全文获取类型
收费全文 | 11589篇 |
免费 | 602篇 |
国内免费 | 32篇 |
专业分类
耳鼻咽喉 | 158篇 |
儿科学 | 667篇 |
妇产科学 | 191篇 |
基础医学 | 1003篇 |
口腔科学 | 270篇 |
临床医学 | 916篇 |
内科学 | 2986篇 |
皮肤病学 | 260篇 |
神经病学 | 621篇 |
特种医学 | 321篇 |
外科学 | 1858篇 |
综合类 | 254篇 |
一般理论 | 1篇 |
预防医学 | 607篇 |
眼科学 | 370篇 |
药学 | 681篇 |
中国医学 | 26篇 |
肿瘤学 | 1033篇 |
出版年
2023年 | 60篇 |
2022年 | 170篇 |
2021年 | 381篇 |
2020年 | 187篇 |
2019年 | 260篇 |
2018年 | 349篇 |
2017年 | 208篇 |
2016年 | 222篇 |
2015年 | 262篇 |
2014年 | 356篇 |
2013年 | 471篇 |
2012年 | 711篇 |
2011年 | 762篇 |
2010年 | 425篇 |
2009年 | 333篇 |
2008年 | 567篇 |
2007年 | 637篇 |
2006年 | 588篇 |
2005年 | 511篇 |
2004年 | 507篇 |
2003年 | 431篇 |
2002年 | 418篇 |
2001年 | 280篇 |
2000年 | 247篇 |
1999年 | 231篇 |
1998年 | 114篇 |
1997年 | 66篇 |
1996年 | 59篇 |
1995年 | 70篇 |
1993年 | 52篇 |
1992年 | 174篇 |
1991年 | 178篇 |
1990年 | 174篇 |
1989年 | 158篇 |
1988年 | 147篇 |
1987年 | 138篇 |
1986年 | 120篇 |
1985年 | 116篇 |
1984年 | 116篇 |
1983年 | 84篇 |
1982年 | 68篇 |
1981年 | 50篇 |
1980年 | 50篇 |
1979年 | 89篇 |
1978年 | 47篇 |
1977年 | 70篇 |
1975年 | 42篇 |
1974年 | 55篇 |
1972年 | 49篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Phyllis W Sharps Ayman A E El-Mohandes M Nabil El-Khorazaty Michele Kiely Tessa Walker 《Journal of perinatology》2003,23(5):414-419
OBJECTIVE: To describe breastfeeding initiation among 210 urban African-American mothers with inadequate prenatal care. METHODS: This study is a case-control study of postpartum mothers recruited from four large urban hospitals. RESULTS: Mothers who chose to breastfeed were more educated, employed before birth, married, and using contraception postnatally. Regression model analysis controlling for demographic differences revealed that breastfeeding was significantly associated with a higher perception of severity of illness and higher confidence in the ability of health care to prevent illness. Breastfeeding mothers were less likely to reverse parent-child roles and had a lower perception of hassle from their infant's behavior. When comparing mothers who breastfed longer than 8 weeks to those who did not breastfeed, breastfeeding mothers had high scores related to empathy toward infants on the Adult-Adolescent Parenting Inventory as well as a low perception of hassle on the Parenting Daily Hassle. The perception of existing formal or informal social support did not influence breastfeeding behavior. CONCLUSION: Personal attributes of low-income urban mothers such as health beliefs and parental attitudes may play a role in the initiation and duration of breastfeeding. Low-income African-American mothers may be influenced in their choice to breastfeed by supportive messages from physicians and nurses delivering care to mothers and their newborns. Emphasis should be placed on the role breastfeeding can play in preventing childhood illnesses. 相似文献
12.
Calis Sema Jeyanthi Ramasubbu Tsai Tsuimin Mehta Rahul C. DeLuca Patrick P. 《Pharmaceutical research》1995,12(7):1072-1076
Purpose. The interaction of salmon calcitonin (sCT) and poly (d,l-lactide-co-glycolide) was detected during preparation and evaluation of microspheres. The purpose of this study was to quantitate the extent and nature of the interaction.
Methods. Blank microspheres were prepared by an aqueous emulsification solvent extraction technique. Adsorption studies were carried out at six concentrations of sCT and three concentrations of microspheres. Adsorption isotherms were constructed using the Langmuir and Freundlich treatments.
Results. Adsorption at 1 mg/ml sCT concentration resulted in almost complete depletion of the peptide from the adsorption medium with the time to reach maximum adsorption decreasing with increasing microsphere concentration. At sCT concentrations below 100 µg/ml, a true equilibrium occurred in 1 hour or less while at higher concentrations (up to 350 µg/ml), a transient equilibrium was reached in 1 to 2 hours, followed by further adsorption of the peptide. The adsorption followed the Langmuir isotherm at concentrations below 200 µg/ml, indicating formation of a monolayer. Multilayer interaction, described by the Freundlich isotherm, occurred at higher concentrations and resulted in complete depletion of sCT from the adsorption medium. The affinity constant during monolayer formation was 0.09 and the plateau surface concentration was 5.1 µg/mg. The multilayer peptide-peptide adsorption showed a lower affinity (0.025) but higher capacity (24 µg/mg) than the monolayer peptide-polymer adsorption.
Conclusions. The results show that poly (d,l-lactide-co-glycolide) microspheres have a high adsorption capacity for sCT which must be considered in formulating a controlled delivery product of this peptide. 相似文献
13.
Ganglioglioma can involve any part of the central nervous system. Mostly ganglioglioma occur in temporal lobe. Spinal cord ganglioglioma is a very rare entity. We report two cases of cervico-dorsal region ganglioglioma, who underwent complete surgical excision. In the postoperative period they had transient deterioration of their neurological status that gradually recovered with follow-up. 相似文献
14.
15.
16.
R R Mehta L Valcourt J Graves R Green T K Das Gupta 《International journal of cancer. Journal international du cancer》1987,40(3):305-308
Total and subcellular (cytosol and nuclear) concentrations of estrone (E1), estradiol (E2), and androstenedione were determined in non-malignant (n = 61) and malignant (n = 65) human breast tissues obtained from post-menopausal women. The 17 beta-hydroxysteroid dehydrogenase (17 beta-OH-SDH) activity was determined in 800g supernatant fraction. Total estrogens, E1 and E2 levels and 17 beta-OH-SDH activity were significantly (p less than 0.005, 0.0005, 0.001, respectively) higher in malignant than in non-malignant breast tissues. We failed to observe significant changes in subcellular steroid concentrations or enzyme activity associated with patients' obesity or tumor estrogen receptor status. When the steroid levels were analyzed in relation to clinical staging of the disease, nuclear contents of estradiol were significantly higher (p less than 0.005) in Stage-IV patients than in those with less advanced disease (Stages I to III). 17 beta-OH-SDH activity was significantly (p less than 0.001) lower in patients with advanced disease than in those with relatively less advanced (Stages I to III) disease and was positively correlated with tissue concentration of androstenedione. Our present data indicate that differential intracellular metabolism of steroid hormones may have some influence on availability of estradiol at nuclear sites. In postmenopausal women, local interconversion of estrogens may provide sufficient estrogenic stimulus to enhance the growth and progression of breast tumors. 相似文献
17.
Dominant A1: angiographic and clinical correlations with anterior communicating artery aneurysms. 总被引:1,自引:0,他引:1
It has been observed but never proven that anomalies of the anterior communicating artery complex are associated with anterior communicating artery aneurysms (ACAA). Therefore, in an effort to understand the significance of haemodynamic factors in the genesis, as well as the clinical course of ACAA, we evaluated the correlation between certain angiographic patterns of flow in the anterior circulation and the clinical findings of 51 patients with ACAA compared with 50 matched controls. Four significant associations which have never been validated were identified: 1) a dominant A1 (filling both A2's) was found in 57% of ACAA patients versus 14% of controls (p less than 0.001). 2) Unilateral hypoplasia of the opposite A1 was present in 24% of ACAA patients versus 6% of controls (p = 0.01). 3) Exclusive filling of the ACAA from one A1 occurred in 78%. 4) No statistically significant relationship was found between the anatomic flow patterns studied and the patients clinical presentation including age, sex, or grade. We conclude that anterior communicating artery aneurysms are significantly related in a majority of patients with the presence of a dominant A1, probably as the result of enhanced haemodynamic stress caused by this anatomic abnormality in the circulation. However, this association is not constant, and a dominant pattern of flow did not correlate with the clinical course. This is probably a reflection of the differences between factors initiating aneurysm formation and those influencing its growth, as well as of the relative limitations of angiography when pathophysiological extrapolations are attempted. 相似文献
18.
Fat absorption in premature infants: medium-chain triglycerides and long-chain triglycerides are absorbed from formula at similar rates 总被引:1,自引:0,他引:1
M Hamosh N R Mehta C S Fink J Coleman P Hamosh 《Journal of pediatric gastroenterology and nutrition》1991,13(2):143-149
Fat absorption from two different premature infant formulas and one full-term formula containing three different fat blends was investigated in two groups of premature infants. The first group of nine infants (gestational age, 29.1 +/- 0.88 weeks; postnatal age, 3.13 +/- 0.71 weeks) was fed alternately for 1 week each SMA preterm formula containing either high levels (50%) of medium-chain triglycerides (MCT) (6:0, 8:0, and 10:0) or high levels (86%) of long-chain triglycerides (LCT) (greater than or equal to C12). Except for fat blends, the formulas were otherwise identical. The second group of 11 infants (gestational age, 30.5 +/- 0.77 weeks, studied at a postnatal age of 4.33 +/- 0.91 weeks) was fed for 1 week a full-term infant formula, S-26, containing 98% LCT. Fat absorption (studied during a 3-day fat balance period) was similar irrespective of fat blend: 89.08 +/- 2.37% during feeding of preterm SMA, 50% MCT; 87.0 +/- 3.81% during feeding of preterm SMA, 86% LCT; and 83.00 +/- 2.89% during feeding of S-26, 98% LCT. Weight gain (grams per day) and increase in length (centimeters per day) were 23.2 +/- 1.7, 21.20 +/- 1.7, and 14.28 +/- 2.9, and 0.17 +/- 0.06, 0.16 +/- 0.04, and 0.22 +/- 0.07 during feeding of the three fat blends, respectively. Lipase activity levels in fasting gastric aspirates were higher during feeding of the LCT than the MCT formula. The possible stimulation of gastric lipase secretion secondary to long-chain fatty acid stimulation of cholecystokinin secretion might be related to the efficient digestion of formula fat, irrespective of triglyceride-fatty acid chain length.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
19.
Nabil El-Sherif 《The International Journal of Cardiac Imaging》1991,7(3-4):141-150
In this work the electrophysiologic mechanisms of ventricular arrhythmias have been briefly summarized. Ventricular arrhytmias can be caused either by pacemaker activity or by reentrant excitation. Enhancement of normal automaticy can generate a parasystolic rhythm in normal fibers. Abnormal automaticity may arise fom fibers in which maximum diastolic potential has been reduced by a variety of interventions. Triggered activity is caused by either an early (EAD) or delayed (DAD) afterdepolarization and requires a prior normal action potential for initiation. While there is growing evidence that EAD-induced triggered activity plays a significant role in the Long QTU syndrome and Torsade de Pointes, no clinical arrhythmias has definitely been ascribed to DADs, although DADs have been recorded in man after acute digoxin intoxication.Ventricular arrhytmias can be also caused by reentrant excitation, which can be subdivided into reflection or circus movement reentry (CMR). In the reflection model impulses in both directions are transmitted over the same pathway. In the CMR three models can be differentiated: the ring model, which requires a fixed anatomical obstacle; the figure-eight model and the leading circle model, where functional rather than fixed anatomical obstacles are involved.Abbreviations AV
atrio-ventricular
- CMR
circus movement reentry
- DAD
delayed afterdepolarization
- EAD
early afterdepolarization
- ECG
electrocardiogram
- LV
left ventricle
- MAP
monophasic action potential
- MF
muscle fiber
- PF
Purkinje fiber
- RV
right ventricle
- TdP
Torsade de Pointes 相似文献
20.