首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   15269篇
  免费   840篇
  国内免费   101篇
耳鼻咽喉   154篇
儿科学   296篇
妇产科学   167篇
基础医学   2126篇
口腔科学   220篇
临床医学   1556篇
内科学   3782篇
皮肤病学   329篇
神经病学   1822篇
特种医学   1010篇
外科学   2310篇
综合类   75篇
一般理论   7篇
预防医学   626篇
眼科学   234篇
药学   752篇
中国医学   7篇
肿瘤学   737篇
  2023年   140篇
  2022年   180篇
  2021年   407篇
  2020年   245篇
  2019年   327篇
  2018年   375篇
  2017年   268篇
  2016年   392篇
  2015年   388篇
  2014年   555篇
  2013年   763篇
  2012年   1215篇
  2011年   1190篇
  2010年   745篇
  2009年   694篇
  2008年   1080篇
  2007年   1062篇
  2006年   1020篇
  2005年   1006篇
  2004年   900篇
  2003年   799篇
  2002年   719篇
  2001年   170篇
  2000年   131篇
  1999年   147篇
  1998年   154篇
  1997年   132篇
  1996年   77篇
  1995年   75篇
  1994年   55篇
  1993年   45篇
  1992年   53篇
  1991年   43篇
  1990年   53篇
  1989年   38篇
  1988年   26篇
  1987年   30篇
  1986年   26篇
  1985年   21篇
  1984年   26篇
  1983年   23篇
  1982年   23篇
  1980年   15篇
  1979年   17篇
  1978年   15篇
  1977年   23篇
  1975年   18篇
  1974年   20篇
  1973年   16篇
  1930年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Seeing or hearing manual actions activates the mirror neuron system, i.e., specialized neurons within motor areas which fire not only when an action is performed but also when it is passively perceived. Although it has been shown that mirror neurons respond to either action-specific vision or sound, it remains a topic of debate whether and how vision and sound interact during action perception.Here we used transcranial magnetic stimulation to explore multimodal interactions in the human motor system, namely at the level of the primary motor cortex (M1). Corticomotor excitability in M1 was measured while subjects perceived unimodal visual (V), unimodal auditory (A), or multimodal (V + A) stimuli of a simple hand action. In addition, incongruent multimodal stimuli were included, in which incongruent vision or sound was presented simultaneously with the auditory or visual action stimulus. A selective response increase was observed to the congruent multimodal stimulus as compared to the unimodal and incongruent multimodal stimuli.These findings speak in favour of ‘shared’ action representations in the human motor system that are evoked in a ‘modality-dependent’ way, i.e., they are elicited most robustly by the simultaneous presentation of congruent auditory and visual stimuli. Multimodality in the perception of hand movements bears functional similarities to speech perception, suggesting that multimodal convergence is a generic feature of the mirror system which applies to action perception in general.  相似文献   
992.
Aims  This prospective study was designed to determine the diagnostic value of adenosine stress cardiac magnetic resonance imaging (CMRI) in patients referred to elective coronary angiography. Methods and results  Myocardial perfusion measurements at rest and adenosine stress were performed in 141 patients (105 men, 36 women, mean age 63.4 years) at 1.5 T with a Turbo Flash sequence. Stress-induced perfusion deficits were correlated to angiographic stenoses ≥75%. The overall sensitivity for CMRI depicting coronary artery disease (CAD) with relevant stenoses was 90.4%, the specificity was 77.4%, the positive predictive value was 85.9%, the negative predictive value was 84.2% and the accuracy 85.2%. Subgroup analysis was performed for 3-vessel disease (n = 44, sensitivity 92.3%, specificity 75.0%), 2-vessel disease (n = 43, sensitivity 92.6%, specificity 92.9%), 1-vessel disease (n = 27, sensitivity 93.1%, specificity 71.4%) and patients without CAD (n = 27, specificity 70.4%) as well as for patients with prior myocardial infarction (n = 44, sensitivity 92.9%, specificity 86.7%), prior coronary artery bypass surgery (n = 21, sensitivity 88.2%, specificity 66.7%), prior coronary interventions (n = 88, sensitivity 91.9%, specificity 75.0%), or diabetics (n = 27, sensitivity 90.5%, specificity 83.3%). Conclusion  Our study shows that stress perfusion CMRI can accurately predict relevant CAD and contributes to the identification of hemodynamic relevant stenoses in patients scheduled for coronary angiography. C. Doesch and A. Seeger have equally contributed to this publication.  相似文献   
993.
Aniline is an important starting material in the manufacture of polyurethane-based plastic materials. Aniline-derived methemoglobinemia (Met-Hb) is well described in exposed workers although information on the dose–response association is limited. We used an experimental design to study the association between aniline in air with the formation of Met-Hb in blood and the elimination of aniline in urine. A 6-h exposure of 2 ppm aniline in 19 non-smoking volunteers resulted in a time-dependent increase in Met-Hb in blood and aniline in urine. The maximum Met-Hb level in blood (mean 1.21 ± 0.29 %, range 0.80–2.07 %) and aniline excretion in urine (mean 168.0 ± 51.8 µg/L, range 79.5–418.3 µg/L) were observed at the end of exposure, with both parameters rapidly decreasing after the end of exposure. After 24 h, the mean level of Met-Hb (0.65 ± 0.18 %) returned to the basal level observed prior to the exposure (0.72 ± 0.19 %); whereas, slightly elevated levels of aniline were still present in urine (means 17.0 ± 17.1 vs. 5.7 ± 3.8 µg/L). No differences between males and females as well as between slow and fast acetylators were found. The results obtained after 6-h exposure were also comparable to those observed in four non-smoking volunteers after 8-h exposure. Maximum levels of Met-Hb and aniline in urine were 1.57 % and 305.6 µg/L, respectively. Overall, our results contribute to the risk assessment of aniline and as a result, the protection of workers from aniline-derived adverse health effects at the workplace.  相似文献   
994.
995.
Investigation of the Madagascan endemic plant Ambavia gerrardii for antiproliferative activity against the A2780 ovarian cancer cell line led to the isolation of the three new alkaloids 8-hydroxyeupolauridine (1), 9-methoxyeupolauridine 1-oxide (2), and 11-methoxysampangine (3) and the three known alkaloids 4-6. The structures of 1 and 2 were confirmed by synthesis. Compounds 3, 4, and 6 showed moderate to good antiproliferative activities, with IC50 values of 10.3, 3.5, and 0.60 μM, respectively, against the A2780 human ovarian cancer cell line and with IC50 values of 0.57, 1.77, and 0.58 μM, respectively, against the H460 human lung cancer cell line.  相似文献   
996.
PurposeTo determine if the associations among established risk factors and reduced kidney function vary by age.MethodsWe pooled cross-sectional data from 14,788 nondiabetics aged 40 to 100 years in 4 studies: Cardiovascular Health Study, Health, Aging, and Body Composition Study, Multi-Ethnic Study of Atherosclerosis, and Prevention of Renal and Vascular End-Stage Disease cohort.ResultsHypertension and low high-density lipoprotein (HDL) cholesterol were associated with reduced cystatin C-based estimated glomerular filtration rate (eGFR) across the age spectrum. In adjusted analyses, hypertension was associated with a 2.3 (95% confidence interval [CI], 0.1, 4.4), 5.1 (95% CI, 4.1, 6.1), and 6.9 (95% CI, 3.0, 10.4) mL/min/1.73 m2 lower eGFR in participants 40 to 59, 60 to 79, and at least 80 years, respectively (P for interaction < .001). The association of low HDL cholesterol with reduced kidney function was also greater in the older age groups: 4.9 (95% CI, 3.5, 6.3), 7.1 (95% CI, 6.0, 8.3), 8.9 (95% CI, 5.4, 11.9) mL/min/1.73 m2 (P for interaction < .001). Smoking and obesity were associated with reduced kidney function in participants under 80 years. All estimates of the potential population impact of the risk factors were modest.ConclusionsHypertension, obesity, smoking, and low HDL cholesterol are modestly associated with reduced kidney function in nondiabetics. The associations of hypertension and HDL cholesterol with reduced kidney function seem to be stronger in older adults.  相似文献   
997.
The ability of T cells to activate antimicrobial pathways in infected macrophages is essential to host defence against many intracellular pathogens. Here, we compared the ability of two T‐cell‐mediated mechanisms to trigger antimicrobial responses against Mycobacterium tuberculosis in humans, CD40 activation and the release of interferon‐γ (IFN‐γ). Given that IFN‐γ activates a vitamin D‐dependent antimicrobial response, we focused on induction of the key components of this pathway. We show that activation of human monocytes via CD40 ligand (CD40L) and IFN‐γ, alone, and in combination, induces the CYP27b1‐hydroxylase, responsible for the conversion of 25‐hydroxyvitamin D (25D) to the bioactive 1,25‐dihydroxyvitamin D (1,25D), and the vitamin D receptor (VDR). The activation of the vitamin D pathway by CD40L and IFN‐γ results in up‐regulated expression of the antimicrobial peptides, cathelicidin and DEFB4, as well as induction of autophagy. Finally, activation of monocytes via CD40L and IFN‐γ results in an antimicrobial activity against intracellular M. tuberculosis. Our data suggest that at least two parallel T‐cell‐mediated mechanisms, CD40L and IFN‐γ, activate the vitamin D‐dependent antimicrobial pathway and trigger antimicrobial activity against intracellular M. tuberculosis, thereby contributing to human host defence against intracellular infection.  相似文献   
998.
Self-etching primers are now considered the new generation of dentin bonding systems that modify and incorporate the bacteria-containing smear layer into their bonding mechanism. The antibacterial effects of the self-etching primers Clearfil SE Bond, Mac Bond, Imperva FL Bond, One-Up BondF and Prompt L-Pop were evaluated using the bacteria Streptococcus mutans ATCC25175, Peptostreptococcus anaerobius, Peptostreptococcus prevotii, Peptostreptococcus asaccharolyticus, Lactobacillus acidophilus, Lactobacillus catenaforme, Lactobacillus jensenii, Actinomyces odontolyticus, Porphyromonas endodontalis, Clostridium ramosum, Prevotella oris, Prevotella denticola and Fusobacterium nucleatum, with a disk diffusion method. A single-bottle total-etch dentin adhesive (Excite) was used for comparisons and chlorhexidine (0.2%) was used as the positive control. After incubation, zones of inhibited bacterial growth were observed. One-Up BondF, Prompt L-Pop and Excite showed growth inhibition for all bacterial strains. The bonding agents of Clearfil SE Bond, Mac Bond and Imperva FL Bond were unable to inhibit the growth of Lactobacillus jensenii and Actinomyces odontolyticus, while the primers of these systems produced inhibition halos to all tested microorganisms greater than that of chlorhexidine.  相似文献   
999.
Emerging evidence suggests oxidative stress plays a role in the pathophysiology of both atopic dermatitis (AD) and psoriasis (PSO). We established in vitro models of AD and PSO skin, and characterized these models in regard to their oxidative stress state. Both AD and PSO model keratinocytes exhibited elevated reactive oxygen species (ROS) levels and accumulated more DNA damage than control cells after oxidative stress induced by 250 µmol/L H2O2. Elevated ROS levels and DNA damage accumulation could be inhibited by the NADPH oxidase (NOX) inhibitor diphenyleneiodonium (DPI). Further, immunofluorescence analysis revealed the presence of both NOX1 and NOX4 in keratinocytes. By inhibiting NOX1, stress-related signalling cascades and elevated ROS levels could be abrogated, and survival of AD and PSO cells improved. Taken together, this study reveals that inhibition of NOX inhibition could abrogate elevated oxidative stress in a 2D model of AD and PSO.  相似文献   
1000.
In Germany about 0.7 % of the adult population have a chronic leg ulcer. Although chronic venous insufficiency accounts for at least 80 % of all chronic leg ulcers, knowledge of the relevant differential diagnostic considerations is of crucial importance, in particular for patients who are refractory to therapy. In addition to vascular disease, other causes include neuropathic, metabolic, hematologic and exogenous factors as well as neoplasias, infections, drugs, genetic defects and some primary skin disorders. For the long‐term successful treatment of patients with chronic leg ulcers, it is necessary to identify all relevant factors, in order to enable a pathogenesis‐oriented, interdisciplinary therapeutic approach.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号