全文获取类型
收费全文 | 15444篇 |
免费 | 1804篇 |
出版年
2021年 | 168篇 |
2018年 | 172篇 |
2017年 | 133篇 |
2016年 | 280篇 |
2015年 | 371篇 |
2014年 | 426篇 |
2013年 | 552篇 |
2012年 | 665篇 |
2011年 | 644篇 |
2010年 | 490篇 |
2009年 | 463篇 |
2008年 | 632篇 |
2007年 | 656篇 |
2006年 | 545篇 |
2005年 | 569篇 |
2004年 | 548篇 |
2003年 | 546篇 |
2002年 | 466篇 |
2001年 | 425篇 |
2000年 | 431篇 |
1999年 | 382篇 |
1998年 | 175篇 |
1997年 | 184篇 |
1996年 | 171篇 |
1995年 | 146篇 |
1994年 | 177篇 |
1993年 | 141篇 |
1992年 | 351篇 |
1991年 | 339篇 |
1990年 | 341篇 |
1989年 | 295篇 |
1988年 | 296篇 |
1987年 | 268篇 |
1986年 | 251篇 |
1985年 | 271篇 |
1984年 | 258篇 |
1983年 | 261篇 |
1982年 | 207篇 |
1981年 | 152篇 |
1980年 | 167篇 |
1979年 | 229篇 |
1978年 | 201篇 |
1977年 | 183篇 |
1976年 | 178篇 |
1975年 | 173篇 |
1974年 | 182篇 |
1973年 | 177篇 |
1972年 | 160篇 |
1971年 | 143篇 |
1970年 | 128篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Christopher Williams Philip Wilson Jill Morrison Alex McMahon Walker Andrew Lesley Allan Alex McConnachie Yvonne McNeill Louise Tansey 《PloS one》2013,8(1)
Background
Access to Cognitive behavioural therapy (CBT) for depression is limited. One solution is CBT self-help books. Trial Objectives: To assess the impact of a guided self-help CBT book (GSH-CBT) on mood, compared to treatment as usual (TAU).Hypotheses:- GSH-CBT will have improved mood and knowledge of the causes and treatment of depression compared to the control receiving TAU
- Guided self-help will be acceptable to patients and staff.
Methods and Findings
Participants: Adults attending seven general practices in Glasgow, UK with a BDI-II score of ≥14. 141 randomised to GSH-CBT and 140 to TAU. Interventions: RCT comparing ‘Overcoming Depression: A Five Areas Approach’ book plus 3–4 short face to face support appointments totalling up to 2 hours of guided support, compared with general practitioner TAU. Primary outcome: The BDI (II) score at 4 months. Numbers analysed: 281 at baseline, 203 at 4 months (primary outcome), 117 at 12 months. Outcome: Mean BDI-II scores were lower in the GSH-CBT group at 4 months by 5.3 points (2.6 to 7.9, p<0.001). At 4 and 12 months there were also significantly higher proportions of participants achieving a 50% reduction in BDI-II in the GSH-CBT arm. The mean support was 2 sessions with 42.7 minutes for session 1, 41.4 minutes for session 2 and 40.2 minutes of support for session 3. Adverse effects/Harms: Significantly less deterioration in mood in GSH-CBT (2.0% compared to 9.8% in the TAU group for BDI—II category change).Limitations
Weaknesses: Our follow-up rate of 72.2% at 4 months is better than predicted but is poorer at 12 months (41.6%). In the GSH-CBT arm, around 50% of people attended 2 or fewer sessions. 22% failed to take up treatment.Conclusions
GSH-CBT is substantially more effective than TAU.Trial Registration
Controlled-Trials.com ISRCTN13475030 相似文献992.
Jiang Gui Jason H. Moore Scott M. Williams Peter Andrews Hans L. Hillege Pim van der Harst Gerjan Navis Wiek H. Van Gilst Folkert W. Asselbergs Diane Gilbert-Diamond 《PloS one》2013,8(6)
We present an extension of the two-class multifactor dimensionality reduction (MDR) algorithm that enables detection and characterization of epistatic SNP-SNP interactions in the context of a quantitative trait. The proposed Quantitative MDR (QMDR) method handles continuous data by modifying MDR’s constructive induction algorithm to use a T-test. QMDR replaces the balanced accuracy metric with a T-test statistic as the score to determine the best interaction model. We used a simulation to identify the empirical distribution of QMDR’s testing score. We then applied QMDR to genetic data from the ongoing prospective Prevention of Renal and Vascular End-Stage Disease (PREVEND) study. 相似文献
993.
Rachel B. Slayton George Turabelidze Sarah D. Bennett Colin A. Schwensohn Anna Q. Yaffee Faisal Khan Cindy Butler Eija Trees Tracy L. Ayers Marjorie L. Davis Alison S. Laufer Stephen Gladbach Ian Williams Laura B. Gieraltowski 《PloS one》2013,8(2)
Background
Shiga toxin-producing Escherichia coli (STEC) O157:H7 is the causal agent for more than 96,000 cases of diarrheal illness and 3,200 infection-attributable hospitalizations annually in the United States.Materials and Methods
We defined a confirmed case as a compatible illness in a person with the outbreak strain during 10/07/2011-11/30/2011. Investigation included hypothesis generation, a case-control study utilizing geographically-matched controls, and a case series investigation. Environmental inspections and tracebacks were conducted.Results
We identified 58 cases in 10 states; 67% were hospitalized and 6.4% developed hemolytic uremic syndrome. Any romaine consumption was significantly associated with illness (matched Odds Ratio (mOR) = 10.0, 95% Confidence Interval (CI) = 2.1–97.0). Grocery Store Chain A salad bar was significantly associated with illness (mOR = 18.9, 95% CI = 4.5–176.8). Two separate traceback investigations for romaine lettuce converged on Farm A. Case series results indicate that cases (64.9%) were more likely than the FoodNet population (47%) to eat romaine lettuce (p-value = 0.013); 61.3% of cases reported consuming romaine lettuce from the Grocery Store Chain A salad bar.Conclusions
This multistate outbreak of STEC O157:H7 infections was associated with consumption of romaine lettuce. Traceback analysis determined that a single common lot of romaine lettuce harvested from Farm A was used to supply Grocery Store Chain A and a university campus linked to a case with the outbreak strain. An investigation at Farm A did not identify the source of contamination. Improved ability to trace produce from the growing fields to the point of consumption will allow more timely prevention and control measures to be implemented. 相似文献994.
Observing organisms that evolve in response to strong selection over very short time scales allows the determination of the molecular mechanisms underlying adaptation. Although dissecting these molecular mechanisms is expensive and time-consuming, general patterns can be detected from repeated experiments, illuminating the biological processes involved in evolutionary adaptation. The bacteriophage φX174 was grown for 50 days in replicate chemostats under two culture conditions: Escherichia coli C as host growing at 37°C and Salmonella typhimurium as host growing at 43.5°C. After 50 days, greater than 20 substitutions per chemostat had risen to detectable levels. Of the 97 substitutions, four occurred in all four chemostats, five arose in both culture conditions, eight arose in only the high temperature S. typhimurium chemostats, and seven arose only in the E. coli chemostats. The remaining substitutions were detected only in a single chemostat, however, almost half of these have been seen in other similar experiments. Our findings support previous studies that host recognition and capsid stability are two biological processes that are modified during adaptation to novel hosts and high temperature. Based upon the substitutions shared across both environments, it is apparent that genome replication and packaging are also affected during adaptation to the chemostat environment, rather than to temperature or host per se. This environment is characterized by a large number of phage and very few hosts, leading to competition among phage within the host. We conclude from these results that adaptation to a high density environment selects for changes in genome replication at both protein and DNA sequence levels. 相似文献
995.
Djesika D. Amendah George Mukamah Albert Komba Carolyne Ndila Thomas N. Williams 《PloS one》2013,8(4)
Background
More than 70% of children with sickle cell disease (SCD) are born in sub-Saharan Africa where the prevalence at birth of this disease reaches 2% or higher in some selected areas. There is a dearth of knowledge on comprehensive care received by children with SCD in sub-Saharan Africa and its associated cost. Such knowledge is important for setting prevention and treatment priorities at national and international levels. This study focuses on routine care for children with SCD in an outpatient clinic of the Kilifi District Hospital, located in a rural area on the coast of Kenya.Objective
To estimate the per-patient costs for routine SCD outpatient care at a rural Kenyan hospital.Methods
We collected routine administrative and primary cost data from the SCD outpatient clinic and supporting departments at Kilifi District Hospital, Kenya. Costs were estimated by evaluating inputs - equipment, medication, supplies, building use, utility, and personnel - to reflect the cost of offering this service within an existing healthcare facility. Annual economic costs were similarly calculated based on input costs, prorated lifetime of equipment and appropriate discount rate. Sensitivity analyses evaluated these costs under different pay scales and different discount rate.Results
We estimated that the annual economic cost per patient attending the SCD clinic was USD 138 in 2010 with a range of USD 94 to USD 229.Conclusion
This study supplies the first published estimate of the cost of routine outpatient care for children born with SCD in sub-Saharan Africa. Our study provides policy makers with an indication of the potential future costs of maintaining specialist outpatient clinics for children living with SCD in similar contexts. 相似文献996.
997.
998.
999.
Xuefeng Wang Ping Ji Yuanhao Zhang Joseph F. LaComb Xinyu Tian Ellen Li Jennie L. Williams 《PloS one》2016,11(4)
BackgroundIncidence and mortality rates of colorectal carcinoma (CRC) are higher in African Americans (AAs) than in Caucasian Americans (CAs). Deficient micronutrient intake due to dietary restrictions in racial/ethnic populations can alter genetic and molecular profiles leading to dysregulated methylation patterns and the inheritance of somatic to germline mutations.ResultsDNA from the tumor of AA CRC patients, compared to adjacent normal tissues, contained 1,588 hypermethylated and 100 hypomethylated differentially methylated regions (DMRs). Whereas, 109 hypermethylated and 4 hypomethylated DMRs were observed in DNA from the tumor of CA CRC patients; representing a 14.6-fold and 25-fold change, respectively. Specifically; CHL1, 4 anti-inflammatory genes (i.e., NELL1, GDF1, ARHGEF4, and ITGA4), and 7 miRNAs (of which miR-9-3p and miR-124-3p have been implicated in CRC) were hypermethylated in DNA samples from AA patients with CRC. From the same sample set, RNAseq analysis revealed 108 downregulated genes (including 14 ribosomal proteins) and 34 upregulated genes (including POLR2B and CYP1B1 [targets of miR-124-3p]) in AA patients with CRC versus CA patients.ConclusionDNA methylation profile and/or products of its downstream targets could serve as biomarker(s) addressing racial health disparity. 相似文献
1000.
Rebecca S. Williams Jana H. Stollings ?ucja Bundy Regine Haard?rfer Matthew W. Kreuter Patricia Dolan Mullen Mel Hovell Marti Morris Michelle C. Kegler 《PloS one》2016,11(11)
This study examined the extent to which delivery of the minimal Smoke-Free Homes intervention by trained 2-1-1 information and referral specialists had an effect on the adoption of home smoking bans in low-income households. A randomized controlled trial was conducted among 2-1-1 callers (n = 500) assigned to control or intervention conditions. 2-1-1 information and referral specialists collected baseline data and delivered the intervention consisting of 3 mailings and 1 coaching call; university-based data collectors conducted follow-up interviews at 3 and 6 months post-baseline. Data were collected from June 2013 through July 2014. Participants were mostly female (87.2%), African American (61.4%), and smokers (76.6%). Participants assigned to the intervention condition were more likely than controls to report a full ban on smoking in the home at both 3- (38.1% vs 19.3%, p = < .001) and 6-month follow-up (43.2% vs 33.2%, p = .02). The longitudinal intent-to-treat analysis showed a significant intervention effect over time (OR = 1.31, p = .001), i.e. OR = 1.72 at 6 months. This study replicates prior findings showing the effectiveness of the minimal intervention to promote smoke-free homes in low-income households, and extends those findings by demonstrating they can be achieved when 2-1-1 information and referral specialists deliver the intervention. Findings offer support for this intervention as a generalizable and scalable model for reducing secondhand smoke exposure in homes. 相似文献