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   1605篇
  免费   87篇
  国内免费   12篇
耳鼻咽喉   30篇
儿科学   40篇
妇产科学   38篇
基础医学   197篇
口腔科学   4篇
临床医学   146篇
内科学   473篇
皮肤病学   15篇
神经病学   120篇
特种医学   64篇
外科学   121篇
综合类   10篇
预防医学   85篇
眼科学   30篇
药学   171篇
中国医学   9篇
肿瘤学   151篇
  2023年   24篇
  2022年   119篇
  2021年   200篇
  2020年   55篇
  2019年   68篇
  2018年   82篇
  2017年   46篇
  2016年   52篇
  2015年   67篇
  2014年   61篇
  2013年   72篇
  2012年   124篇
  2011年   109篇
  2010年   64篇
  2009年   43篇
  2008年   71篇
  2007年   99篇
  2006年   80篇
  2005年   60篇
  2004年   72篇
  2003年   48篇
  2002年   48篇
  2001年   6篇
  2000年   5篇
  1999年   5篇
  1998年   1篇
  1996年   5篇
  1995年   1篇
  1994年   2篇
  1992年   5篇
  1991年   1篇
  1990年   2篇
  1989年   2篇
  1988年   1篇
  1982年   1篇
  1974年   1篇
  1971年   1篇
  1966年   1篇
排序方式: 共有1704条查询结果,搜索用时 15 毫秒
71.
Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide expression of which has been found in various tumors of the brain and peripheral organs. Despite numerous studies, the exact role the peptide plays in the development and progression of tumors is not fully understood. In the present study, we investigated the effect of PACAP on human retinoblastoma Y79 cell viability. We found that both PACAP38 and PACAP6-38, a selective PAC1 receptor antagonist, did not affect Y79 cell viability at nanomolar concentrations, but when used at 1–5 μM potently reduced cell survival in a dose-dependent manner. PACAP27 and maxadilan, a high affinity agonist of PAC1 receptors, had negligible effects. Two membrane-penetrating analogs of PACAP38 inactive at PAC1/VPAC receptors, [Disc6]PACAP38 and FITC-Ahx-PACAP11-38, also decreased viability of Y79 cells, albeit with lower potency than PACAP38. The cytotoxic effect of PACAP38 was augmented by p38, MEK1/2, and JNK inhibitors, indicating that high concentrations of the peptide might decrease the activity of these kinases, leading to cell death. It is suggested that the cytotoxic activity of PACAP38 and PACAP6-38 against human retinoblastoma Y79 cell line may result from their interaction with target sites other than PAC1 and VPAC receptors, but this is yet unknown.  相似文献   
72.
Diabetes mellitus (DM) is a heterogeneous group of disorders whose common trait is chronic hyperglycemia. Gestational diabetes mellitus (GDM) is one of the subtypes of DM that manifests during pregnancy. It is believed that 2%–5% of pregnancies worldwide are complicated with GDM, with the prevalence having significantly increased over the last decade. While the pathogenesis of the disease remains largely unknown, GDM is believed to be a result of interactions between genetic, epigenetic, and environmental factors. Linkage and association studies, including those that are genome-wide, have allowed us to identify complex genetic and epigenetic mechanisms that lead to the development of GDM. Multiple common variants in candidate genes such as potassium inwardly rectifying channel subfamily J, member 11 (KCNJ11), glucokinase (GCK), or hepatocyte nuclear factor 1α (HNF1A) have been found to increase the disease risk. In this review, we provide a detailed overview of the current knowledge concerning the influence of genetics and epigenetics on the development of GDM.  相似文献   
73.
74.
75.
With the continuing growth of waste sulfur production from the petroleum industry processes, its utilization for the production of useful, low-cost, and environmentally beneficial materials is of primary interest. Elemental sulfur has a significant and established history in the modification of bitumen binders, while the sulfur-containing high-molecular compounds are limited in this field. Herein, we report a novel possibility to utilize the sulfur/organic copolymers obtained via the inverse vulcanization process as modifiers for bitumen binders. Synthesis and thermal characterization (TGA-DSC) of polysulfides derived from elemental sulfur (S8) and unsaturated organic species (dicyclopentadiene, styrene, and limonene) have been carried out. The performance of modified bitumen binders has been studied by several mechanical measurements (softening point, ductility, penetration at 25 °C, frass breaking point, adhesion to glass and gravel) and compared to the unmodified bitumen from the perspective of normalized requirements concerning polymer-modified bitumen. The interaction of bitumen binder with sulfur/organic modifier has been studied by means of FTIR spectroscopy and DSC measurements. The impact of the modification on the performance properties of bitumen has been demonstrated. The bitumen binders modified with sulfur/organic copolymers are in general less sensitive to higher temperatures (higher softening point up to 7 °C), more resistant to permanent deformations (lower penetration depth), and more resistant to aging processes without intrusive deterioration of parameters at lower temperatures. What is more, the modification resulted in significantly higher adhesion of bitumen binders to both glass (from 25% up to 87%) and gravel surfaces in combination with a lower tendency to form permanent deformations (more elastic behavior of the modified materials).  相似文献   
76.
Poly-ɛ-caprolactone (PCL) is now widely studied in relation to the engineering of bone, cartilage, tendons, and other tissues. Standard histological protocols can destroy the carefully created trabecular and honeycomb-like architecture of PCL scaffolds, and could lead to scaffold fibers swelling, resulting in the displacement or compression of tissues inside the scaffold. The aim of this study was to modify a standard histopathological protocol for PCL scaffold preparation and evaluate it on porous cylindrical PCL scaffolds in a rat model. In 16 inbred Wag rats, 2 PCL scaffolds were implanted subcutaneously to both inguinal areas. Two months after implantation, harvested scaffolds were first subjected to μCT imaging, and then to histopathological analysis with standard (left inguinal area) and modified histopathological protocols (right inguinal area). To standardize the results, soft tissue percentages (STPs) were calculated on scaffold cross-sections obtained from both histopathological protocols and compared with corresponding µCT cross-sections. The modified protocol enabled the assessment of almost 10× more soft tissues on the scaffold cross-section than the standard procedure. Moreover, STP was only 1.5% lower than in the corresponding µCT cross-sections assessed before the histopathological procedure. The presented modification of the histopathological protocol is cheap, reproducible, and allows for a comprehensive evaluation of PCL scaffolds while maintaining their trabecular, honeycomb-like structure on cross-sections.  相似文献   
77.
When treating historical beeswax seals, it seems a natural choice to use materials as similar to the original as possible. The properties of analogous recent materials, however, differ from those of the aged ones, not to mention the fact that the exact composition of the particular sealing wax is usually uncertain. In order to obtain the material of desired properties, recent beeswax is often combined with various additives, including petroleum waxes, or even replaced by mixtures based solely on these products. Within this study, the relevant properties of Permulgin 3274, a ceresin-type wax, were compared with the characteristics of recent and historical beeswaxes. The aim was to evaluate its advantages and limitations, in terms of its possible use for the conservation of beeswax seals. The properties studied were comprised of the chemical composition, thermal properties, mechanical properties, possibilities of colour adjustment and ageing properties. Permulgin 3274′s workability was evaluated by conservators from the National Archives in Prague. The results indicate that, from the technological point of view, Permulgin 3274 could be considered a welcome alternative to the use of traditional conservation mixtures.  相似文献   
78.
79.
OBJECTIVES: Evaluation of the complications rate, as well as pregnancy outcome, in women who underwent early and mid-trimester amniocentesis. MATERIAL AND METHODS: The study was conducted among 454 patients, including 162 women after the procedure performed before 15 gestational week and 292 patients who underwent classic amniocentesis. All patients were hospitalized in Division of Reproduction of University of Medical Sciences in Poznan between 1999 and 2005. The analysis, based both on clinical observations and questionnaire sent to patients, concerned especially the frequency of following complications: miscarriage, premature rupture of membranes and club foot in newborns. RESULTS: Total pregnancy loss rate due to amniocentesis amounted to 1.2% and 0.3% in early and mid-trimester amniocentesis, respectively, not reaching statistical significance. The frequency of club foot in newborns of mothers who underwent amniocentesis did not differ significantly between the groups, although it was four times higher in early amniocentesis group than in patients in whom mid-trimester amniocentesis had been performed. CONCLUSIONS: The safety of early amniocentesis is comparable with safety of mid-trimester amniocentesis.  相似文献   
80.
Torrefaction is one of the methods of thermal treatment of biomass, which allows obtaining a product of better quality in the form of biochar. The aim of the paper was to analyze the possibility of using goldenrod (Solidago canadensis, Solidago gigantea) for the production of biochar. The torrefaction process involved the vegetative and generative parts as well as the whole plant at temperatures of 250 °C and 275 °C, for 3 h. Next, the physicochemical properties of the raw material and biochar were determined, namely moisture content, ash content, volatile matter content, calorific value, and heat of combustion. The bulk density of raw biomass and biochar was also determined. It was found that after biomass torrefaction, the ash content, calorific value, and heat of combustion increased, while volatile matter content decreased. It has been observed that in both the case of raw biomass and biochar, the plant species and the sampled parts have a significant impact on the ash content, volatile matter content, calorific value, and heat of combustion.  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