全文获取类型
收费全文 | 108055篇 |
免费 | 1393篇 |
国内免费 | 1382篇 |
专业分类
测绘学 | 3082篇 |
大气科学 | 7474篇 |
地球物理 | 20531篇 |
地质学 | 41271篇 |
海洋学 | 8838篇 |
天文学 | 21390篇 |
综合类 | 2380篇 |
自然地理 | 5864篇 |
出版年
2022年 | 633篇 |
2021年 | 1091篇 |
2020年 | 1176篇 |
2019年 | 1254篇 |
2018年 | 6961篇 |
2017年 | 6077篇 |
2016年 | 5132篇 |
2015年 | 1571篇 |
2014年 | 2693篇 |
2013年 | 4511篇 |
2012年 | 3738篇 |
2011年 | 6149篇 |
2010年 | 5234篇 |
2009年 | 6373篇 |
2008年 | 5470篇 |
2007年 | 5992篇 |
2006年 | 3600篇 |
2005年 | 2703篇 |
2004年 | 2829篇 |
2003年 | 2670篇 |
2002年 | 2502篇 |
2001年 | 2013篇 |
2000年 | 2004篇 |
1999年 | 1548篇 |
1998年 | 1617篇 |
1997年 | 1465篇 |
1996年 | 1243篇 |
1995年 | 1243篇 |
1994年 | 1042篇 |
1993年 | 1007篇 |
1992年 | 934篇 |
1991年 | 968篇 |
1990年 | 935篇 |
1989年 | 817篇 |
1988年 | 751篇 |
1987年 | 883篇 |
1986年 | 773篇 |
1985年 | 946篇 |
1984年 | 1071篇 |
1983年 | 1031篇 |
1982年 | 950篇 |
1981年 | 906篇 |
1980年 | 808篇 |
1979年 | 748篇 |
1978年 | 726篇 |
1977年 | 618篇 |
1976年 | 632篇 |
1975年 | 613篇 |
1974年 | 589篇 |
1973年 | 656篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
For agriculture, there are three major options for mitigating greenhouse gas (GHG) emissions: 1) productivity improvements, particularly in the livestock sector; 2) dedicated technical mitigation measures; and 3) human dietary changes. The aim of the paper is to estimate long-term agricultural GHG emissions, under different mitigation scenarios, and to relate them to the emissions space compatible with the 2 °C temperature target. Our estimates include emissions up to 2070 from agricultural soils, manure management, enteric fermentation and paddy rice fields, and are based on IPCC Tier 2 methodology. We find that baseline agricultural CO2-equivalent emissions (using Global Warming Potentials with a 100 year time horizon) will be approximately 13 Gton CO2eq/year in 2070, compared to 7.1 Gton CO2eq/year 2000. However, if faster growth in livestock productivity is combined with dedicated technical mitigation measures, emissions may be kept to 7.7 Gton CO2eq/year in 2070. If structural changes in human diets are included, emissions may be reduced further, to 3–5 Gton CO2eq/year in 2070. The total annual emissions for meeting the 2 °C target with a chance above 50 % is in the order of 13 Gton CO2eq/year or less in 2070, for all sectors combined. We conclude that reduced ruminant meat and dairy consumption will be indispensable for reaching the 2 °C target with a high probability, unless unprecedented advances in technology take place. 相似文献
92.
Automated Image Registration for Hydrologic Change Detection in the Lake-Rich Arctic 总被引:1,自引:0,他引:1
93.
Numerical modeling of the Rideau Valley Watershed 总被引:1,自引:0,他引:1
Ferdous Ahmed 《Natural Hazards》2010,55(1):63-84
Using the Mike11 modeling system by the Danish Hydraulic Institute, a detailed model of the Rideau Valley Watershed was constructed.
It includes 532 km of rivers and lakes, 106 basins, 122 bridges and culverts, and 20 water control structures. The model was
calibrated using measured streamflow data for a time period of 5 years; additional 5 years of data was used for validation.
Various methods, both qualitative and quantitative, were used to evaluate the model performance. It was found that the model
can simulate the hydrological response with a reasonable to high degree of accuracy. This model is now being used for various
watershed management purposes, including flood forecasting, dam safety assessment, quantification of wetland functions, and
derivation of design flows. 相似文献
94.
Sylwia Tomecka-Suchoń Bogdan Żogała Tomisław Gołębiowski Grażyna Dzik Tomasz Dzik Krzysztof Jochymczyk 《Acta Geophysica》2017,65(4):743-755
The results of geophysical studies conducted with selected electrical and electromagnetic methods in the Kondratowa Valley in the Tatra Mountains (the Carpathian Mountains, Poland) are presented in the article. The surveys were performed with the following methods: electrical resistivity tomography (ERT), georadar (GPR) and conductivity meter (CM). The objective of the noninvasive geophysical measurements was to determine the thickness of the Quaternary postglacial sediments that fill the bottom of the valley and to designate the accumulation of boulders deposited on Quaternary sediments. The results of ERT surveys conducted along the axis of the valley allowed to determine the changeability of the thickness of the postglacial sediments and allowed to designate a few areas of occurrence of boulders. The ERT, GPR and CM surveys conducted across the valley allowed to designate with high accuracy the thickness of the accumulation of boulders sliding down the valley bottom from the couloirs surrounding the valley. 相似文献
95.
96.
Charles A. Stock Michael A. Alexander Nicholas A. Bond Keith M. Brander William W.L. Cheung Enrique N. Curchitser Thomas L. Delworth John P. Dunne Stephen M. Griffies Melissa A. Haltuch Jonathan A. Hare Anne B. Hollowed Patrick Lehodey Simon A. Levin Jason S. Link Kenneth A. Rose Ryan R. Rykaczewski Jorge L. Sarmiento Ronald J. Stouffer Franklin B. Schwing Francisco E. Werner 《Progress in Oceanography》2011,88(1-4):1-27
The study of climate impacts on Living Marine Resources (LMRs) has increased rapidly in recent years with the availability of climate model simulations contributed to the assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Collaboration between climate and LMR scientists and shared understanding of critical challenges for such applications are essential for developing robust projections of climate impacts on LMRs. This paper assesses present approaches for generating projections of climate impacts on LMRs using IPCC-class climate models, recommends practices that should be followed for these applications, and identifies priority developments that could improve current projections. Understanding of the climate system and its representation within climate models has progressed to a point where many climate model outputs can now be used effectively to make LMR projections. However, uncertainty in climate model projections (particularly biases and inter-model spread at regional to local scales), coarse climate model resolution, and the uncertainty and potential complexity of the mechanisms underlying the response of LMRs to climate limit the robustness and precision of LMR projections. A variety of techniques including the analysis of multi-model ensembles, bias corrections, and statistical and dynamical downscaling can ameliorate some limitations, though the assumptions underlying these approaches and the sensitivity of results to their application must be assessed for each application. Developments in LMR science that could improve current projections of climate impacts on LMRs include improved understanding of the multi-scale mechanisms that link climate and LMRs and better representations of these mechanisms within more holistic LMR models. These developments require a strong baseline of field and laboratory observations including long time series and measurements over the broad range of spatial and temporal scales over which LMRs and climate interact. Priority developments for IPCC-class climate models include improved model accuracy (particularly at regional and local scales), inter-annual to decadal-scale predictions, and the continued development of earth system models capable of simulating the evolution of both the physical climate system and biosphere. Efforts to address these issues should occur in parallel and be informed by the continued application of existing climate and LMR models. 相似文献
97.
I. S. Lykova I. V. Pekov N. N. Kononkova A. K. Shpachenko 《Geology of Ore Deposits》2010,52(8):837-842
Jinshanjiangite (acicular crystals up to 2 mm in length) and bafertisite (lamellar crystals up to 3 × 4 mm in size) have been found in alkali granite pegmatite of the Gremyakha-Vyrmes Complex, Kola Peninsula. Albite, microcline, quartz, arfvedsonite, zircon, and apatite are associated minerals. The dimensions of a monoclinic unit cell of jinshanjiangite and bafertisite are: a = 10.72(2), b=13.80(2), c = 20.94(6) Å, β = 97.0(5)° and a = 10.654(6), b = 13.724(6), c = 10.863(8) Å, β = 94.47(8)°, respectively. The typical compositions (electron microprobe data) of jinshanjiangite and bafertisite are: (Na0.57Ca0.44)Σ1.01(Ba0.57K0.44)Σ1.01 (Fe3.53Mn0.30Mg0.04Zn0.01)Σ3.88(Ti1.97Nb0.06Zr0.01)Σ2.04(Si3.97Al0.03O14)O2.00(OH2.25F0.73O0.02)Σ3.00 and (Ba1.98Na0.04K0.03)Σ2.05(Fe3.43Mn0.37Mg0.03)Σ3.83(Ti2.02Nb0.03)Σ2.05 (Si3.92Al0.08O14)(O1.84OH0.16)Σ2.00(OH2.39F1.61)Σ3.00, respectively. The minerals studied are the Fe-richest members of the bafertisite structural family. 相似文献
98.
Fossil diatom algae first found in the Paleogene marine succession (Alugivayam Formation) of the Il’pinskii Peninsula, northeastern Kamchatka are studied, and new data on molluscan assemblages from the same sequences are presented. Some of the diatom forms identified suggest the Oligocene age of their host deposits. This is consistent with earlier inference from benthic groups of marine organisms. 相似文献
99.
100.
Mineralogical alluvial prospecting search for base metals have been carried out from 1968 to 1970 in the Friuli — Venezia Giulia region. The Carnia, a part of this region, was well known from ancient times as an important mining district. Numerous anomalies of the content of some elements and minerals in river sands have been recognized by means of the above mentioned searches. This indicates that important and till now unknown ore concentrations are possible in this region. In fact three new sphalerite and/or galena concentrations and one fluorite concentration in association with As-sulphides have already been discovered during a partial development of these surveys. In the present work the advantages of alluvial prospecting in mining searches are remarked. Moreover method and application of mineralogical alluvial prospecting are described. In the last paragraph the steps which allowed the discovering of the new metal concentrations are reported in detail. The discovered concentrations are shortly analyzed. Strict aim of this note is to indicate the value and scientific importance of the described method.For reasons not within author's control, the results of these researches can be published only to day. But, owing the importance of some recent discoveries, the authors remind that these results have already been discussed at 2nd Int. Symp. on the Mineral Deposits on the Alps Bled, 1971, and at the meeting of Società di Mineralogia e Petrografia Pisa, 1974. 相似文献