 |
自然地理 | 2327篇 |
出版年
2021年 | 325篇 |
2020年 | 357篇 |
2019年 | 385篇 |
2018年 | 841篇 |
2017年 | 835篇 |
2016年 | 980篇 |
2015年 | 603篇 |
2014年 | 997篇 |
2013年 | 1867篇 |
2012年 | 1156篇 |
2011年 | 1464篇 |
2010年 | 1228篇 |
2009年 | 1639篇 |
2008年 | 1444篇 |
2007年 | 1426篇 |
2006年 | 1369篇 |
2005年 | 1018篇 |
2004年 | 1024篇 |
2003年 | 945篇 |
2002年 | 940篇 |
2001年 | 833篇 |
2000年 | 832篇 |
1999年 | 657篇 |
1998年 | 621篇 |
1997年 | 683篇 |
1996年 | 548篇 |
1995年 | 552篇 |
1994年 | 542篇 |
1993年 | 437篇 |
1992年 | 450篇 |
1991年 | 423篇 |
1990年 | 437篇 |
1989年 | 398篇 |
1988年 | 400篇 |
1987年 | 429篇 |
1986年 | 362篇 |
1985年 | 495篇 |
1984年 | 489篇 |
1983年 | 513篇 |
1982年 | 478篇 |
1981年 | 440篇 |
1980年 | 461篇 |
1979年 | 375篇 |
1978年 | 339篇 |
1977年 | 345篇 |
1976年 | 326篇 |
1975年 | 309篇 |
1974年 | 320篇 |
1973年 | 298篇 |
1971年 | 190篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
891.
C. Schnitchen D. J. Charman E. Magyari M. Braun I. Grigorszky B. Tóthmérész M. Molnár Zs. Szántó 《Journal of Paleolimnology》2006,36(1):1-17
Peatlands offer the potential for high resolution records of water balance over Holocene timescales, yet this potential is
under-exploited in many areas of the world. Within Europe, peatlands are mostly confined to areas north of 55° N, but several
areas of southern and eastern Europe contain small peatlands which may be suitable for palaeoclimatic reconstruction. In this
paper we test the potential of peatlands in the Carpathian region for deriving quantified estimates of water table changes
using testate amoebae analysis. A training set for palaeohydrological reconstruction from testate amoebae assemblages was
obtained by collecting surface samples from 13 peatlands, including 9 from Hungary and 4 from Transylvania (Romania). Using
a simple measure of mean annual water tables estimated from staining of PVC tape, we found that some peatlands were heavily
influenced by runoff and groundwater, and were therefore not suitable as modern analogues of ombrotrophic climatically sensitive
sites. The relationship between the testate amoebae assemblages in the modern samples and the environmental variables was
explored using CCA. The CCA biplot showed that the most important variables are depth to water table and moisture content,
confirming that hydrology is a key control on taxon distribution. pH was a secondary gradient. A transfer function for % moisture
and depth to water table was established and applied to fossil assemblages from a sequence from Fenyves-tető, Transylvania,
Romania. The reconstructed water table shows a number of variations which have parallels with other palaeoclimatic records
from Europe and the North Atlantic prominent phases of higher water tables are associated with the periods 8000–8300 cal BP,
3000–2500 cal BP and after 600 cal BP. We suggest that these were periods of particular intensification of westerly airflow
which affected eastern Europe as well as western and central Europe. 相似文献
892.
Sven O. Franz Lorenz Schwark Cathrin Brüchmann Burkhard Scharf Ralf Klingel Jon D. Van Alstine Namık Çagatay Umut B. Ülgen 《Journal of Paleolimnology》2006,35(4):715-736
A limnogeological reconnaissance study was carried out on Lake Iznik, located in the southeast of the Marmara region of Turkey,
involving a seismic survey and collection of short sediment cores. This lake is located on the middle branch of the North
Anatolian Fault Zone (NAFZ), a transform plate boundary between the Eurasian and Anatolian Plates. It is, therefore, tectonically
active and offers an opportunity to investigate the interplay of sedimentary and seismo-tectonic processes, as well as climate
change and human impact in the region. Short cores of the three sub-basins, maximum length of 35.5 cm, recovered non-laminated,
blackish clays and silts with varying amounts of biogenic and minerogenic (allochthonous, autochthonous) material, which documented
almost the last 80 years of deposition and environmental history. High sedimentation rates in the deeper core sections are
accompanied by changes in land use (conversion of woodland to farmland) in the northern areas of Lake Iznik, which caused
the deposition of more weathered material (high K/Na ratios) and higher contents of Mn in the lake. A tendency towards eutrophic
conditions within the last 20 years is indicated by high nutrient content (N, TOC, P), decreasing C/N-ratios, and characteristic
diatom and cladoceran associations. Also increased pollution is revealed by higher Pb, Cu, and Zn contents and increased supply
of human and animal faeces (high coprostanol content) during the last two decades. But simultaneous lower sedimentation rates
towards the core tops complicate the reconstruction of recent and past eutrophication and pollution states of Lake Iznik.
This requires an extension of the pilot study and deeper sediment cores, to recover non-anthropogenic influenced sediment
levels. 相似文献
893.
M. Catherine Eimers Andrew M. Paterson Peter J. Dillon Sherry L. Schiff Brian F. Cumming Roland I. Hall 《Journal of Paleolimnology》2006,35(1):99-109
Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in cores from 6 lakes in
the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopic composition of S in deep sediment (> ~
20 cm) was approximately constant in all lakes, and indicated a pre-industrial δ 34S value between +4.0 and +5.3‰, which is similar to current bulk deposition. Similarly, total S concentrations in deep sediment
were relatively low (1.9–5 mg S g−1 dwt) and approximately constant with depth within cores. All lakes exhibited up-core increases in total S and decreases in
δ 34S at a depth corresponding to the beginning of industrialization in the Great Lakes region ( ~ 1900), resulting in a generally
reciprocal depth pattern between total S concentration and δ 34S ratios. While initial shifts in total S and δ 34S were likely due to enhanced SO4 reduction of newly available anthropogenic SO4, both the magnitude and pattern of up-core S enrichment and shifts in δ 34S varied greatly among lakes, and did not match changes in S deposition post 1900. Differences between lakes in total S and
δ 34S were not related to any single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lake
characteristic. This work indicates that sediment cores do not provide consistent records of changes in post-industrial S
deposition in this region, likely due to redox-related mobility of S in upper sediment. 相似文献
894.
Ground motion scaling in the Marmara region, Turkey 总被引:1,自引:0,他引:1
A. Akinci L. Malagnini R. B. Herrmann R. Gok M. B. Sørensen 《Geophysical Journal International》2006,166(2):635-651
895.
896.
897.
898.
899.
The Dahuiyeh (Zarand) earthquake of 2005 February 22 in central Iran: reactivation of an intramountain reverse fault 总被引:3,自引:0,他引:3
900.