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   1725篇
  免费   83篇
  国内免费   11篇
耳鼻咽喉   26篇
儿科学   74篇
妇产科学   68篇
基础医学   318篇
口腔科学   9篇
临床医学   88篇
内科学   419篇
皮肤病学   17篇
神经病学   217篇
特种医学   22篇
外科学   72篇
综合类   18篇
预防医学   142篇
眼科学   97篇
药学   141篇
中国医学   2篇
肿瘤学   89篇
  2023年   4篇
  2022年   54篇
  2021年   96篇
  2020年   34篇
  2019年   43篇
  2018年   58篇
  2017年   40篇
  2016年   39篇
  2015年   55篇
  2014年   59篇
  2013年   78篇
  2012年   124篇
  2011年   133篇
  2010年   69篇
  2009年   36篇
  2008年   117篇
  2007年   128篇
  2006年   145篇
  2005年   125篇
  2004年   137篇
  2003年   98篇
  2002年   84篇
  2001年   3篇
  2000年   4篇
  1999年   4篇
  1998年   8篇
  1997年   9篇
  1996年   8篇
  1995年   5篇
  1994年   4篇
  1993年   4篇
  1991年   4篇
  1988年   2篇
  1987年   1篇
  1985年   2篇
  1983年   1篇
  1981年   1篇
  1980年   2篇
  1978年   1篇
排序方式: 共有1819条查询结果,搜索用时 15 毫秒
81.
82.
This paper discusses the results of studies on the transport of Ag(i) across polymer inclusion membranes (PIMs), derivatives of calixpyrroles with methyl (KP1) and carboxyl (KP2) groups, as ion carriers, o-nitrophenyl pentyl ether (o-NPPE) as a plasticizer and cellulose triacetate (CTA) as support. The influence of the pH of the source phase, metal concentration, stripping phase as well as carrier and plasticizer concentration on the efficiency of Ag(i) transport through PIM is presented. Long-term experiments with a supported liquid membrane and a plasticizer membrane demonstrate the durability of the studied PIMs. The obtained results indicate that the competitive transport of Cu(ii), Zn(ii), Ag(i) and Cd(ii) from the aqueous nitrate source phase through KP1 and KP2 is an effective separation method for Ag(i) ions. The prepared PIMs were characterized by scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques.

The transport of Ag(i) across polymer inclusion membranes is reported with derivatives of calixpyrroles with methyl (KP1) and carboxyl (KP2) groups as ion carriers, o-nitrophenyl pentyl ether as a plasticizer and cellulose triacetate as support.  相似文献   
83.

Introduction

The objective was to assess the quality of pregnant women''s diet in Poland concerning macro-elements and to analyze reasons for low or high quality diets.

Material and methods

Five hundred and twelve pregnant women in their 20th to 30th week of pregnancy took part in the research conducted by means of a 7-day observation of diet. Consumed products were analyzed by means of DIETETYK software developed by the Polish National Food and Nutrition Institute. Obtained macro values were averaged. The results were compared with the recommendations from the World Health Organization, European Union and Polish National Food and Nutrition Institute and analyzed statistically (χ2 test).

Results

The pregnant women consumed an average of 1898 ±380 kcal daily. Average value of macro components supplied with the diet did not deviate from EU and NFNI nutrition recommendations: protein – 72.1 g/person daily, fats overall – 72.8 g, polyunsaturated fatty acids – 10.93 g, cholesterol – 283 mg, carbohydrates – 257 g. The study proved a significant relation between a higher quality diet of pregnant women and tertiary or secondary education (p = 0.05) as well as urban residence (p = 0.01).

Conclusions

Pregnant women''s diet in Poland is not significantly different from diet quality of pregnant women from other countries. A lower quality diet was observed among women who smoked during pregnancy and lived in rural areas.  相似文献   
84.
Our experiments aimed to study the influence of layered materials with nanometric-scale particles, which are part of lubricant oils, on their tribological properties. The object of this study was a lubricant oil made using base oil PAO4, which contained nanoparticle hexagonal boron nitride (nano h-BN) and a dispersant based on succinic acid imide. Comparative tests for engine oil (CB30) were also performed. The paper presents the method of preparing the test material and the tribological test results, including wear spot diameter (wear mark), limit wear load, and seizure load. The test results obtained demonstrate that nano-hexagonal boron nitride improves the tribological properties of lubricant oils. However, oil preparation and the quantitative selection of components markedly influence the results.  相似文献   
85.
Results of research on hydration of four-component binders containing very high amounts of supplementary cementitious materials were presented. The samples were composed of blended pozzolana (a mix of conventional fly ash and spent aluminosilicate catalyst), cement (about 20 wt.% in the binder) and Ca(OH)2. Spent aluminosilicate catalyst was proposed as activating component which can improve properties of low-cement blends, while the role of Ca(OH)2 was to enhance pozzolanic reaction. Early and later hydration periods of such blends were investigated by calorimetry, TG/DTG, FTIR and X-ray diffraction. Initial setting time as well as compressive strength were also determined. It was concluded that enhancement of reactivity and improvement of properties of fly ash–cement binders are possible by replacing a part of fly ash with more active fine-grained pozzolana and introducing additional amounts of Ca(OH)2. The spent catalyst is mainly responsible for accelerating action during the first hours of hydration and for progress of early pozzolanic reaction. Fly ash develops its activity over time, thus synergic effect influences the later properties of composites. Samples containing blended pozzolana exhibit shorter initial setting times and higher compressive strength, as well as faster consumption of Ca(OH)2 compared to the reference. Investigated mixtures seem to be promising as “green” binders, alternatives to cement, after optimizing their compositions or additional activating procedure.  相似文献   
86.
OBJECTIVES: Ovarian carcinoma (OVC) is often diagnosed at an advanced stage and requires effective chemotherapy as a first-line treatment. However, chemotherapy may be associated with significant side-effects, like nausea, vomiting, hair loss, cognitive dysfunction, fatigue and changes in sexual functioning. Leucopenia is one of the most common and dangerous side effects of chemotherapy. Little is known about possible effects of chemotherapy on dendritic cells (DCs) counts and function, although it is well documented that primary and secondary cell-mediated immune response are suppressed during this treatment. DESIGN: In this study we evaluated the myeloid and lymphoid DCs in the peripheral blood (PB) of 37 women with OVC before and after first-line based on platin and taxane chemotherapy, and in 24 healthy blood donors. Patients received 6 courses of treatment, administered at 21-day intervals. MATERIAL AND METHODS: The myeloid (M) and lymphoid (L) DCs were estimated by flow cytometry before and after 9th and 15th week of treatment. RESULTS: The percentage of both MDCs and LDCs was significantly lower (0.09% and 0.04%) in PB of patients with ovarian cancer comparing to healthy women (0.25% and 0.33%). The percentage of both, myeloid and lymphoid DCs after 9th and 15th week (0.08% vs 0.08% and 0.06% vs 0.08%) of chemotherapy did not differ from that found before treatment (0.09% and 0.04%). The Myeloid to Lymphoid DCs ratio was significantly lower in patients receiving chemotherapy.  相似文献   
87.
An analysis of the literature generated within the past 20 year-span concerning risks of uterine fibroids (UFs) occurrence and dietary factors was carried out. A link between Vitamin D deficiency and UFs formation is strongly indicated, making it a potent compound in leiomyoma therapy. Analogs of the 25-hydroxyvitamin D3, not susceptible to degradation by tissue 24-hydroxylase, appear to be especially promising and tend to show better therapeutic results. Although research on the role of Vitamin A in the formation of fibroids is contradictory, Vitamin A-enriched diet, as well as synthetic retinoid analogues, may be preventative or limit the growth of fibroids. Unambiguous conclusions cannot be drawn regarding Vitamin E and C supplementation, except for alpha-tocopherol. Alpha-tocopherol as a phytoestrogen taking part in the modulation of estrogen receptors (ERs) involved in UF etiology, should be particularly avoided in therapy. A diet enriched in fruits and vegetables, as sources of carotenoids, polyphenols, quercetin, and indole-3-carbinol, constitutes an easily modifiable lifestyle element with beneficial results in patients with UFs. Other natural substances, such as curcumin, can reduce the oxidative stress and protect against inflammation in leiomyoma. Although the exact effect of probiotics on uterine fibroids has not yet been thoroughly evaluated at this point, the protective role of dairy products, i.e., yogurt consumption, has been indicated. Trace elements such as selenium can also contribute to antioxidative and anti-inflammatory properties of a recommended diet. In contrast, heavy metals, endocrine disrupting chemicals, cigarette smoking, and a diet low in antioxidants and fiber were, alongside genetic predispositions, associated with UFs formation.  相似文献   
88.
Impaired interatrial conduction or interatrial block is well documented but is not described as an individual electrocardiographic (ECG) pattern in most of ECG books, although the term atrial abnormalities to encompass both concepts, left atrial enlargement (LAE) and interatrial block, has been coined. In fact, LAE and interatrial block are often associated, similarly to what happens with ventricular enlargement and ventricular block. The interatrial blocks, that is, the presence of delay of conduction between the right and left atria, are the most frequent atrial blocks. These may be of first degree (P-wave duration >120 milliseconds), third degree (longer P wave with biphasic [±] morphology in inferior leads), and second degree when these patterns appear transiently in the same ECG recording (atrial aberrancy). There are evidences that these electrocardiographic P-wave patterns are due to a block because they may (a) appear transiently, (b) be without associated atrial enlargement, and (c) may be reproduced experimentally. The presence of interatrial blocks may be seen in the absence of atrial enlargement but often are present in case of LAE. The most important clinical implications of interatrial block are the following: (a) the first degree interatrial blocks are very common, and their relation with atrial fibrillation and an increased risk for global and cardiovascular mortality has been demonstrated; (b) the third degree interatrial blocks are less frequent but are strong markers of LAE and paroxysmal supraventricular tachyarrhythmias. Their presence has been considered a true arrhythmological syndrome.  相似文献   
89.
Background: A well-balanced nutritional diet pattern has a significant role in the management of diet-related disorders. Currently, there are no specific dietary guidelines to refer to when advising non-diabetic patients with symptoms attributed to hypoglycemia in the postprandial period or patients with confirmed reactive hypoglycemia (RH). The aim of this study was to investigate the impact of the dietary interventions, and their sustained outcome, on the severity of hypoglycemic-like symptoms occurring in non-diabetic patients. Methods: The study group included forty non-diabetic individuals with symptoms consistent with RH. At the baseline, each patient underwent RH diagnosis and complex dietary evaluation. Over a period of six months, each patient had four appointments with a dietitian. Two sessions were focused on a dietary education about low glycemic index diet (LGID) and Mediterranean diet (MD). The said diets were to be followed for a period of three months, with two additional dietary check-ups. Once dietary supervision was completed, patients had no imposed dietary patterns. The final follow-up appointment took place twelve months later and that is when each patient underwent a detailed assessment of their current dietary habits and evaluation of the frequency of symptoms consistent with hypoglycemia. Results: There was a statistically significant reduction in the severity in eight out of the ten analyzed hypoglycemic-like symptoms after the dietary interventions. The most significant change was observed in the following symptoms: hunger (η2 = 0.66), impaired concentration (η2 = 0.61), hand tremor (η2 = 0.55), and fatigue (η2 = 0.51). The outcomes were comparable for both recommended diets, the LGID and the MD. The reduction in hypoglycemic-like symptoms continued after the twelve-month period. The individualized dietary counselling significantly improved the patients’ eating habits in comparison to those present prior to intervention in terms of healthy diet index (F(2,78) = 27.30, p < 0.001, η2 = 0.41, 90%CI [0.26; 0.51]) and unhealthy diet index (F(2,78) = 433.39, p < 0.001, η2 = 0.91, 90%CI [0.89; 0.93]). Conclusions: Healthy modifications in dietary habits may improve patient’s well-being and reduce the severity of their postprandial symptoms attributed to hypoglycemia. Therefore, dietary intervention focused on appropriate nutritional management combined with follow-up consultations may be a beneficial step towards comprehensive treatment of non-diabetic patients who present with hypoglycemic-like symptoms in the postprandial period.  相似文献   
90.
Two Zn(ii) complexes, K1 and K2, obtained from the template reaction of zinc(ii) acetate dihydrate with o-phenylenediamine and 2-hydroxy-5-methylisophthalaldehyde (K1) or 2-hydroxy-5-tert-butyl-1,3-benzenedicarboxaldehyde (K2), respectively, were characterized by X-ray crystallography, spectroscopic (UV-vis, fluorescence and IR), and thermal methods. In the complex [Zn2(MeO)1.4(OH)0.6(L1)]·2H2O K1, there are two binding sites in the macrocyclic ligand and they are occupied by zinc(ii) cations found in slightly distorted square pyramidal environment. The zinc(ii) cations are connected by slightly asymmetric oxo bridges with a Zn1–O14–Zn1[−x, −y + 1, −z + 1] angle of 104.8(2)°. In the dimer [Zn2(CH3COO)2(L2)]·2EtOH K2, there are two crystallographically independent binding sites both occupied by zinc(ii) cations. There is a significant difference between both complexes, since in K1 only one site is independent and the second is occupied due to the application of symmetry rules, and the geometry of both sites is identical. Thin layers of the obtained Zn(ii) complexes were deposited on Si(111) by the spin coating method and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), fluorescence spectroscopy and ellipsometry. In the non-absorbing range, the value of the refractive index exhibits normal dispersion between 1.8 and 2.1 for K1_1–K1_3; and between 2.3 and 2.6 for the K2 series of samples established for long wavelengths (longer than 500 nm). The Zn(ii) complexes and their thin layers exhibited fluorescence between 534–573 nm and 495–572 nm for the compounds and the layers, respectively. The highest quantum yield of fluorescence was achieved for K2 in benzene and in the solid state ϕ = 0.78 and 0.58, respectively. The influence of the solvent polarity on the fluorescence properties of the obtained complexes was studied. Additionally, DFT calculations were performed to explain the structures and electronic spectral properties of the complexes.

Tin fluorescent materials were obtained using a spin coating method.  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