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   1747篇
  免费   121篇
  国内免费   13篇
耳鼻咽喉   65篇
儿科学   41篇
妇产科学   71篇
基础医学   178篇
口腔科学   60篇
临床医学   164篇
内科学   305篇
皮肤病学   34篇
神经病学   105篇
特种医学   62篇
外科学   226篇
综合类   43篇
预防医学   138篇
眼科学   65篇
药学   191篇
中国医学   40篇
肿瘤学   93篇
  2024年   3篇
  2023年   26篇
  2022年   73篇
  2021年   98篇
  2020年   73篇
  2019年   86篇
  2018年   95篇
  2017年   79篇
  2016年   66篇
  2015年   68篇
  2014年   86篇
  2013年   92篇
  2012年   145篇
  2011年   125篇
  2010年   70篇
  2009年   53篇
  2008年   109篇
  2007年   71篇
  2006年   82篇
  2005年   58篇
  2004年   45篇
  2003年   46篇
  2002年   44篇
  2001年   20篇
  2000年   16篇
  1999年   17篇
  1998年   12篇
  1997年   9篇
  1996年   4篇
  1995年   3篇
  1994年   3篇
  1992年   7篇
  1991年   5篇
  1990年   13篇
  1989年   10篇
  1988年   10篇
  1987年   10篇
  1986年   5篇
  1985年   8篇
  1984年   8篇
  1983年   3篇
  1982年   3篇
  1981年   5篇
  1978年   3篇
  1977年   4篇
  1976年   2篇
  1975年   3篇
  1973年   1篇
  1969年   2篇
  1928年   1篇
排序方式: 共有1881条查询结果,搜索用时 250 毫秒
991.
Acute lymphoblastic leukemia (ALL) presenting with musculoskeletal pain may be difficult to distinguish from juvenile idiopathic arthritis (JIA). The objective of this study, which separates it from most studies investigating these two diseases, is to determine the role of plain radiography in the initial approach toward patients presenting with musculoskeletal symptoms and to look for signs suggestive of each of the two disease entities. X-rays of patients referred to our center for musculoskeletal symptoms and ultimately diagnosed with JIA or ALL over a period of 10 years were studied retrospectively. The X-rays had been performed in the preliminary stage of the disease process and before the initiation of specific therapeutic measures. Soft tissue swelling, osteopenia, radiolucent metaphyseal bands, coarse trabeculation, and periosteal reactions were studied, and data analysis was performed by SPSS. Among a total of 174 patients, 118 had been diagnosed with JIA and 56 with ALL. The average age of JIA patients and ALL patients were 7.5 and 7.2 years, respectively. Soft tissue swelling was significantly more common among JIA patients (89.8%) than among those with ALL (1.8%) (P < 0.0001). Therefore, it is of the utmost importance to note the presence or absence of soft tissue swelling on plain radiography in the initial diagnostic approach. Osteopenia was seen in 60.2% of JIA patients compared with 14.3% of ALL patients (P < 0.0001). Radiolucent metaphyseal bands were seen among 7.1% of ALL cases but were notably absent in all cases of JIA. Coarse trabeculation was significantly higher in patients with ALL (7.1% ) than among JIA patients (0.8%). Periosteal reactions were seen in 6.8% of JIA group compared with 1.8% of ALL patients. We concluded that plain X-ray may be useful in selecting patients requiring bone marrow examination among those presenting with musculoskeletal symptoms mimicking JIA.  相似文献   
992.
ObjectivesTo find whether polymorphisms of methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C are risk factors for diabetic nephropathy (DN) among type 2 diabetes mellitus (T2DM) patients from Western Iran.Design and methodsThe MTHFR polymorphisms were detected in 72 microalbuminuric, 68 macroalbuminuric and 72 normoalbuinuric T2DM patients by PCR-RFLP.ResultsThe possession of both MTHFR 677T and 1298C alleles increase the risk of microalbuminuria to 4.3-fold (p = 0.007) in T2DM patients. The presence of either MTHFR 677T, 1298C allele is sufficient to increase the risk of macroalbuminuria in T2DM patients by 4.1 and 5.5 times (p = 0.027, and p = 0.006, respectively). The concomitant presence of both 677T and 1298C alleles act in synergy to increase the risk of macroalbuminuria by 20.4-fold (p < 0.001) and progression of DN from microalbuminuria to macroalbuminuria (OR = 4.73, p = 0.01).ConclusionBoth MTHFR 677T and 1298C alleles increased the susceptibility to the onset and progression of DN in Iranians with T2DM.  相似文献   
993.
There are increasing reports of emergence of multiple drug resistant (MDR) Acinetobacter spp in the world; however there are a few reports in our country. 145 A. baumannii isolates from distinct wards and Children's Medical Center (CMC) in Tehran were studied in order to find the profile of antibiotic resistance among them. 40.6% (59/145) of A. baumannii isolates were identified as MDR. Overall susceptibility rates to cotrimoxazole, chloramphenicole and ciprofloxacin were 23.4%, 16.9% and 20.1%, respectively. Frequency susceptibility rates to amikacin, kanamycin, gentamycin and tobramycin decreased gradually from 81.2%, 50%, 50% and 62.5% in 2002 to 25%, 15.6%, 28.1% and 25% in 2007 respectively. Overall susceptibility rates to cephalosporines cephalotin, ceftazidime, cefteriaxon, ceftizoxime and cefixime were 9.3%, 14.7%, 16.2%, 15.9% and 18%, respectively. Susceptibility to carbapenems was assessed only in 2007. The susceptibility rates of Imipenem and meropenem were shown to be 50% and 46.8%, respectively. Our data indicates that MDR A. baumannii strains are spreading and carbapenem resistance is becoming more common in Iran. Our findings also highlight the importance of clinicians' access to updated susceptibility data regarding A. baumannii in developing countries such as Iran.  相似文献   
994.
Objectives: In order to identify genes with the greatest contribution to bladder cancer, we proposed a sparse model making the best discrimination from other patients. Methods: In a cross-sectional study, 22 genes with a key role in most cancers were considered in 21 bladder cancer patients and 14 participants of the same age (± 3 years) without bladder cancer in Shiraz city, Southern Iran. Real time-PCR was carried out using SYBR Green and for each of the 22 target genes 2-Δct as a quantitative index of gene expression was reported. We determined the most affective genes for the discriminant vector by applying penalized linear discriminant analysis using LASSO penalties. All the analyses were performed using SPSS version 18 and the penalized LDA package in R.3.1.3 software. Results: Using penalized linear discriminant analysis led to elimination of 13 less important genes. Considering the simultaneous effects of 22 genes with important influence on many cancers, it was found that TGFβ, IL12A, Her2, MDM2, CTLA-4 and IL-23 genes had the greatest contribution in classifying bladder cancer patients with the penalized linear discriminant vector. The receiver operating characteristic (ROC) curve revealed that the proposed vector had good performance with minimal (only 3) mis- classification. The area under the curve (AUC) of our proposed test was 96% (95% CI: 83%- 100%) and sensitivity, specificity, positive and negative predictive values were 90.5%, 85.7%, 90.5% and 85.7%, respectively. Conclusions: The penalized discriminant method can be considered as appropriate for classifying bladder cancer cases and searching for important biomarkers.  相似文献   
995.
Herbal-derived medicines have introduced as sources of novel drugs due to minimum systemic side effects. Silibinin as a flavonoid compound has showed with effective chemotherapeutic effects on different cancers. Here, we investigated the impact of combination therapy of silibinin, with paclitaxel and cisplatin in inhibition of proliferation and induction of apoptosis in MCF-7 cells. Cell proliferation was assessed by MTT assay and the percentage of apoptotic cells was measured using flowcytometric assay. Understand of molecular mechanism of this combination related to apoptotic pathway were evaluated by Real Time RT-PCR assays. The IC50 values for silibinin, paclitaxel and cisplatin were 160 ± 22.2 μM, 33.7 ± 4.2 nM and 3.2 ± 0.5 μM, respectively. Paclitaxel and cisplatin induced higher percentage of apoptosis in MCF-7 (P < 0.05). Treatment of cell line with combination of silibinin and paclitaxel or cisplatin showed enhanced early apoptosis 56% and 61%, respectively (P < 0.05). Gene expression patterns demonstrated a significant decrease in anti-apoptotic Bcl-2 with increase in pro-apoptotic Bax, P53, BRCA1 and ATM mRNA levels. Taken together combination therapy of breast cancer cells by applying paclitaxel or cisplatin with silibinin synergistically increases the anti-proliferative effect of single agents.  相似文献   
996.
Objective: To identify appropriate weight gain in triplet gestations, which may aid in reducing the risk of perinatal morbidity within this high-risk cohort.

Methods: This retrospective cohort study evaluated all non-anomalous triplet pregnancies between 23 and 40 weeks’ gestation resulting in live births at five tertiary-care medical centers between 1991 and 2011. Subjects were divided by pre-pregnancy BMI into underweight, normal-weight, overweight, and obese groups, and then stratified by low (<0.5?lb/week), moderate (0.5–1.49 lbs/week), or excess weight gain (≥1.5 lbs/week). Primary outcomes included spontaneous preterm birth and preeclampsia.

Results: We included 116 mothers and 348 corresponding neonates for final analysis. The incidence of preeclampsia and preterm delivery less than 32 weeks’ gestation was 37% and 41%, respectively. The incidence of preeclampsia increased with weight gain per week, but was not statistically different from subjects who gained less weight. We found no statistical correlation between weight gain per week and preterm delivery.

Conclusion: We found no association between preeclampsia or preterm delivery and increasing weight gain in triplet pregnancies. The association with increased risk for preeclampsia was predominantly due to BMI effect. Based on the current study, recommendations for optimal weight gain in mothers with triplet gestations could not be defined.  相似文献   
997.
Opinion statement  Acute demyelinating disorders of the central nervous system represent some of the most formidable management and therapeutic challenges to clinicians. These disorders include acute relapses of multiple sclerosis, neuromyelitis optica, acute disseminated encephalomyelitis, optic neuritis, and transverse myelitis. This paper summarizes clinical manifestations of these disorders, as well as treatment strategies. Currently, immunosuppression with corticosteroids for the acute events is the mainstay of treatment. Other experimental therapies, which may be effective in certain patients, are discussed.  相似文献   
998.
Dysferlinopathies belong to the heterogeneous group of autosomal recessive muscular dystrophies. Mutations in the gene encoding dysferlin (DYSF) lead to distinct phenotypes, mainly Limb Girdle Muscular Dystrophy type 2B (LGMD2B) and Miyoshi myopathy (MM). Here, we analysed the mutational data from the largest cohort described to date, a cohort of 134 patients, included based on clinical suspicion of primary dysferlinopathy and/or dysferlin protein deficiency identified on muscle biopsy samples. Data were compiled from 38 patients previously screened for mutations in our laboratory (Nguyen, et al., 2005; Nguyen, et al., 2007), and 96 supplementary patients screened for DYSF mutations using genomic DHPLC analysis, and subsequent sequencing of detected variants, in a routine diagnostic setting. In 89 (66%) out of 134 patients, molecular analysis identified two disease causing mutations, confirming the diagnosis of primary Dysferlinopathy on a genetic basis. Furthermore, one mutation was identified in 30 patients, without identification of a second deleterious allele. We are currently developing complementary analysis for patients in whom only one or no disease-causing allele could be identified using the genomic screening procedure. Altogether, 64 novel mutations have been identified in this cohort, which corresponds to approximately 25% of all DYSF mutations reported to date. The mutational spectrum of this cohort significantly shows a higher proportion of nonsense mutations, but a lower proportion of deleterious missense changes as compared to previous series. (c) 2008 Wiley-Liss, Inc.  相似文献   
999.
Modeling soft tissue using the finite element method is one of the most challenging areas in the field of biomechanical engineering. To date, many models have been developed to describe heart valve leaflet tissue mechanics, which are accurate to some extent. Nevertheless, there is no comprehensive method to modeling soft tissue mechanics, This is because (1) the degree of anisotropy in the heart valve leaflet changes layer by layer due to a variety of collagen fiber densities and orientations that cannot be taken into account in the model and also (2) a constitutive material model fully describing the mechanical properties of the leaflet structure is not available in the literature. In this framework, we develop a new high-order element using p-type finite element formulation to create anisotropic material properties similar to those of the heart valve leaflet tissue in only one single element. This element also takes the nonlinearity of the leaflet tissue into consideration using a bilinear material model. This new element is composed a two-dimensional finite element in the principal directions of leaflet tissue and a p-type finite element in the direction of thickness. The proposed element is easy to implement, much more efficient than standard elements available in commercial finite element packages. This study is one step towards the modeling of soft tissue mechanics using a meshless finite element approach to be applied in real-time haptic feedback of soft-tissue models in virtual reality simulation.  相似文献   
1000.
Objective To explore the effect of hepatocyte growth factor (HGF) and fibroblast growth factor (FGF) on preimplantation embryo development of mouse.
Methods Mated mice were killed by cervical dislocation to collect two pronucleous (2 PN) zygotes from oviduct of pregnant 1 d NMRI mice and were cultured to the hatching blastocyst stage and the number of embryo in different stages was recorded under an invert microscope. The cleavage rates of formed 2 PN zygotes were compared with blastocyst and hatching blastocyst stage in drops of T6 medium with or without HGF or FGF (0 ng/ml, 10 ng/ml, 20 ng/ml, 50 ng/ml, 1 000 ng/ml).
Results HGF and FGF enriched embryo culture media promotea the aevetopment from 2 PN stage embryos to blastocyst. Adding 20 ng/ml of FGF or HGF to the culture medium significantly increased the percentage of 2PN embryos that developed into blastocysts (P〈0.05), but culture of embryos in drops of T6 medium with HGF (20 ng/ml) had no improvement in in-vitro hatching.
Conclusion Exogenous HGF and FGF at low concentrations promote in-vitro mouse blastocyst formation.  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