全文获取类型
收费全文 | 759篇 |
免费 | 54篇 |
专业分类
813篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 12篇 |
2020年 | 11篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 20篇 |
2015年 | 28篇 |
2014年 | 28篇 |
2013年 | 59篇 |
2012年 | 51篇 |
2011年 | 35篇 |
2010年 | 17篇 |
2009年 | 33篇 |
2008年 | 39篇 |
2007年 | 33篇 |
2006年 | 35篇 |
2005年 | 42篇 |
2004年 | 37篇 |
2003年 | 32篇 |
2002年 | 26篇 |
2001年 | 13篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1973年 | 7篇 |
1972年 | 6篇 |
1970年 | 7篇 |
1968年 | 3篇 |
排序方式: 共有813条查询结果,搜索用时 15 毫秒
241.
Alpha2(I) collagen gene regulation by protein kinase C signaling in human dermal fibroblasts 下载免费PDF全文
We investigated the mechanisms by which protein kinase C (PKC) regulates the expression of the α2(I) collagen gene in normal dermal fibroblasts. Reduction of PKC-α activity by treatment with Gö697-6 or by overexpression of a dominant negative (DN) mutant form decreased α2(I) collagen gene expression. This decrease required a sequence element in the collagen promoter that contains Sp1/Sp3 binding sites. Reduction of PKC-δ activity by rottlerin or overexpression of DN PKC-δ also decreased α2(I) collagen gene expression. This effect required a separate sequence element containing Sp1/Sp3-binding sites and an Ets-binding site. In both cases, point mutations within the response elements abrogated the response to PKC inhibition. Forced overexpression of Sp1 rescued the PKC inhibitor-mediated reduction in collagen protein expression. A DNA affinity precipitation assay revealed that inhibition of PKC-δ by rottlerin increased the binding activity of endogenous Fli1 and decreased that of Ets1. On the other hand, TGF-β1, which increased the expression of PKC-δ, had the opposite effect, increasing the binding activity of Ets1 and decreasing that of Fli1. Our results suggest that PKC-δ is involved in the regulation of the α2(I) collagen gene in the presence or absence of TGF-β. Alteration of the balance of Ets1 and Fli1 may be a novel mechanism regulating α2(I) collagen expression. 相似文献
242.
Kenzaka T Tamaki S Yamaguchi N Tani K Nasu M 《Applied and environmental microbiology》2005,71(11):7236-7244
Cycling primed in situ amplification-fluorescent in situ hybridization (CPRINS-FISH) was developed to recognize individual genes in a single bacterial cell. In CPRINS, the amplicon was long single-stranded DNA and thus retained within the permeabilized microbial cells. FISH with a multiply labeled fluorescent probe set enabled significant reduction in nonspecific background while maintaining high fluorescence signals of target bacteria. The ampicillin resistance gene in Escherichia coli, chloramphenicol acetyltransferase gene in different gram-negative strains, and RNA polymerase sigma factor (rpoD) gene in Aeromonas spp. could be detected under identical permeabilization conditions. After concentration of environmental freshwater samples onto polycarbonate filters and subsequent coating of filters in gelatin, no decrease in bacterial cell numbers was observed with extensive permeabilization. The detection rates of bacterioplankton in river and pond water samples by CPRINS-FISH with a universal 16S rRNA gene primer and probe set ranged from 65 to 76% of total cell counts (mean, 71%). The concentrations of cells detected by CPRINS-FISH targeting of the rpoD genes of Aeromonas sobria and A. hydrophila in the water samples varied between 2.1 x 10(3) and 9.0 x 10(3) cells ml(-1) and between undetectable and 5.1 x 10(2) cells ml(-1), respectively. These results demonstrate that CPRINS-FISH provides a high sensitivity for microscopic detection of bacteria carrying a specific gene in natural aquatic samples. 相似文献
243.
Shumpei?KitamuraEmail author Shunsuke?Suzuki Takakazu?Yumoto Phitaya?Chuailua Kamol?Plongmai Pilai?Poonswad Naohiko?Noma Tamaki?Maruhashi Chumphon?Suckasam 《Biodiversity and Conservation》2005,14(5):1241-1261
The diversity of plants in tropical forests makes dietary studies of frugivores difficult. This paper provides a botanical inventory of a tropical seasonal forest community in Khao Yai National Park, Thailand. The forest is valuable from a conservation perspective because it is one of the last remaining intact forests in northeastern Thailand, and is an important refuge for many animal and plant species. A 4-ha inventory plot measuring 200 × 200 m was established and all plants greater than or equal to 10 cm in diameter at breast height (dbh) were measured and permanently labeled. We found 1610 stems belonging to 105 species, 76 genera and 35 families, with a combined basal area of 142.5 m2. The community was dominated by species of Lauraceae, Cornaceae, Euphorbiaceae, Meliaceae, and Elaeocarpaceae. About one-third of the plant species (40 spp.) identified in this study were vulnerable to extinction because they were mostly dispersed by large frugivores, which were intolerant of human impact. If they disappear, these forests may become dominated by plant species that are dispersed by abiotic means and species with small-seeded fruits. 相似文献
244.
Gene deletion in the pathogenic fungus Candida albicans has relied heavily on a URA3 cassette and a recipient delta ura3 strain CAI4. The IRO1 gene adjacent to URA3 was inadvertently deleted during construction of CAI4. We report here that a mutation in IRO1 reduces virulence of C. albicans. 相似文献
245.
Okishima N Yoshizumi M Tsuchiya K Cui P Kitamura H Tamaki T Kido H 《Life sciences》2001,68(18):2073-2080
An effective method for determination of the levels of newly discovered 31-amino acid endothelins [ETs(1-31)] as well as big ETs and 21-amino acid ETs [ETs(1-21)], in human lungs has been developed. About 85% of ETs in human lung homogenates were recovered on acid extraction 8 times. Most of the published protocols for the determination of tissue ETs involve a reverse-phase minicolumn to separate proteins from peptides, after which the levels of ETs are directly determined by enzyme immunoassay. The levels determined, however, include fairly high amounts of non-bioactive ET metabolites in tissues and the data reported are diverse. We established an effective methods for the extraction and the separation of nine different muscle constricting ETs from their metabolites on a reverse-phase C18 column. Using this protocol, the levels of ETs in human lungs were determined by means of a sandwich-enzyme immunoassay specific for each ET derivative. The levels of ET-2(1-21) were the highest among those of ETs, and the levels of ETs(1-31) were in a similar range to those of big ETs but were lower than those of ETs(1-21). This method can be utilized to assess the pathophysiological roles of ETs(1-31) in various human organs. 相似文献
246.
Shimazaki H Anzai M Aida S Endo H Kato K Yamasaki T Tamaki K Tamai S 《Acta cytologica》2001,45(3):435-440
BACKGROUND: Trichoblastoma is a rare benign skin appendage tumor constituted mostly of follicular germinative cells. It can arise on any part of the body except the palms, soles, nail units and mucosal membranes. No case of it in breast skin has been reported before. Furthermore, fine needle aspiration cytology findings on this lesion have not been described before. CASE: A 76-year-old female presented with a firm nodule in her left breast. The tumor was well demarcated, about 1.5 cm in diameter. Fine needle aspiration cytology revealed clusters composed of relatively uniform cells with a high nuclear/cytoplasmic ratio. In the midst of some clusters, the tumor cells had a more abundant cytoplasm. Fibrocellular interstitium or dense cyanophilic acellular material occasionally was attached to them. The tumor cells had oval or fusiform nuclei that had fine, evenly dispersed chromatin. To exclude a diagnosis of breast cancer, it is important to recognize that the clusters are composed of basaloid cells with focal squamous eddies and that there is at least focally peripheral palisading. The histopathologic diagnosis was trichoblastoma. CONCLUSION: Fine needle aspiration cytology can distinguish trichoblastoma from malignant diseases of the breast and may be used to diagnose the lesion in conjunction with clinical findings. 相似文献
247.
Oda T Matsumoto S Masuho Y Takasaki J Matsumoto M Kamohara M Saito T Ohishi T Soga T Hiyama H Matsushime H Furuichi K 《Biochimica et biophysica acta》2002,1569(1-3):135-138
Fast muscle myosin responds in similar way to F-actin and to phalloidin F-actin. It is activated 7.5 fold at infinite F-actin concentration and 6.8 fold at infinite phalloidin F-actin. The actomyosin dissociation constants are 0.89 +/- 0.34 microM with F-actin and 0.90 +/- 0.71 microM with phalloidin F-actin. Slow muscle myosin responds differently to F-actin and to phalloidin F-actin. It is activated 3.76 fold at infinite F-actin concentration and only 2.27 fold at infinite phalloidin F-actin concentration. The actomyosin dissociation constants are 1.95 +/- 1.27 microM with F-actin and 0.27 +/- 0.16 microM with phalloidin F-actin. At first glance this means that substitution of F-actin with phalloidin F-actin magnifies the difference between fast muscle and slow muscle myosins. Furthermore the change of the dissociation constants may affect the contractile force of the attached crossbridge. 相似文献
248.
249.
Yoshinori Tamaki 《Animal genetics》1975,6(3):195-200
The effects of neuraminidase treatment on the electrophoretic pattern of alkaline phosphatase (AP) isozymes and AP activity were investigated in chicken plasma. AP comprised three isozymes. The zymogram of an individual chicken plasma had two bands, either the faster (F) or the slower (S) moving band by isozyme types and the B band irrespective of isozyme types. Mobility of the S band and AP activity in chicken plasma were not affected by neuraminidase treatment. The treatment has a reduced migration rate of the F band equal to that of the S band and the B band of both types closer to the origin. The genetic control of these bands is discussed. 相似文献
250.