全文获取类型
收费全文 | 35593篇 |
免费 | 6859篇 |
国内免费 | 106篇 |
学科分类
医药卫生 | 42558篇 |
出版年
2024年 | 199篇 |
2023年 | 1311篇 |
2022年 | 857篇 |
2021年 | 1603篇 |
2020年 | 1769篇 |
2019年 | 1159篇 |
2018年 | 1913篇 |
2017年 | 1785篇 |
2016年 | 2099篇 |
2015年 | 2074篇 |
2014年 | 2801篇 |
2013年 | 3225篇 |
2012年 | 2280篇 |
2011年 | 2228篇 |
2010年 | 1914篇 |
2009年 | 2227篇 |
2008年 | 1708篇 |
2007年 | 1515篇 |
2006年 | 1647篇 |
2005年 | 1242篇 |
2004年 | 1097篇 |
2003年 | 932篇 |
2002年 | 807篇 |
2001年 | 370篇 |
2000年 | 311篇 |
1999年 | 343篇 |
1998年 | 446篇 |
1997年 | 355篇 |
1996年 | 308篇 |
1995年 | 271篇 |
1994年 | 214篇 |
1993年 | 157篇 |
1992年 | 155篇 |
1991年 | 139篇 |
1990年 | 151篇 |
1989年 | 107篇 |
1988年 | 89篇 |
1987年 | 75篇 |
1986年 | 76篇 |
1985年 | 76篇 |
1984年 | 71篇 |
1983年 | 65篇 |
1982年 | 35篇 |
1981年 | 38篇 |
1980年 | 37篇 |
1979年 | 21篇 |
1978年 | 36篇 |
1977年 | 29篇 |
1976年 | 22篇 |
1972年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Nicholas J Pastorek H Julia Hannay Charles S Contant 《Journal of the International Neuropsychological Society》2004,10(6):807-817
Delaying assessment until emergence from post-traumatic amnesia increases completion rates, but this practice causes variable time delays from the date of injury to testing, which can complicate the interpretation of research findings. In the current study, the performance of 105 head injury survivors on simple tests of language comprehension and attention was used to predict global outcome. It was hypothesized that 1 month performance on these measures would aid in the prediction of Disability Rating Scale (DRS) and Glasgow Outcome Scale (GOS) scores collected at 6 months post injury. Only raw scores on the modified Test of Complex Ideational Material accounted for a significant amount of the variance in DRS scores (4.4%) above that accounted for by age, education, Glasgow Coma Scale score, and pupil response. However, testability at 1 month post injury on all four tests consistently accounted for a larger portion of the variance in DRS scores (10.1-13.2%) and significantly improved prediction of GOS scores. Galveston Orientation and Amnesia Test scores collected at 1 month post injury accounted for substantially less variance in DRS scores (7.7-8.4%). Neuropsychological data, including the testability of patients, collected uniformly at 1 month following injury can contribute to the prediction of global outcome. 相似文献
132.
133.
Amy Y. Chen MD MPH Nicole Schrag MSPH Yongping Hao PhD W. Dana Flanders MD DSc James Kepner PhD Andrew Stewart MS Elizabeth Ward PhD 《Otolaryngology--head and neck surgery》2006,135(6):831-837
OBJECTIVE: In 1991, a randomized study was published and demonstrated that use of nonsurgical therapy (chemoradiation) provided similar survival to total laryngectomy (the gold standard) for patients with advanced-stage laryngeal cancer. The purpose of this study was to assess how treatment of advanced laryngeal cancer was influenced by such developments in non-surgical therapy. STUDY DESIGN: Patterns of care study using National Cancer Database (1985-2001). RESULTS: The percentage of advanced-stage patients treated with chemoradiation increased from 8.3% to 20.8% while the proportion treated with radiation alone decreased from 38.9% to 23.0%. Use of chemoradiation increased at a significantly faster rate after the 1991 publication at both community cancer centers and teaching research facilities. The use of total laryngectomy decreased slightly during this period. CONCLUSIONS: The use of chemoradiation increased after the 1991 publication. It was impossible to determine from the NCDB whether additional patients who could benefit from chemo-RT were not offered or did not complete this treatment option. We recommend that treatment recommendations discussed at tumor boards be recorded in cancer registries. 相似文献
134.
Darik K. Taniguchi MD Roy W. Martin PhD Eugene A. Trowers MPH MD Fred E. Silverstein MD 《Gastrointestinal endoscopy》1995,41(6)
We report the simultaneous measurement of esophageal wall layer thickness and intraluminal pressure in the sheep esophagus using a miniature suction device incorporating a high-frequency ultrasound transducer and a manometry system. Transnasal placement of the device into the distal esophagus of a conscious sheep allowed observation of 133 swallowing events during three trials, each lasting from 45 to 60 minutes. In a fourth trial, 11 sequential dry and 23 sequential wet swallows were compared. Maximum manometric pressure, esophageal wall layer thickness, and duration of contraction were measured. All swallowing events produced simultaneous increases in intraluminal pressure and esophageal wall thickness. Mean maximal pressures were lower for dry swallows (18 ± 2.1 mm Hg) than wet swallows (22 ± 3.0 mm Hg) (p < .01). Thickness of the inner (circular) muscle layer increased above baseline by 124% for dry swallows and 161% for wet swallows (p < .01). We conclude that thickening of the esophageal inner (circular) muscle layer may be important in the generation of intraluminal esophageal pressure in the sheep esophagus. (Gastrointest Endosc 1995;41:582-6.) 相似文献
135.
136.
Dai Z Weichenhan D Wu YZ Hall JL Rush LJ Smith LT Raval A Yu L Kroll D Muehlisch J Frühwald MC de Jong P Catanese J Davuluri RV Smiraglia DJ Plass C 《Genome research》2002,12(10):1591-1598
Knudson's two-hit hypothesis postulates that genetic alterations in both alleles are required for the inactivation of tumor-suppressor genes. Genetic alterations include small or large deletions and mutations. Over the past years, it has become clear that epigenetic alterations such as DNA methylation are additional mechanisms for gene silencing. Restriction Landmark Genomic Scanning (RLGS) is a two-dimensional gel electrophoresis that assesses the methylation status of thousands of CpG islands. RLGS has been applied successfully to scan cancer genomes for aberrant DNA methylation patterns. So far, the majority of this work was done using NotI as the restriction landmark site. Here, we describe the development of RLGS using AscI as the restriction landmark site for genome-wide scans of cancer genomes. The availability of AscI as a restriction landmark for RLGS allows for scanning almost twice as many CpG islands in the human genome compared with using NotI only. We describe the development of an AscI-EcoRV boundary library that supports the cloning of novel methylated genes. Feasibility of this system is shown in three tumor types, medulloblastomas, lung cancers, and head and neck cancers. We report the cloning of 178 AscI RLGS fragments via two methods by use of this library. 相似文献
137.
SUMO modification of a novel MAR-binding protein, SATB2, modulates immunoglobulin mu gene expression 下载免费PDF全文
Nuclear matrix attachment regions (MARs) are regulatory DNA sequences that are important for higher-order chromatin organization, long-range enhancer function, and extension of chromatin modifications. Here we characterize a novel cell type-specific MAR-binding protein, SATB2, which binds to the MARs of the endogenous immunoglobulin micro locus in pre-B cells and enhances gene expression. We found that SATB2 differs from the closely related thymocyte-specific protein SATB1 by modifications of two lysines with the small ubiquitive related modifier (SUMO), which are augmented specifically by the SUMO E3 ligase PIAS1. Mutations of the SUMO conjugation sites of SATB2 enhance its activation potential and association with endogenous MARs in vivo, whereas N-terminal fusions with SUMO1 or SUMO3 decrease SATB2-mediated gene activation. Sumoylation is also involved in targeting SATB2 to the nuclear periphery, raising the possibility that this reversible modification of a MAR-binding protein may contribute to the modulation of subnuclear DNA localization. 相似文献
138.
Monoclonal Antibodies to Trypanosoma cruzi Inhibit Motility and Nucleic Acid Synthesis of Culture Forms 总被引:2,自引:1,他引:2 下载免费PDF全文
Maria Julia Manso Alves Masamichi Aikawa Ruth S. Nussenzweig 《Infection and immunity》1983,39(1):377-382
Monoclonal antibodies were raised against the surface of epimastigotes and metacylic trypomastigotes of Trypanosoma cruzi, as shown by electron microscopy, agglutination, and immunofluorescence. The antibodies were stage specific but not strain specific. A deleterious effect of the antibodies on T. cruzi culture forms was shown by the drastic reduction of parasite motility and incorporation of nucleic acid precursors. Some fraction of the parasite population, however, was viable and replicated and infected mouse macrophages in culture. The antibodies were found to also mediate complement-induced lysis of culture forms of T. cruzi. 相似文献
139.
140.
Cell extract-derived differentiation of embryonic stem cells 总被引:1,自引:0,他引:1
Various means have been used to encourage the differentiation of embryonic stem cells (ESCs) toward specific lineages, including growth factor administration, genetic modification, and coculture with relevant cells/tissues. Cell extract-based reprogramming has recently been used to derive mature cells from nonrelated phenotypes. In this communication, we tested whether this in vitro reprogramming approach can be used to direct ESC differentiation. Permeabilized murine ESCs exposed to extracts of murine type II pneumocytes showed increased expression of surfactant protein C and its corresponding mRNA, reflecting enhanced differentiation of pneumocytes. Subsequent differentiation to a type I phenotype was demonstrated by expression of aquaporin 5. Pneumocyte formation occurred quicker than with growth factor-induced differentiation. Our findings establish that ESCs can be differentiated in vitro using cellular extracts. This model provides a tool for analysis of the key factors involved in the differentiation of ESCs to type II pneumocytes. 相似文献