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   10859篇
  免费   592篇
  国内免费   116篇
耳鼻咽喉   50篇
儿科学   254篇
妇产科学   301篇
基础医学   1207篇
口腔科学   138篇
临床医学   893篇
内科学   2736篇
皮肤病学   278篇
神经病学   1063篇
特种医学   432篇
外科学   1917篇
综合类   29篇
一般理论   1篇
预防医学   394篇
眼科学   152篇
药学   724篇
中国医学   27篇
肿瘤学   971篇
  2023年   81篇
  2022年   234篇
  2021年   291篇
  2020年   189篇
  2019年   222篇
  2018年   292篇
  2017年   198篇
  2016年   273篇
  2015年   340篇
  2014年   433篇
  2013年   573篇
  2012年   859篇
  2011年   822篇
  2010年   550篇
  2009年   448篇
  2008年   718篇
  2007年   725篇
  2006年   651篇
  2005年   651篇
  2004年   605篇
  2003年   490篇
  2002年   480篇
  2001年   67篇
  2000年   66篇
  1999年   76篇
  1998年   98篇
  1997年   71篇
  1996年   62篇
  1995年   66篇
  1994年   64篇
  1993年   49篇
  1992年   76篇
  1991年   64篇
  1990年   56篇
  1989年   36篇
  1988年   46篇
  1987年   34篇
  1986年   33篇
  1985年   39篇
  1984年   57篇
  1983年   45篇
  1982年   21篇
  1981年   25篇
  1980年   25篇
  1979年   33篇
  1978年   32篇
  1977年   17篇
  1976年   18篇
  1975年   27篇
  1972年   19篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
The transdermal and oral administration of estrogens for one year were compared with respect to the effects on lipid metabolism. Eighty-one postmenopausal women (1.5-3 years after menopause) were randomly divided into three groups. The first two groups received sequential estrogen treatment with either transdermal estradiol (Estraderm TTS, Ciba Geigy; 50 μg/day; 24 women) or 0.625 mg/day conjugated estrogens (Premarin, Wyeth; 20 subjects), respectively. In both groups medroxyprogesterone (10 mg/day per os) was added for 12 days of each cycle. Thirty-five subjects served as control group without therapy. No significant changes in the lipid profile was observed in control subjects after 1 year of follow-up. Serum triglycerides decreased significantly (-10.9 ± 26% S.D.; P < 0.05) in transdermal treated women, whereas it slightly rose in oral estrogen group. Comparable significant decreases in total and low density lipoprotein (LDL) cholesterol (mean range -6.5/-18.0%) were observed in women on estrogen replacement therapy. High density lipoprotein (HDL) cholesterol significantly diminished in transdermal estradiol group, but it rose slightly in the oral estrogen group. Thus the fraction of HDL cholesterol over LDL cholesterol did not change in the transdermal group whereas it significantly rose in subjects treated with oral estrogens. It remains to be established to what extent these differences on lipid metabolism are relevant for the prevention of cardiovascular diseases.  相似文献   
42.
OBJECTIVE: The purpose of this study was to compare the cardiovascular responses of patients with chronic fatigue syndrome (CFS) to healthy control subjects when performing stressful cognitive tasks before and after strenuous exercise. METHOD: Beat-by-beat blood pressure and electrocardiogram were recorded on 19 women with CFS and 20 healthy nonexercising (ie, sedentary) women while they performed cognitive tests before, immediately after, and 24 hours after incremental exercise to exhaustion. RESULTS: Diminished heart rate (p <.01) and systolic (p <.01) and diastolic (p <.01) blood pressure responses to stressful cognitive testing were seen in patients with CFS when compared with healthy, sedentary controls. This diminished stress response was seen consistently in patients with CFS across three separate cognitive testing sessions. Also, significant negative correlations between self-ratings of CFS symptom severity and cardiovascular responses were seen (r = -0.62, p <.01). CONCLUSIONS: Women with CFS have a diminished cardiovascular response to cognitive stress; however, exercise did not magnify this effect. Also, the data showed that the patients with the lowest cardiovascular reactivity had the highest ratings of CFS symptom severity, which suggests that the individual response of the patient with CFS to stress plays a role in the common complaint of symptoms worsening after stress.  相似文献   
43.
Rare monogenic forms of Parkinson's disease (PD) are promoting our understanding of the molecular pathways involved in the common, non-Mendelian forms of the disease. Here, we focus on PARK7, an autosomal recessive form of early-onset parkinsonism caused by mutations in the DJ-1 gene. We first review the genetics of this form and the rapidly expanding knowledge about the structure and biochemical properties of the DJ-1 protein. We also discuss how DJ-1 dysfunction might lead to neurodegeneration, and the implications of this novel piece of information for the pathogenesis of the common PD forms. Although much work remains to be done to clarify the biology of DJ-1, its proposed activity as a molecular chaperone and/or as oxidative sensor appear intriguing in the light of the current theories on the pathogenesis of PD.  相似文献   
44.
A variable energy proton accelerator was commissioned at Fermi National Accelerator Laboratory for use in cancer treatment at the Loma Linda University Medical Center. The advantages of precise dose localization by proton therapy, while sparing nearby healthy tissue, are well documented [R. R. Wilson, Radiology 47, 487 (1946); M. Wagner, Med. Phys. 9, 749 (1982); M. Goitein and F. Chen, Med. Phys. 10, 831 (1983)]. One of the components of the proton therapy facility is a beam delivery system capable of delivering precise dose distributions to the target volume in the patient. To this end, a prototype beam delivery system was tested during the accelerator's commissioning period. The beam delivery system consisted of a beam spreading device to produce a large, uniform field, a range modulator to generate a spread out Bragg peak (SOBP), and various beam detectors to measure intensity, beam centering, and dose distributions. The beam delivery system provided a uniform proton dose distribution in a cylindrical volume of 20-cm-diam area and 9-cm depth. The dose variations throughout the target volume were found to be less than +/- 5%. Modifications in the range modulator should reduce this considerably. The central axis dose rate in the region of the SOBP was found to be 0.4 cGy/spill with an incident beam intensity of 6.7 x 10(9) protons/spill. With an accelerator repetition rate of 30 spills/min and expected intensity of 2.5 x 10(10) protons/spill for patient treatment, this system can provide 50 cGy/min for a 20-cm-diam field and 9-cm range modulation.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
45.
The B cell line 721.174 has lost the ability to present intracellular antigens to major histocompatibility complex (MHC) class I-restricted cytotoxic T lymphocytes (CTL). This phenotype results from a homozygous deletion in the MHC that includes the peptide transporter genes TAP1 and TAP2, and the proteasome subunits LMP2 and LMP7. Recent work has shown that such cells transfected with TAP genes load their class I molecules with endogenous peptides, and present several viral epitopes to class I-restricted CTL. These data implied that the LMP2 and LMP7 genes were not required for the presentation of most epitopes through class I molecules. By contrast, while confirming the previous reports, we have identified several epitopes that appear to require genes in the MHC in addition to the TAP for their presentation. Further analysis localizes the defect to proteolysis in the cytosol. In one case, presentation could be partially restored by re-expression of full-length LMP7. Control experiments with LMP7, from which the putative pro-region had been removed, failed to restore presentation, and this lack of effect correlated with failure of the shortened LMP7 to incorporate into the proteasome. These results suggest a role for LMP7 in the generation of a viral epitope, but leave open the possibility that additional genes within the .174 deletion are required for full restoration of antigen presentation.  相似文献   
46.
N DeLuca  S Person  D J Bzik  W Snipes 《Virology》1984,137(2):382-389
A plasmid containing a herpes simplex virus type 1 (HSV-1) insert from strain KOS, prototypic coordinates 0.345 to 0.368 (3.45 kilobases) was mutagenized in vitro, and potential mutations were introduced into intact viral DNA by cotransfection. Functions normally associated with the glycoprotein gB are in the 1-9 complementation group, and the above coordinates include those that specify the gB glycoprotein gene. Following cotransfection, individual plaques were screened for temperature sensitivity (ts) of viral growth. A total of seven ts mutants was obtained, of which four were spurious mutations due to alterations outside the cloned sequences, presumably mediated by some aspect of the Ca-precipitation-cotransfection method. The remaining three did not complement known mutants of the 1-9 complementation group. These three mutants, along with tsJ12 (P.A. Schaffer, G.M. Aron, N. Biswal, and M. Benyesh-Melnick, 1973, Virology 52, 57-71) and tsJ33 (C.-T. Chu, D.S. Parris, R.A.F. Dixon, F.E. Farber, and P.A. Schaffer, 1979, Virology 98, 168-181), were physically located by marker-rescue experiments to three different restriction fragments between 0.345 to 0.368 map units. Sodium dodecyl sulfate-gel electrophoresis was used to analyze the glycoproteins synthesized during continuous or pulse-chase labeling protocols. All five mutants were found to synthesize a precursor of gB but did not accumulate mature gB during a pulse, a chase, or continuous labeling at the nonpermissive temperature.  相似文献   
47.
Magnesium (Mg2+) deficiency is probably the most underestimated electrolyte imbalance in Western countries. It is frequent in obese patients, subjects with type-2 diabetes and metabolic syndrome, both in adulthood and in childhood. This narrative review aims to offer insights into the pathophysiological mechanisms linking Mg2+ deficiency with obesity and the risk of developing metabolic syndrome and type 2 diabetes. Literature highlights critical issues about the treatment of Mg2+ deficiency, such as the lack of a clear definition of Mg2+ nutritional status, the use of different Mg2+ salts and dosage and the different duration of the Mg2+ supplementation. Despite the lack of agreement, an appropriate dietary pattern, including the right intake of Mg2+, improves metabolic syndrome by reducing blood pressure, hyperglycemia, and hypertriglyceridemia. This occurs through the modulation of gene expression and proteomic profile as well as through a positive influence on the composition of the intestinal microbiota and the metabolism of vitamins B1 and D.  相似文献   
48.
Background: The restrictions taken to control the rapid spread of COVID-19 resulted in a sudden, unprecedented change in people’s lifestyle, leading to negative consequences on general health. This study aimed to estimate the impact of such changes on migraine severity during 2020 March–May lockdown. Methods: Patients affected by migraine with or without aura, diagnosed by expert physicians, completed a detailed interview comprehensive of: assessment of migraine characteristics; measure of physical activity (PA) levels; measure of the intake frequency of main Italian foods; the Insomnia Severity Index (ISI) questionnaire investigating sleep disorders. Results: We included 261 patients with a mean age of 44.5 ± 12.3 years. During social distancing, 72 patients (28%) reported a headache worsening, 86 (33%) an improvement, and 103 (39%) a stable headache frequency. A significant decrease of the PA levels during COVID-19 quarantine in the whole study sample was observed (median total metabolic equivalent task (METs) decreased from 1170 to 510; p < 0.001). Additionally, a significant difference was reported on median ISI scores (from 7 to 8; p < 0.001), which were increased in patients who presented a stable or worsening headache. Conclusions: Our study confirmed that the restrictions taken during the pandemic have affected the practice of PA levels and sleep quality in migraine. Hence, PA and sleep quality should be assessed to find strategies for an improvement in quality of life.  相似文献   
49.
Preservation of vascular endothelium integrity and functionality represents an unmet medical need. Indeed, endothelial dysfunction leads to decreased nitric oxide biosynthesis, which is prodromic of hypertension and hypercoagulability. In this panorama, the nutraceutical supplement Taurisolo®, a polyphenolic extract from Aglianico cultivar grape, rich in catechin and procyanidins, was evaluated as a vasoprotective, vasorelaxing, anti-hypertensive and anti-coagulant agent in: cell lines, isolated vessels, in vivo models of chronic hypertension and hypercoagulability, and in clinical tests of endothelial reactivity. Taurisolo® demonstrated to fully protect vascular cell viability from oxidative stimulus at 100 µg/mL and evoke vasorelaxing effects (Emax = 80.6% ± 1.9 and pEC50 = 1.19 ± 0.03) by activation of the Sirtuins-AMPK-pathway. Moreover, Taurisolo®, chronically administered at 20 mg/Kg/die in in vivo experiments, inhibited the onset of cardiac hypertrophy (heart weight/rat weight = 3.96 ± 0.09 vs. 4.30 ± 0.03), hypercoagulability (decrease of fibrinogen vs. control: p < 0.01) and hypertension (mean of Psys: 200 ± 2 vs. control 234 ± 2 mmHg) and improved endothelial function (Emax = 88.9% ± 1.5 vs. control 59.6% ± 3.6; flow-mediated dilation in healthy volunteers after 400 mg twice daily for 8 weeks vs. baseline: p = 0.019). In conclusion, Taurisolo® preserves the vascular function against ox-inflamm-ageing process and the consequent cardiovascular accidents.  相似文献   
50.
BackgroundWe aim to evaluate the impact of multiparametric magnetic resonance imaging and fusion-target biopsy for early reclassification of patients with low-risk Prostate Cancer in a randomized trial.Materials and methodsBetween 2015 and 2018, patients diagnosed with Prostate Cancer after random biopsy fulfilling PRIAS criteria were enrolled and centrally randomized (1:1 ratio) to study group or control group. Patients randomized to study group underwent multiparametric magnetic resonance imaging at 3 months from enrollment: patients with positive findings (PIRADS-v2>2) underwent fusion-target biopsy; patients with negative multiparametric magnetic resonance imaging or confirmed ISUP - Grade Group 1 at fusion-target biopsy were managed according to PRIAS schedule and 12-core random biopsy was performed at 12 months. Patients in control group underwent PRIAS protocol, including a confirmatory 12-core random biopsy at 12 months. Primary endpoint was a reduction of reclassification rate at 12-month random biopsy in study group at least 20% less than controls. Reclassification was defined as biopsy ISUP Grade Group 1 in >2 biopsy cores or disease upgrading.ResultsA total of 124 patients were randomized to study group (n = 62) or control group (n = 62). Around 21 of 62 patients (34%) in study group had a positive multiparametric magnetic resonance imaging, and underwent fusion-target biopsy, with 11 (17.7%) reclassifications. Considering the intention-to-treat population, reclassification rate at 12-month random biopsy was 6.5% for study group and 29% for control group, respectively (P < 0.001).ConclusionsThe early employment of multiparametric magnetic resonance imaging for active surveillance patients enrolled after random biopsy consents to significantly reduce reclassifications at 12-month random biopsy.  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