全文获取类型
收费全文 | 212279篇 |
免费 | 7978篇 |
国内免费 | 901篇 |
专业分类
221158篇 |
出版年
2023年 | 687篇 |
2022年 | 769篇 |
2021年 | 1629篇 |
2020年 | 1393篇 |
2019年 | 1426篇 |
2018年 | 14473篇 |
2017年 | 12956篇 |
2016年 | 11024篇 |
2015年 | 5888篇 |
2014年 | 5809篇 |
2013年 | 7577篇 |
2012年 | 12473篇 |
2011年 | 19582篇 |
2010年 | 16231篇 |
2009年 | 11551篇 |
2008年 | 15205篇 |
2007年 | 16473篇 |
2006年 | 6011篇 |
2005年 | 5391篇 |
2004年 | 5806篇 |
2003年 | 5394篇 |
2002年 | 4793篇 |
2001年 | 3333篇 |
2000年 | 3049篇 |
1999年 | 2330篇 |
1998年 | 1103篇 |
1997年 | 813篇 |
1996年 | 861篇 |
1995年 | 786篇 |
1994年 | 708篇 |
1992年 | 1437篇 |
1991年 | 1353篇 |
1990年 | 1224篇 |
1989年 | 1279篇 |
1988年 | 1116篇 |
1987年 | 1085篇 |
1986年 | 1000篇 |
1985年 | 1071篇 |
1984年 | 896篇 |
1983年 | 788篇 |
1979年 | 931篇 |
1978年 | 679篇 |
1975年 | 764篇 |
1974年 | 825篇 |
1973年 | 784篇 |
1972年 | 958篇 |
1971年 | 928篇 |
1970年 | 699篇 |
1969年 | 755篇 |
1968年 | 715篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
H. Štorchová 《Biologia Plantarum》1994,36(3):358-358
62.
63.
M Górska 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1992,47(46-48):1069-1071
64.
65.
Effect of pharmacological agents on the activity of the circular and longitudinal smooth muscle layers of human fallopian tube ampullar segments 总被引:1,自引:0,他引:1
The in vitro determination of the effects of some pharmacological agents on the outer diameter and axial tension of human Fallopian tube ampullar segments showed that some drugs may act on the circular and longitudinal smooth muscle layers relatively separately. PGF2 alpha elicited an excitatory response in both muscle layers while norepinephrine and isoproterenol decreased the activity. Oxytocin and indomethacin had relatively limited effects on the spontaneous motility of the ampullar segments. The calcium antagonist verapamil inhibited the spontaneous periodic activity. 相似文献
66.
Recently three biogeographical units were identified along the Chilean coast (the Magellanic Province, an Intermediate Area, and the Peruvian Province), however few studies have focused on the factors and dynamic processes that formed these spatial units (e.g. Rapoport's rule and its causal mechanisms). In this study we used benthic polychaetes of the Chilean coast to evaluate patterns of latitudinal distribution and species richness, and the existence of the three main biogeographical provinces described for the Chilean coast. Additionally, we evaluated the latitudinal Rapoport effects and geometric constraint as a null hypothesis explaining the species richness distribution.
We found that benthic polychaete diversity increased towards southern latitudes. The cluster and ordination (non-metric MultiDimensional Scaling, nMDS) analyses of the distribution data, presented only two statistically significant (bootstrapping techniques) biogeographic provinces along the Chilean coast, with a break occurring between 41° and 42°S. While, our results did not support a latitudinal Rapoport effect, they did support the view that latitudinal Rapoport effects are a local phenomenon, occurring only for the Northeastern Pacific marine taxa. The relationship between latitudinal range extent and mean latitude indicated the existence of two hard boundaries at either extreme of the Chilean coast, limiting the geographical ranges of the species. However, geometric constraints tested using a Monte Carlo simulation approach showed a weak level of mid-domain effect on species richness. Finally, we propose that geometric constraint together with the geomorphology and historical characteristics of the Chilean coast explain the biogeographical patterns of benthic polychaete taxa in Chile. 相似文献
We found that benthic polychaete diversity increased towards southern latitudes. The cluster and ordination (non-metric MultiDimensional Scaling, nMDS) analyses of the distribution data, presented only two statistically significant (bootstrapping techniques) biogeographic provinces along the Chilean coast, with a break occurring between 41° and 42°S. While, our results did not support a latitudinal Rapoport effect, they did support the view that latitudinal Rapoport effects are a local phenomenon, occurring only for the Northeastern Pacific marine taxa. The relationship between latitudinal range extent and mean latitude indicated the existence of two hard boundaries at either extreme of the Chilean coast, limiting the geographical ranges of the species. However, geometric constraints tested using a Monte Carlo simulation approach showed a weak level of mid-domain effect on species richness. Finally, we propose that geometric constraint together with the geomorphology and historical characteristics of the Chilean coast explain the biogeographical patterns of benthic polychaete taxa in Chile. 相似文献
67.
The purpose of this review is to provide a global perspective on Oncorhynchus salmonine introductions and put-and-take fisheries based on modern stocking programs, with special emphasis on freshwater
ecosystems. We survey the global introductions of nine selected salmonines of the genus Oncorhynchus: golden trout, cutthroat trout, pink salmon, chum salmon, coho salmon, masu/cherry salmon, rainbow trout/steelhead, sockeye
salmon/kokanee, and chinook salmon. The information is organized on a geographical basis by continent, and then by species
and chronology. Two different objectives and associated definitions of ‘success’ for introductions are distinguished: (a)
seed introduction: release of individuals with the purpose of creating a wild-reproducing, self-sustaining population; and
(b) put-and-take introduction: release of individuals with the purpose of maintaining some level of wild population abundance,
regardless of wild reproduction. We identify four major phenomena regarding global salmonine introductions: (1) general inadequacy
of documentation regarding introductions; (2) a fundamental disconnect between management actions and ecological consequences
of introductions; (3) the importance of global climate change on success of previous and future introductions; and (4) the
significance of aquaculture as a key uncertainty in accidental introductions. We conclude this review with a recognition of
the need to terminate ongoing stocking programs for introduced salmonines worldwide. 相似文献
68.
69.
70.
A strain of 1,507 typised donors enables 15.97 average donors to be selected for a thrombocyte transfusion in one of 75 patients selected at random with HLA antibodies being previously determined (1 to 66 donors per patient). HLA compatible donors were found for 72 patients (97.33 per cent). More than 5 HLA compatible donors could be found for 58 patients. The high number of compatible donors is based on the fact that among 1,507 donors there were 156 HLA homozygotes and 556 donors with 3 HLA-A or B-antigens respectively. Compatibility in the ABO-system was not taken into account. 相似文献