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   5917篇
  免费   408篇
  国内免费   21篇
耳鼻咽喉   26篇
儿科学   282篇
妇产科学   54篇
基础医学   600篇
口腔科学   107篇
临床医学   705篇
内科学   1142篇
皮肤病学   52篇
神经病学   623篇
特种医学   533篇
外科学   611篇
综合类   200篇
一般理论   3篇
预防医学   565篇
眼科学   253篇
药学   324篇
中国医学   39篇
肿瘤学   227篇
  2022年   50篇
  2021年   84篇
  2020年   59篇
  2019年   67篇
  2018年   91篇
  2017年   60篇
  2016年   91篇
  2015年   74篇
  2014年   115篇
  2013年   148篇
  2012年   213篇
  2011年   225篇
  2010年   195篇
  2009年   156篇
  2008年   215篇
  2007年   213篇
  2006年   227篇
  2005年   200篇
  2004年   211篇
  2003年   189篇
  2002年   179篇
  2001年   173篇
  2000年   165篇
  1999年   143篇
  1998年   93篇
  1997年   92篇
  1996年   99篇
  1995年   74篇
  1994年   68篇
  1993年   61篇
  1992年   120篇
  1991年   119篇
  1990年   134篇
  1989年   149篇
  1988年   139篇
  1987年   148篇
  1986年   167篇
  1985年   137篇
  1984年   93篇
  1983年   92篇
  1982年   70篇
  1981年   60篇
  1980年   63篇
  1979年   98篇
  1978年   77篇
  1977年   68篇
  1976年   55篇
  1975年   48篇
  1974年   55篇
  1973年   52篇
排序方式: 共有6346条查询结果,搜索用时 10 毫秒
31.
The cytologic diagnosis of malignancy is frequently straightforward. For difficult cases, multiple immunostains and immunostain panels have been investigated without consensus. beta-human chorionic gonadotropin (hCG) has been reportedly expressed in malignancies, but not in normal tissue. HCG also has been reported as a specific marker of metastases in serous fluids when detected with laboratory assays. We investigated the clinical utility of hCG in this cytologic setting. A total of 97 cases of benign and malignant effusions were studied. Each case was immunostained with monoclonal hCG using the avidin-biotin technique and diaminobenzidine as a chromogen. Additionally, a mucicarmine stain was performed on most cases. Cases were evaluated for hCG expression and mucin in a blinded fashion. After the cases were reviewed, the diagnoses were unblinded and staining patterns were evaluated. Of the 47 benign cases studied, 23 (49%) exhibited immunoreactivity to hCG in at least 5% of mesothelial cells present. In contrast, 28 of 44 (64%) adenocarcionomas exhibited a similar degree of immunostaining. In all, 21 (48%) of the adenocarcinomas were also positive for mucin; five of these mucin-positive cases were negative for hCG. The combination of mucin and hCG detected 33 of 44 (75%) adenocarcinomas. We conclude that hCG lacks the specificity for malignant cells to be of clinical use in effusion cytology.  相似文献   
32.
Inhibition by prostaglandin E1 (PGE1) of superoxide anion (O2-.) production by isolated intact human neutrophils (PMNs) was investigated utilizing initial-velocity enzyme kinetics. Lag time, linearity, rate, and extent of reaction were simultaneously examined. Dose-response data indicate progressive PGE1-induced suppression of O2-. synthesis by activated PMNs with a Ki value of 0.50 and 0.98 mumol/L for initial velocity and extent of reaction, respectively. There were no significant dose-related trends for either lag time or linearity for reactions with PGE1 concentrations less than 10(-6) mol/L; however, at concentrations of 10(-8) mol/L and greater, the length of reaction was progressively shortened. PGE1 inhibition of PMN-induced O2-. production does not involve PMN activation/desensitization since PGE1 itself cannot stimulate O2-. generation. Moreover, PGE1 does not function as a free-radical scavenger. These data indicate the clinical feasibility of utilizing PGE1 to titrate PMN-induced synthesis of active oxygen metabolites, in order to attenuate PMN-associated host autoinjury.  相似文献   
33.
The three most widely used diagnostic systems in American psychiatry--the Feighner criteria, the Research Diagnostic Criteria, and DSM-III--appeared sequentially at 4-year intervals. The fact that the latter two systems each incorporated changes in essentially all diagnostic categories implied progress toward greater validity; however, this assumption has rarely been tested directly. To do this, the authors applied each of these three systems to 98 consecutively admitted patients with nonmanic psychoses. Although family history and 6-month follow-up data strongly supported the validity of diagnostic distinctions made in each of the three systems, they did not show increments in validity with successively developed criteria sets.  相似文献   
34.
The effect of sulfasalazine and olsalazine on the transport of [3H]folic acid and of [3H]methotrexate (MTX) was investigated in organ-cultured endoscopic biopsy specimens of small intestinal mucosa from normal subjects. Biopsy specimens obtained from patients undergoing routine diagnostic upper gastrointestinal endoscopy were organ-cultured at pH 5.5 and the effect of these two drugs on the initial rate of uptake of the two folates was determined. Both drugs inhibited the transport of [3H]folic acid with similar Ki values (1.38 and 1.32 mM for sulfasalazine and olsalazine, respectively). However, the uptake of [3H]MTX was only partially inhibited by sulfasalazine and was unaffected by olsalazine. Sulfasalazine inhibited 26.2% of the total flux of MTX, in close agreement with the fraction of MTX flux that has been shown previously to be inhibited by folic acid. These data corroborate previous findings of heterogeneity of transport of MTX in the mucosa of the human small intestine.  相似文献   
35.
Use of antibiotic and analgesic drugs during lactation.   总被引:2,自引:0,他引:2  
During lactation, multiple situations can arise that require maternal pharmacological treatment. Because of the many health advantages of human milk to infants, breast feeding should be interrupted only when the needed drug might be harmful to the nursing child and exposure via the breast milk will be sufficient to pose a risk. Since the majority of drugs have not been shown to cause adverse effects when used during lactation, and even temporary interruption of breast feeding can be difficult for the nursing dyad, decisions regarding maternal medication use during breast feeding should be based on accurate and up-to-date information. This article reviews available data on the most commonly used antibiotics and analgesics. The use of most antibiotics is considered compatible with breast feeding. Penicillins, aminopenicillins, clavulanic acid, cephalosporins, macrolides and metronidazole at dosages at the low end of the recommended dosage range are considered appropriate for use for lactating women. Fluoroquinolones should not be administered as first-line treatment, but if they are indicated, breast feeding should not be interrupted because the risk of adverse effects is low and the risks are justified. Paracetamol (acetaminophen), low-dose aspirin (acetylsalicylic acid) [up to 100 mg/day] and short-term treatment with NSAIDs, codeine, morphine and propoxyphene are considered compatible with breast feeding. Safer alternatives should be considered instead of dipyrone, aspirin at a dosage >100 mg/day and pethidine (meperidine). In the light of the many safe alternatives for pain control, breast-feeding mothers should not be allowed to experience pain or be made to feel that they must choose between analgesia and breast feeding.  相似文献   
36.
OBJECTIVE: The purpose of this study was to estimate the excess mortality attributable to hip fracture. METHODS: The 6-year survival rate of community-dwelling White female hip fracture patients aged 70 years and older entering one of seven hospitals from 1984 to 1986 (n = 578) was compared with that of White female respondents aged 70 years and older interviewed in 1984 for the Longitudinal Study on Aging (n = 3773). RESULTS: After age, education, comorbidity, and functional impairment were controlled, the mortality differential between the two groups accumulated to an excess among hip fracture patients of 9 deaths per 100 women 5 years postfracture. Among those with three or more functional impairments or one or more comorbidities, the excess was 7 deaths per 100: the effect of the fracture had disappeared in these groups by 4 years. In contrast, those with two or fewer impairments and those with no comorbidities had a continuing trend of increased mortality, with an excess of 14 deaths per 100 by 5 years. CONCLUSIONS: There is an immediate increase in mortality following a hip fracture in medically ill and functionally impaired patients, whereas among those with no comorbidities and few impairments, there is a gradual increase in mortality that continues for 5 years postfracture.  相似文献   
37.
Background: Exercise is an important strategy with potential to improve recovery in older adults following a hip fracture.Purpose: The purpose of this study was to test the impact of a self-efficacy based intervention, the Exercise Plus Program, and the different components of the intervention, on self-efficacy, outcome expectations, and exercise behavior among older women post-hip fracture.Methods: Participants were randomized to one of four groups: exercise plus, exercise only, plus only (i.e., motivation), or routine care. Data collection was done at baseline (within 22 days of fracture), 2, 6, and 12 months post-hip fracture.Results: A total of 209 women were recruited with an average age of 81.0 years (SD=6.9). The majority was White (97.1%), was widowed (57.2%), and had a high school education (66.7%). Generalized Estimating Equations were used to perform repeated measures analyses. No differences in trajectories of recovery were observed for self-efficacy or outcome expectations. A statistically significant difference in the overall trajectory of time in exercise was seen (p<.001), with more time spent exercising in all three treatment groups.Conclusions: The study demonstrated that it was possible to engage these women in a home-based exercise program and that the plus only, exercise only, and the exercise plus groups all increased exercise. Support for this project was provided by National Institute on Aging grants R37 AG09901, R01-AG18668, R01 AG17082, and the Claude D. Pepper Older Americans Independence Center P60-AG12583.  相似文献   
38.
39.
PURPOSETo evaluate abnormalities of the cerebral operculum in infants and children and to propose the embryogenic basis of abnormal opercular formation as determined from MR imaging findings.METHODSEighty-six infants and children who had abnormally wide interopercular distances and/or distorted opercular topography seen on MR images were studied retrospectively. Clinically, patients presented with tonal abnormalities, macrocephaly, microcephaly, seizures, developmental delay, cerebral palsy, or facial dysmorphism. The abnormal opercula were compared with developing opercula at different stages of gestation.RESULTSAmong the 86 infants and children, two categories of opercular abnormalities were identified: an underdeveloped operculum (n = 64) and a malformed operculum (n = 22). The malformed operculum was further classified into three subtypes: nonformation of the operculum with lissencephaly (n = 1, 1%), abnormal opercular formation with pachygyria (n = 11, 13%), and nonformation or abnormal formation of the operculum without pachygyria or lissencephaly (n = 10, 12%). Two subtypes of the underdeveloped operculum were identified: an open operculum without a normal insula (n = 6, 7%) and an open operculum with a normal insula (n = 58, 67%). The five subtypes of abnormal opercular configuration showed a range of maturity that was comparable to the developing operculum at different ages.CONCLUSIONOpercular anomalies appear to follow sequentially predetermined normal steps in development. Arrest in opercular development or malformation may occur after an initial insult. MR imaging is the method of choice by which to identify these abnormalities.  相似文献   
40.
Abstract. 15 adults, each providing 4 non-adjacent untreated periodontal pockets with a probing depth (PD) exceeding 6 mm. volunteered for a randomized, split-mouth, double-blind, clinical study evaluating subgingival irrigation with chlorhexidine (CHX) or tetracycline HCl (TTC). The study protocol included oral hygiene instructions followed by scaling and root planing. Experimental and immediately adjacent teeth did not receive instrumentation. The 4 deep periodontal pockets in each patient were assigned to be irrigated with 150 ml CHX (0.12%). TTC (10 or 50 mg/ml; TTC10, TTC50), or sterile saline (control) in a single episode. Post-irrigation mechanical plaque control was supported by 2× daily CHX rinses throughout the 12-week observation interval. Recordings of oral hygiene (PlI), gingival health (GI). bleeding on probing (BoP). probing depth (PD), clinical attachment level (CAL), and microbial morphotypes from subgingival paper point samples were performed pre-irrigation. and at 1, 2, 4, 6, 8, 10, and 12 weeks post-irrigation. Mean post-irrigation PlI was low, fluctuating between 0.0 and 0.4, without significant differences between experimental groups. Mean pre-irrigation GI approximated 1.4 and reached 0.8 at the exit of study without significant differences between experimental groups. All experimental sites exhibited BoP pre-irrigation. BoP was significantly reduced in TTC50 compared to TTC10, CHX and control sites from week 8 post-irrigation. PDs were reduced for the experimental groups with TTC50 exhibiting the strongest reduction. CALs remained unaltered from pre-irrigation for TTC10. CHX and control sites over the 12-week observation interval, whereas TTC50 sites consistently improved to significantly differ from all other groups at week 10 and 12 post-irrigation. The distribution of bacterial morphotypes was significantly altered towards one of periodontal health for all experimental groups with a profound effect for TTC50 sites. Our results suggest that subgingival irrigation with TTC solutions at high concentrations may have a rôle in the management of adult periodontitis.  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