全文获取类型
收费全文 | 905篇 |
免费 | 34篇 |
出版年
2023年 | 6篇 |
2022年 | 15篇 |
2021年 | 23篇 |
2020年 | 15篇 |
2019年 | 14篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 26篇 |
2015年 | 33篇 |
2014年 | 33篇 |
2013年 | 47篇 |
2012年 | 69篇 |
2011年 | 70篇 |
2010年 | 30篇 |
2009年 | 25篇 |
2008年 | 31篇 |
2007年 | 38篇 |
2006年 | 33篇 |
2005年 | 36篇 |
2004年 | 18篇 |
2003年 | 34篇 |
2002年 | 20篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1992年 | 9篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1981年 | 4篇 |
1978年 | 5篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1973年 | 11篇 |
1972年 | 9篇 |
1971年 | 14篇 |
1970年 | 16篇 |
1969年 | 12篇 |
1968年 | 14篇 |
1967年 | 11篇 |
1966年 | 14篇 |
1965年 | 7篇 |
排序方式: 共有939条查询结果,搜索用时 15 毫秒
111.
Van Eck M Hoekstra M Out R Bos IS Kruijt JK Hildebrand RB Van Berkel TJ 《Journal of lipid research》2008,49(1):136-146
Scavenger receptor class B type I (SR-BI) functions as an HDL receptor that promotes the selective uptake of cholesteryl esters (CEs). The physiological role of SR-BI in VLDL metabolism, however, is largely unknown. SR-BI deficiency resulted in elevated VLDL cholesterol levels, both on chow diet and upon challenge with high-cholesterol diets. To specifically elucidate the role of SR-BI in VLDL metabolism, the plasma clearance and hepatic uptake of (125)I-beta-VLDL were studied in SR-BI(+/+) and SR-BI(-/-) mice. At 20 min after injection, 66 +/- 2% of the injected dose was taken up by the liver in SR-BI(+/+) mice, as compared with only 22 +/- 4% (P = 0.0007) in SR-BI(-/-) mice. In vitro studies established that the B(max) of (125)I-beta-VLDL binding was reduced from 469 +/- 30 ng/mg in SR-BI(+/+) hepatocytes to 305 +/- 20 ng/mg (P = 0.01) in SR-BI(-/-) hepatocytes. Both in vivo and in vitro, limited to no selective uptake of CEs from beta-VLDL was found. Interestingly, HDL effectively competed for the association of beta-VLDL in the presence as well as in the absence of SR-BI, indicating a second common recognition site. In conclusion, SR-BI plays an important physiological role in the metabolism of VLDL (remnants). 相似文献
112.
Catalase plays a central role in plant stress responses but is highly susceptible to photoinhibition. A rice catalase-B protein
avoiding photoinhibition was developed by mutagenesis of specific amino acids: Leu-189 to Trp-189 and His-225 to Thr-225 and
then recombinantly expressed in E. coli. In addition, the site specific mutation also induced 2–2.5-fold increase in enzyme velocity with high affinity for its substrate
and showed nearly a 3-fold lower K
m
than the wild protein. These characteristic of mutated rice catalase-B is highly promising in transgenic research to increase
plant productivity under stress conditions. 相似文献
113.
The aim of this study was to investigate the Helicobacter pylori (Hp) status of patients who underwent successful eradication therapy 1 year prior to the study and to evaluate their current symptoms. METHODS: all of the patients were initially evaluated by oesophago-gastro-bulboscopy and the Hp status was determined by at least two different methods [rapid urease test, histology or urea breath test (UBT)]. The Hp infection was treated with a 1-week triple therapy protocol, and the UBT was repeated 4-6 weeks later. We invited back 110 patients who had negative post-eradication UBT results 12+/-3 months prior to the study period. UBT was repeated and a questionnaire was completed about the previous and present complaints and medication. RESULTS: 80 of the 110 patients (73%) came back for the follow-up. Twenty five patients had peptic ulcer disease, 36 patients had gastritis or duodenitis without erosive lesions, and 19 patients had erosive form of gastritis or duodenitis initially. All of the patients except one in the erosive gastritis group had negative control UBT 1 year after the eradication, which means 1.25% recurrence rate within 1 year. The eradication therapy completely revealed the symptoms of 16 patients in the ulcer group (64%), 13 patients in the gastroduodenitis group (36%, P=0.03 vs. ulcer patients), 10 patients with erosive gastroduodenitis (52%), but this was only temporary. One year after the eradication therapy seven of the ulcer patients (28%), 11 patients with gastroduodenitis (31%) and seven patients with erosive gastroduodenitis (37%) were symptom-free. Most of the patients had epigastric pain (44%), heartburn (43%) and/or abdominal distension (33%). Nine ulcer patients (36%), 10 patients with gastroduodenitis (28%) and five patients with erosive gastroduodenitis (26%) were taking H(2)-blockers regularly. CONCLUSION: the 1-month post-eradication UBT was probable true negative in all of the evaluated cases, since 79 patients (98.75%) were also negative after 1 year. The Hp recurrence rate is very low (1.25%) in a 1-year period. The symptoms were relieved shortly after eradication therapy in the majority of patients with ulcer disease or erosive lesions. However, significantly smaller portion of the patients with gastroduodenitis became symptom-free. Only about one third of the treated patients remained symptom-free 1 year after the eradication. 相似文献
114.
Nidhi Batra Manuel A. Riquelme Sirisha Burra Rekha Kar Sumin Gu Jean X. Jiang 《The Journal of biological chemistry》2014,289(15):10582-10591
Connexin (Cx) 43 hemichannels in osteocytes are thought to play a critical role in releasing bone modulators in response to mechanical loading, a process important for bone formation and remodeling. However, the underlying mechanism that regulates the opening of mechanosensitive hemichannels is largely unknown. We have recently shown that Cx43 and integrin α5 interact directly with each other, and activation of PI3K appears to be required for Cx43 hemichannel opening by mechanical stimulation. Here, we show that mechanical loading through fluid flow shear stress (FFSS) increased the level of active AKT, a downstream effector of PI3K, which is correlated with the opening of hemichannels. Both Cx43 and integrin α5 are directly phosphorylated by AKT. Inhibition of AKT activation significantly reduced FFSS-induced opening of hemichannels and disrupted the interaction between Cx43 and integrin α5. Moreover, AKT phosphorylation on Cx43 and integrin α5 enhanced their interaction. In contrast to the C terminus of wild-type Cx43, overexpression of the C-terminal mutant containing S373A, a consensus site previously shown to be phosphorylated by AKT, failed to bind with α5 and hence could not inhibit hemichannel opening. Together, our results suggest that AKT activated by FFSS directly phosphorylates Cx43 and integrin α5, and Ser-373 of Cx43 plays a predominant role in mediating the interaction between these two proteins and Cx43 hemichannel opening, a crucial step to mediate the anabolic function of mechanical loading in the bone. 相似文献
115.
Genetic variability and association of ISSR markers with some biochemical traits in mulberry (Morus spp.) genetic resources available in India 总被引:2,自引:0,他引:2
Prasanta K. Kar Prem P. Srivastava Arvind K. Awasthi S. Raje Urs 《Tree Genetics & Genomes》2008,4(1):75-83
Utilizing intersimple sequence repeat (ISSR) markers, 18 mulberry (Morus spp.) germplasm collections were studied for genetic variability, phylogenetic relationship, and association with protein
and sugar content. The genetic polymorphism exhibited by ISSR primers was 100%, and the genetic diversity recorded among the
mulberry accessions had an average of 0.263 ± 0.094. Dendrogram (unweighted pair group method analysis) clustered the mulberry
accessions into two major groups, one comprised the accessions collected from north or northeast regions of India, and the
other comprised three subclusters and one isolate, i.e., Assamjati, a collection from Assam. Another subcluster contained
accessions collected from Kerala, which belong to Morus indica. These accessions of M. indica from Kerala were found to be genetically diverse from north and northeast India. Multidimensional scaling of the ISSR data
clearly separated the mulberry accessions according to their genetic diversity and protein content. Mulberry accessions were
arbitrarily grouped into three classes viz. very low, moderate, and high in terms of protein and sugar content using standard
statistical programs. Stepwise multiple regression analysis identified four ISSR markers (8351,600, 8355,600, 8222,500, and 8072,500) associated with protein content with highly positive correlation (p < 0.001) with linear curves with high F values (18.055 to 48.674; p < 0.001). In case of sugar content, four ISSR markers viz. 812900, 8171,500, 8261,500, and 8108,000 showed negative correlation. Hence, DNA markers for proteins seem promising and may be used in marker-assisted breeding program. 相似文献
116.
117.
Debajyoti Bhaumik Binayak Dutta-Roy Avijit Lahiri 《Bulletin of mathematical biology》1982,44(5):705-713
Macromolecules and their aggregates (such as protein bundles in biomembranes) possess polar modes which, when excited, tend
to deform the system and call into play elastic restoring forces. A model of such systems, characterised typically by electric
polarisation modes stabilised on the one hand by quartic self-interactions and on the other through coupling to the elastic
deformations, admits the possibility of localised excitations (solitary waves) propagating with subsonic velocities, possessing
the features of relative stability and efficient transport characteristics (associated with the collective nature of the phenomena),
and at the same time provides a mechanism of control and variability which could be of considerable interest in biology. 相似文献
118.
Rosetta C. Blackman Kar Keun Sean Ling Lynsey R. Harper Peter Shum Bernd Hnfling Lori LawsonHandley 《Ecology and evolution》2020,10(23):13248
- The early detection of invasive non‐native species (INNS) is important for informing management actions. Established monitoring methods require the collection or observation of specimens, which is unlikely at the beginning of an invasion when densities are likely to be low. Environmental DNA (eDNA) analysis is a highly promising technique for the detection of INNS—particularly during the early stages of an invasion.
- Here, we compared the use of traditional kick‐net sampling with two eDNA approaches (targeted detection using both conventional and quantitative PCR and passive detection via metabarcoding with conserved primers) for detection of quagga mussel, Dreissena rostriformis bugensis, a high priority INNS, along a density gradient on the River Wraysbury, UK.
- All three molecular tools outperformed traditional sampling in terms of detection. Conventional PCR and qPCR both had 100% detection rate in all samples and outperformed metabarcoding when the target species was at low densities. Additionally, quagga mussel DNA copy number (qPCR) and relative read count (metabarcoding) were significantly influenced by both mussel density and distance from source population, with distance being the most significant predictor.
- Synthesis and application. All three molecular approaches were more sensitive than traditional kick‐net sampling for the detection of the quagga mussel in flowing water, and both qPCR and metabarcoding enabled estimates of relative abundance. Targeted approaches were more sensitive than metabarcoding, but metabarcoding has the advantage of providing information on the wider community and consequently the impacts of INNS.
119.
Man Lung Yeung Jade Lee Lee Teng Lilong Jia Chaoyu Zhang Chengxi Huang Jian-Piao Cai Runhong Zhou Kwok-Hung Chan Hanjun Zhao Lin Zhu Kam-Leung Siu Sin-Yee Fung Susan Yung Tak Mao Chan Kelvin Kai-Wang To Jasper Fuk-Woo Chan Zongwei Cai Susanna Kar Pui Lau Kwok-Yung Yuen 《Cell》2021,184(8):2212-2228.e12
120.
Chromosomal variability in callus culture ofAsparagus racemosus was comparatively higher in the presence of 2,4-D than of NAA. The frequency of polyploid cells was enhanced with the increase
in the concentration of 2,4-D or with the addition of coconut water. Gradual polyploidization with increasing age of the callus
has been recorded. 相似文献