全文获取类型
收费全文 | 71292篇 |
免费 | 1131篇 |
国内免费 | 660篇 |
专业分类
测绘学 | 1717篇 |
大气科学 | 5042篇 |
地球物理 | 14223篇 |
地质学 | 25253篇 |
海洋学 | 6172篇 |
天文学 | 16335篇 |
综合类 | 208篇 |
自然地理 | 4133篇 |
出版年
2022年 | 398篇 |
2021年 | 706篇 |
2020年 | 778篇 |
2019年 | 825篇 |
2018年 | 1899篇 |
2017年 | 1764篇 |
2016年 | 2240篇 |
2015年 | 1322篇 |
2014年 | 2181篇 |
2013年 | 3770篇 |
2012年 | 2278篇 |
2011年 | 3123篇 |
2010年 | 2607篇 |
2009年 | 3510篇 |
2008年 | 3255篇 |
2007年 | 3049篇 |
2006年 | 2878篇 |
2005年 | 2353篇 |
2004年 | 2255篇 |
2003年 | 2110篇 |
2002年 | 1928篇 |
2001年 | 1801篇 |
2000年 | 1716篇 |
1999年 | 1377篇 |
1998年 | 1471篇 |
1997年 | 1387篇 |
1996年 | 1100篇 |
1995年 | 1142篇 |
1994年 | 962篇 |
1993年 | 872篇 |
1992年 | 856篇 |
1991年 | 762篇 |
1990年 | 857篇 |
1989年 | 717篇 |
1988年 | 650篇 |
1987年 | 814篇 |
1986年 | 664篇 |
1985年 | 856篇 |
1984年 | 922篇 |
1983年 | 862篇 |
1982年 | 831篇 |
1981年 | 707篇 |
1980年 | 663篇 |
1979年 | 606篇 |
1978年 | 603篇 |
1977年 | 552篇 |
1976年 | 539篇 |
1975年 | 499篇 |
1974年 | 506篇 |
1973年 | 468篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
J. García-Abdeslem J.M. Romo E. Gómez-Treviño J. Ramírez-Hernández F.J. Esparza-Hernández C.F. Flores-Luna 《Geophysical Prospecting》2005,53(6):755-765
The subsurface geometry of the Sebastián Vizcaíno Basin is obtained from the 2D inversion of gravity data, constrained by a density-versus-depth relationship derived from an oil exploration deep hole. The basin accumulated a thick pile of marine sediments that evolved in the fore-arc region of the compressive margin prevalent along western North America during Mesozoic and Tertiary times. Our interpretation indicates that the sedimentary infill in the Sebastián Vizcaíno Basin reaches a maximum thickness of about 4 km at the centre of a relatively symmetric basin. At the location of the Suaro-1 hole, the depth to the basement derived from this work agrees with the drilled interface between calcareous and volcaniclastic members of the Alisitos Formation. A sensitivity analysis strongly suggests that the assumed density function leads to a nearly unique solution of the inverse problem. 相似文献
132.
133.
134.
135.
M. D. Max 《Geological Journal》1973,8(2):375-386
Lewisian gneisses, Moinian and Dalradian sediments, and dolerites have been deformed and metamorphosed under Amphibolite Fades conditions. The metamorphic climax, with the growth of kyanite and staurolite, occurred after the cessation of the second deformational episode and before the onset of the third. Plagioclase growth ceased at or about the time of kyanite and staurolite nucleation. Metamorphic effects become less to the south and southeast while the most advanced stages occur around Inver. A single heat pulse appears to be not directly related to any structure. 相似文献
136.
137.
G. M. Richter 《Astronomische Nachrichten》1971,293(3):111-117
On the basis of a radio index-surface brightness diagram recently published, the luminosity function and the luminosity diameter function are obtained. The uncertainties due to the incompleteness of the sample are of the same order as the statistical uncertainties. The luminosity function differs considerably from a simple power law and supports the distinction of two populations. The density of the weak population (P<1035 W Hz−1 ster−1 at 1400 MHz) follows nearly a power law in P and increases towards small diameters at least down to I kpc. The density of the strong population (the high luminosity and small diameter part of which is occupied by the quasars) has a maximum between 1025 and 1028 W Hz−1 ster−1 and around 100 kpc. A strong evolution effect is clearly present and is in a good agreement with the models obtained from the log N-log S counts. 相似文献
138.
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
139.
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
140.
A 2D finite volume model for bebris flow and its application to events occurred in the Eastern Pyrenees 总被引:1,自引:0,他引:1
V.MEDINA A.BATEMAN M.HüRLIMANN Ph.D student Sediment Transport Research Group Department of Engineering Hydraulic Marine Environmental Engineering Technical University of Catalonia 《国际泥沙研究》2008,23(4):348-360
FLATModel is a 2D finite volume code that contains several original approaches to improve debris-flow simulation. Firstly, FLATModel incorporates a "stop-and-go" technique in each cell to allow continuous collapses and remobilizations of the debris-flow mass. Secondly, flow velocity and consequently yield stress is directly associated with the type of rheology to improve boundary accuracy. Thirdly, a simple approach for entrainment is also included in the model to analyse the effect of basal erosion of debris flows. FLATMODEL was tested at several events that occurred in the Eastern Pyrenees and simulation results indicated that the model can represent rather well the different characteristics observed in the field. 相似文献