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   4216篇
  免费   298篇
  国内免费   17篇
耳鼻咽喉   39篇
儿科学   169篇
妇产科学   84篇
基础医学   521篇
口腔科学   105篇
临床医学   448篇
内科学   909篇
皮肤病学   90篇
神经病学   305篇
特种医学   83篇
外国民族医学   1篇
外科学   746篇
综合类   75篇
预防医学   305篇
眼科学   101篇
药学   310篇
中国医学   28篇
肿瘤学   212篇
  2023年   70篇
  2022年   113篇
  2021年   180篇
  2020年   122篇
  2019年   171篇
  2018年   202篇
  2017年   141篇
  2016年   140篇
  2015年   155篇
  2014年   209篇
  2013年   231篇
  2012年   347篇
  2011年   328篇
  2010年   205篇
  2009年   149篇
  2008年   222篇
  2007年   196篇
  2006年   168篇
  2005年   159篇
  2004年   172篇
  2003年   116篇
  2002年   117篇
  2001年   55篇
  2000年   71篇
  1999年   82篇
  1998年   21篇
  1997年   12篇
  1996年   8篇
  1995年   7篇
  1994年   8篇
  1992年   28篇
  1991年   27篇
  1990年   28篇
  1989年   29篇
  1988年   24篇
  1987年   30篇
  1986年   24篇
  1985年   22篇
  1984年   19篇
  1983年   5篇
  1982年   7篇
  1981年   11篇
  1979年   7篇
  1978年   11篇
  1977年   10篇
  1974年   11篇
  1973年   9篇
  1972年   8篇
  1971年   6篇
  1970年   6篇
排序方式: 共有4531条查询结果,搜索用时 15 毫秒
31.
32.
Quality of Life Research - Uncertainties exist in how respondents interpret response options in patient-reported outcome measures (PROMs), particularly across different domains and for different...  相似文献   
33.
The objectives of this study were: i) to analyse the effects of morphine and naloxone on the rat's behaviour in the hot plate test using an ethological approach, and ii) to compare the effectiveness of repeated versus single test paradigms. Animals received either morphine (0, 3, 6 or 9 mg/kg SC) or naloxone (0, 0.01, 0.1 or 1 mg/kg SC). For repeated hot plate measures, rats were tested before and 60, 120, 180 and 240 min following morphine treatment, as well as 30, 60, 90 and 120 min after naloxone injection. For the single test schedule, rats were tested only once 60 min after morphine or 30 min after naloxone administration, or at 60, 120, 180, 240 and 300 min after 9 mg/kg morphine treatment. Behaviour was videotaped and analysed by an ethogram and ethological techniques. A cluster analysis revealed that the most frequently displayed patterns could be categorised into exploratory sniffing reactions (walk-sniff, immobile-sniff) and noxious-evoked elements, including primary (paw-licking, stamping), escape (jumping, leaning posture) and independent (hindleg-withdrawal) patterns. During repeated tests, morphine treatment induced: i) a maximum hypoalgesic effect 60 min post-injection (noxious-evoked patterns were significantly reduced), and ii) an unexpected thermal hyperreactivity rebound effect after 120 min (paw-licking and hindleg-withdrawal were enhanced), although changes in hindpaw-licking are more indicative of a hyperalgesic rebound effect. Most changes were quite similar during the single test schedule at 60 and 120 min after morphine injection. With regard to naloxone treatment, jumping latency was significantly decreased during the repeated test schedule, but not on single exposure to the plate. Other elements were facilitated, however, in the single test (stamping, leaning posture, hindleg-withdrawal). The results indicated that both repeated and single tests paradigms are of value for testing the effects of morphine and naloxone on rats. However, under our conditions the single test paradigm gave a better picture of the overall effects of the drug. Learning as well as habituation and sensitization may mask certain effects during repeated tests. In conclusion, an ethological analysis of the rat's behaviour in the hot plate test following administration of morphine and naloxone has been validated in this study.  相似文献   
34.
Background: General anaesthetics inhibit mitochondrial function in animal models. However, very few studies have been performed in humans, and the results have not been conclusive. Methods: We prospectively studied the oxygen consumption and the individual enzyme activity of each complex of the mitochondrial respiratory chain of skeletal muscle mitochondria in 54 healthy individuals who underwent general anaesthesia for orthopaedic surgery. The control group (n = 54) was made up of individuals submitted to the same orthopaedic procedure under regional anaesthesia (n = 31), and patients who underwent muscle biopsies for diagnostic purposes by local anaesthesia (n = 23). Results: We found a significant decrease in the oxidation of glutamate (−36%), succinate (−25%) and ascorbate (−29%) in the general anaesthetic group compared with the controls (P < 0.001 for all substrates). The level of such inhibition was similar for volatile anaesthetics with strong (halothane) or weak (isoflurane) negative inotropic effect. By contrast, the enzymatic activity of all individual complexes and the coupling of oxidative phosphorylation did not differ between the two groups. Conclusion: We conclude that during general anaesthetic procedures there is an extensive inhibition of substrate oxidation in human muscle mitochondria, and that it is not caused by a direct effect on complexes of the mitochondrial respiratory chain or through uncoupling oxidative phosphorylation. Received: 27 July 1998 / Accepted in revised form: 27 October 1998  相似文献   
35.
The antihepatotoxic activity of elaterium (dried juice of the fruits of Ecballium elaterium, Cucurbitaceae) and cucurbitacin B (isolated from the juice) was studied against CCl4-induced hepatotoxicity. Pre- and posttreatment with elaterium and cucurbitacin B reduced CCl4-hepatotoxicity, as shown reduction in the anormally increased sGPT levels. Posttreatment caused a significant reduction in the degree of steatosis observed inthe control group, treated only with CCl4. In conclusion, elaterium and cucurbitacin B had preventive and curative effects against CCl4-induced hepatotoxicity.  相似文献   
36.
2-(2-Benzofuranyl)-2-imidazoline (2-BFI) has recently been characterised as a selective ligand for the I2-type of imidazoline-receptor binding site(s) (I2-RBS). The present studies determined the relative levels of specific [3H]2-BFI binding to membrane homogenates of brain and kidney from rat, guinea pig and rabbit and identified the pharmacological characteristics of [3H]2-BFI binding sites in rabbit kidney membranes. Rabbit kidney membranes had the highest relative density of specific [3H]2-BFI binding of all tissues studied (2000?fmol/mg protein). Rabbit brain and guinea pig kidney had moderate levels of specific [3H]2-BFI binding (350–500?fmol/mg protein), while rat kidney and guinea pig and rat brain displayed much lower densities of binding (40–65?fmol/mg protein). Studies of [3H]2-BFI binding kinetics in rabbit kidney homogenates revealed binding to two distinct sites with K d values of 0.10?±?0.01?nmol/l and 1.00?±?0.36?nmol/l respectively. Equilibrium saturation studies were also consistent with the presence of two binding sites – [3H]2-BFI (0.01–20?nmol/l) bound to sites with affinities of 0.10?± 0.01?nmol/l and 0.92?±?0.13?nmol/l and binding densities of 470?±?80 and 840?±?60?fmol/mg protein (n=3), representing 36 and 64% respectively. Drug inhibition studies revealed that l-adrenaline; α1-adrenoceptor drugs (prazosin, l-phenylephrine) and α2-adrenoceptor drugs (rauwolscine, methoxyidazoxan, 2-(2,4-(O-methoxyphenyl)-piperazin-1-yl)-ethyl-4,4-dimethyl-1,3-(2H,4H)-isoquinolindione (ARC-239) had extremely low affinities for [3H]2-BFI binding sites (IC50?≥?10?μmol/l). Putative I1-RBS compounds, p-aminoclonidine, moxonidine, imidazole-4-acetic acid and cimetidine, inhibited [3H]2-BFI binding to rabbit renal membranes with low to very low affinities (K i values 3 to ≥100?μmol/l), suggesting [3H]2-BFI does not label I1-RBS in rabbit kidney membranes. I2-RBS compounds – 2-(4,5-dihydroimidaz-2-yl)-quinoline (BU224), 2-(4,5-dihydroimidaz-2-yl)-quinoxaline (BU239), idazoxan and cirazoline – potently inhibited [3H]2-BFI binding (K i values 0.37–1.6?nmol/l), confirming the labelling of I2-RBS. Inhibition of [3H]2-BFI binding by certain compounds was consistent with their interaction with two binding site populations – for example (drug, K i values) guanabenz, 0.65?nmol/l and 0.17?μmol/l; naphazoline, 0.94?nmol/l and 2.8?μmol/l; amiloride, 76?nmol/l and 26?μmol/l rilmenidine, 150?nmol/l and 50?μmol/l; and clonidine, 230?nmol/l and 70?μmol/l. The high affinity of amiloride for a high proportion (85%) of the binding is consistent with the presence of the I2A-subtype of I-RBS in rabbit kidney. These results demonstrate that [3H]2-BFI is a highly selective and high affinity radioligand for I2-RBS which should be useful for the further characterisation of these sites in mammalian tissues.  相似文献   
37.
We hypothesized that the pathological effects on the neonatal rat heart could be aggravated by Cu deficiency due to the combined effects of caffeine exposure and malnutrition. Upon birth, pups were mixed and randomly picked; 8 pups were assigned to each dam and then divided into 4 groups. Group 1 dams received a normal diet containing 20% protein. Group 2 dams were fed 20% protein diet supplemented with caffeine (4 mg/100 g BW). Group 3 dams received 6% protein diet as a malnourished group, and group 4 dams received 6% protein diet supplemented with caffeine (4 mg/100 g BW). On postnatal day 10, dams and pups were killed. Group 2 tended to have a decrease in the Cu levels of dams' plasma and milk and in pups' plasma and heart tissue compared to those of group 1. This pattern was not observed consistently between groups 3 and 4. Transmission electron microscopy of group 2 pups' hearts revealed a degree of disruption in the mitochondria compared to normal mitochondria seen in group 1. There was no consistent change in the mitochondria of group 4 compared to group 3. The caffeine level observed in all categories of group 4 (dams' plasma and milk, pups' plasma and heart tissue) was lower than those in group 2. Although malnutrition affected body weight and heart weight, combined effects of caffeine and malnutrition on Cu content in the neonatal heart was relatively minor compared to the well nourished group. This well nourished group showed that the effects of caffeine on Cu were more consistent, resulting the changes of mitochondria.  相似文献   
38.
BACKGROUND: The aim of the present study was to investigate renal vascular resistive changes in children with different stages of liver cirrhosis without obvious renal failure. METHODS: Twenty-nine children (14 girls, 15 boys, mean age 11.6 years) with cirrhosis and 20 healthy children (mean age 10.3 years) were investigated for renal vascular resistance with Doppler ultrasonography, urinary sodium, N-acetyl-beta-D glucosaminidase (NAG) and microalbuminuria excretion. RESULTS: The measurements of renal resistive indexes (RRI) were significantly higher in cirrhotic patients than the control group (0.69 +/- 0.07 vs 0.62 +/- 0.02, P < 0.0001). RRI measurement was found to be increased in decompensated cirrhotic patients than in compensated cirrhotic patients (0.73 +/- 0.05 vs 0.67 +/- 0.08, P < 0.0001). A significant positive relationship was observed between RRI and child score (r = 0.53). Urine NAG/Cr ratio was significantly higher in cirrhotic patients than in the control subjects (P < 0.001). Microalbumin concentrations were increased in the patients with decompensated cirrhosis than in the controls (P = 0.02). Patients with ascites and portal hypertension showed increased RRI values. CONCLUSIONS: We conclude that patients with cirrhosis are at risk of renal deterioration, which can not be detected by serum urea, creatinine, and glomerular filtration rate. The increase of RRI is associated with the progress of hepatocellular disease, and also the development of ascites and portal hypertension. Elevated urinary sodium excretion, elevated urinary NAG/Cr ratio and microalbuminuria might have a prognostic value especially in patients with Child scores> 6. Hence, monitoring RRI is a non-invasive means of studying early renal hemodynamic alteration in childhood cirrhosis.  相似文献   
39.
Acanthamoeba is an opportunistic protozoan pathogen and known to be one of the most ubiquitous organisms, play a vital role in ecosystem, and recognized to cause blinding keratitis and rare but fatal granulomatous encephalitis involving the central nervous system with a very poor prognosis. This is due to limited availability of effective anti-Acanthamoeba drugs. The objective of the present study was to determine the efficacy of methanolic plants crude extracts on the viability and biological properties of Acanthamoeba castellanii (T4 genotype) and its cytotoxic effects on human corneal epithelial cells (HCEC). Using HCEC, it was observed that Acanthamoeba exhibited binding (>90 %) and cytotoxicity (>80 %) to host cells. However, plant crude extracts remarkably inhibited more than 70 and 60 % of Acanthamoeba binding and cytotoxicity to HCEC, respectively. It was further established that crude extracts (ranging from 0.1 to 1.5 mg/ml) exhibited amoebicidal effects, i.e., >50 % of trophozoites were killed/reduced at maximum dose (1.5 mg/ml) within 1 h incubation. However, the residual subpopulation remained static over longer incubations. Furthermore, growth assay demonstrated crude extracts inhibited >50 % Acanthamoeba numbers up to 7 days. Our results confirmed that plant crude extracts has inhibitory effects on Acanthamoeba growth and viability. Overall, these findings revealed that tested plant extracts is inhibitory to Acanthamoeba properties associated with pathogenesis. To the best of our knowledge, our findings demonstrated for the first time that selected methanol plant crude extracts exhibits inhibitory effects on biological properties of Acanthamoeba without any toxic effects on HCEC cells in vitro.  相似文献   
40.
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