全文获取类型
收费全文 | 9417篇 |
免费 | 706篇 |
国内免费 | 813篇 |
专业分类
10936篇 |
出版年
2024年 | 18篇 |
2023年 | 138篇 |
2022年 | 305篇 |
2021年 | 520篇 |
2020年 | 316篇 |
2019年 | 451篇 |
2018年 | 424篇 |
2017年 | 269篇 |
2016年 | 438篇 |
2015年 | 605篇 |
2014年 | 725篇 |
2013年 | 815篇 |
2012年 | 910篇 |
2011年 | 793篇 |
2010年 | 449篇 |
2009年 | 446篇 |
2008年 | 466篇 |
2007年 | 408篇 |
2006年 | 364篇 |
2005年 | 261篇 |
2004年 | 252篇 |
2003年 | 205篇 |
2002年 | 149篇 |
2001年 | 135篇 |
2000年 | 121篇 |
1999年 | 104篇 |
1998年 | 101篇 |
1997年 | 91篇 |
1996年 | 85篇 |
1995年 | 73篇 |
1994年 | 68篇 |
1993年 | 48篇 |
1992年 | 78篇 |
1991年 | 47篇 |
1990年 | 33篇 |
1989年 | 37篇 |
1988年 | 22篇 |
1987年 | 25篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1976年 | 4篇 |
1973年 | 5篇 |
1971年 | 4篇 |
1968年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Rb1 and Rg1 are the major ginsenosides in protopanaxadiol and protopanaxatriol. Their content in ginsenosides was 23.8 and 17.6%, respectively.
A total of 22 isolates of β-glucosidase producing microorganisms were isolated from the soil of a ginseng field using Esculin-R2A
agar. Among these isolates, the strain GH21 showed the strongest activities to convert ginsenoside Rb1 and Rg1 to minor ginsenosides compound-K and F1, respectively. Ginsenosides Rb1 and Rg1 bioconversion rates were 74.2 and 89.3%, respectively. Meanwhile, the results demonstrated that the ginsenoside Rg1 could change the biotransformation pathway of ginsenoside Rb1 by inhibiting the formation of the intermediate metabolite gypenoside-XVII. GH21 was identified as a Cladosporium cladosporioides species based on the internal transcribed spacers (ITS) ITS1-5.8S-ITS2 rRNA gene sequences constructed phylogenetic trees. 相似文献
52.
Endotoxin-induced cytokine gene expression in vivo. III. IL-6 mRNA and serum protein expression and the in vivo hematologic effects of IL-6 总被引:19,自引:0,他引:19
T R Ulich K Z Guo D Remick J del Castillo S M Yin 《Journal of immunology (Baltimore, Md. : 1950)》1991,146(7):2316-2323
Endotoxin (LPS) at sublethal doses injected i.v. into rats was found to induce IL-6 mRNA expression peaking at 1 to 2 h in whole organ RNA preparations of the spleen, liver, lung, bowel, and kidney. IL-6 serum protein levels also peaked at 2 h. TNF and IL-1, generally considered to be among the most rapidly released cytokines, also induced IL-6 expression. IL-6 in turn inhibited TNF and IL-1 expression, suggesting that IL-6 may be part of a negative feedback mechanism in the cytokine cascade. Dexamethasone down-regulated and Corynebacterium parvum up-regulated IL-6 expression, although the possibility cannot be excluded that these immunomodulating factors may in part have exerted their effects indirectly via the up- and down-regulation of TNF and IL-1. IL-6 injected i.v. at a pathophysiologically relevant dose caused a peripheral neutrophilia and mild myeloproliferative effect in the bone marrow. 相似文献
53.
54.
Ju Cao Chun K. Wong Yibing Yin Christopher W.K. Lam 《Journal of cellular physiology》2010,223(3):788-797
Interleukin (IL)‐27 is a member of IL‐6/IL‐12 family cytokines produced by antigen‐presenting cells in immune responses. IL‐27 can drive the commitment of naive T cells to a T helper type 1 (Th1) phenotype and inhibit inflammation in later phases of infection. Human bronchial epithelial cells have been shown to express IL‐27 receptor complex. In this study, we investigated the in vitro effects of IL‐27, alone or in combination with inflammatory cytokine tumor necrosis factor (TNF)‐α on the pro‐inflammatory activation of human primary bronchial epithelial cells and the underlying intracellular signaling mechanisms. IL‐27 was found to enhance intercellular adhesion molecule 1 (ICAM‐1) expression on the surface of human bronchial epithelial cells, and a synergistic effect was observed in the combined treatment of IL‐27 and TNF‐α on the expression of ICAM‐1. Although IL‐27 did not alter the basal IL‐6 secretion from bronchial epithelial cells, it could significantly augment TNF‐α‐induced IL‐6 release. These synergistic effects on the up‐regulation of ICAM‐1 and IL‐6 were partially due to the elevated expression of TNF‐α receptor (p55TNFR) induced by IL‐27. Further investigations showed that the elevation of ICAM‐1 and IL‐6 in human bronchial epithelial cells stimulated by IL‐27 and TNF‐α was differentially regulated by phosphatidylinositol 3‐OH kinase (PI3K)‐Akt, p38 mitogen‐activated protein kinase, and nuclear factor‐κB pathways. Our results therefore provide a new insight into the molecular mechanisms involved in airway inflammation. J. Cell. Physiol. 223:788–797, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
55.
Tzyy‐Rong Jinn Suey‐Sheng Kao Yin‐Chin Tseng Ying‐Ju Chen Tzong‐Yuan Wu 《Biotechnology progress》2009,25(2):384-389
The baculovirus–insect expression system is a popular tool for recombinant protein production. The standard method for infecting insect larvae with recombinant baculovirus for protein production involves either feeding occlusion bodies or injecting budded virus into the cuticle. In this study, we showed that the recombinant Autographa californica multiple nucleopolyhedrovirus (AcMNPV) at titers >108 pfu/mL efficiently infected Trichoplusia ni (T. ni) larvae through aerosol inoculation of budded virus at a pressure of 5.5 × 104 Pa. The dipping T. ni larvae in virus‐containing solution efficiently infected them. These results indicate that surface contamination, either by aerosol or dipping, lead to infection via spiracles. The aerosol infection route for AcMNPV was restricted to T. ni and Plutella xylostella larvae, whereas Spodoptera litura and Helicoverpa armigera larvae were resistant to this inoculation process. The yields of the reporter proteins DsRed and EGFP from T. ni larvae following aerosol infection were nearly identical to those following oral feeding or injection. This alternative baculovirus infection strategy facilitates recombinant protein and virus production by insect larvae. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 相似文献
56.
Xiaoxia Xue Zhihua Yin Yao Lu Haibo Zhang Ying Yan Yuxia Zhao Xuelian Li Zeshi Cui Miao Yu Lu Yao Baosen Zhou 《PloS one》2013,8(8)
Background
The human 8-oxoguanine DNA glycosylase 1 (hOGG1), apurinic/apyrimidinic endonuclease 1 (APE1), and adenosine diphosphate ribosyl transferase (ADPRT) genes play an important role in the DNA base excision repair pathway. Single nucleotide polymorphisms (SNPs) in critical genes are suspected to be associated with the risk of lung cancer. This study aimed to identify the association between the polymorphisms of hOGG1 Ser326Cys, APE1 Asp148Glu, and ADPRT Val762Ala, and the risk of lung adenocarcinoma in the non-smoking female population, and investigated the interaction between genetic polymorphisms and environmental exposure in lung adenocarcinoma.Methods
We performed a hospital-based case-control study, including 410 lung adenocarcinoma patients and 410 cancer-free hospital control subjects who were matched for age. Each case and control was interviewed to collect information by well-trained interviewers. A total of 10 ml of venous blood was collected for genotype testing. Three polymorphisms were analyzed by the polymerase chain reaction-restriction fragment length polymorphism technique.Results
We found that individuals who were homozygous for the variant hOGG1 326Cys/Cys showed a significantly increased risk of lung adenocarcinoma (OR = 1.54; 95% CI: 1.01–2.36; P = 0.045). When the combined effect of variant alleles was analyzed, we found an increased OR of 1.89 (95% CI: 1.24–2.88, P = 0.003) for lung adenocarcinoma individuals with more than one homozygous variant allele. In stratified analyses, we found that the OR for the gene-environment interaction between Ser/Cys and Cys/Cys genotypes of hOGG1 codon 326 and cooking oil fumes for the risk of lung adenocarcinoma was 1.37 (95% CI: 0.77–2.44; P = 0.279) and 2.79 (95% CI: 1.50–5.18; P = 0.001), respectively.Conclusions
The hOGG1 Ser326Cys polymorphism might be associated with the risk of lung adenocarcinoma in Chinese non-smoking females. Furthermore, there is a significant gene-environment association between cooking oil fumes and hOGG1 326 Cys/Cys genotype in lung adenocarcinoma among female non-smokers. 相似文献57.
Weimin Zhou Min Zhu Ming Gui Lihua Huang Zhi Long Li Wang Hui Chen Yinghao Yin Xianzhen Jiang Yingbo Dai Yuxin Tang Leye He Kuangbiao Zhong 《PloS one》2014,9(10)
Alterations of mitochondrial DNA (mtDNA) have been associated with the risk of a number of human cancers; however, the relationship between mtDNA copy number in peripheral blood leukocytes (PBLs) and the risk of prostate cancer (PCa) has not been investigated. In a case-control study of 196 PCa patients and 196 age-paired healthy controls in a Chinese Han population, the association between mtDNA copy number in PBLs and PCa risk was evaluated. The relative mtDNA copy number was measured using quantitative real-time PCR; samples from three cases and two controls could not be assayed, leaving 193 cases and 194 controls for analysis. PCa patients had significantly higher mtDNA copy numbers than controls (medians 0.91 and 0.82, respectively; P<0.001). Dichotomized at the median value of mtDNA copy number in the controls, high mtDNA copy number was significantly associated with an increased risk of PCa (adjusted odds ratio = 1.85, 95% confidence interval: 1.21–2.83). A significant dose-response relationship was observed between mtDNA copy number and risk of PCa in quartile analysis (Ptrend = 0.011). Clinicopathological analysis showed that high mtDNA copy numbers in PCa patients were significantly associated with high Gleason score and advanced tumor stage, but not serum prostate-specific antigen level (P = 0.002, 0.012 and 0.544, respectively). These findings of the present study indicate that increased mtDNA copy number in PBLs is significantly associated with an increased risk of PCa and may be a reflection of tumor burden. 相似文献
58.
Juan Huang Jialin Wang Lijie Gu Jinfang Bao Jun Yin Zhihuan Tang Ling Wang Weijie Yuan 《PloS one》2013,8(11)
A low-protein diet supplemented with ketoacids maintains nutritional status in patients with diabetic nephropathy. The activation of autophagy has been shown in the skeletal muscle of diabetic and uremic rats. This study aimed to determine whether a low-protein diet supplemented with ketoacids improves muscle atrophy and decreases the increased autophagy observed in rats with type 2 diabetic nephropathy. In this study, 24-week-old Goto-Kakizaki male rats were randomly divided into groups that received either a normal protein diet (NPD group), a low-protein diet (LPD group) or a low-protein diet supplemented with ketoacids (LPD+KA group) for 24 weeks. Age- and weight-matched Wistar rats served as control animals and received a normal protein diet (control group). We found that protein restriction attenuated proteinuria and decreased blood urea nitrogen and serum creatinine levels. Compared with the NPD and LPD groups, the LPD+KA group showed a delay in body weight loss, an attenuation in soleus muscle mass loss and a decrease of the mean cross-sectional area of soleus muscle fibers. The mRNA and protein expression of autophagy-related genes, such as Beclin-1, LC3B, Bnip3, p62 and Cathepsin L, were increased in the soleus muscle of GK rats fed with NPD compared to Wistar rats. Importantly, LPD resulted in a slight reduction in the expression of autophagy-related genes; however, these differences were not statistically significant. In addition, LPD+KA abolished the upregulation of autophagy-related gene expression. Furthermore, the activation of autophagy in the NPD and LPD groups was confirmed by the appearance of autophagosomes or autolysosomes using electron microscopy, when compared with the Control and LPD+KA groups. Our results showed that LPD+KA abolished the activation of autophagy in skeletal muscle and decreased muscle loss in rats with type 2 diabetic nephropathy. 相似文献
59.
Lu Xu Fan Ping Jinhua Yin Xinhua Xiao Hongding Xiang Christie M. Ballantyne Huaizhu Wu Ming Li 《PloS one》2013,8(12)
Objective
Recent studies suggested that secreted protein acidic and rich in cysteine (SPARC), a novel adipokine, is a key player in the pathology of obesity and type 2 diabetes. We aimed to determine whether concentrations of SPARC were altered in patients with gestational diabetes mellitus (GDM) compared to normal glucose tolerance (NGT) controls and to investigate the relationships between SPARC and metabolic parameters in pregnant women.Design/Methods
Cross-sectional study of 120 pregnant women with GDM and 60 controls with NGT, in a university hospital setting. Plasma levels of SPARC, adiponectin, fibroblast growth factor 21 (FGF21), insulin and proinsulin were determined by ELISA.Results
GDM women had higher SPARC and lower adiponectin than NGT subjects; no difference was found in FGF21. SPARC levels were the lowest in subjects in the third tertile of insulin sensitivity index (ISIOGTT) and correlated positively with pre-pregnant BMI, insulin and 3 h glucose during 100-g OGTT, HOMA-IR, fasting proinsulin, hsCRP and white blood cells count, and negatively with ISIOGTT, when adjusting for gestational age. Triglyceride (TG), Apolipoprotein A1, apolipoprotein B and lipoprotein (a) correlated with SPARC in partial Pearson correlation. Correlations between SPARC with adiponectin, systolic blood pressure and TG were marginally significant in partial Spearman correlation analysis. In multivariate regression analysis, SPARC was an independent negative indicator of ISIOGTT.Conclusions
SPARC levels are correlated significantly with inflammation and may also be correlated with dyslipidemia and represent an independent determinant of insulin resistance in late pregnancy, indicating a potential role of SPARC in the pathophysiology of GDM. 相似文献60.
Chaoyang Zhao Shaoming Miao Yanfang Yin Yanjuan Zhu Paul Nabity Raman Bansal Chenxi Liu 《Ecology and evolution》2021,11(11):7018
Herbivory is a highly sophisticated feeding behavior that requires abilities of plant defense suppression, phytochemical detoxification, and plant macromolecule digestion. For plant‐sucking insects, salivary glands (SGs) play important roles in herbivory by secreting and injecting proteins into plant tissues to facilitate feeding. Little is known on how insects evolved secretory SG proteins for such specialized functions. Here, we investigated the composition and evolution of secretory SG proteins in the brown marmorated stink bug (Halyomorpha halys) and identified a group of secretory SG phospholipase C (PLC) genes with highest sequence similarity to the bacterial homologs. Further analyses demonstrated that they were most closely related to PLCs of Xenorhabdus, a genus of Gammaproteobacteria living in symbiosis with insect‐parasitizing nematodes. These suggested that H. halys might acquire these PLCs from Xenorhabdus through the mechanism of horizontal gene transfer (HGT), likely mediated by a nematode during its parasitizing an insect host. We also showed that the original HGT event was followed by gene duplication and expansion, leading to functional diversification of the bacterial‐origin PLC genes in H. halys. Thus, this study suggested that an herbivore might enhance adaptation through gaining genes from an endosymbiont of its parasite in the tripartite parasitic and symbiotic interactions. 相似文献