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   6196篇
  免费   341篇
  国内免费   36篇
耳鼻咽喉   65篇
儿科学   153篇
妇产科学   122篇
基础医学   1037篇
口腔科学   481篇
临床医学   481篇
内科学   1345篇
皮肤病学   148篇
神经病学   494篇
特种医学   87篇
外科学   585篇
综合类   22篇
一般理论   3篇
预防医学   532篇
眼科学   73篇
药学   497篇
中国医学   60篇
肿瘤学   388篇
  2024年   8篇
  2023年   97篇
  2022年   210篇
  2021年   371篇
  2020年   217篇
  2019年   281篇
  2018年   283篇
  2017年   192篇
  2016年   224篇
  2015年   253篇
  2014年   359篇
  2013年   404篇
  2012年   549篇
  2011年   551篇
  2010年   294篇
  2009年   219篇
  2008年   333篇
  2007年   326篇
  2006年   329篇
  2005年   233篇
  2004年   216篇
  2003年   168篇
  2002年   127篇
  2001年   33篇
  2000年   47篇
  1999年   18篇
  1998年   22篇
  1997年   17篇
  1996年   15篇
  1995年   13篇
  1994年   13篇
  1993年   7篇
  1992年   20篇
  1991年   12篇
  1990年   6篇
  1989年   4篇
  1988年   7篇
  1987年   6篇
  1986年   10篇
  1984年   4篇
  1983年   5篇
  1982年   4篇
  1978年   3篇
  1976年   6篇
  1975年   5篇
  1974年   5篇
  1972年   4篇
  1971年   3篇
  1970年   3篇
  1962年   3篇
排序方式: 共有6573条查询结果,搜索用时 0 毫秒
81.
82.
Bovine herpesviruses 1 (BoHV-1) and 5 (BoHV-5) are closely related alphaherpesviruses of cattle. While BoHV-1 is mainly associated with respiratory/genital disease and rarely associated with neurological disease, BoHV-5 is the primary agent of meningoencephalitis in cattle. The envelope glycoprotein D of alphaherpesviruses (BoHV-1/gD1 and BoHV-5/gD5) is involved in the early steps of virus infection and may influence virus tropism and neuropathogenesis. This study performed a sequence analysis of the 3′ region of gD gene (gD3′) of BoHV-1 isolates recovered from respiratory/genital disease (n = 6 and reference strain Cooper) or from neurological disease (n = 7); and from seven typical neurological BoHV-5 isolates. After PCR amplification, nucleotide (nt) sequencing, and aminoacid (aa) sequence prediction; gD3′ sequences were compared, identity levels were calculated, and selective pressure was analyzed. The phylogenetic reconstruction based on nt and aa sequences allowed for a clear differentiation of BoHV-1 (n = 14) and BoHV-5 (n = 7) clusters. The seven BoHV-1 isolates from neurological disease are grouped within the BoHV-1 branch. A consistent alignment of 346 nt revealed a high similarity within each viral species (gD1 = 98.3 % nt and aa; gD5 = 97.8 % nt and 85.8 % aa) and an expected lower similarity between gD1 and gD5 (73.7 and 64.1 %, nt and aa, respectively). The analysis of molecular evolution revealed an average negative selection at gD3′. Thus, the phylogeny and similarity levels allowed for differentiation of BoHV-1 and BoHV-5 species, but not further division in subspecies. Sequence analysis did not allow for the identification of genetic differences in gD3′ potentially associated with the respective clinical/pathological phenotypes, yet revealed a lower level of gD3′ conservation than previously reported.  相似文献   
83.
Since insect species are poikilothermic organisms, they generally exhibit different growth patterns depending on the temperature at which they develop. This factor is important in forensic entomology, especially for estimating postmortem interval (PMI) when it is based on the developmental time of the insects reared in decomposing bodies. This study aimed to estimate the rates of development, viability, and survival of immatures of Sarcophaga (Liopygia) ruficornis (Fabricius 1794) and Microcerella halli (Engel 1931) (Diptera: Sarcophagidae) reared in different temperatures: 10, 15, 20, 25, 30, and 35?±?1 °C. Bovine raw ground meat was offered as food for all experimental groups, each consisting of four replicates, in the proportion of 2 g/larva. To measure the evolution of growth, ten specimens of each group were randomly chosen and weighed every 12 h, from initial feeding larva to pupae, and then discarded. Considering the records of weight gain, survival rates, and stability of growth rates, the range of optimum temperature for the development of S. (L.) ruficornis is between 20 and 35 °C, and that of M. halli is between 20 and 25 °C. For both species, the longest times of development were in the lowest temperatures. The survival rate at extreme temperatures (10 and 35 °C) was lower in both species. Biological data such as the ones obtained in this study are of great importance to achieve a more accurate estimate of the PMI.  相似文献   
84.
85.
Clenbuterol is known to improve competition resistance and muscular growth in athletes. Although it is an illegal drug, its use by farmers is widely spread to induce growth of their cattle. Thus, when clenbuterol is found in the urine of an athlete, there is doubt whether it was consumed with doping purposes or if it is due to the consumption of meat from a clenbuterol‐fed animal. Previous studies suggest that enantiomeric relationship of clenbuterol may be different according to the intake source. However, the enantiomeric relationship throughout a doping cycle or a continuous intake of contaminated meat has not yet been explored. In this first approximation, our aim was the development and validation of a sensitive and rapid method for the determination of S‐ (+) and R‐ (─) clenbuterol enantiomers to be used in a controlled study in rats fed for one week with contaminated meat or simulating a doping cycle. Enantiomers were measured using liquid chromatography coupled to mass spectrometry with a triple quadrupole analyzer (LC‐TQ‐MS) and were separated on an AGP Chiralpak column. The method was fully validated following the VICH (Veterinary International Conference on Harmonization guidelines) and was linear in the range of 12.5–800 pg/mL with a correlation coefficient of ≥0.98 for each enantiomer, and with a limit of quantitation and detection (LOQ and LOD) of 12.5 pg/mL and 6.5 pg/mL, respectively, for both enantiomers. The application of this method pointed out the shift of the enantiomeric relationship in urine from rats during the first five days of the doping cycle compared to those fed with contaminated meat. This finding can be of substantial importance in further doping studies.  相似文献   
86.
BackgroundThe regulation of the immune system by the sympathetic nervous system is allowing the design of novel treatments for inflammatory disorders such as arthritis. In this study, we have analyzed the effects of α- and β-adrenoceptor agonists injected subcutaneously, intrathecally, or intra-articularly in zymosan-induced arthritis.MethodsMurine arthritis was induced by intra-articular (knee joint) injection of zymosan. α1 (phenylephrine), α2 (clonidine), β1 (dobutamine), or β2 (salbutamol)-adrenoceptor agonists were injected subcutaneously (sc), intrathecally (it), or intra-articularly (ia) to activate peripheral, spinal, or intra-articular adrenoceptors and to study their effects on articular edema formation and neutrophil migration into the synovial cavity.ResultsTreatments with phenylephrine did not affect the edema formation, but it increased neutrophil migration when injected subcutaneously (155.3%) or intra-articularly (187.7%). Treatments with clonidine inhibited neutrophil migration (59.9% sc, 68.7% it, 42.8% ia) regardless of the route of administration, but it inhibited edema formation only when injected intrathecally (66.7%) or intra-articularly (36%) but not subcutaneously. Treatments with dobutamine inhibited both edema (42.0% sc, 69.5% it, 61.6% ia) and neutrophil migration (28.4% sc, 70.3% it, 82.4% ia) in a concentration dependent manner. Likewise, all the treatments with salbutamol also inhibited edema formation (89.9% sc, 62.4% it, 69.8% ia) and neutrophil migration (76.6% sc, 39.1% it, 71.7% ia).ConclusionWhereas the β-adrenoceptor agonists induced anti-inflammatory effects regardless of their route of administration, α1- and α2-adrenoceptor agonists induced either pro- and anti-inflammatory effects, respectively.  相似文献   
87.
In the United States, Spanish-speaking patients with diabetes often receive inadequate dietary counseling. Providing language and culture-concordant dietary counseling on an ongoing basis is critical to diabetes self-care. To determine if automated telephone nutrition support (ATNS) counseling could help patients improve glycemic control by duplicating a successful pilot in Mexico in a Spanish-speaking population in Oakland, California. A prospective randomized open-label trial with blinded endpoint assessment (PROBE) was performed. The participants were seventy-five adult patients with diabetes receiving care at a federally qualified health center in Oakland, California. ATNS, a computerized system that dialed patients on their phones, prompted them in Spanish to enter (via keypad) portions consumed in the prior 24 hours of various cultural-specific dietary items, and then provided dietary feedback based on proportion of high versus low glycemic index foods consumed. The control group received the same ATNS phone calls 14 weeks after enrollment. The primary outcome was hemoglobin A1c % (A1c) 12 weeks following enrollment. Participants had no significant improvement in A1c (–0.3% in the control arm, –0.1% in the intervention arm, P = .41 for any difference) or any secondary parameters. In our study, an ATNS system did not improve diabetes control in a Spanish-speaking population in Oakland.  相似文献   
88.
89.
The aim of the present study was to compare the restorative time for filling cavities in posterior teeth using bulk‐fill and conventional resin composites through a systematic review and meta‐analysis. A search for clinical trials and laboratory studies was performed in PubMed/MEDLINE, Scopus, the Latin American and Caribbean Health Sciences Literature database, the Brazilian Library in Dentistry, Cochrane Library, Clinical Trials, and ReBEC (Registro Brasileiro de Ensaios Clínicos) databases without publication year or language restriction. Two reviewers identified eligible studies according to the inclusion criteria: bulk‐fill compared to conventional resin in class I or II, and the restorative time as an outcome. A meta‐analysis of the restorative time mean difference between composites was performed (inverse variance method, random effects model; Z‐test, P ≤ .05). From the 662 eligible studies, 133 were selected for full‐text analysis; three were included in the systematic review and in the meta‐analysis. Overall, the restorative time was lower when bulk‐fill was used (P = .0007, Z = 3.37), as the subgroup full‐body bulk‐fill (P < .00001, Z = 21.00). There was no difference in restorative time between flowable bulk‐fill and conventional resins (P = .08, Z = 1.76). Moderate‐to‐substantial heterogeneity was detected. Full‐body bulk‐fill composites decrease the restorative time in posterior teeth compared to conventional resins. Full‐body bulk‐fill resins require a shorter restorative time to perform restorations in posterior teeth than conventional resins, but the same is not valid for flowable bulk‐fill resin composites.  相似文献   
90.

Background

The Duke Activity Status Index (DASI) assesses the functional capacity of patients with cardiovascular disease (CVD), but there is no Portuguese version validated for CVD.

Objectives

To translate and adapt cross-culturally the DASI for the Portuguese-Brazil language, and to verify its psychometric properties in the assessment of functional capacity of patients with CVD.

Methods

The DASI was translated into Portuguese, then checked by back-translation into English and evaluated by an expert committee. The pre-test version was first evaluated in 30 subjects. The psychometric properties and correlation with exercise testing was performed in a second group of 67 subjects. An exploratory factor analyses was performed in all 97 subjects to verify the construct validity of the DASI.

Results

The intraclass correlation coefficient for test-retest reliability was 0.87 and for the inter-rater reliability was 0.84. Cronbach''s α for internal consistency was 0.93. The concurrent validity was verified by significant positive correlations of DASI scores with the VO2max (r = 0.51, p < 0.001). The factor analysis yielded two factors, which explained 54% of the total variance, with factor 1 accounting for 40% of the variance. Application of the DASI required between one and three and a half minutes per patient.

Conclusions

The Brazilian version of the DASI appears to be a valid, reliable, fast and easy to administer tool to assess functional capacity among patients with CVD.  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