全文获取类型
收费全文 | 5014篇 |
免费 | 390篇 |
国内免费 | 10篇 |
专业分类
耳鼻咽喉 | 54篇 |
儿科学 | 191篇 |
妇产科学 | 124篇 |
基础医学 | 540篇 |
口腔科学 | 137篇 |
临床医学 | 682篇 |
内科学 | 915篇 |
皮肤病学 | 35篇 |
神经病学 | 286篇 |
特种医学 | 372篇 |
外科学 | 534篇 |
综合类 | 132篇 |
一般理论 | 2篇 |
预防医学 | 505篇 |
眼科学 | 179篇 |
药学 | 399篇 |
中国医学 | 28篇 |
肿瘤学 | 299篇 |
出版年
2021年 | 71篇 |
2020年 | 51篇 |
2019年 | 54篇 |
2018年 | 76篇 |
2017年 | 71篇 |
2016年 | 57篇 |
2015年 | 71篇 |
2014年 | 119篇 |
2013年 | 154篇 |
2012年 | 212篇 |
2011年 | 226篇 |
2010年 | 149篇 |
2009年 | 126篇 |
2008年 | 189篇 |
2007年 | 226篇 |
2006年 | 200篇 |
2005年 | 185篇 |
2004年 | 173篇 |
2003年 | 191篇 |
2002年 | 179篇 |
2001年 | 147篇 |
2000年 | 138篇 |
1999年 | 121篇 |
1998年 | 97篇 |
1997年 | 74篇 |
1996年 | 73篇 |
1995年 | 60篇 |
1994年 | 64篇 |
1993年 | 57篇 |
1992年 | 95篇 |
1991年 | 135篇 |
1990年 | 111篇 |
1989年 | 135篇 |
1988年 | 102篇 |
1987年 | 118篇 |
1986年 | 98篇 |
1985年 | 109篇 |
1984年 | 56篇 |
1983年 | 57篇 |
1982年 | 56篇 |
1980年 | 39篇 |
1979年 | 63篇 |
1978年 | 56篇 |
1977年 | 40篇 |
1976年 | 38篇 |
1975年 | 40篇 |
1974年 | 41篇 |
1973年 | 41篇 |
1972年 | 44篇 |
1971年 | 44篇 |
排序方式: 共有5414条查询结果,搜索用时 15 毫秒
1.
2.
Intracranial circulation: pulse-sequence considerations in three- dimensional (volume) MR angiography 总被引:2,自引:0,他引:2
The technique and feasibility of magnetic resonance (MR) angiography of intracranial vessels were studied in 35 healthy volunteers. Variations in image orientation, repetition time (TR), and flip angle were evaluated to determine their effects on flow-related enhancement. Gradient modifications--including echo time (TE), motion compensation, bandwidth, and field of view--were also studied in an effort to reduce motion-induced phase shifts. Results indicated that a FISP (fast imaging with steady precession) sequence with a TR of 50 msec, TE of 15 msec, velocity compensation in the read and section-select directions, acceleration compensation in the read direction, anisotropic volume, and a 1.25-mm partition thickness produced three-dimensional angiographic MR images that were accurate and reproducible in the depiction of the major intracranial vessels. Difficulties with field of view, persistent signal void secondary to higher-order motion, and spatial resolution remain major problems requiring additional study. 相似文献
3.
Patricia K P Burnell Lars Asking Lars Borgstr?m Steve C Nichols Bo Olsson David Prime Ian Shrubb 《Journal of aerosol medicine》2007,20(3):269-281
Magnetic resonance imaging (MRI) of the oropharyngeal region from 20 adult volunteers using four model inhalation devices (varying mouthpiece diameters, airflow resistances) and tidal breathing was carried out. Statistical analysis (convex hull method) selected 12 scans from 80 data sets representing the extremes of all dimensions in the population. Twelve physical mouth-throat models were made by stereolithography using the exact scan data. The aim was to produce models with varying dimensions to span the adult population, and to investigate if oropharyngeal dimensions affected throat retention for different delivery systems. In an in vitro analysis, the models were used to determine the retention effect of the oropharyngeal airspaces when drug aerosols were administered from four inhalation delivery systems: a pressurised metered dose inhaler (pMDI), two different dry powder inhalers (DPIs A and B), and a nebulizer. The aims of this work were to determine the key parameters governing mouth-throat retention and whether retention was dependent on the delivery system used. Characterizing the throat models by measuring 51 different dimensional variables enabled determination of the most influential variables for dose retention for each inhalation delivery system. Throat model retention was found to be dependent on the delivery system (pMDI approximately DPI(A) > DPI(B) > Neb.). The most influential variable was the total throat model volume. Throat models representing high, median, and low oropharyngeal filtration in healthy adults have been identified. 相似文献
4.
M P Johnson X M Huang R Oberlender J F Nash D E Nichols 《European journal of pharmacology》1990,191(1):1-10
The present set of experiments was designed to examine the effects of extension of the alpha-methyl of p-chloroamphetamine (PCA) to an alpha-ethyl. Therefore, the alpha-ethyl homologue of PCA, 1-(4-chlorophenyl)-2-aminobutane (CAB), was compared to PCA in a number of pharmacological assays. CAB was 2-fold less potent than PCA at inhibiting synaptosomal uptake of [3H]5-hydroxytryptamine ([3H]5-HT), and 5-fold less potent at inhibiting uptake of [3H]dopamine ([3H]DA). In drug discrimination assays, CAB was approximately 3-fold less potent than PCA in animals trained to discriminate 3,4-methylenedioxymethamphetamine (MDMA) or its alpha-ethyl homologue, S-(+)-N-methyl-1-(1,3-benzodioxol-5-yl)-2-butanamine (S-(+)-MBDB), from saline. Monitoring with in vivo microdialysis, 10 mg/kg of PCA caused a large increase in extracellular DA and a significant decrease in 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum. In contrast, 11 mg/kg CAB caused no increase and 22 mg/kg CAB caused only a slight increase in extracellular DA. Both doses of CAB caused a decrease in extracellular DOPAC. The potential 5-HT neurotoxicity of CAB was examined by measuring monoamine and metabolite levels and [3H]paroxetine binding at one week following acute doses. A 10 mg/kg dose of PCA caused an 80% decrease in cortical and hippocampal serotonergic markers, while an equimolar dose of CAB decreased only hippocampal 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels. However, 22 mg/kg of CAB produced a 20-40% decrease in all serotonergic markers. Thus, extension of the alpha-alkyl significantly decreases the dopaminergic effects of PCA. The similar decrease in relative 5-HT neurotoxicity and the decreased ability to alter dopaminergic systems in vivo and in vitro supports the involvement of DA in the neurotoxicity of PCA. 相似文献
5.
Purpose: To illuminate the history of nurses' participation in institution-building in the early 1900s, using the Baby Hospital in Oakland, California (now called Children's Hospital Oakland) as a case.
Design: Historical research using a framework of women's history theory focused on the women who founded Oakland's Baby Hospital, 1910–1930.
Method: Data collection included studying original sources, archival material, and interviews. Data evaluation included external criticism for authenticity and genuineness, and internal criticism for accuracy and bias.
Findings: In 1912, nurse Bertha Wright and social worker Mabel Weed, with a circle of community women, including Jessica Peixotto and Jean Howard McDuffie, established the Baby Hospital. Their activism included home visits, education, research, publications, political lobbying, and state policy and program development. At the center of this activity, was the lifelong commitment of Wright and Weed, who created new definitions of family. With social changes in the late 1920s, the male Board of Directors seized control of the hospital, and relegated women to auxiliary roles.
Conclusions: Health and social issues of the United States at the turn of the century are still problematic as a new century approaches and pertain to maternal-child health, foster care, and immigration. Feminists, including nurses, have played a central role in creating solutions. Knowledge of some of their incredible effort has been lost, particularly nursing's history in the western United States. 相似文献
Design: Historical research using a framework of women's history theory focused on the women who founded Oakland's Baby Hospital, 1910–1930.
Method: Data collection included studying original sources, archival material, and interviews. Data evaluation included external criticism for authenticity and genuineness, and internal criticism for accuracy and bias.
Findings: In 1912, nurse Bertha Wright and social worker Mabel Weed, with a circle of community women, including Jessica Peixotto and Jean Howard McDuffie, established the Baby Hospital. Their activism included home visits, education, research, publications, political lobbying, and state policy and program development. At the center of this activity, was the lifelong commitment of Wright and Weed, who created new definitions of family. With social changes in the late 1920s, the male Board of Directors seized control of the hospital, and relegated women to auxiliary roles.
Conclusions: Health and social issues of the United States at the turn of the century are still problematic as a new century approaches and pertain to maternal-child health, foster care, and immigration. Feminists, including nurses, have played a central role in creating solutions. Knowledge of some of their incredible effort has been lost, particularly nursing's history in the western United States. 相似文献
6.
Maxillary sinusitis in adults: an evaluation of placebo-controlled double-blind trials 总被引:1,自引:0,他引:1
BACKGROUND: In general practice, acute sinusitis is frequently diagnosed
and treated with antibiotics. OBJECTIVE: This study aimed to determine the
evidence for the effectiveness of antibiotic treatment in acute maxillary
sinusitis in adults by assessing the methodological quality of
placebo-controlled double-blind randomized trials. METHOD: An evaluation by
four raters through a 35-item scoring-scale for internal and external
validity of all placebo-controlled double-blind randomized trials on acute
sinusitis found between January 1966 and July 1996. RESULTS: Eighty-five
trials were excluded because they were not placebo-controlled,
double-blind, randomized, or were carried out in patients with chronic
sinusitis or in children. The three remaining trials were performed in
different populations (one in general practice) between 1973 and 1978. Only
one study claimed superiority of antibiotic treatment. Different inclusion
criteria and major outcome measures were used by the authors. The
reliability of major outcome events was reported poorly or not at all and
in two studies outcome measures were clinically inappropriate. The studies
scored 30-62% of the maximum attainable score for internal validity and
10-20% for external validity. CONCLUSION: The effectiveness of antibiotic
treatment in acute maxillary sinusitis in a general practice population is
not based sufficiently on evidence.
相似文献
7.
Piceatannol (3,4,3',5'-tetrahydroxy-trans-stilbene) (NSC 365798) has recently been isolated and was subsequently synthesized for NCI tumor panel testing as a new antileukemic natural product from the seeds of Euphorbia lagascae. During the synthesis, a bioactive reaction mixture of several partially O-methylated piceatannol analogues was obtained. This mixture has now been maximized and subjected to bioactivity-directed fractionation, using brine shrimp lethality, to yield 3,3',5'-tri-O-methylpiceatannol (NSC 381281); this new compound has improved stability and better bioactivity in several systems than piceatannol itself. To confirm the structure, 5 was synthesized from vanillin. In addition, the isovanillin analogue, 4,3',5'-tri-O-methylpiceatannol (NSC 381864), another new compound, was synthesized and found to be bioactive. 相似文献
8.
9.
Nine strains of Oryzaephilus surinamensis have been kept in laboratory culture for periods ranging from 5 to 30 years (30–180 generations). Two RAPD primers provided sufficient information to separate the strains reliably and unambiguously. The strains are maintained at a population size of 200 breeding adults. The marked divergence between strains is consistent with the small population size, which for the older strains, according to population genetics theory, implies that roughly half the original genetic variation should now be lost from within strains. However, there is no indication that the older strains have less inter-strain variation. The results demonstrate RAPD loci can reliably detect population subdivision, which in field populations of pest species is of fundamental importance in understanding the population genetics of insecticide resistance. 相似文献
10.
D H Nichols 《American journal of obstetrics and gynecology》1991,164(3):714-721