首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   85730篇
  免费   1140篇
  国内免费   532篇
测绘学   1756篇
大气科学   5627篇
地球物理   16321篇
地质学   30881篇
海洋学   7893篇
天文学   19923篇
综合类   223篇
自然地理   4778篇
  2022年   619篇
  2021年   1051篇
  2020年   1117篇
  2019年   1251篇
  2018年   2554篇
  2017年   2364篇
  2016年   2722篇
  2015年   1354篇
  2014年   2625篇
  2013年   4507篇
  2012年   2865篇
  2011年   3697篇
  2010年   3381篇
  2009年   4272篇
  2008年   3730篇
  2007年   3838篇
  2006年   3561篇
  2005年   2527篇
  2004年   2448篇
  2003年   2288篇
  2002年   2275篇
  2001年   1974篇
  2000年   1961篇
  1999年   1539篇
  1998年   1599篇
  1997年   1471篇
  1996年   1245篇
  1995年   1247篇
  1994年   1049篇
  1993年   1012篇
  1992年   943篇
  1991年   969篇
  1990年   937篇
  1989年   819篇
  1988年   752篇
  1987年   886篇
  1986年   777篇
  1985年   951篇
  1984年   1075篇
  1983年   1035篇
  1982年   952篇
  1981年   894篇
  1980年   797篇
  1979年   752篇
  1978年   731篇
  1977年   620篇
  1976年   633篇
  1975年   621篇
  1974年   591篇
  1973年   658篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
This paper reports investigation data on the temporal variability of total ozone content (TOC) in the Central Asian and Tibet Plateau mountain regions obtained by conventional methods, as well as by spectral, cross-wavelet, and composite analyses. The data of ground-based observation stations located at Huang He, Kunming, and Lake Issyk-Kul, along with the satellite data obtained at SBUV/SBUV2 (SBUV merged total and profile ozone data, Version 8.6) for 1980–2013 and OMI (Ozone Monitoring Instrument) and TOU (Total Ozone Unit) for 2009–2013 have been used. The average relative deviation from the SBUV/SBUV2 data is less than 1% in Kunming and Issyk-Kul for the period of 1980–2013, while the Huang He Station is characterized by an excess of the satellite data over the ground-based information at an average deviation of 2%. According to the Fourier analysis results, the distribution of amplitudes and the periods of TOC oscillations within a range of over 14 months is similar for all series analyzed. Meanwhile, according to the cross-wavelet and composite analyses results, the phase relationships between the series may considerably differ, especially in the periods of 5–7 years. The phase of quasi-decennial oscillations in the Kunming Station is close to the 11-year oscillations of the solar cycle, while in the Huang He and Issyk-Kul stations the TOC variations go ahead of the solar cycle.  相似文献   
962.
The Weather Research and Forecast numerical model (WRF) with the dynamic Advanced Research WRF (ARW) solver was used to simulate the winter (January 2016) and summer (July 2015) atmospheric state over the North Atlantic with a high (15 km) spatial resolution. The quality of precipitation modeling was validated by remote sensing Global Precipitation Measurements (GPM) data and atmospheric ERA-Interim reanalysis. Nonhydrostatic and hydrostatic equations for the vertical velocity were additionally used to investigate their influence on the accuracy of the precipitation modeling results. It was shown that the model in this configuration satisfactorily reproduces the precipitation field. No evidence of hydrostatic approximation was revealed (over a simulation domain with a resolution of 15 km, simplified topography, and parameterizations of convection and microphysical processes).  相似文献   
963.
As a result of mooring of autonomous seabed stations in bays of Shikotan Island, the records of two tsunamis were obtained from strong earthquakes that occurred off the coast of Chile on April 1, 2014, and September 16, 2015. In both cases, prolonged intense vibrations with a pronounced group structure were observed in various bays, mainly with periods of the main modes of resonance oscillations. The second event was more dangerous, and the wave height was 0.9 m at Malokurilskaya Bay. The increase in the energy of fluctuations in 2015 was more significant, manifesting itself in a wider range of periods. Numerical simulation of the tsunami showed that the nature of wave propagation in both earthquakes was identical in the northern part of the Pacific Ocean, approaching Russia’s Pacific coast, and was characterized by weak damping, in contrast to waves propagating to the south and southwest. This explains why expect large waves can be expected on the coasts of the Kurils from earthquakes off the coast of South America, despite the considerable distance.  相似文献   
964.
For the past four decades, the CPT has played a key role in onshore and offshore soil investigations. One of the main applications of cone penetration test (CPT) is the soil behavioral classification. Most of the developed methods for soil identification using CPT and CPTu (piezocone) data are well categorized for common soils, such as clays, silts, and sands. Soils with low resistance or more compressibility generally involve problems in geotechnical engineering practice and construction projects. Consequently, these unusual deposits require further evaluation and more detailed data. Five major groups of problematic soils including: liquefiable, sensitive, peaty, collapsible, and expansive soils have been considered in this study. One hundred and forty CPT and CPTu test records were collected from fifteen countries. Sixty-one of the records are related to difficult soils. A brief comparison is performed for currently used soil behavioral classification charts, such as by Campanella et al. (1985 Campanella, R. G., P. K. Robertson, D. Gillespie, and J. Greig. 1985. Recent developments in in-situ testing of soils. Proceedings of 11th International Conference on Soil Mechanics and Foundation Engineering, ICSMFE, San Francisco, Vol. 2, 849–54. [Google Scholar]), Robertson (1990 Robertson, P. K. 1990. Soil classification using the cone penetration test. Canadian Geotechnical Journal 27 (1):15158. doi:10.1139/t90–014[Crossref], [Web of Science ®] [Google Scholar]), Jefferies and Davies (1991 Jefferies, M. G., and M. P. Davies. 1991. Soil classification using the cone penetration test: Discussion. Canadian Geotechnical Journal 28 (1):17376. doi:10.1139/t91–023[Crossref], [Web of Science ®] [Google Scholar]) and Eslami and Fellenius (1997 Eslami, A., and B. H. Fellenius. 1997. Pile capacity by direct CPT and CPTu methods applied to 102 case histories. Canadian Geotechnical Journal 34 (6):886904. doi:10.1139/cgj-34–6-886[Crossref], [Web of Science ®] [Google Scholar]). Analysis based on CPT data indicates that a few commonly used charts recognize relatively well problematic deposits. However, further studies are needed to increase the accuracy and capability of methods. Existing charts have some problems due to the limitations of the nature of rectangular charts based on two axes. A new format of classification chart, i.e., triangular form containing cone tip resistance (qc), sleeve friction (fs), and pore pressure (u2) is proposed for soil identification which can be realized in practice. The proposed chart with more accuracy and less scattering of data than the previous charts is able to identify soil types particularly for deltaic soils.  相似文献   
965.
The different mineral phases of the ferromanganese (Fe–Mn) crusts stem from the interaction of biotic and abiotic components. It is therefore vital to study the activity of these components to decipher their contribution to the enrichment/depletion of metals in the crust. Thus, the present study examined sorption and release of Co and Ni by Fe-Mn crusts with associated microbial communities in the presence and absence of the metabolic poison sodium azide (15?mM). The study was conducted in the presence (G+) and absence (G?) of added glucose (0.1%) at temperatures of 4?±?1°C and 28?±?2°C. Results showed that the microbial community had maximal sorption of Co of 66.12?µg?g?1 at 4?±?1°C in the absence of added glucose and 479.75?µg?g?1 at 28?±?2°C in the presence of added glucose. Maximum sorption of Ni in the absence of added glucose was 1.89?µg?g?1 at 4?±?1°C and release of Ni was 51.28?µg?g?1 in the presence of added glucose. Under abiotic conditions with 15?mM sodium azide as a metabolic inhibitor, significant amounts of Co and Ni were released in the G+ medium. Total cell counts on the Fe-Mn crust in the presence of added glucose increased by an order of magnitude from 106 to 107 cells g?1 and in the absence of added glucose remained within the order of 106 cells?g?1 irrespective of temperature of incubation. Microscopic observation of the samples from biotic incubations showed numerous bacterial cells, exopolysaccharides, and structures resembling secondary minerals formed by bacteria. The results indicate that bacteria promote the enrichment of Co and Ni on the hydrogenetic Fe-Mn crusts by sorption processes and release of Ni by reductive dissolution of the oxides. The higher enrichment of Co than Ni is attributed to the way in which microbes interact with the metals.  相似文献   
966.
Under the action of marine currents, non-cohesive sediments evolve by bed-load, by saltation or suspension depending on their granulometry. Several authors have considered that the movement of sediment...  相似文献   
967.
The results of wind-wave measurements with bottom-pressure sensors are discussed. These measurements were performed at the southeastern coast of the Island of Sakhalin in 2006–2009. The problems of converting data obtained with these sensors into water-level displacent in the context of the linear theory are noted. Twenty records with a duration of 2 weeks to 3 months were obtained. These records contain from 150000 to 1200000 waves for three different observation points located at the southeastern coast of Sakhalin in the regions of the village of Vzmor’ye, Lake Izmenchivoye, and the Cape of Ostryi. The estimates obtained for wave-height distributions were approximated by the Weibull distribution. They were compared to the theoretical Rayleigh, Forristall, Weibull, and Glukhovskii distributions. As one would expect, in the region of small wave heights, all distributions prove to be close to one another, and, for large wave heights, the Weibull distribution is preferred.  相似文献   
968.
969.
A classification of sea ice in the Arctic by age (multiyear; first-year; and first-year deformed ice, nilas, etc.) is developed based on the Bayesian approach using satellite radar data and taking into account regional peculiarities of these types of ice for different sectors of the Arctic. Estimations of a priori probabilities for each ice type, which are required for the use of the Bayesian classification, are obtained by the analysis of ice charts in the Arctic seas developed at the AARI in 2008–2013 using satellite data. A posterior probabilities are estimated visually by an expert. Types of sea ice distinguished by the expert on satellite images make it possible to create sample values of the radar-scattering cross section (RSCS). Examples of the proposed Bayesian classification of ice in the Laptev Sea according to Envisat satellite data are given.  相似文献   
970.
Based on the archived data of the ocean color scanner MODIS-Aqua for 2003–2011, we constructed the long-term monthly mean distributions of the reflectance Rrs of the Black Sea for April, May, June, and September in order to visualize the contributions of seasonal factors to the long-term variability of the basin’s images. In April, the Rim Current’s branch west of 34° E is visualized by higher Rrs in different regions of the visible spectrum due to the transport of suspended matter caused by intensification of the Rim Current during the winter-spring period. During the June coccolithophore “blooms,” the long-term Rrs level is 2–3 times higher when compared to the previous and subsequent months. This excess is particularly considerable outside the shelf and coastal areas. The open sea Rrs distribution in June features horizontal inhomogeneity. The seasonal trend of the Rrs spectra on the Black Sea NW shelf is explicitly related to the annual cycle of the continental runoff effects.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号