全文获取类型
收费全文 | 24423篇 |
免费 | 2053篇 |
国内免费 | 44篇 |
专业分类
耳鼻咽喉 | 267篇 |
儿科学 | 816篇 |
妇产科学 | 564篇 |
基础医学 | 3192篇 |
口腔科学 | 556篇 |
临床医学 | 2409篇 |
内科学 | 4537篇 |
皮肤病学 | 570篇 |
神经病学 | 2534篇 |
特种医学 | 687篇 |
外科学 | 3368篇 |
综合类 | 432篇 |
一般理论 | 34篇 |
预防医学 | 2397篇 |
眼科学 | 558篇 |
药学 | 1597篇 |
中国医学 | 21篇 |
肿瘤学 | 1981篇 |
出版年
2022年 | 152篇 |
2021年 | 267篇 |
2020年 | 212篇 |
2019年 | 340篇 |
2018年 | 394篇 |
2017年 | 330篇 |
2016年 | 353篇 |
2015年 | 423篇 |
2014年 | 566篇 |
2013年 | 1059篇 |
2012年 | 1294篇 |
2011年 | 1429篇 |
2010年 | 836篇 |
2009年 | 762篇 |
2008年 | 1401篇 |
2007年 | 1434篇 |
2006年 | 1436篇 |
2005年 | 1420篇 |
2004年 | 1320篇 |
2003年 | 1261篇 |
2002年 | 1215篇 |
2001年 | 399篇 |
2000年 | 353篇 |
1999年 | 403篇 |
1998年 | 331篇 |
1997年 | 269篇 |
1996年 | 242篇 |
1995年 | 232篇 |
1994年 | 228篇 |
1993年 | 237篇 |
1992年 | 314篇 |
1991年 | 313篇 |
1990年 | 321篇 |
1989年 | 288篇 |
1988年 | 237篇 |
1987年 | 199篇 |
1986年 | 259篇 |
1985年 | 219篇 |
1984年 | 240篇 |
1983年 | 216篇 |
1982年 | 259篇 |
1981年 | 227篇 |
1980年 | 187篇 |
1979年 | 200篇 |
1978年 | 145篇 |
1977年 | 158篇 |
1976年 | 148篇 |
1974年 | 168篇 |
1973年 | 144篇 |
1972年 | 147篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Mozammil Hussain Raghu N. Natarajan Amir H. Fayyazi Brian R. Braaksma Gunnar B.J. Andersson Howard S. An 《The spine journal》2009,9(12):1016-1023
Background contextAnterior corpectomy and reconstruction with bone graft and a rigid screw-plate construct is an established procedure for treatment of cervical neural compression. Despite its reliability in relieving symptoms, there is a high rate of construct failure, especially in multilevel cases.PurposeThere has been no study evaluating the biomechanical effects of screw angulation on construct stability; this study investigates the C4–C7 construct stability and load-sharing properties among varying screw angulations in a rigid plate-screw construct.Study designA finite element model of a two-level cervical corpectomy with static anterior cervical plate.MethodsA three-dimensional finite element (FE) model of an intact C3–T1 segment was developed and validated. From this intact model, a fusion model (two-level [C5, C6] anterior corpectomy) was developed and validated. After corpectomy, allograft interbody fusion with a rigid anterior screw-plate construct was created from C4 to C7. Five additional FE models were developed from the fusion model corresponding to five different combinations of screw angulations within the vertebral bodies (C4, C7): (0°, 0°), (5°, 5°), (10°, 10°), (15°, 15°), and (15°, 0°). The fifth fusion model was termed as a hybrid fusion model.ResultsThe stability of a two-level corpectomy reconstruction is not dependent on the position of the screws. Despite the locked screw-plate interface, some degree of load sharing is transmitted to the graft. The load seen by the graft and the shear stress at the bone-screw junction is dependent on the angle of the screws with respect to the end plate. Higher stresses are seen at more divergent angles, particularly at the lower level of the construct.ConclusionThis study suggests that screw divergence from the end plates not only increases load transmission to the graft but also predisposes the screws to higher shear forces after corpectomy reconstruction. In particular, the inferior screw demonstrated larger stress than the upper-level screws. In the proposed hybrid fusion model, lower stresses on the bone graft, end plates, and bone-screw interface were recorded, inferring lower construct failure (end-plate fractures and screw pullout) potential at the inferior construct end. 相似文献
13.
14.
15.
16.
Ki-Won Kim Kee-Yong Ha Jun-Seok Lee Suk-Woo Nam Young-Kyun Woo Tae-Hong Lim Howard S. An 《The spine journal》2009,9(4):323-329
Background contextIt was recently demonstrated that the postnatal transition from a notochordal to a fibrocartilaginous nucleus pulposus (NP) is accomplished exogenously by chondrocytes migrating from hyaline cartilage end plates (CEs) into the ectopic notochordal NP region. Although our previous in vivo studies showed evidences for the migration of CE chondrocyte from hyaline CEs into the notochordal NP, it is unknown whether CE chondrocytes of the intervertebral disc (IVD) really have a motile property. In addition, the effect of notochordal cells on this property has not been elucidated.PurposeThe purpose of this in vitro study was to demonstrate whether CE chondrocytes of the IVD are capable of migration, and whether there is any biological link between notochordal cells and CE chondrocytes that may regulate the CE chondrocyte migration.Study design/settingIn vitro cell migration assays were performed using rat IVDs.MethodsNotochordal cells and chondrocytes were obtained from the NP and CE tissues, respectively, and were cultured separately. The different numbers of notochordal cells and the supernatant (conditioned medium) that contained soluble factors produced by notochordal cells were used to demonstrate their effects on the migration of CE chondrocytes. Bovine serum albumin (BSA) and lysophosphatidic acid (LPA) were used as negative and positive controls, respectively.ResultsCompared with BSA, LPA, notochordal cells (N=4×, 2×, 1×, and 0.5×105), and its conditioned media (unconcentrated and fivefold concentrated) significantly increased migration of CE chondrocytes (p<.05 in all comparisons). Particularly, notochordal cells and its conditioned media increased migration in a number- and concentration-dependent manner, respectively.ConclusionsThis study demonstrates that CE chondrocytes of the IVD are capable of migration and that soluble factors produced by notochordal cells stimulate the migration. These results provide a plausible explanation to the question of why CE chondrocytes of the IVD migrate into the ectopic NP region during the natural transition from the notochordal to fibrocartilaginous NP. 相似文献
17.
Timson C Appanna Shareen H Doak Spencer A Jenkins Howard G Kynaston Timothy P Stephenson James M Parry 《International journal of urology》2007,14(6):539-544
OBJECTIVE: Tumors arising within augmentation cystoplasties are aggressive, have poor prognosis and the majority are not detected at follow-up cystoscopy. Genetic changes in tumors precede morphological abnormalities. Therefore, the aim of this study was to investigate whether genetic abnormalities detected by comparative genomic hybridization (CGH) could be used to identify those patients with augmentation cystoplasties at increased risk of tumorigenesis. METHODS: Bladder biopsy samples were obtained from 16 augmentation cystoplasty patients both distant from and near to the enterovesical anastomosis. CGH was used to detect genetic abnormalities in DNA extracted from the biopsies, archival specimens of two augmentation cystoplasties and two de novo bladder adenocarcinomas. RESULTS: A greater number of amplifications on 2p, 3q, 8q, 9p, 17p, 18pq and 20pq, were observed in bladder biopsies obtained near to the enterovesical anastomosis compared to those taken distant to the suture line. CGH of archival augmentation cystoplasty tumor DNA indicated abnormalities at several loci with amplifications at 2q, 5q, 10p and 21pq, while deletions occurred at 5p and 16p. CONCLUSIONS: The results of this study suggest that the urothelium adjacent to the bladder and/or bowel anastomosis in augmentation cystoplasties is genetically unstable. Furthermore, longitudinal studies are required to establish whether or not patients exhibiting genetic instability following augmentation cystoplasty are at greater risk of developing tumors than those with genetically stable epithelia. 相似文献
18.
Endla K. Anday Michelle E. Cohen Howard S. Hoffman 《Developmental medicine and child neurology》1991,33(2):130-137
This study compared the results of reflex modification (RM)--an objective technique for assessing brainstem sensorineural processing--with those of auditory brainstem response (ABR) for a group of high-risk infants at comparable postconceptional ages. For the RM procedure, an eyeblink-eliciting tap to the glabella was presented either alone or accompanied by a brief 90dB SPL tone. 37 high-risk infants were tested with both RM and ABR at a mean postconceptional age of 37.3 weeks. Seven had an increased brainstem conduction time ('failed ABR') and eight did not exhibit significant reflex augmentation ('failed RM'), seven of whom also failed the ABR. These data provide evidence that sensory stimuli which affect the neural mechanisms responsible for the organization of the startle response and auditory processing share essential neural components. 相似文献
19.
In-vitro/in-vivo correlation of pulsatile drug release from press-coated tablet formulations: a pharmacoscintigraphic study in the beagle dog. 总被引:1,自引:0,他引:1
Manish Ghimire Fiona J McInnes David G Watson Alexander B Mullen Howard N E Stevens 《European journal of pharmaceutics and biopharmaceutics》2007,67(2):515-523
The aim of the current study was to investigate the in-vitro and in-vivo performance of a press-coated tablet (PCT) intended for time delayed drug release, consisting of a rapidly disintegrating theophylline core tablet, press-coated with barrier granules containing glyceryl behenate (GB) and low-substituted hydroxypropylcellulose (L-HPC). The PCTs showed pulsatile release with a lag time dependent upon the GB and L-HPC composition of the barrier layer. In-vivo gamma-scintigraphic studies were carried out for PCTs containing GB:L-HPC at 65:35 w/w and 75:25 w/w in the barrier layer in four beagle dogs, in either the fed or fasted state. The in-vivo lag time in both the fed and fasted states did not differ significantly (p>0.05) from the in-vitro lag time. Additionally, no significant difference (p<0.05) between in-vivo fed and fasted disintegration times was observed, demonstrating that in-vivo performance of the PCT was not influenced by the presence or absence of food in the gastrointestinal tract. A distinct lag time was obtained prior to the appearance of drug in plasma and correlated (R2=0.98) with disintegration time observed from scintigraphic images. However, following disintegration, no difference in pharmacokinetic parameters (AUC(0-6 dis), K(el), Cmax) was observed. The current study highlighted the potential use of these formulations for chronopharmaceutical drug delivery. 相似文献
20.