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   7062篇
  免费   300篇
  国内免费   23篇
耳鼻咽喉   77篇
儿科学   155篇
妇产科学   101篇
基础医学   1088篇
口腔科学   255篇
临床医学   367篇
内科学   1490篇
皮肤病学   67篇
神经病学   746篇
特种医学   315篇
外科学   1038篇
综合类   30篇
预防医学   294篇
眼科学   133篇
药学   455篇
中国医学   14篇
肿瘤学   760篇
  2023年   37篇
  2022年   69篇
  2021年   121篇
  2020年   59篇
  2019年   84篇
  2018年   112篇
  2017年   99篇
  2016年   103篇
  2015年   114篇
  2014年   123篇
  2013年   203篇
  2012年   326篇
  2011年   361篇
  2010年   214篇
  2009年   198篇
  2008年   341篇
  2007年   374篇
  2006年   387篇
  2005年   395篇
  2004年   443篇
  2003年   434篇
  2002年   404篇
  2001年   199篇
  2000年   179篇
  1999年   157篇
  1998年   127篇
  1997年   107篇
  1996年   93篇
  1995年   73篇
  1994年   72篇
  1993年   86篇
  1992年   136篇
  1991年   108篇
  1990年   98篇
  1989年   107篇
  1988年   89篇
  1987年   70篇
  1986年   94篇
  1985年   78篇
  1984年   69篇
  1983年   61篇
  1982年   28篇
  1981年   36篇
  1980年   41篇
  1979年   39篇
  1978年   32篇
  1977年   42篇
  1976年   29篇
  1975年   20篇
  1969年   15篇
排序方式: 共有7385条查询结果,搜索用时 390 毫秒
11.
12.
1-O-3-(4-Vinylphenyl)propyl-β-D -glucopyranose ( 1 ) undergoes in water a closed association under formation of N-mers. The unimer/N-mer association is directly visible in the Schlieren pattern of ultracentrifugal synthetic boundary experiments. Association numbers and mass-concentration-based equilibrium constants of association were calculated from the variation of N-mer concentrations with unimer concentrations and from the concentration dependence of inverse apparent average molar masses as measured by both vapor phase osmometry and sedimentation equilibrium. Association numbers were also calculated from the combination of sedimentation coefficients with diffusion coefficients, sedimentation coefficients with intrinsic viscosities, and diffusion coefficients with interinsic viscosities as well as from the dependence of apparent mass-average molar masses on inverse apparent number-average molar masses. All methods gave in general different association numbers and equilibrium constants. The effect, which was not found for other non-ionic amphiphiles, is probably due to the existence of consecutive equilibria between the unimer and a low molar mass P-mer which associates to a higher molar mass R-mer. Viscosity data are in agreement with the picture of a spherical micelle for the dominant P-mers with about 10 water molecules per glucose residue. The micellization of 1 is both enthalpy- and entropy-driven, in contrast to the micellization of 1-O-octyl-β-D -glucopyranose which is a strictly entropy-driven process.  相似文献   
13.
14.
In order to estimate the diagnostic validity of chemical fecal occult blood tests, i.e. orthotolidine (Shionogi A) and guajac (Shionogi B) slides for detecting cancers of the esophagus, stomach and colorectum, the authors followed up all the examinees (n=3,449) of comprehensive medical check-ups at the Center for Adult Diseases, Osaka, by means of record linkage to the Osaka Cancer Registry's files. Then, diagnostic validity was calculated based on the results of two years' follow-up. Sensitivity for the respective cancers was 20.0%, 11.8% and 62.5% for Shionogi A, and 20.0%, 5.9% and 43.8% for Shionogi B slides. Likelihood ratio for the respective cancers was 1.4, 0.8 and 4.5 for Shionogi A, and 3.3, 1.0 and 7.5 for Shionogi B. Specificity was analogous among the three cancer sites, being 86% for Shionogi A and 94% for Shionogi B. These results suggest that the diagnostic validity of chemical occult blood tests for detecting cancers of the esophagus and the stomach is very poor, and therefore imply that close examinations of these sites for screening positives is unnecessary in mass screenings for colorectal cancer.  相似文献   
15.
Abstract The effectiveness of a 5% potassium nitrate dentifrice as a daily home treatment for dentinal hypersensitivity was evaluated in a double-blind study in 36 Japanese subjects who complained of cold and/or tactile hypersensitivity. The subjects were divided into 2 groups, with 18 being given a 5% potassium nitrate dentifrice (treated group) and the other 18 a vehicle paste (control group). Both groups were instructed to brush their teeth 2 × a day. The hypersensitivity levels of the affected teeth were assessed by 2 stimuli, one tactile and the other cold air, and by the perception of pain. The results of all 3 assessment methods indicated that the potassium nitrate dentifrice significantly decreased the level of hypersensitivity at weeks 4, 8, and 12. In the treated group, a rapid decrease of positive scores for both the cold air stimulus and the subjective symptoms appeared from week 2. Although a significant decrease of the assessment score was also observed in the control group, the reduction rate of the score was much greater in the treated group by ail 3 assessment methods at weeks 4, 8, and 12. Complete relief of subjective symptoms throughout the 12 weeks’examination was noted in 67% of the subjects in the treated group, but in only 6% in the control group. These results suggest the usefulness of a 5% potassium nitrate dentifrice in Japanese patients with dentinal hypersensitivity.  相似文献   
16.
Intracytoplasmic lumina (ICL) in human oviduct epithelium were investigated with transmission electron microscopy. ICL were found in 43 out of 60 cases examined. They were ultra-structurally characterized by microvilli lining the lumina, periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) staining-positive finely granular material in the lumina, and secretory vesicles in the cytoplasm surrounding the lumina. Although ICL were observed at various heights within the epithelium, they were mainly seen in basally located cells that did not face the oviduct lumen. Various stages of formation and development of ICL were observed in the basally located epithelial cells with secretory activities. Primary ICL were originated in the cytoplasm where the secretory granules were aggregated with smooth-surfaced tubular vesicles. Electron microscopic observations after PA-TCH-SP staining revealed that ICL were formed by fusion of the secretory granules with the tubular vesicles. ICL were enlarged into round profiles by further fusion of secretory granules and tubular vesicles, and subsequently opened to the oviduct lumen, or fused to each other to develop into large extracellular cysts within the epithelium.  相似文献   
17.
A woman aged 21 years noticed numbness of the left hand, dysarthria, and right hemiparesis. Magnetic resonance imaging (MRI) showed homogeneously enhanced lesions in the bilateral cerebral white matter; these enlarged within 2 weeks, showing ringlike enhancement, and then spontaneously decreased in size and enhancement. Neurocysticercosis was confirmed by repeated, significantly positive serology results and the dramatic response to praziquantel. Subsequently, positron emission tomography (PET) revealed persisting regions of possibly decreased cerebral uptake of [18F]2–fluoro–2–deoxyglucose. This is the first documentation of such distinctive serial MRI changes and the results of PET in neurocysticercosis.  相似文献   
18.
Objective. This prospective study was undertaken to evaluate the safety and efficacy of neodymium:yttrium-aluminium-garnet (Nd:YAG) laser for treatment of symptomatic benign prostatic hyperplasia (BPH).Methods. A total of 61 patients at a mean age of 71.6 years with symptomatic bladder outlet obstruction due to BPH underwent transurethral evaporation of prostate (TUEP) using Nd:YAG laser. Twelve of the patients were experiencing acute retention. Pre- and postoperative evaluation consisted of American Urological Association (AUA) symptom questionnaire and a sexual function questionnaire, uroflowmetry, postvoid residual urine, electrolytes, blood urea nitrogen, creatinine, hematocrit, and prostate volume estimation by transrectal ultrasound. TUEP was achieved by employing a side-firing Nd:YAG laser fiber with a durable quartz reflector and high-power density (Ultraline, Heraeus LaserSonics, Milpitas, CA) that was used in a contact mode.Results. All patients have been evaluated for three months, 26 for six rnonths, and 7 for twelve months. Mean prostatic size was 41.1 g. The mean improvement in symptom scores at one, three, six, and twelve months was 69.8 percent, 70.9 percent, 76.0 percent, and 70.9 percent, respectively (P = < 0.0001). The mean increase in maximum uroflow at one, three, six, and twelve months was 63.4 percent, 66.7 percent, 41.94 percent, and 164.52 percent, respectively (P = < 0.0001). There was no instance of significant fluid absorption or bleeding. The duration of postoperative catheterization was two days in 43 patients, three to seven days in 16 patients, and two to three weeks in 2 patients. There were no deaths. All patients evaluated by TRUS at six months had open channeling defects. Videocystoscopy performed in 16 patients at two to three months postoperatively revealed tissue slough. At repeat cystoscopy in these patients at six months, the prostatic fossa was completely healed with no evidence of tissue slough.Conclusions. It is concluded that the technique of TUEP using Nd:YAG laser is safe and, in preliminary results, appears apparently effective in the management of BPH.  相似文献   
19.
A 63-year-old female, with a chief complaint of right chest pain was referred to our hospital because of an abnormal right chest wall shadow on chest X-ray. A rib tumor was suspected based on her chest CT scan. Percutaneous needle biopsy yielded a diagnosis of well-differentiated adenocarcinoma. As metastatic rib tumor was suspected, the primary tumor was sought for. A thyroid gland nodule was recognized by ultrasonography, and the cytological diagnosis was class V. Immunohistological demonstration of the thyroglobulin studies of the rib tumor tissue revealed papillary and trabecular patterns of cell arrangement and the presence of thyroglobulin existence. Definitive diagnosis of metastatic rib tumor from thyroid cancer was established. Immunohistological examination is useful to confirm the diagnosis of metastatic cancer of thyroid origin.  相似文献   
20.
Serum levels of CA-50, SLX and ST-439 were measured in 213 patients with lung cancer (92 adenocarcinomas, 63 squamous cell carcinomas, 37 small cell carcinomas and 21 large cell carcinomas) and 87 patients with benign lung disease. The overall positive rates in patients with lung cancer were 12.8% for CA-50, 29.7% for SLX and 25.3% for ST-439. The positive rates for CA-50, SLX and ST-439 in adenocarcinoma patients were 22.8%, 42.4% and 38.0%, respectively. Of the patients with benign lung disease, 4.8% were false positive for CA-50, 15.3% for SLX and 3.6% for ST-439. In the patients with adenocarcinoma of the lung, the combination assay of CEA and ST-439 had a highly accurate rate (61.9%).  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