全文获取类型
收费全文 | 182980篇 |
免费 | 1305篇 |
国内免费 | 40篇 |
专业分类
耳鼻咽喉 | 1228篇 |
儿科学 | 6818篇 |
妇产科学 | 3074篇 |
基础医学 | 17458篇 |
口腔科学 | 1829篇 |
临床医学 | 12785篇 |
内科学 | 32632篇 |
皮肤病学 | 796篇 |
神经病学 | 16995篇 |
特种医学 | 9274篇 |
外科学 | 30221篇 |
综合类 | 2336篇 |
预防医学 | 18173篇 |
眼科学 | 2839篇 |
药学 | 9867篇 |
中国医学 | 640篇 |
肿瘤学 | 17360篇 |
出版年
2023年 | 39篇 |
2022年 | 81篇 |
2021年 | 127篇 |
2020年 | 65篇 |
2019年 | 120篇 |
2018年 | 22039篇 |
2017年 | 17479篇 |
2016年 | 19630篇 |
2015年 | 1047篇 |
2014年 | 1016篇 |
2013年 | 1021篇 |
2012年 | 7361篇 |
2011年 | 21459篇 |
2010年 | 19069篇 |
2009年 | 11779篇 |
2008年 | 19909篇 |
2007年 | 22143篇 |
2006年 | 1059篇 |
2005年 | 2676篇 |
2004年 | 3908篇 |
2003年 | 4838篇 |
2002年 | 2985篇 |
2001年 | 335篇 |
2000年 | 479篇 |
1999年 | 284篇 |
1998年 | 357篇 |
1997年 | 350篇 |
1996年 | 237篇 |
1995年 | 208篇 |
1994年 | 212篇 |
1993年 | 176篇 |
1992年 | 98篇 |
1991年 | 146篇 |
1990年 | 182篇 |
1989年 | 127篇 |
1988年 | 97篇 |
1987年 | 79篇 |
1986年 | 67篇 |
1985年 | 68篇 |
1984年 | 65篇 |
1983年 | 69篇 |
1982年 | 68篇 |
1981年 | 43篇 |
1980年 | 72篇 |
1978年 | 36篇 |
1974年 | 37篇 |
1938年 | 60篇 |
1934年 | 32篇 |
1932年 | 57篇 |
1930年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Analysis of Eight Organophosphorus Pesticide Residues in Fresh Vegetables Retailed in Agricultural Product Markets of Nanjing,China 总被引:1,自引:0,他引:1
A method to effectively remove pigments in fresh vegetables using activated carbon followed cleanup through solid phase extraction (SPE) cartridge to further reduce matrix interference and contamination, was established to determine eight organophosphorous pesticides (OPPs) by gas chromatography (GC) with nitrogen-phosphorus detection (NPD) in this study, and it has been successfully applied for the determination of eight OPPs in various fresh vegetables with the recoveries ranging from 61.8% to 107%. To evaluate eight OPPs residue level, some fresh vegetables retailed at three agricultural product markets (APM) of Nanjing in China were detected, the results showed that phorate in Shanghai green (0.0257 mug g(-1)) and Chinese cabbage (0.0398 mug g(-1)), dimethoate in Shanghai green (0.0466-0.0810 mug g(-1)), Chinese cabbage (0.077 mug g(-1)), and spinach (0.118-0.124 mug g(-1)), methyl-parathion in Shanghai green (0.0903 mug g(-1)), Chinese cabbage (0.157 mug g(-1)), and spinach (0.0924 mug g(-1)), malathion in Shanghai green (0.0342-0.0526 mug g(-1)), chorpyrifos in spinach (0.106-0.204 mug g(-1)), and Chinese cabbage (0.149 mug g(-1)), chlorfenvinfos in carrot (0.094-0.131 mug g(-1)), were found. However, fonofos and fenthion were not detected in all the collected vegetable samples. 相似文献
992.
Neetu Bauri Pradip Bauri Krishan Kumar V. K. Jain 《Air quality, atmosphere, & health》2016,9(1):95-106
In Dehradun, ambient volatile organic compounds (VOC) samples were collected for three seasons viz. summer, winter and monsoon (during period 2012–2013) to investigate seasonal variations at five different sampling sites. The samples were quantified for aromatic VOCs by gas chromatography (GC-FID) to monitor benzene, toluene, m, p-xylene, o-xylene and ethylbenzene. BTXE comprise an important group of VOCs mostly prevalent in a typical urban environment. They were monitored because they are known to cause impacts on climate, health and on vegetation. Toluene was found to be the most abundant VOC among the measured ones in the atmosphere of Dehradun. The maximum mean concentration of VOCs was observed in winters and lowest during summers for BE species. Toluene ambient concentration was rather found to register highest during winters and lowest in monsoons. Kruskal–Wallis test showed statistically significant differences seasonally (p?<?0.05). High toluene to benzene T/B (>1) observed ratio indicates vehicular emission as their major source. BTEX were also evaluated for their ozone-forming potential (OFP). Toluene and xylenes were found as the highest contributing hydrocarbons towards ozone forming potential among BTXE. 相似文献
993.
Trends in dietary fiber intake in Japan over the last century 总被引:5,自引:0,他引:5
Nakaji S Sugawara K Saito D Yoshioka Y MacAuley D Bradley T Kernohan G Baxter D 《European journal of nutrition》2002,41(5):222-227
Summary. Background: Insufficient intake of dietary fiber (DF) is currently a major problem in the overall promotion of health in the general
population in Japan. Aim of the study: To analyze the time trends in DF intake, including DF density (total DF intake/1,000 kcal), and the ratio of water-insoluble
fiber to water-soluble fiber (IS ratio) in Japan. Methods: The time trend in DF intake in Japan was calculated from data compiled in the Japanese National Nutrition Survey. Results: The mean daily DF intake (total DF intake) in 1952 was 20.5 g/day, which rapidly declined to about 70 % of the 1952 level
in 1970, after which there was little change to 1998. DF density in 1952 was 9.7 g/1000 kcal, which declined by about 30 %
in 1970, and remained at about the same level to 1998. The IS ratio has remained stable over this period. Whereas total DF
intake and DF density in Japan are similar to those in Western countries, the IS ratios are higher in Japan. Therefore, the
higher incidence of, and mortality from, colon diverticulosis, coronary heart disease, hyperlipidemia, etc., which are all
thought to be related to fiber deficiency, in Western countries compared to Japan might be due to the differences in the IS
ratio. Conclusions: A decline in total DF intake and DF density is predicted for Japan in the future, because these parameters were lower among
the younger generation. This may be due to the marked changes in the dietary habits of the younger generation, and is a problematic
trend for Japanese health.
Received: 26 April 2002, Accepted: 22 August 2002
Correspondence to: Shigeyuki Nakaji, MD, PhD 相似文献
994.
Raul Zamora-Ros Valerie Cayssials Mazda Jenab Joseph A. Rothwell Veronika Fedirko Krasimira Aleksandrova Anne Tjønneland Cecilie Kyrø Kim Overvad Marie-Christine Boutron-Ruault Franck Carbonnel Yahya Mahamat-Saleh Rudolf Kaaks Tilman Kühn Heiner Boeing Antonia Trichopoulou Elissavet Valanou Effie Vasilopoulou Giovanna Masala Valeria Pala Salvatore Panico Rosario Tumino Fulvio Ricceri Elisabete Weiderpass Torkjel M. Sandanger Cristina Lasheras Antonio Agudo Maria-Jose Sánchez Pilar Amiano Carmen Navarro Eva Ardanaz Emily Sonestedt Bodil Ohlsson Lena Maria Nilsson Martin Rutegård Bas Bueno-de-Mesquita Kay-Thee Khaw Nicholas J. Wareham Kathryn Bradbury Heinz Freisling Isabelle Romieu Amanda J. Cross Paolo Vineis Augustin Scalbert 《European journal of epidemiology》2018,33(11):1063-1075
Polyphenols may play a chemopreventive role in colorectal cancer (CRC); however, epidemiological evidence supporting a role for intake of individual polyphenol classes, other than flavonoids is insufficient. We evaluated the association between dietary intakes of total and individual classes and subclasses of polyphenols and CRC risk and its main subsites, colon and rectum, within the European Prospective Investigation into Cancer and Nutrition (EPIC) study. The cohort included 476,160 men and women from 10 European countries. During a mean follow-up of 14 years, there were 5991 incident CRC cases, of which 3897 were in the colon and 2094 were in the rectum. Polyphenol intake was estimated using validated centre/country specific dietary questionnaires and the Phenol-Explorer database. In multivariable-adjusted Cox regression models, a doubling in total dietary polyphenol intake was not associated with CRC risk in women (HRlog2?=?1.06, 95% CI 0.99–1.14) or in men (HRlog2?=?0.97, 95% CI 0.90–1.05), respectively. Phenolic acid intake, highly correlated with coffee consumption, was inversely associated with colon cancer in men (HRlog2?=?0.91, 95% CI 0.85–0.97) and positively associated with rectal cancer in women (HRlog2?=?1.10, 95% CI 1.02–1.19); although associations did not exceed the Bonferroni threshold for significance. Intake of other polyphenol classes was not related to colorectal, colon or rectal cancer risks. Our study suggests a possible inverse association between phenolic acid intake and colon cancer risk in men and positive with rectal cancer risk in women. 相似文献
995.
How Many Imputations are Really Needed? Some Practical Clarifications of Multiple Imputation Theory 总被引:1,自引:0,他引:1
Multiple imputation (MI) and full information maximum likelihood (FIML) are the two most common approaches to missing data
analysis. In theory, MI and FIML are equivalent when identical models are tested using the same variables, and when m, the number of imputations performed with MI, approaches infinity. However, it is important to know how many imputations
are necessary before MI and FIML are sufficiently equivalent in ways that are important to prevention scientists. MI theory
suggests that small values of m, even on the order of three to five imputations, yield excellent results. Previous guidelines for sufficient m are based on relative efficiency, which involves the fraction of missing information (γ) for the parameter being estimated, and m. In the present study, we used a Monte Carlo simulation to test MI models across several scenarios in which γ and m were varied. Standard errors and p-values for the regression coefficient of interest varied as a function of m, but not at the same rate as relative efficiency. Most importantly, statistical power for small effect sizes diminished as
m became smaller, and the rate of this power falloff was much greater than predicted by changes in relative efficiency. Based
our findings, we recommend that researchers using MI should perform many more imputations than previously considered sufficient.
These recommendations are based on γ, and take into consideration one’s tolerance for a preventable power falloff (compared to FIML) due to using too few imputations. 相似文献
996.
Halileh S Abu-Rmeileh N Watt G Spencer N Gordon N 《Maternal and child health journal》2008,12(5):606-612
The objective of this cross sectional study is to look at determinants of birth weight and their association with the gender
of the baby in 2,795 full term children living in the occupied Palestinian territory, derived from a stratified random sample
of 2,994 households in the West Bank and 2,234 households in the Gaza Strip. The response rate was 85%. Multivariable analysis
using analysis of variance for mixed models showed that sex and birth order, maternal age and education and to a lesser extent
region were determinants of birth weight for all children. The effect of maternal education on birth weight differed for female
and male infants, tending to be relatively unchanged for male infants and with mean birth weights increasing with maternal
education in female infants. The effect of birth order differed by maternal age, with mean birth weight increasing with maternal
age for first and second births; but being unaffected by maternal age for infants of birth order greater than two. We conclude
that birth weight is influenced by common biological determinants across cultures, but is also influenced by social, ethnic,
and environmental factors that are culture specific, of which some might be gender related.
相似文献
Samia HalilehEmail: |
997.
Su M Liu M Tian DP Li XY Zhang GH Yang HL Fan X Huang HH Gao YX 《European journal of epidemiology》2007,22(1):43-48
The purpose of our study was to investigate the temporal malignant tumor incidence rates among the 70,000 residents at the
relatively isolated Nanao Island in South China Sea. The data on all malignant tumor cases from Nanao Cancer Registry during
1995–2004 were coded, computerized, and analyzed using the software SPSS10.0. The tumor incident cases, crude incident rate,
age-standardized incidence rate, their sex distribution and temporal trend were assessed. A total of 1450 new cancer cases
(990 males and 460 females) were identified. The annual average age-standardized incidence rate (ASR) of malignant tumors
was 208.18/100,000. The age-standardized incidence rate of the ten leading cancers in both sexes combined per 100,000 population
were 74.47 for esophageal cancer (EC), 34.81 for cardiac cancer (CC), 25.66 for liver cancer, 26.01 for lung cancer, 18.52
for stomach cancer, 4.45 for nasopharyngeal cancer, 3.91 for breast cancer, 2.53 for colon/rectum cancer, 2.45 for bladder
cancer and 1.92 for pancreatic cancer. These ten types of cancers make up to 93% of all cancer cases, with EC and CC being
the most prevalent and making up 52% of the total cases. The incidence rates of esophagus, liver, lung, breast, nasopharyngeal,
and colon/rectum cancers showed increasing trends during the period from 1995 to 2004 in Nanao Island. Astounding the EC ASR
were 72–150/100,000 among male and 26–64/100,000 among female in Nanao Island during 1995–2004. The EC incidence rate in Nanao
population is among the highest across the world, which suggests that there are potential genetic and/or environmental factors
affecting this particular population. 相似文献
998.
Annaheim B Rehm J Neuenschwander M Gmel G 《International journal of public health》2007,52(4):233-241
Summary Quitting hash. The readiness for behaviour change among cannabis users in Switzerland.
Objectives: The study aims to identify factors that are associated with the willingness of adolescents and young adults to modify their
cannabis use. It is hypothesized that frequency of use, cannabis-related problems and age of onset are associated with their
willingness to change.
Methods: In 2004, a survey on cannabis use was conducted among 13 to 29 year-olds living in Switzerland. Of the 5025 participants 593
had taken cannabis during the past six months. They were then asked about their willingness to change. Three groups of users
were compared: those not willing to change, those considering change, and those determined to change. Pearson Chi-square-tests
and logistic regressions were performed to test the hypotheses.
Results: Experience of problems motivates users to start thinking about changing their behavior. Frequent use and early onset are associated
with young people not making the transition from considering changing behavior to resolving to do so.
Conclusions: The need to perceive problematic use as a first step towards change and the inhibiting effect of dependencerelated factors
on the transition from consideration to determination calls for tailored intervention approaches that are matched to the willingness
to change.
Eingereicht: 10. Dezember 2005; überarbeitet: 13. September 2006; Angenommen: 6. M?rz 2007 相似文献
999.
1000.
Feng Xie Shu-Chuen Li Ron Goeree Jean-Eric Tarride Daria O’Reilly Ngai-Nung Lo Seng-Jin Yeo Kuang-Ying Yang Julian Thumboo 《Quality of life research》2008,17(4):595-601
Objective Our aim was to cross-culturally validate Chinese Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) in
patients with knee osteoarthritis (OA) scheduled for total knee replacement in Singapore.
Methods Chinese WOMAC was translated from the original English version following standard guidelines. Patients were asked to complete
a questionnaire containing the WOMAC (twice within 6 days), the Short Form 36 (SF-36), and the EuroQoL EQ-5D. Reliability
was assessed using Cronbach’s alpha and intraclass correlation coefficients (ICC), dimensionality using item-to-domain correlations
and factor analyses. Convergent and discriminant construct validity was assessed using six each a priori hypotheses.
Results Chinese WOMAC was well accepted by the patients in the pilot test. The Chinese and English versions were therefore administered
to a consecutive sample of 131 Chinese- and 127 English-speaking subjects, respectively, with knee OA. Cronbach’s alpha exceeded
0.7 for all domains except for Chinese pain domain, whereas the ICC exceeded 0.7 for all domains. Hypothesized item-to-domain
correlations were observed for all items except for four items in Chinese physical function domain. The factor analyses yielded
seven and five factors with eigenvalues of more than 1.0 in the Chinese and English versions, respectively. A total of 10/12
a priori construct validity hypotheses were satisfied for the Chinese version. Weak correlations between WOMAC pain and SF-36
bodily pain and moderate correlation between WOMAC pain and EQ-5D anxiety/depression were observed.
Conclusions Chinese WOMAC was well accepted and demonstrated acceptable psychometric properties in Singaporean patients with severe knee
OA. 相似文献