全文获取类型
收费全文 | 5139篇 |
免费 | 525篇 |
国内免费 | 86篇 |
专业分类
耳鼻咽喉 | 69篇 |
儿科学 | 202篇 |
妇产科学 | 121篇 |
基础医学 | 731篇 |
口腔科学 | 141篇 |
临床医学 | 674篇 |
内科学 | 1028篇 |
皮肤病学 | 51篇 |
神经病学 | 343篇 |
特种医学 | 382篇 |
外科学 | 495篇 |
综合类 | 129篇 |
一般理论 | 3篇 |
预防医学 | 504篇 |
眼科学 | 54篇 |
药学 | 334篇 |
中国医学 | 2篇 |
肿瘤学 | 487篇 |
出版年
2021年 | 53篇 |
2020年 | 33篇 |
2019年 | 64篇 |
2018年 | 83篇 |
2017年 | 57篇 |
2016年 | 77篇 |
2015年 | 74篇 |
2014年 | 85篇 |
2013年 | 145篇 |
2012年 | 187篇 |
2011年 | 180篇 |
2010年 | 155篇 |
2009年 | 140篇 |
2008年 | 164篇 |
2007年 | 220篇 |
2006年 | 182篇 |
2005年 | 214篇 |
2004年 | 136篇 |
2003年 | 160篇 |
2002年 | 167篇 |
2001年 | 143篇 |
2000年 | 172篇 |
1999年 | 160篇 |
1998年 | 144篇 |
1997年 | 131篇 |
1996年 | 152篇 |
1995年 | 134篇 |
1994年 | 135篇 |
1993年 | 108篇 |
1992年 | 149篇 |
1991年 | 135篇 |
1990年 | 135篇 |
1989年 | 125篇 |
1988年 | 126篇 |
1987年 | 101篇 |
1986年 | 105篇 |
1985年 | 107篇 |
1984年 | 70篇 |
1983年 | 70篇 |
1982年 | 64篇 |
1981年 | 50篇 |
1980年 | 50篇 |
1979年 | 63篇 |
1978年 | 52篇 |
1977年 | 42篇 |
1976年 | 42篇 |
1974年 | 34篇 |
1973年 | 32篇 |
1972年 | 34篇 |
1970年 | 35篇 |
排序方式: 共有5750条查询结果,搜索用时 0 毫秒
1.
Heidi J Kalkwarf John A Shepherd Didier Hans Elena Gonzalez Rodriguez Joseph M Kindler Joan M Lappe Sharon Oberfield Karen K Winer Babette S Zemel 《Journal of bone and mineral research》2022,37(4):776-785
Trabecular bone score (TBS) is used for fracture prediction in adults, but its utility in children is limited by absence of appropriate reference values. We aimed to develop reference ranges for TBS by age, sex, and population ancestry for youth ages 5 to 20 years. We also investigated the association between height, body mass index (BMI), and TBS, agreement between TBS and lumbar spine areal bone mineral density (aBMD) and bone mineral apparent density (BMAD) Z-scores, tracking of TBS Z-scores over time, and precision of TBS measurements. We performed secondary analysis of spine dual-energy X-ray absorptiometry (DXA) scans from the Bone Mineral Density in Childhood Study (BMDCS), a mixed longitudinal cohort of healthy children (n = 2014) evaluated at five US centers. TBS was derived using a dedicated TBS algorithm accounting for tissue thickness rather than BMI. TBS increased only during ages corresponding to pubertal development with an earlier increase in females than males. There were no differences in TBS between African Americans and non-African Americans. We provide sex-specific TBS reference ranges and LMS values for calculation of TBS Z-scores by age and means and SD for calculation of Z-scores by pubertal stage. TBS Z-scores were positively associated with height Z-scores at some ages. TBS Z-scores explained only 27% and 17% of the variance of spine aBMD and BMAD Z-scores. Tracking of TBS Z-scores over 6 years was lower (r = 0.47) than for aBMD or BMAD Z-scores (r = 0.74 to 0.79), and precision error of TBS (2.87%) was greater than for aBMD (0.85%) and BMAD (1.22%). In sum, TBS Z-scores provide information distinct from spine aBMD and BMAD Z-scores. Our robust reference ranges for TBS in a well-characterized pediatric cohort and precision error estimates provide essential tools for clinical assessment using TBS and determination of its value in predicting bone fragility in childhood and adolescence. © 2022 American Society for Bone and Mineral Research (ASBMR). 相似文献
2.
In cystic fibrosis (CF), perturbations of total daily energy expenditure (TDEE) may be a major determinant of altered nutrition and growth. Measurement of TDEE is problematic, though the flex-heart rate method (FHRM) provides a close estimation of TDEE, as compared to the cost-prohibitive, gold standard, the double-labeled water method, and permits estimates of the energy cost of daily activities (ECA) above resting energy expenditure (REE). We hypothesize that alterations in ECA affects TDEE in CF. PURPOSE: To measure components of TDEE in adolescents with CF and normal lung function compared with controls, and to determine whether ECA can be improved by diet and exercise. METHODS: Clinically stable CF subjects (aged 9-13, n=12) and age- and gender-matched controls (n=13) had repeated measurements of TDEE by FHRM, REE, and maximal cardiopulmonary exercise testing (CPET) during a 6-week exercise and diet program. RESULTS: While the mean REE was similar in both groups, ECA was significantly lower in CF adolescents as compared to controls (p=0.02). During CPET, maximal exercise in CF was characterized by hyperventilation, which was unrelated to ventilation-perfusion mismatching. There were no changes in REE after dietary intervention. CONCLUSION: ECA in CF adolescents with normal lung function is lower when compared to healthy controls. These findings support the hypothesis that clinically stable patients with CF have inefficient energy metabolism or alternatively conserve energy during activities of daily living. 相似文献
3.
4.
Olfactory transduction is thought to occur by processes that are mainly restricted to the specialized cilia emanating from the distal end of the receptor neuron's single dendrite. The involvement of a cAMP-based second messenger system seems likely, and a cyclic nucleotide-sensitive current has been recorded in patches of membrane from the cilia. However, the small diameter of the cilia and the high density of channels within the membrane limit the application of the patch recording technique in the cilia. We have found that the cAMP-sensitive channels also exist at a much lower density within the far more accessible dendritic membrane. Recording from on-cell patches, we have observed single-channel activity in response to extracellularly applied odor substances. The channels have a single-channel conductance of 40 pS and a reversal potential near 0 mV. These same channels are activated by treatments that elevate intracellular cyclic nucleotide concentrations. The results provide a direct demonstration that the cyclic nucleotide-gated channel is the conductance pathway for the odor-elicited current. 相似文献
5.
D. Caroline Blanchard Jon K. Shepherd Antonio De Padua Carobrez Robert J. Blanchard 《Neuroscience and biobehavioral reviews》1991,15(4):461-468
Female rats consistently show a pattern of differences in defensive behaviors compared to males which parallel the effects of exposure to a nonpainful threat stimulus (cat or cat odor) in the same tests and measures. These indications of greater defensiveness for females are particularly common in situations involving potential, as opposed to actual and present, threat, a factor which probably also reflects ceiling or floor effects in situations involving very intense defensiveness. In addition, pharmacological studies indicate sex differences in the effects of selective serotonin (5-HT) receptor agonists and antagonists on defensive responding. These findings indicate that sex effects must be considered in studies of the pharmacological control of defensive behaviors, and suggest that responsivity to sex effects may be an additional criterion for the suitability of animal models of anxiety. 相似文献
6.
7.
8.
9.
10.
A S Lamont M S Roberts D G Holdsworth A Atherton J J Shepherd 《Anaesthesia and intensive care》1986,14(4):360-364
Recently, a family tree with a predisposition for the gene of multiple endocrine neoplasia Type 1 has been identified in Tasmania. As the surgical identification and localisation of parathyroid adenomas is facilitated by the administration of methylene blue, an opportunity has presented to measure the plasma concentration of methylene blue and methaemoglobin production. The study was undertaken to establish whether significant methaemoglobin concentrations were generated during the infusion and whether these concentrations could be related to the corresponding methylene blue concentrations. Mean peak methylene blue concentrations of 3.72 micrograms l-1, mean percentage methaemoglobin of 10.0 and a PaO2 within acceptable clinical ranges were found. No apparent relationship between methylene blue concentration and methaemoglobin production was found. 相似文献