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   2467篇
  免费   167篇
  国内免费   9篇
耳鼻咽喉   19篇
儿科学   83篇
妇产科学   80篇
基础医学   447篇
口腔科学   82篇
临床医学   198篇
内科学   513篇
皮肤病学   53篇
神经病学   246篇
特种医学   52篇
外科学   307篇
综合类   16篇
预防医学   151篇
眼科学   34篇
药学   124篇
肿瘤学   238篇
  2023年   18篇
  2022年   47篇
  2021年   72篇
  2020年   37篇
  2019年   47篇
  2018年   44篇
  2017年   39篇
  2016年   58篇
  2015年   50篇
  2014年   72篇
  2013年   119篇
  2012年   153篇
  2011年   172篇
  2010年   88篇
  2009年   89篇
  2008年   163篇
  2007年   156篇
  2006年   147篇
  2005年   132篇
  2004年   121篇
  2003年   93篇
  2002年   101篇
  2001年   68篇
  2000年   64篇
  1999年   66篇
  1998年   27篇
  1997年   14篇
  1996年   15篇
  1995年   10篇
  1994年   17篇
  1992年   25篇
  1991年   23篇
  1990年   18篇
  1989年   15篇
  1988年   15篇
  1987年   12篇
  1986年   19篇
  1985年   18篇
  1984年   10篇
  1983年   10篇
  1982年   10篇
  1979年   14篇
  1978年   11篇
  1977年   11篇
  1975年   10篇
  1974年   21篇
  1973年   14篇
  1972年   10篇
  1970年   9篇
  1969年   15篇
排序方式: 共有2643条查询结果,搜索用时 62 毫秒
21.
Maturation of the murine ectoplacental cone results in the development of the placental tissue which essentially consists of two trophoblastic zones, the spongiotrophoblast and labyrinthine trophoblast. In this study we attempted to investigate the action of cytokines on ectoplacental cone cell differentiation to mature trophoblast cells. After determining the cellular composition of the ectoplacental cone cell suspensions based on the expression of cytokeratin, vimentin, Mac-1, class I and class II MHC antigens, the cells were exposed to the differentiation-inducing cytokines IL-3, GM-CSF, CSF-1 and IFN-gamma. From the four factors employed, only IFN-gamma increased the levels of cytokeratin-positive cells without inducing Mac-1 expression. IL-3 increased the percentages of cytokeratin as well as Mac-1- and vimentin-positive cells whereas GM-CSF and CSF-1 preferentially promoted an increase of the Mac-1 and vimentin markers. For further analysis, ectoplacental cone cells were negatively selected for Mac-1, class I and class II antigens to exclude non-trophoblastic contaminants and thereafter treated with the same cytokines. We show here that only IFN-gamma leads the sorted ectoplacental cone cells to a pure trophoblastic population composed of 100% cytokeratin-positive cells. The specificity of IFN-gamma on this differentiation pathway is strengthened by the fact that murine maternal serum on the day of EC formation contains high levels of this cytokine, suggesting that its natural presence supports - at least phenotypically - the in vivo differentiation of EC cells to trophoblasts.  相似文献   
22.
The presence of Y chromosome sequences in Turner syndrome (TS) patients may predispose them to gonadoblastoma formation with an estimated risk of 15–25%. The aim of this study was to determine the presence and the incidence of cryptic Y chromosome material in the genome of TS patients. The methodology involved a combination of polymerase chain reaction (PCR) and nested PCR followed by Southern blot analysis of three genes—the sex determining region Y (SRY), testis specific protein Y encoded (TSPY) and RNA binding motif protein (RBM) (previously designated as YRRM) and nine additional STSs spanning all seven intervals of the Y chromosome. The methodology has a high sensitivity as it detects one 46, XY cell among 105 46, XX cells. Reliability was ensured by taking several precautions to avoid false positive results. We report the results of screening 50 TS patients and the identification of cryptic Y chromosome material in 12 (24%) of them. Karyotypes were divided in four groups: 5 (23.8%) patients out of the 21 TS patients which have the 45, X karyotype (group A) also have cryptic Y sequences; none (0%) of the 7 patients who have karyotypes with anomalies on one of the X chromosomes have Y mosaicism (group B); 1 (6.3%) of the 16 patients with a mosaic karyotype have Y material (group C); and 6 (100%) out of 6 patients with a supernumerary marker chromosome (SMC) have Y chromosome sequences (group D). Nine of the 12 patients positive for cryptic Y material were recalled for a repeat study. Following new DNA extraction, molecular analysis was repeated and, in conjunction with fluorescent in situ hybridization (FISH) analysis using the Y centromeric specific probe Yc-2, confirmed the initial positive DNA findings. This study used a reliable and sensitive methodology to identify the presence of Y chromosome material in TS patients thus providing not only a better estimate of a patient's risk in developing either gonadoblastoma or another form of gonadal tumor but also the overall incidence of cryptic Y mosaicism.  相似文献   
23.
Thirty-nine primary gastric and 22 intestinal malignant lymphomas collected from 1969 to 1980 have been studied morphologically and immunohistochemically. Eighteen of the 61 gastrointestinal lymphomas were of low-grade malignancy (9 lymphoplasmacytoid/cytic, 3 centrocytic, 6 centroblastic/centrocytic) and 43 were of high-grade malignancy (14 centroblastic, 7 lymphoblastic, 22 immunoblastic malignant lymphomas) according to the Kiel classification. The peroxidase-antiperoxidase (PAP) method was used in 53 of the 61 cases. Twenty-seven of them revealed a monoclonal positivity for intracytoplasmic IgS: kappa light chains in 18 and lambda light chains in 7 cases. Two cases represented alpha chain disease, revealing only a heavy chain positivity. The most frequent staining pattern of the lymphoma cells was that of kappa/mu. Cells with a mixed centrocytic and plasma cell configuration (centrocytoid plasma cells) proved to be positive for intracytoplasmic IgS. Lymphoma cells of all tested cases proved to be negative for all histiocytic markers. Histologically and immunohistochemically, the Greek cases of primary gastrointestinal malignant lymphomas seem to resemble "western" type lymphomas.  相似文献   
24.
Study of serum prolactin during electroconvulsive therapy (ECT) in depressive patients revealed a greater prolactin increase after bilateral than after unilateral ECT. A linear correlation between the two types of prolactin response was found for a group of 10 patients, a finding that suggests a quantitative rather than a qualitative difference between bilateral and unilateral ECT with regard to their prolactin-releasing properties. The magnitude of prolactin response did not differ between right and left unilateral ECT, nor in a systematically studied case of postictal dysphoric excitement that occurred after right, but not after left, unilateral ECT. In this case, maximal prolactin response occurred earlier with right than with left unilateral ECT. Prolactin increase after ECT was not correlated with such factors as severity of depression nor seizure duration.  相似文献   
25.
A 75 year woman with chronic vitreous hemorrhage underwent extraction of a senile cataract. Surgery was complicated by the flow of brown fluid from the vitreous to the anterior chamber, which was not entirely removed. Post-operatively there was pain, 2 mm of brown hypopyon and intraocular pressure elevation to 60 mm Hg with the preoperative diagnosis of endophthalmitis, a pars plana vitreous tap and instillation of intravitreal antibiotics was performed. Bacterial cultures were negative and the presence of erythrocyte "ghost cells" established the diagnosis of hemolytic glaucoma. As medical management proved ineffective, a pars plana vitrectomy was performed. One year post-operatively the patient had a visual acuity of 0.4-0.5, normal intraocular pressure without medication and evidence of an old branch retinal vein occlusion. The mechanism of hemolytic "ghost-cell" glaucoma in this case is discussed.  相似文献   
26.
Gravieras are ‘gruyere’ type hard cheeses with a variety of different products and the second highest consumption in Greece. In this study, we present a dietary intake assessment and a nutritional characterization of pre-packed graviera products sold in the Greek market using Nutri-Score Front of Pack Label (FoPL). The nutrient contents of 92 pre-packed graviera products were combined with daily individual consumption data extracted from the Hellenic National Nutrition Health Survey (n = 93), attempting to evaluate the contribution of graviera’s consumption to the Greek diet. The analysis of nutrients’ intake as a Reference Intake (RI) percentage ranked saturated fat first on the nutrients’ intake list, with RI percentage ranging from 36.1 to 109.2% for the 95th percentile of consumption. The respective % RI for energy, total fat, carbohydrates, sugars, proteins and salt ranged from 12.7–20.7%, 21.6–50.4%, 0–3.1%, 0–6.1%, 37–57.1% and 6.3–42%. Nutri-Score classified 1% of the products to C—light orange class, 62% to D—orange and 37% to E—dark orange, while no products were classified to A—dark green or B—green classes. The comparison between the Nutri-Score classification and the nutrients’ intake assessment, also separately conducted within the classes, showed a higher salt intake after the consumption of products classified as D—orange and E—dark orange.  相似文献   
27.
Aim: To investigate the effect of normalizing vitamin B12 (B12) levels with oral B12 (methylcobalamin) 1000 μg/day for one year in patients with diabetic neuropathy (DN). Patients and methods: In this prospective, double-blind, placebo-controlled trial, 90 patients with type 2 diabetes on metformin for at least four years and both peripheral and autonomic DN were randomized to an active treatment group (n = 44) receiving B12 and a control group (n = 46) receiving a placebo. All patients had B12 levels less than 400 pmol/L. Subjects underwent measurements of sural nerve conduction velocity (SNCV), sural nerve action potential (amplitude) (SNAP), and vibration perception threshold (VPT), and they performed cardiovascular autonomic reflex tests (CARTs: mean circular resultant (MCR), Valsalva test, postural index, and orthostatic hypotension). Sudomotor function was assessed with the SUDOSCAN that measures electrochemical skin conductance in hands and feet (ESCH and ESCF, respectively). We also used the Michigan Neuropathy Screening Instrument Questionnaire and Examination (MNSIQ and MNSIE, respectively) and questionnaires to evaluate quality of life (QoL) and level of pain (pain score). Results: B12 levels increased from 232.0 ± 71.8 at baseline to 776.7 ± 242.3 pmol/L at follow-up, p < 0.0001, in the active group but not in the control group. VPT, MNSIQ, QoL, pain score, SNCV, SNAP, and ESCF significantly improved in the active group (p < 0.001, p = 0.002, p < 0.0001, p < 0.000, p < 0.0001, p < 0.0001, and p = 0.014, respectively), whereas CARTS and MNSIE improved but not significantly. MCR, MNSIQ, SNCV, SNAP, and pain score significantly deteriorated in the control group (p = 0.025, p = 0.017, p = 0.045, p < 0.0001, and p < 0.0001, respectively). Conclusions: The treatment of patients with DN with 1 mg of oral methylcobalamin for twelve months increased plasma B12 levels and improved all neurophysiological parameters, sudomotor function, pain score, and QoL, but it did not improve CARTS and MNSIE.  相似文献   
28.
Fast self-reported eating rate (SRER) has been associated with increased adiposity in children and adults. No studies have been conducted among high-school students, and SRER has not been validated vs. objective eating rate (OBER) in such populations. The objectives were to investigate (among high-school student populations) the association between OBER and BMI z-scores (BMIz), the validity of SRER vs. OBER, and potential differences in BMIz between SRER categories. Three studies were conducted. Study 1 included 116 Swedish students (mean ± SD age: 16.5 ± 0.8, 59% females) who were eating school lunch. Food intake and meal duration were objectively recorded, and OBER was calculated. Additionally, students provided SRER. Study 2 included students (n = 50, mean ± SD age: 16.7 ± 0.6, 58% females) from Study 1 who ate another objectively recorded school lunch. Study 3 included 1832 high-school students (mean ± SD age: 15.8 ± 0.9, 51% females) from Sweden (n = 748) and Greece (n = 1084) who provided SRER. In Study 1, students with BMIz ≥ 0 had faster OBER vs. students with BMIz < 0 (mean difference: +7.7 g/min or +27%, p = 0.012), while students with fast SRER had higher OBER vs. students with slow SRER (mean difference: +13.7 g/min or +56%, p = 0.001). However, there was “minimal” agreement between SRER and OBER categories (κ = 0.31, p < 0.001). In Study 2, OBER during lunch 1 had a “large” correlation with OBER during lunch 2 (r = 0.75, p < 0.001). In Study 3, fast SRER students had higher BMIz vs. slow SRER students (mean difference: 0.37, p < 0.001). Similar observations were found among both Swedish and Greek students. For the first time in high-school students, we confirm the association between fast eating and increased adiposity. Our validation analysis suggests that SRER could be used as a proxy for OBER in studies with large sample sizes on a group level. With smaller samples, OBER should be used instead. To assess eating rate on an individual level, OBER can be used while SRER should be avoided.  相似文献   
29.
High adherence to the Mediterranean diet (MD) has been associated with a lower prevalence of Metabolic Syndrome (MetS). The present study aimed to investigate the impact of MD adherence on parameters of MetS. A systematic literature search was performed in PubMed, Cochrane Central Registry of Clinical Trials (CENTRAL), Scopus, EMBASE, Web of Science and Google Scholar databases. Observational studies that recorded adherence to MD and components/measures of the MetS, such as waist circumference (WC), blood pressure (BP), fasting blood glucose (FBG), high-density lipoprotein (HDL) cholesterol and triglycerides (TG), were included in this study. A total of 58 studies were included in our study. WC and TG were significantly lower in the high adherence MD group (SMD: −0.20, (95%CI: −0.40, −0.01), SMD: −0.27 (95%CI: −0.27, −0.11), respectively), while HDL cholesterol was significantly higher in the same group (SMD: −0.28 (95%CI: 0.07, 0.50). There was no difference in FBG and SBP among the two groups (SMD: −0.21 (95%CI: −0.54, 0.12) & SMD: −0.15 (95%CI: −0.38, 0.07), respectively). MD may have a positive impact on all parameters of MetS. However, further research is needed in this field.  相似文献   
30.
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