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   11058篇
  免费   726篇
  国内免费   50篇
耳鼻咽喉   72篇
儿科学   326篇
妇产科学   191篇
基础医学   1570篇
口腔科学   209篇
临床医学   1035篇
内科学   2516篇
皮肤病学   216篇
神经病学   850篇
特种医学   420篇
外科学   1702篇
综合类   92篇
一般理论   4篇
预防医学   846篇
眼科学   333篇
药学   720篇
中国医学   10篇
肿瘤学   722篇
  2023年   37篇
  2022年   162篇
  2021年   280篇
  2020年   124篇
  2019年   215篇
  2018年   288篇
  2017年   188篇
  2016年   194篇
  2015年   237篇
  2014年   303篇
  2013年   468篇
  2012年   727篇
  2011年   740篇
  2010年   423篇
  2009年   372篇
  2008年   648篇
  2007年   701篇
  2006年   631篇
  2005年   707篇
  2004年   625篇
  2003年   585篇
  2002年   592篇
  2001年   123篇
  2000年   152篇
  1999年   157篇
  1998年   146篇
  1997年   129篇
  1996年   95篇
  1995年   108篇
  1994年   92篇
  1993年   97篇
  1992年   109篇
  1991年   129篇
  1990年   103篇
  1989年   102篇
  1988年   88篇
  1987年   90篇
  1986年   67篇
  1985年   68篇
  1984年   73篇
  1983年   69篇
  1982年   62篇
  1981年   57篇
  1980年   54篇
  1979年   33篇
  1978年   35篇
  1977年   33篇
  1974年   23篇
  1973年   22篇
  1970年   20篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Ge2Sb2Te5 (GST225) looks to be a promising material for rewritable memory devices due to its relatively easy processing and high optical and electrophysical contrast for the crystalline and amorphous phases. In the present work, we combined the possibilities of crystallization and anisotropic structures fabrication using femtosecond laser treatment at the 1250 nm wavelength of 200 nm thin amorphous GST225 films on silicon oxide/silicon substrates. A raster treatment mode and photoexcited surface plasmon polariton generation allowed us to produce mutually orthogonal periodic structures, such as scanline tracks (the period is 120 ± 10 μm) and laser-induced gratings (the period is 1100 ± 50 nm), respectively. Alternating crystalline and amorphous phases at the irradiated surfaces were revealed according to Raman spectroscopy and optical microscopy studies for both types of structures. Such periodic modulation leads to artificial optical and electrophysical anisotropy. Reflectance spectra in the near infrared range differ for various polarizations of probing light, and this mainly results from the presence of laser-induced periodic surface structures. On the other hand, the scanline tracks cause strong conductivity anisotropy for dc measurements in the temperature range of 200–400 K. The obtained results are promising for designing new GST225-based memory devices in which anisotropy may promote increasing the information recording density.  相似文献   
92.
93.
94.

Objectives

To assess the risk of vertical transmission in HIV-infected pregnant women undergoing diagnostic amniocentesis, and to identify possible predictive factors.

Study design

This was a single center retrospective study. The records of 330 HIV-infected pregnant women booked in our antenatal clinic from 31 January 2001 to 31 January 2006 were analyzed. Women who actually underwent diagnostic amniocentesis (“amniocentesis performed” group) were compared to those eligible for amniocentesis but who did not undergo the procedure (“amniocentesis withheld” group).

Results

During the time period, 318 liveborn babies were delivered (9 HIV infected (2.8%)). Thirty-four women (35 fetuses) were eligible for diagnostic amniocentesis. Amniocentesis was performed in 11 (32.4%) of these women (12 fetuses, none infected among the 9 liveborns) and withheld in 23 (67.6%) women. Among the 19 liveborn babies in this latter group, 1 (5.3%) was infected. There was no statistical difference in vertical transmission rate between the whole cohort of HIV-infected pregnant women and the group of women eligible for amniocentesis; or between the women who actually had or did not have an amniocentesis.The women who did undergo amniocentesis all received highly active antiretroviral combination therapy with three drugs; all but two had an undetectable HIV viral load, only one had immunosuppression and none had HCV co-infection.

Conclusion

No vertical transmission was observed in a group of nine liveborn babies after amniocentesis performed in selected HIV-infected pregnant women. In the presence of high genetic risk during pregnancy, amniocentesis can be considered after proper patient counselling.  相似文献   
95.
96.
Original 1CP powder was studied and it was founded that powder material partially consists of the amorphous phase, in which crystallization begins at 450 °C and ends at 575 °C. Selective laser melting parameters were investigated through the track study, and more suitable ones were found: laser power P = 90, 120 W; scanning speed V = 1200 mm/s. Crack-free columnar elements were obtained. The sample obtained with P = 90 W, contains a small amount of amorphous phase. X-ray diffraction of samples shows the presence of α-Fe(Si) and Fe2B. SEM-image analysis shows the presence of ordered Fe3Si in both samples. Annealed samples show 40% less microhardness; an annealed sample containing amorphous phase shows higher soft-magnetic properties: 2.5% higher saturation magnetization, 35% higher residual magnetization and 30% higher rectangularity coefficient.  相似文献   
97.
IntroductionDespite the high prevalence of malnutrition in patients at all levels of healthcare, early prevention and treatment of malnourished patients are often neglected and overlooked in clinical practice. The aim of this systematic literature review was to identify the factors considered most important by healthcare professionals in the identification and treatment of malnourished patients or those at risk of malnutrition.MethodsA systematic literature review of qualitative research was conducted. Documents published in scientific journals in English from 2011 to 2021 were searched in the PubMed (MEDLINE), CINAHL and ProQuest databases. The results were analysed with a thematic analysis of qualitative research findings.ResultsFrom the search set of 1010 results, 7 sources were included in the final analysis. Factors identified by health professionals as important in the identification and treatment of malnourished patients in clinical practice were grouped into five themes: unclear organizational structure; indefinite structure of nutritional care; poor continuity of nutritional care; lack of knowledge and skills of health professionals; lack of time and human resources.ConclusionsHealth policy must provide resources for nutritional care for patients at all levels of health care on the initiative of the highest professional bodies at the state level. To improve the nutritional care of patients in clinical practice, the management of health care institutions must promote and enable the professional and organizational establishment of clinical nutrition as a regular medical activity of the institution, develop clinical nutritional pathways, and promote evidence-based clinical practice and interprofessional collaboration.  相似文献   
98.
Childhood maladaptive aggression is associated with disrupted functional connectivity within amygdala-prefrontal circuitry. In this study, neural correlates of childhood aggression were probed using the intrinsic connectivity distribution, a voxel-wise metric of global resting-state brain connectivity. This sample included 38 children with aggressive behavior (26 boys, 12 girls) ages 8–16 years and 21 healthy controls (14 boys, 6 girls) matched for age and IQ. Functional MRI data were acquired during resting state, and differential patterns of intrinsic functional connectivity were tested in a priori regions of interest implicated in the pathophysiology of aggressive behavior. Next, correlational analyses tested for associations between functional connectivity and severity of aggression measured by the Reactive-Proactive Aggression Questionnaire in children with aggression. Children with aggressive behavior showed increased global connectivity in the bilateral amygdala relative to controls. Greater severity of aggressive behavior was associated with decreasing global connectivity in the dorsal anterior cingulate and ventromedial prefrontal cortex. Follow-up seed analysis revealed that aggression was also positively correlated with left amygdala connectivity with the dorsal anterior cingulate, ventromedial and dorsolateral prefrontal cortical regions. These results highlight the potential role of connectivity of the amygdala and medial prefrontal and anterior cingulate cortices in modulating the severity of aggressive behavior in treatment-seeking children.  相似文献   
99.
We report a case of unusual human anaplasmosis in the Amazon rainforest of French Guiana. Molecular typing demonstrated that the pathogen is a novel Anaplasma species, distinct to all known species, and more genetically related to recently described Anaplasma spp. causing infections in rainforest wild fauna of Brazil.  相似文献   
100.

Introduction

African Americans' (AAs) late-onset Alzheimer's disease (LOAD) genetic risk profile is incompletely understood. Including clinical covariates in genetic analyses using informed conditioning might improve study power.

Methods

We conducted a genome-wide association study (GWAS) in AAs employing informed conditioning in 1825 LOAD cases and 3784 cognitively normal controls. We derived a posterior liability conditioned on age, sex, diabetes status, current smoking status, educational attainment, and affection status, with parameters informed by external prevalence information. We assessed association between the posterior liability and a genome-wide set of single-nucleotide polymorphisms (SNPs), controlling for APOE and ABCA7, identified previously in a LOAD GWAS of AAs.

Results

Two SNPs at novel loci, rs112404845 (P = 3.8 × 10?8), upstream of COBL, and rs16961023 (P = 4.6 × 10?8), downstream of SLC10A2, obtained genome-wide significant evidence of association with the posterior liability.

Discussion

An informed conditioning approach can detect LOAD genetic associations in AAs not identified by traditional GWAS.  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