全文获取类型
收费全文 | 36663篇 |
免费 | 1948篇 |
国内免费 | 4360篇 |
出版年
2024年 | 54篇 |
2023年 | 435篇 |
2022年 | 541篇 |
2021年 | 792篇 |
2020年 | 882篇 |
2019年 | 1141篇 |
2018年 | 903篇 |
2017年 | 883篇 |
2016年 | 984篇 |
2015年 | 1090篇 |
2014年 | 1660篇 |
2013年 | 2369篇 |
2012年 | 1535篇 |
2011年 | 1609篇 |
2010年 | 1382篇 |
2009年 | 1805篇 |
2008年 | 2000篇 |
2007年 | 2142篇 |
2006年 | 1974篇 |
2005年 | 1871篇 |
2004年 | 1697篇 |
2003年 | 1643篇 |
2002年 | 1404篇 |
2001年 | 1179篇 |
2000年 | 956篇 |
1999年 | 976篇 |
1998年 | 982篇 |
1997年 | 796篇 |
1996年 | 713篇 |
1995年 | 766篇 |
1994年 | 705篇 |
1993年 | 575篇 |
1992年 | 582篇 |
1991年 | 552篇 |
1990年 | 430篇 |
1989年 | 348篇 |
1988年 | 390篇 |
1987年 | 317篇 |
1986年 | 270篇 |
1985年 | 250篇 |
1984年 | 234篇 |
1983年 | 138篇 |
1982年 | 198篇 |
1981年 | 157篇 |
1980年 | 157篇 |
1979年 | 105篇 |
1978年 | 96篇 |
1977年 | 66篇 |
1976年 | 64篇 |
1973年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Plant somatic cells have the capability to switch their cell fates from differentiated to undifferentiated status under proper
culture conditions, which is designated as totipotency. As a result, plant cells can easily regenerate new tissues or organs
from a wide variety of explants. However, the mechanism by which plant cells have such remarkable regeneration ability is
still largely unknown. In this study, we used a set of meristem-specific marker genes to analyze the patterns of stem cell
differentiation in the processes of somatic embryogenesis as well as shoot or root organogenesis in vitro. Our studies furnish preliminary and important information on the patterns of the de novo stem cell differentiation during various types of in vitro organogenesis. 相似文献
2.
Papers on the mechanisms of translation initiation in mammals studied by reconstruction of initiation complexes from individual components are reviewed. The author points to the constraints of this approach and to the pitfalls ignoring which one might come to erroneous conclusions and even artifacts. In addition, some methods employed in the field as well as some technical problems are discussed in the paper, together with the means of obviating them. The review could be a guidebook for newcomers into this quite labor-consuming field. 相似文献
3.
4.
Solange Faria Lua Figueiredo Norma Albarello Vera Regina Campos Viana 《In vitro cellular & developmental biology. Plant》2001,37(4):471-475
Summary A protocol for in vitro propagation of Rollinia mucosa, an important medicinal plant, was developed. The presence of 500 mg l−1 polyvinylpyrrolidone (PVP) during explant excision was important to avoid browning. Axillary buds, adventitious buds, and
shoot cluster proliferation were achieved from epicotyl and hypocotyl explants from nursery-grown seedlings. The highest direct
organogenesis percentage from hypocotyl explants was obtained upon culture of explants on Murashige and Skoog medium supplemented
with 2.2 μM benzyladenine (BA) plus 2.32 μM kinetin. Epicotyl explants display highest regeneration frequency on a medium containing 8.8 μM BA and 0.54 μM naphthaleneacetic acid. Gibberellic acid was necessary for shoot elongation. Root induction was observed when shoots were
pretreated with activated charcoal for 7 d in the dark before culture on Woody Plant Medium supplemented with 49.21 μM indolebutyric acid for 10 d. Root development was observed when 20 g l−1 sucrose was used. Rooted plantlets were acclimatized and grown in the greenhouse. 相似文献
5.
6.
Sandrine Poncet Armelle Delecluse Guido Anello ré Klier Georges Rapoport 《FEMS microbiology letters》1994,117(1):91-95
Abstract The genes encoding the CryIVB and CryIVD crystal polypeptides of B. thuringiensis subsp. israelensis were cloned indepently on a stable shuttle vector, and transfered into B. sphaericus 2297. Recombinant cells expressed the B. thuringiensis toxins during sporulation and were shown to be toxic to Aedes aegypti fourth instar larvae, whereas the parental strain was not. 相似文献
7.
Steven J. Tucker David McClelland Kristina Sep?i? Roderick H. Scott 《生物化学与生物物理学报:生物膜》2003,1614(2):171-181
The ability of two alkyl pyridinium sponge toxin preparations (poly-APS and halitoxin) to form transient pores/lesions in cell membranes and allow transfection of plasmid cDNA have been investigated using HEK 293 cells. Poly-APS and halitoxin preparations caused a collapse in membrane potential, reductions in input resistance and increased Ca2+ permeability. At least partial recovery was observed after poly-APS application but recovery was more rarely seen with halitoxin. The transfection with plasmid cDNAs for an enhanced green fluorescent protein (EGFP) and human tumour necrosis factor receptor 2 (TNFR2) was assessed for both toxin preparations and compared with lipofectamine. Stable transfection was achieved with poly-APS although it was less efficient than lipofectamine. These results show that viable cells transfected with alien cDNA can be obtained using novel transient pore-forming alkyl pyridinium sponge toxins and a simple pre-incubation protocol. This provides the first proof of principle that pore-forming alkyl pyridinium compounds can be used to deliver cDNA to the intracellular environment without permanently compromising the plasma membrane. 相似文献
8.
9.
Several unit-length minicircles from the kinetoplast DNA of Leishmania tarentolae were cloned into pBR322 and into M13 phage vectors. The complete nucleotide sequences of three different partially homologous minicircles were obtained. The molecules contained a region of approx. 80% sequence homology extending for 160–270 bp and a region unique to each minicircle. A 14-mer was found to be conserved in all kinetoplast minicircle sequences reported to date. The frequency distributions of various minicircle sequence classes in L. tarentolae were obtained by quantitative gel electrophoresis and by examination of the “T ladder” patterns of minicircles randomly cloned into M13 at several sites. By these methods we could assign approx. 50% of the total minicircle DNA into a minimum of five sequence classes. A sequence-dependent polyacrylamide gel migration abnormality was observed with several minicircle fragments both cloned and uncloned. The abnormality was dependent on the presence of a portion of the conserved region of the minicircle. 相似文献
10.
Andreas Barth 《BBA》2007,1767(9):1073-1101
This review discusses the application of infrared spectroscopy to the study of proteins. The focus is on the mid-infrared spectral region and the study of protein reactions by reaction-induced infrared difference spectroscopy. 相似文献