全文获取类型
收费全文 | 63493篇 |
免费 | 969篇 |
国内免费 | 446篇 |
专业分类
测绘学 | 1415篇 |
大气科学 | 4482篇 |
地球物理 | 12557篇 |
地质学 | 23052篇 |
海洋学 | 5619篇 |
天文学 | 13783篇 |
综合类 | 147篇 |
自然地理 | 3853篇 |
出版年
2022年 | 378篇 |
2021年 | 652篇 |
2020年 | 745篇 |
2019年 | 803篇 |
2018年 | 1588篇 |
2017年 | 1579篇 |
2016年 | 1764篇 |
2015年 | 954篇 |
2014年 | 1686篇 |
2013年 | 3168篇 |
2012年 | 1948篇 |
2011年 | 2643篇 |
2010年 | 2274篇 |
2009年 | 2910篇 |
2008年 | 2570篇 |
2007年 | 2625篇 |
2006年 | 2474篇 |
2005年 | 1761篇 |
2004年 | 1764篇 |
2003年 | 1733篇 |
2002年 | 1622篇 |
2001年 | 1454篇 |
2000年 | 1378篇 |
1999年 | 1160篇 |
1998年 | 1146篇 |
1997年 | 1207篇 |
1996年 | 990篇 |
1995年 | 983篇 |
1994年 | 905篇 |
1993年 | 778篇 |
1992年 | 751篇 |
1991年 | 730篇 |
1990年 | 777篇 |
1989年 | 696篇 |
1988年 | 670篇 |
1987年 | 722篇 |
1986年 | 714篇 |
1985年 | 882篇 |
1984年 | 901篇 |
1983年 | 929篇 |
1982年 | 859篇 |
1981年 | 777篇 |
1980年 | 776篇 |
1979年 | 694篇 |
1978年 | 637篇 |
1977年 | 646篇 |
1976年 | 587篇 |
1975年 | 579篇 |
1974年 | 573篇 |
1973年 | 587篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Marine molluscan shells from para-type and other loclities of the Holsteinian interglaciation were dated by Th/U and the electron spin resonance (ESR) method to more than 350,000 and 370,000 yr B.P., beyond the limit of Th/U dating. The high age estimate is corroborated by a K/Ar age of 420,000 yr B.P. determined from volcanic ash near the base of the Ariendorf paleosol in the Middle Rhine valley believed to be a pedostratigraphic equivalent of the Holsteinian. Shells from the Herzeele marine unit III, an equivalent of the Wacken (Dömnitz) warm stage in northern France and subsequent to the Holsteinian, revealed ages between 300,000 and 350,000 yr B.P. A correlation of these two warm stages with marine oxygen-isotope stages 11 and 9 on the SPECMAP and CARTUNE time scales is suggested. From the benthic oxygen-isotope record one may infer that no exceptionally high global sea-level rise corresponds to the large transgressions of the Holstein Sea in northern Germany. Therefore, a significant proportion of the transgression was probably the result of an unusually large local glacial-isostatic depression caused by the extreme buildup of ice during the preceding Elster glaciation (stage 12). According to the deep-sea record, it lasted approximately 50% longer than the subsequent cold stage 10. The outstanding soil formation with Braunlehm and the well-developed thermal optimum of the Holsteinian are tentatively related to a phase of minimum sea-ice cover in the Norwegian-Greenland Sea, as deduced from long benthic carbon-isotope records from the central Atlantic. 相似文献
103.
In a field near M3 photographed in U,B,V from 1963 to 1969 one of 750 compact galaxies shows a brightening of 1 mag in B during 1966/67. 相似文献
104.
In this 8th compilation, the following results of observations are given: 207 observed minima of 56 eclipsing binaries, 100 maxima of 21 RR Lyrae- and δ Cephei-stars, 82 results of 32 Mira stars and long period variables, and 47 results of 9 RV Tauri stars, semiregular, and irregular variables, from the years 1966 up to 1968. 相似文献
105.
The sodian stellerite (a zeolite) occurs as lustrous white or slightly pink, easily cleavable lamellae, filling cavities and fractures in an acid lava (andesite or rhyolite) in the cliff below S. Efisio Tower, near Capo Pula, Cagliari, Sardegna, Italy. The principal forms present are {010}, {011}, {111}. Single crystal photographs show an orthorhombic symmetry and Ammm (or Ammm) space group. An indexed X-ray diffraction powder pattern is provided. Unit cell dimensions, chemical formula, density, optical properties and thermal behaviour are given. 相似文献
106.
Investigations in a newly constructed subsea road tunnel in the Iddefjord granite at Hvaler and test-pumping of boreholes on land indicate that a topographic or geophysical anomaly is no guarantee of a substantially transmissive fracture zone. Many prominent fracture zones appear to have depressed transmissivity due to secondary swelling-clay mineral infillings. No current geophysical technique can adequately distinguish these zones from transmissive ones. Given that siting of boreholes on the basis of geology alone can be unreliable, hydrogeologists should concentrate on quantifying the chances of a successful boring, and optimizing those chances by sensible location, favourable borehole orientation and use of artificial enhancement techniques. 相似文献
107.
108.
E. G. Kolomyts 《Russian Meteorology and Hydrology》2008,33(7):430-440
The gradient (ordination) analysis was used to find the tendencies and the rate of changes in discrete parameters of the cycle of forest phytomasses accompanying a growing thermoarid climatic trend. The prognostic estimates of biotic regulation of the carbon cycle by forest biogeocenoses according to the HadCM3 (version A2) climatic scenarios, describing the most powerful coming global warming, are presented. 相似文献
109.
B. E. Peskov A. A. Alekseeva A. E. Nikiforova 《Russian Meteorology and Hydrology》2008,33(10):644-650
The physical-synoptic principles of the automated method of summer precipitation forecasting introduced into operational prognostic practice in 2006 by the decree of the Central Methodical Commission of the Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet) are presented. Beside that, improved modifications of this method, which are automatically updated, are shown. Validation of those updates based on observational data collected in 2004 has shown improvement of all major criteria of forecasts efficiency. The performed improvement is based on the more detailed quantitative realization of mechanism of various showers formation (including heavy rainfalls). 相似文献
110.
Authigenic iron and titanium oxides occur in three main textural varieties in the St. Bees Sandstone, a Triassic red bed succession in Cumbria. These are: (a) overgrowths of haematite, titaniferous haematite, anatase, and rutile which generally occur on detrital host grains of similar compositions. The overgrowths may occur as syntaxial rim cements or rhombohedral and prismatic projections and are always in optical continuity, (b) discrete crystals of anatase (including octahedrite) and haematite 10-40 μm in size occur in pore spaces, and (c) fine grained ( < 1 μm) pigmentary haematite occurs as grain coatings around detrital grains and in the interstitial matrix. The euhedral nature and pore-filling habit clearly indicate the authigenic origin of these iron- and titanium oxides. All three textural varieties are believed to have been precipitated from ground waters containing dissolved ferrous and titanium ions. These ions were derived from the intrastratal solution of detrital iron and titanium bearing grains including ferromagnesian silicates and iron-titanium oxides. The precipitation of iron oxides from migrating ground waters in the manner described here goes some way to explaining how thick, uniformly red successions can be formed. 相似文献