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   21618篇
  免费   1470篇
  国内免费   61篇
耳鼻咽喉   231篇
儿科学   660篇
妇产科学   462篇
基础医学   2839篇
口腔科学   355篇
临床医学   2302篇
内科学   4544篇
皮肤病学   362篇
神经病学   2313篇
特种医学   553篇
外国民族医学   1篇
外科学   2622篇
综合类   239篇
一般理论   8篇
预防医学   2297篇
眼科学   359篇
药学   1267篇
中国医学   43篇
肿瘤学   1692篇
  2024年   37篇
  2023年   251篇
  2022年   446篇
  2021年   980篇
  2020年   504篇
  2019年   767篇
  2018年   904篇
  2017年   648篇
  2016年   640篇
  2015年   705篇
  2014年   941篇
  2013年   1251篇
  2012年   1947篇
  2011年   1901篇
  2010年   1045篇
  2009年   826篇
  2008年   1345篇
  2007年   1311篇
  2006年   1124篇
  2005年   1143篇
  2004年   958篇
  2003年   765篇
  2002年   761篇
  2001年   196篇
  2000年   121篇
  1999年   151篇
  1998年   114篇
  1997年   89篇
  1996年   81篇
  1995年   84篇
  1994年   66篇
  1993年   49篇
  1992年   70篇
  1991年   56篇
  1990年   66篇
  1989年   44篇
  1988年   49篇
  1987年   41篇
  1986年   64篇
  1985年   42篇
  1984年   41篇
  1983年   52篇
  1982年   37篇
  1981年   32篇
  1980年   30篇
  1979年   30篇
  1977年   25篇
  1976年   25篇
  1975年   21篇
  1974年   29篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
OBJECTIVE: Hormone therapy use has been positively associated with mammographic density in several studies. However, few studies have examined the association between endogenous hormone levels and mammographic density. Therefore, we evaluated the relationship of endogenous sex hormones, insulin-like growth factor (IGF), and lipids with mammographic density in 88 overweight, postmenopausal women not taking hormone therapy. METHODS: Percent density and dense area were evaluated as continuous measures using a computer-assisted program. We used multiple linear regression to evaluate the associations of sex hormones, IGF, and cholesterol with mammographic density, adjusting for confounders, including adiposity. We evaluated stratification by history of hormone therapy use (former versus never) and hormone therapy latency (<5 versus > or = 5 years). RESULTS: Among former hormone therapy users, mammographic density was inversely associated with circulating levels of estrone (P = 0.01), estradiol (P = 0.003), free estradiol (P = 0.004), testosterone (P = 0.04), free testosterone (P = 0.02), androstenedione (P < 0.001), dehydroepiandrosterone (P = 0.01), and the ratio of IGF-I to its binding protein (IGF-I/IGFBP-3; P = 0.04). We found similar associations when we limited the analyses to women who had used hormone therapy within the past 5 years. We also noted positive associations of mammographic density with total cholesterol (P = 0.03) and low-density lipoprotein (P = 0.03) among former hormone therapy users. No associations were noted among women who had never used hormone therapy. CONCLUSIONS: These results suggest that there is an inverse relationship between endogenous sex hormones and mammographic density in postmenopausal women among former users of hormone therapy. This is not consistent with the hormone therapy literature and should be confirmed in larger studies.  相似文献   
103.
BACKGROUND AND PURPOSE: To investigate the effect of radiotherapy planning with a dedicated combined PET-CT simulator of patients with locally advanced non-small cell lung cancer. PATIENTS AND METHODS: Twenty-one patients underwent a pre-treatment simulation on a dedicated hybrid PET-CT-simulator. For each patient, two 3D conformal treatment plans were made: one with a CT based PTV and one with a PET-CT based PTV, both to deliver 60Gy in 30 fractions. The maximum tolerable prescribed radiation dose for CT versus PET-CT PTV was calculated based on constraints for the lung, the oesophagus, and the spinal cord, and the Tumour Control Probability (TCP) was estimated. RESULTS: For the same toxicity levels of the lung, oesophagus and spinal cord, the dose could be increased from 55.2+/-2.0Gy with CT planning to 68.9+/-3.3Gy with the use of PET-CT (P=0.002), with corresponding TCP's of 6.3+/-1.5% for CT and 24.0+/-5.6% for PET-CT planning (P=0.01). CONCLUSIONS: The use of a combined dedicated PET-CT-simulator reduced radiation exposure of the oesophagus and the lung, and thus allowed significant radiation dose escalation whilst respecting all relevant normal tissue constraints.  相似文献   
104.
It has been suggested that expression of anti-apoptotic proteins such as Bcl-2 or BAG-1 may confer cellular resistance to chemotherapy. A corollary of this hypothesis is that expression of these proteins may predict clinical response to treatment and that Bcl-2- or BAG-1-positive cells may selectively be enriched in postchemotherapy tissue specimens. The goal of this exploratory pilot study was to assess these two predictions by using immunohistochemistry in 29 paired pre- and postchemotherapy breast tissue specimens obtained from patients who underwent preoperative doxorubicin-based chemotherapy. All breast cancers expressed BAG-1 protein, and, in individual tumors, 40-100% of neoplastic cells stained positive for this protein. Homogenous cytoplasmic staining was typically observed, though neoplastic cells also showed nuclear staining in many specimens. We found no correlation between prechemotherapy expression of BAG-1 and subsequent pathological response to cytotoxic therapy. Paired pre- and posttreatment specimens showed similar levels of BAG-1 expression when residual tumor could be assessed. Bcl-2 was expressed in 55% of cancers and was localized to the cytoplasm. Absence of Bcl-2 expression in prechemotherapy specimens was associated with more frequent complete pathological response (58% vs. 20%; p = 0.04). However, similar to BAG-1, no difference between pre- and posttherapy expression of Bcl-2 was observed in neoplastic cells in paired tissue specimens. These observations suggest that BAG-1 contributes an important cellular function to breast epithelial cells, which is reflected by its ubiquitous expression in these tissues. However, it does not appear to determine response to doxorubicin-based chemotherapy. In contrast, lack of Bcl-2 expression was associated with a higher probability of complete pathological response to doxorubicin-based chemotherapy.  相似文献   
105.
106.
This study’s objective was to compare the total and outside the cleft prevalence of dental anomalies (DA) between patients with cleft lip and palate (CLP) and a control group. This retrospective cross-sectional study was done under a case–control design. The case group consisted of 192 non-syndromic patients with complete CLP, while the control group included 411 patients. All subjects had orthopantomography, intra, and extraoral photographs. The prevalence of dental agenesis, supernumerary teeth, impacted teeth, dental transposition, and microdontia were compared using a chi-squared test (P < .05). Next, a second test was made, but only the anomalies outside the cleft were considered for this study. Total prevalence was 89.1% for cases, and 20.9% for controls (P < .01). The prevalence of each DA was significantly higher for the case group. In the analysis of DAs outside the cleft, the total prevalence was still significantly associated (P < .01); however, only dental agenesis was statistically significant (P < .01). Further analysis found that a high rate of upper premolar absence (P < .01) could explain this event. Patients with CLP have a higher prevalence of DAs compared to controls. After considering only the DAs outside the cleft, the total prevalence remains significantly higher. However, this phenomenon is explained mainly by the elevated prevalence of upper premolars’ agenesis. This study’s results suggest that environmental factors are behind the high prevalence of DAs in subjects with CLP.  相似文献   
107.
IntroductionProcedural specialties are at higher risk for malpractice claims than non-procedural specialties. Previous studies have examined common damages and malpractice lawsuits resulting from specific procedures. Our goal was to analyze urological interventions that led to sexual dysfunction (SD) claims.MethodsThe Casetext legal research platform was queried using search terms for medical malpractice and common men’s health procedures between 1993 and 2020. In total, 236 cases were found, and 21 cases met the inclusion criteria: malpractice cases against a urologist or urology group, clearly stated legal outcome, and allegation of sexual dysfunction from an intervention that directly caused damages.ResultsA total of 42 damages were cited in 21 lawsuits. The top three damages claimed were erectile dysfunction (ED) (14/42, 33.3%), genital pain syndrome (7/42, 16.7%), and urinary incontinence (5/42, 11.9%). The most commonly cited treatments were urinary catheter placement or removal (3/21, 14.3%), robotic-assisted laparoscopic radical prostatectomy (RALP) (3/21, 14.3%), circumcision (3/21, 14.3%), and penile implant (3/21, 14.3%). In 19 of 21 suits (90.4%), the outcome favored the defendant. Two cases favored the plaintiff: penile implant (failure to prove the patient was permanently, organically impotent prior to the procedure; missed urethral injury at time of surgery, $300 000) and vasectomy (damage to vasculature resulting in loss of testicle, $300 000).ConclusionsMost suspected malpractice cases resulting in SD favored the defendant urologist. Interestingly, urinary catheter placement is as likely to result in litigation as other operative interventions, such as RALP, inflatable penile prosthesis, and circumcision. It is possible that thorough preoperative counselling and increased responsiveness to patients’ postoperative concerns may have avoided litigation in several cases.  相似文献   
108.
Bronchopulmonary arterial fistula consists of an abnormal connection between the bronchus and the vascular tree and is a rare but serious complication associated with a variety of lung interventions. We present a case of a 61-year-old female with a history of metastatic breast cancer treated with lumpectomy and radiation 20 years prior, who was found to have a fistula between the right pulmonary artery and the right mainstem bronchus. Our patient was treated endovascularly with coil embolization in the setting of massive hemoptysis flooding the trachea, which was successful in controlling the acute bleed, although care was withdrawn in the following days following a discussion with the family given the presence of advanced metastatic disease. This case illustrates the use of endovascular techniques to treat an actively bleeding bronchopulmonary arterial fistulae, including a review of the existing literature regarding the optimal endovascular management strategy. Although our patient did not achieve the best outcome, endovascular intervention with stent-placement or embolization can serve to temporarily halt blood flow through the fistula, stabilizing the patient and allowing for more radical therapy after improvement.  相似文献   
109.
Human metapneumovirus (HMPV) is an important respiratory pathogen and is divided in two main groups (A and B). HMPV strains with partial duplications (111-nt and 180-nt duplication) of the G gene have been reported in recent years. Since the initial reports, viruses with these characteristics have been reported in several countries. We analyzed all complete HMPV G gene ectodomain sequences available at GenBank to determine if viruses with 111-nt or 180-nt duplication have become the leading HMPV strains worldwide, and to describe their temporal and geographic distribution. We identified 1462 sequences that fulfilled study criteria (764 HMPV A and 698 HMPV B) reported from 37 countries. The most frequent HMPV A genotype was A2b2 (n = 366), and the most frequent B genotype was B2 (n = 374). A total of 84 sequences contained the 111-nt duplication, and 90 sequences contained the 180-nt duplication. Since 2016, viruses with a partial duplication comprise the most frequent HMPV A sequences globally and have displaced other HMPV A viruses in Asia, Europe, and South America; no sequences of viruses with partial duplication have been reported in North America or Africa so far. Continued surveillance of HMPV is required to identify the emergence and spread of epidemiologically relevant variants.  相似文献   
110.
We tested swab specimens from pets in households in Ontario, Canada, with human COVID-19 cases by quantitative PCR for SARS-CoV-2 and surveyed pet owners for risk factors associated with infection and seropositivity. We tested serum samples for spike protein IgG and IgM in household pets and also in animals from shelters and low-cost neuter clinics. Among household pets, 2% (1/49) of swab specimens from dogs and 7.7% (5/65) from cats were PCR positive, but 41% of dog serum samples and 52% of cat serum samples were positive for SARS-CoV-2 IgG or IgM. The likelihood of SARS-CoV-2 seropositivity in pet samples was higher for cats but not dogs that slept on owners’ beds and for dogs and cats that contracted a new illness. Seropositivity in neuter-clinic samples was 16% (35/221); in shelter samples, 9.3% (7/75). Our findings indicate a high likelihood for pets in households of humans with COVID-19 to seroconvert and become ill.  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