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   1658篇
  免费   42篇
  国内免费   29篇
耳鼻咽喉   33篇
儿科学   6篇
妇产科学   29篇
基础医学   356篇
口腔科学   90篇
临床医学   104篇
内科学   169篇
皮肤病学   18篇
神经病学   145篇
特种医学   59篇
外科学   207篇
综合类   188篇
预防医学   78篇
眼科学   32篇
药学   104篇
  1篇
中国医学   63篇
肿瘤学   47篇
  2023年   12篇
  2022年   22篇
  2021年   40篇
  2020年   27篇
  2019年   21篇
  2018年   43篇
  2017年   27篇
  2016年   34篇
  2015年   23篇
  2014年   74篇
  2013年   117篇
  2012年   78篇
  2011年   87篇
  2010年   63篇
  2009年   82篇
  2008年   73篇
  2007年   99篇
  2006年   82篇
  2005年   50篇
  2004年   57篇
  2003年   52篇
  2002年   43篇
  2001年   48篇
  2000年   40篇
  1999年   31篇
  1998年   35篇
  1997年   31篇
  1996年   30篇
  1995年   25篇
  1994年   24篇
  1993年   23篇
  1992年   26篇
  1991年   19篇
  1990年   19篇
  1989年   20篇
  1988年   13篇
  1987年   17篇
  1986年   16篇
  1985年   22篇
  1984年   9篇
  1983年   4篇
  1982年   11篇
  1981年   15篇
  1980年   11篇
  1979年   7篇
  1978年   5篇
  1977年   4篇
  1976年   4篇
  1974年   7篇
  1970年   2篇
排序方式: 共有1729条查询结果,搜索用时 468 毫秒
51.
Zebrafish embryos are increasingly used for developmental toxicity screening of candidate drugs and are occasionally co-incubated with a metabolic activation system at 32 °C for 1, 2 or 4 h, depending on their developmental stage. As this temperature is higher than the optimal temperature for zebrafish embryonic development (26–28.5 °C), we investigated whether continuous incubation of zebrafish embryos from 2.5 until 96 h post fertilization (hpf) at high temperatures (30.5–36.5 °C) causes malformations. At 32.5 °C tail malformations were observed as early as 24 hpf, and these became even more prominent at 34.5 and 36.5 °C. Cardiovascular and head malformations, edema and blood accumulations throughout the body were present at 36.5 °C. Finally, temperatures higher than 28.5 °C accelerated embryonic development except for 36.5 °C, at which a lower hatching rate and hatching enzyme activity were observed. In conclusion, incubation of zebrafish embryos at 32.5 °C and above from 2.5 until 96 hpf causes malformations as early as 24 hpf.  相似文献   
52.
目的 验证高清胃镜下早期胃癌筛检策略的效能。方法 前瞻性纳入2018年12月—2019年1月在解放军总医院第七医学中心行胃镜检查的849例年龄≥35岁的患者。在胃镜检查时,从未感染过幽门螺杆菌者对任何可疑病灶活检;溃疡型病灶于溃疡边缘活检;萎缩区域外,贲门部对白光下呈红色的病灶活检,非贲门部对具有清晰边界或白光下呈白色的病灶活检;萎缩区域内,隆起型病灶中具有清晰边界或顶部有不规则凹陷者活检,平坦/凹陷型病灶中边界不规则或窄带光下呈赭色者活检。此外,可对不符合上述策略但认为有必要活检的任何病灶进行活检。其后根据活检或手术病理,对胃癌高危患者进行胃镜随访,分析该策略对胃部早期肿瘤性病变的检出及漏诊情况,明确该策略的敏感度和阳性预测值。结果 共对548例患者的781处病灶进行了活检。在符合上述策略的327处病灶中,诊断上皮肿瘤性病灶16处(4.9%,16/327),其中高级别肿瘤10处(3.1%,10/327);而在不符合上述策略的454处病灶中,诊断上皮肿瘤性病灶仅1处(0.2%,1/454),无高级别肿瘤。该筛检策略对胃上皮肿瘤性病灶和高级别肿瘤的阳性预测值均高于不符合策略而取活检者(4.9%比0.2%,χ2=19.49,P<0.001;3.1%比0,P<0.001)。共有146例(17.2%,146/849)患者接受胃镜随访,随访中发现2处黏膜内高级别肿瘤,符合筛检策略。该筛检策略在初次胃镜检查中检出了84.2%(16/19)的上皮肿瘤性病灶和83.3%(10/12)的高级别肿瘤。结论 高清胃镜下早期胃癌筛检策略可以高效地检出早期胃癌。  相似文献   
53.
目的探寻冠状动脉慢血流现象(CSFP)的临床危险因素,了解冠状动脉形态对心肌梗死溶栓治疗试验(TIMI)血流的影响,推测CSFP的发病机制。方法回顾性收集2017年1月至2019年7月于兰州大学第一医院心脏中心行冠状动脉造影无狭窄病变的患者256例,根据TIMI血流帧数将其中血流减慢的患者设为CSFP组(100例),将血流正常患者设为对照组(156例),按年龄和性别匹配。收集患者临床数据和冠状动脉造影数据,采用二元logistic回归模型分析CSFP的危险因素,并采用Pearson相关分析检验冠状动脉形态学参数与平均校正的TIMI帧数(cTFC)的相关性。结果CSFP组同型半胱氨酸[(22.07±7.27)mmol/L比(18.16±6.63)mmol/L]、中性粒细胞百分比[(44.40±15.60)%比(35.43±12.49)%]、淋巴细胞百分比[3.65%(1.32%,24.65%)比1.80%(1.02%,6.22%)]、平均血小板体积(MPV)[(13.17±1.82)fl比(12.20±1.57)fl]、血小板分布宽度(PDW)[(14.17±2.17)f l比(13.21±2.42)f l]与对照组相比更高,三酰甘油[(3.05±1.37)mmol/L比(3.44±1.36)mmol/L]、纤维蛋白原[(2.65±0.68)g/L比(2.86±0.66)g/L]与对照组相比更低,术中血压更低,冠状动脉平均直径更大,平均远端分支数更少,差异均有统计学意义(均P<0.05)。二元logistic回归模型拟合显示:同型半胱氨酸(OR 1.077,95%CI 1.034~1.123,P<0.001)、中性粒细胞百分比(OR 1.064,95%CI 1.032~1.097,P<0.001)、PDW(OR 1.194,95%CI 1.051~1.356,P=0.006)、MPV(OR 1.338,95%CI 1.127~1.588,P=0.001)是预测CSFP的独立危险因素。相关性分析显示,冠状动脉平均直径与平均cTFC呈显著正相关(r=0.583,P<0.05);冠状动脉平均远端分支数与平均cTFC呈显著负相关(r=-0.508,P<0.05)。结论同型半胱氨酸、中性粒细胞百分比、PDW和MPV是预测CSPF的独立危险因素。冠状动脉平均直径和远端分支数均与冠状动脉平均cTFC密切相关。炎症可能是CSFP发生的关键机制。  相似文献   
54.
Summary We have studied the morphology and cytochemistry in relation to the immunological phenotyping and functional properties of T cells from eight patients with chronic T lymphocytosis. At the light microscopic level the morphology of the patients' lymphocytes was similar to that described for large granular lymphocytes. Ultrastructurally, a division into two groups could be made on differences in the amount of cytoplasm and the location and the more irregular form of the nuclei. The lymphocytes of one group (five patients) had in common the phenotype Fc+, T3+, T4–, T8+, Ia–, M1– and demonstrated (with the exception of one patient) the same functions: presence of K-cell activity, absence of NK, helper and suppressor cell activities. In the other group (three patients), the lymphocytes of one patient showed the same phenotype and functions as those indicated above. The other two patients both lacked the T8 antigen on their lymphocytes but were different with regard to other surface markers. In addition, their cells were functionally identical: both demonstrated NK- and K-cell activity. Thus in this group of eight patients with chronic T lymphocytosis, the immunological and functional subdivision paralleled in part a morphological division at the ultrastructural level.  相似文献   
55.
A central question for theories of inflected word processing is to determine under what circumstances compositional procedures apply. Some accounts (e.g., the dual-mechanism model; Clahsen, 1999 Clahsen, H. 1999. Lexical entries and rules of language: A multidisciplinary study of German inflections. Behavioral and Brain Sciences, 22: 9911060. [Crossref], [PubMed], [Web of Science ®] [Google Scholar]) propose that compositional processes only apply to verbs that take productive affixes. For all other verbs, inflected forms are assumed to be stored in the lexicon in a nondecomposed manner. This account makes clear predictions about the consequences of disruption to the lexical access mechanisms involved in the spoken production of inflected forms. Briefly, it predicts that nonproductive forms (which require lexical access) should be more affected than productive forms (which, depending on the language task, may not). We tested these predictions through the detailed analysis of the spoken production of a German-speaking individual with an acquired lexical impairment resulting from a stroke. Analyses of response accuracy, error types, and frequency effects revealed that combinatorial processes are not restricted to verbs that take productive inflections. On this basis, we propose an alternative account, the stem-based assembly model (SAM), which posits that combinatorial processes may be available to all stems and not only to those that combine with productive affixes.  相似文献   
56.
57.
58.
Bone defects can occur in various forms and present challenges to performing a standard micro-CT evaluation of bone quality because most measures are suited to homogeneous structures rather than ones with spatially focal abnormalities. Such defects are commonly associated with pain and fragility. Research involving bone defects requires quantitative approaches to be developed if micro-CT is to be employed. In this study, we demonstrate that measures of inter-microarchitectural bone spacing are sensitive to the presence of focal defects in the proximal tibia of two distinctly different mouse models: a burr-hole model for fracture healing research, and a model of osteolytic bone metastases. In these models, the cortical and trabecular bone compartments were both affected by the defect and were, therefore, evaluated as a single unit to avoid splitting the defects into multiple analysis regions. The burr-hole defect increased mean spacing (Sp) by 27.6%, spacing standard deviation (SpSD) by 113%, and maximum spacing (Spmax) by 72.8%. Regression modeling revealed SpSD (β = 0.974, p < 0.0001) to be a significant predictor of the defect volume (R2 = 0.949) and Spmax (β = 0.712, p < 0.0001) and SpSD (β = 0.271, p = 0.022) to be significant predictors of the defect diameter (R2 = 0.954). In the mice with osteolytic bone metastases, spacing parameters followed similar patterns of change as reflected by other imaging technologies, specifically bioluminescence data which is indicative of tumor burden. These data highlight the sensitivity of spacing measurements to bone architectural abnormalities from 3D micro-CT data and provide a tool for quantitative evaluation of defects within a bone.  相似文献   
59.
There has long been interest in why languages are shaped the way they are, and in the relationship between sign language and gesture. In sign languages, entity classifiers are handshapes that encode how objects move, how they are located relative to one another, and how multiple objects of the same type are distributed in space. Previous studies have shown that hearing adults who are asked to use only manual gestures to describe how objects move in space will use gestures that bear some similarities to classifiers. We investigated how accurately hearing adults, who had been learning British Sign Language (BSL) for 1–3 years, produce and comprehend classifiers in (static) locative and distributive constructions. In a production task, learners of BSL knew that they could use their hands to represent objects, but they had difficulty choosing the same, conventionalized, handshapes as native signers. They were, however, highly accurate at encoding location and orientation information. Learners therefore show the same pattern found in sign-naïve gesturers. In contrast, handshape, orientation, and location were comprehended with equal (high) accuracy, and testing a group of sign-naïve adults showed that they too were able to understand classifiers with higher than chance accuracy. We conclude that adult learners of BSL bring their visuo-spatial knowledge and gestural abilities to the tasks of understanding and producing constructions that contain entity classifiers. We speculate that investigating the time course of adult sign language acquisition might shed light on how gesture became (and, indeed, becomes) conventionalized during the genesis of sign languages.  相似文献   
60.
A case of Crohn's colitis with unusual endoscopic and morphologic appearances is reported. The colitis was asymptomatic and discovered incidentally. Histologic confirmation was obtained following segmental colectomy.  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