全文获取类型
收费全文 | 12489篇 |
免费 | 812篇 |
出版年
2021年 | 187篇 |
2020年 | 162篇 |
2019年 | 167篇 |
2018年 | 365篇 |
2017年 | 338篇 |
2016年 | 432篇 |
2015年 | 416篇 |
2014年 | 479篇 |
2013年 | 786篇 |
2012年 | 681篇 |
2011年 | 691篇 |
2010年 | 555篇 |
2009年 | 427篇 |
2008年 | 444篇 |
2007年 | 353篇 |
2006年 | 400篇 |
2005年 | 286篇 |
2004年 | 327篇 |
2003年 | 283篇 |
2002年 | 231篇 |
2001年 | 250篇 |
2000年 | 234篇 |
1999年 | 198篇 |
1998年 | 147篇 |
1997年 | 110篇 |
1995年 | 112篇 |
1994年 | 111篇 |
1993年 | 116篇 |
1992年 | 149篇 |
1991年 | 125篇 |
1990年 | 142篇 |
1989年 | 125篇 |
1988年 | 138篇 |
1987年 | 117篇 |
1986年 | 115篇 |
1985年 | 123篇 |
1984年 | 134篇 |
1981年 | 108篇 |
1979年 | 128篇 |
1978年 | 117篇 |
1977年 | 125篇 |
1975年 | 133篇 |
1974年 | 141篇 |
1973年 | 149篇 |
1972年 | 131篇 |
1971年 | 108篇 |
1970年 | 123篇 |
1969年 | 144篇 |
1967年 | 111篇 |
1966年 | 111篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
The binding of isolated high mobility group proteins HMG (1+2) with nucleosomes was studied using gel electrophoresis. The interaction of HMG (1+2) with mononucleosomes could be detected as a new discrete electrophoretic band with a decreased mobility only after cross-linking of HMG (1+2)-nucleosome complex by formaldehyde. Approximately two molecules of the large HMG proteins were bound per nucleosomal particle of a DNA length of 185 base pairs, lacking histones H1 and H5. Using the same techniques, no binding was observed with core particles of a DNA length of 145 base pairs. 相似文献
123.
Dr. Berend van der Lei Charles R. H. Wildevuur Paul Nieuwenhuis Engbert H. Blaauw Freark Dijk Caesar E. Hulstaert Izaäk Molenaar 《Cell and tissue research》1985,242(3):569-578
Summary The ultrastructure of a new type of vascular graft, prepared from a mixture of polyurethane (95 weight %) and poly-L-lactic acid (5 weight %), was examined six weeks after implantation into the abdominal aorta of rats. These microporous, compliant, biodegradable, vascular grafts function as temporary scaffolds for the regeneration of the arterial wall.Smooth muscle cells, covering the grafts, regenerated a neo-media underneath an almost completely regenerated endothelial layer (neo-intima). These smooth muscle cells varied in morphology from normal smooth muscle cells to myofibroblasts. They were surrounded by elastic laminae and collagen fibers.Macrophages, epithelioid cells, multinucleated giant cells, fibroblasts and capillaries were present in the disintegrating graft lattices. The epithelioid cells and multinucleated giant cells engulfed polymer particles of the disintegrating grafts.The regeneration of the endothelial and smooth muscle cells is similar to the natural response of arterial tissue upon injury. The presence of macrophages, epithelioid cells, multinucleated giant cells, fibroblasts and capillaries in the graft lattices resembles the natural response of tissue against foreign body implants. Both of these responses result in the formation of a neo-artery that possesses sufficient strength, compliance and thromboresistance to function as a small caliber arterial substitute.Supported by Grant nr. 82.042 from the Dutch Heart Foundation 相似文献
124.
Formation of protoplasts and their reversion were followed in 7 strains of brevibacteria. The formation of protoplasts and
their reversion differed both between various species of brevibacteria and between various mutant strains of the same species. 相似文献
125.
The addition of 2–4% oils to the synthetic fermentation medium used for the cultivation ofStreptomyces cinnamonensis increased the production of monensin three times on the average. When the amount of the added oil was lower than 2% and higher
than 4% the production sharply decreased. The maximal production preceded the maximal consumption of individual fatty acids
of the added oils, the content of oleic acid decreasing most pronouncedly. 相似文献
126.
In an open gas exchange system with a thermocouple psychrometer the transpiration rate of the first leaf in 8-day plants of
spring barley was measured in dependence on the water saturation deficit (ΔW
sat). The plants were cultivated in Richter’s nutrient solution, either complete, or deficient in nitrogen or phosphorus. The
cuticular transpiration (as measured in the dark) was unaffected by N and P deficiency. The N deficiency reduced the transpiration
rate by increasing stomatal resistance since full water saturation of the leaf (67% rate of the control variant) up to stomatal
closing at Δ Wsat = 14%. The P deficiency does not affect the transpiration rate at initial phases of wilting, but the stomata close only at
a higher Δ Wsat (25%) than those in the control. 相似文献
127.
Five cultivars and the half diallel set of 10 F1 hybrids of flue-cured tobacco (Nicotiana tabacum L.) were grown in two seasons. Highly significant differences were assessed between genotypes as concerns flowering time, plant height, number of leaves, leaf length and width and yield per plot. High to moderate values for heritability in the broad sense were obtained in all cases. Hybrids, in general, flowered earlier, were taller, had fewer but shorter and wider leaves and slightly increased yield when compared with the mean value of all parents. The variance associated with general combining ability (GCA) was highly significant in all characters. The estimates of SCA were significant in most cases. High GCA/SCA ratios which largely exceeded the unity were obtained for most attributes. The negative and positive alleles were unequally distributed in the parents for all the studied traits. A small number of effective genes was obtained for all characters except plant height, where one to two groups of genes were distinguished 相似文献
128.
The effect of plant tissue culture medium with different concentrations and combinations of growth regulators (kinetin, indol-3-ylacetic acid, 2,4-dichlorophenoxyacetic acid) was evaluated on mitosis ofAllium sativum meristem root tip cells. Different combinations of growth regulators at low concentrations had no effect on induction of mitotic aberrations or inhibition of mitotic activity. Inhibition of mitotic activity, a tendency to chromosome stickiness and clumping and a slight increase in the frequency of mitotic aberrations were observed at higher concentrations. It may be proposed that plant tissue culture media have no direct effect on induction of mitotic aberrations in plant tissue culturesin vitro. 相似文献
129.
F. Plhák 《Biologia Plantarum》1984,26(6):441-447
Growth, dark transpiration rate (DTR) as well as water saturation deficit (WSD) of 30 single plants of 8 alfalfa genotypes growing in experimental field of 50 × 10 cm spacing, in four cuts at early bud stage, were studied. The growth and WSD of genotypes examined were significantly different, the differences in DTR were not significant. The growth of alfalfa plants was in negative correlation with both DTR which reflects non-effective water loss and WSD. Significant negative correlation established between plant growth and its variability shows that fodder productivity in alfalfa genotypes was dependent on growth variability of individual plants. Positive correlations established between WSD or DTR and the growth variability show some of the causes of growth variability. 相似文献
130.
Zdeněk Hostounský 《Journal of invertebrate pathology》1984,44(2):166-171
The microsporida Nosema gastroideae and N. equestris, which are highly pathogenic for Leptinotarsa, have been successfully produced in some other chrysomelid species, Gastrophysa polygoni and G. viridula. As the principal target host, Leptinotarsa is very susceptible to these pathogens, and death occurs before massive sporulation by the microsporidia. By contrast, the infected larvae of G. polygoni or G. viridula are able to develop until the adult stage when most of the tissues become filled with spores. In addition, the larvae and adults of these species can be reared in the laboratory on Polygonum aviculare and Rumex obtusifolius. These plants have longer vegetative periods and are better sources of food than potato leaves. In both species of Gastrophysa the yields of spores related to unit weight were about five times higher than in Leptinotarsa. In the adults of G. viridula there was up to 4.8 × 106 spores mg?1 body weight of N. gastroideae, or 9.1 × 106 spores mg?1 of N. equestris. The higher content of microsporidian spores facilitates their purification and isolation. 相似文献