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   2448161篇
  免费   172231篇
  国内免费   4811篇
耳鼻咽喉   33008篇
儿科学   80053篇
妇产科学   66987篇
基础医学   348790篇
口腔科学   70917篇
临床医学   221189篇
内科学   469575篇
皮肤病学   55724篇
神经病学   189568篇
特种医学   93413篇
外国民族医学   437篇
外科学   369585篇
综合类   53884篇
现状与发展   5篇
一般理论   757篇
预防医学   179910篇
眼科学   57934篇
药学   184957篇
  13篇
中国医学   6179篇
肿瘤学   142318篇
  2021年   18326篇
  2019年   18979篇
  2018年   27541篇
  2017年   21157篇
  2016年   23511篇
  2015年   26613篇
  2014年   36723篇
  2013年   53778篇
  2012年   74146篇
  2011年   78150篇
  2010年   46351篇
  2009年   43310篇
  2008年   72407篇
  2007年   77285篇
  2006年   77928篇
  2005年   74485篇
  2004年   71639篇
  2003年   68439篇
  2002年   65896篇
  2001年   127881篇
  2000年   130890篇
  1999年   108552篇
  1998年   28396篇
  1997年   24844篇
  1996年   24930篇
  1995年   23820篇
  1994年   21745篇
  1993年   20320篇
  1992年   81986篇
  1991年   79075篇
  1990年   76852篇
  1989年   73760篇
  1988年   67051篇
  1987年   65332篇
  1986年   61749篇
  1985年   58524篇
  1984年   42854篇
  1983年   36477篇
  1982年   20483篇
  1979年   38162篇
  1978年   26241篇
  1977年   22829篇
  1976年   20709篇
  1975年   22520篇
  1974年   26907篇
  1973年   25929篇
  1972年   24216篇
  1971年   22606篇
  1970年   20904篇
  1969年   19769篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
Nitrosation of amines by stimulated macrophages   总被引:10,自引:2,他引:8  
Rats and mice treated in vivo with Escherichia coli lipopolysaccharide (LPS) synthesize and excrete large quantities of nitrate. Murine peritoneal macrophages, elicited in vivo with thioglycolate and stimulated in vitro with LPS and/or gamma-interferon (IFN), produce copious amounts of nitrate and nitrite. We report here experiments showing N-nitrosamine formation by macrophages immunostimulated in vitro. Macrophage cell lines J774.1, PU5-1.8, WEHI-3 and RAW 264 and freshly isolated macrophages from C3H/He mice were used. Macrophages were cultured in Dulbecco's modified Eagle's medium (pH 7.5) supplemented with calf serum (10%). Supernatant NO2- and NO3- were measured. N-Nitrosamines were extracted with dichloromethane and the extracts analyzed by a gas chromatography--thermal energy analyzer. Cells (1.5 X 10(6)/ml) were incubated with LPS (10 micrograms/ml) and morpholine (15 mM) for 72 h at 37 degrees C. Under these conditions, all of the cell types listed above produced nitrite (40-70 microM) and N-nitrosomorpholine (NMOR; 114-940 nM). LPS was required for both processes, and this effect was enhanced by IFN. Nitrite (150 microM) incubated with morpholine in cell-free medium did not form NMOR nor did cells plus morpholine and NO2-. The rate of NMOR formation in the J774.1 cell line was highest in the middle incubation period (24-36 h) although [NO2-] was highest in the final incubation period (48-72 h). Thus, the cells do not catalyze nitrosamine formation per se, rather the amine traps out a reactive nitrosating species prior to the formation of NO2- and NO3-. These results suggest that immunostimulated macrophages may be capable of nitrosamine formation under physiological conditions.  相似文献   
992.
During the time period 1958-1967 190 cases of male breast cancer were reported to the Swedish Cancer Registry. The reported cases were thoroughly re-evaluated from the evidence of the clinical records and histopathologic specimens. The material contained 166 cases of histologically verified invasive breast carcinoma which were analyzed with respect to different clinical and histopathologic parameters. In contrast to the rate in females, the breast cancer incidence rate in males did not increase significantly during the period under review, and the age-specific incidence rate did not show a Clemmesen's hook but increased relatively more rapidly at high ages than for female breast carcinoma. The mean age at diagnosis was 4 to 5 years higher in male breast cancer patients than in females. Larger tumours were more frequent among older patients and there was a 5-year shift between the age-distribution curves for small (less than 2 cm) and larger (2-5 cm) tumours. A similar difference was found between pN0 and pN1 tumours. This difference might reflect the progression rate of male breast cancer. The histopathology pattern and distribution of histologic malignancy grades were similar to those in female breast carcinoma with the exception that lobular carcinoma and medullary carcinoma with lymphoid infiltration were lacking in the male material.  相似文献   
993.
Serum protein electrophoresis (SPEP) data obtained at diagnosis were available for 98 of 342 patients with chronic lymphocytic leukemia (CLL) identified in a population-based case-control epidemiologic study. Patients tested with SPEP at diagnosis were significantly younger, more likely to have lymphadenopathy, and more likely to have had their conditions diagnosed at a university hospital than those not tested. Four categories of electrophoretic patterns were identified: normal (N = 56), hypogammaglobulinemia (N = 28), hypergammaglobulinemia (N = 11), and monoclonal gammopathy (N = 3). A higher proportion of those with hypergammaglobulinemia were black, and patients with hypergammaglobulinemia and monoclonal gammopathy were more likely to die within the first year following diagnosis than patients in the other SPEP groups. No association was found, however, between SPEP pattern and a clinical staging classification for CLL. These findings suggest that SPEP may be a useful adjunct in categorizing possible subtypes of CLL and developing future clinical staging classifications.  相似文献   
994.
995.
The pharmacokinetics of 1-(tetrahydro-2-furanyl)-5-fluorouracil (FT) and its conversion into 5-fluorouracil (FUra) in liver tissue were studied in ten patients with hepatocellular carcinoma (HCC). The plasma concentration of FT after its intravenous injection (dosage: 800 mg) was computerfitted to a bi-exponential function (C = Ae-alpha t + Be-beta t), indicating a two-compartment disposition. The pharmacokinetic parameters did not significantly differ between the five patients with, and the five without cirrhosis of the liver. The plasma concentrations of FUra likewise showed no significant difference between the two groups. The rates of FT degradation in the liver tissue homogenate were similar for four of the patients with cirrhosis (0.10 +/- 0.05 mumol/g liver protein/30 min) and four of those without it (0.13 +/- 0.05). The rates of cytochrome P-450-dependent FUra formation in the microsomal fraction of liver tissue from two patients (1.1 and 1.3 nmol/mg microsomal protein/30 min) were dramatically reduced to less than half of those of two control subjects (2.4 and 2.7). The estimated rates of FUra formation in the soluble fraction (105,000 X g supernatant fraction) from the two patients (0.1 and 0.13 nmol/mg protein/30 min) were almost identical to those from the controls (0.12 and 0.14), suggesting that the rate in the soluble fraction from HCC patients may not be as strongly affected as the rate in the microsomal fraction.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
996.
Can carotid endarterectomy be justified? No   总被引:1,自引:0,他引:1  
  相似文献   
997.
998.
3-(Methylnitrosamino)propionitrile (MNPN), a potent carcinogen in F344 rats, was detected for the first time in the saliva of betel quid chewers at levels ranging from 0.5 to 11.4 micrograms/liter. The tumorigenic properties of MNPN and its potential to methylate DNA in F344 rats were evaluated. Groups of 21 male and 21 female rats were given 60 s.c. injections over a 20-week period (total doses 0.055 and 0.23 mmol per rat). The experiment was terminated after 106 weeks. MNPN at the higher dose induced 18 (86%) malignant tumors of the nasal cavity in male and 15 (71%) in female rats. The lower dose induced nine (43%) liver tumors. Groups of four or five male F344 rats were treated with a single s.c. or i.v. injection of MNPN (0.4 mmol/kg). MNPN was also administered to rats by swabbing the oral cavity (2.21 mmol/kg). The levels of 7-methylguanine and O6-methylguanine, formed 0.5-36 h after treatment, were measured in the liver, nasal mucosa, esophagus, and oral issues. The highest levels of methylated guanines were detected in the nasal cavity independent of the route of administration. The results of this study demonstrate that MNPN is present in the saliva of betel quid chewers and is a potent carcinogen in F344 rats.  相似文献   
999.
Correlation of fetal posture and congenital dislocation of the hip   总被引:1,自引:0,他引:1  
A statistical study was carried out on the incidence of CDH associated with mechanical factors in the uterus, including congenital genu recurvatum. There were 72 cases of CDH among 6559 infants (1.1 per cent). The incidence of CDH was 0.7 per cent in cephalic presentation, 2 per cent in footling presentation and 20 per cent in single-breech presentation. In another series, CDH was found in six of seven infants with congenital genu recurvatum. These findings suggest that a fetal posture with the hip flexed and the knee extended predisposes to the development of CDH.  相似文献   
1000.
Caffeine is the most widely consumed drug in Western society. The intake of caffeine-containing beverages in many adults and children often reaches levels that can induce pharmacological effects. Ninety-nine percent of ingested caffeine is absorbed and distributed to all tissues and organs. The effects of caffeine intake differ greatly according to acute or chronic intake, level of intake, and the development of tolerance. Caffeine administered acutely to non-users or recent abstainers can induce hypertension, arrhythmias, altered myocardial function, increased plasma catecholamine levels, plasma renin activity, serum cholesterol levels, increased production of urine, gastric acid secretion, and alterations in mood and sleep patterns. Tolerance to chronic caffeine intake develops in most individuals, with the cessation of its effects on the renal system, the cardiovascular system, the gastrointestinal system and, to some extent, the central nervous system. Moderate caffeine consumers probably need to have little concern for the effect of caffeine intake on their health if their other life-style habits are also moderate.  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