全文获取类型
收费全文 | 5271篇 |
免费 | 508篇 |
国内免费 | 209篇 |
专业分类
5988篇 |
出版年
2023年 | 48篇 |
2022年 | 119篇 |
2021年 | 190篇 |
2020年 | 126篇 |
2019年 | 143篇 |
2018年 | 150篇 |
2017年 | 93篇 |
2016年 | 170篇 |
2015年 | 279篇 |
2014年 | 293篇 |
2013年 | 355篇 |
2012年 | 388篇 |
2011年 | 380篇 |
2010年 | 244篇 |
2009年 | 205篇 |
2008年 | 259篇 |
2007年 | 230篇 |
2006年 | 247篇 |
2005年 | 189篇 |
2004年 | 204篇 |
2003年 | 151篇 |
2002年 | 130篇 |
2001年 | 106篇 |
2000年 | 107篇 |
1999年 | 97篇 |
1998年 | 41篇 |
1997年 | 43篇 |
1996年 | 38篇 |
1995年 | 36篇 |
1994年 | 43篇 |
1993年 | 41篇 |
1992年 | 66篇 |
1991年 | 74篇 |
1990年 | 47篇 |
1989年 | 57篇 |
1988年 | 57篇 |
1987年 | 55篇 |
1986年 | 46篇 |
1985年 | 55篇 |
1984年 | 43篇 |
1983年 | 31篇 |
1982年 | 23篇 |
1981年 | 20篇 |
1979年 | 31篇 |
1978年 | 23篇 |
1977年 | 18篇 |
1975年 | 21篇 |
1974年 | 22篇 |
1973年 | 25篇 |
1971年 | 17篇 |
排序方式: 共有5988条查询结果,搜索用时 0 毫秒
81.
82.
Proteomic analysis of differentially expressed proteins in Penaeus vannamei hemocytes upon Taura syndrome virus infection 总被引:4,自引:0,他引:4
To understand molecular responses of crustacean hemocytes to virus infection, we applied 2-DE proteomics approach to investigate altered proteins in hemocytes of Penaeus vannamei during Taura syndrome virus (TSV) infection. At 24 h postinfection, quantitative intensity analysis and nano-LC-ESI-MS/MS revealed 11 forms of 8 proteins that were significantly up-regulated, whereas 9 forms of 5 proteins were significantly down-regulated in the infected shrimps. These altered proteins play important roles in host defense (hemocyanin, catalase, carboxylesterase, transglutaminase, and glutathione transferase), signal transduction (14-3-3 zeta), carbohydrate metabolism (acetylglucosamine pyrophosphorylase), cellular structure and integrity (beta-tubulin, beta-actin, tropomyosin, and myosin), and ER-stress response (protein disulfide isomerase). Semiquantitative RT-PCR and Western blot analysis confirmed the upregulation of 14-3-3 at both mRNA and protein levels. Interestingly, several altered protein spots were identified as fragments of hemocyanin. Mass spectrometric analysis showed that the hemocyanin spots at acidic and basic regions represented the C- and N-terminal hemocyanin fragments, respectively. As three-quarters of C-terminal fragments were up-regulated, whereas two-thirds of N-terminal hemocyanin fragments were down-regulated, we therefore hypothesize that C- and N-terminal hemocyanin fragments may have differential roles in hemocytes. Further investigation of these data may lead to better understanding of the molecular responses of crustacean hemocytes to TSV infection. 相似文献
83.
葉跳蝉的为害,不但普遍而且严重。普通对于莊稼、果树、蔬菜等都能直接为害,还可以传染植物病菌。世界上各农业科学先进国家都久已注意到这类害虫,但在我国还没有能详细研究。在华北一带,葉跳蟬的种类很多,据我们已经採到的标杆標本、已经有一百数十种。其中最普遍而为数也特别显得多的,要算青葉跳蟬。 相似文献
84.
85.
Xiaohong Gu Yuechun Li Kaixin Chen Xingang Wang Zhongyu Wang Hao Lian Yuanzheng Lin Xing Rong Maoping Chu Jiafeng Lin Xiaoling Guo 《Journal of cellular and molecular medicine》2020,24(13):7515-7530
Human umbilical cord mesenchymal stem cell‐derived exosomes (hucMSC‐exosomes) have been implicated as a novel therapeutic approach for tissue injury repair and regeneration, but the effects of hucMSC‐exosomes on coxsackievirus B3 (CVB3)‐induced myocarditis remain unknown. The object of the present study is to investigate whether hucMSC‐exosomes have therapeutic effects on CVB3‐induced myocarditis (VMC). HucMSC‐exosomes were identified using nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM) and Western blot. The purified hucMSC‐exosomes tagged with PKH26 were tail intravenously injected into VMC model mice in vivo and used to administrate CVB3‐infected human cardiomyocytes (HCMs) in vitro, respectively. The effects of hucMSC‐exosomes on myocardial pathology injury, proinflammatory cytokines and cardiac function were evaluated through haematoxylin and eosin (H&E) staining, quantitative polymerase chain reaction (qPCR) and Doppler echocardiography. The anti‐apoptosis role and potential mechanism of hucMSC‐exosomes were explored using TUNEL staining, flow cytometry, immunohistochemistry, Ad‐mRFP‐GFP‐LC3 transduction and Western blot. In vivo results showed that hucMSC‐exosomes (50 μg iv) significantly alleviated myocardium injury, shrank the production of proinflammatory cytokines and improved cardiac function. Moreover, in vitro data showed that hucMSC‐exosomes (50 μg/mL) inhibited the apoptosis of CVB3‐infected HCM through increasing pAMPK/AMPK ratio and up‐regulating autophagy proteins LC3II/I, BECLIN‐1 and anti‐apoptosis protein BCL‐2 as well as decreasing pmTOR/mTOR ratio, promoting the degradation of autophagy flux protein P62 and down‐regulating apoptosis protein BAX. In conclusion, hucMSC‐exosomes could alleviate CVB3‐induced myocarditis via activating AMPK/mTOR‐mediated autophagy flux pathway to attenuate cardiomyocyte apoptosis, which will be benefit for MSC‐exosome therapy of myocarditis in the future. 相似文献
86.
Lipopolysaccharide is strongly associated with septic shock, leading to multiple organ failure. It can activate monocytes and macrophages to release proinflammatory mediators such as tumor necrosis factor- (TNF-), interleukin-1 (IL-1), and nitric oxide (NO). The present experiments were designed to induce endotoxin shock by an intravenous injection ofKlebsiella pneumoniae lipopolysaccharide (LPS, 10 mg/kg) in conscious rats. Arterial pressure and heart rate (HR) were continuously monitored for 48 h after LPS administration. N-Acetyl-cysteine was used to study its effects on organ damage. Biochemical substances were measured to reflect organ functions. Biochemical factors included blood urea nitrogen (BUN), creatinine (Cre), lactic dehydrogenase (LDH), creatine phosphokinase (CPK), aspartate transferase (GOT), alanine transferase (GPT), TNF-, IL-1, methyl guanidine (MG), and nitrites/nitrates. LPS caused significant increases in blood BUN, Cre, LDH, CPK, GOT, GPT, TNF-, IL-1, MG levels, and HR, as well as a decrease in mean arterial pressure and an elevation of nitrites/nitrates. N-Acetylcysteine suppressed the release of TNF-, IL-1, and MG, but enhanced NO production. These actions ameliorate LPS-induced organ damage in conscious rats. The beneficial effects may suggest a potential chemopreventive effect of this compound in sepsis prevention and treatment. 相似文献
87.
Concanavalin A (Con A)-induced hepatitis is thought to be a T-cell-mediated disease with active destruction of liver cells. Interleukin (IL)-17 is a cytokine produced principally by CD4(+) T cells. However, whether IL-17/IL-17 receptor (IL-17/IL-17R)-mediated responses are involved in T-cell-mediated Con A-induced liver injury remains unclear. In this study, we found that IL-17 expression was highly elevated in liver tissues during Con A-induced hepatitis. The increased levels of IL-17 were paralleled with the severity of liver injury reflected by Alanine aminotransaminase and histological assay as well as the secretion of tumor necrosis factor (TNF)-α and IL-6. Blockage of IL-17 significantly ameliorated Con A-induced hepatitis, while overexpression of IL-17 systemically resulted in massive hepatocyte necrosis in mice. Furthermore, overexpression of an IL-17R immunoglobulin G1 fusion protein significantly attenuated liver inflammation after acute Con A treatment. High expression of IL-17R on Kupffer cells was also observed along with the production of cytokines including TNF-α and IL-6. Inhibition of Kupffer cells by gadolinium chloride completely prevented Con A-induced liver injury and cytokine release. Finally, IL-17-expressing CD4(+) T and natural killer T cells were greatly increased in Con A-injected mice compared with that in controls. Overall, our results indicate that IL-17R signaling is critically involved in the pathogenesis in Con A-induced hepatitis, and blockade of IL-17/IL-17R signaling pathway may represent a novel therapeutic intervention in human autoimmune-related hepatitis. 相似文献
88.
Screening and production of erythritol by newly isolated osmophilic yeast-like fungi 总被引:7,自引:0,他引:7
Twenty-eight erythritol-producing strains were isolated from pollen, honey and high sugar food samples collected in Taiwan. Amongst these, six strains (166-2, 262-1, 278-3, 440, 441 and 442) were high erythritol-producers with a yield higher than 30% for 30% glucose. The erythritol productivity of these strains ranged from 90.9 to 116.4 g l−1. 1H- and 13C-NMR analyses confirmed that the fermentation product was erythritol. The results of morphological and physiological studies indicate that strains 166-2, 262-1, 278-3, 440, and 442 may be members of the genus Moniliella. More studies are required to determine the taxonomic position of strain 441. The use of a medium containing 30% glucose and 1% yeast extract gave the highest erythritol productivity. On batch fermentation in a 5-l fermentor using strain 166-2, a maximal erythritol productivity of 111.0 g l−1 was obtained after cultivation for 144 h. 相似文献
89.
Hoang Ha Chu Viet Hoang Peter Kreutzmann Brigitte Hofemeister Michael Melzer Jürgen Hofemeister 《European journal of biochemistry》2002,269(2):458-469
The use of Bacillus amyloliquefaciens for enzyme production and its exceptional high protein export capacity initiated this study where the presence and function of multiple type I signal peptidase isoforms was investigated. In addition to type I signal peptidases SipS(ba) [Meijer, W.J.J., de Jong, A., Bea, G., Wisman, A., Tjalsma, H., Venema, G., Bron, S. & van Dijl, J.M. (1995) Mol. Microbiol. 17, 621-631] and SipT(ba) [Hoang, V. & Hofemeister, J. (1995) Biochim. Biophys. Acta 1269, 64-68] which were previously identified, here we present evidence for two other Sip-like genes in B. amyloliquefaciens. Same map positions as well as sequence motifs verified that these genes encode homologues of Bacillus subtilis SipV and SipW. SipU-encoding DNA was not found in B. amyloliquefaciens. SipW-encoding DNA was also found for other Bacillus strains representing different phylogenetic groups, but not for Bacillus stearothermophilus and Thermoactinomyces vulgaris. The absence of these genes, however, could have been overlooked due to sequence diversity. Sequence alignments of 23 known Sip-like proteins from Bacillus origin indicated further branching of the P-group signal peptidases into clusters represented by B. subtilis SipV, SipS-SipT-SipU and B. anthracis Sip3-Sip5 proteins, respectively. Each B. amyloliquefaciens sip(ba) gene was expressed in an Escherichia coli LepBts mutant and tested for genetic complementation of the temperature sensitive (TS) phenotype as well as pre-OmpA processing. Although SipS(ba) as well as SipT(ba) efficiently restored processing of pre-OmpA in E. coli, only SipS(ba) supported growth at TS conditions, indicating functional diversity. Changed properties of the sip(ba) gene disruption mutants, including cell autolysis, motility, sporulation, and nuclease activities, seemed to correlate with specificities and/or localization of B. amyloliquefaciens SipS, SipT and SipV isoforms. 相似文献
90.
Junli Hu Xiangui Lin Junhua Wang Xiangchao Cui Jue Dai Haiyan Chu Jiabao Zhang 《Applied microbiology and biotechnology》2010,88(3):781-787
The P efficiency, crop yield, and response of wheat to arbuscular mycorrhizal fungus (AMF) Glomus caledonium were tested in an experimental field with long-term (19 years) fertilizer management. The experiment included five fertilizer
treatments: organic amendment (OA), half organic amendment plus half mineral fertilizer (1/2 OM), mineral fertilizer NPK,
mineral fertilizer NK, and the control (without fertilization). AMF inoculation responsiveness (MIR) of wheat plants at acquiring
P were estimated by comparing plants grown in unsterilized soil inoculated with G. caledonium and in untreated soil containing indigenous AMF. Without AMF inoculation, higher crop yields but lower colonization rates
were observed in the NPK and two OA-inputted treatments, and NPK had significantly (P < 0.05) lower impacts on organic C and available P in soils and thereby P acquisition of wheat plants compared with OA and
1/2 OM. G. caledonium inoculation significantly (P < 0.05) increased colonization rates with the NPK and two P-deficient treatments but significantly (P < 0.05) increased vegetative biomass, crop yield, and P acquisition of wheat as well as soil alkaline phosphatase (ALP) activity,
only with the NPK treatment. This gave an MIR of ca. 45% on total P acquisition of wheat plants. There were no other remarkable
MIRs. It suggested that the MIR is determined by soil available P status, and rational combination of AMF with chemical NPK
fertilizer can compensate for organic amendments by improving P-acquisition efficiency in arable soils. 相似文献