全文获取类型
收费全文 | 53247篇 |
免费 | 3369篇 |
国内免费 | 2607篇 |
出版年
2023年 | 800篇 |
2022年 | 775篇 |
2021年 | 1586篇 |
2020年 | 1546篇 |
2019年 | 2061篇 |
2018年 | 1739篇 |
2017年 | 1222篇 |
2016年 | 1351篇 |
2015年 | 1717篇 |
2014年 | 2609篇 |
2013年 | 3476篇 |
2012年 | 1903篇 |
2011年 | 2448篇 |
2010年 | 1818篇 |
2009年 | 2186篇 |
2008年 | 2289篇 |
2007年 | 2439篇 |
2006年 | 2212篇 |
2005年 | 2109篇 |
2004年 | 1873篇 |
2003年 | 1694篇 |
2002年 | 1619篇 |
2001年 | 1413篇 |
2000年 | 1194篇 |
1999年 | 1134篇 |
1998年 | 1074篇 |
1997年 | 1017篇 |
1996年 | 872篇 |
1995年 | 927篇 |
1994年 | 927篇 |
1993年 | 858篇 |
1992年 | 858篇 |
1991年 | 834篇 |
1990年 | 681篇 |
1989年 | 638篇 |
1988年 | 598篇 |
1987年 | 515篇 |
1986年 | 420篇 |
1985年 | 521篇 |
1984年 | 587篇 |
1983年 | 304篇 |
1982年 | 413篇 |
1981年 | 424篇 |
1980年 | 341篇 |
1979年 | 294篇 |
1978年 | 212篇 |
1977年 | 179篇 |
1976年 | 194篇 |
1974年 | 66篇 |
1973年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 968 毫秒
51.
Regeneration of Triticum aestivum apical explants after microinjection of germ line progenitor cells with DNA 总被引:2,自引:0,他引:2
A highly efficient method of regenerating fertile, phenotypically normal plants from shoot apex cultures of T. aestivum was developed. The hypodermal layer (L2) of the vegetative apex containing germ line precursor cells could be located with bright field microscopy and targeted for microinjection. Fluorescently labelled dextrans were used as markers to develop a microinjection procedure which did not disrupt nuclear or cytoplasmic structure. This procedure was used to inject plasmid DNA into L2 cells. Capillary microinjection did not shear the plasmid DNA and delivery of DNA was confirmed by polymerase chain reaction analysis of DNA isolated from injected apices. The significance of these findings in relation to the development of cereal transformation systems will be discussed. 相似文献
52.
Pollen isolated from cold treated and precultivated anthers of tobacco (Nicotiana tabacum L. var. Wisconsin 38) were separated into different fractions with counter-current distribution using an aqueous Dextran-polyethylene glycol two-phase system. It was possible to distinguish among eight pollen classes differing in developmental stage and in partitioning. A part of each fraction was cultivated for analysis of embryo formation. This was highest in a fraction with an intermediate to high partition in the phase system. Enriched in this fraction were also pollen that were fairly well stained with acetocarmine, contained several nuclei and had a relatively low mitochondrial activity. The enrichment of embryogenic pollen offers several advantages especially to physiological studies on embryogenesis. 相似文献
53.
《基因组蛋白质组与生物信息学报(英文版)》2020,18(2):104-119
To address the increasing need for detecting and validating protein biomarkers in clinical specimens, mass spectrometry (MS)-based targeted proteomic techniques, including the selected reaction monitoring (SRM), parallel reaction monitoring (PRM), and massively parallel data-independent acquisition (DIA), have been developed. For optimal performance, they require the fragment ion spectra of targeted peptides as prior knowledge. In this report, we describe a MS pipeline and spectral resource to support targeted proteomics studies for human tissue samples. To build the spectral resource, we integrated common open-source MS computational tools to assemble a freely accessible computational workflow based on Docker. We then applied the workflow to generate DPHL, a comprehensive DIA pan-human library, from 1096 data-dependent acquisition (DDA) MS raw files for 16 types of cancer samples. This extensive spectral resource was then applied to a proteomic study of 17 prostate cancer (PCa) patients. Thereafter, PRM validation was applied to a larger study of 57 PCa patients and the differential expression of three proteins in prostate tumor was validated. As a second application, the DPHL spectral resource was applied to a study consisting of plasma samples from 19 diffuse large B cell lymphoma (DLBCL) patients and 18 healthy control subjects. Differentially expressed proteins between DLBCL patients and healthy control subjects were detected by DIA-MS and confirmed by PRM. These data demonstrate that the DPHL supports DIA and PRM MS pipelines for robust protein biomarker discovery. DPHL is freely accessible at https://www.iprox.org/page/project.html?id=IPX0001400000. 相似文献
54.
Differential regulation of basic protein phosphorylation by calcium phospholipid and cyclic-AMP-dependent protein kinases 总被引:2,自引:0,他引:2
Myelin basic protein, an 80-kilodalton (kDa) protein in rat oligodendrocytes, and an 80-kDa basic protein in neuroblastoma x neonatal Chinese hamster brain explant hybrids were phosphorylated extensively when the cells were treated with either phorbol esters (TPA) or diacylglycerols (e.g., oleyoyl-acetylglycerol). TPA-stimulated phosphorylation was inhibited by pre-incubation with 50 microM psychosine (galactosyl-sphingosine), confirming that it is mediated through the phospholipid-dependent protein kinase C (PK-C). Surprisingly, phosphorylation of these proteins was inhibited by incubation of cells with agents which result in activation of cyclic-AMP-dependent protein kinase (dibutyryl cyclic AMP or forskolin). In contrast, phosphorylation of other nonbasic proteins, for example, the oligodendrocyte-specific 2',3'-cyclic nucleotide phosphohydrolase, was stimulated under these conditions (Vartanian et al.: Proceedings of the National Academy of Sciences of the United States of America 85:939, 1988). The possible role of cyclic AMP in activating specific phosphatases or restricting the availability of diacylglycerol for PK-C activation is discussed. 相似文献
55.
Jameel M. Al-Khayri 《In vitro cellular & developmental biology. Plant》2001,37(4):453-456
Summary This study was conducted to examine the effect of biotin and thiamine concentrations on callus growth and somatic embryogenesis
of date palm (Phoenix dactylifera L.). Embryogenic callus derived from offshoot tip explants was cultured on hormone-free MS medium containing biotin at 0,
0.1, 1, or 2 mg l−1 combined with thiamine at 0.1, 0.5, 2, or 5 mg l−1. Embryogenic callus weight, number of resultant embryos, and embryo length were significantly influenced by thiamine and
biotin concentration. The optimum callus growth treatment consisted of 0.5 mg l−1 thiamine and 2 mg l−1 biotin. This treatment also gave the highest number of embryos. Embryo elongation was greatest at 0.5 or 2 mg l−1 thiamine combined with 1 mg l−1 biotin. Embryos from all treatments germinated and regenerants exhibited normal growth in soil. This study provides an insight
into the importance of optimizing various culture medium components to overcome in vitro recalcitrace of date palm. 相似文献
56.
Chelsea E. Matisz Cameron P. Goater Douglas Bray 《International journal for parasitology》2010,40(3):307-312
Evidence for the presumed linkage between the enigmatic rodlet cells of fish and exposure to helminths is anecdotal and indirect. We evaluated the proliferation and development of rodlet cells in the optic lobes of fathead minnows exposed to cercariae of Ornithodiplostomum ptychocheilus. Mean rodlet cell densities (ca. 10/mm2) in the optic lobes were similar between unexposed controls and minnows with 1- and 2-week old infections. Rodlet cell densities increased at 4 weeks p.i., reaching maxima (ca. 200/mm2) at 6 weeks p.i., followed by a decline at 9 weeks. This temporal pattern of proliferation and maturation paralleled the development of metacercariae within the optic lobes. Unencysted metacercariae develop rapidly within tissues of the optic lobes for approximately 4 weeks after penetration by cercariae, then shift to the adjacent meninges to encyst. The former stage is associated with tissue damage, the latter with massive inflammation of the meninges. Thus, peak densities and maturation of rodlet cells correspond to the period when inflammation of the meninges caused by the large metacercarial cysts is at a maximum. Our results support recent contentions that rodlet cells comprise part of the host inflammatory defence response. 相似文献
57.
58.
59.
The aim of this study was to investigate the possibility of enhancing the yield of tissue plasminogen activator (tPA) from two epithelial cell lines of normal (non-malignant) derivation grown in tissue culture. The three agents used in this investigation were chosen because of their proven enhancing effect on analogous cells or products. The anabolic hormone stanozolol was found to have no significant stimulatory effect on these cell lines. A phorbol acetate (12-O-tetradecanoylphorbol 13-acetate) caused a twofold enhancement in tPA yield but the most significant results were obtained with 5-azacytidine. This agent increased the yield by up to fourfold in small stationary cultures and threefold in large-scale microcarrier cultures. A combination of azacytidine and phorbol acetate did not have an additive effect on total yield but did alter the kinetics of tPA expression with time. Indications were that the maximum yield with these types of potentiating agents was achieved as it could not be increased by using a combination of two different agents. 相似文献
60.