全文获取类型
收费全文 | 1198篇 |
免费 | 82篇 |
出版年
2022年 | 12篇 |
2021年 | 14篇 |
2019年 | 17篇 |
2018年 | 20篇 |
2017年 | 16篇 |
2016年 | 31篇 |
2015年 | 32篇 |
2014年 | 59篇 |
2013年 | 70篇 |
2012年 | 72篇 |
2011年 | 76篇 |
2010年 | 55篇 |
2009年 | 44篇 |
2008年 | 60篇 |
2007年 | 55篇 |
2006年 | 43篇 |
2005年 | 46篇 |
2004年 | 58篇 |
2003年 | 46篇 |
2002年 | 45篇 |
2001年 | 32篇 |
2000年 | 32篇 |
1999年 | 25篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 24篇 |
1991年 | 20篇 |
1990年 | 15篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 15篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1968年 | 5篇 |
排序方式: 共有1280条查询结果,搜索用时 31 毫秒
41.
An improved approach for transformation of plant cells by microinjection: molecular and genetic analysis 总被引:4,自引:0,他引:4
Martin Schnorf Gabriele Neuhaus-Url Alessandro Galli Shigeru Iida Ingo Potrykus Gunther Neuhaus 《Transgenic research》1991,1(1):23-30
A new culture method for the injection of tobacco mesophyll protoplasts has been established. The protoplasts are embedded
in a thin layer of alginate and are nourished from the medium in the underlying basislayer. In the alginate layer the protoplasts
regenerate to calli at a frequency of up to 80%. Embedded protoplasts can be selected either with 50 mg l−1 kanamycin or 5 mg l−1 paromomycin. Single resistant cells can be recovered from about 10 000 sensitive cells in one alginate layer. Injection of
theneo gene (coding for neomycin phosphotransferase II) into protoplast derived single cells in the alginate layer results in kanamycin
resistant colonies that can be regenerated to mature plants. These plants express the neomycin phosphotransferase as shown
by enzyme activity assay. The integration of the transgene into the plant genome could be proved by Southern hybridization
to high molecular weight DNA. With this culture method 100 cells can be injected per hour. Transformation frequencies range
from 2 to 20%. In crossing experiments, it was shown that the foreign gene is transmitted to the next generation in a Mendelian
fashion. 相似文献
42.
Summary Cartilage cubes, prepared from the proximal epiphyses of neonatal rat humeri and consisting of cartilage tissue only, were cultured in the presence of retinoic acid. The retinoid induced the loss of metachromatic staining with toluidine blue, which correlates with the loss of proteoglycan, followed by tissue degradation processes resulting in a distinct reduction of the cartilage mass. Histologically, fibroblast-like cells appeared within chondrones, indicating a transformation of chondroblasts. Focal tissue degradation was observed after only 2 days. Electron microscopically, the clustered cells within the zone of tissue degradation were rich in various lysosomal structures indicating their lytic activity. Cycloheximide and EDTA completely blocked the retinoic acid effects suggesting that protein synthesis was required and that metalloproteinases may be involved in the degradation processes. In conclusion, with the new test system described here we demonstrated that cartilage cells themselves performed the tissue degradation induced by retinoic acid. 相似文献
43.
44.
A new method for the evaluation of 3-hydroxy-3-methylglutaryl-CoA reductase activity is described, based on the multiple-selected ion monitoring of the amount of mevalonate formed in incubations of 3-hydroxy-3-methylglutaryl-CoA with microsomal proteins. Analysis is carried out on crude extracts using deuterated mevalonic acid lactone as internal standard. The sensitivity of the technique allows the quantitative evaluation of mevalonate in microassays (100 μg microsomal protein) of the enzyme activity at the minimum value of the diurnal rhythm. 相似文献
45.
C Spagnuolo L Sautebin G Galli G Racagni C Galli S Mazzari M Finesso 《Prostaglandins》1979,18(1):53-61
The effects of ligation of both common carotid arteries in the gerbil on the levels of PGF2 alpha, TXB2, HETE and of energy metabolites in brain cortex, have been investigated. Also, in the same experimental conditions the changes of cyclic AMP in brain cortex, cerebellum, striatum and hippocampus have been monitored. ATP, glycogen, glucose and phosphocreatine decrease whereas, lactate and cyclic AMP are enhanced in the ischemic brain, as previously reported. In contrast, levels of arachidonic acid metabolites are not modified. During ischemia following decapitation, instead, PGF2 alpha, and TXB2, show considerable increase. 相似文献
46.
Probenecid in single or repeated doses does not modify levels of PGF2 alpha and TXB2 in rat brain cortex. After administration of subconvulsant dose of pentamethylene tetrazole (PMT) PGF2 alpha increases sharply and rapidly declines subsequently, whereas the elevation of TXB2 is smaller but of longer duration. After probenecid pretreatment PGF2 alpha levels do not decline up to 30 minutes after the initial peak and are still elevated after 60 minutes. Levels of TXB2 tend to be reduced after pretreatment. Differences in transport process or in biosynthetic compartments for these arachidonic acid (AA) metabolites may account for the observed data. 相似文献
47.
C. Spagnuolo A. Petroni M. Blasevich C. Galli 《Prostaglandins & other lipid mediators》1979,18(2):311-315
Probenecid in single or repeated doses does not modify levels of PGF2α and TXB2 in rat brain cortex. After administration of subconvulsant dose of pentamethylene tetrazone (PMT) PGF2α increases sharply and rapidly declines subsequently, whereas the elevation of TXB2 is smaller but of longer duration. After probenecid pretreatment PGF2α levels do not decline up to 30 minutes after the initial peak and are still elevated after 60 minutes. Levels of TXB2 tend to be reduced after pretreatment. Differences in transport process or in biosynthetic compartments for these arachidonic acid (AA) metabolites may account for the observed data. 相似文献
48.
Substrate and steric specificity of hydropyrimidine hydrase. 总被引:7,自引:0,他引:7
49.
A method for the evaluation of PGF-2alpha and PGE-2 biosynthesis in rat cerebral cortex is described. Tissue slices were incubated without any added precursor for different lengths of time. The analytical procedure involves prostaglandin extraction, purification and quantitative determination by mass fragmentography. Significant amounts of both prostaglandins were synthesized. The biosynthesis reached a plateau after 30 minutes and the ratio of PGF-2alpha to PGE-2 was approximately 3. 相似文献
50.
A method for the evaluation of PGF2α and PGE2 biosynthesis in rat cerebral cortex is described. Tissue slices were incubated without any added precursor for different lengths of time. The analytical procedure involves prostaglandin extraction, purification and quantitative determination by mass fragmentography. Significant amounts of both prostaglandins were synthesized. The biosynthesis reached a plateau after 30 minutes and the ratio of PGF2α to PGE2 was approximately 3. 相似文献