全文获取类型
收费全文 | 529篇 |
免费 | 38篇 |
专业分类
567篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 22篇 |
2015年 | 24篇 |
2014年 | 17篇 |
2013年 | 31篇 |
2012年 | 31篇 |
2011年 | 35篇 |
2010年 | 18篇 |
2009年 | 24篇 |
2008年 | 28篇 |
2007年 | 24篇 |
2006年 | 26篇 |
2005年 | 30篇 |
2004年 | 31篇 |
2003年 | 22篇 |
2002年 | 16篇 |
2001年 | 18篇 |
2000年 | 9篇 |
1999年 | 14篇 |
1998年 | 13篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 7篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1974年 | 4篇 |
1971年 | 2篇 |
1967年 | 4篇 |
1965年 | 1篇 |
1961年 | 1篇 |
1950年 | 1篇 |
1874年 | 1篇 |
排序方式: 共有567条查询结果,搜索用时 8 毫秒
1.
The mutagenic effect of an antihypertensive drug, propranolol, was studied on somatic and germ cells of Swiss albino mice. The induction of a significant increase in the frequency of micronuclei in erythrocytes was observed at higher dose levels, whereas, in germ cells, propranolol failed to induce significant chromosomal aberrations at any dose tested. 相似文献
2.
A leaf tip hooded mutant was isolated in the progenies of the irradiated seeds of a commercial tobacco variety, namely Delcrest. The mutant character was determined as monogenic recessive. Along with leaf tip hooding, certain other characters such as increase in size of leaves, number and clasping arrangement of leaves on stem, and delayed flowering, were found to be closely associated and this was attributed to the pleiotropic effect of the leaf tip hooding gene. 相似文献
3.
A 2-month-old female with intrauterine and postnatal growth retardation, multiple congenital anomalies, absent right kidney, congenital heart disease was investigated. Her karyotype revealed, 46,XX,-10,+der(10), t(10;18) (p15;q12) pat. The child died at 2 months 2 weeks. This is the third case of trisomy 18q resulting from translocation of chromosome 10 and 18. 相似文献
4.
Segregation of Cytoplasmic Incompatibility Properties in CULEX PIPIENS FATIGANS 总被引:2,自引:2,他引:0 下载免费PDF全文
Sarala K. Subbarao B. S. Krishnamurthy C. F. Curtis T. Adak R. K. Chandrahas 《Genetics》1977,87(2):381-390
Maternally inherited variants, which arose within a laboratory colony of Culex pipiens fatigans, have been studied by rearing cultures from single egg rafts. Segregation, i.e, variation of cytoplasmic incompatibility properties between the male progeny of individual females, was demonstrated. Also, from the daughters of individual females, sub-lines were derived within which all the males showed the same incompatibility or compatibility properties. Among the descendants of tetracycline-treated individuals were lines which superficially simulated these phenomena, but theses lines ultimately reverted to the cytoplasmic compatibility type of the strain which was submitted to the treatment. The types of variation s in cytoplasmic incompatibility properties that have been studied are discussed. 相似文献
5.
The results presented in this paper show that lysis of human erythrocytes by linoleic acid is not caused by peroxidation of
the fatty acid. Peroxidase, superoxide dismutase and scavengers of O
2
−
and OH had no effect on the lysis while catalase showed only marginal inhibition suggesting that O
2
−
, OH, O
2
−
and H2O2 do not play any direct role in hemolysis by linoleic acid. Generators of H2O2 inhibited the lysis completely and methemoglobin cells were more resistant to hemolysis by linoleic acid. The fatty acid
did neither bind to nor fomed complex with red cell ghosts. Membrane oxidation of sulphydryl groups was also not involved
in the lysis. Β-Carotene, retinol and bile salts enhanced the lysis, while, cholesterol but not cholesterol acetate, inhibited
it. Taurocholate-pretreated cells were more susceptible to linoleic acid lysis. These observations suggested-that lysis by
linoleic acid may be due to its detergent property. 相似文献
6.
7.
Vishnu Vardhan Krishnamurthy John S. KhamoEllen Cho Cara SchornakKai Zhang 《Analytical biochemistry》2015
Precise DNA manipulation is critical for molecular biotechnology. Restriction enzyme-based approaches are limited by their requirement of specific enzyme sites. Restriction-free cloning has greatly improved the flexibility and speed of precise DNA assembly. Most of these approaches focus on DNA assembly rather than gene removal. Here we present a polymerase chain reaction (PCR)-based cloning method that allows removal of multiple gene segments from plasmids without using restriction enzymes and thermostable ligase. We demonstrate simultaneous removal of three gene segments from a plasmid. This approach could be beneficial to DNA library construction, genetic and protein engineering, and synthetic biology. 相似文献
8.
Rhamnose Biosynthesis Pathway Supplies Precursors for Primary and Secondary Metabolism in Saccharopolyspora spinosa 总被引:1,自引:0,他引:1 下载免费PDF全文
Rhamnose is an essential component of the insect control agent spinosad. However, the genes coding for the four enzymes involved in rhamnose biosynthesis in Saccharopolyspora spinosa are located in three different regions of the genome, all unlinked to the cluster of other genes that are required for spinosyn biosynthesis. Disruption of any of the rhamnose genes resulted in mutants with highly fragmented mycelia that could survive only in media supplemented with an osmotic stabilizer. It appears that this single set of genes provides rhamnose for cell wall synthesis as well as for secondary metabolite production. Duplicating the first two genes of the pathway caused a significant improvement in the yield of spinosyn fermentation products. 相似文献
9.
Dipankar Ray Shirish Shukla Uday Sankar Allam Abigail Helman Susmita Gurjar Ramanand Linda Tran Michael Bassetti Pranathi Meda Krishnamurthy Matthew Rumschlag Michelle Paulsen Lei Sun Thomas P. Shanley Mats Ljungman Mukesh K. Nyati Ming Zhang Theodore S. Lawrence 《PloS one》2013,8(2)
The efficacy of radiation therapy for lung cancer is limited by radiation-induced lung toxicity (RILT). Although tumor necrosis factor-alpha (TNF-α) signaling plays a critical role in RILT, the molecular regulators of radiation-induced TNF-α production remain unknown. We investigated the role of a major TNF-α regulator, Tristetraprolin (TTP), in radiation-induced TNF-α production by macrophages. For in vitro studies we irradiated (4 Gy) either a mouse lung macrophage cell line, MH-S or macrophages isolated from TTP knockout mice, and studied the effects of radiation on TTP and TNF-α levels. To study the in vivo relevance, mouse lungs were irradiated with a single dose (15 Gy) and assessed at varying times for TTP alterations. Irradiation of MH-S cells caused TTP to undergo an inhibitory phosphorylation at Ser-178 and proteasome-mediated degradation, which resulted in increased TNF-α mRNA stabilization and secretion. Similarly, MH-S cells treated with TTP siRNA or macrophages isolated from ttp (−/−) mice had higher basal levels of TNF-α, which was increased minimally after irradiation. Conversely, cells overexpressing TTP mutants defective in undergoing phosphorylation released significantly lower levels of TNF-α. Inhibition of p38, a known kinase for TTP, by either siRNA or a small molecule inhibitor abrogated radiation-induced TNF-α release by MH-S cells. Lung irradiation induced TTPSer178 phosphorylation and protein degradation and a simultaneous increase in TNF-α production in C57BL/6 mice starting 24 h post-radiation. In conclusion, irradiation of lung macrophages causes TTP inactivation via p38-mediated phosphorylation and proteasome-mediated degradation, leading to TNF-α production. These findings suggest that agents capable of blocking TTP phosphorylation or stabilizing TTP after irradiation could decrease RILT. 相似文献
10.