全文获取类型
收费全文 | 816篇 |
免费 | 60篇 |
国内免费 | 34篇 |
专业分类
910篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 9篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 10篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 2篇 |
2012年 | 109篇 |
2011年 | 117篇 |
2010年 | 19篇 |
2009年 | 12篇 |
2008年 | 70篇 |
2007年 | 82篇 |
2006年 | 71篇 |
2005年 | 78篇 |
2004年 | 69篇 |
2003年 | 58篇 |
2002年 | 38篇 |
2001年 | 29篇 |
2000年 | 50篇 |
1999年 | 17篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1933年 | 1篇 |
1924年 | 1篇 |
1923年 | 1篇 |
1922年 | 2篇 |
1921年 | 1篇 |
排序方式: 共有910条查询结果,搜索用时 0 毫秒
1.
Different radioactive precursors were added to 8-day potato-dextrose liquid cultures of Aspergillus terreus 23-1. Territrems were isolated from chloroform extracts of the cultures at day 14 and purified by thin-layer chromatography and high-pressure liquid chromatography. The territrem B obtained was treated with alkaline hydrogen peroxide, and 3, 4, 5-trimethoxy benzoic acid was isolated from an ethyl acetate extract of the reaction mixture and purified by thin-layer chromatography and high-pressure liquid chromatography. By comparison of the specific radioactivities of territrem B and its cleaved aromatic product (disintegrations per minute per micromole of compound), it was demonstrated that the radioactivity of territrem B was located mainly on its aromatic moiety when [U-C]shikimate, l-[methyl-C]methionine, and l-[methyl-H]methionine were precursors; however, the radioactivity of territrem B was located mainly on its nonaromatic moiety when [2-C]mevalonate was the precursor. Mevinolin, a specific inhibitor of beta-hydroxyl beta-methyl glutaryl coenzyme A reductase, was shown to inhibit production of territrems by A. terreus 23-1. When [U-C]acetate was used as a precursor, mevinolin inhibited the incorporation of radioactive carbon into territrem but mevinolin did not inhibit incorporation of radioactive carbon from [2-C]mevalonate into territrem. 相似文献
2.
The application of green fluorescent protein (GFP) to identify the portal(s) of entry of bacterial pathogens in animal hosts was studied using the fish pathogen Edwardsiella tarda and blue gourami, Trichogaster trichopterus. An immersion challenge model was utilized to mimic natural infection conditions in fish. Gastrointestinal tract, gills and the body surface of fish were found to be the sites of entry of virulent E. tarda (PPD130/91) by histological and infection kinetics studies. On the other hand, avirulent E. tarda (PPD125/87) was mainly found in the gastrointestinal tract, and the bacterial population in tissue declined over a period of 7 days. 相似文献
3.
4.
The role of reactive nitrogen species in secondary spinal cord injury: formation of nitric oxide, peroxynitrite, and nitrated protein 总被引:8,自引:0,他引:8
To determine whether reactive nitrogen species contribute to secondary damage in CNS injury, the time courses of nitric oxide, peroxynitrite, and nitrotyrosine production were measured following impact injury to the rat spinal cord. The concentration of nitric oxide measured by a nitric oxide-selective electrode dramatically increased immediately following injury and then quickly declined. Nitro-L-arginine reduced nitric oxide production. The extracellular concentration of peroxynitrite, measured by perfusing tyrosine through a microdialysis fiber into the cord and quantifying nitrotyrosine in the microdialysates, significantly increased after injury to 3.5 times the basal level, and superoxide dismutase and nitro-L-arginine completely blocked peroxynitrite production. Tyrosine nitration examined immunohistochemically significantly increased at 12 and 24 h postinjury, but not in sham-control sections. Mn(III) tetrakis(4-benzoic acid)-porphyrin (a novel cell-permeable superoxide dismutase mimetic) and nitro-L-arginine significantly reduced the numbers of nitrotyrosine-positive cells. Protein-bound nitrotyrosine was significantly higher in the injured tissue than in the sham-operated controls. These results demonstrate that traumatic injury increases nitric oxide and peroxynitrite production, thereby nitrating tyrosine, including protein-bound tyrosine. Together with our previous report that trauma increases superoxide, our results suggest that reactive nitrogen species cause secondary damage by nitrating protein through the pathway superoxide + nitric oxide peroxynitrite protein nitration. 相似文献
5.
Lee JC Won SJ Chao CL Wu FL Liu HS Ling P Lin CN Su CL 《Biochemical and biophysical research communications》2008,372(1):236-242
Morusin is a pure compound isolated from root bark of Morusaustralis (Moraceae). In this study, we demonstrated that morusin significantly inhibited the growth and clonogenicity of human colorectal cancer HT-29 cells. Apoptosis induced by morusin was characterized by accumulation of cells at the sub-G1 phase, fragmentation of DNA, and condensation of chromatin. Morusin also inhibited the phosphorylation of IKK-α, IKK-β and IκB-α, increased expression of IκB-α, and suppressed nuclear translocation of NF-κB and its DNA binding activity. Dephosphorylation of NF-κB upstream regulators PI3K, Akt and PDK1 was also displayed. In addition, activation of caspase-8, change of mitochondrial membrane potential, release of cytochrome c and Smac/DIABLO, and activation of caspase-9 and -3 were observed at the early time point. Downregulation in the expression of Ku70 and XIAP was exhibited afterward. Caspase-8 or wide-ranging caspase inhibitor suppressed morusin-induced apoptosis. Therefore, the antitumor mechanism of morusin in HT-29 cells may be via activation of caspases and inhibition of NF-κB. 相似文献
6.
N-乙酰半胱氨酸抗脂多糖诱导的肺动脉损伤的研究 总被引:6,自引:0,他引:6
目的 :探讨N 乙酰半胱氨酸 (N acetylcysteine,NAC)减轻脂多糖 (lipopolysaccharide ,LPS)所致的肺损伤及其机制。方法 :应用血管环张力检测技术和扫描电镜方法 ,观察了NAC对LPS引起的肺动脉反应性及肺动脉内皮细胞超微结构变化的影响 ;并测定了肺动脉组织中丙二醛 (malondialhyde ,MDA)、超氧化物歧化酶 (superoxidedismutes ,SOD)及一氧化氮 (nitricoxide,NO)的变化。结果 :LPS(4μg/ml,7h)可降低肺动脉对乙酰胆碱 (ACh)介导的内皮依赖性舒张反应 ,NAC(0 .5mmol/L)可逆转此种反应降低而对正常肺动脉舒缩反应无明显影响 ;NAC可改善LPS引起的肺动脉内皮细胞超微结构损伤并可逆转LPS引起的肺动脉组织中MDA、NO含量增高和SOD活性降低。结论 :NAC可通过抗氧化作用保护肺动脉内皮细胞并增强肺动脉内皮依赖性舒张反应 ,提示此可能是其发挥抗肺动脉压增高从而改善内毒素所致肺损伤的机制之一。 相似文献
7.
Xiaoqiong Wu Yu Pang Zhilin Zhang Xiabin Li Chao Wang Yingqing Lei Ailing Li Ling Yu Jian Ye 《Acta biochimica et biophysica Sinica》2019,(4):411-421
To investigate the neuroprotective effects of the mitochondria-targeted antioxidant Szeto-Schiller peptide 31 (SS-31) in a rat experimental glaucoma model, SS-31 was intraperitoneally (IP) injected into Sprague-Dawley rats, followed by intracameral injection of polystyrene microspheres to induce elevated intraocular pressure (IOP). After 6 weeks, electroretinography (ERG) and flash visual-evoked potentials (F-VEPs) were recorded to assess retinal function. Hematoxylin-eosin staining was performed on retinal cross-sections to measure ganglion cell complex (GCC) thickness. Apoptotic retinal cells were assessed by TUNEL staining. Brn3a-positive retinal ganglion cells (RGCs) were counted in retinal flat mounts via immunofluorescence. The retinal total SOD, SOD2, and MDA expression levels were assessed in retinal tissue homogenates. The cyt c, Baxz and Bcl-2 protein levels in rat retinas were detected by western blot analysis. Bax and Bcl-2 expressions were also evaluated using immunohistochemistry in paraffinized sections. Our results showed that the rats that received microsphere injection developed elevated IOP. SS-31 ameliorated the reductions in the a- and b-wave amplitudes on ERG and the F-VEP amplitude in glaucomatous eyes. GCC thickness was preserved, TUNEL-positive cells were decreased in the retina, and Brn3a-positive RGCs were in creased in the SS-31-treated glaucoma group compared with those in the non-treated glaucoma group. SS-31 significantly reduced MDA levels and increased SOD2 levels after glaucoma induction. Significant suppression of cyt c release, upregulation of Bcl-2, and downregulation of Bax were observed following SS-31 administration. In summary, SS-31 exerts neuroprotective effects in this experimental glaucoma model by inhibiting mitochondrial dysfunction and therefore represents a promising therapeutic agent for glaucoma. 相似文献
8.
Chuansong Zhan Long Lei Hao Guo Shen Zhou Congping Xu Zixin Liu Zichen Wu Yuan Deng Yuanyuan Miao Yu Han Meng Zhang Hua Li Sishu Huang Chenkun Yang Feng Zhang Yufei Li Ling Liu Xianqing Liu Hafiz Muhammad Khalid Abbas Alisdair R.Fernie Meng Yuan Jie Luo 《中国科学:生命科学英文版》2023,(5):1108-1118
The sesquiterpene alpha-bisabolol is the predominant active ingredient in essential oils that are highly valued in the cosmetics industry due to its wound healing, anti-inflammatory, and skin-soothing properties. Alpha-bisabolol was thought to be restricted to Compositae plants. Here we reveal that alpha-bisabolol is also synthesized in rice, a non-Compositae plant, where it acts as a novel sesquiterpene phytoalexin. Overexpressing the gene responsible for the biosynthesis of alpha-bisabolol, Os... 相似文献
9.
Ling Zhao Meng Liu Hua Sun Jia-Cheng Yang Yu-Xuan Huang Jia-Qiang Huang Xingen Lei Lv-Hui Sun 《中国科学:生命科学英文版》2023,(9):2056-2069
Broiler chicks are fast-growing and susceptible to dietary selenium(Se) deficiency. This study sought to reveal the underlying mechanisms of how Se deficiency induces key organ dysfunctions in broilers. Day-old male chicks(n=6 cages/diet, 6 chicks/cage) were fed with a Se-deficient diet(Se-Def, 0.047 mg Se/kg) or the Se-Def+0.3 mg Se/kg(Control, 0.345 mg Se/kg) for 6weeks. The serum, liver, pancreas, spleen, heart, and pectoral muscle of the broilers were collected at week 6 to assay for Se conc... 相似文献
10.
Wu He Ling Zhou Ke Xu Huihui Li James Jiqi Wang Chen Chen DaoWen Wang 《中国科学:生命科学英文版》2023,(9):2112-2137
Myocarditis is an inflammatory cardiac disease characterized by the destruction of myocardial cells, infiltration of interstitial inflammatory cells, and fibrosis, and is becoming a major public health concern. The aetiology of myocarditis continues to broaden as new pathogens and drugs emerge. The relationship between immune checkpoint inhibitors, severe acute respiratory syndrome coronavirus 2, vaccines against coronavirus disease-2019, and myocarditis has attracted increased attention. Immuno... 相似文献