全文获取类型
收费全文 | 347112篇 |
免费 | 38674篇 |
国内免费 | 198篇 |
出版年
2018年 | 3198篇 |
2017年 | 3015篇 |
2016年 | 4431篇 |
2015年 | 6230篇 |
2014年 | 7111篇 |
2013年 | 9770篇 |
2012年 | 11312篇 |
2011年 | 11223篇 |
2010年 | 7557篇 |
2009年 | 6761篇 |
2008年 | 9686篇 |
2007年 | 10125篇 |
2006年 | 9384篇 |
2005年 | 8931篇 |
2004年 | 8589篇 |
2003年 | 8309篇 |
2002年 | 8272篇 |
2001年 | 18321篇 |
2000年 | 18491篇 |
1999年 | 14248篇 |
1998年 | 4335篇 |
1997年 | 4569篇 |
1996年 | 4386篇 |
1995年 | 4054篇 |
1994年 | 4000篇 |
1993年 | 3837篇 |
1992年 | 11567篇 |
1991年 | 11185篇 |
1990年 | 10748篇 |
1989年 | 10305篇 |
1988年 | 9506篇 |
1987年 | 8890篇 |
1986年 | 8112篇 |
1985年 | 8001篇 |
1984年 | 6437篇 |
1983年 | 5588篇 |
1982年 | 4128篇 |
1981年 | 3615篇 |
1980年 | 3382篇 |
1979年 | 6155篇 |
1978年 | 4599篇 |
1977年 | 4147篇 |
1976年 | 3776篇 |
1975年 | 4356篇 |
1974年 | 4519篇 |
1973年 | 4420篇 |
1972年 | 4109篇 |
1971年 | 3508篇 |
1970年 | 3188篇 |
1969年 | 2987篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
Carmen de Sena-Tomás Mónica Navarro-González Ursula Kües José Pérez-Martín 《Genetics》2013,195(1):47-57
The fungal fruiting body or mushroom is a multicellular structure essential for sexual reproduction. It is composed of dikaryotic cells that contain one haploid nucleus from each mating partner sharing the same cytoplasm without undergoing nuclear fusion. In the mushroom, the pileus bears the hymenium, a layer of cells that includes the specialized basidia in which nuclear fusion, meiosis, and sporulation occur. Coprinopsis cinerea is a well-known model fungus used to study developmental processes associated with the formation of the fruiting body. Here we describe that knocking down the expression of Atr1 and Chk1, two kinases shown to be involved in the response to DNA damage in a number of eukaryotic organisms, dramatically impairs the ability to develop fruiting bodies in C. cinerea, as well as other developmental decisions such as sclerotia formation. These developmental defects correlated with the impairment in silenced strains to sustain an appropriated dikaryotic cell cycle. Dikaryotic cells in which chk1 or atr1 genes were silenced displayed a higher level of asynchronous mitosis and as a consequence aberrant cells carrying an unbalanced dose of nuclei. Since fruiting body initiation is dependent on the balanced mating-type regulator doses present in the dikaryon, we believe that the observed developmental defects were a consequence of the impaired cell cycle in the dikaryon. Our results suggest a connection between the DNA damage response cascade, cell cycle regulation, and developmental processes in this fungus. 相似文献
162.
We re-engineered a classic tool for mutagenesis and gene expression studies in Gram-negative bacteria. Our modified Tn5-based transposon contains multiple features that allow rapid selection for mutants, direct quantification of gene expression and straightforward cloning of the inactivated gene. The promoter-less gfp-km cassette provides selection and reporter assay depending on the activity of the promoter upstream of the transposon insertion site. The cat gene facilitates positive antibiotic selection for mutants, while the narrow R6Kγ replication origin forces transposition in recipient strains lacking the pir gene and enables cloning of the transposon flanked with the disrupted gene from the chromosome. The suicide vector pCKD100, a plasmid that could be delivered into recipient cells through biparental mating or electroporation, harbours the modified transposon. We used the transposon to mutagenize Pectobacterium versatile KD100, Pseudumonas coronafaciens PC27R and Escherichia coli 35150N. The fluorescence intensities of mutants expressing high GFP could be quantified and detected qualitatively. Transformation efficiency from conjugation ranged from 1600 to 1900 CFU per ml. We sequenced the upstream flanking regions, identified the putative truncated genes and demonstrated the restoration of the GFP phenotype through marker exchange. The mini-Tn5 transposon was also utilized to construct mutant a library of P. versatile for forward genetic screens. 相似文献
163.
F. Hubert M.-H. Rodier A. Minoza V. Portet-Sulla E. Cateau K. Brunet 《Letters in applied microbiology》2021,72(1):82-89
Candida auris is an emerging species responsible for life-threatening infections. Its ability to be resistant to most systemic antifungal classes and its capacity to persist in a hospital environment have led to health concerns. Currently, data about environmental reservoirs are limited but remain essential in control of C. auris spread. The aim of our study was to explore the interactions between C. auris and two free-living amoeba (FLA) species, Vermamoeba vermiformis and Acanthamoeba castellanii, potentially found in the same water environment. Candida auris was incubated with FLA trophozoites or their culture supernatants. The number of FLA and yeasts was determined at different times and transmission electron microscopy (TEM) was performed. Supernatants of FLAs promoted yeast survival and proliferation. Internalization of viable C. auris within both FLA species was also evidenced by TEM. A water environmental reservoir of C. auris can therefore be considered through FLAs and contamination of the hospital water networks would consequently be possible. 相似文献
164.
Study of the posterior abdominal epidermis in hypophysectomized/thyroidectomized male and female tokays following surgery, and subsequent androgen therapy, indicates that, contrary to a previous model, all aspects of β-gland differentiation are under direct androgenic control. On the other hand, another epidermal specialization, the digital foot-pad, shows a pattern of histogenesis directly comparable to that of β-glands, but is unaffected by androgens. These data are discussed with respect to the evolution of glandular epidermal specializations in gekkonid lizards and the possible role of androgens in modifying the control of cell differentiation in lizard epidermis. 相似文献
165.
166.
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
167.
S Kumar M Antony N K Mehrotra 《Biochemical and biophysical research communications》1984,125(3):967-973
Single cutaneous application of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) increased epidermal oxidised glutathione reductase activity in adult mouse by almost 100%. Pretreatment of animals with vitamin A for a week resulted in 75% inhibition of TPA induced change in the enzyme activity which remained unaffected in skin treated with vitamin A alone. This biochemical change in skin induced by TPA and modulated by vitamin A has been discussed in relation to epidermal hyperplasia. 相似文献
168.
The influence of wilting on the levels of free proline, soluble proteins, reducing sugars, starch and on the activities of
nitrate reductase, invertase, amylase and pyrophosphatases have been studied in the leaf tissue of five cultivars of pearl
millet at their vegetative stage under pot culture conditions. The metabolic changes could not be correlated with the yield
behaviour of the cultivars under a drought condition in the field. 相似文献
169.
170.