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   15415篇
  免费   1222篇
  国内免费   37篇
耳鼻咽喉   297篇
儿科学   321篇
妇产科学   210篇
基础医学   1961篇
口腔科学   528篇
临床医学   1483篇
内科学   3112篇
皮肤病学   201篇
神经病学   1724篇
特种医学   560篇
外科学   2164篇
综合类   242篇
一般理论   10篇
预防医学   1421篇
眼科学   265篇
药学   1042篇
  1篇
中国医学   9篇
肿瘤学   1123篇
  2023年   84篇
  2022年   143篇
  2021年   272篇
  2020年   198篇
  2019年   227篇
  2018年   296篇
  2017年   231篇
  2016年   241篇
  2015年   239篇
  2014年   388篇
  2013年   662篇
  2012年   866篇
  2011年   946篇
  2010年   550篇
  2009年   544篇
  2008年   949篇
  2007年   985篇
  2006年   1033篇
  2005年   980篇
  2004年   962篇
  2003年   971篇
  2002年   955篇
  2001年   165篇
  2000年   109篇
  1999年   146篇
  1998年   214篇
  1997年   197篇
  1996年   195篇
  1995年   162篇
  1994年   140篇
  1993年   107篇
  1992年   113篇
  1991年   108篇
  1990年   101篇
  1989年   75篇
  1988年   93篇
  1987年   79篇
  1986年   90篇
  1985年   95篇
  1984年   125篇
  1983年   136篇
  1982年   161篇
  1981年   140篇
  1980年   153篇
  1979年   72篇
  1978年   114篇
  1977年   91篇
  1976年   96篇
  1974年   72篇
  1972年   60篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
171.
Although RNA can be retrieved from formalin-fixed, paraffin-embedded (FFPE) tissues, the yield is low, and the RNA is fragmented. Recent advances in gene expression profiling underscore the importance of identifying a fixative that preserves histology and mRNA. We demonstrated that, for immersion fixation of brains, 70% ethanol is superior to formalin for mRNA preservation. RNA yield from ethanol-fixed tissues was 70% of the yield from fresh frozen specimens, but only a negligible quantity was recovered from formalin-fixed tissues. RNA from ethanol-fixed brains showed integrity comparable to RNA from fresh frozen tissues, and RT-PCR using RNA from ethanol-fixed tissues was consistently successful. RNA from FFPE tissues composed of low-molecular weight fragments, and their use in RT-PCR failed repeatedly. The yield and quality of RNA from ethanol-fixed brains were unaffected after immersion at 4 degrees C for 2 weeks. In a blinded comparison to FFPE tissues, ethanol-fixed specimens were judged to show comparable histology and superior immunostaining. After laser capture microdissection (LCM), we failed to recover mRNA from FFPE tissues but retrieved mRNA from ethanol-fixed tissues for RT-PCR and cDNA microarray analysis. We conclude that 70% ethanol preserves RNA integrity and is suitable for expression profiling of brain tissues by LCM and cDNA microarray.  相似文献   
172.
Twenty-four control and 104 stinging insect—allergic patients were tested in this multicenter study, which compared the utility of individual venom and whole body extract (WBE) preparations for diagnosis. This study indicates that venom skin testing is more specific and more reliable than is testing with WBE. There was a high rate of WBE skin-test reactivity among controls. False-positive skin testing with venom was not a problem at concentrations of 1 μg/ml or less. Only one mild and easily treated adverse reaction occurred in this study.  相似文献   
173.
Skeletal differences exist between closely matched Black and White women, although it is unknown if similar differences also exist between Black and White men after controlling for age, body weight, and stature. The aim of this study was twofold: to test the hypothesis that Black men have greater bone mass, higher bone mineral density, and longer limbs compared to White men of similar age, weight, and height; and second, to establish if ethnic variation in skeletal characteristics has an impact on the models upon which three widely used methods for estimating total body fat are based. Twenty-four healthy Black men were matched by age (±5 years), height (±3 cm), and weight (±2 kg) to 24 healthy White men. Skeletal characteristics and body composition were studied using anatomical and compartment estimates derived by anthropometry, 3H2O dilution, hydrodensitometry, whole-body 40K counting, and dual photon systems. Black men had greater bone mineral mass (P = 0.007), higher bone density (P = 0.054), longer femurs (P = 0.002), longer anthropometric arm and thigh lengths (P = 0.001 and P = 0.002, respectively), lower spine to femur ratio (P = 0.004), and similar spine length (P = 0.271) compared to White men. Total body fat and fat-free body mass (FFM) were estimated in the men using a four-compartment model. Black and White men had similar total body fat, K (TBK), water (TBW), and FFM. Density of FFM and TBK/FFM were also similar between Black and White men, suggesting that current two-compartment hydrodensitometry and TBK models for estimating fat may not require adjustments for ethnicity. The TBW/FFM ratio, which is the main assumed steady-state relation for the two-compartment TBW method of estimating fat, was modestly increased (P = 0.05) in Black men (x? ± SD, 0.744 ± 0.018) compared to White men (0.732 ± 0.021). These results confirm that Black and White men differ significantly in some skeletal characteristics and these differences have implications in the study of both osteoporosis and human body composition. © 1994 Wiley-Liss, Inc.  相似文献   
174.
Distributed computing can be applied to CT or MRI scanner image acquisition, printing, and archiving by interfacing the scanner with a computer network. Also on the network must be a computer workstation that has image management software to capture the images sent over the network by the scanner. This software must also allow the radiology staff to print and archive the images. Several benefits are realized by this network configuration. First, the scanner console is solely used for scanning patients; delays are not encountered because the console is being used for printing and archiving images. Also, the workstation printing software can be developed so that useful features not available at the scanner console can be incorporated. Finally, sophisticated archiving strategies can be implemented at the workstation. We have developed a network image management station at the Fox Chase Cancer Center using a reduced instruction set computer (RISC) workstation. Hardware and software is utilized to convert all scanner image data to the American College of Radiology-National Electrical Manufacturers Association format. All workstation software is developed using the open X-Windows standard. Digital audio tape is used for image archiving.  相似文献   
175.
Pathologic anxiety, marked by inappropriate apprehension and/or fear, causes patients to seek help. Anxiety is associated with a wide variety of physical illnesses, and these must be initially considered when making a diagnosis. Similarly, anxiety associated with a wide variety of psychiatric syndromes must also be considered. Finally, the possibility of transient situational anxiety is ever present. Once it is determined that a primary anxiety disorder exists, then the presence or absence of phobias, panic attacks, and chronic "free-floating" anxiety will fully characterize the disorder. With an accurate diagnosis in hand, a multifaceted treatment approach can be designed. Effective treatments now exist for phobic and panic disorders, and more effective treatment for chronic generalized anxiety may be forthcoming.  相似文献   
176.
Summary Resistance to teniposide (VM-26) by VM-26 selected resistant L1210 cells in culture was attributed to alterations in the flux of VM-26 across the plasma membrane and to functions of homogeneously staining regions that appeared on one or more chromosomes. In the present study, electrophoresis of membrane-cytosol fractions of these resistant sublines demonstrated a protein band, Mr 22 kd, that was not evident in similar fractions of drugsensitive L1210 cells or three revertant sublines. The distribution of this protein among various cellular fractions could be altered by manipulation of the concentration of calcium ions. A representative subline, LIa5 M, was observed to have vesicles that reacted with Sudan black B stain, an indication of altered lipid metabolism. The LIa5 M subline was cross-resistant to etoposide, vincristine, doxorubicin, amsacrine, and actinomycin D. Concentrations of VM-26 that inhibited cell division to the same extent caused an accumulation of fewer cells in the G2 stage of cell division in LIa5 M cultures than in L1210 cultures. These observations indicate that the LIa5 M subline expressed multiple drug resistance, as well as changes in the expression of cytotoxicity to VM-26.This investigation was supported by Research Project Grant CA 35319, by Cancer Center Support (CORE) Grant CA 21765 from the National Cancer Institute, and by the American Lebanese Syrian Associated Charities.Recipient of research support from a training grant, American Cancer Society Grant IN-85-06, to the University of Tennessee Center for the Health Sciences  相似文献   
177.
178.
Functional and nutraceutical foods provide an alternative way to improve immune function to aid in the management of various diseases. Traditionally, many medicinal products have been derived from natural compounds with healing properties. With the development of research into nutraceuticals, it is becoming apparent that many of the beneficial properties of these compounds are at least partly due to the presence of polyphenols. There is evidence that dietary polyphenols can influence dendritic cells, have an immunomodulatory effect on macrophages, increase proliferation of B cells, T cells and suppress Type 1 T helper (Th1), Th2, Th17 and Th9 cells. Polyphenols reduce inflammation by suppressing the pro-inflammatory cytokines in inflammatory bowel disease by inducing Treg cells in the intestine, inhibition of tumor necrosis factor-alpha (TNF-α) and induction of apoptosis, decreasing DNA damage. Polyphenols have a potential role in prevention/treatment of auto-immune diseases like type 1 diabetes, rheumatoid arthritis and multiple sclerosis by regulating signaling pathways, suppressing inflammation and limiting demyelination. In addition, polyphenols cause immunomodulatory effects against allergic reaction and autoimmune disease by inhibition of autoimmune T cell proliferation and downregulation of pro-inflammatory cytokines (interleukin-6 (IL-6), IL-1, interferon-γ (IFN-γ)). Herein, we summarize the immunomodulatory effects of polyphenols and the underlying mechanisms involved in the stimulation of immune responses.  相似文献   
179.
PurposeExploring the impact of the COVID-19 pandemic on young people’s mental health is an increasing priority. Studies to date are largely surveys and lack meaningful involvement from service users in their design, planning, and delivery. The study aimed to examine the mental health status and coping strategies of young people during the first UK COVID-19 lockdown using coproduction methodology.MethodsThe mental health status of young people (aged 16–24) in April 2020 was established utilizing a sequential explanatory coproduced mixed methods design. Factors associated with poor mental health status, including coping strategies, were also examined using an online survey and semi-structured interviews.ResultsSince the lockdown, 30.3% had poor mental health, and 10.8% had self-harmed. Young people identifying as Black/Black-British ethnicity had the highest increased odds of experiencing poor mental health (odds ratio [OR] 3.688, 95% CI .54–25.40). Behavioral disengagement (OR 1.462, 95% CI 1.22–1.76), self-blame (OR 1.307 95% CI 1.10–1.55), and substance use (OR 1.211 95% CI 1.02–1.44) coping strategies, negative affect (OR 1.109, 95% CI 1.07–1.15), sleep problems (OR .915 95% CI .88–.95) and conscientiousness personality trait (OR .819 95% CI .69–.98) were significantly associated with poor mental health. Three qualitative themes were identified: (1) pre-existing/developed helpful coping strategies employed, (2) mental health difficulties worsened, and (3) mental health and nonmental health support needed during and after lockdown.ConclusionPoor mental health is associated with dysfunctional coping strategies. Innovative coping strategies can help other young people cope during and after lockdowns, with digital and school promotion and application.  相似文献   
180.
We describe trends in acute rheumatic fever (ARF), rheumatic heart disease (RHD), and RHD deaths among population groups in New Zealand. We analyzed initial primary ARF and RHD hospitalizations during 2000–2018 and RHD mortality rates during 2000–2016. We found elevated rates of initial ARF hospitalizations for persons of Māori (adjusted rate ratio [aRR] 11.8, 95% CI 10.0–14.0) and Pacific Islander (aRR 23.6, 95% CI 19.9–27.9) ethnicity compared with persons of European/other ethnicity. We also noted higher rates of initial RHD hospitalization for Māori (aRR 3.2, 95% CI 2.9–3.5) and Pacific Islander (aRR 4.6, 95% CI 4.2–5.1) groups and RHD deaths among these groups (Māori aRR 12.3, 95% CI 10.3–14.6, and Pacific Islanders aRR 11.2, 95% CI 9.1–13.8). Rates also were higher in socioeconomically disadvantaged neighborhoods. To curb high rates of ARF and RHD, New Zealand must address increasing social and ethnic inequalities.  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