全文获取类型
收费全文 | 2422篇 |
免费 | 105篇 |
国内免费 | 81篇 |
专业分类
耳鼻咽喉 | 42篇 |
儿科学 | 73篇 |
妇产科学 | 17篇 |
基础医学 | 285篇 |
口腔科学 | 57篇 |
临床医学 | 310篇 |
内科学 | 418篇 |
皮肤病学 | 59篇 |
神经病学 | 112篇 |
特种医学 | 361篇 |
外科学 | 266篇 |
综合类 | 36篇 |
一般理论 | 2篇 |
预防医学 | 165篇 |
眼科学 | 53篇 |
药学 | 260篇 |
中国医学 | 4篇 |
肿瘤学 | 88篇 |
出版年
2021年 | 15篇 |
2020年 | 13篇 |
2019年 | 24篇 |
2018年 | 49篇 |
2017年 | 24篇 |
2016年 | 48篇 |
2015年 | 31篇 |
2014年 | 48篇 |
2013年 | 90篇 |
2012年 | 87篇 |
2011年 | 79篇 |
2010年 | 87篇 |
2009年 | 79篇 |
2008年 | 85篇 |
2007年 | 148篇 |
2006年 | 98篇 |
2005年 | 95篇 |
2004年 | 84篇 |
2003年 | 52篇 |
2002年 | 44篇 |
2001年 | 71篇 |
2000年 | 73篇 |
1999年 | 62篇 |
1998年 | 81篇 |
1997年 | 86篇 |
1996年 | 59篇 |
1995年 | 68篇 |
1994年 | 42篇 |
1993年 | 43篇 |
1992年 | 38篇 |
1991年 | 48篇 |
1990年 | 44篇 |
1989年 | 59篇 |
1988年 | 54篇 |
1987年 | 40篇 |
1986年 | 45篇 |
1985年 | 60篇 |
1984年 | 34篇 |
1983年 | 34篇 |
1982年 | 32篇 |
1981年 | 22篇 |
1980年 | 33篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1977年 | 23篇 |
1976年 | 24篇 |
1975年 | 15篇 |
1974年 | 11篇 |
1970年 | 12篇 |
1968年 | 11篇 |
排序方式: 共有2608条查询结果,搜索用时 15 毫秒
61.
Ionic liquids are largely used to leach metals from primary (ores) and secondary sources (end-of-life products). However, dry ionic liquids with a carboxylic function on the cation have not yet been used to leach metals at temperature above 100 °C and under atmospheric pressure. The ionic liquid betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N], was used in the dry state to recover neodymium, dysprosium and cobalt from NdFeB magnets and NdFeB production scrap. The magnets and the scrap were crushed, milled and roasted before being leached above 100 °C. Recovery efficiencies below 10% and a lack of selectivity for all the parameters tested pointed to the importance of water in the dissolution process. The influence of the viscosity of the ionic liquid and the composition of the metal oxides after roasting was investigated as well. Although the dissolution of pure metal oxides was faster than the dissolution of the magnets, the low leaching efficiencies could not be attributed to the composition and crystal structure of the samples, since magnets roasted with the same protocol have already been successfully leached in the past, albeit in the presence of water. The role of water on the mass transfer and on the coordination of the metals was studied by viscometry and by spectroscopic methods, respectively. It is shown that for leaching of rare earths with [Hbet][Tf2N], the presence of ligands such as water is mandatory to saturate the first coordination sphere of the dissolved rare-earth ions. This paper provides new insights in the dissolution mechanism of metal oxides by [Hbet][Tf2N] at leaching temperatures higher than those typically used in hydrometallurgical leaching processes.Recovery of neodymium, dysprosium and cobalt from NdFeB magnets with the dry ionic liquid [Hbet][Tf2N] was investigated at 175 °C and atmospheric pressure. 相似文献
62.
Rafaela Azevedo Abrantes de Oliveira RN Vander Monteiro da Conceição RN Jeferson Santos Araujo RN Márcia Maria Fontão Zago RN 《International journal of nursing practice》2018,24(1)
Aim
This study aims to analyse the concept of cancer survivorship using Rodgers' evolutionary concept analysis model.Background
The lack of a consensus definition as well as the confusion and debate concerning the definitions of “survivor” and “cancer survivorship” hinder an understanding of the intrinsic needs associated with the latter.Design
Concept analysis.Method
A systematic literature search was performed using the following databases: PubMed, CINAHL, Web of Science, LILACS, and PsycINFO with studies published between 2000 and 2014. The final sample contained 39 studies that were analysed on the basis of Rodgers' model and inductive thematic analysis, discussed through the lens of the medical anthropology concept of culture.Findings
Cancer survivorship is a broad concept that can be understood using 8 themes: changes in life plans, positive and negative aspect dualities, life reflections, identity change, individual experiences, symptom control, the need for support, and quality of care. These themes are summarized using 2 attributes: liminality process and culturally congruent care.Conclusions
This article contributes to understanding of cancer survivorship and the processes that are intrinsic to this concept. It calls for future investigations to enhance cancer survivorship across its 2 domains at the personal (patient's life) and clinical (nursing practice) levels. 相似文献63.
64.
In this study we examined the effect of mitogens and epidermal cells in inducing a Sezary cell morphology in normal peripheral blood lymphocytes. Peripheral blood mononuclear cells from six healthy volunteers were stimulated with the mitogens phytohemaglutinin and concanavalin A, and also cocultivated with human epidermal cell cultures. Incubation times with mitogens and epidermal cells were four days and stimulation of the lymphocytes by mitogens was confirmed by standard 3H-thymidine uptake. Standard transmission electron microscopy showed that in the mitogen-driven system 20% to 60% (33 +/- 15%) and in the epidermal cell-driven system 5% to 15% (8 +/- 4%) of the lymphoid cells exhibited mild to moderate indentation of the nuclei with nuclear contour indices (NCI) of 4.6 to 6.5 but no Sezary cells were observed (cells with NCI greater than 6.5 and up to 19.2). In the mitogen- stimulated preparation 2% to 5% (3 +/- 1%) of the lymphoid cells showed nuclear multilobulation resembling the cells seen in adult T cell lymphoma/leukemia. Incubation of mononuclear cells for longer periods of up to 4 weeks with mitogens and exogenous IL-2 resulted in no further morphologic changes. Using an indirect immunogold technique at the electron microscopic level, the cells showing nuclear indentation or lobulation were shown to bear both T helper (CD4) and T suppressor (CD8) cell phenotypes in a similar ratio to the total numbers of T helper and T suppressor cells present. Mitogens and epidermal cells are thus not able to induce a morphologic change to Sezary cells in normal peripheral blood lymphocytes. 相似文献
65.
Janneke AL van Kempen Henk J Schers Anne Jacobs Sytse U Zuidema Franca Ruikes Sarah HM Robben René JF Melis Marcel GM Olde Rikkert 《The British journal of general practice》2013,63(608):e225-e231
Background
Primary care is increasingly interested in the identification of frailty, as it selects the target population for integrated care. However, instruments for the identification of frailty specifically validated for use in primary care are scarce. This study developed the Easycare Two-step Older persons Screening (Easycare-TOS), which provides a valid, efficient, and pragmatic screening procedure to identify frail older people.Aim
This paper aims to describe the development of the Easycare-TOS and the data from the pilot studies.Design and setting
Observational pilot study in seven academic GP practices in and around Nijmegen, The Netherlands.Method
The Easycare-TOS was developed in a cyclic process with the input of stakeholders. In every cycle, the requirements were first defined, then translated into a prototype that was tested in a pilot study. The Easycare-TOS makes optimal use of prior knowledge of the GP, and the professionals’ appraisal is decisive in the frailty decision, instead of a cut-off score. Further, it considers aspects of frailty, as well as aspects of the care context of the patient.Results
The pilot data have shown that after step 1, two-thirds of the patients do not need further assessment, because they are judged as not frail, based on prior knowledge of the GP. The overall prevalence of frailty in this pilot study is 24%. Most professionals who participated in the pilot studies considered the time investment acceptable and the method to be of added value.Conclusion
The Easycare-TOS instrument meets the predefined efficiency, flexibility, and acceptability requirements for use as an identification instrument for frailty in primary care. 相似文献66.
Clarice Monteiro Taissa Kasahara Priscila M. Sacramento Aleida Dias Simone Leite Vander G. Silva Sudhir Gupta Anshu Agrawal Cleonice A. M. Bento 《European journal of immunology》2021,51(1):167-179
Circulating TFH (cTFH) cells express CXCR5, PD-1, and, when activated, ICOS, and release IL-21. According to the production of IFN-γ, IL-4, and IL-17 and expression of FoxP3, these cells are also classified as cTFH1, cTFH2, cTFH17, and cTFR cells, respectively. This CD4+T-cell subset is pivotal to efficient humoral immunity, and pregnancy appears to favor IgG production. Here, not only pregnancy amplified the in vivo production of anti-HBsAg IgG in HBV immunized women, but the frequency of cTFH cells was directly correlated with estradiol levels. In vitro, pregnancy-related dose of 17-β-estradiol (E2) directly increased the percentage of different cTFH subsets. While E2 and progesterone (P4) increased the proportion of differentiated TFH cells derived from naïve CD4+T-cells, only E2 amplified the release of IL-21 in those cell cultures. In addition, E2 and P4 increased the proportion of memory B cells and plasma cells, respectively. In SEB-activated B/TFH cell co-cultures, E2, in the presence of P4, increased the production of total IgG. Finally, among the hormones, P4 was stronger in upregulating the percentage of IL-10+TFR cells. Collectively, our findings suggested that E2 and P4 cooperate in the humoral immune response by favoring the expansion of different cTFH and B cell subsets. 相似文献
67.
Packham MA; Perry DW; Kinlough-Rathbone RL; Rand ML; Guccione MA; Evans RM; Mustard JF 《Blood》1985,65(3):564-570
Rabbit platelets were aggregated by adenosine diphosphate (ADP), allowed to deaggregate and then separated into density subpopulations by centrifugation through discontinuous Stractan density gradients. Although ADP causes little or no release of the contents of the amine storage granules of rabbit platelets, ADP caused a decrease in platelet density as compared with control platelets subjected to the same procedures except for exposure to ADP. The density change persisted for at least four hours. The apparent size of platelets stimulated with ADP increased initially, but returned to control values during a one-hour period. A similar decrease in platelet density was observed with an albumin density gradient. Under conditions in which aggregation did not occur in response to ADP with ethylenediaminetetraacetic acid (EDTA) in the medium, little or no decrease in platelet density was observed. Agglutination with polylysine did not change platelet density. Thus, not only agents such as thrombin and plasmin that cause the release of the contents of the platelet granules decrease platelet density, but ADP also has this effect. Platelets would be exposed to all of these stimuli during thromboembolic processes, and their effect on platelets may account for the decrease in platelet density observed previously in experiments with rabbits with indwelling aortic catheters. Agents that increase the concentration of cyclic AMP (cAMP) in platelets (PGE1, adenosine, dibutyryl cAMP, forskolin, and papaverine) also decreased platelet density. This effect persisted when the platelets were washed and resuspended in fresh medium and was also demonstrable in plasma. Platelet size was gradually increased by prostaglandin E1 (PGE1) which maintains platelets in a disc shape and does not cause the release of granule contents, indicating that the decrease in platelet density caused by PGE1 may be attributable to platelet swelling. 相似文献
68.
F Comite R J Schiebinger B D Albertson F G Cassorla K Vander Ven T F Cullen D L Loriaux G B Cutler 《The Journal of clinical endocrinology and metabolism》1984,58(3):435-440
We report a 2 10/12-yr-old girl with precocious pseudopuberty due to a feminizing adrenal carcinoma without Cushing's syndrome. The patient had marked elevation of plasma concentrations of the delta 5 adrenal steroids dehydroepiandosterone and dehydroepiandrosterone sulfate and increased levels of androstenedione, estrone, estradiol, and testosterone. Adrenal microsomal 3 beta-hydroxysteroid dehydrogenase-isomerase 17-hydroxylase, 17,20-desmolase, and 21-hydroxylase activities in the tumor and adjacent normal adrenal gland were measured. The tumor had approximately normal levels of 17-hydroxylase and 17,20-desmolase activity, with low levels of 21-hydroxylase and 3 beta-hydroxysteroid dehydrogenase-isomerase activities. This combination of enzyme activity may explain the absence of Cushing's syndrome and the high levels of delta 5 adrenal steroids. This patient demonstrates that adrenal neoplasms arising in girls may mimic isosexual true precocious puberty and should be included in the differential diagnosis of precocious puberty. 相似文献
69.
Involvement of guanine nucleotide binding proteins in neutrophil activation and priming by GM-CSF 总被引:4,自引:0,他引:4
Pre-incubation of human neutrophils with pertussis toxin significantly inhibited the neutrophil-directed biologic actions of granulocyte- macrophage colony-stimulating factor (GM-CSF) in three separate assays: the induction of c-fos mRNA, the enhancement of both platelet- activating factor-induced mobilization of intracellular calcium, and stimulation of leukotriene synthesis by the calcium ionophore A23187. Cholera toxin did not have an effect on the latter two assays. Pre- treatment of human neutrophils with pertussis toxin did not affect the binding of GM-CSF to its surface receptor. These results provide the first evidence that a pertussis toxin substrate plays an important mediatory role in the mechanism of action of GM-CSF. 相似文献
70.
STUDY OBJECTIVES: To study the incidence of upper airway obstruction, as measured on the flow volume loop (FVL), in patients with bulky mediastinal Hodgkin's disease; to correlate the FVL with CT of the chest; and to follow the changes in the FVL after treatment of the tumor. DESIGN: Retrospective study of pulmonary function tests (PFTs) and chest CTs performed as part of a clinical trial for Hodgkin's disease. SETTING: Memorial Sloan-Kettering Cancer Center, a comprehensive cancer care center. PATIENTS: Twenty-five patients (15 men and 10 women; age range, 20 to 57 years) with bulky mediastinal Hodgkin's disease enrolled in a clinical trial of chemotherapy followed by external beam radiation therapy. MEASUREMENTS AND RESULTS: Fourteen of 25 patients (56%) had an abnormal FVL prior to therapy; after chemotherapy, only 7 of 25 patients (28%) had an abnormal FVL. The abnormal patterns seen were either those typical of fixed obstruction or variable extrathoracic obstruction. No patient had a pattern typical of variable intrathoracic obstruction. On chest CT scan, 16 patients had grade-I tracheal deformity; 6 had grade-II deformity, and 3 had grade-III deformity. All three patients with grade-III deformity had a fixed obstruction pattern, as did three patients with a grade-I pattern. Patients with a fixed pattern on FVL had significant decreases in inspiratory and expiratory flow rates. CONCLUSION: FVL abnormalities suggesting upper airway obstruction occurred in > 50% of patients with bulky mediastinal Hodgkin's disease. A fixed pattern of obstruction was associated with the lower flow rates and severe tracheal distortion on CT; these patients may warrant special attention prior to general anesthesia or invasive procedures. Asymptomatic patients with abnormal FVLs but normal tracheal profiles need not undergo extensive evaluation. No patients showed the expected pattern typical of intrathoracic obstruction, but rather the major effect was on the inspiratory loop. The authors speculate on the mechanism for this unexpected finding. 相似文献