全文获取类型
收费全文 | 9519篇 |
免费 | 996篇 |
国内免费 | 395篇 |
专业分类
耳鼻咽喉 | 79篇 |
儿科学 | 62篇 |
妇产科学 | 53篇 |
基础医学 | 2247篇 |
口腔科学 | 184篇 |
临床医学 | 679篇 |
内科学 | 1422篇 |
皮肤病学 | 166篇 |
神经病学 | 976篇 |
特种医学 | 457篇 |
外国民族医学 | 4篇 |
外科学 | 477篇 |
综合类 | 1209篇 |
现状与发展 | 7篇 |
预防医学 | 491篇 |
眼科学 | 150篇 |
药学 | 1131篇 |
2篇 | |
中国医学 | 448篇 |
肿瘤学 | 666篇 |
出版年
2024年 | 34篇 |
2023年 | 184篇 |
2022年 | 296篇 |
2021年 | 415篇 |
2020年 | 336篇 |
2019年 | 296篇 |
2018年 | 271篇 |
2017年 | 322篇 |
2016年 | 343篇 |
2015年 | 382篇 |
2014年 | 571篇 |
2013年 | 667篇 |
2012年 | 564篇 |
2011年 | 594篇 |
2010年 | 570篇 |
2009年 | 537篇 |
2008年 | 525篇 |
2007年 | 481篇 |
2006年 | 484篇 |
2005年 | 430篇 |
2004年 | 399篇 |
2003年 | 346篇 |
2002年 | 318篇 |
2001年 | 244篇 |
2000年 | 179篇 |
1999年 | 142篇 |
1998年 | 146篇 |
1997年 | 137篇 |
1996年 | 115篇 |
1995年 | 86篇 |
1994年 | 74篇 |
1993年 | 57篇 |
1992年 | 62篇 |
1991年 | 41篇 |
1990年 | 28篇 |
1989年 | 26篇 |
1988年 | 14篇 |
1987年 | 18篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 15篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1973年 | 10篇 |
1972年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Objective
To investigate the effects of chronic aluminum (Al) exposure on learning and memory function of rats by observing the changes of Ras/Raf/ERK (Ras/ERK) signaling pathway.Methods
Eighty weaned Wistar rats were divided into four groups ad libitum, 20 rats in each group. The four groups were fed with drinking water containing 0% (control), 0.2%, 0.4% and 0.6% (Al exposure) AlCl3 for 3 months individually to set up aluminum exposure models. The laboratory was maintained at 18–23 °C and 45–55% relative humidity. Graphite furnace atomic absorption spectrometry was used to detect the content of Al in brain and blood. Western blot and real-time PCR (RT-PCR) were used to determine the protein and mRNA expression levels for Ras, Raf1, ERK2 and CREB.Results
Chronic Al exposure increased the content of Al in rats’ blood and brain. It increased expression of Ras in the hippocampi compared with the control but the expression decreased along the Al exposure groups (p < 0.05). Similarly, Raf1, ERK2 and CREB expressions decreased compared to the control in a dose-dependent manner (p < 0.05).Conclusion
Chronic Al exposure may affect learning and memory through impact on Ras/ERK signal pathway. 相似文献952.
Barbounis EG Tzatzarakis MN Alegakis AK Kokkinaki A Karamanos N Tsakalof A Tsatsakis AM 《Toxicology letters》2012,210(2):225-231
Polychlorinated biphenyls (PCBs) levels were assessed in human hair samples, originating from two main agricultural regions of Greece. The analysis was performed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-double focusing high resolution mass spectrometry (GC-DFHRMS). The main analytical procedure involved hair decontamination, solid-liquid extraction and cleanup steps. The recoveries of PCBs ranged from 71.2% to 101.6%, with accuracies greater than 87.5% and the between-run precisions (%RSD) lower than 25% for all analytes. Differences in the frequencies of detection and the median values of PCBs were detected between the examined regions and between the applied analytical techniques. All Peloponnesus' hair examined samples were found positive for each examined PCB, while the percentage of the total positive samples ranged from 86.1% (for PCB 138) to 94.4% (for PCB 28 and 153 congeners) using GC-DFHRMS. The Cretan hair samples were less contaminated (SUM PCBs=0.61 and 1.47pg/mg) unlike the Peloponnesus' samples (SUM PCBs=24.68 and 38.74pg/mg) measured by GC-DFHRMS and GC-MS, respectively. PCBs with high chlorination gave lower concentration values compared to low chlorination PCBs in both populations. No significant differences were observed between women and men. The GC-DFHRMS technique provided higher percentage of positive samples and low PCBs median values, due to higher sensitivity and interferences from isobaric ions in the GC-MS technique and is therefore considered as a powerful tool for such assessments in hair specimens. 相似文献
953.
Yan Li Zhengtao HuBo Chen Qian BuWenjie Lu Yi DengRuiming Zhu Xue ShaoJing Hou Jinxuan ZhaoHongyu Li Baolai ZhangYina Huang Lei LvYinglan Zhao Xiaobo Cen 《Toxicology letters》2012
Methamphetamine (METH), a commonly abused psychostimulant, has been shown to induce neuronal damage by causing reactive oxygen species (ROS) formation, apoptosis and autophagy. Taurine (2-aminoethanesulfonic acid) is involved in several physiological actions in the brain, including neuroprotection, osmoregulation and neurotransmission. In this study, we investigate the protective effect of taurine against METH-induced neurotoxicity in PC12 cells and the underlying mechanism. The results showed that taurine significantly increased the cell viability inhibited by METH. LC3-II expression was elevated by METH treatment, whereas such increase was obviously attenuated by taurine. Co-treatment of taurine strongly reversed the decline of antioxidase activities induced by METH. Moreover, phosphorylated mammalian target of rapamycin (p-mTOR) was significantly inhibited by METH, whereas complementation of taurine markedly increased the expression of p-mTOR in PC12 cells, rather than phosphorylated Erk. Interestingly, taurine-induced decreasing expression of LC3-II was partially blocked by pretreatment of RAD001, an mTOR inhibitor. These results indicated that taurine inhibits METH-induced autophagic process through activating mTOR rather than Erk signaling. Collectively, our study shows that taurine protects METH-induced PC12 cells damage by attenuating ROS production, apoptosis and autophagy, at least in part, via mTOR signaling pathway. 相似文献
954.
955.
Near-infrared spectroscopy (NIRS) can detect two different kinds of signals from the human brain: the hemodynamic response (slow) and the neuronal response (fast). This paper explores a nonlinear aspect in the tactile-stimulus-evoked neuronal optical response over a NIRS time series (light intensity variation). The existence of the fast optical responses (FORs) over the time series recorded in stimulus sessions is confirmed by event-related averaging. The chaos levels of the NIRS time series recorded both in stimulus and in rest sessions are then identified according to the estimated largest Lyapunov exponent. The obtained results ascertain that stimulus-evoked neuronal optical responses can be detected in the somatosensory cortex using continuous-wave NIRS equipment. Further, the results strongly suggest that the chaos level can be used to recognize the FORs in NIRS time series and, thereby, the state of the pertinent brain activity. 相似文献
956.
Ono K Nakamura A Yoshiyama K Kinkori T Bundo M Kato T Ito K 《Neuroscience letters》2011,504(2):141-145
In the monkey's visual cortex, there are two well-documented information processing streams: the dorsal motion and ventral form/color pathways. Similarly, two corresponding information streams were also found in the cat's visual cortices, and PMLS and area 21a are the gateways for distinct motion and form information processing. It has been shown that the feedback from PMLS solely modulates motion direction, but not orientation response, while the feedback from area 21a modulates form related features, such as spatial frequency dependency and neuronal oblique effect. Here, we postulate that feedback signals from higher cortical areas in the form or the motion information pathway may solely modulate the corresponding properties in neurons in the lower areas of the visual system. To examine the above hypothesis, the impact of feedback from higher area 21a on both orientation and direction maps was investigated in area 17 of the cat using intrinsic signal optical imaging. The results showed that the feedback from area 21a did not affect the amplitude and preference of direction, but did modulate orientation response in area 17, supporting the above hypothesis. 相似文献
957.
958.
During the last two decades, imaging of neural activation has become an invaluable tool for assessing the functional organization of the human brain in vivo. Due to its widespread application in neuroscience, functional neuroimaging has raised the interest of clinical researchers in its possible use as a diagnostic biomarker. A hallmark feature of many neurodegenerative diseases is their chronic non-linear dynamic and highly complex preclinical course. Neurodegenerative diseases unfold over years to decades through clinically silent and asymptomatic stages of early adaptive, compensatory to pathophysiological (i.e. actively neurodegenerative) and decompensatory mechanisms in the brain - phases that are increasingly being considered as critical for primary and secondary preventive and therapeutic measures. Emerging evidence supports the concept of a potentially fully reversible functional phase that may precede the onset of micro- and macrostructural and cognitive decline, a potentially late-stage "neurodegenerative" phase of a primary neurodegenerative disorder. Alzheimer's disease serves as an ideal model to test this hypothesis supported by the neural network model of the healthy and diseased brain. Being highly dynamic in nature, brain activation and neuronal network functional connectivity represent not only candidate diagnostic but also candidate surrogate markers for interventional trials. Potential caveats of functional imaging are critically reviewed with focus on confound variables such as altered neurovascular coupling as well as parameters related to task- and study design. 相似文献
959.
960.