全文获取类型
收费全文 | 973篇 |
免费 | 54篇 |
专业分类
林业 | 41篇 |
农学 | 31篇 |
基础科学 | 15篇 |
93篇 | |
综合类 | 173篇 |
农作物 | 41篇 |
水产渔业 | 23篇 |
畜牧兽医 | 516篇 |
园艺 | 48篇 |
植物保护 | 46篇 |
出版年
2023年 | 6篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 22篇 |
2015年 | 15篇 |
2014年 | 21篇 |
2013年 | 39篇 |
2012年 | 21篇 |
2011年 | 36篇 |
2010年 | 32篇 |
2009年 | 47篇 |
2008年 | 27篇 |
2007年 | 40篇 |
2006年 | 33篇 |
2005年 | 28篇 |
2004年 | 29篇 |
2003年 | 26篇 |
2002年 | 26篇 |
2001年 | 26篇 |
2000年 | 24篇 |
1999年 | 27篇 |
1998年 | 26篇 |
1997年 | 13篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 22篇 |
1991年 | 24篇 |
1990年 | 28篇 |
1989年 | 31篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 24篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1979年 | 7篇 |
1977年 | 6篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1973年 | 8篇 |
1972年 | 8篇 |
1970年 | 10篇 |
1968年 | 6篇 |
1956年 | 5篇 |
排序方式: 共有1027条查询结果,搜索用时 17 毫秒
71.
Turner CH 《Science (New York, N.Y.)》1892,19(466):16-17
72.
73.
Halite crystals from the Zag H3-6 chondrite contain essentially pure (monoisotopic) xenon-129 ((129)Xe) produced in the early history of the solar system by the decay of short-lived iodine-129 ((129)I) (half-life = 15.7 million years). Correlated release of (129)Xe and (128)Xe, produced artificially from (127)I by neutron irradiation, corresponds to an initial ((129)I/(127)I) ratio of (1.35 +/- 0.05) x 10(-4), close to the most primitive early solar system value. If the (129)Xe was produced by in situ decay, then the halite formed from an aqueous fluid within 2 million years of the oldest known solar system minerals. 相似文献
74.
Turner AP 《Science (New York, N.Y.)》2000,290(5495):1315-1317
75.
Turner RD 《Science (New York, N.Y.)》1973,180(4093):1377-1379
Wood exposed for 104 days at a depth of 1830 meters at the permanent station of the research submersible D.S.R.V. Alvin was completely riddled by two species of bivalve wood borers (subfamily Xylophagainae, family Pholadidae). Their high reproductive rate, high population density, rapid growth, early maturity, and utilization of a transient habitat classify them as opportunistic species, the first recorded from the deep sea. Xylophaga is shown to be the most important species involved in decomposing woody plant material in the deep sea. 相似文献
76.
Progress has recently been made in implementing magnetic resonance imaging (MRI) techniques that can be used to obtain images in a fraction of a second rather than in minutes. Echo-planar imaging (EPI) uses only one nuclear spin excitation per image and lends itself to a variety of critical medical and scientific applications. Among these are evaluation of cardiac function in real time, mapping of water diffusion and temperature in tissue, mapping of organ blood pool and perfusion, functional imaging of the central nervous system, depiction of blood and cerebrospinal fluid flow dynamics, and movie imaging of the mobile fetus in utero. Through shortened patient examination times, higher patient throughput, and lower cost per MRI examination, EPI may become a powerful tool for early diagnosis of some common and potentially treatable diseases such as ischemic heart disease, stroke, and cancer. 相似文献
77.
78.
The ground pattems found in Pulitrouser Swamp, northern Belize, are vestiges of raised and channelized fields, types of wetland cultivation used by the ancient Maya. This form of hydraulic cultivation was apparently employed sometime between 200 B.C. and A.D. 850. The environment of the swamp, the fields and canals, and one nearby settlement, Kokeal, are described. The evidence indicates that the large number of well-defined ground patterns reported in other areas in the central Maya lowlands are probably vestiges of Maya wetland cultivation. 相似文献
79.
80.
PC Sereno DB Dutheil M Iarochene HCE Larsson GH Lyon PM Magwene CA Sidor DJ Varricchio JA Wilson 《Science (New York, N.Y.)》1996,272(5264):986-991
Late Cretaceous (Cenomanian) fossils discovered in the Kem Kem region of Morocco include large predatory dinosaurs that inhabited Africa as it drifted into geographic isolation. One, represented by a skull approximately 1.6 meters in length, is an advanced allosauroid referable to the African genus Carcharodontosaurus. Another, represented by a partial skeleton with slender proportions, is a new basal coelurosaur closely resembling the Egyptian genus Bahariasaurus. Comparisons with Cretaceous theropods from other continents reveal a previously unrecognized global radiation of carcharodontosaurid predators. Substantial geographic differentiation of dinosaurian faunas in response to continental drift appears to have arisen abruptly at the beginning of the Late Cretaceous. 相似文献