全文获取类型
收费全文 | 41771篇 |
免费 | 3329篇 |
国内免费 | 2438篇 |
专业分类
47538篇 |
出版年
2024年 | 60篇 |
2023年 | 484篇 |
2022年 | 1132篇 |
2021年 | 1966篇 |
2020年 | 1223篇 |
2019年 | 1506篇 |
2018年 | 1410篇 |
2017年 | 1084篇 |
2016年 | 1623篇 |
2015年 | 2427篇 |
2014年 | 2848篇 |
2013年 | 3092篇 |
2012年 | 3586篇 |
2011年 | 3399篇 |
2010年 | 1944篇 |
2009年 | 1794篇 |
2008年 | 2087篇 |
2007年 | 1868篇 |
2006年 | 1604篇 |
2005年 | 1420篇 |
2004年 | 1199篇 |
2003年 | 1053篇 |
2002年 | 905篇 |
2001年 | 851篇 |
2000年 | 740篇 |
1999年 | 716篇 |
1998年 | 435篇 |
1997年 | 464篇 |
1996年 | 441篇 |
1995年 | 390篇 |
1994年 | 378篇 |
1993年 | 308篇 |
1992年 | 441篇 |
1991年 | 383篇 |
1990年 | 331篇 |
1989年 | 246篇 |
1988年 | 236篇 |
1987年 | 198篇 |
1986年 | 141篇 |
1985年 | 185篇 |
1984年 | 121篇 |
1983年 | 104篇 |
1982年 | 80篇 |
1981年 | 60篇 |
1980年 | 55篇 |
1979年 | 72篇 |
1978年 | 66篇 |
1977年 | 46篇 |
1976年 | 48篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
991.
Meng-Bo Hu Pei-De Bai Yi-Shuo Wu Li-Min Zhang Hua Xu Rong Na Hao-Wen Jiang Qiang Ding 《PloS one》2015,10(4)
Objective
To investigate the relationship between body mass index (BMI) and prostate cancer (PCa) risk at biopsy in Chinese men.Patients and Methods
We retrospectively reviewed the records of 1,807 consecutive men who underwent initial multicore (≥10) prostate biopsy under transrectal ultrasound guidance between Dec 2004 and Feb 2014. BMI was categorised based on the Asian classification of obesity as follows: <18.5 (underweight), 18.5–22.9 (normal weight), 23–24.9 (overweight), 25–29.9 (moderately obese), and ≥30 kg/m2 (severely obese). The odds ratios (OR) of each BMI category for risk of PCa and high-grade prostate cancer (HGPCa, Gleason score ≥4+3) detection were estimated in crude, age-adjusted and multivariate-adjusted models. Prevalence ratios and accuracies of PSA predicted PCa were also estimated across BMI groups.Results
In total, PCa was detected by biopsy in 750 (45.4%) men, and HGPCa was detected in 419 (25.4%) men. Compared with men of normal weight, underweight men and obese men were older and had higher prostate specific antigen levels. The risk of overall PCa detection via biopsy presented an obvious U-shaped relationship with BMI in crude analysis. Overall, 50.0%, 37.4%, 45.6% 54.4% and 74.1% of the men in the underweight, normal weight, overweight, moderately obese and severely obese groups, respectively, were diagnosed with PCa via biopsy. In multivariate analysis, obesity was significantly correlated with a higher risk of PCa detection (OR = 1.17, 95%CI 1.10–1.25, P<0.001). However, higher BMI was not correlated with HGPCa detection (OR = 1.03, 95%CI 0.97–1.09, P = 0.29). There were no significant differences in the accuracy of using PSA to predict PCa or HGPCa detection across different BMI categories.Conclusion
Obesity was associated with higher risk of PCa detection in the present Chinese biopsy population. No significant association was detected between obesity and HGPCa. 相似文献992.
Gongguan Liu Jinjun Xu Hui Wu Donglei Sun Xiquan Zhang Xiaoping Zhu Stefan Magez Meiqing Shi 《PLoS pathogens》2015,11(7)
African trypanosomes are extracellular protozoan parasites causing a chronic debilitating disease associated with a persistent inflammatory response. Maintaining the balance of the inflammatory response via downregulation of activation of M1-type myeloid cells was previously shown to be crucial to allow prolonged survival. Here we demonstrate that infection with African trypanosomes of IL-27 receptor-deficient (IL-27R-/-) mice results in severe liver immunopathology and dramatically reduced survival as compared to wild-type mice. This coincides with the development of an exacerbated Th1-mediated immune response with overactivation of CD4+ T cells and strongly enhanced production of inflammatory cytokines including IFN-γ. What is important is that IL-10 production was not impaired in infected IL-27R-/- mice. Depletion of CD4+ T cells in infected IL-27R-/- mice resulted in a dramatically reduced production of IFN-γ, preventing the early mortality of infected IL-27R-/- mice. This was accompanied by a significantly reduced inflammatory response and a major amelioration of liver pathology. These results could be mimicked by treating IL-27R-/- mice with a neutralizing anti-IFN-γ antibody. Thus, our data identify IL-27 signaling as a novel pathway to prevent early mortality via inhibiting hyperactivation of CD4+ Th1 cells and their excessive secretion of IFN-γ during infection with African trypanosomes. These data are the first to demonstrate the essential role of IL-27 signaling in regulating immune responses to extracellular protozoan infections. 相似文献
993.
994.
Background
To investigate the surgical complications of scleral buckling (SB) and pars plana vitrectomy (PPV) performed on primary rhegmatogenous retinal detachment (RRD) and to discover which surgical procedures bring fewer complications.Methods
An electronic literature search using the PubMed database, ISI Web of Knowledge and the Cochrane Central Register of Controlled Trials to identify randomized controlled trials and observational studies comparing SB with PPV on primary RRD. Outcome measures included intra-operative complications and early and late post-operative complications.Results
During the operation, significantly less subretinal hemorrhage occurred in the PPV group than in the SB group (OR = 4.71; 95%CI, 1.33–16.64; p = 0.02) and the hypotony incidence was significantly higher in the SB group (OR = 18.24; 95%CI, 2.37–140.44; p = 0.005); however, the occurrence of iatrogenic breaks was significantly lower in the SB group (OR = 0.05; 95%CI, 0.01–0.21; p<0.0001). In the early stage of post-operation, significantly higher incidence of choroidal detachment was identified in the SB group than in the PPV group (OR = 10.19; 95%CI, 2.36–44.09; p = 0.002); patients undergoing SB had significantly higher odds of residual subretinal fluid (OR = 14.71; 95%CI, 1.84–117.32; p = 0.01); the occurrence of high intraocular pressure was significantly lower in the SB group (OR = 0.46; 95%CI, 0.23–0.89; p = 0.02); and no significant difference was shown in the incidence of epithelia defect (p = 0.37) between the two groups. In the late stage of post-operation, the incidence of diplopia/extraocular muscle dysfunction was significantly higher in the SB group (OR = 4.04; 95%CI, 1.30–12.52; p = 0.02); and significantly less cataract was observed in the SB group (OR = 0.20; 95%CI, 0.14–0.30; p<0.00001); no significant difference was found in the incidences of cystoid macular edema (p = 0.65), macular pucker (p = 0.52), post-operative proliferative vitreoretinopathy (p = 0.73) and epiretinal membrane (p = 0.47) in other late post-operative complications.Conclusions
This meta-analysis suggests that PPV could be considered as potential surgical management on primary RRD. 相似文献995.
Guoli Zhao Yingga Wu Li Du Wenhua Li Ying Xiong Aiyu Yao Qifu Wang Yong Q. Zhang 《PLoS genetics》2015,11(3)
Synaptic connections must be precisely controlled to ensure proper neural circuit formation. In Drosophila melanogaster, bone morphogenetic protein (BMP) promotes growth of the neuromuscular junction (NMJ) by binding and activating the BMP ligand receptors wishful thinking (Wit) and thickveins (Tkv) expressed in motor neurons. We report here that an evolutionally conserved, previously uncharacterized member of the S6 kinase (S6K) family S6K like (S6KL) acts as a negative regulator of BMP signaling. S6KL null mutants were viable and fertile but exhibited more satellite boutons, fewer and larger synaptic vesicles, larger spontaneous miniature excitatory junctional potential (mEJP) amplitudes, and reduced synaptic endocytosis at the NMJ terminals. Reducing the gene dose by half of tkv in S6KL mutant background reversed the NMJ overgrowth phenotype. The NMJ phenotypes of S6KL mutants were accompanied by an elevated level of Tkv protein and phosphorylated Mad, an effector of the BMP signaling pathway, in the nervous system. In addition, Tkv physically interacted with S6KL in cultured S2 cells. Furthermore, knockdown of S6KL enhanced Tkv expression, while S6KL overexpression downregulated Tkv in cultured S2 cells. This latter effect was blocked by the proteasome inhibitor MG132. Our results together demonstrate for the first time that S6KL regulates synaptic development and function by facilitating proteasomal degradation of the BMP receptor Tkv. 相似文献
996.
目的探讨炎症细胞因子白介素-1β(interleukin-1βIL-1β)对高糖刺激的人肾小管上皮细胞转分化的影响。-方法体外培养人肾近曲小管上皮细胞株(HKCs),随机分为正常对照组(5.5 mmol/L normal glucose);高糖组(30 mmol/L high glucose);高糖+IL-1β(5ng/ml)组。分别于处理后24h、48h、72h收集细胞,采用免疫细胞化学染色和Western蛋白印迹法检测细胞角蛋白-18(cytokeratin-18 CK-18)、α-平滑肌肌动蛋白(α-smooth muscle actinα-SMA)水平。结果高糖能够诱导肾小管上皮细胞α-SMA蛋白的合成增加,而肾小管上皮细胞的标志物CK-18的表达逐渐减少;IL-1β与高糖同时刺激可使肾小管上皮细胞α-SMA蛋白表达进一步增多,而其自身标志物CK-18的表达则明显下降。结论炎症因子IL-1β能增强高糖对肾小管上皮细胞转分化的作用。 相似文献
997.
A two-dimensional copper(II) polymer with formula of [Cu4(H2O)4(dmapox)2(btc)]n · 10nH2O, where dmapox is the dianion of N,N′-bis[3-(dimethylamino)propyl]oxamide and btc is the tetra-anion of 1,2,4,5-benzenetetracarboxylic acid, was synthesized and characterized by elemental analysis, conductivity measurement, IR and electronic spectral studies. The crystal structure of the complex has been determined by X-ray single-crystal diffraction. The structure consists of crystallized water molecules and neutral two-dimensional copper(II) coordination polymeric networks constructed both by the bis-tridentate μ-trans-dmapox and tetra-monodentate μ4-btc bridging ligands. Each btc ligand links four trans-dmapox-bridged binuclear copper(II) building blocks [Cu2(H2O)2(trans-dmapox)]2+ and each binuclear copper(II) building block attaches to two btc ligands forming an infinite 2D layer which consists of 4+4 grids with dimensions of 13.563(5) × 15.616(5) Å. The environment around the copper(II) atom can be described as a distorted square-pyramid and the Cu?Cu separations through μ-trans-dmapox and μ4-btc bridging ligands are 5.225 Å (Cu1-Cu1i), 5.270 Å (Cu2-Cu2ii), 6.115 Å (Cu1-Cu2), 9.047 Å (Cu1-Cu2iii) and 10.968 Å (Cu1-Cu1iii), respectively. Abundant hydrogen bonds among the crystallized, the coordinated water molecules, and the uncoordinated carboxyl oxygen atoms cross-link the two-dimensional layers into an overall three-dimensional channel-like framework. The interaction of the copper(II) polymer with calf thymus DNA (CT-DNA) has been investigated by using absorption, emission spectral and electrochemical techniques. The results indicate that the copper(II) polymer interacts with DNA strongly (Kb = 4.8 × 105 M−1 and Ksv = 1.1 × 104) and the interaction mode between the copper(II) polymer and DNA may be the groove binding. To the best of our knowledge, this is the first report about the crystal structure and DNA-binding studies of a two-dimensional copper(II) polymer bridged both by the trans-oxamidate and btc ligands. 相似文献
998.
Yun-He Li Yong-Jie Wu Bei Wu Ming-Hong Zou Zhi Zhang Guang-Ming Sun 《Acta Physiologiae Plantarum》2011,33(5):1715-1722
In mainland China, the most popular pineapple cultivar is ‘Comte de Paris’. Gibberellic acids have been widely applied to
enhance fruit growth in various species. To evaluate the effect of gibberellic acid (GA3) on ‘Comte de Paris’ pineapple production and quality, pineapple fruits were sprayed with GA3 at concentrations of 5, 20, 50, or 100 mg l−1 at both 0 and 15 days after flowering (DAF). Fruits were sampled every 15 days from 0 to 60 DAF (maturation) for flow cytometric
analysis and histological observation. The results showed that the treatments with the three highest concentrations of GA3 significantly increased fruit weight, and the most effective concentration was 50 mg l−1 GA3, which increased the flesh weight by 20.3% compared to the control. Although treatment with GA3 had little effect on the total soluble solids and fruit juice pH, it increased the vitamin C content. Although flow cytometric
analysis showed that the 50 mg l−1 GA3 treatment had only a slight impact on the number of S phase cells, histological observations indicated that the increase
of fruit volume and flesh weight under this GA3 treatment was not due to the increase of cell number but a result of the increase of cell area in the fruit flesh. 相似文献
999.
Calpastatin (CAST) is an important gene for meat quality traits in livestock and poultry. The cDNA of caprine CAST gene was amplified for the first time using RACE-PCR. Results showed the full-length cDNA of caprine CAST gene (Accession no. GU944861) was 2435 base pair (bp) and contained a 2187 bp open reading frame encoding a protein with
728 amino acid residues. Bioinformatic analysis indicated that caprine CAST cDNA was 89.8–95.4, 83.5–92.2, 72.8–81.8 and 69.8–73.5% identical to sheep, cattle, pig and human CAST cDNA. It was predicted that caprine CAST contained four conserved domains with 42 serine phosphorylation loci, 18 threonine
phosphorylation loci, 1 tyrosine phosphorylation locus and 5 specific PKC phosphorylation loci. This work provided an important
experimental basis for further research on the function of CAST in goat. 相似文献
1000.
Chih-Yen Wang Jen-Kun Chen Yi-Ting Wu May-Jywan Tsai Song-Kun Shyue Chung-Shi Yang Shun-Fen Tzeng 《Journal of biomedical science》2011,18(1):13