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   5964篇
  免费   321篇
  国内免费   36篇
耳鼻咽喉   59篇
儿科学   256篇
妇产科学   118篇
基础医学   529篇
口腔科学   174篇
临床医学   648篇
内科学   1481篇
皮肤病学   81篇
神经病学   292篇
特种医学   153篇
外科学   1167篇
综合类   77篇
一般理论   4篇
预防医学   430篇
眼科学   135篇
药学   368篇
中国医学   29篇
肿瘤学   320篇
  2023年   42篇
  2022年   91篇
  2021年   227篇
  2020年   113篇
  2019年   179篇
  2018年   241篇
  2017年   137篇
  2016年   180篇
  2015年   173篇
  2014年   329篇
  2013年   349篇
  2012年   530篇
  2011年   556篇
  2010年   312篇
  2009年   234篇
  2008年   396篇
  2007年   381篇
  2006年   366篇
  2005年   295篇
  2004年   295篇
  2003年   250篇
  2002年   268篇
  2001年   40篇
  2000年   17篇
  1999年   31篇
  1998年   35篇
  1997年   34篇
  1996年   24篇
  1995年   19篇
  1994年   21篇
  1993年   16篇
  1992年   12篇
  1991年   11篇
  1990年   9篇
  1989年   8篇
  1988年   9篇
  1987年   9篇
  1986年   6篇
  1985年   8篇
  1984年   9篇
  1983年   3篇
  1982年   6篇
  1981年   7篇
  1980年   11篇
  1979年   3篇
  1977年   5篇
  1974年   4篇
  1972年   4篇
  1971年   2篇
  1962年   2篇
排序方式: 共有6321条查询结果,搜索用时 671 毫秒
991.
An infection trial and a production trial over 35 days were conducted in parallel to study the influence of feeding crimped kernel maize silage (CKMS) on the intestinal Campylobacter jejuni colonization and broiler performance, respectively. The CKMS was used at dietary inclusion levels of 15% and 30% in maize-based diets. Broilers were orally inoculated with 2?×?105?log?cfu/ml C. jejuni on day 14. Four birds from each pen were randomly selected and killed by cervical dislocation on days 3, 6, 9, 14 and 21 post infection and intestinal contents from ileum, caeca and rectum as well as liver samples were taken. Body weight and feed consumption of broilers were registered on days 13, 22 and 35. On day 35, litter dry matter (DM) was measured and the condition of the foot pads was evaluated. There was no significant effect of CKMS on the colonization of C. jejuni. Body weight of the broilers supplemented with 15% CKMS was comparable with the control maize-based feed, whereas addition of 30% CKMS reduced broiler body weight (P?Campylobacter colonization, but improved the foot pad health of broilers.  相似文献   
992.
993.
There are no reports about the association of interleukin (IL)-17A and IL-17F gene polymorphism and susceptibility to pediatric systemic lupus erythematosus (pSLE). Objective: To examine the possible role of IL-17A rs2275913, IL-17F rs763780 and rs2397084 polymorphisms as risk factors for pSLE in a cohort of Egyptian children and to investigate their association with the clinico-pathological features including lupus nephritis (LN). Methods: Typing of IL-17A and IL-17F polymorphisms was done using restriction fragment length polymorphism for 115 children with SLE and 259 age- and sex-matched healthy controls. Results: No significant differences were found between pSLE patients and healthy controls for the allele and genotype frequencies of IL-17A rs2275913, IL-17F rs763780 and rs2397084 (p?>?0.05). However, the combined genotype GGAGAA and the haplotype GGA had significant association with pSLE (pc?=?0.042 and <0.001, respectively). The AA genotype of IL-17F rs763780 is more frequent in female patients (p?=?0.002) and the AA genotype of IL-17F rs2397084 is more associated with positivity of ds-DNA (p?=?0.007). No more associations were found for the demographic and clinical data of pSLE patients including risk of LN development, risk of non-remission, overall survival, activity and chronicity indices. Conclusion: The GGAGAA combined genotype and the GGA haplotype of IL-17A rs2275913, IL-17F rs763780 and rs2397084 can be considered risk factors for the development of SLE in Egyptian children. IL-17A rs2275913, IL-17F rs763780 and rs2397084 are not related to the LN development, SLE disease activity or overall survival.  相似文献   
994.
Phytochemical investigation of Ficus pandurata Hance (Moraceae) fruits has led to the isolation of two new triterpenoids, ficupanduratin A [1β-hydroxy-3β-acetoxy-11α-methoxy-urs-12-ene] (11) and ficupanduratin B [21α-hydroxy-3β-acetoxy-11α-methoxy-urs-12-ene] (17), along with 20 known compounds: α-amyrin acetate (1), α-amyrin (2), 3β-acetoxy-20-taraxasten-22-one (3), 3β-acetoxy-11α-methoxy-olean-12-ene (4), 3β-acetoxy-11α-methoxy-12-ursene (5), 11-oxo-α-amyrin acetate (6), 11-oxo-β-amyrin acetate (7), palmitic acid (8), stigmast-4,22-diene-3,6-dione (9), stigmast-4-ene-3,6-dione (10), stigmasterol (12), β-sitosterol (13), stigmast-22-ene-3,6-dione (14), stigmastane-3,6-dione (15), 3β,21β-dihydroxy-11α-methoxy-olean-12-ene (16), 3β-hydroxy-11α-methoxyurs-12-ene (18), 6-hydroxystigmast-4,22-diene-3-one (19), 6-hydroxystigmast-4-ene-3-one (20), 11α,21α-dihydroxy-3β-acetoxy-urs-12-ene (21), and β-sitosterol-3-O-β-d-glucopyranoside (22). Compound 21 is reported for the first time from a natural source. The structures of the 20 compounds were elucidated on the basis of IR, 1D (1H and 13C), 2D (1H–1H COSY, HSQC, HMBC and NOESY) NMR and MS spectroscopic data, in addition to comparison with literature data. The isolated compounds were evaluated for their anti-microbial, anti-malarial, anti-leishmanial, and cytotoxic activities. In addition, their radioligand displacement affinity on opioid and cannabinoid receptors was assessed. Compounds 4, 11, and 15 exhibited good affinity towards the CB2 receptor, with displacement values of 69.7, 62.5 and 86.5 %, respectively. Furthermore, the binding mode of the active compounds in the active site of the CB2 cannabinoid receptors was investigated through molecular modelling.  相似文献   
995.
Hepatitis C virus (HCV) infection is a considerable public-health problem and an important cause of liver disease with about 71 million people infected worldwide and more than 399 000 people die every year from hepatitis C-related liver diseases. The present study was, therefore, initiated to investigate the association of polymorphism in interferon λ3 (IFNL3) also known as interleukin-28B (IL-28B) gene with chronic HCV infection and association of these polymorphic variants with the combination daclatasvir and sofosbuvir HCV therapy response. Genotypes were determined by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay in a total of 250 chronic HCV genotype three patients and 500 number of healthy controls. Our data revealed that the TT (minor) genotype of IFNL3 (rs12979860) and GG (minor) genotype of IFNL3 (rs8099917) exhibited a significant association with chronic HCV genotype 3 infection when compared with controls. The results of treatment response showed that CC (major) genotype of IFNL3 (rs12979860) and TT (major) genotype of IFNL3 (rs8099917) are associated with the likelihood of achieving a higher sustained virological response (SVR), to combined daclatasvir and sofosbuvir therapy, in genotype 3-infected HCV patients, whereas the individuals with TT (minor) genotype of IFNL3 (rs12979860) and GG (minor) genotype of IFNL3 (rs8099917) are more susceptible to chronic HCV infection and treatment relapse, suggesting a role of IFNL3 (rs12979860) and (rs8099917) in the treatment outcome of combined daclatasvir and sofosbuvir therapy in chronic HCV genotype 3 infection.  相似文献   
996.
OBJECTIVE: To evaluate a new self-etch conditioner used with resin-modified glass ionomers (RMGIs) in bonding orthodontic brackets. MATERIALS AND METHODS: Sixty human molars were cleaned, mounted, and randomly divided into three groups. In group 1 (control), 20 orthodontic brackets were bonded to teeth using Transbond Plus Self-etching Primer; in group 2, 20 brackets were bonded using an RMGI with a 10% polyacrylic acid conditioner. In group 3, 20 brackets were bonded using Fuji Ortho LC with a new no-rinse self-conditioner for RMGIs. The same bracket type was used on all groups. The teeth were debonded in shear mode using a universal testing machine, and the amount of residual adhesive remaining on each tooth was evaluated. Analysis of variance was used to compare the shear bond strength (SBS), and the chi(2) test was used to compare the Adhesive Remnant Index (ARI) scores. RESULTS: There were no significant differences in the SBS (P = .556) between the groups. The mean SBS for Transbond Plus was 8.6 +/- 2.6 MPa, for Fuji Ortho LC using 10% polyacrylic acid 9.1 +/- 4.6 MPa, and for Fuji Ortho LC using GC Self-conditioner 9.9 +/- 4.1 MPa. The comparisons of the ARI scores between the three groups (chi(2) = 35.5) indicated that bracket failure mode was significantly different (P < .001), with more adhesive remaining on the teeth bonded using Transbond. Conclusions: The new self-etch conditioner can be used with an RMGI to successfully bond brackets. In addition, brackets bonded with Fuji Ortho LC resulted in less residual adhesive remaining on the teeth.  相似文献   
997.
OBJECTIVE: To compare the effects of a standardized thermocycling protocol on the shear bond strength (SBS) of two adhesive systems: a resin-modified glass ionomer and a composite resin used with a new self-etching primer. MATERIALS AND METHODS: Forty human molars were cleaned, mounted, and randomly divided into two groups. In group 1, brackets were bonded to the teeth using Fuji Ortho LC adhesive, and in group 2, the Transbond Plus system was used. The teeth were stored in water at 37 degrees C for 24 hours, thermocycled between 5 and 55 degrees C, and debonded using a universal testing machine. The enamel surface was examined under 10x magnification to determine the amount of residual adhesive remaining on the tooth. Student's t-test was used to compare the SBS and the chi-square test was used to compare the adhesive remnant index (ARI) scores. RESULTS: The mean SBS for the brackets bonded using the Fuji Ortho LC was 6.4 +/- 4.5 MPa, and the mean SBS for the Transbond Plus system was 6.1 +/- 3.2 MPa. The result of the t-test comparisons (t = 0.207) indicated that there was no significant difference (P = .837) between the two groups. The comparisons of the ARI scores (chi(2) = 0.195) indicated that bracket failure mode was not significantly different (P = .907) between the two adhesives. CONCLUSION: Although SBS and ARI scores were not significantly different for the two adhesives, clinicians need to take into consideration the other properties of the adhesives before using them.  相似文献   
998.
Influence of HAP-gel (2 g of 2% solution of hyaluronic acid mixed with 0,5 g of hydroxyapatite and 0,1 ml of colloidal silver) upon osseointegration in case of delayed introduction of titanium implantates in dog jaw. By scanning electron microscopy it was shown that solely use either of HAP-gel or of ceramic spraying increased direct contact area between bone and implantates in the 6 and 9 months time period. Combination of spray-coated ceramic with HAP-gel was effective in 3 months after implantation, when solely the HAP-gel or the ceramic spraying were little effective. In the following terms of experiment (6 and 9 months) significant differences between groups 3 and 4 (implantate with ceramic spraying but without HAP-gel in the alveolus and implantate with ceramic spraying and with HAP-gel in the alveolus) were not found. The area of implantate integration with jaw bone (cortical part of it was excluded) was equal to 80% and was maximal for the given conditions of the experiment.  相似文献   
999.
Pulsed-field gel electrophoresis (PFGE) is a powerful molecular biology technique which has provided important insights into the epidemiology and population biology of many pathogens. However, few studies have used PFGE for the molecular epidemiology of Mycobacterium tuberculosis. A laboratory protocol was developed to determine the typeability, stability, and reproducibility of PFGE typing of M. tuberculosis. Formal data-analytical techniques were used to assess the genetic diversity elucidated by PFGE analyses using four separate restriction enzymes and by IS6110 RFLP analyses, as well as to assess the concordance among these typing methods. One hundred epidemiologically characterized clinical isolates of M. tuberculosis were genotyped with four different PFGE enzymes (AseI, DraI, SpeI, and XbaI), as well as by RFLP analysis with IS6110. Identical patterns were found among 34 isolates known to be genetically related, suggesting that the PFGE protocol is robust and reproducible. Among 66 isolates representing population-sampled cases, heterozygosity and information content dependency estimates indicate that all five genotyping systems capture quantitatively similar levels of genetic diversity. Nevertheless, comparisons between PFGE analyses and IS6110 typing reveals that PFGE provided more discrimination among isolates with fewer than five copies of IS6110 and less clustering in isolates with five or more copies. The comparisons confirm the hypothesis that the resolution of IS6110 RFLP genotyping is dependent upon the number of IS6110 elements in the genome of isolates. The general concordance among the results obtained with four independent enzymes suggests that M. tuberculosis is a clonal organism. The availability of a robust genotyping technique largely independent of repetitive elements has implications for the molecular epidemiology of M. tuberculosis.  相似文献   
1000.
The fission yeast Schizosaccharomyces pombe provides a simple eukaryotic model for the study of cytokinesis. S. pombe cells are rod-shaped, grow mainly by elongation at their tips, and divide by binary fission after forming a centrally placed division septum. Analysis of mutants has begun to shed light upon how septum formation and cytokinesis are regulated both spatially and temporally. Some of the proteins involved in these events have been functionally conserved throughout eukaryotic evolution, suggesting that aspects of this control will be common to all eukaryotic cells. Received: 16 December 1998 / 10 March 1999  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