全文获取类型
收费全文 | 824篇 |
免费 | 112篇 |
国内免费 | 147篇 |
专业分类
测绘学 | 203篇 |
大气科学 | 143篇 |
地球物理 | 172篇 |
地质学 | 280篇 |
海洋学 | 128篇 |
天文学 | 54篇 |
综合类 | 68篇 |
自然地理 | 35篇 |
出版年
2024年 | 6篇 |
2023年 | 29篇 |
2022年 | 82篇 |
2021年 | 77篇 |
2020年 | 68篇 |
2019年 | 74篇 |
2018年 | 30篇 |
2017年 | 43篇 |
2016年 | 62篇 |
2015年 | 31篇 |
2014年 | 34篇 |
2013年 | 17篇 |
2012年 | 26篇 |
2011年 | 39篇 |
2010年 | 35篇 |
2009年 | 39篇 |
2008年 | 59篇 |
2007年 | 36篇 |
2006年 | 41篇 |
2005年 | 38篇 |
2004年 | 24篇 |
2003年 | 31篇 |
2002年 | 23篇 |
2001年 | 25篇 |
2000年 | 23篇 |
1999年 | 25篇 |
1998年 | 13篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1083条查询结果,搜索用时 31 毫秒
991.
基于体验视角的历史街区旅游复兴——以福州市三坊七巷为例 总被引:7,自引:1,他引:6
目前国内历史街区在旅游开发上存在模式雷同、体验质量相似等问题,从旅游体验视角探讨了历史街区旅游复兴的新思路,分析了历史街区旅游体验要素,提出包含审美怀旧、文化教育、休闲娱乐、遁世逃避、社交生活和情感升华在内的6E体验模型及各体验要素营造方法。以福州市三坊七巷旅游发展策划为例,具体阐释了6E模型在历史街区旅游复兴中的应用,结合体验的层次性、综合性和场地分析,将整个街区由动到静、由表层到深度体验过渡,依次划分为南后老街摩尔、温馨休闲之巷、安泰水岸风情和小众定制名坊四个功能区。应用6E模型解决历史街区旅游功能分区和产品策划,有益于从文化、社会、经济层面上再造老街区的鲜活面貌,是一种可持续发展的思路。 相似文献
992.
A regional scale (a few km to a few hundred km, minutes to days)planetary boundary layer (PBL) numerical model (RPBLM) has been successfully developed to simulateprecisely the boundary-layer three-dimensional characteristics. The RPBLM model with a high-resolutionnon-hydrostatic E - turbulence closure scheme has been applied to diagnose and prognosticate the PBL characteristicsover a complex underlying surface in the Hong Kong area of 60 km × 48 km. It is shown that the RPBLMmodel can be used to simulate the PBL characteristics including wind, temperature, water vapour andturbulence over such a complex underlying surface and that the simulated result is reasonably in agreementwith observations. 相似文献
993.
在十二烷基硫酸钠存在下,于pH48~74的缓冲溶液中,2_〔2_(6_甲基苯并噻唑)偶氮〕_5_二乙氨基苯甲酸(6_Me_BTAEB)与Co(Ⅱ)发生显色反应,形成稳定的蓝紫色络合物,其组成为nCo(Ⅱ)∶n6_Me_BTAEB=1∶2,最大吸收波长为650nm,ε为138×105L·mol-1·cm-1,Co(Ⅱ)质量浓度在0~032mg/L时服从比尔定律。方法可直接用于维生素B12和含钴分子筛中微量Co(Ⅱ)的测定,结果与原子吸收法相符。对于w(Co)=0.82%的含钴分子筛测定8次,其RSD为134%。 相似文献
994.
It is demonstrated that the blind deconvolution method is fully capable of recovering the unknown Greens function and of estimating the source time functions from observed seismic data of small earthquakes. Based on the assumption of the Gaussian-mixture model of the Greens function, the newly-formulated algorithm is evaluated using synthetic seismic data along with those of the May 8, 1996 Mexico earthquake (Mc = 4.6). Since the estimated results closely match the theoretical input very well, the method is then employed to analyze the source time functions of the July 7, 1995 Pu-Li, Taiwan earthquake (ML = 5.3). The stations triggered by this event were azimuthally well covered. Using the estimated source time functions, information pertaining to the directivity effect is readily obtained, and the actual fault plane of this event is identified, thus clearly indicating that this method provides a most efficient way to estimate the source time function of a small earthquake.Acknowledgment The authors would like to express their thanks to two anonymous reviewers for their valuable suggestions and Dr. I. Santamarias courteous assistance. They also appreciate the efforts of Drs. H.C. Chiu and R.J. Rau, who provided the seismic data and the fault plane solutions. The National Science Council, Taiwan, has supported this research (NSC 91-2119-M-194-011). 相似文献
995.
Jörn Wilms Christopher S. Reynolds † Mitchell C. Begelman James Reeves Silvano Molendi Rüdiger Staubert Eckhard Kendziorra 《Monthly notices of the Royal Astronomical Society》2001,328(3):L27-L31
We present XMM-Newton European Photon Imaging Camera (EPIC) observations of the bright Seyfert 1 galaxy MCG–6-30-15, focusing on the broad Fe K α line at ∼6 keV and the associated reflection continuum, which is believed to originate from the inner accretion disc. We find these reflection features to be extremely broad and redshifted, indicating an origin in the very central regions of the accretion disc. It seems likely that we have caught this source in the 'deep minimum' state first observed by Iwasawa et al. The implied central concentration of X-ray illumination is difficult to understand in any pure accretion disc model. We suggest that we are witnessing the extraction and dissipation of rotational energy from a spinning black hole by magnetic fields connecting the black hole or plunging region to the disc. 相似文献
996.
E. L. Zodrow 《Mathematical Geology》1976,8(1):37-42
Chayes' t-test for closure correlations is developed from various approximations and assumptions. The empirical behavior of this test is observed through the use of random-sampling number matrices of order to thirteen. The experiments demonstrate a lower limit for the reliability of Chayes' model of about 91/100. That is, about one chance in ten remains that an error due to the statistical testing is committed on some product-moment correlations in a given matrix of correlation, given a confidence level of 90 percent. With increase in the number of variables, the test for departure from zero correlation can be used provided the sample size remains small. 相似文献
997.
The optical properties and spatial distribution of chromophoric dissolved organic matter (CDOM) in Meiliang Bay of Lake Taihu were evaluated and compared to the results in literature. Concentrations of dissolved organic carbon (DOC) ranged from 8.75 to 20.19 mg L?1 with an average of (13.10 ± 3.51) mg L?1. CDOM absorption coefficients a(λ) at 280 nm, 355 nm, and 440 nm were in the range 11.28...33.46 m?1 (average (20.95 ± 5.52) m?1), 2.42...7.90 m?1 (average (4.92 ± 1.29) m?1), and 0.65...2.44 m?1 (average (1.46 ± 0.44) m?1), respectively. In general, CDOM absorption coefficient and DOC concentration were found to decrease away from the river inflow to Meiliang Bay towards the lake center. The values of the DOC‐specific absorption coefficients a*(λ), given as absorption coefficient related to mass concentration of organic carbon (C) ranged from 0.28 to 0.47 L mg?1 m?1 at 355 nm. The determination coefficients between CDOM absorption and DOC concentration decreased with the increase of wavelength from 280 to 550 nm. The linear regression relationship between CDOM absorption at 280 nm and DOC concentration was following: a(280 nm) = 1.507 L mg?1 m?1 · DOC + 1.215 m?1. The spectral slope S values were dependent on the wavelength range used in the regression. The estimated S values decreased with increasing wavelength range used. A significant negative linear relationship was found between CDOM absorption coefficients, DOC‐specific absorption coefficients and estimated S values especially in longer wavelength range. The linear regression relationship between DOC‐specific absorption coefficients at 440 nm and estimated S values during the wavelength range from 280 to 500 nm was following: a*(440 nm) = (–0.021 μm · S + 0.424) L mg?1 m?1. 相似文献
998.
999.
Photocatalytic Reduction of Cr^Ⅵ by Natural Sphalerite Suspensions under Visible Light Irradiation 总被引:4,自引:0,他引:4
LI Yan LU Anhuai WANG Changqiu 《《地质学报》英文版》2006,80(2):267-272
The photocatalytic reductive capability of a natural semiconducting mineral, sphalerite has been studied for the first time. The sphalerite from the Huangshaping deposit of Hunan Province performed great photoreductive capability that 91.95% of the Cr^6+ was reduced under 9 h visible light irradiation, higher than the 70.58% under 9.5 h UV light irradiation. The highly reductive ability results from its super negative potential of electrons in the conduction band. Furthermore, Fe substitution for Zn introduces donor states, and the oxidation process of Fe^2+ to Fe^3+ makes it an effective hole-scavenger. Cd and Cu substitute for Zn also reduce the bandgap and help broaden the absorbing edge towards the visible light. These substituting metal ions in natural sphalerite make it a hyper-active photocatalyst and very attractive for solar energy utilization. 相似文献
1000.
The objective of this study was to quantify by experiments the initial seawater–suspended basaltic glass interactions following the 1996 outburst flood from the Vatnajökull glacier, Iceland. The altered basaltic glass dissolved in seawater as recorded by the Si release from the glass. The dissolved concentrations of Na, Ca, Si, Ba, Cd, Co, Cu, Hg, Mn, Ni and total dissolved inorganic N increased with time but the concentrations of Mg, K, S, Sr, Fe, Pb and Zn decreased. Calculated 1 to 10 day fluxes for Si range from 38,000 tons/day to 70,000 tons/10 days. The fluxes for other major elements are more uncertain, but the positive flux (release from suspended matter to seawater) of Ca and Na, and negative flux of Mg, K and S are greater than the Si flux. 相似文献