全文获取类型
收费全文 | 6892篇 |
免费 | 324篇 |
国内免费 | 179篇 |
专业分类
耳鼻咽喉 | 51篇 |
儿科学 | 95篇 |
妇产科学 | 99篇 |
基础医学 | 1285篇 |
口腔科学 | 91篇 |
临床医学 | 955篇 |
内科学 | 810篇 |
皮肤病学 | 68篇 |
神经病学 | 369篇 |
特种医学 | 327篇 |
外科学 | 620篇 |
综合类 | 913篇 |
预防医学 | 442篇 |
眼科学 | 49篇 |
药学 | 535篇 |
中国医学 | 119篇 |
肿瘤学 | 567篇 |
出版年
2023年 | 26篇 |
2022年 | 80篇 |
2021年 | 145篇 |
2020年 | 110篇 |
2019年 | 107篇 |
2018年 | 125篇 |
2017年 | 153篇 |
2016年 | 142篇 |
2015年 | 156篇 |
2014年 | 318篇 |
2013年 | 393篇 |
2012年 | 339篇 |
2011年 | 433篇 |
2010年 | 331篇 |
2009年 | 341篇 |
2008年 | 348篇 |
2007年 | 391篇 |
2006年 | 330篇 |
2005年 | 325篇 |
2004年 | 270篇 |
2003年 | 280篇 |
2002年 | 229篇 |
2001年 | 219篇 |
2000年 | 194篇 |
1999年 | 182篇 |
1998年 | 148篇 |
1997年 | 164篇 |
1996年 | 140篇 |
1995年 | 141篇 |
1994年 | 125篇 |
1993年 | 76篇 |
1992年 | 73篇 |
1991年 | 55篇 |
1990年 | 56篇 |
1989年 | 48篇 |
1988年 | 33篇 |
1987年 | 32篇 |
1986年 | 28篇 |
1985年 | 43篇 |
1984年 | 29篇 |
1983年 | 24篇 |
1982年 | 36篇 |
1981年 | 24篇 |
1980年 | 20篇 |
1979年 | 12篇 |
1975年 | 10篇 |
1974年 | 8篇 |
1973年 | 27篇 |
1972年 | 16篇 |
1971年 | 19篇 |
排序方式: 共有7395条查询结果,搜索用时 234 毫秒
81.
Physics-Driven CFD Modeling of Complex Anatomical Cardiovascular Flows—A TCPC Case Study 总被引:5,自引:0,他引:5
Pekkan K de Zélicourt D Ge L Sotiropoulos F Frakes D Fogel MA Yoganathan AP 《Annals of biomedical engineering》2005,33(3):284-300
Recent developments in medical image acquisition combined with the latest advancements in numerical methods for solving the Navier-Stokes equations have created unprecedented opportunities for developing simple and reliable computational fluid dynamics (CFD) tools for meeting patient-specific surgical planning objectives. However, for CFD to reach its full potential and gain the trust and confidence of medical practitioners, physics-driven numerical modeling is required. This study reports on the experience gained from an ongoing integrated CFD modeling effort aimed at developing an advanced numerical simulation tool capable of accurately predicting flow characteristics in an anatomically correct total cavopulmonary connection (TCPC). An anatomical intra-atrial TCPC model is reconstructed from a stack of magnetic resonance (MR) images acquired in vivo. An exact replica of the computational geometry was built using transparent rapid prototyping. Following the same approach as in earlier studies on idealized models, flow structures, pressure drops, and energy losses were assessed both numerically and experimentally, then compared. Numerical studies were performed with both a first-order accurate commercial software and a recently developed, second-order accurate, in-house flow solver. The commercial CFD model could, with reasonable accuracy, capture global flow quantities of interest such as control volume power losses and pressure drops and time-averaged flow patterns. However, for steady inflow conditions, both flow visualization experiments and particle image velocimetry (PIV) measurements revealed unsteady, complex, and highly 3D flow structures, which could not be captured by this numerical model with the available computational resources and additional modeling efforts that are described. Preliminary time-accurate computations with the in-house flow solver were shown to capture for the first time these complex flow features and yielded solutions in good agreement with the experimental observations. Flow fields obtained were similar for the studied total cardiac output range (1–3 l/min); however hydrodynamic power loss increased dramatically with increasing cardiac output, suggesting significant energy demand at exercise conditions. The simulation of cardiovascular flows poses a formidable challenge to even the most advanced CFD tools currently available. A successful prediction requires a two-pronged, physics-based approach, which integrates high-resolution CFD tools and high-resolution laboratory measurements. 相似文献
82.
Joanne Hopmeyer Erika Whitney Dana A. Papp Manisha S. Navathe Robert A. Levine Young H. Kim Ajit P. Yoganathan 《Annals of biomedical engineering》1996,24(5):561-572
Mitral regurgitation results from the incomplete closure of the mitral valve, and the noninvasive diagnosis of this disease
remains an important clinical goal. In this study, steady flow computer simulations were used to evaluate flow convergence
method for flow rate estimation. The hemispheric and hemielliptic formulae were compared for accuracy in the presence of complicating
factors such, as ventricular confinement, orifice shape, and aortic outflow. Results showed that in the absence of aortic
outflow and ventricular confinement, there was a plateau zone where the hemispheric formula approximated the true flow rate,
independent of orifice shape. However, in the presence of complicating factors such as aortic outflow and ventricular confinement,
there was no clear zone where the hemispheric formula could be applied. The hemielliptic formula, however, worked in, all
cases, regardless of chamber size or magnitude of aortic outflow. Therefore, application of the hemielliptic formula shold
be considered in future clinical studies. 相似文献
83.
In the search for a serology tool for the diagnosis of nonpatent as well as patent infections with Oesophagostomum dentatum in pigs a water-soluble, unglycosilated antigen of about 30 kDa specific for the third-stage larvae of the parasite was purified
by ion-exchange chromatography. In Western blots, the antigen was first detected by antibodies at day 7 postinfection. Cross-reactivity
with O. quadrispinulatum, Ascaris suum, or Trichuris suis was not detected. It is suggested that this protein is a suitable tool for the species-specific serodiagnosis of O. dentatum infection in pigs.
Received: 15 June 1998 / Accepted: 28 September 1998 相似文献
84.
目的:通过分析槲皮素对淋巴细胞早期活化标记物CD69表达的影响,探讨其对T淋巴细胞体外活化抑制作用的机制。方法:分离小鼠淋巴结细胞,加入多克隆刺激剂及槲皮素共同培养,分别于2、6、24h收获细胞,进行双色免疫荧光标记,以流式细胞仪对T细胞的CD69分子表达情况进行分析并计算抑制率。结果:槲皮素(终浓度10μmol/L)对未受刺激的T细胞CD69表达百分率无明显影响,而经佛波醇酯(PDB)及刀豆蛋白A(ConA)活化同时加入槲皮素的T细胞CD69表达百分率在2h、6h及24h均显著下降(P<0.01)。槲皮素对PDB的抑制率随作用时间延长而明显下降,对ConA的抑制率平缓而持久。结论:槲皮素对PDB、ConA活化的T淋巴细胞均显示明显的抑制效应,表明该药可能作用于T细胞活化信号传递通路蛋白激酶Cθ或其下游部位,并且,这种抑制效应表现出一定的可逆性。 相似文献
85.
L. J. Gardner J. M. Polski R. Fallon C. H. Dunphy 《Virchows Archiv : an international journal of pathology》1998,433(1):35-40
CD56 and CD57 are commonly considered as natural killer and neuroectodermal markers, but their expression has been identified
in a wide spectrum of neoplasms including some cases of Ewing’s sarcoma (ES) and primitive neuroectodermal tumor (PNET). We
report two cases of small, round blue cell tumor (SRBCT), in which flow cytometry immunophenotyping (FCI) detected strong
expression of CD56 and CD57 (one case). Immunohistochemical staining with Leu-19 and Leu-7 confirmed the FI results. Although
CD56 and CD57 expression is consistent with ES/PNET, it can be potentially misleading if results of FCI are interpreted in
the absence of other findings. These cases suggest the utility of FCI in undifferentiated SRBCT. The literature on CD56 and
CD57 expression in ES/PNET is reviewed and discussed.
Received: 5 January 1998 / Accepted: 19 February 1998 相似文献
86.
Purification of bovine conglutinin using pepsin digestion 总被引:6,自引:0,他引:6
This paper describes a new method for the purification of bovine conglutinin based on the relative resistance of this protein to pepsin digestion. First, conglutinin is purified by absorption on yeast, then the preparation is treated with 2% pepsin (w/w) at 4°C for 18 hr, and finally gel filtrated on agarose A5m. The yield is 60–75% and conglutinin thus prepared appears physically, immunochemically and functionally intact. This procedure allows for a rapid production of sufficient amounts of conglutinin for immune complex detection or purification methods. 相似文献
87.
Purification of biologically active rubella virus antigens by immunoaffinity chromatography 总被引:1,自引:0,他引:1
A general procedure for isolating biologically active rubella virus antigens (VPI, Mr = 61,000; VP2, Mr = 45,000; VP3, Mr = 36,000) by monoclonal antibody affinity chromatography is described. Complexes formed between monoclonal antibodies and rubella virus antigens were found to be stable either at low pH or in Tris buffer containing detergent and high salt, but were efficiently dissociated by 5% diethanolamine, pH 11.5, or 50 mM lithium diiodosalicylate buffer, pH 8.0. Chromatographically purified rubella viral antigens retained their antigenicity as determined by enzyme-linked immunosorbent assays. Biological studies showed that rubella structural proteins VP2 and VP3 had no hemagglutinin function while the mixture of VP1 and VP2 and VP3 directly demonstrated hemagglutination activity. These results indicate that VP1 is at least in part responsible for the hemagglutinin function of rubella virus. 相似文献
88.
The structuring of an allergy index based on IgE-mediated skin sensitivity to common environmental allergens 总被引:1,自引:0,他引:1
L R Freidhoff D G Marsh D A Meyers R Hussain 《The Journal of allergy and clinical immunology》1983,72(3):274-287
We computed skin-test sensitivity levels in 485 adults puncture-tested with eight standardized, high-quality inhalant allergens tested at single concentrations. In order to quantitate the "average" IgE-mediated skin sensitivity of each subject, we used both nonparametric and parametric statistical methods to generate two "allergy indices" (Allergy Index I and Allergy Index II) based on sensitivity end-point data from the subpopulations of individuals positive to six of the eight allergens. For the 192 skin test-positive subjects, Allergy Index I and Allergy Index II were significantly correlated with each other (rs = 0.98, p less than 0.001) and with the number of positive skin-test reactions (rs congruent to 0.9, p less than 0.001) as well as with log[total serum IgE] (r congruent to 0.4, p less than 0.01). In 102 ragweed-positive subjects, log[specific IgE to ragweed] was significantly correlated with ragweed-specific "ragweed indices I and II" (r congruent to 0.6, p less than 0.01). Furthermore, the average daily symptom scores reported by 14 ragweed-positive subjects during the ragweed pollination season were significantly correlated with ragweed indices I and II (p less than 0.05). We propose the use of Allergy Index II in epidemiologic and genetic studies of allergic phenotypes as well as in clinical decisions for diagnosis and immunotherapeutic intervention. 相似文献
89.
D. W. Suobank A. P. Yoganathan E. C. Harrison W. H. Corcoran 《Medical & biological engineering & computing》1984,22(1):40-47
A comparative study was made of the sounds produced by a normal Starr-Edwards 2400 aortic valve prosthesis with those produced
by the same valve but having a simulated overgrowth at the apex of the struts. Comparisons were made over the entire cardiac
cycle for time and amplitude, power-density spectra, power-distribution spectra, power-distribution surfaces associated with
individual valves, and three-dimensional power-distribution-difference surface. Power-density spectra were compared for portions
of the cycle corresponding to the opening, systolic, and closing sounds of the valve. Physical parameters of an acoustical
model were estimated from the power-density spectra. The results showed that each comparison gave information pertinent to
the simulated malfunction. Opening. systolic and closing sounds, respectively, were different for each valve. The opening
sound of the abnormal valve displayed a much lower frequency. Systolic sounds for the two valves were similar in frequency,
but the normal valve produced more total power for this sound. The closing sound of the abnormal valve occurred later than
that of the normal valve. These differences were more clearly seen when viewed in the frequency domain. 相似文献
90.
Salganik MP Hardie DL Swart B Dandie GW Zola H Shaw S Shapiro H Tinckam K Milford EL Wand MP 《Journal of immunological methods》2005,305(1):67-74
The blind panel collected for the 8th Human Leucocyte Differentiation Antigens Workshop (HLDA8; ) included 49 antibodies of known CD specificities and 76 antibodies of unknown specificity. We have identified groups of antibodies showing similar patterns of reactivity that need to be investigated by biochemical methods to evaluate whether the antibodies within these groups are reacting with the same molecule. Our approach to data analysis was based on the work of Salganik et al. (in press) [Salganik, M.P., Milford E.L., Hardie D.L., Shaw, S., Wand, M.P., in press. Classifying antibodies using flow cytometry data: class prediction and class discovery. Biometrical Journal]. 相似文献