全文获取类型
收费全文 | 329653篇 |
免费 | 11760篇 |
国内免费 | 627篇 |
专业分类
耳鼻咽喉 | 2861篇 |
儿科学 | 10412篇 |
妇产科学 | 5579篇 |
基础医学 | 37049篇 |
口腔科学 | 4956篇 |
临床医学 | 27426篇 |
内科学 | 63491篇 |
皮肤病学 | 3895篇 |
神经病学 | 30666篇 |
特种医学 | 15609篇 |
外国民族医学 | 14篇 |
外科学 | 53328篇 |
综合类 | 4251篇 |
一般理论 | 109篇 |
预防医学 | 29430篇 |
眼科学 | 5989篇 |
药学 | 19352篇 |
中国医学 | 861篇 |
肿瘤学 | 26762篇 |
出版年
2023年 | 894篇 |
2022年 | 1490篇 |
2021年 | 3404篇 |
2020年 | 2103篇 |
2019年 | 3164篇 |
2018年 | 25061篇 |
2017年 | 19754篇 |
2016年 | 22164篇 |
2015年 | 4460篇 |
2014年 | 5862篇 |
2013年 | 7597篇 |
2012年 | 17093篇 |
2011年 | 31404篇 |
2010年 | 24612篇 |
2009年 | 17165篇 |
2008年 | 28686篇 |
2007年 | 31286篇 |
2006年 | 10580篇 |
2005年 | 12191篇 |
2004年 | 12571篇 |
2003年 | 12792篇 |
2002年 | 10640篇 |
2001年 | 2415篇 |
2000年 | 2252篇 |
1999年 | 2304篇 |
1998年 | 2128篇 |
1997年 | 1756篇 |
1996年 | 1423篇 |
1995年 | 1354篇 |
1994年 | 1228篇 |
1993年 | 1080篇 |
1992年 | 1353篇 |
1991年 | 1290篇 |
1990年 | 1192篇 |
1989年 | 1079篇 |
1988年 | 981篇 |
1987年 | 958篇 |
1986年 | 932篇 |
1985年 | 913篇 |
1984年 | 951篇 |
1983年 | 830篇 |
1982年 | 990篇 |
1981年 | 876篇 |
1980年 | 774篇 |
1979年 | 673篇 |
1978年 | 661篇 |
1977年 | 538篇 |
1976年 | 525篇 |
1974年 | 538篇 |
1973年 | 457篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Joanne R. Less Mitchel C. Posner Thomas C. Skalak Norman Wolmark Rakesh K. Jain 《Microcirculation (New York, N.Y. : 1994)》1997,4(1):25-33
Objective : To measure the geometric resistance to blood flow in human colorectal carcinoma. Although tumor blood flow is of central importance in both the detection and the treatment of cancer, the determinants of blood flow through the neoplastic circulation are poorly understood. Methods : Human colorectal carcinomas (tissue weight = 272 g ± 43 g (SD), n = 6) were perfused ex vivo with a buffered physiological salt solution of known viscosity at flow rates ranging from 2.5 to 40 ml/min and perfusion pressures from 8 to 100 mm Hg. The geometric resistance was determined from the slope of the pressure-flow curve. For examination of the principal determinant of geometric resistance, the vascular architecture, one of the tumors was perfused with Batson's No. 17 polymer and macerated in KOH to produce a positive vascular cast that was used for measurement of vascular branching patterns and dimensions. Results : The pressure-flow relationship was linear at perfusion pressures above 40 mm Hg, and the geometric resistance, z0, was constant at approximately 6.5 ± 109g/cm3. Below 40 mm Hg, z0 increased rapidly. The architecture of the arteriolar and capillary networks of human colorectal carcinoma is similar to those of experimental rodent tumors. Capillaries in planar and nonplanar mesh-works had mean segment diameters of 11 ± 2 and 9.6 ± 2 μm, lengths of 46 ± 24 and 107 ± 40 μm, and intercapillary distances of 46 ± 13 and 74 ± 24 μm, respectively. Conclusions : The geometric flow resistance in neoplastic tissue is 1–2 orders of magnitude higher than that observed in normal tissues. A decrease in functional vascular cross-sectional area may explain the additional increase in resistance at small perfusion pressures. The observed flow resistance may be due to the specialized arteriolar and capillary network architecture, pressures exerted by proliferating cancer cells, and/or coupling between vascular and extravascular flow. These observations demonstrate that tumor vascularity alone may not be indicative of flow resistance or tumor susceptibility to blood-borne therapeutic agents. 相似文献
992.
993.
Margret S. Magid Wallace G. Campbell Jr MD Sutini Ngadiman Thomas A. Godwin MD Robert Ward 《Fetal and pediatric pathology》1997,17(2):303-314
We report a case of an infantile myofibromatosis with hemangiopericytoma-like features arising in the tongue of a 5-month-old female infant. Many authors now classify neoplasms as infantile myofibromatosis that were previously called infantile hemangiopericytoma. The ultrastructural features of our tumor illustrate its biphasic nature and provide a possible explanation for its histogenesis. Infantile myofibromatosis, including those diagnosed as infantile hemangiopericytomas, rarely arise in any intraoral location. Despite the generally good prognosis associated with these neoplasms, complete surgical excision is recommended to avoid recurrences. 相似文献
994.
995.
Yuji Miyamoto Robert L. Kormos Harvey S. Borovetz Thomas Gaisor John M. Pristas John M. Armitage Robert L. Hardesty Bartley P. Griffith 《Artificial organs》1990,14(6):454-457
The interrelationships between hemodynamic variables including right ventricular (RV) performance with filling/ejection dynamics of the Novacor left ventricular assist system (LVAS) were determined in 10 of 11 patients who received LVAS as a bridge to heart transplant. Nine were successfully transplanted. Data were obtained intraoperatively, at periodic intervals up to 48 h postimplant and at explant. The hypotheses investigated included (a) RV performance influences LVAS filling characteristics and (b) LVAS pump output is influenced by systemic vascular resistance (SVR). During the period of LVAS support (2-126 days), pumping characteristics included a mean filling volume of 51 ml (range, 24-70), residual volume of 4.9 ml (range, 1-18), pump rate of 113/min (range, 63-175), and pump output of 5.81/min (range, 2.8-8.2). Multiple regression analysis identified pulmonary vascular resistance (PVR), RV stroke work index (RVSWI), and pulmonary capillary wedge pressure, but not RV ejection fraction, pulmonary artery pressure, or central venous pressure (CVP) as the most important correlates with LVAS filling volume (p less than 0.001, R2 = 0.6). In addition, LVAS pump output was influenced mainly by RVSWI, PVR, and SVR (p less than 0.001, R2 = 0.7). It was concluded that LVAS performance is highly dependent on RV function and systemic/pulmonary vascular resistances. 相似文献
996.
997.
Rita Shiang Stephen G. Ryan Ya-Zhen Zhu Thomas J. Fielder Richard J. Allen Alan Fryer Sumimasa Yamashita Peter O'Connell John J. Wasmuth 《Annals of neurology》1995,38(1):85-91
Hyperekplexia is a rare, autosomal dominant neurological disorder characterized by hypertonia, especially in infancy, and by an exaggerated startle response. This disorder is caused by mutations in the ?1 subunit of the inhibitory glycine receptor (GLRA1). We previously reported two GLRA1 point mutations detected in 4 unrelated hyperekplexia families; both mutations were at nucleotide 1192 and resulted in the replacement of Arg271 by a glutamine (R271Q) in one case and a leucine (R271L) in the other. Here, 5 additional hyperekplexia families are shown to have the most common G-to-A transition mutation at nucleotide 1192. Haplotype analysis using polymorphisms within and close to the GLRA1 locus suggests that this mutation has arisen at least twice (and possibly four times). In 2 additional families, a third mutation is also presented that changes a tyrosine at amino acid 279 to a cysteine (Y279C). Five patients with atypical clinical features and equivocal or absent family history of hyperekplexia and 1 patient with a classical presentation but no family history are presented in whom a mutation in the GLRA1 gene was not detected. Thus, only clinically typical hyperekplexia appears to be consistently associated with GLRA1 mutations, and these affect a specific extracellular domain of the protein. 相似文献
998.
999.
1000.
We created a microcomputer-based system that uses characteristics of the patient at admission to predict death within 30 days of hospital admission for Medicare patients with stroke, pneumonia, myocardial infarction, and congestive heart failure. These conditions account for 13% of discharges and 31% of 30-day mortality for Medicare patients over 64 years of age. The system was calibrated on a stratified, random sample of 5888 discharges (about 1470 for each condition) from seven states, with stratification by hospital type to make the sample nationally representative. The predictors must be specially abstracted from the medical record. The cross-validated R2 for predictions is 0.14 to 0.25, which is better than the values for other systems for which we have data. Risk-adjusted predicted group mortality rates may be useful in interpreting information on unadjusted mortality rates, and patient-specific predictions may be useful in identifying unexpected deaths for clinical review. 相似文献