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   2819篇
  免费   135篇
  国内免费   25篇
耳鼻咽喉   23篇
儿科学   114篇
妇产科学   97篇
基础医学   319篇
口腔科学   271篇
临床医学   223篇
内科学   549篇
皮肤病学   63篇
神经病学   171篇
特种医学   182篇
外科学   322篇
综合类   43篇
预防医学   266篇
眼科学   11篇
药学   194篇
中国医学   24篇
肿瘤学   107篇
  2023年   18篇
  2022年   35篇
  2021年   86篇
  2020年   55篇
  2019年   83篇
  2018年   94篇
  2017年   62篇
  2016年   64篇
  2015年   99篇
  2014年   113篇
  2013年   141篇
  2012年   175篇
  2011年   187篇
  2010年   131篇
  2009年   111篇
  2008年   132篇
  2007年   142篇
  2006年   124篇
  2005年   100篇
  2004年   73篇
  2003年   75篇
  2002年   85篇
  2001年   46篇
  2000年   53篇
  1999年   49篇
  1998年   58篇
  1997年   51篇
  1996年   51篇
  1995年   25篇
  1994年   41篇
  1993年   32篇
  1992年   40篇
  1991年   26篇
  1990年   29篇
  1989年   34篇
  1988年   25篇
  1987年   38篇
  1986年   25篇
  1985年   15篇
  1984年   16篇
  1983年   14篇
  1982年   15篇
  1981年   12篇
  1980年   14篇
  1977年   16篇
  1976年   10篇
  1975年   10篇
  1970年   8篇
  1967年   4篇
  1964年   5篇
排序方式: 共有2979条查询结果,搜索用时 0 毫秒
991.
Huntington's disease (HD) is an inherited neurodegenerative disorder caused by the expansion of a CAG repeat in a gene coding for a protein of unknown function. We have raised a polyclonal antibody against a 12 amino acid peptide (residues 2110-2121 of human huntingtin) which specifically recognises huntingtin on Western blots of human, rat and mouse brain. We have characterised huntingtin expression in the mouse. The protein was detected on Western blots of all mouse tissues examined, with the highest expression seen in brain. Human, mouse and rat brain were fractionated by differential centrifugation and discontinuous Percoll gradients. The fractions were analysed by Western blotting for huntingtin and synaptophysin (a synaptic vesicle localised protein). In mouse brain, huntingtin was localised in the soluble S3 fraction; in rat brain it was localised in the soluble S3 fraction and also in the membrane P2 and P3 fractions; in both normal and HD- affected human brain, huntingtin was membrane bound with a distribution essentially the same as that of synaptophysin. These observed differences in the subcellular localisation of huntingtin between mouse and human brain are important in the context of mouse models for HD.   相似文献   
992.

Background  

Septic shock is the most feared complication of chemotherapy-induced febrile neutropenia. So far, there are no robust biomarkers that can stratify patients to the risk of sepsis complications. The VEGF-A axis is involved in the control of microvascular permeability and has been involved in the pathogenesis of conditions associated with endothelial barrier disruption such as sepsis. sFlt-1 is a soluble variant of the VEGF-A receptor VEGFR-1 that acts as a decoy receptor down-regulating the effects of VEGF-A. In animal models of sepsis, sFlt-1 was capable to block the barrier-breaking negative effects of VEGF-A and to significantly decrease mortality. In non-neutropenic patients, sFlt-1 has been shown to be a promising biomarker for sepsis severity.  相似文献   
993.
Objective: The effects of cafeteria and high fat diets were investigated on animal models of behavior.

Methods: Male Wistar rats were treated with Control (C), Cafeteria (CD) and High Fat (FD) diets and tested in the Elevated Plus-Maze (EPM) and Morris Water Maze (MWM) procedures. Body weight, length, abdominal circumference, retroperitoneal and epididymal adipose tissues were recorded. Physical parameters, weight of tissues, EPM, and MWM data were subjected to ANOVA followed by Newman–Keuls test (P?Results: There were no differences on weight and length parameters between CD and C rats up to 98 days of age. However, abdominal circumferences were higher in CD as compared to C at 35 and 70 days of age, respectively, the 5th and the 7th weeks. FD presented lower measures of weight and abdominal circumference; nevertheless there was an increase on those parameters at the end of the nutritional treatment. Even without an apparent weight gain of CD and FD these animals presented a greater accumulation of retroperitoneal and epididymal adipose tissues. In addition, CD and FD demonstrated behaviors that can suggest lower anxiety. CD showed a better learning performance and FD showed better recall of previous learned information in the memory retention test.

Discussion: According to those data it was concluded that hypercaloric diet ingestion was capable of triggering metabolic alterations and possibly lowering anxiety associated to learning or memory improvement on a spatial task.  相似文献   
994.
995.

Objective

The aim of this study was to evaluate the effect of simulated periodontal ligament (SPDL) on custom cast dowel and core removal by ultrasonic vibration.

Material and Methods

Thirty-two human maxillary canines were included in resin cylinders with or without SPDL made from polyether impression material. In order to allow tensile testing, the roots included in resin cylinders with SPDL were fixed to cylinders with two stainless steel wires. Post-holes were prepared by standardizing the length at 8 mm and root canal impressions were made with self-cured resin acrylic. Cast dowel and core sets were fabricated and luted with Panavia F resin cement. Half of the samples were submitted to ultrasonic vibration before the tensile test. Data were analyzed statistically by two-way ANOVA and Tukey''s post-hoc tests (p<0.05).

Results

The ultrasonic vibration reduced the tensile strength of the samples directly included in resin cylinders. There was no difference between the values, whether or not ultrasonic vibration was used, when the PDL was simulated. However, the presence of SPDL affected the tensile strength values even when no ultrasonic vibration was applied.

Conclusion

Simulation of PDL has an effect on both ultrasonic vibration and tensile testing.  相似文献   
996.
BACKGROUND: The aim of this study was to monitor changes in periodontal inflammation in patients with juvenile idiopathic arthritis (JIA) for 2 years. We investigated the influence of rheumatic disease activity and antirheumatic medication on clinical and immunological parameters of periodontal inflammation in these individuals. METHODS: Two years after a baseline examination, the periodontal and rheumatological conditions of 18 adolescents with JIA and 14 control subjects were described. The clinical periodontal inflammation was monitored by registration of visual plaque, marginal bleeding, probing depth, and clinical attachment loss (AL). Periodontal inflammation was also assessed by analysis of the cytokines interleukin (IL)-1beta and IL-18 and the collagenase matrix metalloproteinase (MMP)-8 by enzyme-linked immunosorbent assay. RESULTS: The erythrocyte sedimentation rate and clinical rheumatological parameters were significantly improved at the 2-year follow-up. The number of sites with plaque decreased, and the number of pockets >/=4 mm increased, whereas bleeding levels and the extension of AL remained unchanged. IL-1beta in gingival crevicular fluid decreased significantly in the JIA group after 2 years. No differences were observed for IL-1beta, MMP-8, or IL-18 levels between groups after 2 years. CONCLUSION: Two years after the baseline examination, no clinical or laboratory differences in periodontal inflammation could be found between JIA patients and control subjects.  相似文献   
997.
A modification of a high pressure liquid chromatographic (HPLC) procedure is described that enables the complete separation and quantitation of the A gamma T, A gamma I, and G gamma chains in human fetal hemoglobin. The method, which is fast and accurate, requires 5 to 2000 micrograms Hb F. The purity of the Hb F is not essential and admixture of up to 70% adult Hb does not interfere with the determination. The method has been applied to the Hb F of 64 Black SS patients and 7 persons with the Hb S-HPFH (G gamma A gamma type) conditions. (A) Both "adult" G gamma to A gamma (2:3) and "newborn" G gamma to A gamma (3:2) ratios were observed in adult SS patients, 8 yr and older. Only 12% of the SS patients had the "newborn" ratio. This high G gamma to A gamma ratio may be due to a modification of the genetic switch mechanism that regulates the change of this ratio after birth. (B) Intermediate G gamma to A gamma ratios were only found in young SS patients, 5 yr of age or less. The results suggest a delayed switch of the newborn leads to adult ratio in sickle cell anemia. (C) The A gamma T chain was present in only 6% of all SS patients. One patient is homozygous for this variant chain. (D) Three of the 7 subjects with Hb S-HPFH were positive for the A gamma T chain. Its percentage was low, which suggests that the A gamma T chain gene is in trans of the HPFH determinant. (E) Quantitation of the three gamma chain types is also possible in the Hb F from Hb S heterozygotes with (nearly) normal Hb F levels. Such an analysis is useful for an evaluation of genetic conditions involving variations in the production of (different types of) Hb F.  相似文献   
998.
Prevalence of Babesia antibody in a selected blood donor population   总被引:6,自引:0,他引:6  
Human babesiosis, a parasitic disease transmitted by the tick, Ixodes dammini, was confined previously to limited areas of the northeastern United States. It is a rare but potentially life-threatening complication of transfusion. Red cells and platelets prepared from asymptomatic donors have been implicated in transfusion-transmitted cases. More cases of babesiosis are being reported as the range of the vector expands in the United States. Blood donors from an endemic area were tested for antibody to Babesia microti during the summer. Only 3.7 percent of the 779 donors were seropositive, compared with 4.7 percent (p greater than 0.05) of donors from a nonendemic area. An epidemiologic survey of seropositive and matched seronegative controls demonstrated no significant differences that would assist in screening donors.  相似文献   
999.
Schmallenberg virus (SBV)‐like clinical cases of abortions in northern Jordan in early 2013, together with the emergence of SBV in Europe in 2011, its rapid spread within the following years and the detection of this virus in Turkey, raised questions about the distribution of SBV or related orthobunyaviruses. To evaluate the occurrence of SBV or related members of the Simbu serogroup of orthobunyaviruses in Jordan, bulk milk (cattle) and serum samples (cattle, sheep and goat) collected in northern Jordan in 2013 were first tested by commercially available SBV antibody ELISAs. Indeed, 3 of 47 bulk milk samples and 57 of 115 serum samples provided positive results, but SBV specificity of the ELISA results could not be confirmed by virus neutralization assays. Instead, subsequent cross‐neutralization tests were able to further investigate the specificity of these antibodies. Here, a significant inhibition of Aino virus was observed. Thus, the causative agent was most likely a Simbu serogroup virus closely related to Aino virus. Consequently, these results confirm that members of this group of virus are not only present in Europe, Africa or Australia, but also in the Middle East.  相似文献   
1000.
Bone mineral density (BMD) measurement by hip dual-energy X-ray absorptiometry (DXA) is considered the best predictor of osteoporotic fracture risk. BMD takes into account only in part the bone cross-sectional area that is an important determinant of both bone compression strength and of bending breaking resistance. From DXA measurements of proximal radius (Osteoplan, NIM, Verona, Italy) we obtained the projected outer diameter (D) and the mean diameter of the medulla (d), by an algorithm based on the assumption of a constant cortical volumetric density of 1050 g/cm3. The algorithm was validated by the good correlation found (r= 0.8) between calculated d and that actually measured by peripheral quantitative tomography (pQCT; XCT 960, Stratec, Unitrem, Italy) at the same radial site. The D and d values were used to calculate a bending breaking resistance index (BBRI) that is a component of the cross-sectional moment of inertia. The BBRI measured in 5460 women aged 35–89 years, was stable up to the age of 65–70 years and rapidly declined thereafter by 0.7% per year. This profile appears to be due to the fact that the increase in medullary area is compensated in terms of mechanical resistance by enlargement of cross-sectional area. In 68 women with either previous femoral neck (n= 41) or pertrochanteric fracture (n= 27) DXA measurements at proximal and ultradistal radius, lumbar spine and femoral neck were obtained together with the evaluation of proximal radius BBRI. The diagnostic accuracy of BBRI was somewhat comparable to that of spine and femoral neck BMD and significantly superior to that of ultradistal and proximal radius BMD, from which it was derived. Despite the obvious limitation of the cross-sectional nature of this study, our results indicate that a simple re-elaboration of the data obtained by peripheral radial densitometry may achieve diagnostic accuracy for hip fracture risk assessment only marginally lower than that of the direct measure of the BMD of the femoral neck. They also give additional support to the view that bone geometry, particularly for compact skeletal segments, is a determinant of its strength at least as important as bone density. Received: 25 July 2000 / Accepted: 9 April 2001  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