全文获取类型
收费全文 | 13934篇 |
免费 | 1243篇 |
国内免费 | 506篇 |
专业分类
耳鼻咽喉 | 58篇 |
儿科学 | 75篇 |
妇产科学 | 54篇 |
基础医学 | 866篇 |
口腔科学 | 951篇 |
临床医学 | 1098篇 |
内科学 | 854篇 |
皮肤病学 | 42篇 |
神经病学 | 446篇 |
特种医学 | 491篇 |
外科学 | 826篇 |
综合类 | 1981篇 |
一般理论 | 3篇 |
预防医学 | 2081篇 |
眼科学 | 93篇 |
药学 | 3717篇 |
19篇 | |
中国医学 | 1837篇 |
肿瘤学 | 191篇 |
出版年
2024年 | 35篇 |
2023年 | 271篇 |
2022年 | 452篇 |
2021年 | 635篇 |
2020年 | 536篇 |
2019年 | 530篇 |
2018年 | 529篇 |
2017年 | 535篇 |
2016年 | 550篇 |
2015年 | 564篇 |
2014年 | 935篇 |
2013年 | 1461篇 |
2012年 | 957篇 |
2011年 | 998篇 |
2010年 | 719篇 |
2009年 | 728篇 |
2008年 | 815篇 |
2007年 | 718篇 |
2006年 | 613篇 |
2005年 | 535篇 |
2004年 | 376篇 |
2003年 | 305篇 |
2002年 | 282篇 |
2001年 | 259篇 |
2000年 | 213篇 |
1999年 | 154篇 |
1998年 | 113篇 |
1997年 | 125篇 |
1996年 | 93篇 |
1995年 | 64篇 |
1994年 | 77篇 |
1993年 | 75篇 |
1992年 | 64篇 |
1991年 | 44篇 |
1990年 | 37篇 |
1989年 | 36篇 |
1988年 | 40篇 |
1987年 | 34篇 |
1986年 | 26篇 |
1985年 | 29篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
The ripple-free deadbeat control problem for SISO plants subjected to arbitrary reference signals is considered. The trade-off between the settling time and the integral square error between the system output and reference signal is investigated. Given a specific order of the controller, it is shown how to design an optimal ripple-free deadbeat controller. An illustrative example is presented to show the feasibility of the proposed algorithm. 相似文献
64.
Richard M. Pearson 《Clinical & experimental optometry》1990,73(6):172-177
A simple but reliable method was used to measure the axial edge lift at the total diameter over a range of back optic zone radii of several proprietary designs of rigid gas-permeable corneal lens. One of these was found to have a constant axial edge lift construction. 相似文献
65.
Ross D. King Jonathan D. Hirst Michael J. E. Sternberg 《Perspectives in Drug Discovery and Design》1993,1(2):279-290
Summary Neural networks and machine learning are two methods that are increasingly being used to model QSARs. They make few statistical assumptions and are nonlinear and nonparametric. We describe back-propagation from the field of neural networks, and GOLEM from machine learning, and illustrate their learning mechanisms using a simple expository problem. Back-propagation and GOLEM are then compared with multiple linear regression (using the parameters and their squares) on two real drug design problems: the inhibition ofEscherichia coli dihydrofolate reductase (DHFR) by pyrimidines and the inhibition of rat/mouse tumour DHFR by triazines. 相似文献
66.
67.
68.
G. M. Howard T. V. Nguyen N. A. Pocock P. J. Kelly J. A. Eisman 《Osteoporosis international》1997,7(3):190-194
Calcaneal ultrasound has been increasingly studied for its potential in the assessment of osteoporotic fracture risk. The accuracy of such an assessment is, in part, dependent on the reproducibility of the measurement. This study examines the impact of handedness on ultrasound measurements [broadband ultrasound attenuation (BUA) and velocity of sound (VOS)] in the calcaneus. Two hundred and sixty-four subjects (57 men and 297 women) aged 51.1+13.6 years (mean ± SD) were studied. For each subject, calcaneal ultrasound measurements were performed on both heels with a McCue CUBA ultrasound densitometer. Right-handed dominance (94.7%) was determined by structured interview. In men, BUA measurements were significantly higher on the dominant side: mean difference 4.1±1.5 dB/MHz (mean ± SD;p=0.009), equivalent to 4.2+1.5% and more than 4 times the average rate of annual change in BUA. The difference between sides was greater in young (<50 years) than old men (>50 years). Among the women, the difference was not statistically significant (0.7±0.9 dB/MHz;p=0.4); however, it was significant in younger women (20–30 years) (99±4 vs 90±4 dB/MHz,p=0.01). By contrast VOS did not differ between sides in either men or women irrespective of age. Within-subject standard deviation of BUA was 9.8 dB/MHz for men and 8.6 dB/ MHz for women and the component due to right and left difference was 8.4 dB/MHz for men and 6.9 dB/MHz for women. This variability of BUA between right and left heels could increase the false-positive rate by up to 28% for a cut-off of 2 SD below the mean. These data indicate that variation between left and right heel measurements of BUA is higher than that of random error measurements, particularly in men and younger, presumably more physically active subjects. Although VOS measurements were not side dependent, in the smaller number of studies examining VOS and fracture risk, VOS appears to have a weaker predictive power than BUA. Clinical and epidemiological studies involving calcaneal BUA measurements should standardize the side measured to either the dominant or non-dominant heel, to reduce within-subject variation and increase their power. 相似文献
69.
70.
结合国外图书馆网上实时参考咨询服务的研究与试验情况,详细阐述和分析了基于实时的虚拟参考咨询系统的功能和设计策略. 相似文献