全文获取类型
收费全文 | 538697篇 |
免费 | 60829篇 |
国内免费 | 83236篇 |
专业分类
测绘学 | 48803篇 |
大气科学 | 63402篇 |
地球物理 | 115132篇 |
地质学 | 247438篇 |
海洋学 | 70397篇 |
天文学 | 56385篇 |
综合类 | 24889篇 |
自然地理 | 56316篇 |
出版年
2024年 | 2557篇 |
2023年 | 7053篇 |
2022年 | 15966篇 |
2021年 | 20591篇 |
2020年 | 17843篇 |
2019年 | 20003篇 |
2018年 | 23185篇 |
2017年 | 22081篇 |
2016年 | 24602篇 |
2015年 | 21110篇 |
2014年 | 26143篇 |
2013年 | 33798篇 |
2012年 | 30880篇 |
2011年 | 33824篇 |
2010年 | 32867篇 |
2009年 | 34505篇 |
2008年 | 33205篇 |
2007年 | 31884篇 |
2006年 | 29841篇 |
2005年 | 24342篇 |
2004年 | 19666篇 |
2003年 | 16143篇 |
2002年 | 15545篇 |
2001年 | 14044篇 |
2000年 | 14316篇 |
1999年 | 11233篇 |
1998年 | 8745篇 |
1997年 | 7779篇 |
1996年 | 7687篇 |
1995年 | 7171篇 |
1994年 | 6413篇 |
1993年 | 4568篇 |
1992年 | 4207篇 |
1991年 | 3723篇 |
1990年 | 3624篇 |
1989年 | 3200篇 |
1988年 | 2951篇 |
1987年 | 3253篇 |
1986年 | 3053篇 |
1985年 | 3467篇 |
1984年 | 3712篇 |
1983年 | 3347篇 |
1982年 | 3034篇 |
1981年 | 2774篇 |
1980年 | 2515篇 |
1979年 | 2372篇 |
1978年 | 2228篇 |
1977年 | 1985篇 |
1976年 | 1869篇 |
1973年 | 1777篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
272.
The change in the darkness of the Great Red Spot (GRS) of Jupiter (1894–1974) has been analysed with Fourier (FFT), Maximum Entropy and Power spectrum (Blackman-Tukey window) (PSA) methods of spectrum analysis. Significance, non-randomness and stationarity tests assigned high variance to periodicities of 33 ± 4, 13–15, about 11, 9 and 3 yrs. The highest correlation between solar activity and GRS darkness was found for the 14th and 16th solar cycle. The periodicities obtained are interpreted as the combined eftects of solar activity, planetary resonances and internal jovian mechanisms. 相似文献
273.
本文使用红外天文卫星(IRAS)巡天数据的最新版本IRAS天空巡天图(ISSA),经过进一步处理,得到了S140S141和S142SharplessHII区-分子云复合体的红外发射强度、温度及其光深的分布.在此基础上对各HII区的一些物理参量进行了统计分析,得到了分子云复合体的红外发射总光度以及复合体中尘埃的分布情况,对小尺度尘埃(VSG)的丰度进行了分析.并对各恒星形成区中的致密团块进行了研究,揭示出其中一些可能的恒星形成区域.同时,对S140区中的有关红外点源作出了能谱分析,并对S141区的激发星进行了讨论. 相似文献
274.
四川石棉大水沟独立碲矿床堪称世界首例,其矿体两侧的围岩蚀变较窄,且蚀变带与矿脉及未蚀变岩呈清楚而截然的接触关系。主要围岩蚀变为白云石化、白(绢)云母化、云英岩化及电气石化等。这些蚀变作用分别发生于177.7~165.1Ma和91.71~80.19Ma。蚀变作用过程中SiO2大量析出,Al2O3、TiO2、CaO、MgO、K2O、H2O、CO2、Fe2O3、MnO则有不同程度地带入。与此同时,REE在此过程中包集体迁出,Te、Bi、AS等元素的含量则决定于蚀变作用及其强度,而与原岩无关。 相似文献
275.
The emergence of artificial neural network (ANN) technology has provided many promising results in the field of hydrology and water resources simulation. However, one of the major criticisms of ANN hydrologic models is that they do not consider/explain the underlying physical processes in a watershed, resulting in them being labelled as black‐box models. This paper discusses a research study conducted in order to examine whether or not the physical processes in a watershed are inherent in a trained ANN rainfall‐runoff model. The investigation is based on analysing definite statistical measures of strength of relationship between the disintegrated hidden neuron responses of an ANN model and its input variables, as well as various deterministic components of a conceptual rainfall‐runoff model. The approach is illustrated by presenting a case study for the Kentucky River watershed. The results suggest that the distributed structure of the ANN is able to capture certain physical behaviour of the rainfall‐runoff process. The results demonstrate that the hidden neurons in the ANN rainfall‐runoff model approximate various components of the hydrologic system, such as infiltration, base flow, and delayed and quick surface flow, etc., and represent the rising limb and different portions of the falling limb of a flow hydrograph. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
276.
277.
The Dergaon (H5) chondrite: Fall,classification, petrological and chemical characteristics,cosmogenic effects,and noble gas records 总被引:1,自引:0,他引:1
P. N. SHUKLA A. D. SHUKLA V. K. RAI S. V. S. MURTY N. BHANDARI J. N. GOSWAMI A. C. MAZUMDAR P. PHUKON K. DUORAH R. E. GREENWOOD I. A. FRANCHI 《Meteoritics & planetary science》2005,40(4):627-637
Abstract— A multiple fall of a stony meteorite occurred near the town of Dergaon in Assam, India, on March 2, 2001. Several fragments weighing <2 kg and a single large fragment weighing ~10 kg were recovered from the strewn field, which extended over several tens of square kilometers. Chemical, petrographic, and oxygen isotopic studies indicate it to be, in most aspects, a typical H5 chondrite, except the unusually low K content of ~340 ppm. A cosmic ray exposure of 9.7 Ma is inferred from the cosmogenic noble gas records. Activities of eleven cosmogenic radionuclides were measured. 26Al and 22Na activities as well as the 22Na/26Al activity ratio are close to the values expected on the basis of solar modulation of galactic cosmic rays. The low 60Co activity (<1 dpm/kg) is indicative of a small preatmospheric size of the meteorite. Cosmic ray heavy nuclei track densities in olivine grains range from ~106 cm?2 in samples from the largest fragment to approximately (4–9) × 105 cm?2 in one of the smaller fragments. The combined track, radionuclide, and noble gas data suggest a preatmospheric radius of ~20 cm for the Dergaon meteorite. 相似文献
278.
A new species,Clathrocorys gracilis nov. spec. of Tripocyrtidae (Radiolarians: Nassellaria) from surface water in northern South China Sea, is described in this
paper. The new species has four radial beams arising from the cephalic base centre, each foot with cup-shaped structure and
ramified bar in the proximal section (near cephalic base), and each wing with a large mesh in the middle, a medium mesh and
a small mesh on each side respectively.
Project supported by the NSFC (No. 40276044) and the Chinese Academy of Sciences (No. KSCX2-SW-101B). 相似文献
279.
The dynamics of clumps observed in planetary nebulae are considered. The possibility that SiO maser spots in evolved stars and the planetary nebula clumps are formed by the Parker instability behind shocks in pulsating stars' atmospheres is raised. Molecular observations of the clumps are suggested. The effects of the ablation of clumps on the global flow structure of a more tenuous plasma in which they are embedded are reviewed. 相似文献
280.
We obtain some cosmological models that are exact solutions of Einstein's field equations. The metric utilized is Marder's metric which is Bianchi Type I and the curvature source is a cloud of strings which are one dimensional objects. Bianchi type cosmological models play an important role in the study of the universe on a scale which anisotropy is not ignored. In this paper we have investigated the effect of cosmic strings on the cosmic microwave background anisotropy. Various physical and geometrical properties of the model are also discussed. The solutions have reported that the cosmic microwave background anisotropy may due to the cosmic strings. 相似文献