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101.
This theoretical study explored whether the directions of loads to which modern human molars are commonly subjected to are reflected in the biomechanical behavior of the tissue itself. A detailed finite element model of a piece of decussating enamel (M3 paracone) was created, taking into account differences in crystal orientation between the prism head and the interprismatic matrix, and was tested under differently angled mediolateral loads (i.e., mimicking various stages of the chewing cycle). Second, although teeth are highly mineralized, they also contain organic material and water, while in modern humans, there are systematic differences in chemical composition from the outer enamel surface to the dentinoenamel junction. To test the biomechanical effects of this gradient in mineralization a second set of models with gradually changing properties was created and subjected to the same loads. Chemically heterogeneous enamel yielded overall lower stress levels than homogenous enamel, especially at extreme loading angles. However, the general trends regarding the increase in tensile stresses at more oblique angles, and the number of nodes exhibiting tension, were comparable between the different set‐ups. The findings support suggestions that (a) the biomechanical behavior of dental tissue is the combined result of micromorphology and chemical composition and (b) that the range of loading directions, to which teeth are normally subjected to, can be inferred from dental microanatomy. For (palaeo)biological applications, the findings suggest that the absolute strength of teeth (e.g., bite force) cannot be predicted with certainty, whereas kinematic parameters of the masticatory apparatus can. Anat Rec, 2007. © 2008 Wiley‐Liss, Inc. 相似文献
102.
103.
Substance P stimulates release of RANKL via COX-2 expression in human dental pulp cells 总被引:2,自引:0,他引:2
Objective: Our previous study found that substance P (SP), a sensory neuropeptide, was expressed in the dental pulp of rats during experimental
tooth movement. We examined the effects of SP on the production of prostaglandin (PG) E2 and the receptor activator of nuclear factor- B ligand (RANKL) by human dental pulp fi broblast-like (HDPF) cells.
Materials and methods: SP was added to cultured HDPF cells at concentrations ranging from of 10−4 to 10−12 mol/L. PGE2 and soluble RANKL (sRANKL) levels were determined using enzyme-linked immunosorbent assay kits. Gene expression was confi
rmed by RT-PCR analysis. Pit formation assays using dentin slices were carried out to examine the effect of SP on osteoclastogenesis.
Results: The levels of PGE2 and sRANKL increased in the presence of SP, though the increases were greater in the experimental groups in both a time-
and concentration-dependent manner, and the increase of RANKL was partially mediated by PGE2 . The gene expression of cyclooxygenase (COX)-2 and RANKL was up-regulated, and conditioned medium samples obtained from
HDPF cells treated with SP induced bone resorption.
Conclusions: SP stimulated the production of PGE2 and RANKL, and promoted bone resorption. Therefore, SP may be involved in pulpal inflammation and root resorption during
orthodontic tooth movement.
Received 11 April 2005; returned for revision 27 July 2005; returned for final revision 20 September 2005; accepted by M.
Katori 2 November 2005 相似文献
104.
Coping strategies and anxiety responding of dental patients were studied in order to test the generalizability of previous findings based on volunteer blood donors. State and trait coping measures were administered once, and a process coping scale was administered at three points throughout treatment. Self-report, behavioral observation, and psychophysiological measures of anxiety were sampled for the same periods as process coping. Findings included the replication of a negative relationship between avoidant coping and patient anxiety ratings. Fluctuations in coping were evident across periods, and impact of situational demands and constraints was introduced as an explanation for these variations. A method for direct assessment of coping consistency was introduced. On the basis of the replicable associations with anxiety measures, the ability to detect changes in coping within a situation, and the ability to provide direct evidence of coping consistency, the use of process methodology for coping assessment is encouraged.This research was conducted while the first author was supported by funding from the Medical Research Council of Canada.Portions of this research were presented at the annual convention of the Society of Behavioral Medicine, Philadelphia, 1984. 相似文献
105.
Myrin Borysenko Samuel Turesky Joan Z. Borysenko Fred Quimby Herbert Benson 《Journal of behavioral medicine》1980,3(3):233-243
The stress of crowding and exposure to inescapable electric shock increased both the incidence and the severity of dental caries in rats housed in a conventional animal facility. Male Osborne-Mendel rats were inoculated intraorally with cariogenic bacteria, fed a high-sucrose diet, and housed in either a conventional or a sheltered facility. Rats in both housing conditions were subdivided into control and stress groups. At the end of the 56-day trial period, stressed rats from conventional housing had a significant increase in both incidence and severity of dental caries in comparison to their controls. In contrast, stressed rats from sheltered housing had a trend toward increased cariogenesis which reached significance in only one of five scores. These rats also failed to gain weight comparable to their controls, making it possible that stress-induced reduction in appetite partially offset stress-induced exacerbation in cariogenesis.This investigation was supported in part by the following Grants from the United States Public Health Service: CA 20093, HL 22727, and HL 07374. 相似文献
106.
M.?YamaguchiEmail author T.?Kojima M.?Kanekawa N.?Aihara A.?Nogimura K.?Kasai 《Inflammation research》2004,53(5):199-204
Objective:Orthodontic tooth movement causes inflammatory reactions in the periodontal membrane and dental pulp. It has been reported that substance P (SP) and calcitonin gene-related peptide (CGRP), both sensory neuropeptides, are manifested in the dental pulp of rats during experimental tooth movement, suggesting that they might be involved in the dental pulp inflammation during orthodontic tooth movement. However, the relationships between neuropeptides and pro-inflammatory cytokines have not been fully elucidated.Materials and methods:Human dental pulp (HDP) fibroblasts were prepared from 6 healthy young volunteers (3 males, 3 females; 15–25 years old) during the course of orthodontic treatment. HDP cells were incubated for 24 h in fresh medium containing 2% FCS in the presence of various concentrations of CGRP (10–12 to 10–4 M) and SP (10–12 to 10–4 M), and the levels of interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF)- present in the media were determined using commercially available high-sensitivity enzyme-linked immunosorbent assay kit.Results:We examined the effects of stimulation by these neuropeptides on the production of inflammatory cytokines in HDP fibroblasts, and found that the levels of IL-1, IL-6, and TNF- increased in a time- and concentration-dependent manner. However, the neuropeptides did not act synergistically to increase cytokine secretion in HDP cells or significantly modify LPS-induced cytokine production by HDP cells.Conclusions:Our results suggest that human pulp fibroblasts may be involved in the progress of inflammation in pulp tissue during orthodontic tooth movement, as they produced large amounts of IL-1, IL-6, and TNF- following stimulation with neuropeptides.Received 2 March 2003; returned for revision 14 July 2003; accepted by M.J. Parnham 17 December 2003 相似文献
107.
G. H. Sperber G. A. Machin F. J. Bamforth 《American journal of medical genetics. Part A》1994,51(1):41-45
A pair of monozygotic twins had similar but not identical dental anomalies. One twin had fusion of deciduous mandibular lateral incisor and canine on the left, with normal dentition on the right; the co-twin had right mandibular incisor/canine fusion, with aplasia of the lateral incisor on the left. These findings are discussed in the context of the related phenomena of situs inversus, mirror-imaging in twins, and gradients of severity of anomalies in the four copies of the mandibular developmental dental field. © 1994 Wiley-Liss, Inc. 相似文献
108.
Little is known concerning the employment characteristics of hygienists practicing in nontraditional settings. Respondents were identified through screening (n = 38,380) a listing of the entire population of hygienists licensed in the United States. The screening identified 1,301 hygienists practicing in nontraditional settings. These hygienists were mailed comprehensive questionnaires; completed questionnaires were returned by 84.3 percent of the hygienists. Data were collected describing hygienists' reasons for seeking employment in nontraditional settings, their sources of information concerning job opportunities in nontraditional settings, benefits, and job satisfaction. The main source of information concerning employment opportunities in nontraditional settings was "word of mouth." Hygienists were motivated to seek employment in nontraditional settings primarily by a desire for a more challenging position and personal satisfaction. The hygienists were overwhelmingly satisfied with all aspects of nontraditional employment except opportunities for advancement. Respondents were found to receive standard benefits similar to those of employees in other industries. 相似文献
109.
The effects of heat labile, high molecular weight water-soluble toxins from bacterial plaque on HL60 promyelocytic cells were examined. On gel filtration, four inhibitors of HL60 cell growth and two inhibitors of HeLa cell growth (PT1, PT2) were detected. The first and third HL60 cell inhibitors corresponded to the two HeLa cell inhibitors. The last eluted HL60 cell inhibitor (plaque leukotoxin, PL) did not inhibit HeLa cell growth. Anti-PT2 antibodies reduced the activity of enriched PT2 by 20-50%, but all other antisera tested exhibited no effect. Anti-PL antibodies detected antigens from Actinobacillus actinomycetemcomitans, although anti-A. actinomycetemcomitans and anti-Capnocytophaga sputigena antibodies did not react with plaque extract. These findings suggest that the plaque toxins examined in this study were probably not derived from these two bacteria. 相似文献
110.
Robin N. Powell John T. Gilhooly Errol R. McKenna 《Community dentistry and oral epidemiology》1986,14(2):110-114
A study of caries experience and gingivitis prevalence in 6-, 9- and 12-yr-old children attending primary schools in Brisbane was undertaken in November/December 1983. Children from high socioeconomic level (SEL) schools exhibited lower dmft and DMFT scores at all ages. At age 6 yr the proportion of children with caries-free primary dentitions was for high SEL Schools 70%, for middle SEL schools 52% and for low SEL Schools 23%. At 12 yr DMFT scores were 1.8 (high), 2.1 (middle) and 3.3 (low). Similar differences in gingivitis prevalence occurred, children from high SEL schools displaying a much lower proportion of bleeding sites than those from middle and low SEL schools. For selection of children at "high risk" to gingival disease for intensive prevention programmes, an increased emphasis on probing techniques is indicated to achieve diagnostic consistency. 相似文献