全文获取类型
收费全文 | 4464991篇 |
免费 | 354870篇 |
国内免费 | 15562篇 |
专业分类
耳鼻咽喉 | 60975篇 |
儿科学 | 141854篇 |
妇产科学 | 116377篇 |
基础医学 | 680000篇 |
口腔科学 | 123875篇 |
临床医学 | 406827篇 |
内科学 | 808391篇 |
皮肤病学 | 109118篇 |
神经病学 | 371199篇 |
特种医学 | 175334篇 |
外国民族医学 | 523篇 |
外科学 | 680570篇 |
综合类 | 132919篇 |
现状与发展 | 24篇 |
一般理论 | 2587篇 |
预防医学 | 371192篇 |
眼科学 | 105725篇 |
药学 | 312966篇 |
28篇 | |
中国医学 | 12558篇 |
肿瘤学 | 222381篇 |
出版年
2021年 | 56393篇 |
2020年 | 35819篇 |
2019年 | 59051篇 |
2018年 | 74761篇 |
2017年 | 57073篇 |
2016年 | 63262篇 |
2015年 | 76384篇 |
2014年 | 110909篇 |
2013年 | 176493篇 |
2012年 | 123363篇 |
2011年 | 128676篇 |
2010年 | 126525篇 |
2009年 | 127585篇 |
2008年 | 114483篇 |
2007年 | 122023篇 |
2006年 | 130187篇 |
2005年 | 124998篇 |
2004年 | 126248篇 |
2003年 | 115827篇 |
2002年 | 104578篇 |
2001年 | 173468篇 |
2000年 | 169283篇 |
1999年 | 153569篇 |
1998年 | 73325篇 |
1997年 | 68700篇 |
1996年 | 66785篇 |
1995年 | 62448篇 |
1994年 | 56385篇 |
1993年 | 52401篇 |
1992年 | 112059篇 |
1991年 | 107738篇 |
1990年 | 103065篇 |
1989年 | 100275篇 |
1988年 | 92347篇 |
1987年 | 90399篇 |
1986年 | 85477篇 |
1985年 | 83779篇 |
1984年 | 69647篇 |
1983年 | 61614篇 |
1982年 | 48900篇 |
1981年 | 45431篇 |
1980年 | 42664篇 |
1979年 | 59447篇 |
1978年 | 47773篇 |
1977年 | 42543篇 |
1976年 | 39303篇 |
1975年 | 39084篇 |
1974年 | 42939篇 |
1973年 | 41361篇 |
1972年 | 38606篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
P Rubinstein M Walker N Mollen C Carpenter S Beckerman N Suciu-Foca R McEvoy F Ginsberg-Fellner 《Diabetes》1990,39(9):1138-1143
The gene frequencies, haplotype relative risks, and zygotic assortments of HLA-DR in three ethnically defined samples of insulin-dependent diabetes mellitus (IDDM) patients were determined in a prospective family study. Although DR3 and DR4 were positively associated with IDDM in the probands of 123 northern European, 94 Ashkenazi Jewish, and 49 New York Hispanic families, significant excess of DR*3/4 heterozygotes was observed only among the probands from families of northern European ancestry. There was also a significant decrease in the frequency of Bw62,DR4 haplotypes derived by northern European patients from their mothers compared with their fathers. This difference, together with data reported in the literature, suggests that the expressivity of the susceptible genotype(s) in IDDM patients may be modified by protective maternal effects associated with Bw62,DR4 and probably other DR4 haplotypes. Samples of IDDM patients from populations with high frequencies of these modifiers should have different DR-gene frequencies contributed by fathers and mothers, capable of accounting for the observed Hardy-Weinberg disequilibrium. We postulate that, because the mechanism of action of these modifiers is distinct from that of the susceptibility gene, the difference must be considered in devising strategies for elucidation of the mode of inheritance of the disease and for understanding the molecular nature of the susceptibility. 相似文献
992.
Summary Intracavitary application of ultrasound was first performed for diagnostic purposes in 1967; since that time, it has been
more and more widely used. As far as the gastrointestinal tract is concerned, endoscopically controlled ultrasonic probes
provide visualization of the various layers of the intestinal wall. It is therefore possible to describe lesions of the esophagus,
stomach, and the rectum with regard to their nature and depth of infiltration. Furthermore, periesophageal and perigastric
organs can be visualized. It has become evident that endosonography is particularly important for pretherapeutic staging of
tumors of the esophagus, stomach, and rectum. Here prospective comparative studies confirm the superiority of this new diagnostic
procedure when compared to the methods available to date. 相似文献
993.
It has become common practice to rely on fitted estimates ofapparent in vivo metabolic constants (e.g., Vmax and KM) inparameterization of PBPK models. Yet, quantitative estimatesof precision in these fitted parameters are not routinely reported.Such information is needed to assess the reliability of modelpredictions. The purpose of this study was to assess the precisionin estimates of Vmax and KM for chloroform, accounting for boththe statistical uncertainties in parameter estimates from individualdata sets and any additional uncertainty due to differencesin the parameter estimates derived from various experiments.Joint confidence regions for Vmax and KM from each experiment,generated using maximum likelihood techniques, were used toevaluate these questions. Three previously published data setswere considered. Estimates of Vmax and KM obtained from thesedata sets differed more than could be explained as a consequenceof a limited number of observations, measurement error, or stochasticerror. Issues associated with the use of maximum likelihoodtechniques to estimate joint confidence regions, the estimationof metabolic constants from individual experiments within agas uptake study versus the full data set, the degree of overlapin the joint confidence regions for metabolic constants obtainedfrom separate data sets, and the implications for risk assessmentare discussed. 相似文献
994.
995.
996.
猕猴桃汁抗环磷酰胺致突变作用的机理 总被引:12,自引:1,他引:11
目的用大鼠外周血双核淋巴细胞微核测试法(CBMNT),在哺乳动物整体水平,研究猕猴桃汁抗环磷酰胺(CP)的致突变作用以及生物转化Ⅱ相酶的作用。方法测定大鼠外周血双核淋巴细胞微核细胞率及肝组织中总谷胱甘肽硫转移酶(GST)、尿苷二磷酸葡萄糖醛酸转移酶(UDPGT)、谷氨酰胺转肽酶(γGT)活性。结果猕猴桃汁对CP诱发的大鼠外周血双核淋巴细胞微核细胞率有显著抑制作用,能明显诱导大鼠肝脏总GST、UDGTP活性,但对γGT活性无显著影响。大鼠外周血双核淋巴细胞微核细胞率与总GST、UDGTP活性呈明显负相关。结论猕猴桃汁抗CP致微核形成作用的机理可能是通过诱导机体外来化合物代谢解毒酶系,加速CP的代谢灭活 相似文献
997.
998.
Measurements were made of glutathione (GSH) levels, catalase activity and the oxidant sensitivity of the erythrocytes from
the koala (Phascolarctos cinereus) and the common brushtail possum (Trichosurus vulpecula). The oxidant sensitivity was tested by treating the haemolysates with either 0.55 him H2O2 or 1.4mm NaNO2. The erythrocytes of the koala had greater levels of GSH and catalase and yet were found to be more susceptible to oxidation
induced by both these oxidants. 相似文献
999.
1000.
Aaron H. Burstein Pharm.D. William G. Reiss Pharm.D. Eric Kantor B.A. Gail D. Anderson Ph.D. 《Pharmacotherapy》1998,18(6):1271-1276
Study Objective . To characterize cytochrome P450 (CYP) 3A4 activity in premenopausal and postmenopausal women by evaluating the urinary 6-β-hydroxycortisokcortisol ratio. Design . Prospective study. Subjects . Thirteen premenopausal and 13 postmenopausal women who were healthy and not receiving drugs known to affect CYP3A4 activity. Interventions . Beginning on day 2 of menses, premenopausal women collected first morning urine samples every other day for a complete menstrual cycle. Postmenopausal women collected first morning urine every other day for 28 days. Measurements and Main Results . Mean weekly 6-β-hydroxycortisol:cortisol ratios did not differ during the phase (week) of the menstrual cycle. Daily ratios did not differ in postmenopausal women. No difference between premenopausal and postmenopausal women was found on comparing overall median ratios. Conclusion . Cytochrome P450 3A4 activity as measured by 6-β-hydroxy cortisol:cortisol ratio did not differ by week of menstrual cycle, suggesting no menstrual cycle-related changes. Menopause does not appear to be associated with differences in CYP3A4 activity, compared with premenopause. 相似文献