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   17737篇
  免费   1106篇
  国内免费   141篇
耳鼻咽喉   111篇
儿科学   492篇
妇产科学   370篇
基础医学   2869篇
口腔科学   342篇
临床医学   1464篇
内科学   4495篇
皮肤病学   300篇
神经病学   1800篇
特种医学   447篇
外科学   1326篇
综合类   48篇
一般理论   5篇
预防医学   1393篇
眼科学   205篇
药学   1329篇
中国医学   61篇
肿瘤学   1927篇
  2024年   24篇
  2023年   193篇
  2022年   386篇
  2021年   660篇
  2020年   394篇
  2019年   540篇
  2018年   583篇
  2017年   484篇
  2016年   547篇
  2015年   596篇
  2014年   753篇
  2013年   998篇
  2012年   1621篇
  2011年   1619篇
  2010年   891篇
  2009年   799篇
  2008年   1306篇
  2007年   1205篇
  2006年   1153篇
  2005年   996篇
  2004年   907篇
  2003年   758篇
  2002年   652篇
  2001年   84篇
  2000年   47篇
  1999年   94篇
  1998年   122篇
  1997年   99篇
  1996年   92篇
  1995年   50篇
  1994年   44篇
  1993年   49篇
  1992年   28篇
  1991年   25篇
  1990年   23篇
  1989年   9篇
  1988年   12篇
  1987年   17篇
  1986年   10篇
  1985年   7篇
  1984年   17篇
  1983年   11篇
  1982年   12篇
  1981年   10篇
  1980年   9篇
  1979年   6篇
  1978年   5篇
  1975年   5篇
  1973年   10篇
  1971年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
A wound and abscess clinic, held concurrently with a syringe exchange, provided economical treatment and aftercare for injection-associated soft tissue infections. During 20 two-hour clinic sessions, 173 treatment episodes were logged, and the visit cost was estimated at $5 per patient. Increased patient-clinician interactions provided opportunities beyond those afforded by the syringe exchange for patients to obtain resources and referrals to services such as HIV counseling and testing, medical care, and drug treatment. Distribution of cards advertising the clinic was substantially less effective than word of mouth in increasing community awareness of the clinic.  相似文献   
962.
The 8344C/T polymorphism of the apoB gene was genotyped by an original modification of PCR allele-specific amplification consisting in a single amplification reaction double-primed by two opposite allele-specific oligonucleotides nested in a larger amplified fragment. This method was used to genotype 200 randomly selected healthy individuals (113 males, 87 females). The frequency of the rare allele in this random Italian population was 0.240, i.e. not far from the 0.282 frequency observed in hypocholesterolemic Norwegians and suggestive of a moderating effect on LDL levels of our population. However, we did not find any significant cholesterol-lowering effect of this polymorphism either by comparing the frequency of mutant alleles in the population stratified for its plasma lipoprotein levels or by studying the association between ApoB genotype and the different lipoproteins. In conclusion this ApoB polymorphism appeared to have a secondary role in LDL- and HDL-cholesterol variations of our population.  相似文献   
963.
Possible cell death mechanisms for pars compacta nigro-striatal dopamine neurons in Parkinson's disease include oxidative stress, inflammatory processes, nitric oxide iron accumulation, glutamate toxicity and diminished neurotrophic factor responses. There is a notion that Parkinson's disease is not a single disorder but a syndrome that can be initiated by several factors. Because of limitations of biochemical methods in the global analysis of neuronal death, a full picture of events has not been established. However, recently developed cDNA microarray or microchips, in which the global expression of thousands of genes can be assessed simultaneously, is changing the prospect for understanding the disease process, its progression, response to drugs, etc. The neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is considered the most valid model of Parkinson's disease. We employed the technique of cDNA microarray gene expression to determine the mechanism of action of MPTP in mouse substantia nigra. Also, we studied neuroprotective processes induced by several compounds, including R-apomorphine and the green tea polyphenol epigallo-catechin-3-gallate (EGCG). This was done in two ways: (1) the time-dependent acute effect of MPTP, for determining which of the initial genes might lead to dopamine neuron death and (2) gene expression at the time of MPTP-induced dopamine neuron death. We observed that early (acute MPTP) gene expression differs from effects seen at the time of death (chronic MPTP), and that early gene changes are crucial for setting into action genes that eventually cause dopamine neuron death. Furthermore, this process is a cascade of "domino" effects, some of which were previously established by biochemical means. However, our findings show an additional large number of events previously unknown. The neuroprotective drugs reversed some but not all of the gene expression, suggesting involvement of these genes in the neurodegenerative process. Because of the profound complexity of "domino" effect it is now reasonable to understand why a single neuroprotective drug has not shown clinical neuroprotective efficacy. Future multi neuroprotective drugs may be necessary for treatment of not only Parkinson's disease, but other neurodegenerative diseases (e.g. Alzheimer's disease) and detrimental states (e.g. ischaemia).  相似文献   
964.
A human immunodeficiency virus-positive patient receiving indinavir therapy developed a slowly progressive paraparesis. Magnetic resonance imaging findings were consistent with epidural lipomatosis. On discontinuing indinavir, symptoms gradually remitted. Although indinavir, a protease inhibitor, is known to cause abnormal fat accumulation, to the best of our knowledge this is the first report of epidural lipomatosis.  相似文献   
965.
Predictors of ovulatory failure in women with epilepsy   总被引:5,自引:0,他引:5  
Women with epilepsy (WWE) are at increased risk for reproductive disorders. This study was designed to evaluate whether WWE are more likely to have anovulatory cycles and to assess the relative association of the epilepsy syndrome category and antiepileptic drugs (AEDs) to ovulatory dysfunction. Subjects included women aged 18 to 40 years not receiving hormones. Women without epilepsy (23 controls) and women with localization-related epilepsy (LRE, n = 59) or idiopathic (primary) generalized epilepsy (IGE, n = 35) receiving either a cytochrome P450 enzyme (cP450) inducing AED (carbamazepine, phenytoin, and phenobarbital), a cP450 inhibiting AED (valproate), or an AED that does not alter cP450 enzymes (lamotrigine and gabapentin) in monotherapy for 6 months or more were followed for three menstrual cycles. A transvaginal ovarian ultrasound was obtained. Endocrine and metabolic variables were measured and luteinizing hormone sampled over 8 hours on days 2 to 5 of one cycle. Anovulatory cycles occurred in 10.9% of cycles in controls, 14.3% of cycles with LRE, and 27.1% of cycles with IGE. Of women using valproate currently or within the preceding 3 years, 38.1% had at least one anovulatory cycle in contrast with 10.7% of women not using valproate within the preceding 3 years. Predictors of ovulatory failure included IGE syndrome, use of valproate currently or within 3 years, high free testosterone, and fewer numbers of luteinizing hormone pulses, but not polycystic-appearing ovaries. WWE are more likely to experience anovulatory menstrual cycles and the effects of epilepsy syndrome, and AED therapy may be additive. Women with IGE receiving valproate were at highest risk for anovulatory cycles, polycystic-appearing ovaries, elevated body mass index, and hyperandrogynism. WWE with anovulatory cycles may have no other signs of reproductive dysfunction. Therefore, clinicians must be alert to this potential complication of epilepsy.  相似文献   
966.
Hippocampal cytoarchitectural abnormalities may be part of the cerebral substrate of schizophrenia. Amongst the chemical components being abnormal in brains of schizophrenics are altered calcium concentrations and reduced expression of the neurotrophin receptor, trkB. We studied by immunohistochemical methods the distribution of visinin-like protein-1 (VILIP-1), which is a calcium sensor protein and at the same time a trkB mRNA binding protein, in hippocampi of nine schizophrenic patients and nine matched control subjects. In normal hippocampi VILIP-1 immunoreactivity was found in multiple pyramidal cells and interneurons. A portion of VILIP-1 immunoreactive interneurons co-express calretinin (60%) and parvalbumin (<10%). In schizophrenics fewer pyramidal cells but more interneurons were immunostained. Our data point to an involvement of the protein in the altered hippocampal circuitry in schizophrenia.  相似文献   
967.
In order to provide tailor-made care, governments are considering the implementation of output-pricing based on hospital case-mix measures, such as diagnosis related groups (DRG). The question is whether the current DRG classification system can provide a satisfactory prediction of the variance of costs in stroke patients and if not, in what way other variables may enhance this prediction. In this study, data from 731 stroke patients hospitalized at University Hospital Maastricht during 1996-1998 are used in the cost analysis. The DRG classification for this group uses information--in addition to the DRG classification operation or no operation--on the patient's age combined with discharge status. The results of regression analysis show that using DRGs, the variance explained in the costs amounts to 34%. Adding other variables to the DRGs, the variance explained increases to about 61%. Additional factors highly correlating with inpatient costs are the level of functioning after stroke, comorbidity, complications, and 'days of stay for non-medical reasons'. Costs decreased for stroke patients discharged during the latter part of the years studied, and if stroke patients happened to die during their hospital stay. The results do suggest that future implementation of output-pricing based on the DRG case-mix measures is feasible for stroke patients only if it is enhanced with information on complications and the level of functioning.  相似文献   
968.
The risk of needing help with household tasks or of requiring care in old age increases. Using semi-structured, qualitative interviews, beliefs about the usefulness versus uselessness of planning ahead for future care needs (FCN) were investigated in 23 East German, 10 U.S., and 10 Canadian elderly-community dwelling women (> or= 65 years). Primary reasons in favor of planning for FCN were: gaining a feeling of security regarding the future, avoiding being a burden to potential helpers, and coping with one's present health conditions. Factors that prevent planning for FCN were: the difficulty foreseeing FCN, the lack of resources to plan, and low levels of perceived vulnerability. The women dealt with the contradictions between these factors that promote and prevent preparation by making general plans which could be adapted in the case of needing help by developing alternative plans or by avoidance of thinking about possible future health crises.  相似文献   
969.
HCC is a common cancer and HBV and AFB(1) are well-documented, major risk factors. Epidemiologic studies have documented that cigarette smoking also contributes to the development of HCC. PAHs are ubiquitous environmental pollutants and products of incomplete combustion. They are present in both mainstream and sidestream cigarette smoke. PAHs are metabolically activated by phase I enzymes, including CYP1A1, into electrophilic reactants (diol epoxides), which covalently bind to DNA to form adducts. Diol epoxides are also substrates for phase II detoxifying enzymes, including GSTM and GSTP. To examine the association between PAH-DNA adducts and HCC, adduct levels were determined in liver tissue by relative staining intensity with an immunoperoxidase method using a polyclonal antiserum against BPDE-modified DNA. Subjects were also genotyped for polymorphism in several genes involved in the metabolism of PAH, including GSTM1 and GSTP1. Liver tissue was collected from patients with histologically confirmed HCC (n = 105) and from non-HCC controls (n = 37). There was a significant positive correlation (r = 0.3, p < 0.01) between adducts in tumor and adjacent nontumor tissues among HCC cases. The risk of HCC was higher after adjustment for age, sex and HBsAg in the group with the highest tertile tissue levels of PAH-DNA adducts (mean relative nuclear staining intensity of tumor and nontumor tissue > 344) than in the group with the lowest tertile (staining < 241, OR = 3.9, 95% CI = 1.0-14.9). Among non-HCC controls, there were no significant associations between adduct levels and cigarette smoking, GSTM1 null genotype and HBsAg positivity. A strikingly increased HCC risk was observed (OR = 20.3, 95% CI = 5.0-81.8) among HBsAg-positive subjects whose PAH-DNA adduct levels were high (mean relative nuclear staining intensity of tumor and nontumor tissue > 301, median of control tissues) compared to HBsAg-negative subjects who had low PAH-DNA adduct levels. 4-ABP- and AFB(1)-DNA adducts had been measured previously in these same tissues. Subjects with elevated DNA adduct levels of PAH, 4-ABP and AFB(1) had a significantly higher HCC risk with an OR of 36.7 (95% CI 7.2-187.2) compared to those who had low DNA adduct levels. These results suggest that PAHs may play a role in human hepatocarcinogenesis in conjunction with HBsAg carrier status, GSTM1 and GSTP1 genotypes and exposure to 4-ABP and AFB(1).  相似文献   
970.
Post-menopausal hormonal therapy and gallbladder cancer risk   总被引:3,自引:0,他引:3  
The relation between post-menopausal hormone replacement therapy (HRT) and gallbladder cancer was analyzed in women above age 45 years, using data of a case-control study conducted in Italy between 1985 and 1997, on 31 incident, histologically confirmed cases and 3,702 controls in hospital for acute, non-neoplastic conditions. The multivariate odds ratio (OR) was 3.2 (95% confidence interval: 1.1-9.3) for those who had ever used HRT and the OR tended to rise with longer duration. Although based on small numbers, due to the rarity of the disease, these findings provide the first direct epidemiological evidence of an association between HRT and gallbladder cancer.  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