全文获取类型
收费全文 | 26039篇 |
免费 | 458篇 |
国内免费 | 326篇 |
专业分类
测绘学 | 733篇 |
大气科学 | 1831篇 |
地球物理 | 5029篇 |
地质学 | 9031篇 |
海洋学 | 2366篇 |
天文学 | 6398篇 |
综合类 | 60篇 |
自然地理 | 1375篇 |
出版年
2021年 | 211篇 |
2020年 | 249篇 |
2019年 | 317篇 |
2018年 | 626篇 |
2017年 | 611篇 |
2016年 | 752篇 |
2015年 | 430篇 |
2014年 | 717篇 |
2013年 | 1340篇 |
2012年 | 821篇 |
2011年 | 1080篇 |
2010年 | 984篇 |
2009年 | 1282篇 |
2008年 | 1171篇 |
2007年 | 1184篇 |
2006年 | 1153篇 |
2005年 | 868篇 |
2004年 | 858篇 |
2003年 | 780篇 |
2002年 | 730篇 |
2001年 | 634篇 |
2000年 | 644篇 |
1999年 | 573篇 |
1998年 | 565篇 |
1997年 | 532篇 |
1996年 | 405篇 |
1995年 | 405篇 |
1994年 | 420篇 |
1993年 | 321篇 |
1992年 | 318篇 |
1991年 | 263篇 |
1990年 | 313篇 |
1989年 | 275篇 |
1988年 | 258篇 |
1987年 | 288篇 |
1986年 | 242篇 |
1985年 | 327篇 |
1984年 | 348篇 |
1983年 | 332篇 |
1982年 | 321篇 |
1981年 | 256篇 |
1980年 | 270篇 |
1979年 | 224篇 |
1978年 | 214篇 |
1977年 | 218篇 |
1976年 | 189篇 |
1975年 | 193篇 |
1974年 | 186篇 |
1973年 | 169篇 |
1972年 | 114篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
871.
X. Zheng Y. Zhang T. Cheng M. Zhao H. Kong Z. Jin 《International Journal of Environmental Science and Technology》2016,13(8):2091-2096
In order to prepare iron phosphate by waste sludge, we report a method for effective utilization of the sludge obtained from the electrocoagulation treatment of source-separated urine. The sludge was dissolved with hydrochloric acid and pretreated with H2O2 and Na3PO4; finally, NaOH was added to precipitate iron phosphate from the solution. Thermal treatment of the precipitate at 750 °C in air yielded crystalline quartz-like anhydrous FePO4. The precipitate was characterized by a number of thermal techniques such as thermogravimetry/differential thermal analysis, scanning electron microscopy, and X-ray powder diffraction. 相似文献
872.
Potential of river bank filtration (RBF) in Egypt 总被引:1,自引:0,他引:1
873.
874.
875.
876.
The KwaZulu-Natal Bight is a shallow indentation of the eastern seaboard of South Africa, characterised by a narrow (45 km wide) extension of the continental shelf, with a shelf break at about 100 m. It has a complex hydrography: the waters of the bight are derived from the fast-flowing, southward-trending Agulhas Current, which is fed mostly by the tropical and subtropical surface waters of the South-West Indian Ocean subgyre, which are generally oligotrophic in nature, notably depleted in reduced nitrogen and phosphate except at river mouths and during periodic upwelling of deeper nutrient-rich water. Despite this, the bight is believed to be relatively productive, and it is suggested that efficient nutrient recycling by prokaryotes may sustain primary productivity efficiently, even in the absence of new nutrient inputs. Here we have measured bacterial numbers, biomass and heterotrophic productivity during summer and winter in conjunction with phytoplankton standing stock and factors that influence it. Bacterial distribution closely matched phytoplankton distribution in surface waters, and was highest close to the coast. Bacterial standing stocks were similar to those of oligotrophic systems elsewhere (0.5–5.0 × 105 cells ml–1; 1 × 10–8 to 1.25 × 10–7 g C ml–1) and increased in association with the development of phytoplankton blooms offshore and with inputs of allochthonous material by rivers at the coast. Heterotrophic productivity in summer was lowest in the far south and north of the bight (0.5 × 10–10 g C ml–1 h–1) but higher close to the shore, over shallow banks, and in association with increased phytoplankton abundance over the midshelf (1.0–3.5 × 10–9 g C ml–1 h–1). There were marked seasonal differences with lower bacterial standing stocks (5 × 104 to 2 × 105 cells ml–1; 4–5 × 10–9 to 1–2 × 10–8 g C ml–1) and very low bacterial productivity (4 × 10–11 to 1 × 10–10 g C ml–1 h–1) in winter, probably resulting from lowered rates of primary productivity and dissolved organic matter release as well as reduced riverine allochthonous inputs during the winter drought. 相似文献
877.
878.
879.
T. K. Zlobin 《Doklady Earth Sciences》2018,480(1):599-601
The peculiarities of catastrophic earthquakes that occurred in the Northwest Pacific region on January 13, 2007, and January 15, 2007, east of the Kuril Islands and the Tohoku megaearthquake of March 11, 2011, east of Japan are considered and analyzed. It is revealed that these earthquakes, apart from the fact that they occurred in the transition zone from the Pacific to island arcs and the Eurasian continent, have common features and similar characteristics. The seismotectonic slip in the source of the chronologically first event, the 2006 Kuril earthquake, was a gentle thrust, while that of the second event of January 13, 2007, was a downthrow beneath the Kuril deep trench. 相似文献
880.
T. A. Gornostaeva A. V. Mokhov P. M. Kartashov O. A. Bogatikov 《Doklady Earth Sciences》2018,478(2):204-207
Using high-resolution analytical electron microscopy, heterogeneous fragments of cosmogenic substances, such as nickelphosphide Ni3P and the unnamed intermetallide ZnAl2, are detected for the first time for a large meteorite crater, the Zhamanshin circular structure. Due to the impossibility of simultaneous finding these phases in the same meteorite, an assumption is made on the cometary nature of the impactor of the Zhamanshin crater. 相似文献