全文获取类型
收费全文 | 16589篇 |
免费 | 2378篇 |
国内免费 | 4116篇 |
专业分类
测绘学 | 434篇 |
大气科学 | 2540篇 |
地球物理 | 2664篇 |
地质学 | 7321篇 |
海洋学 | 2553篇 |
天文学 | 5167篇 |
综合类 | 801篇 |
自然地理 | 1603篇 |
出版年
2024年 | 57篇 |
2023年 | 166篇 |
2022年 | 440篇 |
2021年 | 480篇 |
2020年 | 546篇 |
2019年 | 658篇 |
2018年 | 564篇 |
2017年 | 545篇 |
2016年 | 571篇 |
2015年 | 648篇 |
2014年 | 985篇 |
2013年 | 1026篇 |
2012年 | 1060篇 |
2011年 | 1172篇 |
2010年 | 1122篇 |
2009年 | 1501篇 |
2008年 | 1380篇 |
2007年 | 1339篇 |
2006年 | 1290篇 |
2005年 | 1142篇 |
2004年 | 975篇 |
2003年 | 839篇 |
2002年 | 697篇 |
2001年 | 610篇 |
2000年 | 563篇 |
1999年 | 512篇 |
1998年 | 430篇 |
1997年 | 268篇 |
1996年 | 259篇 |
1995年 | 187篇 |
1994年 | 203篇 |
1993年 | 188篇 |
1992年 | 117篇 |
1991年 | 106篇 |
1990年 | 87篇 |
1989年 | 60篇 |
1988年 | 58篇 |
1987年 | 32篇 |
1986年 | 31篇 |
1985年 | 32篇 |
1984年 | 27篇 |
1983年 | 19篇 |
1982年 | 25篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 16篇 |
1954年 | 5篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
利用鄂尔多斯地块及其周缘1970~2014年的垂直形变速率场资料,借助负位错反演研究该区域长期应变积累。结果表明,地块东北缘山西断陷带中北段年均能量积累增量、剪应力强度都较高,西南缘六盘山断裂与渭河断裂西段次之;山西断陷带中南段至晋陕交界处年均剪应力强度较高且显示一定程度的能量积累;西秦岭构造区尤其西秦岭北缘断裂西段、晋冀蒙交界区也反映一定程度的能量积累特性。 相似文献
2.
Water quality is often highly variable both in space and time, which poses challenges for modelling the more extreme concentrations. This study developed an alternative approach to predicting water quality quantiles at individual locations. We focused on river water quality data that were collected over 25 years, at 102 catchments across the State of Victoria, Australia. We analysed and modelled spatial patterns of the 10th, 25th, 50th, 75th and 90th percentiles of the concentrations of sediments, nutrients and salt, with six common constituents: total suspended solids (TSS), total phosphorus (TP), filterable reactive phosphorus (FRP), total Kjeldahl nitrogen (TKN), nitrate-nitrite (NOx), and electrical conductivity (EC). To predict the spatial variation of each quantile for each constituent, we developed statistical regression models and exhaustively searched through 50 catchment characteristics to identify the best set of predictors for that quantile. The models predict the spatial variation in individual quantiles of TSS, TKN and EC well (66%–96% spatial variation explained), while those for TP, FRP and NOx have lower performance (37%–73% spatial variation explained). The most common factors that influence the spatial variations of the different constituents and quantiles are: annual temperature, percentage of cropping land area in catchment and channel slope. The statistical models developed can be used to predict how low- and high-concentration quantiles change with landscape characteristics, and thus provide a useful tool for catchment managers to inform planning and policy making with changing climate and land use conditions. 相似文献
3.
采用香港11个GPS测站的观测资料进行1 h、2 h、3 h和4h静态PPP解算,获得4组PPP坐标序列,利用调和分析求取11个测站处8个主要分潮的负荷位移参数(振幅和相位),将其与海潮模型计算的负荷位移参数进行对比,并比较分析PPP反演值与海潮模型值改正海潮负荷信号的效果。结果表明,垂直和水平方向上,不同PPP结果反演8个分潮的负荷位移分别具有约5 mm和7 mm的差异;PPP反演8个分潮垂向负荷位移优于全球海潮模型,但水平方向上的反演效果稍弱。 相似文献
4.
利用东北地区近几年流动重力观测数据,分析前郭5.8级震群周边重力点值的时序变化特征,并基于重力段差变化对东北地区整体和局部重力变化引入能够反映异常显著性程度的指标量G和C值,最后对前郭5.8级震群前的重力场动态变化作三维密度反演。结果表明:1)前郭5.8级震群发震构造两侧的局部重力变化具有较明显的差异性,其变化趋势可作为识别构造活化或解耦运动的标志;2)显著性指标量G和C值能够为地震重力前兆的定量描述提供新思路;3)震前重力变化的反演结果显示地震发生在质量运移的过渡区域,垂向反演结果对本次地震的震源深度有一定的揭示意义。 相似文献
5.
《Astroparticle Physics》2002,16(4):183-386
Frequency distributions of local muon densities in high-energy extensive air showers (EAS) are presented as signature of the primary cosmic ray energy spectrum in the knee region. Together with the gross shower variables like shower core position, angle of incidence, and the shower sizes, the KASCADE experiment is able to measure local muon densities for two different muon energy thresholds. The spectra have been reconstructed for various core distances, as well as for particular subsamples, classified on the basis of the shower size ratio Nμ/Ne. The measured density spectra of the total sample exhibit clear kinks reflecting the knee of the primary energy spectrum. While relatively sharp changes of the slopes are observed in the spectrum of EAS with small values of the shower size ratio, no such feature is detected at EAS of large Nμ/Ne ratio in the energy range of 1–10 PeV. Comparing the spectra for various thresholds and core distances with detailed Monte Carlo simulations the validity of EAS simulations is discussed. 相似文献
6.
7.
8.
9.
10.
The kinetics of the reactions of C2H radical with ethane (k1), propane (k2), and n-butane (k3) are studied over the temperature range of T = 96-296 K with a pulsed Laval nozzle apparatus that utilizes a pulsed laser photolysis-chemiluminescence technique. The C2H decay profiles in the presence of both the alkane reactant and O2 are monitored by the CH(A2Δ) chemiluminescence tracer method. The results, together with available literature data, yield the following Arrhenius expressions: k1(T) = (0.51 ± 0.06) × 10−10 exp[(−76 ± 30)K/T] cm3 molecule−1 s−1 (T = 96-800 K), k2(T) = (0.98 ± 0.32) × 10−10exp[(−71 ± 60)K/T] cm3 molecule−1 s−1 (T = 96-361 K), and k3(T) = (1.23 ± 0.26) × 10−10 cm3 molecule−1 s−1 (T = 96-297 K). At T = 296 K, k1 is measured as a function of total pressure and has little or no pressure dependence. The results from this work support a direct hydrogen abstraction mechanism for the title reactions. Implications to the atmospheric chemistry of Titan are discussed. 相似文献