全文获取类型
收费全文 | 329472篇 |
免费 | 36857篇 |
国内免费 | 164篇 |
专业分类
366493篇 |
出版年
2018年 | 3288篇 |
2017年 | 2999篇 |
2016年 | 4333篇 |
2015年 | 5927篇 |
2014年 | 6938篇 |
2013年 | 9522篇 |
2012年 | 10853篇 |
2011年 | 10899篇 |
2010年 | 7055篇 |
2009年 | 6629篇 |
2008年 | 9402篇 |
2007年 | 9522篇 |
2006年 | 9140篇 |
2005年 | 8685篇 |
2004年 | 8436篇 |
2003年 | 8210篇 |
2002年 | 7906篇 |
2001年 | 17543篇 |
2000年 | 17644篇 |
1999年 | 13582篇 |
1998年 | 4227篇 |
1997年 | 4364篇 |
1996年 | 4093篇 |
1995年 | 3711篇 |
1994年 | 3679篇 |
1993年 | 3747篇 |
1992年 | 10516篇 |
1991年 | 10456篇 |
1990年 | 9944篇 |
1989年 | 9741篇 |
1988年 | 9089篇 |
1987年 | 8445篇 |
1986年 | 7625篇 |
1985年 | 7497篇 |
1984年 | 5914篇 |
1983年 | 5143篇 |
1982年 | 3692篇 |
1981年 | 3256篇 |
1980年 | 3107篇 |
1979年 | 5413篇 |
1978年 | 4152篇 |
1977年 | 3794篇 |
1976年 | 3334篇 |
1975年 | 3813篇 |
1974年 | 3977篇 |
1973年 | 3931篇 |
1972年 | 3450篇 |
1971年 | 3207篇 |
1970年 | 2838篇 |
1969年 | 2763篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
85.
86.
87.
Hugo R. Permingeat Maria V. Romagnoli Juliana I. Sesma Ruben H. Vallejos 《Plant Molecular Biology Reporter》1998,16(1):89-89
An easy, reproducible and fast procedure to isolate DNA from cotton leaves is described. The addition of 0.5 M glucose in the extraction buffer avoids browning by polyphenolic compounds and improves the quality of DNA for molecular analysis. The DNA yield ranged between 150–400 mg per gram of fresh tissue. The DNA was suitable for digestion by restriction enzymes and amplificatiion by Taq DNA polymerase. 相似文献
88.
T. P. Malyshkina 《Paleontological Journal》2012,46(4):392-399
Two new species of carcharhinid sharks from the Late Eocene deposits (Tavda Formation) of the southern Trans-Urals, Abdounia vassilyevae sp. nov., previously determined as A. aff. beaugei, and A. lata sp. nov., are described. To date, up to five Priabonian species of Abdounia have been recorded. New finds supplement the data on diversity, evolution, and paleobiogeography of Abdounia. 相似文献
89.
90.
Ting Zhang Bai‐Ge Miao Bo Wang Yan‐Qiong Peng Clive T. Darwell 《Ecological Entomology》2019,44(6):844-848
1. Species interactions in tightly bound ecological mutualisms often feature highly specialised species' roles in which competitive exclusion may preclude multi‐species coexistence. Among the 800 fig (Ficus) species, it was originally considered that each was pollinated by their own wasp (Agaonidae). However, recent investigations show that this ‘one‐to‐one’ rule often breaks down, as fig species regularly host multiple agaonids but in ways suggesting that competitive processes still mediate biodiversity outcomes. 2. A phenological survey was conducted of the fig–fig wasp pair, Ficus microcarpa and its associated pollinating wasp, alongside its sister species, the cheating wasp, in Xishuangbanna, China. 3. Reproductive output underwent extreme seasonal variation. Seed and pollinator production fell markedly during cooler, drier months, although high levels of fig production continued. However, this resource was predominantly utilised by the cheater species, which offers no pollination services. Pollinators and cheaters rarely co‐occur, suggesting that temporal coexistence is constrained by competition for access to figs. 4. The overall findings indicate periodic rearrangements of mutualism dynamics, probably resulting from a strongly seasonal environment. Sympatric co‐occurrence may result from a window of opportunity for a functionally divergent agaonid, potentially due to constraints on the main pollinator in adapting to variable year‐round conditions that prevent competitive exclusion. 相似文献