全文获取类型
收费全文 | 19559篇 |
免费 | 1538篇 |
国内免费 | 391篇 |
专业分类
耳鼻咽喉 | 104篇 |
儿科学 | 605篇 |
妇产科学 | 331篇 |
基础医学 | 1604篇 |
口腔科学 | 543篇 |
临床医学 | 1724篇 |
内科学 | 2721篇 |
皮肤病学 | 194篇 |
神经病学 | 1524篇 |
特种医学 | 1412篇 |
外科学 | 1851篇 |
综合类 | 1569篇 |
现状与发展 | 1篇 |
一般理论 | 2篇 |
预防医学 | 3924篇 |
眼科学 | 215篇 |
药学 | 1433篇 |
4篇 | |
中国医学 | 244篇 |
肿瘤学 | 1483篇 |
出版年
2024年 | 46篇 |
2023年 | 292篇 |
2022年 | 445篇 |
2021年 | 586篇 |
2020年 | 687篇 |
2019年 | 678篇 |
2018年 | 596篇 |
2017年 | 638篇 |
2016年 | 669篇 |
2015年 | 593篇 |
2014年 | 1178篇 |
2013年 | 1366篇 |
2012年 | 1102篇 |
2011年 | 1218篇 |
2010年 | 908篇 |
2009年 | 922篇 |
2008年 | 889篇 |
2007年 | 990篇 |
2006年 | 862篇 |
2005年 | 852篇 |
2004年 | 776篇 |
2003年 | 713篇 |
2002年 | 538篇 |
2001年 | 434篇 |
2000年 | 364篇 |
1999年 | 318篇 |
1998年 | 292篇 |
1997年 | 232篇 |
1996年 | 196篇 |
1995年 | 230篇 |
1994年 | 220篇 |
1993年 | 188篇 |
1992年 | 225篇 |
1991年 | 178篇 |
1990年 | 122篇 |
1989年 | 111篇 |
1988年 | 127篇 |
1987年 | 85篇 |
1986年 | 77篇 |
1985年 | 111篇 |
1984年 | 73篇 |
1983年 | 53篇 |
1982年 | 65篇 |
1981年 | 51篇 |
1980年 | 43篇 |
1979年 | 26篇 |
1978年 | 39篇 |
1977年 | 31篇 |
1976年 | 15篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Nikolaos L. Kelekis Richard C. Semelka Paul L. Molina David M. Warshauer Tonya J. Sharp Frank C. Detterbeck 《Journal of magnetic resonance imaging : JMRI》1997,7(4):652-656
To assess the reproducibility and image quality of immediate postgadolinium chelate spoiled gradient-echo MRI in demonstrating disease of the abdominal aorta. All patients (27 patients: 21 men, 6 women) with substantial disease of the abdominal aorta, who underwent abdominal MR examinations at 1.5 T between 1991 and 1995, were entered in the study. Patients were referred for evaluation of suspected aortic disease (14 patients) or other abdominal diseases (13 patients). Three experienced investigators manually measured luminal and external aortic wall diameters and rated image quality, definition of inner and outer walls, extent of disease, and presence of other abdominal abnormalities, in an independent fashion. A cardiovascular surgeon then rated all studies to determine whether clinical management could be based on the MR findings alone. There was 98 to 99% agreement in measurements of luminal and external wall diameter between the three investigators. Overall image quality was rated as good in 77.8 to 88.9% of patients. A total of 31 additional nonaortic abdominal abnormalities were detected by all observers. The cardiovascular surgeon rated 25 of 27 studies as adequate to determine clinical management based on MR findings alone. Immediate postgadolinium spoiled gradient-echo MRI is a reproducible technique for the demonstration of abdominal aortic disease and possesses good image quality. Advantages of this technique include simultaneous evaluation of other nonvascular diseases of the abdomen, short examination time, and easy implementation as part of routine abdominal MRI scanning protocol. 相似文献
102.
P. A. Gevenois B. Stallenberg S. A. Sintzoff I. Salmon G. Van Rogemorter J. Struyven 《European radiology》1992,2(4):365-367
Granulomatous prostatitis is an uncommon disease that can prostatic carcinoma on both digital rectal examination and transrectal ultrasound. Four patients who underwent magnetic resonance imaging of the prostate had a histological diagnosis of graanulomatous prostatitis; three of them had recent urinary tract infections. The other patient had an associated midline prostatic cyst and a focus of malignancy. T1-and T2-weighted spin-echo images were obtained in all cases. Peripheral zone lesions of decreased signal intensity, suggestive of carcinoma,were found in all four patients on T2-weighted images. Granulomatous prostatitis should be considered in the differential diagnosis of low signal intensity areas with prostatic magnetic resonance imaging.
Correspondence to; P.A. Gevenois 相似文献
103.
Lisa Strohschein 《Family relations》2007,56(4):358-368
Abstract: The purpose of this paper is to determine whether divorced parents exhibit a diminished capacity to parent in the period following divorce. Using 2 waves of data from a national survey of Canadian children, the current study prospectively follows 5,004 children living in 2–biological parent households at initial interview and compares changes in parenting practices between households that subsequently divorce and those that remain intact. Results show that divorce is unrelated to changes in parenting behavior, suggesting that there are more similarities than differences in parenting among recently divorced and continuously married parents. 相似文献
104.
L. Portengen G. de Meer G. Doekes D. Heederik 《Clinical and experimental allergy》2004,34(8):1243-1250
BACKGROUND AND OBJECTIVES: We have previously reported that high rat urinary allergen (RUA) exposure was not associated with increased risk of rat allergy in long-term-exposed laboratory animal (LA) workers. We aimed to assess whether strong allergen-specific IgG4 responses could explain the absence of a dose response in these subjects. We investigated whether IgG4 was associated with allergen exposure and prevalence of sensitization or respiratory symptoms to rats. The longitudinal relation between IgG4 and rat allergy was studied using data obtained during 2 years of follow-up. METHODS: Five hundred and twenty-nine LA workers answered a questionnaire on respiratory symptoms and occupational history and participated in skin prick testing. Blood samples were analysed for specific IgG4 and IgE to RUA. Exposure to RUA was estimated based on personal air samples. The relation between IgG4 and newly occurring sensitization or rat allergy was studied in workers who were not sensitized or did not report respiratory symptoms to rats. RESULTS: IgG4 titres were higher in atopic than in non-atopic subjects, and increased with higher allergen exposure. Titres were highest in subjects who were sensitized and reported respiratory symptoms to rats when compared with those who were not (geometric mean [geometric standard deviation] = 202 [5.7] vs. 8.4 [18.3] AU). The association between IgG4 and sensitization or symptomatic rat allergy was independent of estimated allergen exposure. IgG4 was a strong predictor of newly occurring sensitization and symptomatic rat allergy during follow-up in atopic and rat-sensitized subjects. CONCLUSION: High exposure to RUA is associated with a strong allergen-specific IgG4 antibody response. High anti-RUA IgG4 is a strong predictor of prevalent and incident sensitization and symptomatic rat allergy in atopic and rat-sensitized subjects. IgG4 can therefore not explain the absence of a dose response between allergen exposure and allergy in long-term-exposed workers. We consider anti-RUA IgG4 to be a marker that combines aspects of exposure and susceptibility. 相似文献
105.
Quantitative cerebral blood flow (CBF) values can be obtained from dynamic susceptibility contrast (DSC) MR perfusion studies using the standard singular value decomposition (sSVD) deconvolution algorithm. Reports in the literature from simulation and in vivo studies suggest that CBF estimates obtained using sSVD deconvolution depend on the arterial-tissue delay (ATD). By contrast, Fourier transform (FT) deconvolution produces CBF estimates that are independent of ATD. The diagnostic reliability of quantitative CBF measurements to define areas of normal tissue flow and tissue at risk is brought into doubt by such gross sensitivity to the specifics of the deconvolution approach. This variation of CBF values with ATD is shown to be an artifact associated with the current implementation of the sSVD deconvolution algorithm. A reformulated version of the SVD deconvolution algorithm (rSVD) is presented and compared to the standard SVD algorithm through simulation and patient case studies. 相似文献
106.
The purpose of this study was to examine motor learning and retention given extensive practice in two fundamentally different movement sequences. One sequence was a memory-driven task (performing a series of whole body positions from memory) and the other a context-driven task (buttoning). Practice took place over 3 weeks, with performance measured weekly; retention was measured weekly for 3 weeks after practice. There were 7 people with Parkinson's disease (PD) and 7 age-matched neurologically healthy people who participated in this study. Both groups improved performance on both tasks with practice, with the majority of the change for the PD group occurring between 1 and 2 weeks of practice. Although those with PD did not necessarily perform as well as age-matched controls, they learned both sequences in a manner similar to age-matched controls, and exhibited retention across the 3-week retention interval. If people with PD are given sufficient practice they can learn and retain both memory-based and context-driven movement sequences as well as age-matched controls. The results provide support for maintaining physical activity and for intervention through movement therapy. 相似文献
107.
Y. F. He P. D. Ross J. W. Davis R. S. Epstein J. M. Vogel R. D. Wasnich 《Calcified tissue international》1994,55(4):243-248
We calculated how long to wait before repeating bone mineral density (BMD) measurements to reassess fracture risk. Correlation results from serial measurements of 495 postmenopausal Japanese-American women were used to estimate 95% confidence intervals (CI) for future BMD. After 7 years of follow-up, BMD correlations with the initial measurement ranged between 0.81 and 0.94, depending on age group and measurement site. In this analysis, the period between measurements was defined as the time required for the lower 95% CI to fall below the BMD value corresponding to doubling of fracture risk. Progressive bone loss causes fracture risk to double after 10 years, on average. However, the 95% CIs indicate that a second BMD measurement will detect risk doubling after only 2 or 3 years for some women. For untreated, early postmenopausal women, the period between measurements was approximately 2–5 years for the radius and 4–6 years for the calcaneus, depending on the initial BMD level. The period was approximately 1 year longer for women age 60 and older. Treatments that halve the bone loss rate would increase the period by 1–3 years. In the absence of a second measurement of BMD, the CI will continue to expand with time, corresponding to a wider range in risk between individuals, and a greater proportion of women will be at increased fracture risk. Obtaining a second BMD measurement pinpoints the patient's status within the precision of the measurement. We conclude that repeated BMD measurements will provide a more accurate estimate of fracture risk than a single, baseline measurement. 相似文献
108.
Fetal diagnosis has vastly improved over the last decade. Ultrasound has become the imaging modality of choice. As real-time
equipment has improved technologically, the ability to deduce subtle abnormalities has greatly increased.
The fetal genitourinary tract may be evaluated for renal dysplasias, anomalies, or obstruction. Points of obstruction and,
at times, the exact cause of obstruction may be deduced. Abnormalities of the ureter, bladder, urethra, scrotum, or reproductive
system can be detected. 相似文献
109.
The crystal structure of a tripeptide, tryptophanyl-glycyl-glycine dihydrate (C15H18N4O4·2H2O, molecular weight = 354) has been determined. The crystals are orthorhombic, space group P212121 with a= 7.875 (1) A,b= 9.009(1), c= 24.307(1) and Z = 4. The final R-index is 0.058 for 1488 reflections ((sin θ/λ≤ 0.6 A?1) with I < 2σ(I). The molecule exists as a zwitterion, with terminal NH+3 and COO? groups. The peptide units are trans and nearly perpendicular to the plane of the carboxyl group. The backbone torsion angles are: ψ1= 132.7°, ω1= 174.2°, φ2 88.2°, ψ= 8.6°, ω2 - 179.8°, φ= - 85.2°, ψ31, = - 178.1°, ψ32 5.0°. For the sidechain of tryptophan, χ1= - 171.6°, χ2 101.0°. 相似文献
110.
BACKGROUND: It is established that the A3 domain in von Willebrand factor (VWF) contains the major collagen-binding site. However, there are conflicting reports describing the capacity of the A1 domain to interact with collagen types I and III. METHODS: In this study, we have used recombinant VWF-A1 polypeptides, as well as conformation-specific monoclonal antibodies (mAb), to analyze the A1-collagen interaction. RESULTS: The A1 domain bound to collagen with K(d) approximately 8.0 nm and this binding was blocked by the mAb 6G1, which blocks the interaction between ristocetin and VWF. In addition, collagen-bound A1 protein was able to support flow-dependent adhesion of platelets, demonstrating that the binding sites for collagen and glycoprotein (GP)Ib are different. Analysis with two conformation-specific mAb demonstrated that the structure of the A1 domain changed as a result of the binding to collagen. In contrast, the antibodies failed to detect conformational change in the G1324S mutant (type 2M von Willebrand disease). Thus, direct binding to collagen induces a change in the structural conformation within the VWF-A1 domain, and the G1324S substitution prevents this conformational change. CONCLUSION: This study has shown that the isolated A1 domain can simultaneously bind to collagen and platelet GPIb, supporting platelet adhesion under high-flow conditions. In addition, this study has used mAb to demonstrate that the binding of the isolated A1 domain or full-length VWF to collagen is accompanied by a conformational change in A1 domain. 相似文献