全文获取类型
收费全文 | 992407篇 |
免费 | 105655篇 |
国内免费 | 387篇 |
出版年
2018年 | 9327篇 |
2017年 | 8878篇 |
2016年 | 12484篇 |
2015年 | 16061篇 |
2014年 | 19203篇 |
2013年 | 27478篇 |
2012年 | 30833篇 |
2011年 | 31715篇 |
2010年 | 21561篇 |
2009年 | 20170篇 |
2008年 | 28437篇 |
2007年 | 29560篇 |
2006年 | 27794篇 |
2005年 | 26711篇 |
2004年 | 26456篇 |
2003年 | 25518篇 |
2002年 | 25001篇 |
2001年 | 45246篇 |
2000年 | 45162篇 |
1999年 | 35874篇 |
1998年 | 12740篇 |
1997年 | 13030篇 |
1996年 | 12318篇 |
1995年 | 11368篇 |
1994年 | 10993篇 |
1993年 | 11124篇 |
1992年 | 29225篇 |
1991年 | 28755篇 |
1990年 | 27966篇 |
1989年 | 27354篇 |
1988年 | 25203篇 |
1987年 | 23943篇 |
1986年 | 22279篇 |
1985年 | 22106篇 |
1984年 | 17999篇 |
1983年 | 15777篇 |
1982年 | 11832篇 |
1981年 | 10664篇 |
1980年 | 9963篇 |
1979年 | 16798篇 |
1978年 | 13229篇 |
1977年 | 11975篇 |
1976年 | 11248篇 |
1975年 | 12597篇 |
1974年 | 13426篇 |
1973年 | 13256篇 |
1972年 | 12013篇 |
1971年 | 10860篇 |
1970年 | 9567篇 |
1969年 | 9324篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
271.
E A Rybnikova V V Rakitskaia V G Shaliapina 《Rossi?skii fiziologicheski? zhurnal imeni I.M. Sechenova / Rossi?skaia akademiia nauk》1999,85(4):594-597
Intrastriatal corticotrophin-releasing hormone (CRH) was shown to induce a decrease in the plasma tectosterone concentration. Besides, the 6-OHDA pre-treatment completely prevented the suppression of plasma testosterone in response to intrastriatal CRH administration. The findings suggest that the striatum is involved in the extrahypothalamic regulation of the gonadal endocrine function. 相似文献
272.
Morphological variation in intergrade pupfish populations from the Pecos River, Texas, U.S.A. 总被引:1,自引:0,他引:1
In the early 1980s, sheepshead minnow Cyprinodon variegates was introduced into the Pecos River, Texas, U.S.A. where it hybridized with the endemic Pecos pupfish C. pecosensis . By 1985, pupfish populations throughout approximately 300 km of the river consisted exclusively of individuals of hybrid origin (intergrades). There was significant ( P <0·05) geographic variation in most morphological characters; the general pattern of variation was of a bidirectional cline centred near Pecos, Texas. At that site, morphology of intergrade populations resembled mostly that of the introduced species. Upstream and downstream from Pecos, morphology shifted progressively toward that typical of the native form. Intergrade populations were morphologically intermediate to the parental forms, showed a rapid approach to random assortment of characters, and generally exhibited greater morphological variability than occurred in either parent species. These observations and the consistent lack of bimodality in frequency distributions of a morphological hybrid index support the contention that intergrade populations comprise panmictic admixtures of C. variegates and C. pecosensis . 相似文献
273.
A rational attempt to prepare FmocHis(piTrt)OH regiospecifically gave in fact the well-known tau-trityl isomer, and experiments with model systems indicate that the prospects for access to pi-trityl histidine derivatives, which would be of great value for the racemization-free synthesis of histidine-containing peptides, are poor. 相似文献
274.
275.
276.
To control the environmentally detrimental impact of acid rock drainage, two different countermeasures, layers of acid-buffering
materials and sodium dodecyl sulphate addition, were tested for their efficiency in laboratory percolation experiments. In
the experiment with a layer of calcium bentonite, only the iron output was reduced. The experiments with layers of concrete
grains demonstrated a decrease of the microbial activity as well as a precipitation of heavy-metal ions, whereas the cell
numbers did not decrease. Furthermore, finely grained concrete (1–5 mm) formed a water-tight hardpan (self-sealing layer).
In the experiment with 1 mM sodium dodecyl sulphate, all the microorganisms were killed and hence metal sulphide dissolution
was stopped. With 0.1 mM sodium dodecyl sulphate only a short, transient inhibition of leaching was achieved. The bacteria
remained alive.
Received: 16 February 1998 / Accepted: 23 February 1998 相似文献
277.
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
278.
279.
280.
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