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   188142篇
  免费   2268篇
  国内免费   494篇
耳鼻咽喉   1325篇
儿科学   6888篇
妇产科学   3339篇
基础医学   18029篇
口腔科学   2149篇
临床医学   13750篇
内科学   32665篇
皮肤病学   819篇
神经病学   17184篇
特种医学   9220篇
外国民族医学   6篇
外科学   30402篇
综合类   3686篇
现状与发展   2篇
一般理论   1篇
预防医学   18910篇
眼科学   3071篇
药学   10781篇
  12篇
中国医学   1202篇
肿瘤学   17463篇
  2024年   98篇
  2023年   185篇
  2022年   400篇
  2021年   598篇
  2020年   435篇
  2019年   527篇
  2018年   22408篇
  2017年   17798篇
  2016年   19908篇
  2015年   1530篇
  2014年   1578篇
  2013年   1543篇
  2012年   7902篇
  2011年   21965篇
  2010年   19538篇
  2009年   12070篇
  2008年   20193篇
  2007年   22362篇
  2006年   1197篇
  2005年   2726篇
  2004年   3844篇
  2003年   4710篇
  2002年   2810篇
  2001年   515篇
  2000年   635篇
  1999年   375篇
  1998年   336篇
  1997年   333篇
  1996年   201篇
  1995年   183篇
  1994年   187篇
  1993年   146篇
  1992年   125篇
  1991年   179篇
  1990年   213篇
  1989年   154篇
  1988年   115篇
  1987年   87篇
  1986年   60篇
  1985年   55篇
  1984年   42篇
  1983年   36篇
  1982年   33篇
  1980年   53篇
  1974年   25篇
  1938年   60篇
  1937年   25篇
  1934年   30篇
  1932年   56篇
  1930年   46篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
51.

Purpose

Most computerized adaptive testing (CAT) applications in patient-reported outcomes (PRO) measurement to date are reliability-centric, with a primary objective of maximizing measurement efficiency. A key concern and a potential threat to validity is that, when left unconstrained, individual CAT administrations could have items with systematically different attributes, e.g., sub-domain coverage. This paper aims to provide a solution to the problem from an optimal test design framework using the shadow-test approach to CAT.

Methods

Following the approach, a case study was conducted using the PROMIS® (Patient-Reported Outcomes Measurement Information System) fatigue item bank both with empirical and simulated response data. Comparisons between CAT administrations without and with the enforcement of content and item pool usage constraints were examined.

Results

The unconstrained CAT exhibited a high degree of variation in items selected from different substrata of the item bank. Contrastingly, the shadow-test approach delivered CAT administrations conforming to all specifications with a minimal loss in measurement efficiency.

Conclusions

The optimal test design and shadow-test approach to CAT provide a flexible framework for solving complex test-assembly problems with better control of their domain coverage than for the conventional use of CAT in PRO measurement. Applications in a wide array of PRO domains are expected to lead to more controlled and balanced use of CAT in the field.
  相似文献   
52.

Purpose

Measurement invariance issues should be considered during test construction. In this paper, we provide a conceptual overview of measurement invariance and describe how the concept is implemented in several different statistical approaches. Typical applications look for invariance over things such as mode of administration (paper and pencil vs. computer based), language/translation, age, time, and gender, to cite just a few examples. To the extent that the relationships between items and constructs are stable/invariant, we can be more confident in score interpretations.

Methods

A series of simulated examples are reported which highlight different kinds of non-invariance, the impact it can have, and the effect of appropriately modeling a lack of invariance. One example focuses on the longitudinal context, where measurement invariance is critical to understanding trends over time. Software syntax is provided to help researchers apply these models with their own data.

Results

The simulation studies demonstrate the negative impact an erroneous assumption of invariance may have on scores and substantive conclusions drawn from naively analyzing those scores.

Conclusions

Measurement invariance implies that the links between the items and the construct of interest are invariant over some domain, grouping, or classification. Examining a new or existing test for measurement invariance should be part of any test construction/implementation plan. In addition to reviewing implications of the simulation study results, we also provide a discussion of the limitations of current approaches and areas in need of additional research.
  相似文献   
53.
In this study, we aimed to find out the biodegradation efficiency of some soil fungi types on herbicide acetochlor with acetochlor active material, chemical oxygen demand (COD), biochemical oxygen demand (BOD5) and total organic carbon (TOC) parameters. We also try to determine the population dynamics of these fungi via turbidity. The fungi cultures were isolated from agricultural field in in Thrace region of Turkey. Each fungi enriched in malt extract broth media and 1 mL of these enriched media was inoculated into 100 mL of acetochlor solutions that suggested for using application concantrations in agricultural field for farmers (11000 mg L?1) for sunflower and corn agriculture. Bioremediation results of acetochlor have shown different results according to the types of fungi. Our results indicate that Tolypocladium geodes and Cordyceps cicadae might be used in acetochlor bioremediation with a significant acetochlor, COD, TOC and BOD5 reduction and can be used for rehabilitation of agricultural fields or receiving environments for removal the opposite effects of acetochlor or other herbicides.  相似文献   
54.
Single particle inductively coupled plasma mass spectrometry (spICP-MS) was used to detect Ti-containing particles in heavily-used bathing areas of a river (Salt River) and five swimming pools. Ti-containing particle concentrations in swimming pools ranged from 2.8?×?103 to 4.4?×?103 particles/mL and were an order of magnitude lower than those detected in the Salt River. Measurements from the Salt River showed an 80% increase in Ti-containing particle concentration over baseline concentration during peak recreational activity (at 16:00 h) in the river. Cloud point extraction followed by transmission electron microscopy with energy dispersive X-ray analysis confirmed presence of aggregated TiO2 particles in river samples, showing morphological similarity to particles present in an over-the-counter sunscreen product. The maximum particle mass concentration detected in a sample from the Salt River (659 ng/L) is only slightly lower than the predicted no effect concentration for TiO2 to aquatic organisms (<?1 μg/L).  相似文献   
55.
Poland is one of the countries distinguished by a long and colorful past. Undergoing numerous turbulent socio-economic changes forced by the course of history, Poland is now one of the member states of the European Union. Experiencing low water quantity and high contamination levels in surface waters, Poland is following other EU countries in the effort to reach a “good” water status. Herein are presented impacts of changes in Polish history on water legislation, management, and research, as well as explanations for the perceptible split between engineering and scientific approaches to the aquatic issues. Drawbacks caused by unsatisfactory state research funding for the sciences and division of the water related contemporary scientific interests are also discussed.  相似文献   
56.
Comprehensive cancer centers are an important community resource for cancer prevention education in their catchment areas. Colorectal cancer remains one of the most commonly diagnosed cancers in the United States, making prevention a priority. Colorectal cancer prevention targets include lifestyle modifications that are influenced by cultural norms, such as diet change, physical activity and screening behavior. Cancer centers must tailor prevention efforts to multiethnic catchment areas. This paper describes the development and feasibility of a comprehensive cancer center’s approach to community-based colorectal cancer prevention in Houston, Texas, specifically targeting Hispanic and Asian populations. Sites were recruited through a city-wide network of partnerships between the community relations department in the hospital and community organizations. The program consisted of three workshop-style classes per community site. Each class had a similar overall structure, but cultural and site-specific adaptations were made for each group. A total of 33 classes were taught at nine distinct community sites to 1054 participants over 9 months. This program structure may be adapted for the future dissemination of other cancer prevention tools to communities in the area.  相似文献   
57.
Veterans are at an increased risk of being injured or killed in motor vehicle crashes, potentially due to their proclivity to engage in risky driving behaviors. However, most research in this area has focused on driving behaviors of veterans who have recently returned home after deployment. No research has focused on risky driving behaviors of older veterans (aged 65 or older) and if risky driving behaviors extend beyond the time period immediately following return from deployment. The purpose of this research is to determine if differences exist in risky driving behaviors of veterans and non-veterans aged 65 or older. This study used data from the 2011 National Health and Aging Trend Study (NHATS), a nationally representative, longitudinal survey of community-dwelling, Medicare beneficiaries aged 65 or older. Binary logistic regression analyses were conducted in 2017 to determine if veteran’s status was predictive of specific risky driving behaviors. Veteran’s status was found to be predictive of specific driving behaviors for adults aged 65 and older, with non-veterans significantly more likely than veterans to: not currently drive; avoid driving at night; avoid driving alone; avoid driving on busy roads or highways; and avoid driving in bad weather. The results of this study highlight the need to further understand the effects of veteran’s status on risky driving behaviors among older adults, specifically, whether veteran’s status compounds driving-related risks associated with aging-related physical and mental changes.  相似文献   
58.
This study describes clinical characteristics of poor and uninsured patients living with hepatitis C virus (HCV) who received care from a multidisciplinary HCV clinic, reports treatment completion and cure rates, and estimates the cost of HCV medications provided at no cost to uninsured patients. A retrospective chart review was performed and identified 69 uninsured HCV patients who received medical care at Mercy Health Center, a small non-profit community clinic, between January 2008 and March 2015. Three-fourths of the patients were unemployed, a third had multiple HCV exposures, nearly half acquired HCV due to illicit drug use, and more than half had active psychiatric disorders. Of those who received HCV treatment, 81% completed treatment and 85% were achieved virological cure. The multidisciplinary community clinic provided >?$1.4 million of HCV antivirals at no cost to uninsured patients. Findings suggest a multidisciplinary community clinic comprised of a social worker, pharmacist, gastroenterologist, nurse, nurse practitioner, psychologist, and dietitian can help patients achieve HCV treatment completion and cure rates comparable to traditional physician-led clinics, and successfully manage uninsured and underserved HCV patients—who are often regarded as “difficult-to-treat” patients. Public health social workers and other health professionals are encouraged to advocate for treatment and care of poor and uninsured patients living with HCV in health agencies and health systems, otherwise population-wide reductions in HCV morbidity and mortality will not be realized.  相似文献   
59.
Maternal Zika virus infection (ZIKV) has serious health consequences for unborn offspring. Knowledge about prevention is critical to reducing risk, yet what women in the high-risk US–Mexico border region know about protecting themselves and their babies from ZIKV is mostly unknown. This study aimed to assess knowledge of ZIKV among pregnant and inter-conception women and to identify sources of information that might address knowledge gaps. Clients in five federally-funded, border region Healthy Start programs (N?=?326) were interviewed in late 2016 about their knowledge of ZIKV prevention methods and whether they believed themselves or their babies to be at risk. Sources of information about ZIKV and demographic characteristics were also measured. Chi square tests identified important associations between variables; adjusted odds ratios (AOR) and 95% confidence intervals for knowledge and beliefs were calculated. Among the 305 women aware of ZIKV, 69.5% could name two ways to prevent infection. Only 16.1% of women named using condoms or abstaining from sex as a prevention method. While 75.3% heard about ZIKV first from TV/radio, just 9.5% found the information helpful. Women who received helpful information from health care providers had greater odds of knowing two prevention methods (AOR?=?2.0; 1.1–3.7), when to test for ZIKV (AOR?=?5.2; 2.1–13.2), and how long to delay pregnancy after infection in a male partner (AOR?=?1.9; 1.1–3.2). Those who said web-based and social media sources were helpful had greater odds of knowing when to test for ZIKV (AOR?=?2.8; 1.3–6.3). Results can inform messaging for safe pregnancy and ZIKV prevention.  相似文献   
60.
This study includes a comparison analysis of how community resilience and its influence factor of community attachment were changed before and after the closing of the hospital in the rural community. In order to analyze the influence factors of healthcare and medical vulnerability on community resilience, as well as the mean difference from before and after the closing of the hospital, this study conducted matching sample t test, hierarchical regression analysis, difference in differences (DID) analysis. The results indicate that community attachment consists of such factors as closeness, preference, affective bond, and identity, and they showed significance in confidence. It showed that resilience and community attachment are lower after closing than before closing. Moreover, as a result of DID analysis where the variation of community attachment affects community resilience, closeness together with closeness had an influence on the community resilience. It needs to expand public projects to improve the settlement environment of the basic local government, and in particular, it should consider various support measures to overcome vulnerabilities in the healthcare and medical sector.  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