全文获取类型
收费全文 | 8850篇 |
免费 | 866篇 |
国内免费 | 505篇 |
专业分类
耳鼻咽喉 | 84篇 |
儿科学 | 137篇 |
妇产科学 | 116篇 |
基础医学 | 1165篇 |
口腔科学 | 106篇 |
临床医学 | 1133篇 |
内科学 | 1590篇 |
皮肤病学 | 72篇 |
神经病学 | 496篇 |
特种医学 | 282篇 |
外国民族医学 | 1篇 |
外科学 | 787篇 |
综合类 | 1040篇 |
现状与发展 | 4篇 |
一般理论 | 1篇 |
预防医学 | 551篇 |
眼科学 | 433篇 |
药学 | 1068篇 |
6篇 | |
中国医学 | 423篇 |
肿瘤学 | 726篇 |
出版年
2024年 | 25篇 |
2023年 | 138篇 |
2022年 | 319篇 |
2021年 | 402篇 |
2020年 | 315篇 |
2019年 | 269篇 |
2018年 | 257篇 |
2017年 | 244篇 |
2016年 | 229篇 |
2015年 | 408篇 |
2014年 | 427篇 |
2013年 | 444篇 |
2012年 | 622篇 |
2011年 | 651篇 |
2010年 | 422篇 |
2009年 | 282篇 |
2008年 | 458篇 |
2007年 | 403篇 |
2006年 | 423篇 |
2005年 | 418篇 |
2004年 | 321篇 |
2003年 | 283篇 |
2002年 | 264篇 |
2001年 | 244篇 |
2000年 | 228篇 |
1999年 | 245篇 |
1998年 | 101篇 |
1997年 | 110篇 |
1996年 | 104篇 |
1995年 | 111篇 |
1994年 | 63篇 |
1993年 | 65篇 |
1992年 | 120篇 |
1991年 | 106篇 |
1990年 | 89篇 |
1989年 | 104篇 |
1988年 | 70篇 |
1987年 | 69篇 |
1986年 | 54篇 |
1985年 | 43篇 |
1984年 | 40篇 |
1983年 | 28篇 |
1982年 | 17篇 |
1981年 | 29篇 |
1980年 | 25篇 |
1979年 | 30篇 |
1978年 | 22篇 |
1977年 | 15篇 |
1975年 | 11篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
Molecular analysis of microdissected de novo glioblastomas and paired astrocytic tumors 总被引:2,自引:0,他引:2
Cheng Y Ng HK Ding M Zhang SF Pang JC Lo KW 《Journal of neuropathology and experimental neurology》1999,58(2):120-128
Glioblastoma multiforme (GBM) often displays morphological heterogeneity in that low-grade (LG) area with well-differentiated cells are commonly found adjacent to high-grade (HG) area with poorly-differentiated cells. This heterogeneity may cause difficulty in obtaining representative tumor samples. Nevertheless, the genetic composition of these cells has only been occasionally examined. In the present study, we examined 29 de novo glioblastomas in which distinct LG and HG areas of sufficient volumes could be identified. These areas were microdissected from paraffin-embedded tissues and analyzed for genetic alterations: p53 mutations and immunohistochemistry; allelic losses at 17p13.1, 9p21, and 10q23-25; and amplification of the epidermal growth factor receptor (EGFR) gene and immunohistochemistry. We also examined 14 paired astrocytic tumors, in which a primary Grade II astrocytoma progressed over a period of time to a Grade III or Grade IV tumor. Our findings showed that the LG areas of the de novo glioblastomas exhibited numerous genetic aberrations, the proportion of which was increased in the HG areas. Genetic abnormalities seen in the LG areas were conserved in the HG areas suggesting that these morphologically different cellular subsets were derived from a common transformed clone. Also, the LG areas were genetically different from Grade II astrocytomas of the paired tumor group, in spite of their morphological similarity. In particular, the LG areas had more deletions on 10q23-25 (75% vs 20%, p = 0.04), but fewer p53 mutations (24% vs 71%, p = 0.003) and less p53 protein labeling (45% vs 79%, p = 0.04). These differences suggest that LG and HG areas in de novo glioblastoma are genetically closer to each other compared with paired low- and high-grade tumors that have progressed over time. Moreover, only a small proportion (17%) of our de novo glioblastomas exhibited EGFR amplification while a high proportion (62%) showed either p53 mutations or allelic loss of 17p13.1. We speculate that some de novo GBMs with copious LG areas may constitute a separate group with rapid progression from Grade II astrocytomas. 相似文献
132.
Rozniecki JJ Dimitriadou V Lambracht-Hall M Pang X Theoharides TC 《Brain research》1999,840(1-2):1-15
The effects of changes in temperature on primary and secondary endings of isolated cat muscle spindles were investigated under ramp-and-hold stretches and different degrees of pre-stretch. Temperature-induced alterations of the discharge frequency were compared over a temperature range of 25–35°C. Both primary and secondary endings responded to warming with increasing discharge frequencies when the spindle was pre-stretched by 5–10% of its in situ length. The following differences between the temperature effects on primary and secondary endings were observed: (1) The temperature coefficients (Q10) obtained from the discharge frequencies during the dynamic and static phase of a stretch were similar for endings of the same type, but they were larger in primary endings (range of Q10: 2.3–3.3; mean: 2.9) than in secondary endings (range of Q10: 1.6–2.2; mean: 2.0); (2) With primary endings, but not with secondary endings, the temperature sensitivity (imp s−1 °C−1) was larger during the dynamic phase than during the static phase of a stretch; (3) In primary endings, the fast and slow adaptive components occurring in the discharge frequency during the static phase of a stretch clearly increased with warming while in secondary endings, the slow decay was less affected, and the fast decay showed no change; (4) In relaxed spindles, the excitatory effect of warming was overlaid by a strong inhibitory effect as soon as the temperature exceeded about 30°C, resulting in an abrupt cessation of the background activity in most secondary endings, but not usually in primary endings. In general, warming induced an enhanced stretch sensitivity in both types of ending, and additionally an inhibitory effect that is obvious only in secondary endings of relaxed spindles. The different effects of temperature on the discharge frequency of primary and secondary afferents are assumed to be caused by different properties of their sensory membranes. 相似文献
133.
Air-ambulance services are extremely expensive to operate and maintain. The value of their existence has been questioned in this era of rationalization and downsizing. We examined the cost, safety, flight crew composition, types of trauma, and effectiveness of our air-ambulance program at the Children's Hospital of Eastern Ontario (CHEO) over a 3-year period, 1994-1997. During this time, 392 children were aeroevacuated to CHEO, 113 surgical (29%), 136 medical (35%), and 143 neonates (36%). Of the surgical cases, 43% were transferred for orthopaedic trauma, the commonest being fractured femur, 23% for general surgical cases, most common being thoracoabdominal trauma, and 22% for neurosurgical reasons, most commonly basilar skull fractures. The average response time (time from which the call was received to the time when the helicopter reached the patient site) for all of the cases was 46 min. The average travel time (time from departure of patient site to arrival at CHEO) for these same cases was 25.59 min. The air-ambulance program for children in the Ottawa-Carleton Eastern Ontario areas, was found to be safe, effective, and allowed earlier specialized medical care to be provided. 相似文献
134.
135.
目的: 研究1,25-二羟维生素D3 对结肠癌细胞系Caco-2 细胞中报告基因表达的作用,并探讨在报告载体pGL2 序列中存在潜在的抑制性维生素D应答元件(VDRE)的可能性。方法: 采用磷酸钙沉淀法将报告载体转染入Caco-2 细胞。Caco-2细胞经不同浓度1,25-二羟维生素D3 处理后测定细胞裂解液中表达的荧光素酶活性。结果: 应用pGL2 报告载体时,当用pSG5-VDR表达载体共转染后,1,25-二羟维生素D3显著地抑制Caco-2 细胞荧光素酶的表达(P< 0.05);而未使用该表达载体共转染则无抑制作用(P> 0.05)。应用pGL3 报告载体时,不同浓度的1,25-二羟维生素D3 对pLG3转染后Caco-2 细胞表达的荧光素酶活性均无显著抑制作用(P> 0.05),该作用不依赖是否存在有pSG5-VDR表达载体共转染。结论:1,25-二羟维生素D3 对报告载体PGL2 荧光素酶表达具有抑制作用,而对pGL3 则否;类似人类PTH基因中的潜在抑制性VDRE存在于报告载体pGL2,在pGL3 中该VDRE业已改变。 相似文献
136.
137.
138.
139.
Nonsurgical management of extradural hematomas in children 总被引:5,自引:0,他引:5
With the advent of computerized tomography (CT), an increasing number of patients with only minimal neurological symptoms and no signs of brain herniation are found to harbor subacute or chronic extradural hematomas (EH's). The authors present the cases of 11 symptomatic but neurologically normal children with medium to large EH's managed by close observation. These EH's were discovered 4 hours to 6 days after injury; three were in the posterior fossa, seven over the frontoparietal convexity, and one in the temporal fossa. These clots were followed by serial CT scans. Nine children recovered without surgery from 4 to 18 days after injury, and all had evidence on CT of spontaneous clot resorption. Of these nine EH's, five clots displayed volume expansion from 5 to 16 days after injury before final resorption occurred. Expansion correlated with persistence or increase in symptoms, whereas resorption correlated with improvement. Two patients showed gradual uncal herniation on Days 6 and 8, respectively, presumably during the "expansile phase" of their clots. Both had emergency craniotomy and recovered without morbidity. It is hypothesized that the resorption dynamics of the subacute or chronic EH are similar to that of the chronic subdural hematoma, with predictable volume changes, and the outcome of each lesion depends on the interplay between the patient's intracranial pressure buffering capacity and the rate of volume change. If subtle signs of brain dysfunction are adopted to signal the failure of conservative treatment and the need for craniotomy, these patients may be safely, and many successfully, managed without surgery. Factors that influence outcome of medical treatment include the size, location, configuration, and the rapidity of accumulation of the clot, the presence of associated intradural lesions, the extracranial decompression of blood through skull diastases, and the age of the patient. These factors, the criteria for patient selection, and the indications for immediate operative intervention are discussed. 相似文献
140.
Use of an anal sphincter pressure monitor during operations on the sacral spinal cord and nerve roots 总被引:1,自引:0,他引:1
The distinction of sacral roots and conus medullaris from lipoma, fibrous adhesions, and an abnormally thickened filum terminale can be difficult during operations on certain complicated dysraphic lesions. We describe a simple, noninvasive method of monitoring external anal sphincter "squeeze pressure" by means of an elongated, fluid-filled, polyethylene anal balloon connected to a pressure transducer. Cutaneous electrocardiographic (ECG) leads on both hips register the stimulus artifact from a monopolar nerve stimulator. The simultaneous display on the oscilloscope screen of the stimulus artifact and the resultant pressure response form an electromechanical coupling that allows the operator to identify a faulty stimulator probe and to distinguish true stimulus-induced external anal sphincter activity from spontaneous rhythmic contractions of the internal anal sphincter. Unilateral stimulation of the S-2, S-3, and S-4 roots generates tall pressure spikes between 40 and 75 torr in peak amplitudes, whereas S-1 and L-5 stimulation produces a stimulus artifact on the ECG but either no pressure response or a mere "ripple wave" of less than 7 torr. During operations on 11 patients with various dysraphic lesions, the S-2, S-3, and S-4 roots were identified easily and preserved, and the caudal extent of functioning neurons was localized within coni grossly distorted by intramedullary lipoma or chronic tethering. We prefer the anal sphincter pressure monitor to anal sphincter electromyography because of its simplicity, the inexpensive equipment, and its noise-free display that is virtually unaffected by other electronic systems in the operating room. 相似文献