全文获取类型
收费全文 | 2690篇 |
免费 | 228篇 |
国内免费 | 15篇 |
专业分类
耳鼻咽喉 | 25篇 |
儿科学 | 179篇 |
妇产科学 | 185篇 |
基础医学 | 342篇 |
口腔科学 | 94篇 |
临床医学 | 288篇 |
内科学 | 462篇 |
皮肤病学 | 18篇 |
神经病学 | 143篇 |
特种医学 | 117篇 |
外科学 | 275篇 |
综合类 | 76篇 |
一般理论 | 3篇 |
预防医学 | 440篇 |
眼科学 | 12篇 |
药学 | 215篇 |
肿瘤学 | 59篇 |
出版年
2021年 | 34篇 |
2020年 | 22篇 |
2019年 | 27篇 |
2018年 | 36篇 |
2017年 | 32篇 |
2016年 | 38篇 |
2015年 | 47篇 |
2014年 | 52篇 |
2013年 | 93篇 |
2012年 | 95篇 |
2011年 | 109篇 |
2010年 | 70篇 |
2009年 | 72篇 |
2008年 | 120篇 |
2007年 | 120篇 |
2006年 | 110篇 |
2005年 | 109篇 |
2004年 | 129篇 |
2003年 | 113篇 |
2002年 | 88篇 |
2001年 | 101篇 |
2000年 | 100篇 |
1999年 | 78篇 |
1998年 | 30篇 |
1997年 | 43篇 |
1996年 | 38篇 |
1995年 | 33篇 |
1994年 | 33篇 |
1993年 | 22篇 |
1992年 | 53篇 |
1991年 | 51篇 |
1990年 | 55篇 |
1989年 | 53篇 |
1988年 | 59篇 |
1987年 | 48篇 |
1986年 | 51篇 |
1985年 | 51篇 |
1984年 | 46篇 |
1983年 | 30篇 |
1982年 | 25篇 |
1981年 | 21篇 |
1979年 | 35篇 |
1978年 | 26篇 |
1976年 | 28篇 |
1975年 | 19篇 |
1973年 | 21篇 |
1972年 | 23篇 |
1970年 | 22篇 |
1969年 | 28篇 |
1968年 | 19篇 |
排序方式: 共有2933条查询结果,搜索用时 15 毫秒
41.
In an earlier study it was reported that oxytocin was able to block the antimetamorphic action of prolactin (PRL) in larval tiger salamanders, Ambystoma tigrinum (Platt and LiCause, 1980). In this study, we have examined the effects of lysine vasopressin (LVP), arginine vasotocin (AVT), and aldosterone on induced metamorphosis in larval A. tigrinum and on the inhibition of this process by PRL. Both LVP and AVT were found to interfere with the inhibition of gill resorption, tail fin regression, and body weight loss by PRL. An anti-PRL effect of aldosterone was observed but appeared to be limited to the gill. AVT alone had a significant acceleratory effect on body weight loss during metamorphosis. A “water balance” response was observed in only one case. Twenty-four hours after treatment with LVP and PRL, this group of animals did show a significant increase in body weight. These results are discussed with regard to the problem posed by neurohypophysial hormone contamination of PRL preparations and in context with our hypothesis that the antimetamorphic action of PRL is at least partially osmoregulatory in nature. 相似文献
42.
Both neonatal maturity and postnatal maturation are known to be species dependent. For instance, guinea pigs are born with their eyes open, while eye opening takes place 2 weeks after birth in rats. Moreover, several abnormalities have been observed in albino compared to pigmented species. The pigment melanin is proposed to play a protective role and its absence is thought to contribute to neuronal deficits. In the present study, we aimed to investigate functional differences in synaptic transmission in the visual, superficial layers of the superior colliculus (SC) of albino and pigmented rats and pigmented guinea pigs, at eye opening and 1 month after birth. This was achieved by analysing evoked field excitatory postsynaptic potentials (fEPSPs) in vitro, and by investigating the ability of these responses to express gamma-aminobutyric acid (GABA)-induced long-term potentiation (LTPG), an enduring increase in synaptic efficacy resulting from bath application of GABA. Guinea pigs did not show any obvious differences with respect to overall fEPSP characteristics and synaptic plasticity at both ages studied, indicating that maturation must have occurred prenatally. Rats, however, underwent synaptic maturation and refinement to produce stronger fEPSPs and a more robust level of synaptic plasticity 1 month after birth compared to the conditions at eye opening. The state of pigmentation was found to have a crucial influence, with albino rats showing less enhancement of the strength of synaptic transmission in the SC. It can therefore be concluded that profound developmental differences in pre- and postnatal maturation of the superficial SC exist between guinea pigs and rats, and that the state of pigmentation is a crucial factor in this process. 相似文献
43.
Anita Koushik Robert W Platt Eduardo L Franco 《Cancer epidemiology, biomarkers & prevention》2004,13(1):11-22
The Arg/Arg genotype versus Arg/Pro or Pro/Pro at codon 72 of the p53 gene has been implicated as a risk marker in cervical neoplasia. However, research on this topic has produced controversial results. We reviewed the published literature to summarize the association and to identify methodological features that may have contributed to the heterogeneity. Information on specific methodological features of studies addressing this topic published between 1998 and 2002 were obtained. Study-specific odds ratios (ORs) were combined in a meta-analysis, assuming random effects. To identify characteristics that significantly contributed to heterogeneity, we used meta-regression analysis. We identified 50 articles, of which 45 were included in the meta-analyses and regressions. No evidence of association or heterogeneity was detected for preinvasive lesions. For invasive cervical cancer with undefined histology, the Arg/Arg genotype was not found to affect risk (OR, 1.1; 95% confidence interval (CI), 0.9-1.3). However, a slightly increased risk was observed for squamous cell carcinoma (OR, 1.5; 95% CI, 1.2-1.9) and adenocarcinoma (OR, 1.7; 95% CI, 1.0-2.7). Meta-regression analysis identified that the most important factor contributing to heterogeneity among results for invasive lesions was departures from Hardy-Weinberg equilibrium in the control group. Summary ORs for studies in equilibrium were essentially null. A possible susceptibility role by the p53 codon 72 polymorphism at a late carcinogenetic stage in cervical cancer cannot be ruled out. However, various methodological features can contribute to departures from Hardy-Weinberg equilibrium and consequently to less than ideal circumstances for the examination of this polymorphism. Future investigations require appropriate attention to design and methodological issues. 相似文献
44.
45.
Platt JL 《Transplantation proceedings》2000,32(7):1547-1548
46.
47.
Smalley W Shatin D Wysowski DK Gurwitz J Andrade SE Goodman M Chan KA Platt R Schech SD Ray WA 《JAMA》2000,284(23):3036-3039
Context Cisapride, a gastrointestinal tract promotility agent, can cause life-threatening cardiac arrhythmias in patients susceptible either because of concurrent use of medications that interfere with cisapride metabolism or prolong the QT interval or because of the presence of other diseases that predispose to such arrhythmias. In June 1998, the US Food and Drug Administration (FDA) determined that use of cisapride was contraindicated in such patients and informed practitioners through additions to the boxed warning in the label and a "Dear Health Care Professional" letter sent by the drug's manufacturer. Objective To evaluate the impact of the FDA's 1998 regulatory action regarding contraindicated use of cisapride. Design and Setting Analysis of data for the 1-year periods before (July 1997-June 1998) and after (July 1998-June 1999) the regulatory action from the population-based, pharmacoepidemiology research databases of 2 managed care organizations (sites A and B) and a state Medicaid program (site C). Participants Patients with at least 180 days of prior enrollment in 1 of the 3 sites who were prescribed cisapride at least once in the period before (n = 24 840) or after (n = 22 459) regulatory action. Patients could be included in both cohorts. Main Outcome Measures Proportion of cisapride users in each period for whom cisapride use was contraindicated by the product label, based on computerized patient medical encounter records. Results In the year prior to regulatory action, cisapride use was contraindicated for 26%, 30%, and 60% of users in study sites A, B, and C, respectively. In the year after regulatory action, use was contraindicated for 24%, 28%, and 58% of users, a reduction in contraindicated use of approximately 2 per 100 cisapride users at each site. When the analysis was restricted to new users of cisapride after regulatory action, only minor reductions in contraindicated use were found. Conclusion The FDA's 1998 regulatory action regarding cisapride use had no material effect on contraindicated cisapride use. More effective ways to communicate new information about drug safety are needed. 相似文献
48.
CONTEXT: The World Health Organization defines preterm birth as birth at less than 37 completed gestational weeks, but most studies have focused on very preterm infants (birth at <32 weeks) because of their high risk of mortality and serious morbidity. However, infants born at 32 through 36 weeks are more common and their public health impact has not been well studied. OBJECTIVE: To assess the quantitative contribution of mild (birth at 34-36 gestational weeks) and moderate (birth at 32-33 gestational weeks) preterm birth to infant mortality. DESIGN, SETTING, AND PARTICIPANTS: Population-based cohort study using linked singleton live birth-infant death cohort files for US birth cohorts for 1985 and 1995 and Canadian birth cohorts (excluding Ontario) for 1985-1987 and 1992-1994. MAIN OUTCOME MEASURES: Relative risks (RRs) and etiologic fractions (EFs) for overall and cause-specific early neonatal (age 0-6 days), late neonatal (age 7-27 days), postneonatal (age 28-364 days), and total infant death among mild and moderate preterm births vs term births (at >/=37 gestational weeks). RESULTS: Relative risks for infant death from all causes among singletons born at 32 through 33 gestational weeks were 6.6 (95% confidence interval [CI], 6.1-7.0) in the United States in 1995 and 15.2 (95% CI, 13.2-17.5) in Canada in 1992-1994; among singletons born at 34 through 36 gestational weeks, the RRs were 2.9 (95% CI, 2.8-3.0) and 4.5 (95% CI, 4.0-5.0), respectively. Corresponding EFs were 3.2% and 4.8%, respectively, at 32 through 33 gestational weeks and 6.3% and 8.0%, respectively, at 34 through 36 gestational weeks; the sum of the EFs for births at 32 through 33 and 34 through 36 gestational weeks exceeded those for births at 28 through 31 gestational weeks. Substantial RRs were observed overall for the neonatal (eg, for early neonatal deaths, 14.6 and 33.0 for US and Canadian infants, respectively, born at 32-33 gestational weeks; EFs, 3.6% and and 6. 2% for US and Canadian infants, respectively) and postneonatal (RRs, 2.1-3.8 and 3.0-7.0 for US and Canadian infants, respectively, born at 32-36 gestational weeks; EFs, 2.7%-5.8% and 3.0%-7.0% for the same groups, respectively) periods and for death due to asphyxia, infection, sudden infant death syndrome, and external causes. Except for a reduction in the RR and EF for neonatal mortality due to infection, the patterns have changed little since 1985 in either country. CONCLUSIONS: Mild- and moderate-preterm birth infants are at high RR for death during infancy and are responsible for an important fraction of infant deaths. JAMA. 2000;284:843-849 相似文献
49.
Characterization of xenobiotic-metabolizing enzymes and nitrosamine metabolism in the human esophagus 总被引:5,自引:2,他引:5
Smith TJ; Liao A; Wang LD; Yang GY; Starcic S; Philbert MA; Yang CS 《Carcinogenesis》1998,19(4):667-672
Esophageal cancer has been associated with tobacco smoking, and
nitrosamines are possible causative agents for this cancer. The present
study investigated the metabolism of the tobacco carcinogens N'-
nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone
(NNK), and N-nitrosodimethylamine (NDMA), as well as the presence of
xenobiotic-metabolizing enzymes in human esophageal tissues from
individuals in the United States and Huixian, Henan Province, China (a
high-risk area for esophageal cancer). All esophageal microsomal samples
activated NNN and the metabolic rate was 2-fold higher in the esophageal
samples from China than the USA. All microsomal samples activated NDMA.
However, most of the microsomal samples did not activate NNK.
Troleandomycin (an inhibitor of cytochrome P450 3A) decreased the formation
of NNN-derived keto acid by 20-26% in the esophageal microsomes. The
activities for NADPH: cytochrome c reductase, ethoxycoumarin O-deethylase,
NAD(P)H: quinone oxidoreductase and glutathione S-transferase were present
in the esophageal samples. Coumarin 7-hydroxylase (a representative
activity for P450 2A6) activity was not detected in the esophageal
microsomal samples. The activities for nitrosamine metabolism and
xenobiotic- metabolizing enzymes were decreased (by 30-50%) in the squamous
cell carcinomas compared with their corresponding non-cancerous mucosa. The
presence of activation and detoxification enzymes in the esophagus may play
an important role in determining the susceptibility of the esophagus to the
carcinogenic effect of nitrosamines. Our results suggest that P450s 3A4 and
2E1 are involved in the activation of NNN and NDMA, respectively, in the
human esophagus.
相似文献
50.
Andrew L Miner Elena Losina Jeffrey N Katz Anne H Fossel Richard Platt 《Infection control and hospital epidemiology》2005,26(12):910-915
OBJECTIVE: To describe the use of laminar airflow, body exhaust, and ultraviolet lights during total knee replacement (TKR) in four U.S. states. DESIGN: Survey of healthcare facilities. SETTING: Hospitals in Illinois, North Carolina, Ohio, and Tennessee that performed TKR during 2000 as identified by Medicare claims data. PARTICIPANTS: Hospitals responding to a mailed questionnaire. RESULTS: Two hundred ninety-five (73%) of 405 eligible hospitals that performed 18,374 primary and revision TKR procedures responded to the questionnaire. Among responding hospitals, 30% reported regular use (for > 75% of procedures) of laminar airflow, 42% reported regular use of body exhaust, and 5% reported regular use of ultraviolet lights. Among hospitals providing complete data, 150 (58%) performing 66% of procedures reported regular use of at least one of these techniques. On regression analyses, laminar airflow was used more often by hospitals with a TKR volume greater than 25 procedures per year (odds ratio [OR], 2.0; 95% confidence interval [CI95], 1.1-3.7) and orthopedic residency programs (OR, 2.8; CI95, 1.3-6.3), but its use was not significantly related to hospital setting or ownership status. CONCLUSIONS: Although these clean air practices are not recommended by any U.S. governmental or professional organization, they are used in nearly two-thirds of TKR procedures. Better information about their impact on current practice and more explicit guidelines may aid decisions about the use of these resource-intensive infection control practices. 相似文献