全文获取类型
收费全文 | 96301篇 |
免费 | 1196篇 |
国内免费 | 1743篇 |
专业分类
测绘学 | 3115篇 |
大气科学 | 6933篇 |
地球物理 | 18073篇 |
地质学 | 37243篇 |
海洋学 | 7950篇 |
天文学 | 18929篇 |
综合类 | 2364篇 |
自然地理 | 4633篇 |
出版年
2022年 | 541篇 |
2021年 | 900篇 |
2020年 | 994篇 |
2019年 | 1043篇 |
2018年 | 6677篇 |
2017年 | 5865篇 |
2016年 | 5000篇 |
2015年 | 1582篇 |
2014年 | 2493篇 |
2013年 | 4025篇 |
2012年 | 3473篇 |
2011年 | 5804篇 |
2010年 | 4776篇 |
2009年 | 5825篇 |
2008年 | 4933篇 |
2007年 | 5443篇 |
2006年 | 3101篇 |
2005年 | 2330篇 |
2004年 | 2542篇 |
2003年 | 2395篇 |
2002年 | 2203篇 |
2001年 | 1794篇 |
2000年 | 1691篇 |
1999年 | 1325篇 |
1998年 | 1409篇 |
1997年 | 1279篇 |
1996年 | 1110篇 |
1995年 | 1039篇 |
1994年 | 971篇 |
1993年 | 830篇 |
1992年 | 812篇 |
1991年 | 809篇 |
1990年 | 867篇 |
1989年 | 672篇 |
1988年 | 674篇 |
1987年 | 739篇 |
1986年 | 641篇 |
1985年 | 861篇 |
1984年 | 898篇 |
1983年 | 796篇 |
1982年 | 778篇 |
1981年 | 671篇 |
1980年 | 680篇 |
1979年 | 631篇 |
1978年 | 628篇 |
1977年 | 503篇 |
1976年 | 491篇 |
1975年 | 499篇 |
1974年 | 448篇 |
1973年 | 480篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
This article examines the recent progress of geography education as an academic subfield of geography and as an area of activity in K–12 education. Challenges to both endeavors are described. A restructuring of geography education's research program that focuses on spatial thinking and reasoning and merges applied and theoretical research is proposed. 相似文献
143.
144.
145.
Sensitivity kernels for finite-frequency surface waves 总被引:1,自引:1,他引:1
146.
147.
148.
149.
M. Narayanasamy D. Dhanasekaran G. Vinothini N. Thajuddin 《International Journal of Environmental Science and Technology》2018,15(1):119-132
Printed circuit boards contain precious metals. They are produced in large volumes, rendering them an important component of the electronic waste. In view of the heterogeneity of the metals present, reprocessing of electronic waste is a heinous task. The present study focused on leaching of valuable metals from electronic waste printed circuit boards using Aspergillus niger DDNS1. The adaptation phases began at 0.1, 0.5 and 1.0% of fine powder of printed circuit boards with 10% inoculum and were optimized with three effective factors, viz. initial pH, particle size and pulp density, to achieve the maximum simultaneous recovery of the valuable metals. The interactions of these metals were also deciphered using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectrum and atomic absorption spectroscopy. The results indicated that extraction of the precious metals was accomplished mainly through the unique organic acids originating from A. niger DDNS1. The initial pH played an important role in the extraction of the precious metals and the metals precipitate formation. The leaching rate of the metals was generally higher at low powder dosage of printed circuit boards. The toxicity of the printed circuit boards had little effect on two-step bioleaching at the pulp density of 0.1% compared to one-step bioleaching. The two-step bioleaching process was followed under organic acid-forming conditions for the maximum mobilization of metals. Thus, the precious metals from printed circuit boards could be mobilized through fungal bioleaching which promises an important industrial application in recycling of electronic wastes. 相似文献
150.
The study of REE distribution in the clay fraction of sedimentary rocks from two coalfields made it possible to distinguish
several types of REE distribution, which correlate with their mineral composition. It is shown that the REE fractionation
was related to the mineral reconstruction of the primary clay fraction and some detrital minerals in the course of postsedimentary
transformations of rocks during diagenesis, early catagenesis, and beginning of late catagenesis. These transformations were
governed by several factors, such as the composition of sediments; hydrochemical features of accumulation environment; the
chemical composition, dynamics, and feeding sources of pore solutions; the porosity and permeability of sediments and rocks;
and the content of organic matter and its reaction ability. 相似文献