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   2460篇
  免费   227篇
  国内免费   23篇
耳鼻咽喉   20篇
儿科学   92篇
妇产科学   92篇
基础医学   442篇
口腔科学   43篇
临床医学   187篇
内科学   704篇
皮肤病学   35篇
神经病学   239篇
特种医学   60篇
外科学   232篇
综合类   79篇
预防医学   131篇
眼科学   34篇
药学   120篇
中国医学   13篇
肿瘤学   187篇
  2023年   25篇
  2022年   10篇
  2021年   88篇
  2020年   49篇
  2019年   67篇
  2018年   67篇
  2017年   64篇
  2016年   59篇
  2015年   78篇
  2014年   101篇
  2013年   102篇
  2012年   147篇
  2011年   161篇
  2010年   101篇
  2009年   72篇
  2008年   130篇
  2007年   146篇
  2006年   130篇
  2005年   145篇
  2004年   103篇
  2003年   114篇
  2002年   87篇
  2001年   49篇
  2000年   37篇
  1999年   40篇
  1998年   29篇
  1997年   15篇
  1996年   22篇
  1995年   16篇
  1994年   20篇
  1993年   16篇
  1992年   32篇
  1991年   28篇
  1990年   26篇
  1989年   28篇
  1988年   37篇
  1987年   36篇
  1986年   38篇
  1985年   32篇
  1984年   23篇
  1983年   23篇
  1982年   11篇
  1981年   19篇
  1980年   15篇
  1979年   10篇
  1978年   9篇
  1976年   7篇
  1975年   5篇
  1974年   7篇
  1968年   6篇
排序方式: 共有2710条查询结果,搜索用时 312 毫秒
1.
CONTEXT: The physician assistant profession has been moving toward requiring master's degrees for new practitioners, but some argue this could change the face of the discipline. PURPOSE: To see if there is an association between physician assistants' academic degrees and practice in primary care, in rural areas, and with the medically underserved. METHODS: Surveys were sent to 880 graduates of the first 32 University of Washington physician assistant classes through 2000. Respondents noted their academic degree at program entry and the highest degree attained at any time up to the time of survey. Relationships between practice characteristics and academic degree levels were tested by unadjusted odds ratios and logistic regression after controlling for year of graduation and sex. RESULTS: Of the 478 respondents, 54% worked in primary care, about 30% practiced in nonmetropolitan communities, and 42% reported providing care for the medically underserved. Respondents with no degree (33% of total at entry, 24% at survey) were significantly more likely than degree holders to work in primary care and nonmetropolitan areas. Respondents with no degree at program entry were significantly more likely, and those with no degree at the time of the survey were marginally more likely, to self-report work with the medically underserved. CONCLUSION: Respondents with no academic degree are significantly more likely to demonstrate a commitment to primary, rural, and underserved health care. These findings may inform the national debate about the impact of required advanced degrees on the practice patterns of nonphysician providers.  相似文献   
2.
BACKGROUND: Total excision of colonic polyps is not always attainable and in some patients it is clinically contraindicated. Also, a resected polyp may be lost at any step between its endoscopic removal and its embedding in paraffin. The aim of this study was to compare the histological features of colonic polyps as analysed by the study of biopsy-forceps obtained samples with those assessed on scrutinizing the totally resected growths. PATIENTS AND METHODS: This prospective study included a cohort of 59 patients in whom, in the course of an elective colonoscopy, a total excision of a 6 mm-sized or larger polyp was called for. Sizeable biopsies were obtained by means of an Olympus Multibyte forceps prior to the total polypectomy. Subsequent to the study of the polypectomy specimens, the forceps biopsy samples were submitted for histological examination. The pathologists were blinded as to the source of the tissue they were studying. The diagnoses rendered by evaluating the biopsy samples and polypectomy specimens of each patient were contrasted with each other. RESULTS: Major discrepancies between the histological features of the fragments captured by the biopsy-forceps and the factual nature of the totally removed polyps were uncovered in 11 (18.6%) of 59 cases. Intriguingly, the grade of the tumours was underrated in all the 11 cases, as judged by contrasting the tentative diagnoses of the forceps-biopsies with the decisive diagnoses of the polypectomies. Importantly, 2 adenocarcinomas would have been missed by just looking at the forceps-retrieved sample. CONCLUSIONS: In our experience, a discordance of 18.6% is to be expected between the diagnoses rendered after examining forceps-biopsies of and totally excised colonic polyps. Nevertheless, it is advisable to procure biopsies prior to the excision of the growths, because on those occasions in which patients' growths cannot be removed or have not been retrieved for one reason or another, a small forceps-captured tissue sample correctly reflects the characteristics of the polyp in 81.4% of the cases. Finally, the biopsies may be discarded in the event that total removal was successful.  相似文献   
3.
The protective effect of having a first full-term pregnancy (FFTP) at a younger age on women's lifetime risk of breast cancer is well known. Less appreciated is the increased risk seen in the years immediately following pregnancy. This adverse effect is more pronounced and more prolonged in women with later age at FFTP. The mechanisms responsible for this increased risk are still poorly understood. In the present paper, we put forward the hypothesis that the marked peripheral immune changes induced by pregnancy may account for these effects. We highlight immune changes that characterize the unique immune state of pregnancy (a combination of cellular immunosuppression and enhanced inflammatory response), note the resemblance of these changes to cancer escape mechanisms, and discuss why such immune changes may be critical for the development of breast cancer following pregnancy. We further support this idea by initial findings from our own laboratory that the age at FFTP is negatively related to natural killer cell cytotoxicity many years later and propose possible models for the kinetics of the immune changes during and following pregnancy. The effect of age at FFTP on the immune function is currently understudied. Its potential relevance to the development of breast cancer stresses the need for further research.  相似文献   
4.
Gonadal steroid levels were determined in the ovary ofSalamandra salamandra infraimmaculataduring the reproductive cycle in populations from a xeric region in northern Israel. Varying proportions of previtellogenic and vitellogenic oocytes were present throughout the year, and mature oocytes were present in winter and spring. The numbers of mature oocytes were greater between December and April, after parturition. The levels of 17β-estradiol and testosterone rose during oocyte vitellogenesis and maturation. Levels of progesterone and 17α-hydroxy progesterone appeared to be related to the level of vitellogenesis. Gravid females contained greater quantities of all four steroids than did nongravid females.  相似文献   
5.
Because a retrospective study detected 13 negative Western blots out of 38 single-use diagnostic system (SUDS)-positive cases over a 1-year period, we performed a prospective study to compare the performance of the SUDS test with that of enzyme immunoassay (EIA). Of 888 SUDS-tested sera, 875 (98.4%) were both SUDS and EIA negative and 5 (0.6%) were SUDS, EIA, and Western blot positive. The rate of SUDS-positive samples decreased from 3.16/month in the retrospective study to 1.33/month in the prospective study. The immunoassays had sensitivities and specificities of 100 and 99.7 (SUDS) and 100 and 99.4% (traditional EIA), respectively. In laboratories with experienced personnel, the SUDS test performs as well as the EIA as a screen for infection with the human immunodeficiency virus.  相似文献   
6.
In a prospective multicenter study of 1,052 patients with clinical signs of a scaphoid fracture, mammo-graphic films and fine intensifying screens were used at the radiographic examination. 5 standardized projections including 3 special projections focused on the scaphoid were taken. 150 fractures were diagnosed at the first examination but in 10 cases the fracture was first diagnosed at a second radiographic examination after 10-14 days.

The second examination still seems mandatory despite the use of high quality radiographs with optimal spatial resolution and contrast, and the value of supplementary special projections.  相似文献   
7.
8.
Prognostic factors in hormone-resistant progressing cancer of the prostate.   总被引:2,自引:0,他引:2  
In 224 consecutive patients with hormone-resistant prostatic cancer referred to 2 European Cancer Centres for palliation of painful bone metastases the one year survival for all patients was 24% (2-year survival: 7%). The median survival was 8 months. In univariate analyses the following prognostic factors were identified: performance status, serum creatinine, alkaline phosphatase, duration of response to primary hormone treatment, degree of bone scan involvement and hemoglobin. Multivariate analyses confirmed the four first parameters to be independent factors. A prognostic model was established (no or one risk factors vs 2 risk factors vs 3 or 4 risk factors) based on performance status, creatinine, alkaline phosphatase and hormone response duration. The median survival of these groups was 10 months, 6 months and 3 months, respectively. This model proved to be discriminative in an external data set of 214 patients with hormone-resistant prostatic cancer entered in two prospective trials. The above differences in outcome between readily and simply defined prognostic groups are greater than the differences one can realistically hope to produce using new treatment strategies. These prognostic factors should be taken into account both in the design and interpretation of clinical studies dealing with the treatment of hormone-resistant progressing prostatic cancer and painful bone metastases.  相似文献   
9.
用HRP、WGA—HRP及CB—HRP法顺行追踪了大鼠外侧隔核的传出纤维联系。结果表明外侧隔核发生较多的纤维经内侧前脑束投射到下丘脑;经丘脑髓纹投射到丘脑带旁核、双侧内侧缰核,也有少量纤维投射到外侧缰核,外侧隔核向扣带皮质的投射主要终止在扣带皮质前部,少量纤维投射到后部。此外,有少量纤维投射到杏仁中央核、杏仁内侧核、中缝背核、中央灰质腹、外侧部、被盖腹侧区、脚间核及蓝斑等。  相似文献   
10.
The human small-conductance Ca(2+)-activated potassium channel gene KCNN3 has been involved in mechanisms underlying neuronal function and plasticity. A multiallelic CAG repeat polymorphism within the KCNN3 has been associated with schizophrenia and bipolar disorder. We have previously reported in a family-based study that longer CAG repeats are preferentially transmitted to patients with anorexia nervosa (AN). The present study extends the analysis of KCNN3 allele distribution to a larger series of AN female patients and control groups, incorporating information on ethnicity and co-morbidities associated with AN. The data analysis is presented while considering separately the two alleles of each individual, namely a minor (shorter) and a major (longer) allele. This study has found that the KCNN3 allele distribution in the general Israeli population does not differ significantly in at least four Jewish ethnic groups of Ashkenazi, North African, Iraqi, and Yemenite origin. These have been used as control groups in a matched case-control analysis that has demonstrated a significant over-representation of KCNN3 alleles with longer CAG repeats among AN patients (P < 0.001 for the major allele and P = 0.035 for allele sum). Under dichotomization, a significantly higher prevalence of the L allele (>19 repeats) has been observed among AN patients (P < 0.001). While considering AN and co-morbid phenotypes, a tendency towards longer (L) alleles has been observed in the subset of patients with obsessive-compulsive disorder (OCD) co-morbidity. These findings further implicate KCNN3 as a significant contributor to predisposition to AN.  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