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   13652篇
  免费   767篇
  国内免费   138篇
耳鼻咽喉   153篇
儿科学   325篇
妇产科学   375篇
基础医学   1875篇
口腔科学   312篇
临床医学   1365篇
内科学   2791篇
皮肤病学   522篇
神经病学   840篇
特种医学   666篇
外科学   2207篇
综合类   158篇
现状与发展   1篇
一般理论   2篇
预防医学   572篇
眼科学   273篇
药学   1096篇
中国医学   150篇
肿瘤学   874篇
  2023年   78篇
  2022年   165篇
  2021年   418篇
  2020年   196篇
  2019年   269篇
  2018年   409篇
  2017年   294篇
  2016年   343篇
  2015年   440篇
  2014年   637篇
  2013年   650篇
  2012年   1040篇
  2011年   1013篇
  2010年   602篇
  2009年   480篇
  2008年   801篇
  2007年   809篇
  2006年   740篇
  2005年   737篇
  2004年   644篇
  2003年   519篇
  2002年   492篇
  2001年   423篇
  2000年   395篇
  1999年   312篇
  1998年   134篇
  1997年   99篇
  1996年   101篇
  1995年   78篇
  1994年   64篇
  1993年   38篇
  1992年   126篇
  1991年   111篇
  1990年   104篇
  1989年   68篇
  1988年   67篇
  1987年   67篇
  1986年   59篇
  1985年   51篇
  1984年   32篇
  1983年   23篇
  1980年   25篇
  1979年   31篇
  1977年   33篇
  1976年   24篇
  1975年   25篇
  1974年   31篇
  1973年   26篇
  1972年   31篇
  1970年   23篇
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
41.
This study was undertaken to test the hypothesis that malfunction of the nonadrenergic noncholinergic inhibitory system (NANCIS) induces hyperreactive airways. Antigen sensitized guinea pigs were divided into four groups: (1) antigen challenge (n = 6), (2) 2 min oxyhemoglobin (HbO2) + antigen challenge (n = 5), (3) 27 min HbO2 + antigen challenge (n = 4), and (4) 2 min HbO2 + transmural stimulation (TS) + antigen challenge (n = 6). These animals were sensitized with ovalbumin 10 days before the study. In addition, 12 normal control animals without antigen sensitization were used for comparison. Under artificial ventilation, the anesthetized-paralyzed animals were hourly injected with atropine (0.2 mg/kg) and propranolol (1 mg/kg). Cervical segment of the trachea was converted to a closed tracheal pouch filled with Krebs solution containing also atropine (1 microM) and propranolol (3.5 microM). A change in the pouch pressure (Pp) reflected NANCIS TS- or antigen (5 micrograms) challenge-induced relaxation and/or constriction. HbO2 was used to inhibit NANCIS transmitter. There was no significant difference between normal and sensitized animals in the NANCIS TS-induced relaxation. Antigen challenge resulted in biphasic alteration in Pp, an initial increase and then a decrease after about 7 min. HbO2 pretreatment alone did not potentiate antigen-induced increase in Pp. HbO2 + TS, however, significantly abolished the late relaxation phase after antigen challenge.  相似文献   
42.
43.
PURPOSE: This study was designed to obtain an updated population-based perspective on anal canal cancer incidence rates, demographics, and outcomes using a nationwide database. Eight-five percent of all carcinomas of the anus are anal canal cancers, and previous studies suggest that incidence rates may be rising. Although the most successful treatment for anal canal cancer has been chemoradiation, little information at the population-level exists regarding demographics, treatment, and survival. METHODS: All patients diagnosed with anal canal cancer from 1973 to 1998 in the Surveillance Epidemiology and End Results cancer registry were analyzed. Data regarding demographics, cancer characteristics, treatment, and survival were assessed. Univariate and multivariate survival analyses were performed. RESULTS: A total of 4,841 patients were studied (mean age was 61 years; 62 percent female). Female patients were significantly older than male patients (65 vs. 58 years; P < 0.0001). There was a yearly increase in incidence of anal canal cancers (from 1973–1998). Disease prevalence by stage was localized (53 percent), regional (38 percent), and distant (9 percent). Racial/stage differences were seen, because black patients had less localized disease than white patients (46 vs. 53 percent; P < 0.01). Overall five-year survival for the entire cohort was 53 percent, and cancer-specific survival was 84 percent. Survival improved per decade (based on year of diagnosis). Significant survival differences in race were noted, but were less when the receipt of treatment was considered. CONCLUSION: Although most anal canal cancer reviews are single institutional series, this study was performed with population-based data. The incidence of anal canal cancer is increasing, and overall survival rates are improving. Important disparities in care were identified, which need to be addressed.  相似文献   
44.
45.
BACKGROUND: Reactive oxygen species may contribute to the pathogenesis of asthma. Functional genetic polymorphisms of antioxidant enzymes, superoxide dismutase (SOD) and catalase are good candidates for asthma susceptibility. OBJECTIVE: To investigate the association of the manganese-containing form of SOD (MnSOD) gene at amino acid position 16 (Val16Ala) and catalase gene in the promoter at A-21T and C-262T polymorphisms and asthma in a Hong Kong Chinese population. METHODS: The association study was conducted in a case-control design in asthma patients (n=251) and healthy controls (n=316) by genotyping. The functional significance was assessed by determining erythrocyte SOD and catalase activity. RESULTS: The Val allele of MnSOD at Val16Ala and the A allele of catalase gene at A-21T were not different between patients and controls, while the C allele of catalase gene at C-262T was found to be significantly different between patients and controls (P=0.033). The less frequent variant of catalase gene (-262T) was found to be protective from the development of asthma in a Hong Kong Chinese non-smoking population (adjusted odds ratio=0.35, 0.15-0.85; P=0.017). Asthma patients had elevated erythrocyte SOD and catalase activities in comparison with healthy controls (P<0.01). However, their activities were not associated with different genotypes within healthy controls or asthma patients. CONCLUSION: This is the first report showing that SOD and catalase functional activities are not associated with their respective genetic polymorphisms but related to the presence of asthma in a Hong Kong Chinese population.  相似文献   
46.
Based on clinical and pathological features a typical case of haemorrhagic fever with renal syndrome passes through five phases: (1) febrile phase, (2) hypotensive phase, (3) oliguric phase, (4) diuretic phase and (5) convalescent phase. The major manifestations are fever, pain in the back and abdomen, flushed face, prostration, proteinuria, purpura and haemorrhage and acute renal failure. Selective right auricular haemorrhage, marked congestion and haemorrhage in the renal medulla and necrosis of the anterior lobe of the pituitary gland are the three prominent pathological findings. The clinical severity depends upon the causative agents, namely Hantaan virus, Seoul virus and the European form in that order. Specific serological diagnosis of haemorrhagic fever with renal syndrome is made by demonstrating a rise in titre of specific immunofluorescent antibody against Hantaan and related viruses. The management is supportive, based on an understanding of the pathophysiology of the disease.  相似文献   
47.
48.
49.
Leukocyte arylsulphatase A (AS-A) was shown to be significantly high in newly-diagnosed breast cancer patients. Previous reports imply a connection between serum interleukin-6 (IL-6) and breast cancer, possibly through a modulation of enzymes involved in estrogen synthesis. Abnormal distribution of heparan sulphate proteoglycans (HSPGs) in malignant breast epithelial cells suggests that they play a key role in the regulation of cell growth. Estradiol is believed to be effective in modulating glycosaminoglycans (GAGs) and their depolymerizing enzymes. Therefore, in this study, attempts were made to evaluate the activity of leukocyte arylsulphatase A, serum interleukin-6, urinary GAGs and heparan sulphate (HS) in response to tamoxifen (TAM) therapy in mastectomised breast cancer patients. Thirty-four patients (aged 30-82 years) were administered TAM (20 mg twice daily). Blood and urine samples of each patient were collected three times (at the beginning, and in third and sixth month of TAM therapy), and biochemical parameters were measured. There was no difference between baseline leukocyte AS-A activity and that measured after three months. At the end of six months, enzyme activity was significantly higher than the former values (p=0.022), but within the reference intervals reported in the literature. Although this increase might imply a normalization, the duration of TAM therapy is not long enough to make a decision about either regression or aggravation of the disease. TAM did not have any effect on serum IL-6, urinary HS and GAG levels which may be due to insensitivity of these variables to TAM during the short period of therapy. Both urinary GAG and HS levels measured at sixth month exhibited a positive correlation with the baseline level of leukocyte AS-A (p=0.005 and 0.009, respectively), suggesting that positive responses to the drug might be seen in patients with low AS-A activity.  相似文献   
50.
Effects of sodium salts of various monovalent inorganic anions on transdermal permeation of salicylic acid were investigated. In in-vitro experiment using a Franz-type diffusion cell and excised mouse skin, the permeation-enhancing activities of the sodium salts of inorganic anions were roughly proportional to lyotropic Hofmeister swelling abilities of the anions; F?<SO4 2?<Cl? <ClO4 ?<NO3 <SCN? <Br <I?, i.e. l, Br and SCN increased the flux of drugs through the mouse skin, while F?, SO4 2?, Cl?, ClO4 ? and NO3 ? decreased or did not affect the flux. In invivo experiment using the rabbit as the test animal, the plasma concentration of salicylic acid of the rabbit to which 10%-salicylic acid ointment containing 5%-Nal or NaBr was applied was significantly higher than that of the rabbit to which the ointment without the electrolytes was applied. The amounts of sterol leached out of stratum corneum sheet when the sheet was immersed in aqueous solutions of Nal, NaBr, or NaSCN were much more than that of stratum corneum immersed in aqueous solutions of the other inorganic anions. The FTIR/ATR spectroscopy showed that the peaks at 2853 cm?1 and 2924 cm?1 in the IR absorption spectrum of the stratum corneum sheet of the mouse were shifted to higher frequencies by the anions which enhanced the transdermal drug permeation, while not shifted by the anions which did not have any permeation-enhancing activities or have permeation-reducing activities. These results suggest that sodium salts of some anions such as iodide, bromide and thiocyanate enhance transdermal permeation of salicylic acid through swelling and perturbation of the skin structure by these anions.  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