全文获取类型
收费全文 | 4414篇 |
免费 | 294篇 |
国内免费 | 337篇 |
专业分类
耳鼻咽喉 | 3篇 |
儿科学 | 18篇 |
妇产科学 | 8篇 |
基础医学 | 91篇 |
口腔科学 | 20篇 |
临床医学 | 190篇 |
内科学 | 198篇 |
皮肤病学 | 5篇 |
神经病学 | 41篇 |
特种医学 | 117篇 |
外科学 | 102篇 |
综合类 | 955篇 |
预防医学 | 261篇 |
眼科学 | 13篇 |
药学 | 1272篇 |
3篇 | |
中国医学 | 1727篇 |
肿瘤学 | 21篇 |
出版年
2024年 | 12篇 |
2023年 | 50篇 |
2022年 | 95篇 |
2021年 | 90篇 |
2020年 | 93篇 |
2019年 | 74篇 |
2018年 | 72篇 |
2017年 | 119篇 |
2016年 | 119篇 |
2015年 | 140篇 |
2014年 | 306篇 |
2013年 | 389篇 |
2012年 | 502篇 |
2011年 | 479篇 |
2010年 | 341篇 |
2009年 | 247篇 |
2008年 | 236篇 |
2007年 | 269篇 |
2006年 | 247篇 |
2005年 | 206篇 |
2004年 | 157篇 |
2003年 | 122篇 |
2002年 | 96篇 |
2001年 | 100篇 |
2000年 | 71篇 |
1999年 | 58篇 |
1998年 | 40篇 |
1997年 | 51篇 |
1996年 | 32篇 |
1995年 | 26篇 |
1994年 | 24篇 |
1993年 | 17篇 |
1992年 | 35篇 |
1991年 | 29篇 |
1990年 | 15篇 |
1989年 | 22篇 |
1988年 | 16篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有5045条查询结果,搜索用时 15 毫秒
1.
A method is presented for 3D MRI in an extended field of view (FOV) based on continuous motion of the patient table and an efficient acquisition scheme. A gradient-echo MR pulse sequence is applied with lateral (left-right (L/R)) frequency-encoding direction and slab selection along the direction of motion. Compensation for the table motion is achieved by a combination of slab tracking and data alignment in hybrid space. The method allows fast k-space coverage to be achieved, especially when a short sampling FOV is chosen along the direction of table motion, as is desirable for good image quality. The method can be incorporated into different acquisitions schemes, including segmented k-space scanning, which allows for contrast variation with the use of magnetization preparation. Head-to-toe images of volunteers were obtained with good quality using 3D spoiled gradient-echo sequences. As an example of magnetization-prepared imaging, fat/water separated images were acquired using chemical shift selective (CHESS) presaturation pulses. 相似文献
2.
3.
Image processing is a critical part of obtaining high-quality digital radiographs. Fortunately, the user of these systems does not need to understand image processing in detail, because the manufacturers provide good starting values. Because radiologists may have different preferences in image appearance, it is helpful to know that many aspects of image appearance can be changed by image processing, and a new preferred setting can be loaded into the computer and saved so that it can become the new standard processing method.Image processing allows one to change the overall optical density of an image and to change its contrast. Spatial frequency processing allows an image to be sharpened, improving its appearance. It also allows noise to be blurred so that it is less visible. Care is necessary to avoid the introduction of artifacts or the hiding of mediastinal tubes. 相似文献
4.
电位滴定法测定胰激肽释放酶活力测试条件探讨 总被引:8,自引:0,他引:8
本文用FIP推荐的方法,以具有国际单位的参照品为标样,滴定液为0.01mol/LNaOH标准溶液,考查了以BAEE为底物的电位滴定法测定胰激肽释放酶活力的实验条件,通过正交试验得出直观和方差分析的结果,依据酶活力单位高、SD和RSD%较小的原则,求出酶活力测定的最适条件是:酶反应温度为25℃;缓冲液为0.0015mol/LNa2B4O7-0.25mol/LNaCL-2×10(-4)mol/LEDTA,pH为8.00;反应液中酶浓度为0.48IU/ml;底物浓度为5×10(-3)mol/L;胰蛋白酶抑制剂浓度为125μg/ml。胰激肽释放酶活力测定的实验数据的相对标准偏差小于5%。 相似文献
5.
采用正交试验优选出最佳条件为:当乙酰乙酸乙酯为0.2moL时,硫酸铁铵0.7g,环乙烷10mL。乙酰乙酸乙酯和惭二醇摩尔比为1:1.5,反应时间为5h。所得产率为59.2%。 相似文献
6.
L. Poller T. W. Barrowcliffe A. M. H. P. van den Besselaar J. Jespersen A. Tripodi & D. Houghton 《British journal of haematology》1997,98(3):640-647
A simplified method of International Normalized Ratio (INR) derivation using linear regression of certified INR plotted against local prothrombin time (PT) results has been compared with INR from conventional orthogonal regression. Linear regression assumes error only with the local PT results whereas orthogonal regression assumes error with both reference and local results. The reliability of local INR derivation using lyophilized plasmas has been assessed in a collaborative study. INR from conventional fresh plasma International Sensitivity Index (ISI) calibrations have been compared with INR from calibrations with two types of lyophilized plasma, artificially depleted and coumarin.
Although calibration slopes differed with the two types of analysis and the different lyophilized plasmas, both gave reasonable approximations to fresh plasma ISI calibrations. With orthogonal regression the overall percentage INR deviation was 5.25% with the artificially depleted plasmas and 6.85% for the results with lyophilized coumarins. With the linear regression, deviation was 8.40% for the artificially depleted plasmas and 5.05% for coumarin-treated patients' lyophilized plasmas. The simpler regression method appears to be worthy of further study as the present report has demonstrated that if the calibrant plasmas are accurately certified with the thromboplastin International Reference Plasma (IRP) results approximate to the conventionally determined INR using the manual PT technique. Coagulometers require further assessment. 相似文献
Although calibration slopes differed with the two types of analysis and the different lyophilized plasmas, both gave reasonable approximations to fresh plasma ISI calibrations. With orthogonal regression the overall percentage INR deviation was 5.25% with the artificially depleted plasmas and 6.85% for the results with lyophilized coumarins. With the linear regression, deviation was 8.40% for the artificially depleted plasmas and 5.05% for coumarin-treated patients' lyophilized plasmas. The simpler regression method appears to be worthy of further study as the present report has demonstrated that if the calibrant plasmas are accurately certified with the thromboplastin International Reference Plasma (IRP) results approximate to the conventionally determined INR using the manual PT technique. Coagulometers require further assessment. 相似文献
7.
把分段线性函数和斜波脉冲函数进行统一处理,定义成新的函数,使得新的函数既保持了原先两种函数的基本特性,又获得微分和积分递推算法。应用中具有方便,快速计算的优点。 相似文献
8.
该文从疾病谱和死因谱的改变、医学模式的转变、卫生经费的降低、自我保健意识的改变四个角度,论述了全面开展 生活方式教育的必要性和重要性;从以社区为依托、以医院为基础、以生活方式为指导三个方面,探讨了生活方式教 育的工作模式. 相似文献
9.
作者采用正文试验法,以水提醇沉法提取和分离酚戒类有效成分,并以苯乙醇成含量作为含量测定指标,考察了乙醇浓度、提取温度及煎煮时间三个因素对有效成分提取量的影响,从而筛选出芸杞补肾口服液的是佳生产工艺。 相似文献
10.
应用修正正交分段线性函数的时滞和反向特性,推导出求解时滞系统和卷积的公式。数字仿真表明,它具有计算简单,精度高的优点。 相似文献