全文获取类型
收费全文 | 372878篇 |
免费 | 41321篇 |
国内免费 | 198篇 |
出版年
2018年 | 3365篇 |
2017年 | 3194篇 |
2016年 | 4739篇 |
2015年 | 6881篇 |
2014年 | 7779篇 |
2013年 | 10796篇 |
2012年 | 12312篇 |
2011年 | 12023篇 |
2010年 | 8247篇 |
2009年 | 7462篇 |
2008年 | 10653篇 |
2007年 | 11078篇 |
2006年 | 10202篇 |
2005年 | 9814篇 |
2004年 | 9465篇 |
2003年 | 9031篇 |
2002年 | 9071篇 |
2001年 | 19312篇 |
2000年 | 19504篇 |
1999年 | 15133篇 |
1998年 | 4820篇 |
1997年 | 5043篇 |
1996年 | 4852篇 |
1995年 | 4532篇 |
1994年 | 4422篇 |
1993年 | 4305篇 |
1992年 | 12457篇 |
1991年 | 11867篇 |
1990年 | 11461篇 |
1989年 | 10977篇 |
1988年 | 10135篇 |
1987年 | 9433篇 |
1986年 | 8689篇 |
1985年 | 8648篇 |
1984年 | 6934篇 |
1983年 | 5991篇 |
1982年 | 4457篇 |
1981年 | 3905篇 |
1980年 | 3613篇 |
1979年 | 6504篇 |
1978年 | 4909篇 |
1977年 | 4376篇 |
1976年 | 3994篇 |
1975年 | 4543篇 |
1974年 | 4786篇 |
1973年 | 4645篇 |
1972年 | 4286篇 |
1971年 | 3648篇 |
1970年 | 3285篇 |
1969年 | 3098篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
CHRISTIAN K. FELD 《Freshwater Biology》2013,58(4):715-729
1. Although many studies have focussed on the effects of catchment land use on lotic systems, the importance of broad (catchment) and fine (segment/reach) scale effects on stream assemblages remain poorly understood. 2. Nine biological metrics for macrophytes (498 sites), benthic macroinvertebrates (491) and fish (478) of lowland and mountain streams in four ecoregions of France and Germany were related to catchment and riparian buffer land use using partial Redundancy Analysis and Boosted Regression Trees (BRTs). 3. Lotic fauna was better correlated (mean max., r = 0.450) than flora (r = 0.277) to both scales of land use: the strongest correlations were noted for mountain streams. BRTs revealed strong non‐linear relationships between mountain assemblage metrics and land use. Correlations increased with increasing buffer lengths, suggesting the importance of near‐stream land use on biotic assemblages. 4. Several metrics changed markedly between 10–20% (mountain ecoregions) and 40–45% (lowland) of arable land use, irrespective of the buffer size. At mountain sites with >10% catchment arable land use, metric values differed between sites with <30% and sites with >30% forest in the near‐stream riparian area. 5. These findings support the role of riparian land use in catchment management; however, differences between mountain and lowland ecoregions support the need for ecoregion‐specific management. 相似文献
143.
144.
145.
E M Nikulina O V Trapezov N K Popova 《Zhurnal vysshe? nervno? deiatelnosti imeni I P Pavlova》1985,35(6):1142-1146
Content of dopamine in the striatum; of serotonin, 5-hydroxyindolacetic acid and noradrenaline in the hypothalamus, striatum and midbrain was studied in three groups of minks from population of an animal farm, differing by their reaction to humans (cowardly, calm, aggressive). The reaction to humans was estimated by a system of marks at the attempt to catch the mink with a mitten. Aggressive animals had a lowered level of serotonin in the hypothalamus and striatum, a lesser content of serotonin metabolite--5-hydroxyindolacetic acid in the striatum. Minks of different groups did not differ by noradrenaline content, but dopamine level in the striatum of cowardly minks was higher than in calm and aggressive animals. Conclusion is made that polymorphism of behaviour corresponds to polymorphism of the state of monoaminergic systems. 相似文献
146.
Y Tsujimoto K Nagashima M Yamazaki S Furuyama 《The International journal of biochemistry》1988,20(6):591-594
1. Formation of peroxides by benxoyl peroxide (BPO) and CuCl2 was examined in the human red blood cell ghost. 2. Amounts of peroxides formed increased with the amount of the ghost solution added. 3. Of all the cations tested only manganese ion inhibited the formation of peroxides in BPO-CuCl2 reaction system. 4. The formation of peroxides was inhibited approx. 50% with 0.4 microM manganese. 5. The inhibitory manner of manganese was non-competitive against copper. 相似文献
147.
A A Grinev E I Samokhvalov N A Petrov S K Vasilenko V P Iuferov 《Molekuliarnaia genetika, mikrobiologiia i virusologiia》1988,(9):43-45
The primary structure of hemagglutinin (HA) gene of Influenza virus A/USSR/90/77 (H1N1) variants after 3 and 11 passages has been determined. In the HA1 coding region of mice-adapted virus (11 passages) there are two amino acid substitutions: Thr 89----Ala and Asn 127----Asp. At the first stage of adaptation (3-rd passage) only a single mutation was detected: Asn 127----Asp. The adaptation is accompanied by the loss of specific carbohydrate attachment sites adjacent to the receptor-binding site located at HA1 subunit with a concomitant variation in antigenicity. 相似文献
148.
A. GUY PLINT RON K. PICKERILL 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1985,18(4):341-347
Middle Eocene, non-marine sediments from southern England contain examples of Teredolites borings in two contrasting palaeoenvironmental settings, viz.: (A) as in situ borings in an allochthonous lignite in an abandoned river channel and (B) as bored logs in cross-bedded fluvial sandstones of probable point-bar origin. The lignite is 0.30 m thick, of which the upper 0.20 m is intensely bored. Rounded pebbles of ?charcoal at its base also show small borings. A log in a fluvial sandstone shows densely-packed. radial club-shaped borings. now filled with sandstone. The wood substrate has subsequently been oxidized away. To our knowledge, this is the first detailed account of Teredolites from an ancient freshwater setting. 相似文献
149.
150.