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   1476篇
  免费   99篇
  国内免费   20篇
耳鼻咽喉   7篇
儿科学   47篇
妇产科学   20篇
基础医学   147篇
口腔科学   55篇
临床医学   212篇
内科学   324篇
皮肤病学   7篇
神经病学   78篇
特种医学   179篇
外科学   150篇
综合类   32篇
预防医学   115篇
眼科学   14篇
药学   129篇
肿瘤学   79篇
  2023年   16篇
  2022年   15篇
  2021年   34篇
  2020年   18篇
  2019年   23篇
  2018年   24篇
  2017年   17篇
  2016年   25篇
  2015年   17篇
  2014年   29篇
  2013年   46篇
  2012年   46篇
  2011年   47篇
  2010年   38篇
  2009年   59篇
  2008年   68篇
  2007年   70篇
  2006年   46篇
  2005年   49篇
  2004年   40篇
  2003年   52篇
  2002年   48篇
  2001年   44篇
  2000年   41篇
  1999年   31篇
  1998年   50篇
  1997年   43篇
  1996年   53篇
  1995年   40篇
  1994年   32篇
  1993年   33篇
  1992年   21篇
  1991年   17篇
  1990年   16篇
  1989年   37篇
  1988年   41篇
  1987年   27篇
  1986年   19篇
  1985年   31篇
  1984年   21篇
  1983年   16篇
  1982年   24篇
  1981年   13篇
  1980年   18篇
  1979年   12篇
  1978年   16篇
  1977年   14篇
  1976年   11篇
  1973年   8篇
  1972年   10篇
排序方式: 共有1595条查询结果,搜索用时 15 毫秒
21.
22.
The ageing ovary appears to be characterized by depletion of primordial follicles. The relationship between infertility and the number of follicles in the ovarian cortex is not known. Moreover, there are no accurate markers or clinical methods to predict the decline in ovarian reserve. This study investigates the correlation between early follicular follicle stimulating hormone, ovarian size and follicular density in 60 infertile women aged 19-45 years (mean = 34.4 +/- 5.5). An ovarian biopsy was taken from each patient while performing diagnostic laparoscopy (n = 28) or laparotomy for tubal surgery or myomectomy (n = 32). The median number of follicles was similar in tubal and unexplained infertility patients (9.5 versus 5.5). Increasing age showed a significant negative correlation with follicular density and ovarian volume (r = -0.46, P = 0.0003;. r = -0.43, P = 0.0016, respectively). In women > or = 35 years of age the ovarian volume showed a strong correlation with follicular density (r = 0.71, P < 0.0001). Our results indicate that infertile women in their late thirties and over have a decreased ovarian reserve which could possibly be predicted by ovarian volume measurement. Ovarian biopsy may have a place as part of infertility evaluation in older women.   相似文献   
23.
Levin  DC; Gardiner  GA  Jr 《Radiology》1987,164(3):675-680
For many years, atherosclerotic coronary artery lesions have been described by angiographers only in terms of location and degree of narrowing. However, it has become apparent that coronary stenoses generally have distinct morphologic features that can be recognized at angiography and that allow them to be classified as either "simple" or "complex" plaques. Complex plaques are those characterized by ulcerated or ruptured surfaces, subintimal hemorrhage, superimposed partially occluding thrombi, recanalized thrombi, or some combination. Pathologic studies have shown a very high frequency of these lesions at sites of total thrombotic occlusion of coronary arteries. Clinical and angiographic studies have demonstrated a high frequency of such lesions in living patients with both unstable angina and acute myocardial infarction. The presence of complex stenoses has also been found to increase the risk of future myocardial infarction. Plaque morphology thus appears to significantly affect the prognosis of patients with coronary disease and should be carefully evaluated in interpretation of all coronary angiograms.  相似文献   
24.
There is a strong rationale for integrating pharmacoeconomics into research and development (R&D) project selection and termination decisions. The average cost for the typical new drug introduction now exceeds $US300 million. Furthermore, a growing proportion of phase III projects are terminated because of economic factors relative to efficacy and safety concerns. While the use of pharmacoeconomic studies by payers is still evolving, the pressures on firms to show that new products are cost effective will only intensify in future periods. Accordingly, it is important for firms to begin analysing the cost effectiveness of new drug candidates early in the R&D process. The cost effectiveness of a new therapy can be simulated prior to clinical testing using different assumptions about the efficacy, tolerability, pricing and formulation of the new therapy. These models can be refined and updated as data become available from clinical testing and other sources. A key objective is to make uncompetitive projects fail sooner while channelling development resources to projects with high expected returns. Cost-effectiveness analysis should be an integral component of the firms's strategic action plan and its return on investment analyses.  相似文献   
25.
Using oligonucleotide primers based on mammalian nitric oxide synthases (NOS), expression of an inducible NOS (iNOS) gene was detected in head kidney and gill tissue of bacterially-challenged rainbow trout. Three overlapping fragments were amplified by RT-PCR and used to construct a contiguous sequence of 1410bp, with high nucleotide homology to iNOS in birds (61%) and mammals (57-59%). The nucleotide sequence translated in one reading frame to produce a partial peptide containing 470 amino acids, with 69-71% amino acid homology with mammalian iNOS, 81% homology with chicken iNOS and 85% homology with a partial (492bp) goldfish iNOS sequence. In vitro stimulation of head kidney macrophages with LPS also induced expression of the trout iNOS RNA, with optimal expression seen using 20-50 microg/ml LPS at 2h to 6h post-stimulation. The evolutionary and functional significance of the trout iNOS sequence are discussed.  相似文献   
26.
Occupational exposure by inhalation to vanadium-containing particles such as residual oil fly ash results in respiratory tract inflammation. This inflammation, characterized by abundant neutrophilia, appears to be initiated by alveolar macrophages (AMs) encountering particles and the subsequent release of proinflammatory cytokines. Intracellular signaling events in these cells in response to particles or their components are largely unknown. We investigated two immediate responses of AMs to vanadium exposure in vitro, the production of reactive oxygen intermediates (ROI) or respiratory burst (RB), and the tyrosine phosphorylation of cellular proteins. Macrophages exposed in vitro to 100 microM vanadyl chloride/1 microCi 48V incorporated 8.3% of the metal after 30 min. Exposure of AMs to increasing concentrations of sodium metavanadate resulted in a dose-dependent increase in production of ROI as measured by dichlorofluorescin oxidation. The lowest dose yielding a significant response was 50 microM, whereas 1000 microM increased RB activity by 173%. NADPH oxidase inhibitors deoxy-D-glucose (100 mM) and diphenylene iodonium (25 microM) reduced the metavanadate-induced RB by 62 and 71%, respectively, implicating NADPH oxidase as the primary cellular source of ROI. Enhanced cerium chloride oxidation in response to metavanadate localized to the plasma membrane consistent with increased NADPH oxidase activity. Pretreatment of AMs with the epidermal growth factor receptor inhibitor, tryphostin B50 (10 microM), reduced the metavanadate-induced RB, but did not influence overall tyrosine phosphorylation. Metavanadate and H2O2 exposure greatly increased overall tyrosine phosphorylation, yielding a similar but distinguishable pattern of phosphorylation in these cells. These observations demonstrate that in vitro metavanadate exposure regulates two distinct, yet related intracellular signaling pathways important in initiating inflammatory responses in these cells: (1) activation of the NADPH oxidase complex with subsequent increased ROI synthesis, and (2) enhanced tyrosine phosphorylation of cellular proteins.  相似文献   
27.
Osteoradionecrosis occurs in approximately 10% to 15% of patients following radiation therapy for head and neck cancer. In these patients, it is most commonly reported in sites involving the mandible, but it has also been reported in the maxilla, sphenoid, and temporal bones. The majority of these cases are related to some type of trauma such as dental extraction or intraoral biopsies. However, approximately 40% of these entities occur spontaneously and are felt to be secondary to cell kill in intermediate tissues such as bone and periosteum. Our literature review yielded no previously reported cases of osteoradionecrosis involving the anterior cranium. The following two cases present patients who experienced osteoradionecrosis of their frontal bone flaps following subcranial approaches for tumor resection. Both patients suffered from carcinomas involving the ethmoid sinuses; one tumor was a moderately well-differentiated squamous cell carcinoma, the other a mucinous adenocarcinoma. One patient's radiation therapy consisted of external beam photons; the other patient received external beam neutrons. Treatment for these patients, as well as possible causative factors regarding their osteoradionecrosis, are discussed.  相似文献   
28.
Davis  GD; Fulton  RE; Ritter  DG; Mair  DD; McGoon  DC 《Radiology》1978,128(1):133-144
Of 181 patients with severe congenital pulmonary atresia and ventricular septal defect or "type IV truncus" (an obsolete term), all but 11% had true central pulmonary arteries. These arteries were demonstrable by large serial biplane angiograms using multiple selective injections into collateral vessels, frequent photographic subtraction, and occasional pulmonary vein-wedge angiograms. These techniques are extremely important for accurate diagnosis and in planning corrective or palliative surgery, which was done in 77% of patients with pulmonary arteries.  相似文献   
29.
Objectives: To describe the physical growth patterns of infants born to narcotic dependent mothers (INDM) over a 12 months period and, if possible, to relate the growth to drug taking patterns during pregnancy.
Methodology: The growth of a cohort of 43 INDM was measured during the first 12 months of life. Weight and length measurements were compared with percentile charts and converted to Z scores. Questionnaire data about drug taking practices, demographic variables and the neonatal period (including withdrawal scores) were obtained.
Results: Twenty-four (55.8%) of INDM had evidence of neonatal drug withdrawal requiring treatment with phenobarbitone. At birth, Z scores for weight and length indicated relative intrauterine growth retardation. By 12 months, there had been some catch up growth, but Z scores for weight and length were still below zero. Persistent weight retardation at 12 months was correlated with methadone dosage during pregnancy, but not the need for phenobarbitone therapy.
Conclusions: The growth patterns of INDM in the first 12 months of life indicated that at birth there was evidence of intrauterine growth retardation, but by 12 months the growth was little different from the rest of the community. There appears to be some influence of narcotic agents taken while pregnant on subsequent growth of INDM.  相似文献   
30.
OBJECTIVES: To calculate the incidence of type 1 diabetes in Scottish children aged less than 15 years between 1984 and 1993; to examine changes in incidence; and to calculate the prevalence of diabetes at the end of this period. DESIGN: Three data sources were used to construct the Scottish Study Group for the Care of Young Diabetics register: active reporting of all new cases; reports from the Scottish Morbidity Register 1; and local registers. SUBJECTS: All children resident in Scotland diagnosed with primary insulin dependent diabetes mellitus when less than 15 years of age between 1984 and 1993. MAIN OUTCOME MEASURES: Annual incidence and prevalence rate for Scotland; time trend in incidence over the 10 years; differences in incidence between the three different age groups; and completeness of the register. RESULTS: The average annual incidence for Scotland was 23.9/100,000 children. The prevalence rate was 1.5/1000 in 1993. A total of 2326 cases was identified from the three sources. Capture-recapture analysis suggests a case ascertainment of 98.6%. The annual incidence rates increased at a rate of 2% each year (rate ratio = 1.02, 95% confidence interval (CI) 1.01 to 1.03). The incidence was higher in boys than girls (rate ratio = 1.08, 95% CI 1.00 to 1.18), and the incidence rates increased with age: 15.3/100,000/year for age 0-4 years, 24.4/ 100,000/year for age 5-9 years, and 31.9/ 100,000/year for age 10-14 years. CONCLUSIONS: The incidence of type 1 diabetes in Scotland is increasing and the prevalence is relatively high. These findings have important implications for health service resource allocation. The Scottish Study Group for the Care of Young Diabetics' register provides a base for monitoring and research.  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