全文获取类型
收费全文 | 11421篇 |
免费 | 1246篇 |
国内免费 | 789篇 |
专业分类
耳鼻咽喉 | 82篇 |
儿科学 | 108篇 |
妇产科学 | 152篇 |
基础医学 | 1393篇 |
口腔科学 | 238篇 |
临床医学 | 1591篇 |
内科学 | 1676篇 |
皮肤病学 | 88篇 |
神经病学 | 670篇 |
特种医学 | 494篇 |
外国民族医学 | 7篇 |
外科学 | 1077篇 |
综合类 | 2043篇 |
现状与发展 | 3篇 |
一般理论 | 1篇 |
预防医学 | 756篇 |
眼科学 | 300篇 |
药学 | 1235篇 |
23篇 | |
中国医学 | 711篇 |
肿瘤学 | 808篇 |
出版年
2024年 | 39篇 |
2023年 | 194篇 |
2022年 | 551篇 |
2021年 | 642篇 |
2020年 | 528篇 |
2019年 | 428篇 |
2018年 | 464篇 |
2017年 | 441篇 |
2016年 | 360篇 |
2015年 | 567篇 |
2014年 | 643篇 |
2013年 | 518篇 |
2012年 | 834篇 |
2011年 | 911篇 |
2010年 | 563篇 |
2009年 | 448篇 |
2008年 | 551篇 |
2007年 | 575篇 |
2006年 | 553篇 |
2005年 | 590篇 |
2004年 | 394篇 |
2003年 | 321篇 |
2002年 | 320篇 |
2001年 | 258篇 |
2000年 | 270篇 |
1999年 | 317篇 |
1998年 | 179篇 |
1997年 | 173篇 |
1996年 | 130篇 |
1995年 | 101篇 |
1994年 | 114篇 |
1993年 | 44篇 |
1992年 | 71篇 |
1991年 | 70篇 |
1990年 | 73篇 |
1989年 | 55篇 |
1988年 | 38篇 |
1987年 | 26篇 |
1986年 | 32篇 |
1985年 | 31篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1979年 | 4篇 |
1942年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
在动态模拟体液中致密CaP陶瓷表面形貌对类骨磷灰石层形成的影响研究 总被引:7,自引:2,他引:7
磷酸钙陶瓷植入体内后其表面类骨磷灰石层的形成是诱导成骨的先决条件。本实验在模拟体液 (Simu-lated body fluid,SBF)以人体骨骼肌组织的正常生理流率 (2 ml/ 10 0 m l· min)下 ,研究在动态 SBF中致密磷酸钙陶瓷表面形貌对类骨磷灰石层形成的影响。结果表明 :在生理流速条件下 ,材料的粗糙表面有利于类骨磷灰石层的形成 ,加大 SBF中 Ca2 +、HPO4 2 -离子浓度 ,类骨磷灰石层的形成速度加快。本研究进一步证实了材料的几何形貌对类骨磷灰石形成的影响 ,加深了对磷酸钙陶瓷在体内诱导成骨机理的理解 相似文献
92.
Zheng B Cao KY Chan CP Choi JW Leung W Leung M Duan ZH Gao Y Wang M Di B Hollidt JM Bergmann A Lehmann M Renneberg I Tam JS Chan PK Cautherley GW Fuchs D Renneberg R 《Clinical immunology (Orlando, Fla.)》2005,116(1):18-26
Neopterin and C-reactive protein (CRP) concentrations were determined in serum samples from 129 severe acute respiratory syndrome (SARS) patients and 156 healthy blood donors. In the patients with confirmed SARS, an early neopterin elevation was detected already at the day of onset of symptoms and rose to a maximum level of 45.0 nmol/L 3 days after the onset. All SARS patients had elevated neopterin concentrations (>10 nmol/L) within 9 days after the onset. The mean neopterin concentrations were 34.2 nmol/L in acute sera of SARS patients, 5.1 nmol/L in convalescent sera, and 6.7 nmol/L in healthy controls. In contrast, the mean CRP concentrations in both acute and convalescent sera of SARS patients were in the normal range (<10 mg/L). Serum neopterin level in SARS patients was associated with fever period and thus the clinical progression of the disease, while there was no significant correlation between the CRP level and the fever period. Serum neopterin may allow early assessment of the severity of SARS. The decrease of neopterin level was found after steroid treatment, which indicates that blood samples should be collected before steroid treatment for the neopterin measurement. 相似文献
93.
结直肠癌淋巴管生成的特点及其临床病理意义 总被引:24,自引:1,他引:24
目的探讨结直肠癌中淋巴管的分布特点、增殖状态及其与转移和预后的关系。方法采用淋巴管特异标记podoplanin对96例结直肠癌及其相应正常组织进行免疫组织化学染色检测微淋巴管密度,以CD34标记血管检测微血管密度作为对比,并分别与Ki-67进行双标免疫组织化学染色检测淋巴管和血管增殖活性,结合结直肠癌临床病理参数和预后分析。结果结直肠癌中心及浅表部淋巴管多为闭锁的条索状,边缘区淋巴管多呈管样扩张状。结直肠癌边缘区淋巴管密度(51.2±25.5)及较正常结直肠组织(29.4±9.0)和肿瘤其他区域显著性增高(P<0.01),并且其淋巴管内皮Ki67指数(0.23±0.17)也较其他区域显著性增高(P<0.05)。结直肠癌边缘区微淋巴管密度与淋巴管受累、淋巴结转移、远处器官转移及预后密切相关(P<0.01或P<0.05)。结论结直肠癌组织中存在新生淋巴管,且主要分布于肿瘤边缘区,癌周围淋巴管密度增加与癌细胞转移相关,结直肠癌边缘区微淋巴管密度测定对评估其淋巴结转移和预后判断可能具有意义。 相似文献
94.
Carcinoma of the cervix is typically treated with a combination of intracavitary brachytherapy and external beam radiation. The external beam dose is delivered with whole pelvis fields followed by split fields that protect midline organs at risk (bladder and rectum) while treating the parametria. Three approaches have been developed to shield midline structures: a simple rectangular block, a block customized to a single brachytherapy isodose line, and a step wedge filter constructed to conform to multiple brachytherapy isodose lines. A customized step wedge filter has the potential to produce a more homogeneous dose distribution but has not achieved widespread use due to labor intensive construction. We have developed a simple, novel method to produce a custom midline step wedge using dynamic multileaf collimation (dMLC). A comparison of film measurements in a phantom with the dose calculated by a commercial treatment planning system demonstrated agreement within 3% or 3 mm. The technique requires delivery times comparable to conventional techniques. 相似文献
95.
Shen S Duan J Fiveash JB Brezovich IA Plant BA Spencer SA Popple RA Pareek PN Bonner JA 《Medical physics》2003,30(12):3196-3205
The capability of a commercial respiratory gating system based on video tracking of reflective markers to reduce motion-induced CT planning and treatment errors was evaluated. Spherical plastic shells (2.8-82 cm3), simulating the gross target volume (GTV), were placed in a water-filled body phantom that was moved sinusoidally along the longitudinal axis of the CT scanner and the accelerator for +/- 1 cm at 15-30 cycle/min. During gated CT imaging, the x-ray exposure was initiated by the gating system shortly before the end of expiration (so that the imaging time would be centered at the end of expiration); it was terminated by the scanner after completion of each slice. In nongated CT images, the target appeared distorted and often broken up. GTVs volume errors ranged 16%-110% in axial scans, and 7%-36% in spiral scans. In gated CT images, the spheres appeared 3 and 5 mm longer than their actual diameters (volume errors 2%-16%), at the respective respiration rates of 15 and 20 cycles/min. At 30 cycles/min the target appeared 1 cm longer, and volume error ranged 25%-53%. During treatment, gating kept the beam on for a duration equal to the CT acquisition time of 1 s/slice. The difference in positional errors between gated CT and portal films was 1 mm, regardless the size of residual motion errors. Because of the potential of suboptimal placement of the gating window between CT imaging and treatment, an extra 1.5-2.5 mm safety margin can be added regardless of the size of residual motion error. For respiratory rates > or = 30 cycles/min, the effectiveness of gating is limited by large residual motion in the 1 s CT acquisition time. 相似文献
96.
97.
Dosimetric effect of respiration-gated beam on IMRT delivery 总被引:3,自引:0,他引:3
Intensity modulated radiation therapy (IMRT) with a dynamic multileaf collimator (DMLC) requires synchronization of DMLC leaf motion with dose delivery. A delay in DMLC communication is known to cause leaf lag and lead to dosimetric errors. The errors may be exacerbated by gated operation. The purpose of this study was to investigate the effect of leaf lag on the accuracy of doses delivered in gated IMRT. We first determined the effective leaf delay time by measuring the dose in a stationary phantom delivered by wedge-shaped fields. The wedge fields were generated by a DMLC at various dose rates. The so determined delay varied from 88.3 to 90.5 ms. The dosimetric effect of this delay on gated IMRT was studied by delivering wedge-shaped and clinical IMRT fields to moving and stationary phantoms at dose rates ranging from 100 to 600 MU/min, with and without gating. Respiratory motion was simulated by a linear sinusoidal motion of the phantom. An ionization chamber and films were employed for absolute dose and 2-D dose distribution measurements. Discrepancies between gated and nongated delivery to the stationary phantom were observed in both absolute dose and 2-D dose distribution measurements. These discrepancies increased monotonically with dose rate and frequency of beam interruptions, and could reach 3.7% of the total dose delivered to a 0.6 cm3 ion chamber. Isodose lines could be shifted by as much as 3 mm. The results are consistent with the explanation that beam hold-offs in gated delivery allowed the lagging leaves to catch up with the delivered monitor units each time that the beam was interrupted. Low dose rates, slow leaf speeds and low frequencies of beam interruptions reduce the effect of this delay-and-catch-up cycle. For gated IMRT it is therefore important to find a good balance between the conflicting requirements of rapid dose delivery and delivery accuracy. 相似文献
98.
大鼠实验性心肌梗塞时血浆蛋白C,纤溶活性变化及人参皂甙作用的研究 总被引:6,自引:0,他引:6
通过观察实验性大鼠急性心肌梗塞(AMI)时血浆蛋白C(PC)活性和组织型纤溶酶原激活剂(t-PA)及纤溶酶原激活剂的特异性抑制因子(PAI)活性的变化,初步探讨了心肌缺血时PC活性变化与纤溶系统的关系以及人参皂甙对其变化的影响。结果表明,1.AMI时血浆PC活性显著低于正常对照组,且与缺血程度呈负相关。2.AMI时t-PA活性降低,PAI活性增高。3.人参皂甙可提高AMI时血浆PC活性,降低PAI 相似文献
99.
目的: 观察兔股动脉粥样硬化斑块发展过程中斑块内组织因子(TF)及组织因子途经抑制物-1(TFPI-1)、组织因子途经抑制物-2(TFPI-2)的变化。方法: 新西兰雄兔通过高脂饲养合并股动脉球囊损伤建立动脉粥样硬化斑块模型。在建模8周、10周和12周,分别截取球囊损伤处股动脉标本,检测斑块组织内TF、TFPI-1和TFPI-2的蛋白表达;并测定斑块内TF、TFPI-1和TFPI-2的mRNA水平。结果: 自8周、10周到12周,血管斑块中TF、TFPI-1和TFPI-2的观测区域内阳性染色面积均逐渐增加。自8周、10周到12周,血管斑块中TF的mRNA水平和TFPI-1的mRNA水平均逐渐增加;TFPI-2mRNA表现为前期无明显变化,12周时显著下调。结论: 在兔股动脉粥样硬化斑块的形成过程中,随着斑块内TF基因及蛋白表达的增加,TFPI-1和TFPI-2反应性表达增加,但其表达水平未能完全抑制斑块的进展。 相似文献
100.
芦荟大黄素对豚鼠皮肤黑色素细胞NOS的影响--免疫组织化学研究 总被引:2,自引:0,他引:2
目的探讨豚鼠皮肤黑色素细胞在大黄有效成分的作用下,一氧化氮合酶(Nitric OxideSynthse;NOS)表达的变化,阐明大黄在活体皮肤中对黑素细胞的有效作用浓度和作用机制.方法将21只雄性豚鼠随机分成对照组及5个实验组,用芦荟大黄素5种浓度对局部皮肤皮下注射处理,48小时后取材,免疫组织化学方法(SABC)法显示NOS的表达,用光学显微镜和图象分析仪对结果进行统计分析.结果芦荟大黄素作用下,表皮黑素细胞NOS表达明显减少,光密度明显下降(P<0.05);不同浓度药物作用之间无显着差异(P>0.05),加注侧与未加注侧之间无显著差异.结论芦荟大黄素对黑色素细胞NOS的表达具有调节作用,提示大黄对黑素细胞的调节是经NO信号介导途径,为大黄的临床应用提供实验依据. 相似文献