首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1489篇
  免费   84篇
  国内免费   9篇
耳鼻咽喉   7篇
儿科学   57篇
妇产科学   113篇
基础医学   224篇
口腔科学   19篇
临床医学   126篇
内科学   373篇
皮肤病学   41篇
神经病学   121篇
特种医学   65篇
外科学   118篇
综合类   13篇
预防医学   69篇
眼科学   32篇
药学   127篇
中国医学   9篇
肿瘤学   68篇
  2023年   12篇
  2022年   28篇
  2021年   40篇
  2020年   23篇
  2019年   34篇
  2018年   45篇
  2017年   40篇
  2016年   43篇
  2015年   38篇
  2014年   57篇
  2013年   99篇
  2012年   101篇
  2011年   120篇
  2010年   68篇
  2009年   44篇
  2008年   59篇
  2007年   76篇
  2006年   64篇
  2005年   73篇
  2004年   66篇
  2003年   45篇
  2002年   51篇
  2001年   33篇
  2000年   41篇
  1999年   24篇
  1998年   15篇
  1997年   10篇
  1996年   7篇
  1995年   8篇
  1994年   7篇
  1993年   14篇
  1992年   14篇
  1991年   14篇
  1990年   17篇
  1989年   12篇
  1988年   13篇
  1987年   18篇
  1986年   12篇
  1985年   12篇
  1984年   7篇
  1983年   15篇
  1982年   7篇
  1981年   5篇
  1980年   3篇
  1975年   7篇
  1972年   3篇
  1971年   4篇
  1970年   5篇
  1967年   4篇
  1875年   2篇
排序方式: 共有1582条查询结果,搜索用时 31 毫秒
51.
52.
The proliferation, cell cycle exit and differentiation of progenitor cells are controlled by several different factors. The chromodomain protein mortality factor 4-like 1 (Morf4l1) has been ascribed a role in both proliferation and differentiation. Little attention has been given to the existence of alternative splice variants of the Morf4l1 mRNA, which encode two Morf41l isoforms: a short isoform (S-Morf4l1) with an intact chromodomain and a long isoform (L-Morf4l1) with an insertion in or in the vicinity of the chromodomain. The aim of this study was to investigate if this alternative splicing has a function during development. We analysed the temporal and spatial distribution of the two mRNAs and over-expressed both isoforms in the developing retina. The results showed that the S-Morf4l1 mRNA is developmentally regulated. Over-expression of S-Morf4l1 using a retrovirus vector produced a clear phenotype with an increase of early-born neurons: retinal ganglion cells, horizontal cells and cone photoreceptor cells. Over-expression of L-Morf4l1 did not produce any distinguishable phenotype. The over-expression of S-Morf4l1 but not L-Morf4l1 also increased apoptosis in the infected regions. Our results suggest that the two Morf4l1 isoforms have different functions during retinogenesis and that Morf4l1 functions are fine-tuned by developmentally regulated alternative splicing. The data also suggest that Morf4l1 contributes to the regulation of cell genesis in the retina.  相似文献   
53.
54.

Purpose

To directly compare the safety of fluoroscopic guided percutaneous thoracic pedicle screw placement between Caucasians and Asians.

Methods

This was a retrospective computerized tomography (CT) evaluation study of 880 fluoroscopic guided percutaneous pedicle screws. 440 screws were inserted in 73 European patients and 440 screws were inserted in 75 Asian patients. Screw perforations were classified into Grade 0: no violation; Grade 1: <2 mm perforation; Grade 2: 2–4 mm perforation; and Grade 3: >4 mm perforation. For anterior perforations, the pedicle perforations were classified into Grade 0: no violation, Grade 1: <4 mm perforation; Grade 2: 4–6 mm perforation; and Grade 3: >6 mm perforation.

Results

The inter-rater reliability was adequate with a kappa value of 0.83. The mean age of the study group was 58.3 ± 15.6 years. The indications for surgery were tumor (70.3 %), infection (18.2 %), trauma (6.8 %), osteoporotic fracture (2.7 %) and degenerative diseases (2.0 %). The overall screw perforation rate was 9.7 %, in Europeans 9.1 % and in Asians 10.2 % (p > 0.05). Grade 1 perforation rate was 8.4 %, Grade 2 was 1.2 % and Grade 3 was 0.1 % with no difference in the grade of perforations between Europeans and Asians (p > 0.05). The perforation rate was the highest in T1 (33.3 %), followed by T6 (14.5 %) and T4 (14.0 %). Majority of perforations occurred medially (43.5 %), followed by laterally (25.9 %), and anteriorly (23.5 %). There was no statistical significant difference (p > 0.05) in the perforation rates between right-sided pedicle screws and left-sided pedicle screws (R: 10.0 %, L: 9.3 %).

Conclusions

There were no statistical significant differences in the overall perforation rates, grades of perforations, direction of perforations for implantation of percutaneous thoracic pedicle screws insertion using fluoroscopic guidance between Europeans and Asians. The safety profile for this technique was comparable to the current reported perforation rates for conventional open pedicle screw technique.
  相似文献   
55.
The aim of the present study was to compare the efficacy, tolerability and patients’ satisfaction after the use of oral dydrogesterone with vaginal micronized progesterone for luteal-phase support (LPS) among infertile women undergoing in vitro fertilization (IVF). A total of 210 women (aged 20–40 years old) with a history of infertility, who underwent controlled ovarian stimulation for fresh intra-cytoplasmic sperm injection-embryo transfer cycles, were included in the study. Consequently, they were randomized to receive LPS with dydrogesterone 20?mg twice daily (n?=?96) or micronized progesterone 400?mg twice daily at the day of oocyte retrieval (n?=?114). The clinical success rate (31% versus 33%; p?=?0.888), miscarriage rate (5.0% versus 3.0%; p?=?0.721), ongoing pregnancy rate (30.0% versus 30.0%; p?=?1.000), implantation (22.0% versus 24.0%; p?=?0.254) and multiple pregnancy rate (5.30% versus 7.20%; p?=?0.394) were comparable among the two groups. Serum progesterone levels were significantly lower among the patients receiving dydrogesterone than the control group (13.62?±?13.83?ng/ml versus 20.66?±?18.09?ng/ml; p?=?0.001). However, there was no statistically significant difference regarding the patients’ satisfaction (p?=?0.825) and tolerability (0.790) between the two groups. Our results showed that oral dydrogesterone (40?mg/day) is as effective as vaginal micronized progesterone considering its clinical outcomes and patients’ satisfaction and tolerability, for LPS among women undergoing IVF.  相似文献   
56.
BACKGROUND: Exhaled breath contains thousands of volatile organic compounds (VOCs) that could serve as biomarkers of lung disease. Electronic noses can distinguish VOC mixtures by pattern recognition. OBJECTIVE: We hypothesized that an electronic nose can discriminate exhaled air of patients with asthma from healthy controls, and between patients with different disease severities. METHODS: Ten young patients with mild asthma (25.1 +/- 5.9 years; FEV(1), 99.9 +/- 7.7% predicted), 10 young controls (26.8 +/- 6.4 years; FEV(1), 101.9 +/- 10.3), 10 older patients with severe asthma (49.5 +/- 12.0 years; FEV(1), 62.3 +/- 23.6), and 10 older controls (57.3 +/- 7.1 years; FEV(1), 108.3 +/- 14.7) joined a cross-sectional study with duplicate sampling of exhaled breath with an interval of 2 to 5 minutes. Subjects inspired VOC-filtered air by tidal breathing for 5 minutes, and a single expiratory vital capacity was collected into a Tedlar bag that was sampled by electronic nose (Cyranose 320) within 10 minutes. Smellprints were analyzed by linear discriminant analysis on principal component reduction. Cross-validation values (CVVs) were calculated. RESULTS: Smellprints of patients with mild asthma were fully separated from young controls (CVV, 100%; Mahalanobis distance [M-distance], 5.32), and patients with severe asthma could be distinguished from old controls (CVV, 90%; M-distance, 2.77). Patients with mild and severe asthma could be less well discriminated (CVV, 65%; M-distance, 1.23), whereas the 2 control groups were indistinguishable (CVV, 50%; M-distance, 1.56). The duplicate samples replicated these results. CONCLUSION: An electronic nose can discriminate exhaled breath of patients with asthma from controls but is less accurate in distinguishing asthma severities. CLINICAL IMPLICATION: These findings warrant validation of electronic noses in diagnosing newly presented patients with asthma.  相似文献   
57.
The composition of the airway epithelium is dynamic and epithelial differentiation is regulated by endogenous mediators as well as inhaled substances. In atopic asthma the differentiation of the epithelium is altered. Various studies have addressed the ability of cultured airway epithelial cells to release the eosinophil-attractant chemokines eotaxin, eotaxin-2 and eotaxin-3 using epithelial cell lines or poorly differentiated primary cells. Since little is known about the role of the epithelial differentiation state in the response of epithelial cells to stimuli that increase production of mediators such as the eotaxins, we analyzed the effect of differentiation state on the production of the eotaxins. In particular, we investigated the effects of the Th2 cytokines IL-4 and IL-13 on eotaxin-2 and -3 production by primary human bronchial epithelial cells and examined whether their production is affected by epithelial cell differentiation using both submerged and air-liquid interface (ALI) cultures. The results show that both IL-4 and IL-13 increase eotaxin-2 and -3 mRNA expression and protein release in submerged- and ALI-cultures. Moreover, epithelial differentiation in ALI-cultures appeared an important determinant in the regulation of eotaxin-2 and -3. Mucociliary differentiation of the epithelial cells was induced by culture in the presence of a high concentration of retinoic acid (RA), whereas low concentrations of RA resulted in a flattened squamous epithelial phenotype. Mucociliary differentiated ALI-cultures expressed and released more eotaxin-3 upon stimulation with IL-4/IL-13, whereas eotaxin-2 production was predominantly found in squamous differentiated ALI-cultures. TNFalpha reduced IL-4-induced eotaxin-2 release in submerged cultures but not in ALI-cultures; no effects on eotaxin-3 synthesis were observed. The results indicate that epithelial differentiation is an important determinant in Th2 cytokine-induced eotaxin-2 and -3 release by airway epithelial cells. These findings may provide new insights into the role of airway epithelial differentiation and Th2 cytokines in the pathogenesis of inflammatory lung disorders such as asthma.  相似文献   
58.
59.
60.
The objective was to identify dental professionals' attitudes and awareness on evidence based dentistry (EBD), and to elucidate perceived barriers and views on how to move towards EBD. A questionnaire was sent to 290 dental professionals (dental hygienists, general dentists, specialist dentists) in the county of Halland, Sweden. The questionnaire consisted of closed questions and free text sections, related to attitudes, awareness and skills on databases, EBD, and terms related to scientific publications, as well as perceived barriers towards EBD. A majority of the respondents had a welcoming attitude towards EBD. The respondents perceived their colleagues less positive towards EBD. The respondents considered EBD, at least partly, useful in daily dental practice. With the exception of general dentists in private practice, a vast majority of the dental professionals thought that EBD would improve the care of their patients. Dental professionals in the county of Halland, in Sweden, had a welcoming attitude towards EBD, and indicated an open attitude for learning more about interpretation of evidence from scientific publications. The most commonly perceived barriers towards EBD, were 'lack of time' and 'poor availability of evidence'.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号