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   198131篇
  免费   2791篇
  国内免费   75篇
耳鼻咽喉   1498篇
儿科学   7259篇
妇产科学   3506篇
基础医学   19345篇
口腔科学   1797篇
临床医学   14707篇
内科学   35636篇
皮肤病学   1131篇
神经病学   18500篇
特种医学   10013篇
外科学   32589篇
综合类   2555篇
一般理论   23篇
预防医学   19695篇
眼科学   3120篇
药学   11088篇
中国医学   651篇
肿瘤学   17884篇
  2023年   293篇
  2022年   558篇
  2021年   1126篇
  2020年   630篇
  2019年   955篇
  2018年   22804篇
  2017年   17962篇
  2016年   20116篇
  2015年   1789篇
  2014年   1928篇
  2013年   2165篇
  2012年   8941篇
  2011年   22977篇
  2010年   19807篇
  2009年   12333篇
  2008年   20747篇
  2007年   22948篇
  2006年   1776篇
  2005年   3236篇
  2004年   4312篇
  2003年   5130篇
  2002年   3188篇
  2001年   488篇
  2000年   550篇
  1999年   337篇
  1998年   332篇
  1997年   303篇
  1996年   191篇
  1995年   171篇
  1994年   154篇
  1993年   113篇
  1992年   146篇
  1991年   177篇
  1990年   211篇
  1989年   171篇
  1988年   122篇
  1987年   122篇
  1986年   94篇
  1985年   101篇
  1984年   84篇
  1983年   72篇
  1982年   80篇
  1981年   60篇
  1980年   80篇
  1979年   55篇
  1978年   53篇
  1974年   56篇
  1970年   58篇
  1938年   60篇
  1932年   60篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Estradiol stimulates the growth of breast tumor cells in both pre- and post menopausal women. Following the menopause, the levels of estradiol in breast tumor tissues are similar to those from tumors obtained prior to cessation of ovarian function, even though plasma estrogen levels are 10–50 fold lower in post- than in premenopausal women. These observations suggested the possibility of enhanced estradiol uptake from plasma or in situ synthesis in post-menopausal women. We systematically studied these possibilities in a series of model systems. Initially we demonstrated a very high affinity estradiol binding site in tissues from castrated rats. Enhanced uptake occurred under conditions of low plasma estrogen levels when compared to animals with higher estradiol levels. In situ synthesis also occurred both through the sulfatase and aromatase pathways. In further studies, we compared uptake from plasma with in situ synthesis via aromatase in a nude mouse model. Under the conditions utilized, in situ synthesis resulted in much higher tissue estradiol levels and tumor growth rates than did uptake from plasma. During these studies we demonstrated that tumors deprived of estradiol developed mechanisms rendering them more sensitive to estrogen. This involved the ability of cells to adapt to estradiol deprivation to allow them to be responsive to four log lower amounts of estrogen than when studied under wild type conditions. In addition, cells adapted by increasing their level of aromatase and thus developing the capability to become more sensitive to estrogen precursors. Taken together, these studies demonstrate that breast cancer tissue is highly plastic and can adapt to conditions of estrogen deprivation via a variety of mechanisms.  相似文献   
994.
995.
Objective To determine whether increasing maternal age increases the risk of operative delivery and to investigate whether such a trend is due to fetal or maternal factors.
Design Analysis of prospectively collected data on a maternity unit database.
Setting A postgraduate teaching hospital.
Population 6410 nulliparous women with singleton cephalic pregnancies delivering at term (37–42) weeks of gestation) between 1 January 92 and 31 December 95.
Main outcome measures Mode of delivery, rates of prelabour caesarean section, induction of labour and epidural usage.
Results There was a positive, highly significant association between increasing maternal age and obstetric intervention. Prelabour (  P < 0.001  ) and emergency (   P < 0.001  ) caesarean section, instrumental vaginal delivery (spontaneous labour   P < 0.001  ; induced labour   P = 0.001  ), induction of labour (   P < 0.001  ) and epidural usage in spontaneous labour (  P = 0.005  ) all increased with increasing age. In the second stage of labour fetal distress and failure to advance, requiring instrumental delivery, were both more likely with increasing maternal age (in both   P < 0.001  ). Epidural usage in induced labour and the incidence of small for gestational age newborns did not increase with increasing maternal age (P = 0.68 and  P = 0.50  , respectively).
Conclusions This study demonstrates that increasing maternal age is associated with an incremental increase in obstetric intervention. Previous studies have demonstrated a significant effect in women older than 35 years of age, but these data show changes on a continuum from teenage years. This finding may reflect a progressive, age-related deterioration in myometrial function.  相似文献   
996.
Objective. To determine how the addition of generalist care managers and collaborative information technology to an ambulatory team affects the care of patients with diabetes.
Study Setting. Multiple ambulatory clinics within Intermountain Health Care (IHC), a large integrated delivery network.
Study Design. A retrospective cohort study comparing diabetic patients treated by generalist care managers with matched controls was completed. Exposure patients had one or more contacts with a care manager; controls were matched on utilization, demographics, testing, and baseline glucose control. Using role-specific information technology to support their efforts, care managers assessed patients' readiness for change, followed guidelines, and educated and motivated patients.
Data Collection. Patient data collected as part of an electronic patient record were combined with care manager-created databases to assess timely testing of glycosylated hemoglobin (HbA1c) and low-density lipoprotein (LDL) levels and changes in LDL and HbA1c levels.
Principal Findings. In a multivariable model, the odds of being overdue for testing for HbA1c decreased by 21 percent in the exposure group ( n =1,185) versus the control group ( n =4,740). The odds of being tested when overdue for HbA1c or LDL increased by 49 and 26 percent, respectively, and the odds of HbA1c <7.0 percent also increased by 19 percent in the exposure group. The average HbA1c levels decreased more in the exposure group than in the controls. The effect on LDL was not significant.
Conclusions. Generalist care managers using computer-supported diabetes management helped increase adherence to guidelines for testing and control of HbA1c levels, leading to improved health status of patients with diabetes.  相似文献   
997.
To inform New York City’s (NYC’s) tobacco control program, we identified the neighborhoods with the highest smoking rates, estimated the burden of second-band smoke exposure, assessed the early response to state taxation, and examined cessation practices. We used a stratified random design to conduct a digit-dialed telephone survey in 2002 among 9,674 New York City adults. Our main outcome measures included prevalence of cigarette smoking, exposure to second-hand smoke, the response of smokers to state tax increases, and cessation practices. Even after controlling for sociodemographic factors (age, racelethnicity, income, education, marital status, employment status, and foreign-born status) smoking rates were highest in Central Harlem and in the South Bronx. Sixteen percent of nonsmokers reported frequent exposure to second-hand smoke at home or in a workplace. Among smokers with a child with asthma, only 33% reported having a no-smoking policy in their homes. More than one fifth of smokers reported reducing the number of cigarettes they smoked in response to the state tax increase. Of current smokers who tried to quit, 65% used no cessation aid. These data were used to inform New York City’s smoke-free legislation, taxation, public education, and a free nicotine patch give-away program. In conclusion, large, local surveys can provide essential data to effectively advocate for, plan, implement, and evaluate a comprehensive tobacco control program. Dr. Mostashari (the guarantor) made substantial contributions to the conception, design, and supervision of this paper, the analysis and interpretation of data, the drafting of the paper, critical revisions of the paper for important intellectual content, and the acquisition of data and funding for this research. Dr. Kerker made substantial contributions to the analysis and interpretation of data, the drafting of the paper and critical revisions of the paper for important intellectual content. Ms. Hajat made substantial contributions to the acquisition of data and critical revisions of the paper for important intellectual content. Dr. Miller made substantial contributions to the conception of this paper and critical revisions of the paper for important intellectual content. Dr. Frieden made substantial contributions to the conception, design, and supervision of this paper and critical revisions of the paper for important intellectual content.  相似文献   
998.
The incidence of sexual assault continues to escalate, and it is under-reported. Recent literature discusses the medical, legal, and psychological management of the female sexual assault victim, but little has been written regarding appropriate management of male sexual assault. This article focuses on the laboratory investigation in male rape case.  相似文献   
999.
This study evaluated the effects of a school-based intervention on growth trajectories of smoking, drinking, and antisocial behavior among early adolescents. Seven middle schools were randomized to intervention or comparison conditions and students in two successive cohorts (n = 1484) provided five waves of data from sixth to ninth grade. The Going Places Program, included classroom curricula, parent education, and school environment components. Latent growth curve analyses demonstrated significant treatment group effects, including reducing increases in friends who smoke, outcome expectations for smoking, and smoking progression, but had non-significant effects on drinking or antisocial behavior. The Going Places Program was effective in preventing increases in smoking progression, but its efficacy as a more cross-cutting problem behavior preventive intervention was not confirmed.  相似文献   
1000.
The potential use of genetic tests in insurance has raised concerns about discrimination and individuals losing access to health care either because of refusals to test for treatable diseases, or because test-positives cannot afford premiums. Governments have so far largely sought to restrict the use of genetic information by insurance companies. To date the number of tests available with significant actuarial value is limited. However, this is likely to change, raising more clearly the question as to whether the social costs of adverse selection outweigh the social costs of individuals not accessing health care for fear of the consequences of test information being used in insurance markets. In this contribution we set out the policy context and model the potential trade-offs between the losses faced by insurers from adverse selection by insurees (which will increase premiums reducing consumer welfare) and the detrimental health effects that may result from persons refusing to undergo tests that could identify treatable health conditions. It argues that the optimal public policy on genetic testing should reflect overall societal benefit, taking account of these trade-offs. Based on our model, the factors that influence the outcome include: the size of and value attached to the health gains from treatment; deterrent effects of a disclosure requirement on testing for health reasons; incidence of the disease; propensity of test-positives to adverse select; policy value adverse selectors buy in a non-disclosure environment; and price elasticity of demand for insurance. Our illustrative model can be used as a benchmark for developing other scenarios or incorporating real data in order to address the impact of different policies on disclosure and requirement to test.  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