全文获取类型
收费全文 | 1640550篇 |
免费 | 161724篇 |
国内免费 | 1503篇 |
专业分类
1803777篇 |
出版年
2021年 | 18214篇 |
2019年 | 16244篇 |
2018年 | 18821篇 |
2017年 | 17601篇 |
2016年 | 29023篇 |
2015年 | 43208篇 |
2014年 | 51246篇 |
2013年 | 77557篇 |
2012年 | 45439篇 |
2011年 | 35781篇 |
2010年 | 46317篇 |
2009年 | 46966篇 |
2008年 | 33221篇 |
2007年 | 31961篇 |
2006年 | 35718篇 |
2005年 | 36624篇 |
2004年 | 35762篇 |
2003年 | 33065篇 |
2002年 | 31028篇 |
2001年 | 49674篇 |
2000年 | 47879篇 |
1999年 | 43637篇 |
1998年 | 27507篇 |
1997年 | 27508篇 |
1996年 | 26700篇 |
1995年 | 24875篇 |
1994年 | 24666篇 |
1993年 | 24031篇 |
1992年 | 38073篇 |
1991年 | 36568篇 |
1990年 | 35398篇 |
1989年 | 35571篇 |
1988年 | 32758篇 |
1987年 | 31393篇 |
1986年 | 29711篇 |
1985年 | 31431篇 |
1984年 | 29237篇 |
1983年 | 25757篇 |
1982年 | 24090篇 |
1981年 | 22976篇 |
1980年 | 21614篇 |
1979年 | 26160篇 |
1978年 | 22968篇 |
1977年 | 21604篇 |
1976年 | 20609篇 |
1975年 | 20928篇 |
1974年 | 21673篇 |
1973年 | 21872篇 |
1972年 | 19207篇 |
1971年 | 17252篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
821.
822.
823.
A double antibody radioimmunoassay technique is described for the measurement of anti-zona antibodies in the peripheral plasma of marmosets actively immunized against intact cow zonae pellucidae. The method has been shown to be a reliable, repeatable indicator of antibody titer, enabling direct comparison of the response obtained between marmosets. This is the first report of a procedure describing the active immunization of a primate against zona antigens, and the first time a radioimmunoassay technique has been used to monitor profiles of anti-cow zona antibody production following active immunization. The method should prove to be a useful tool in the evaluation of zona antigens as agents for immunocontraception. 相似文献
824.
825.
A microcomputer mainframe linked system is described which allows video camera data capture and storage of one-dimensional whole-cell protein electrophoresis gel images, processing of normalized traces to produce a similarity matrix, and analysis of the matrix using the commercial cluster analysis program CLUSTAN. A new similarity coefficient is introduced which takes into account both band position and intensity. Forty-five strains of Haemophilus influenzae, including the eight biotypes and six serotypes, were analyzed using this system. Results demonstrated groupings which are consistent with known genetic relationships. 相似文献
826.
L E Taplin J P Loveridge 《Comparative biochemistry and physiology. A, Comparative physiology》1988,89(3):443-448
1. Nile crocodiles, reared in fresh water and exposed acutely to seawater, suffer marked dehydration and hypernatraemia. Cloacal urine osmolarity and potassium concentration increased markedly but urine sodium remains low. 2. Hypernatraemia is increased when secretion from the lingual salt glands is prevented. 3. C. niloticus appears not to drink seawater. 4. Similarities in osmoregulatory response between estuarine and Nile crocodiles suggest that the lingual salt glands of C. niloticus are functional in salt water, playing an important role in sodium balance. 5. Significant differences in the function of the renal/cloacal complex of Alligator and Crocodylus emphasize further the differences between these two groups of crocodilian and provide support for the postulated marine ancestry of many or all of the Crocodylidae. 相似文献
827.
828.
The photoacoustic spectroscopic studies of purple pigmented leaves revealed the occurrence of anthocyanins and betalains in
some local weed species growing on soils with low moisture levels. The pigmentation intensities were higher in C4 plants than in C3 plants. An inverse correlation was observed between pigmentation intensities and soil moisture levels.
This work is a part of the UNEP Research Project granted to Prof. D. O. Hall, UNEP Coordinator, Department of Plant Sciences,
King’s College; London. 相似文献
829.
Data are presented to show how the number and growth of juvenile salmon in streams in the Scottish Highlands are influenced by various physical (temperature, water chemistry, depth and velocity, type of substratum) and biotic (food resources, competition, recruitment) factors. 相似文献
830.
Cultured astrocytes from a syncytium after maturation 总被引:2,自引:0,他引:2
The formation of functional gap junctions between astrocytes was investigated during differentiation of these cells in culture. Precursor cells of GFA (glial fibrillary acidic) protein-positive astrocytes were cultured in a chemically defined medium as a homogeneous population. These cells were rarely coupled to one neighbour, as revealed by electrical and dye coupling and never formed a large syncytium, as investigated by injection and spread of Lucifer Yellow. Differentiation with respect to GFA protein accumulation can be induced in these cells by culturing in horse serum-containing medium. The formation of functional junctions developed within 2 weeks in about 20% of the cells. Coupled cells formed a large syncytium. When the astrocytes were co-cultured with primary cerebellar cells (consisting predominantly of small neurons) after the switch to serum-containing medium the percentage of coupled astrocytes increased to about 65%. Again the coupled cells formed a large syncytium. Since no physical contact was possible between the astrocyte cultures and the primary cerebellar cells the stimulation of coupling had to be signalized by soluble factor(s). 相似文献