全文获取类型
收费全文 | 66499篇 |
免费 | 4305篇 |
国内免费 | 1893篇 |
专业分类
耳鼻咽喉 | 440篇 |
儿科学 | 962篇 |
妇产科学 | 585篇 |
基础医学 | 7645篇 |
口腔科学 | 1090篇 |
临床医学 | 6207篇 |
内科学 | 6850篇 |
皮肤病学 | 365篇 |
神经病学 | 8907篇 |
特种医学 | 2091篇 |
外国民族医学 | 2篇 |
外科学 | 4584篇 |
综合类 | 10540篇 |
现状与发展 | 6篇 |
预防医学 | 9772篇 |
眼科学 | 699篇 |
药学 | 7438篇 |
100篇 | |
中国医学 | 2318篇 |
肿瘤学 | 2096篇 |
出版年
2024年 | 219篇 |
2023年 | 1033篇 |
2022年 | 1868篇 |
2021年 | 2597篇 |
2020年 | 2435篇 |
2019年 | 1870篇 |
2018年 | 1818篇 |
2017年 | 1840篇 |
2016年 | 2068篇 |
2015年 | 2063篇 |
2014年 | 4185篇 |
2013年 | 4603篇 |
2012年 | 4067篇 |
2011年 | 4449篇 |
2010年 | 3479篇 |
2009年 | 3340篇 |
2008年 | 3442篇 |
2007年 | 3257篇 |
2006年 | 2945篇 |
2005年 | 2498篇 |
2004年 | 2079篇 |
2003年 | 1843篇 |
2002年 | 1451篇 |
2001年 | 1264篇 |
2000年 | 1060篇 |
1999年 | 900篇 |
1998年 | 887篇 |
1997年 | 865篇 |
1996年 | 722篇 |
1995年 | 687篇 |
1994年 | 670篇 |
1993年 | 577篇 |
1992年 | 549篇 |
1991年 | 534篇 |
1990年 | 439篇 |
1989年 | 394篇 |
1988年 | 399篇 |
1987年 | 379篇 |
1986年 | 347篇 |
1985年 | 469篇 |
1984年 | 401篇 |
1983年 | 246篇 |
1982年 | 266篇 |
1981年 | 246篇 |
1980年 | 228篇 |
1979年 | 147篇 |
1978年 | 136篇 |
1977年 | 122篇 |
1976年 | 88篇 |
1974年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Dr. Yoshihiko Hayakawa Ph.D. Allan G. Farman B.D.S Ph.D. D.Sc. William C. Scarfe B.D.S M.S. Kinya Kuroyanagi D.D.S Ph.D. 《Oral Radiology》1996,12(1):11-18
The RVG-4 permits automatic exposure compensation (AEC). The purpose of this investigation was to determine the effects of
AEC on image contrast. Images were made either with or without a dental QA jaw phantom using a fixed image projection geometry.
Exposures were 6.3 through 27.3 μC/kg using an X-ray generator operated at 70 kVp. Region of interest pixel value distributions
were measured at tissue thicknesses in this phantom, and the average pixel values and signal-to-noise ratios (SNR) were calculated.
The use of AEC without an object in place resulted in a disproportionate relationship between pixel value and exposure with
a marked reduction in SNR. The use of AEC on under- and over-exposed images of the phantom simultaneously enhanced image contrast
and reduced SNR. Thus, AEC provides a convenient and quick method for achieving high-contrast images with sub-optimal exposures,
however, this could lead to inappropriate patient dosages if the function is used for over-exposed images. AEC reduces the
SNR and produces disproportionate pixel values relative to exposure. 相似文献
92.
Fifty couples and their children with Down syndrome (D.S.) were typed for HLA-A and HLA-B antigens and compared to 50 control families and 464 blood donors. The parental origin of the extra chromosome 21 was determined by cytogenetic methods. All individuals were caucasians and there was no history of consanguinity. No excessive HLA sharing was present in D.S. parents. The mothers of D.S. shared no more HLA antigens with their D.S. children than the control mothers with their normal children (14% vs. 18%). Thirteen of the fifty pairs (26%) (parent in whom the nondisjunction occurred and D.S. child) shared three HLA antigens at the A and/or B locus. This was not significantly higher than the proportion in the control group (12/50 or 24%). These data suggest that it is not the sharing of HLA-A and HLA-B antigens between the parents or between the parent who was the origin of the nondisjunction and the D.S. child that is related either to the occurrence of trisomy 21 zygotes or to prenatal survival of affected embryos and fetuses. 相似文献
93.
染色体图象处理系统具有7组67个功能,基本功能有视频处理、图象预处理、染色体配对和排序、图形功能、标注和批处理功能。把该系统应用于苯中毒工人遗传学生物标记研究、兰索拉唑对中国仓鼠肺细胞染色体畸变的影响研究、妇产科病人标本及猴外周血淋巴细胞标本的观察和分析的结果表明,该系统实用性强,并具有先进性、稳定性、灵活性和可拓展性等特点。 相似文献
94.
白细胞介素—2新的功能位点及其中枢镇痛作用 总被引:2,自引:0,他引:2
白细胞介素-2(IL-2)不仅是重要的免疫调节因子,而且还具有重要的中枢调节作用。本实验以钾离子透入引起大鼠甩尾反应为指标,发现侧脑室注射IL—2能显著提高动物痛阈,并能被纳洛酮所阻断,表示IL-2的中枢镇痛作用可能与阿片受体有关。利用基因定位突变技术获得的无免疫活性IL-2实查体仍具有中枢镇痛作用,表明IL—2分子上发挥镇痛和免疫调节作用的功能位点是相互独立的。纳洛酮能够阻断IL—2的中枢镇痛作用,而不能影响IL—2增殖CTLL-2细胞的作用,提示IL-2发挥镇痛和免疫调节作用可能通过不同的受体途径。IL-2分子中第45位Tyr残基突变为Val后,虽仍保留了免疫活性,但丧失了镇痛功能,表示45位Tyr残基是IL—2发挥中枢镇痛功能的关键残基之一。我们推测IL—2的镇痛功能位点可能在IL—2分子中第45位Tyr残基附近区域。 相似文献
95.
It has recently been shown that it is possible to discriminate accurately among myoelectric signals underlying different muscle
contraction types, specifically elbow flexion and extension and forearm pronation and supination. It was reported that once
a number of distinctive features had been extracted from the myoelectric signals, a neural network could be trained to distinguish
the contraction types with an impressively high accuracy. In the present paper, we show that a technique known as parallel
cascade identification can be used to construct classifiers that can also accurately, differentiate the contraction types.
The use of parallel cascades has the benefit of dispensing with the need for feature extraction, so that raw myoelectric signal
data can be used directly. In addition, very little data are required to train the parallel cascades to distinguish accurately
novel incoming myoelectric signals. Results of using parallel cascades to distinguish foream pronation, supination, and elbow
flexion are presented. 相似文献
96.
H. J. SPARR C. LEO E. LADNER E. DEUSCH H. BAUMGARTNER 《Acta anaesthesiologica Scandinavica》1997,41(10):1300-1307
Background : The study aimed to assess the relative influence of anaesthesia and muscle relaxation on intubating conditions and the haemodynamic and catecholamine responses to tracheal intubation.
Methods : Sixty ASA 1 or 2 patients were randomly assigned to one of four groups (15 patients each) that differed in the depth of anaesthesia (thiopentone plus fentanyl 2.5 μg kg-1 or thiopentone alone) and the degree of vecuronium–induced neuromuscular block (100% or _>: 65%) at intubation. Muscle relaxation was measured at 0.1 Hz by means of mechanomyography. Heart rate (HR) and mean arterial blood pressure (MAP) were measured before and after induction of anaesthesia, and 1 min and 5 min following intubation, while adrenaline (A) and noradrenaline concentrations (NA) were determined from arterial blood samples.
Results : Intubating conditions were improved primarily by providing complete muscle relaxation at the adductor pollicis muscle (P<0.001) and to a lesser extent by adding fentanyl to thiopentone (P=0.04). The response of HR and MAP to tracheal intubation was attenuated mainly by fentanyl (P<0.001). Complete muscle relaxation further diminished the response of MAP to intubation (P=0.03). Changes in A and NA were dependent on the depth of anaesthesia only (P =>0.01).
Conclusion : The results of the study demonstrate that the sympathoadrenal response to intubation is attenuated by adding fentanyl (2.5 kg-1 ) to an induction regimen with thiopentone, whereas provision of complete muscle relaxation at the adductor pollicis muscle is necessary to attain smooth intubating conditions. 相似文献
Methods : Sixty ASA 1 or 2 patients were randomly assigned to one of four groups (15 patients each) that differed in the depth of anaesthesia (thiopentone plus fentanyl 2.5 μg kg
Results : Intubating conditions were improved primarily by providing complete muscle relaxation at the adductor pollicis muscle (P<0.001) and to a lesser extent by adding fentanyl to thiopentone (P=0.04). The response of HR and MAP to tracheal intubation was attenuated mainly by fentanyl (P<0.001). Complete muscle relaxation further diminished the response of MAP to intubation (P=0.03). Changes in A and NA were dependent on the depth of anaesthesia only (P =>0.01).
Conclusion : The results of the study demonstrate that the sympathoadrenal response to intubation is attenuated by adding fentanyl (2.5 kg
97.
本文报导了用40只白色短毛家兔所做的动物模拟失重实验,得出各脏器微血管通透性的动态反应曲线。并用微循环研究方法,分析了模拟失重时各脏器微血管功能状态与微血管通透性之间的关系;阐述了各脏器微循环功能变化特点;并对变化机理作了初步探讨。 相似文献
98.
99.
100.
提出了文题所述的控制策略,依据输出分布曲线的特征变量选取方法和依据该项信息的规则控制系统。仿真研究得到了满意的结果。在一个实验性二元精馏塔上用IBM-PC进行试验亦获成功。本法对具有非线性特性的分布参数对象,较常规控制策略有明显的优越性。 相似文献