全文获取类型
收费全文 | 92篇 |
免费 | 14篇 |
专业分类
林业 | 3篇 |
农学 | 5篇 |
基础科学 | 1篇 |
39篇 | |
综合类 | 14篇 |
农作物 | 22篇 |
水产渔业 | 3篇 |
畜牧兽医 | 16篇 |
植物保护 | 3篇 |
出版年
2023年 | 1篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 1篇 |
2013年 | 4篇 |
2012年 | 3篇 |
2011年 | 2篇 |
2010年 | 3篇 |
2009年 | 4篇 |
2008年 | 1篇 |
2007年 | 5篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
1957年 | 1篇 |
1954年 | 2篇 |
1947年 | 1篇 |
1945年 | 1篇 |
1943年 | 1篇 |
1941年 | 3篇 |
1940年 | 1篇 |
1937年 | 1篇 |
1936年 | 3篇 |
1930年 | 2篇 |
1928年 | 5篇 |
1925年 | 2篇 |
排序方式: 共有106条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
75.
Transformations of native soil organic materials, previously labelled with 14C, were investigated in soil planted with maize or perennial ryegrass and in fallow controls. There was more 14C in cold water extracts from planted soils than from fallow controls—an effect apparently caused by suppression of processes that remove labelled organic materials from this fraction of the soil organic matter. Decomposition of the labelled organic matter to 14CO2 was significantly less in the planted soils than in fallow controls. 相似文献
76.
77.
M.J. Goss 《Soil & Tillage Research》1984,4(4):403-404
78.
Bower GC Falcke H Herrnstein RM Zhao JH Goss WM Backer DC 《Science (New York, N.Y.)》2004,304(5671):704-708
We have detected the intrinsic size of Sagittarius A*, the Galactic center radio source associated with a supermassive black hole, showing that the short-wavelength radio emission arises from very near the event horizon of the black hole. Radio observations with the Very Long Baseline Array show that the source has a size of 24 +/- 2 Schwarzschild radii at 7-millimeter wavelength. In one of eight 7-millimeter epochs, we also detected an increase in the intrinsic size of 60(-17)(+25)%. These observations place a lower limit to the mass density of Sagittarius A* of 1.4 x 10(4) solar masses per cubic astronomical unit. 相似文献
79.
WM Folkner RA Preston JS Border J Navarro WE Wilson M Oestreich 《Science (New York, N.Y.)》1997,275(5300):644-646
Although the Galileo probe was designed to communicate only to the orbiter, the probe radio signal was detected at two Earth-based radio observatories where the signal was a billion times weaker. The measured signal frequency was used to derive a vertical profile of the jovian zonal wind speed. Due to the mission geometry, the Earth-based wind estimates are less sensitive to descent trajectory errors than estimates based on probe-orbiter Doppler measurements. The two estimates of wind profiles agree qualitatively; both show high wind speeds at all depths sampled. 相似文献
80.
ABSTRACT The Nuevo Laredo maquiladora sector has grown enormously during the last two decades. The short‐term time series characteristics of this portion of the regional economy are analyzed in an attempt to quantify the trends underlying this remarkable performance. Parameter estimation is accomplished via linear transfer function (LTF) analysis. Data are drawn from the January 1990–December 2000 sample period. Empirical results indicate that real wage rates, maquiladora plants, U.S. industrial activity, and the real exchange rate of the peso play significant roles in determining month‐to‐month fluctuations in maquiladora employment. Furthermore, sub‐sample forecast simulation exercises are conducted as an additional means for verifying model reliability. Empirical results indicate that the forecasts generated with the LTF model are less accurate than those associated with a simple random walk procedure for twelve separate step‐length periods. 相似文献