全文获取类型
收费全文 | 9202篇 |
免费 | 691篇 |
国内免费 | 771篇 |
专业分类
10664篇 |
出版年
2024年 | 18篇 |
2023年 | 129篇 |
2022年 | 294篇 |
2021年 | 506篇 |
2020年 | 310篇 |
2019年 | 441篇 |
2018年 | 400篇 |
2017年 | 255篇 |
2016年 | 426篇 |
2015年 | 595篇 |
2014年 | 699篇 |
2013年 | 789篇 |
2012年 | 887篇 |
2011年 | 766篇 |
2010年 | 439篇 |
2009年 | 436篇 |
2008年 | 459篇 |
2007年 | 398篇 |
2006年 | 361篇 |
2005年 | 258篇 |
2004年 | 249篇 |
2003年 | 202篇 |
2002年 | 148篇 |
2001年 | 133篇 |
2000年 | 121篇 |
1999年 | 102篇 |
1998年 | 102篇 |
1997年 | 91篇 |
1996年 | 85篇 |
1995年 | 72篇 |
1994年 | 64篇 |
1993年 | 46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
71.
环孢素A对人早孕期滋养细胞MMP-9与MMP-2表达的调控作用 总被引:1,自引:0,他引:1
本研究的目的是探讨环孢素A对人早孕期滋养细胞侵袭能力及基质金属蛋白酶9与2 (matrix metalloproteinase 9 and 2,简称MMP-9与MMP-2)表达的调节作用,为治疗反复自然流产等妊娠疾患提供新的线索。侵袭试验观察CsA对人早孕期滋养细胞侵袭能力的调节作用;RT-PCR与明胶酶谱分析CsA对滋养细胞MMP-9与MMP-2 mRNA及蛋白水平表达的影响;In-cell West- ern检测CsA作用后滋养细胞ERK1/2磷酸化水平。结果发现,1.0μmol/L CsA明显增强滋养细胞侵袭能力,MEK激酶抑制剂U0126可抑制CsA对滋养细胞的促侵袭作用;1.0μmol/L CsA可诱导MMP- 9与MMP-2基因的转录与蛋白分泌;该诱导效应同样可被U0126所阻滞;1.0μmol/L CsA以时间依赖方式促进ERK1/2的磷酸化。结果表明,CsA可激活ERK1/2,通过MAPK/ERK1/2途径促进滋养细胞MMP-9与MMP-2基因的转录与蛋白分泌,从而增强滋养细胞的侵袭能力,对滋养细胞生物学功能具有良性调节作用。 相似文献
72.
基于电子病历的急性ST段抬高型心肌梗死临床路径与决策辅助系统 总被引:2,自引:0,他引:2
目的:研究在结构化电子病历上实现计算机化的急性ST段抬高型心肌梗死临床路径,进一步评价该方法的试用结果,为辅助临床医生治疗决策、规范治疗行为,并借此提高医疗质量,合理控制医疗费用提供有效的手段。方法:选取最新的、具有权威性的关于急性ST段抬高型心肌梗死诊治指南作为制定治疗决策方案及编写临床路径的依据;通过程序设计将临床路径编写入医学知识库系统,并将医学知识库系统与结构化电子病历进行无缝连接;将20例无严重并发症的急性ST段抬高型心肌梗死病人均分为两组,其中观察组推行计算机化临床路径,在患者住院天数、住院费用、患者及家属满意度以及医生对该系统的评价方面与对照组进行比较。结果:观察组患者平均住院天数及平均住院费用明显低于对照组(p<0.000);患者及家属满意度普遍提高(p<0.05);该系统得到所有被调查医生的认可。结论:运用计算机化临床路径管理无严重并发症的急性ST段抬高型心肌梗死患者能在维持甚至提高医疗质量的前提下,减少患者平均住院天数、平均住院费用,提高患者及家属对医疗行为的满意度,增强医生对治疗指南的顺从性。 相似文献
73.
Insulin-like growth factors: Putative muscle-derived trophic agents that promote motoneuron survival
Nicola T. Neff David Prevette Lucien J. Houenou Michael E. Lewis Marcie A. Glicksman Qin-Wei Yin Ronald W. Oppenheim 《Developmental neurobiology》1993,24(12):1578-1588
Treatment of chick embryos in ovo with IGF-I during the period of normal, developmentally regulated neuronal death (embryonic days 5–10) resulted in a dose-dependent rescue of a significant number of lumbar motoneurons from degeneration and death. IGF-II and two variants of IGF-I with reduced affinity for IGF binding proteins, des(1-3) IGF-I and long R3 IGF-I, also elicited enhanced survival of motoneurons equal to that seen in IGF-I-treated embryos. IGF-I did not enhance mitogenic activity in motoneuronal populations when applied to embryos during the period of normal neuronal proliferation (E2-5). Treatment of embryos with IGF-I also reduced two types of injury-induced neuronal death. Following either deafferentation or axotomy, treatment of embryos with IGF-I rescued approximately 75% and 50%, respectively, of the motoneurons that die in control embryos as a result of these procedures. Consistent with the survival-promoting activity on motoneurons in ovo, IGF-I, -II, and des(1-3) IGF-I elevated choline acetyltransferase activity in embryonic rat spinal cord cultures, with des (1-3) IGF-I demonstrating 2.5 times greater potency than did IGF-I. A single addition of IGF-I at culture initiation resulted in the maintenance of 80% of the initial ChAT activity for up to 5 days, during which time ChAT activity in untreated control cultures fell to 9%. In summary, these results demonstrate clear motoneuronal trophic activity for the IGFs. These findings, together with previous reports that IGFs are synthesized in muscle and may participate in motoneuron axonal regeneration and sprouting, indicate that these growth factors may have an important role in motoneuron development, maintenance, and recovery from injury. © 1993 John Wiley & Sons, Inc. 相似文献
74.
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
75.
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
76.
77.
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
78.
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
79.
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80.
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