全文获取类型
收费全文 | 10631篇 |
免费 | 1776篇 |
国内免费 | 2454篇 |
专业分类
测绘学 | 594篇 |
大气科学 | 2143篇 |
地球物理 | 2169篇 |
地质学 | 4780篇 |
海洋学 | 2220篇 |
天文学 | 137篇 |
综合类 | 727篇 |
自然地理 | 2091篇 |
出版年
2024年 | 54篇 |
2023年 | 173篇 |
2022年 | 356篇 |
2021年 | 444篇 |
2020年 | 444篇 |
2019年 | 549篇 |
2018年 | 426篇 |
2017年 | 464篇 |
2016年 | 532篇 |
2015年 | 557篇 |
2014年 | 701篇 |
2013年 | 741篇 |
2012年 | 722篇 |
2011年 | 732篇 |
2010年 | 635篇 |
2009年 | 697篇 |
2008年 | 650篇 |
2007年 | 772篇 |
2006年 | 672篇 |
2005年 | 541篇 |
2004年 | 507篇 |
2003年 | 447篇 |
2002年 | 392篇 |
2001年 | 332篇 |
2000年 | 345篇 |
1999年 | 284篇 |
1998年 | 228篇 |
1997年 | 264篇 |
1996年 | 210篇 |
1995年 | 183篇 |
1994年 | 158篇 |
1993年 | 129篇 |
1992年 | 141篇 |
1991年 | 82篇 |
1990年 | 68篇 |
1989年 | 49篇 |
1988年 | 38篇 |
1987年 | 17篇 |
1986年 | 27篇 |
1985年 | 26篇 |
1984年 | 13篇 |
1983年 | 20篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
991.
992.
The index flood procedure coupled with the L‐moments method is applied to the annual flood peaks data taken at all stream‐gauging stations in Turkey having at least 15‐year‐long records. First, screening of the data is done based on the discordancy measure (Di) in terms of the L‐moments. Homogeneity of the total geographical area of Turkey is tested using the L‐moments based heterogeneity measure, H, computed on 500 simulations generated using the four parameter Kappa distribution. The L‐moments analysis of the recorded annual flood peaks data at 543 gauged sites indicates that Turkey as a whole is hydrologically heterogeneous, and 45 of 543 gauged sites are discordant which are discarded from further analyses. The catchment areas of these 543 sites vary from 9·9 to 75121 km2 and their mean annual peak floods vary from 1·72 to 3739·5 m3 s?1. The probability distributions used in the analyses, whose parameters are computed by the L‐moments method are the general extreme values (GEV), generalized logistic (GLO), generalized normal (GNO), Pearson type III (PE3), generalized Pareto (GPA), and five‐parameter Wakeby (WAK). Based on the L‐moment ratio diagrams and the |Zdist|‐statistic criteria, the GEV distribution is identified as the robust distribution for the study area (498 gauged sites). Hence, for estimation of flood magnitudes of various return periods in Turkey, a regional flood frequency relationship is developed using the GEV distribution. Next, the quantiles computed at all of 543 gauged sites by the GEV and the Wakeby distributions are compared with the observed values of the same probability based on two criteria, mean absolute relative error and determination coefficient. Results of these comparisons indicate that both distributions of GEV and Wakeby, whose parameters are computed by the L‐moments method, are adequate in predicting quantile estimates. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
993.
本文用平均风速和最大风速法对若尔盖等三地的韦伯分布参数k、c进行估算,并用韦伯分布计算风能的指标。计算表明:若尔盖、红原属风能可利用区,用风力发电是有利用价值的;阿坝属风能贫乏地区。 相似文献
994.
K. R. Anantharamaiah 《Journal of Astrophysics and Astronomy》1986,7(3):131-139
Radio recombination lines are known to be observable at positions along the galactic ridge which are free of discrete continuum
sources. Based on the results of a recent survey of H272α lines it is shown that most of the observed galactic ridge recombination
lines can be explained as emission from outer low-density envelopes of normal Hn regions. The distribution of low-density
ionized gas and discrete HII regions as a function of the distance from the galactic centre is also derived. 相似文献
995.
多参数神经网络油气检测技术首先提取四大类26 个地震波特征参数,并定量描述这些参数,然后用神经网络技术对这些参数进行分析,预测油气分布,使油气识别工作定量化、计算机化。本次研究开发了一套神经网络油气识别软件,并利用其对东濮凹陷胡19 块进行油藏精细描述,预测沙三下砂组含油面积0-7 km2 ,石油地质储量70 ×104 吨。 相似文献
996.
A consistent approach to the frequency analysis of hydrologic data in arid and semiarid regions, i.e. the data series containing several zero values (e.g. monthly precipitation in dry seasons, annual peak flow discharges, etc.), requires using discontinuous probability distribution functions. Such an approach has received relatively limited attention. Along the lines of physically based models, the extensions of the Muskingum‐based models to three parameter forms are considered. Using 44 peak flow series from the USGS data bank, the fitting ability of four three‐parameter models was investigated: (1) the Dirac delta combined with Gamma distribution; (2) the Dirac delta combined with two‐parameter generalized Pareto distribution; (3) the Dirac delta combined with two‐parameter Weibull (DWe) distribution; (4) the kinematic diffusion with one additional parameter that controls the probability of the zero event (KD3). The goodness of fit of the models was assessed and compared both by evaluation of discrepancies between the results of both estimation methods (i.e. the method of moments (MOM) and the maximum likelihood method (MLM)) and using the log of likelihood function as a criterion. In most cases, the DWe distribution with MLM‐estimated parameters showed the best fit of all the three‐parameter models. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
997.
本文系统研究了羌塘盆地查郎拉地区中、新生代的构造特征,将整个研究区划分为五个构造单元。即那日- 破曲褶皱带、江达- 杜日断褶带、塞仁那来- 巴陇复式向斜断褶带、气相错- 查巴断陷带、查曲公玛- 日昂巴山间盆地。从晚三叠世以来,图幅内经历了印支期、燕山期、喜山期构造运动,印支期主要是在图幅北部上三叠统地层中形成北东向褶皱,燕山运动早期本区构造活动最为强烈,形成了全区范围内的东西向褶皱和断层,其中尤以南部塞仁那来- 巴陇复式向斜断褶带最为强烈,构造最为紧密,燕山晚期,以断陷构造为主,形成中部的查曲公玛- 日昂巴山间盆地和南部的气相错- 查巴断陷带,喜山期主要是形成一些新构造活动。 相似文献
998.
999.
Stream temperature will be subject to changes because of atmospheric warming in the future. We investigated the effects of the diurnal timing of air temperature changes – daytime warming versus nighttime warming – on stream temperature. Using the physically based model, Heat Source, we performed a sensitivity analysis of summer stream temperatures to three diurnal air temperature distributions of +4 °C mean air temperature: i) uniform increase over the whole day, ii) warmer daytime and iii) warmer nighttime. The stream temperature model was applied to a 37‐km section of the Middle Fork John Day River in northeastern Oregon, USA. The three diurnal air temperature distributions generated 7‐day average daily maximum stream temperatures increases of approximately +1.8 °C ± 0.1 °C at the downstream end of the study section. The three air temperature distributions, with the same daily mean, generated different ranges of stream temperatures, different 7‐day average daily maximum temperatures, different durations of stream temperature changes and different average daily temperatures in most parts of the reach. The stream temperature changes were out of phase with air temperature changes, and therefore in many places, the greatest daytime increase in stream temperature was caused by nighttime warming of air temperatures. Stream temperature changes tended to be more extreme and of longer duration when driven by air temperatures concentrated in either daytime or nighttime instead of uniformly distributed across the diurnal cycle. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
1000.
Distribution patterns of interstitial polychaetes in sandy beaches of southern Brazil 总被引:1,自引:0,他引:1
This study describes the distribution patterns of interstitial polychaetes along morphodynamic gradients on six exposed sandy beaches in Santa Catarina and Paraná (South Brazil). Three random transects were sampled at two points on each beach, one at the swash and another at the surf zone, in winter and summer conditions. Six sediment replicates were collected at each sampling point using a corer of 4.6 cm internal diameter that removed 10 cm into the sediment. Abundance and composition of interstitial polychaete were correlated to wave height, slope, grain size, CaCO3 , chlorophyll a , omega indexes, temperature and relative tide range using a canonical correspondence analysis (CCA). A factorial ANOVA showed that taxa richness, mean density and Shannon's diversity were significantly higher at the reflective beaches, but average values differ significantly between transects and these differences change according to the beach zones on both sampling dates. PERMANOVA showed that polychaete associations differ among transects according to the beach zones. The composition of interstitial polychaete associations was significantly correlated to beach morphodynamics and features (P < 0.01). Polychaete associations of reflective beaches were more diverse than in other morphodynamic states. Intermediate beaches may also sustain diverse associations due to temporal variability of the morphodynamic patterns. Beaches presenting extreme dissipative morphodynamics and compacted sediments appear to be unfavourable for the occurrence of interstitial polychaetes. 相似文献