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   12702篇
  免费   975篇
  国内免费   24篇
耳鼻咽喉   70篇
儿科学   539篇
妇产科学   289篇
基础医学   1667篇
口腔科学   112篇
临床医学   2114篇
内科学   2281篇
皮肤病学   125篇
神经病学   1220篇
特种医学   239篇
外科学   1083篇
综合类   135篇
一般理论   29篇
预防医学   1644篇
眼科学   222篇
药学   845篇
中国医学   21篇
肿瘤学   1066篇
  2023年   143篇
  2022年   190篇
  2021年   327篇
  2020年   268篇
  2019年   389篇
  2018年   378篇
  2017年   307篇
  2016年   327篇
  2015年   337篇
  2014年   437篇
  2013年   682篇
  2012年   1028篇
  2011年   1000篇
  2010年   527篇
  2009年   467篇
  2008年   851篇
  2007年   844篇
  2006年   828篇
  2005年   760篇
  2004年   701篇
  2003年   617篇
  2002年   628篇
  2001年   96篇
  2000年   63篇
  1999年   121篇
  1998年   130篇
  1997年   100篇
  1996年   107篇
  1995年   99篇
  1994年   70篇
  1993年   66篇
  1992年   52篇
  1991年   60篇
  1990年   46篇
  1989年   36篇
  1988年   46篇
  1987年   43篇
  1986年   32篇
  1985年   32篇
  1984年   33篇
  1983年   36篇
  1982年   37篇
  1981年   37篇
  1980年   38篇
  1979年   23篇
  1978年   25篇
  1976年   17篇
  1975年   25篇
  1974年   23篇
  1973年   26篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Journal of Prevention - Social and Emotional Learning (SEL) programs seek to enhance social and emotional competencies in children, including self-awareness, self-management, social awareness,...  相似文献   
72.
73.
Purpose: To describe the service utilization patterns of homeless and runaway youth in a “service-rich” area of Los Angeles, California; identify demographic and other correlates of utilization; and contextualize the findings with qualitative data.

Method: During Phase 1 of this study, survey data were collected from an ethnically diverse sample of 296 youth aged 13–23 years, recruited from both service and natural “hang-out” sites using systematic sampling methods. During Phase 2, qualitative data were collected from 46 youth of varying ethnicities and lengths of time homeless.

Results: Drop-in centers and shelters were the most commonly used services (reported by 78% and 40%, respectively). Other services were used less frequently [e.g., medical services (28%), substance abuse treatment (10%) and mental health services (9%)]. Utilization rates differed by ethnicity, length of time in Los Angeles, and city of first homeless episode (Los Angeles versus all others). Shelter use was strongly associated with use of all other services. Despite youths’ generally positive reactions to services, barriers were described including rules perceived to be restrictive, and concerns youth had about confidentiality and mandated reporting. Youth suggested improvements including more targeted services, more long-term services, revised age restrictions, and more and/or better job training and transitional services to get them off the streets.

Conclusions: Because shelters and drop-in centers act as gateways to other services and offer intervention potential for these hard-to-reach youth, it is vital that we understand the perceived barriers to service utilization.  相似文献   

74.
Studies of minority ethnic women and cancer screening have, in the past, suffered from many theoretical and methodological weaknesses. In addition, no attempts have been made to study the complexity of the issue involved in the intercultural context, or the possible contribution of women's experiences to low uptake rates. In order to further our understanding of the issues, an alternative approach, participatory action research (PAR), was adopted to identify factors that might have contributed to the persistently low participation of minority ethnic women in the cervical screening programme, and address them collaboratively. This paper presents the key findings of the ‘problem identification' phase of the project. Using mainly the focus-group method, it explores both smear takers' and minority ethnic women's perceptions and experiences of cervical screening. Data suggest that there was a divergence in perceptions held by these groups regarding cervical screening, which contributed to negative experiences for both groups. There is also clear evidence of dysfunctional clinical communication arising from these differing perceptions. Opportunistic screening at post-natal examination adopted by many general practices appeared to have perpetuated the perceptions that the majority of minority ethnic women held about the purpose of the smear test. Compounded by language differences, the majority of women who had undergone smear testing understood neither the purpose of screening programme nor the procedure of the test. This has clear implications for promoting regular uptake, and more importantly for informed consent and choice.  相似文献   
75.
 Observations in humans suggest that the initial use of tobacco occurs in close temporal proximity to experimentation with alcohol. There have been relatively few research reports, however, examining possible interactions between these two agents. The present experiments examined the effect of nicotine exposure on the acquisition of ethanol drinking behavior in a limited access procedure. In experiment 1, rats were presented with 1-h access to ethanol solutions of increasing concentration for a period of 20 days. Subcutaneous injections of nicotine (0.6 or 1.2 mg/kg salt) or vehicle were administered 30 min prior to each ethanol presentation. Experiment 2 used a similar method, but rats were presented with water along with ethanol during the 1-h test session. Mecamylamine, a nicotinic receptor antagonist, was administered 30 min prior to the nicotine treatment. Nicotine was seen to produce a dose-dependent increase in ethanol drinking behavior which commenced at the 5% ethanol concentration and continued at 8% and again at 10%. In the second experiment, mecamylamine was observed to block completely the nicotine-induced increase in ethanol drinking behavior. The findings suggest that exposure to nicotine can facilitate the acquisition of ethanol drinking behavior in naive rats and that this effect is mediated by nicotine’s interaction at the nicotinic-cholinergic receptor. Received: 11 June 1998 / Final version: 1 October 1998  相似文献   
76.
A method for quantifying mitral and tricuspid regurgitant volume that utilizes a measure of jet orifice velocity U(0) - m/sec), a distal centerline velocity (U(m) - m/sec), and the intervening distance (X - cm) was recently developed; where jet flow rate (Q(cal) - L/min) is calculated as Q(cal) = (U(m)X)(2)/(26.46U(o)). This method, however, modeled the regurgitant jet as a free jet, whereas many atrial jets are counterflowing jets because of jet opposing intra-atrial flow fields (counterflows). This study concentrated on the feasibility of using the free jet quantification equation in the atrium where ambient flow fields may alter jet centerline velocities and reduce the accuracy of jet flow rate calculations. A 4-cm wide chamber was used to pump counterflows of 0, 4, and 22 cm/sec against jets of 2.3, 4.8, and 6.4 m/sec originating from a 2-mm diameter orifice. For each counterflow-jet combination, jet centerline velocities were measured using laser Doppler anemometry. For free jets (no counterflow), flow rate was calculated with 98% mean accuracy. For all jets in counterflow, the calculation was less accurate as: (i) the ratio of jet orifice velocity to counterflow velocity decreased (U(o)/U(c), where U(c) is counterflow velocity), i.e., the counterflow was relatively more intense, and (ii) centerline measurements were made further from the orifice. But although counterflow lowered jet centerline velocities beneath free jet values, it did so only significantly in the jet's distal portion (X/D > 16, i.e., >16 orifice diameters from the origin of the jet). Thus, the initial portion (X/D < 16) of a jet in counterflow behaved essentially as a free jet. As a result, even in significant counterflow, jet flow rate was calculated with >93% accuracy and >85% for jets typical of mitral and tricuspid regurgitation, respectively. Counterflow lowers jet centerline velocities beneath equivalent free jet values. This effect, however, is most significant in the distal portion of the jet. Therefore, regurgitant jets, although not classically free because of systolic atrial inflow or jet-induced intra-atrial swirling flows, will decay in their initial portions as free jets and thus are candidates for quantification with the centerline technique. (ECHOCARDIOGRAPHY, Volume 13, July 1996)  相似文献   
77.
Summary Adriamycin (Adr), the single most active agent used in the treatment of breast cancer, may become ineffective as treatment progresses due to the development of multidrug resistant (MDR) tumors. A major mechanism associated with MDR is increased P-glycoprotein (Pgp) expression. This study examined the abilities of the anti-estrogen tamoxifen (TAM) and the progestin medroxyprogesterone acetate (MPA) as well as cyclosporin A (CsA), a known resistance modifier, to enhance the cytotoxic effects of Adr on human breast epithelial cells (HBEC) in primary culture. Pgp and estrogen receptor (ER) expression were determined in each of the cultures by immunocytochemical assays using the monoclonal antibodies C219 and H222 Sp, respectively. The Adr-sensitive, Pgp-, ER+ MCF-7 cell line and the Adr-resistant, Pgp+, ER-MCF7-AdrR cell line were used as controls. Primary cultures were categorized as HBEC from tissues with or without previous chemotherapy. Pgp was detected in 1 of the 15 cell cultures from tissues without previous chemotherapy and in 5 of the 6 cell cultures from tissues previously exposed to chemotherapy. Incubation with either CsA or MPA plus Adr enhanced Adr toxicity in Pgp+ but not Pgp- cell cultures, whereas TAM had no effect on the sensitivity of any of the cultures. Of the 21 primary cultures of HBEC, 3 were ER+. There was no correlation between the enhancement of Adr cytotoxicity and ER status. The data suggest that MPA as well as CsA may be useful as modifying agents in overcoming Pgp-associated multidrug resistance.  相似文献   
78.
PURPOSE OF THE PAPER: This study provides baseline information on the characteristics of Native Hawaiian mothers and the health status of their infants, comparing residents of Hawaii with those of the continental U.S. The impact of Hawaii residence on low birth weight and infant mortality among Native Hawaiians is assessed. SUMMARY OF METHODS UTILIZED: Data from the National Center for Health Statistics 1983­1987 Linked U.S. Live Birth and Infant Death file were used to examine parental characteristics, prenatal care use and infant outcomes using chi­square and logistic regression procedures. PRINCIPAL FINDINGS: Despite a higher sociodemographic risk profile among Hawaii resident mothers, preterm birth, low and very low birth weight percentages were similar. Continental infants had significantly highter percentages of very pre­term birth and macrosomia. Mortality rates in both the neonatal and post­neonatal periods, and for SIDS and perinatal causes were elevated among continental infants. Hawaii residence had a borderline protective effect on infant mortality, wehn sociodemographic and prenatal care differences were controlled. CONCLUSIONS: This study suggests a possibly protective effect of Hawaii residence on the health of Native Hawaiian infants during the period of following employer­mandated health insurance coverage but before the initiation of "gap­group" coverage and the Native Hawaiian Health Care Systems in Hawaii. RELEVANCE TO ASIAN PACIFIC ISLANDER AMERICAN POPULATIONS. This is the first report documenting the sociodemographic and health status of the growing number of Native Hawaiian mothers and their infants residing outside of Hawaii. Expanded health insurance coverage and culturally appropriate and accessible health care may contribute to improved infant health status in Hawaii. Their absence, along with possible barriers of sociocultural isolation, may account for the poorer than expected outcomes of continental infants and predict a widening gap between them and their counterparts in Hawaii. A follow­up study of the health status of Native Hawaiian mothers and infants, and their access to appropriate care in Hawaii and thei continental U.S. is recommended.  相似文献   
79.

Objectives

To evaluate the efficacy of combined finasteride and flutamide therapy in men with advanced prostate cancer by determining (1 ) the short-term tolerability of finasteride monotherapy and its effect on serum prostate-specific antigen (PSA) and hormone (testosterone, dihydrotestosterone) levels, and (2) the effects of the addition of flutamide on tolerability and on serum PSA and hormone levels.

Methods

Thirteen hormone-naive men with advanced prostate cancer (4 with Stage D2, 1 with Stage D1, 1 with Stage DO, 7 with rising PSA levels after radical prostatectomy [n = 2]or definitive radiation therapy [n = 5]) were initially treated with 5 mg finasteride daily. Flutamide (250 mg three times a day) was added after serum PSA levels stabilized.

Results

Finasteride alone (median 5 weeks) had no significant effect on serum PSA levels (P>0.05). Combined finasteride and flutamide resulted in a mean 91% reduction in serum PSA levels, with 85% of men achieving a nadir serum PSA level of less than 4.0 ng/mL and 46% achieving undetectable levels (0.2 ng/mL or less). Finasteride alone had no significant effect on serum testosterone levels (P>0.05) but did result in a mean 74% reduction in serum dihydrotestosterone levels. Combined finasteride and flutamide resulted in a mean 56% increase in serum testosterone levels but had no additional effect on serum dihydrotestosterone levels (P>0.05). Side effects occurred in 85% (gynecomastia or breast tenderness in 62% [8 of 13]and diarrhea in 23% [3 of 13]) of men on combined therapy. Potency was preserved in 66%. Combined finasteride and flutamide therapy was withdrawn from 15% (2 of 13) because of flutamide-induced diarrhea and from 23% (3 of 13) because of disease progression. All remaining patients (8 of 13) have serum PSA levels below 4.0 ng/mL and 4 of these 8 have undetectable levels. These men have received combined finasteride and flutamide for a median 11 months (range 6 to 19).

Conclusions

Finasteride monotherapy is inadequate therapy for advanced prostate cancer, but combined finasteride and flutamide may be a reasonable alternative for men with advanced prostate cancer who refuse conventional hormone therapy.  相似文献   
80.
The use of a multimedia computer-based patient record (CPR) within ambulatory care is a topic that has not achieved widespread understanding or acceptance. However, if the topic is divided into its parts, multimedia and computer-based patient record, it reflects both highly recognizable and desirable goals that most health care organizations are undertaking. Multimedia technology is quickly maturing. In addition, the goal of attaining a CPR is of primary interest to most health care organizations. It is inevitable that these two technologies will eventually become synergistic. This article presents the case for a multimedia ambulatory CPR and describes one example of this happy marriage.  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