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   51894篇
  免费   3306篇
  国内免费   239篇
耳鼻咽喉   571篇
儿科学   988篇
妇产科学   694篇
基础医学   6848篇
口腔科学   1104篇
临床医学   5430篇
内科学   11188篇
皮肤病学   1089篇
神经病学   6151篇
特种医学   2785篇
外科学   8621篇
综合类   311篇
一般理论   13篇
预防医学   2365篇
眼科学   775篇
药学   3069篇
中国医学   69篇
肿瘤学   3368篇
  2023年   425篇
  2022年   595篇
  2021年   1456篇
  2020年   871篇
  2019年   1319篇
  2018年   1493篇
  2017年   1176篇
  2016年   1392篇
  2015年   1641篇
  2014年   2036篇
  2013年   2532篇
  2012年   4055篇
  2011年   4084篇
  2010年   2424篇
  2009年   2175篇
  2008年   3488篇
  2007年   3572篇
  2006年   3289篇
  2005年   3239篇
  2004年   2891篇
  2003年   2754篇
  2002年   2481篇
  2001年   563篇
  2000年   439篇
  1999年   486篇
  1998年   518篇
  1997年   396篇
  1996年   314篇
  1995年   248篇
  1994年   239篇
  1993年   185篇
  1992年   208篇
  1991年   183篇
  1990年   144篇
  1989年   139篇
  1988年   153篇
  1987年   101篇
  1986年   118篇
  1985年   125篇
  1984年   133篇
  1983年   109篇
  1982年   98篇
  1981年   76篇
  1980年   74篇
  1979年   81篇
  1978年   59篇
  1977年   69篇
  1976年   61篇
  1975年   68篇
  1974年   69篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
BACKGROUND: It has been reported that patients on a very-low-protein diet (VLPD) maintain a satisfactory nutritional status because of a conserved adaptive metabolic response. However, only few studies have examined the course of nutritional status and body composition in the long term (2 years). METHODS: Thirteen stable patients (8 men; age, 55 +/- 12 years; glomerular filtration rate (GFR), 15 +/- 5 mL/min) receiving a VLPD (0.3 g/kg/day protein) supplemented with amino acids and ketoanalogues (SVLPD) were studied for 2 years. A joint visit with a physician and a dietitian and routine blood and urine analyses were performed every month. Dual-energy x-ray absorptiometry (DEXA), which was used to assess modification of body composition, and GFR (urinary 51Cr-EDTA) and urinary urea and creatinine excretion, which were used to assess nutritional status and compliance to the diet, were assessed every 3 months. RESULTS: GFR, albumin, and prealbumin levels remained stable. Urea urinary excretion decreased at 3 months and then slightly increased at 2 years, but the calculated protein intake remained low at 0.38 +/- 0.1 g/kg/day. Energy intake remained close to 30 kcal/kg/day. No significant change was observed for total fat mass or percent fat mass. After an initial decrease, lean body mass stabilized at 6 months and then increased significantly from 6 to 24 months (P =.02, paired t-test); the mean increase during this period was of 2 kg, that is, 4.6%. Urinary creatinine excretion showed the same profile. Total bone mass, lumbar or hip site bone mass, and Z-score significantly decreased from T0 to 1 and 2 years (P <.05). CONCLUSION: This study confirms that a supplemented VLPD is nutritionally safe for a long period, but attention must be paid to bone mass.  相似文献   
192.
193.
BACKGROUND: The isolated perfused canine kidney has been established as a valid model for conducting both renal physiology and transplantation research. This model is of particular importance for developing new strategies to improve graft function after renal transplantation. In the present study, a newly developed method using isolated haemoperfused porcine kidneys was adapted for use in canine kidneys. In contrast to haemoperfusion, synthetic perfusion media can be standardized and can prevent the initiation of blood-mediated reperfusion reactions. Thus, an additional aim was to determine whether blood could be replaced by synthetic cell-free perfusion solutions. METHODS: Canine kidneys (n = 30) were harvested from donors euthanized in veterinary practices for causes unrelated to the present study. The kidneys were isolated and perfused with autologous blood or cell-free synthetic electrolyte buffer (Tyrode solution). During perfusion, we monitored renal perfusate flow (RPF), glomerular filtration rate (GFR), electrolyte and glucose reabsorption, oxygen consumption and urine concentration. RESULTS: Changes in perfusion medium did not affect the RPF. In contrast, GFR, urine concentration and oxygen consumption were significantly higher, whereas fractional excretion of sodium and glucose were significantly lower in blood- than in Tyrode-perfused kidneys. CONCLUSIONS: This system offers a simple model for studying whole-organ functional alterations after acute renal ischaemia. Renal function indicators were below values reported during in vivo physiological conditions. These functions were better conserved when kidneys were perfused with autologous blood than with Tyrode.  相似文献   
194.
195.
Hypothesis: Does occupational exposure to solvents in combination with alcohol intake give rise to acquired color vision defects? Method: A total of 138 individuals exposed to solvents (toluene, xylene, trichloroethylene, tetrachloroethylene) were examined using Lanthony’s D-15 test and compared with 100 nonexposed controls. The extent of color vision loss was quantitatively assessed based on Bowman’s color confusion index (CCI). A cumulative exposure index was calculated from the hours of exposure per day and the years of exposure. In 30 persons who were exposed to trichloroethylene and tetrachloroethylene, urinary trichloroacetic acid was assessed as a parameter of exposure. Alcohol intake was calculated as based on interviews of patients in grams of ethyl alcohol per week. Results: Individuals who consumed more than 250 g alcohol/week and were simultaneously exposed to solvents showed a significantly elevated CCI (P = 0.0044). No significant correlation emerged between trichloroacetid acid excretion in the urine or the cumulative exposure index and the CCI. Conclusion: The combination of alcohol intake and occupational exposure to solvents discloses the risk of acquired subclinical color vision defects.  相似文献   
196.
Summary: Purpose : As shown previously, when temporal lobe complex partial seizures (TLCPS) originate from the language dominant hemisphere, patients cannot read a test phrase correctly within 60 s of the end of the ictal discharge. We wished to assess whether postictal language testing results discordant with this pattern identified patients with non-left (right hemisphere or mixed) language dominance.
Methods : Since 1988, all patients undergoing video/EEG monitoring at our institution have been given a test phrase to read aloud as soon as a seizure is detected. Inclusion criteria for this study were (a) postictal language testing within 60 s of seizure end for at least one TLCPS, (b) >90% seizure reduction after anterior temporal lobectomy with 2-year minimum follow- follow- up, and (c) language localization by either intracarotid amobarbital test (IAT) or direct electrical stimulation of left hemisphere cortex.
Results : Two hundred twenty-four seizures in 64 patients were analyzed. Discordant postictal language patterns were noted in 10 of 11 patients with IAT documented non-left language dominance and in 15 of 53 with left dominance (p = 0.006; sensitivity 90.9%, specificity 71.7%).
Conclusions : Postictal language testing accurately identifies patients with non-left language dominance and may be useful in selecting appropriate patients for IAT.  相似文献   
197.
Eight commercially available HPD-photosensitizers intended for photodynamic therapy were tested in a murine tumour model with regard to their therapeutic efficacy. The regrowth delay of the fibrosarcoma SSK-2 on the mouse C3H, Neuherberg-line, was determined 3, 24, 48 and 72 h after injection of the drugs (dose: 9 mg kg–1 body weight). The corresponding pharmacodynamics, as measured by regrowth delay, were approximated by an exponential function and the characterizing coefficients derived. These coefficients served to quantify the photodynamic properties of the drugs.The pharmacodynamics of five substances were compared with those obtained fluorometrically. The latter showed shorter decay constants than the therapy-correlated substances which indicates different metabolic behaviour of the therapeutic and diagnostically useful fluorescent components of haematoporphyrin-derived photosensitizers.  相似文献   
198.
199.
This study aimed to identify interferon-gamma (IFN-gamma) gene variants in cattle for diagnostic purposes. Therefore, the entire bovine IFN-gamma gene (BoIFNG) and 2605 bp of its promoter DNA were sequenced. The BoIFNG DNA sequence conforms to the published part of Bo-IFN-gamma cDNA. Primer extension experiments show the presence of a 5' extension of exon 1 by 42 nucleotides (nt). One SINE element (Bov-A2) is located in the 5'-region, and two SINE elements (Bov-tA, Bov-B) are contained in the 3'-region of BoIFNG. The variants were detected by comparative sequence analysis of PCR amplicons from different bovine species. Four polymorphic mononucleotide repeats are situated in the promoter and in intron 1. Four distinct series of single nucleotide polymorphisms (SNP) were found in functionally important regions of BoIFNG. The region between the two intron 1 microsatellites contains the highest density of SNPs in Bos taurus breeds. One G-T transversion in the coding region of exon 1 causes a Gly(14) to Val(14) exchange in the BoIFNG signal peptide of different bovine species. A G-A transition in exon 2 encodes a Ser(19) to Asn(19) change in the mature protein of the Tibetan yak. Genotyping of randomly sampled Holstein Friesian cows at selected SNPs and of both intron 1 microsatellites revealed two dominant BoIFNG microhaplotypes. The detected SNPs improve the recently reported genotyping system of cattle.  相似文献   
200.
Chronic ethanol consumption potentiates cocaine-induced liver injury in rodents. Since cocaine has to be bioactivated by a cytochrome P-450-dependent N-oxidative pathway to exert its hepatotoxic effects, we studied the role of the ethanol-inducible P-450IIE1 for cocaine metabolism. Male Sprague-Dawley rats were pretreated with either a liquid diet containing ethanol (30% of calories) for 4 weeks or injected with pyrazole (200 mg/kg/day, ip, for 3 days). Both agents induced microsomal p-nitrophenol hydroxylation which is a probe for the catalytic activity of P-450IIE1. However, only ethanol, but not pyrazole, increased both microsomal cocaine N-demethylase activity (by 47%) and the extent of irreversible binding of [3H]-cocaine to microsomal proteins (by 100%), which was taken as a quantitative endpoint for the formation of a reactive metabolite. Cocaine N-demethylation and irreversible protein binding of cocaine were not inhibited by P-450IIE1 isozyme-selective substrates, nor was the rate of cocaine metabolism and binding decreased by functionally active polyclonal anti-rat P-450IIE1 antibodies. Furthermore, pyrazole pretreatment sensitized cultured hepatocytes to the glutathione-dependent cytotoxic effects of nontoxic concentrations of cocaine. These results indicate that (a) cocaine is not a major substrate for the ethanol-inducible P-450IIE1, (b) the enhancing effects of ethanol on cocaine bioactivation may be due to induction of other P-450 isoforms, and (c) induction of P-450IIE1 may potentiate cocaine-induced hepatocellular toxicity in vitro independently of cocaine metabolism, e.g., by P-450IIE1-dependent oxidative stress.  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