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   7393篇
  免费   606篇
  国内免费   14篇
耳鼻咽喉   117篇
儿科学   182篇
妇产科学   157篇
基础医学   868篇
口腔科学   304篇
临床医学   872篇
内科学   1431篇
皮肤病学   251篇
神经病学   474篇
特种医学   245篇
外国民族医学   1篇
外科学   1240篇
综合类   217篇
一般理论   8篇
预防医学   728篇
眼科学   61篇
药学   524篇
中国医学   6篇
肿瘤学   327篇
  2022年   61篇
  2021年   117篇
  2020年   76篇
  2019年   140篇
  2018年   119篇
  2017年   83篇
  2016年   113篇
  2015年   129篇
  2014年   169篇
  2013年   254篇
  2012年   310篇
  2011年   300篇
  2010年   205篇
  2009年   174篇
  2008年   249篇
  2007年   254篇
  2006年   323篇
  2005年   279篇
  2004年   235篇
  2003年   272篇
  2002年   240篇
  2001年   208篇
  2000年   234篇
  1999年   207篇
  1998年   102篇
  1997年   86篇
  1996年   92篇
  1995年   83篇
  1994年   72篇
  1993年   80篇
  1992年   180篇
  1991年   168篇
  1990年   152篇
  1989年   175篇
  1988年   157篇
  1987年   132篇
  1986年   140篇
  1985年   151篇
  1984年   115篇
  1983年   76篇
  1982年   67篇
  1981年   66篇
  1979年   92篇
  1978年   81篇
  1977年   67篇
  1976年   64篇
  1974年   66篇
  1973年   76篇
  1971年   57篇
  1970年   56篇
排序方式: 共有8013条查询结果,搜索用时 0 毫秒
91.
Real-time nucleic acid sequence-based amplification (NASBA) using molecular beacon technology (NASBA-beacon) was compared to standard NASBA with postamplification hybridization using electrochemiluminescently labeled probes (NASBA-ECL) for detection of enteroviruses (EV) in 133 cerebrospinal fluid and 27 stool samples. NASBA-ECL and NASBA-beacon were similar in sensitivity, detecting 55 (100%) and 52 (94.5%) EV-positive samples, respectively. There were no false positives. Both NASBA assays were significantly more sensitive than culture. Real-time NASBA-beacon reagents and equipment rental were more expensive than those for NASBA-ECL; however, time to result was shortened by 1.5 h, hands-on time was reduced by 25 min, and the assay was much simpler for technologists to learn and perform.  相似文献   
92.
Loss-of-function variants in ANKRD11 were identified as the cause of KBG syndrome, an autosomal dominant syndrome with specific dental, neurobehavioural, craniofacial and skeletal anomalies. We present the largest cohort of KBG syndrome cases confirmed by ANKRD11 variants reported so far, consisting of 20 patients from 13 families. Sixteen patients were molecularly diagnosed by Sanger sequencing of ANKRD11, one familial case and three sporadic patients were diagnosed through whole-exome sequencing and one patient was identified through genomewide array analysis. All patients were evaluated by a clinical geneticist. Detailed orofacial phenotyping, including orthodontic evaluation, intra-oral photographs and orthopantomograms, was performed in 10 patients and revealed besides the hallmark feature of macrodontia of central upper incisors, several additional dental anomalies as oligodontia, talon cusps and macrodontia of other teeth. Three-dimensional (3D) stereophotogrammetry was performed in 14 patients and 3D analysis of patients compared with controls showed consistent facial dysmorphisms comprising a bulbous nasal tip, upturned nose with a broad base and a round or triangular face. Many patients exhibited neurobehavioural problems, such as autism spectrum disorder or hyperactivity. One-third of patients presented with (conductive) hearing loss. Congenital heart defects, velopharyngeal insufficiency and hip anomalies were less frequent. On the basis of our observations, we recommend cardiac assessment in children and regular hearing tests in all individuals with a molecular diagnosis of KBG syndrome. As ANKRD11 is a relatively common gene in which sequence variants have been identified in individuals with neurodevelopmental disorders, it seems an important contributor to the aetiology of both sporadic and familial cases.  相似文献   
93.
Management and outcomes of patients with acute coronary syndromes (ACSs) may vary according to patient race and ethnicity. To assess racial differences in presentation and outcome in high-risk North American patients with non-ST-segment elevation (NSTE) ACS, we analyzed baseline racial/ethnic differences and all-cause death or nonfatal myocardial infarction (MI) in 6,077 white, 586 African-American, and 344 Hispanic patients through 30-day, 6-month, and 1-year follow-up. Frequencies of hypertension were 66% for whites, 83% for African-Americans, and 78% for Hispanics (overall p <0.001). Use of angiography was similar across groups. Use of percutaneous coronary intervention (46% for whites, 41% for African-Americans, and 45% for Hispanics, overall p = 0.046) and coronary artery bypass grafting (20% for whites, 16% for African-Americans, and 22% for Hispanics, overall p = 0.044) differed. African-American patients had significantly fewer diseased vessels compared with white patients (p = 0.0001). Thirty-day death or MI was 14% for whites, 10% for African-Americans, and 14% for Hispanics (overall p = 0.034). After adjustment for baseline variables, African-American patients had lower 30-day death or MI compared with white patients (odds ratio 0.73, 95% confidence interval 0.55 to 0.98). There were no differences in 6-month death or MI across racial/ethnic groups. In conclusion, baseline clinical characteristics differed across North American racial/ethnic groups in the SYNERGY trial. African-American patients had significantly better adjusted 30-day outcomes but similar 6-month outcomes compared with white patients.  相似文献   
94.

Background

The biomechanical role of the posterior spinal ligaments for spinal stability has been stated in previous studies. The investigation of the viscoelastic properties of human lumbar spinal ligaments is essential for the understanding of physiological differences between healthy and degenerated tissues. The stress-relaxation behavior of biological tissues is commonly described with the quasi-linear viscoelastic model of Fung, which assumes that the stress-relaxation response is independent of the applied strain. The goal of this study was to investigate the stress-relaxation response of ovine posterior spinal ligaments at different elongations to verify the above-mentioned hypothesis.

Methods

Twenty-four ovine lumbar spinal segments, consisting of only the supraspinous and interspinous ligaments and adjoining spinous processes, were elongated uniaxially to different strain levels within the physiological elastic region (5–20%). The experimental data were described with a non-linear viscoelastic model: the modified superposition method of Findley.

Findings

A linear dependency of the relaxation rate to the applied strains was observed on intact segments, when both ligaments were considered, as well as on each individual ligament. This result can be applied to the human spinal ligaments, due to similarities observed between the sheep and human spinal segment under physiological loading.

Interpretation

The non-linear viscoelastic modified superposition method of Findley is an appropriate model for describing the viscoelastic properties of lumbar spinal ligaments in vitro due to its ability to address variation in applied strain during the force relaxation measurements.  相似文献   
95.
96.
97.
We have investigated sequential changes in skeletal muscle and hepatic protein synthesis following sepsis, and their relationship to changes in circulating and tissue glutamine concentrations. Male Wistar rats underwent caecal ligation and puncture (CLP) or sham operation, with starvation, and were killed 24, 72 or 96 h later. A group of non-operated animals were killed at the time of surgery. Protein synthesis was determined using a flooding dose of L-[4-(3)H] phenylalanine, and glutamine concentrations were measured by an enzymic fluorimetric assay. Protein synthesis in gastrocnemius muscle fell in all groups. Gastrocnemius total protein content was reduced after CLP and at 72 and 96 h after sham operation. After CLP, protein synthesis was lower at 24 h, and total protein content was lower at 72 and 96 h, than in sham-operated animals. CLP was associated with increased liver protein synthesis at all time points, whereas there was no change after sham operation. Liver protein content did not change after CLP, but was lower at 72 and 96 h after sham operation than in non-operated animals. Plasma glutamine concentrations were reduced at 24 h after sham operation, and at 72 and 96 h after CLP. Muscle glutamine concentrations were reduced in all groups, with the decrease being greater following CLP than after sham operation. In the liver, glutamine concentrations were unchanged after CLP, but increased after sham operation. In rats with sepsis, decreases in muscle protein synthesis and content are associated with markedly reduced muscle glutamine concentrations. Plasma glutamine concentrations are initially maintained, but fall later. In liver, protein synthesis is increased, while glutamine concentrations are preserved. These results support a peripheral-to-splanchnic glutamine flux in sepsis.  相似文献   
98.
    
Bilayer hydrogels with a soft cartilage‐like layer and a stiff bone‐like layer embedded with human mesenchymal stem cells (hMSCs) are promising for osteochondral tissue engineering. The goals of this work were to evaluate the effects of dynamic compressive loading (2.5% applied strain, 1 Hz) on osteogenesis in the stiff layer and spatially map local mechanical responses (strain, stress, hydrostatic pressure, and fluid velocity). A bilayer hydrogel was fabricated from soft (24 kPa) and stiff (124 kPa) poly (ethylene glycol) hydrogels. With hMSCs embedded in the stiff layer, osteogenesis was delayed under loading evident by lower OSX and OPN expressions, alkaline phosphatase activity, and collagen content. At Day 28, mineral deposits were present throughout the stiff layer without loading but localized centrally and near the interface under loading. Local strains mapped by particle tracking showed substantial equivalent strain (~1.5%) transferring to the stiff layer. When hMSCs were cultured in stiff single‐layer hydrogels subjected to similar strains, mineralization was inhibited. Finite element analysis revealed that hydrostatic pressures ≥~600 Pa correlated to regions lacking mineralization in both hydrogels. Fluid velocities were low (~1–10 nm/s) in the hydrogels with no apparent correlation to mineralization. Mineralization was recovered by inhibiting ERK1/2, indicating cell‐mediated inhibition. These findings suggest that high strains (~1.5%) combined with higher hydrostatic pressures negatively impact osteogenesis, but in a manner that depends on the magnitude of each mechanical response. This work highlights the importance of local mechanical responses in mediating osteogenesis of hMSCs in bilayer hydrogels being studied for osteochondral tissue engineering.  相似文献   
99.
100.
    
The purpose of this systematic review was to locate and synthesize peer‐reviewed evidence regarding the effectiveness of providing suicide prevention education to nursing students. Systematic searches were conducted in seven databases (EMBASE, EmCare, Joanna Briggs, MEDLINE, PsycINFO, Scopus, and Web of Science). Results were screened in duplicate at two stages: title and abstract, and full text. Critical appraisal and data extraction were also completed in duplicate. Initial database searching yielded 303 results. Following the addition of seven records from relevant reference lists, and the removal of duplicates, a total of 118 results were included for screening. Eight articles were deemed eligible for inclusion in this review; most (n = 5) were quantitative. While all were conducted within university settings, half were stand‐alone education sessions, while the remaining were integrated with existing programmes/courses. The types of education programmes varied considerably across studies, with only three being established, evidence‐based programmes. The studies explore a range of outcomes, which have been narratively categorized as enhanced skills, abilities, and self‐confidence; development of positive attitudes and beliefs; acquisition of knowledge; and programme experience and evaluation. While there is a small body of evidence indicating that suicide prevention education programmes contribute to improvements in skills, abilities, self‐confidence, and attitudes among nursing students, the variability in educational interventions and outcomes, coupled with short‐term evaluation time frames, makes it difficult to fully understand the impact of this important suicide prevention strategy.  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