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   2285篇
  免费   182篇
  国内免费   5篇
耳鼻咽喉   24篇
儿科学   74篇
妇产科学   34篇
基础医学   315篇
口腔科学   80篇
临床医学   155篇
内科学   524篇
皮肤病学   24篇
神经病学   319篇
特种医学   78篇
外科学   346篇
综合类   49篇
一般理论   1篇
预防医学   160篇
眼科学   24篇
药学   117篇
中国医学   1篇
肿瘤学   147篇
  2021年   39篇
  2020年   30篇
  2019年   33篇
  2018年   52篇
  2017年   26篇
  2016年   31篇
  2015年   34篇
  2014年   50篇
  2013年   71篇
  2012年   115篇
  2011年   113篇
  2010年   74篇
  2009年   47篇
  2008年   103篇
  2007年   106篇
  2006年   113篇
  2005年   95篇
  2004年   108篇
  2003年   93篇
  2002年   98篇
  2001年   59篇
  2000年   71篇
  1999年   68篇
  1998年   47篇
  1997年   20篇
  1996年   19篇
  1995年   19篇
  1994年   20篇
  1993年   18篇
  1992年   42篇
  1991年   48篇
  1990年   40篇
  1989年   33篇
  1988年   42篇
  1987年   38篇
  1986年   38篇
  1985年   58篇
  1984年   37篇
  1983年   15篇
  1982年   21篇
  1981年   12篇
  1980年   12篇
  1979年   26篇
  1977年   17篇
  1976年   20篇
  1975年   15篇
  1974年   16篇
  1973年   22篇
  1972年   16篇
  1971年   15篇
排序方式: 共有2472条查询结果,搜索用时 15 毫秒
31.
In an attempt to validate the animal model of adjunctive ethanol drinking in people, human subjects were allowed access to ad lib beer while playing a game that delivered monetary reinforcements on a FI schedule. Subjects exposed to a longer FI schedule drank significantly more than those exposed to a shorter schedule, confirming the prediction made by the animal model. A pattern of ingestion characteristic of adjunctive drinking was also observed in the longer FI condition, providing evidence that ethanol drinking in humans can be schedule-induced.  相似文献   
32.
The organophosphates, diisopropyl phosphorofluoridate and soman have a common mechanism of action (inhibition of acetylcholinesterase), but result in very different behavioral responses in the rat. Soman rapidly produced persistent tonic convulsions whereas diisopropyl phosphorofluoridate only infrequently produced transient convulsive-like activity. Soman increased local cerebral glucose use in most of the cortex, striato-pallido-nigral pathway, limbic system and in specific thalamic nuclei whereas diisopropyl phosphorofluoridate increased glucose use in a limited fashion, primarily in the dorsal striato-pallido-nigral pathway. When diazepam blocked soman-induced convulsions, the pattern of glucose use was strikingly similar to that caused by diisopropyl phosphorofluoridate. Soman or diisopropyl phosphorofluoridate depressed local cerebral glucose use in rats pretreated with the antidotal mixture of trimedoxime, atropine and benactyzine (muscarinic antagonists). Also, this antidotal mixture blocked the increased glucose use in the dorsal striato-pallido-nigral system produced by either acetylcholinesterase inhibitor, indicating that muscarinic receptors mediate the excitation of this pathway. Both diisopropyl phosphorofluoridate and soman activate the striato-pallido-nigral pathway but soman also causes spread of activity producing overt motor convulsions. Possible explanations for this difference in response to the organophosphates are differential responses in cholinergic actions within specific brain regions or some non-cholinergic action of soman.  相似文献   
33.
The nosologic status of fibrous dysplasia (FD), a well-known and relatively common bone lesion, is controversial. Information collected by the CHromosomes And MorPhology (CHAMP) study group on published and unpublished cases of fibrous dysplasia shows the presence of clonal chromosome changes in at least a proportion of these lesions. The chromosome aberrations found in FD lesions have been quite variable and have included both structural and numerical changes. Two of the three cases investigated at the study group had trisomy 2 as the sole acquired anomaly. Combined with previously published data, +2 and rearrangements involving chromosome band 12p13 have each been detected in 3 of 8 cases with abnormal karyotype of 11 in which chromosomal analysis has been performed, suggesting that FD is a neoplastic lesion rather than a "dysplastic" process, as has been generally believed and as implied by its very name.  相似文献   
34.
A monitoring system to continuously record the daily pattern of drinking and eating of rats is described. This system, based on a North Star microcomputer, can record the amount of food ingested with a temporal resolution of +/- 1.0 second and quantitative accuracy within +/- 5%. Drinking behavior is detected using a drinkometer which also has a temporal resolution of +/- 1.0 second. Data are analyzed by computer to determine absolute amounts of consumption and patterns of intake. The patterns of feeding and drinking recorded by this system are similar to those observed using other monitoring devices.  相似文献   
35.
Effects of microdialysis on brain metabolism in normal and seizure states   总被引:1,自引:0,他引:1  
The effect of intracranial microdialysis on brain glucose metabolism in control and kainic acid-treated rats was assessed by semi-quantitative [14C]2-deoxyglucose autoradiography. A dialysis fiber loop was implanted into the piriform cortex or a horizontal Vita fiber into the hippocampus, and 24 h later, fibers were perfused with Krebs-Ringer bicarbonate solution before and after injection of kainic acid (16 mg/kg, i.p.) [14C]2-Deoxyglucose was injected i.p. 3 h after the injection of kainic acid. Rats injected with kainic acid were initially lethargic and then proceeded through behavioral phases of staring, "wet-dog shakes", Straub tail, rearing, forepaw clonus, and, in some cases, tonic-clonic convulsions. Three hours after kainic acid, the fiber presence in the piriform cortex enhanced kainic acid-induced metabolic activity in areas adjacent to the fiber assembly, whereas the fiber in hippocampus attenuated kainic acid-induced metabolic activity in areas adjacent to the fiber assembly. The results indicate that intracranial microdialysis alters the already abnormal brain metabolism in a kainic acid-induced seizure state, but has no significant effect in the non-seizure control state.  相似文献   
36.
The chemokine receptor CCR5 is encoded by the CMKBR5 gene located on the p21.3 region of human chromosome 3, and constitutes the major co- receptor for the macrophage-tropic strains of HIV-1. A mutant allele of the CCR5 gene, Delta ccr5 , was shown to provide to homozygotes with a strong resistance against infection by HIV. The frequency of the Delta ccr5 allele was investigated in 18 European populations. A North to South gradient was found, with the highest allele frequencies in Finnish and Mordvinian populations (16%), and the lowest in Sardinia (4%). Highly polymorphic microsatellites (IRI3.1, D3S4579 and IRI3.2, D3S4580 ) located respectively 11 kb upstream and 68 kb downstream of the CCR5 gene deletion were used to determine the haplotype of the chromosomes carrying the Delta ccr5 variant. A strong linkage disequilibrium was found between Delta ccr5 and specific alleles of the IRI3.1 and IRI3.2 microsatellites: >95% of the Delta ccr5 chromosomes carried the IRI3.1-0 allele, while 88% carried the IRI3.2-0 allele. These alleles were found respectively in only 2 or 1.5% of the chromosomes carrying a wild-type CCR5 gene. From these data, it was inferred that most, if not all Delta ccr5 alleles originate from a single mutation event, and that this mutation event probably took place a few thousand years ago in Northeastern Europe. The high frequency of the Delta ccr5 allele in Caucasian populations cannot be explained easily by random genetic drift, suggesting that a selection advantage is or has been associated with homo- or heterozygous carriers of the Delta ccr5 allele.   相似文献   
37.
Using positron emission tomography and the 15O continuous inhalation technique, we have measured the regional cerebral blood flow (rCBF) oxygen extraction fraction (rOEF) and oxygen consumption (rCMRO2) of non-infarcted tissue in six patients with either tight stenosis (N = 3) or occlusion (N = 3) of the trunk of the middle cerebral artery (MCA); these arterial lesions were shown to be persistent on late and/or repeated angiograms. The patients were studied 1 to 6 months after their last cerebral ischemic event. The data were analyzed in 4 cm2 regions of interest (fig. 1) and were compared to age-matched control values. Regional right/left ratios were tested for significance individually by comparison to 95 p. 100 confidence limits found in control subjects. We found a significant reduction in mean rCBF in the affected MCA territory; concomitantly, there was a lesser decrease in rCMRO2 significant only in the peri-sylvian area; this was associated with a moderate but significant increase in rOEF in the same areas (Table II, fig. 2 and 3). Individually, the reduction in rCBF and the increased rOEF were significant in 5/6 and 2/6 patients, respectively (Table III). These data indicate that rCBF is decreased distal to persistent hemodynamic MCA obstruction in most patients. This hypoperfusion appears due in part to a mild degree of cerebral ischemia (as demonstrated by the occurrence of "misery perfusion"), indicating inadequate perfusion pressure distal to the MCA obstruction. This was associated with a metabolic depression of the cortex possibly resulting from either neuronal loss, or deactivation (diaschisis), or long-standing hemodynamic local failure or any combination of the three.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
38.
Twelve patients, eleven with a carotid obstruction and one with an occlusion of the middle cerebral artery, were studied before and after a successful unilateral extra-intracranial arterial by-pass, (EIAB) using PET and the 15-0 steady-state technique to measure regional cerebral blood flow (CBF), oxygen extraction fraction and oxygen metabolic rate (CMRO2). In the whole group of patients, both CBF and CMRO2 increased significantly on both cerebral hemispheres after EIAB, returning toward control levels defined in age-matched subjects. Mean oxygen extraction fraction, on the other hand, was not affected. Individually, three different effects of EIAB emerged: 1) Alleviation of a state of long standing unilateral "misery-perfusion", as reported earlier; 2) parallel increase of CBF and CMRO2 bilaterally, which appeared due to improvement of a hemodynamic depression of metabolism, the precise mechanism of which remains obscure; 3) Complex, unexpected changes in the CBF-CMRO2 couple again resulting in increases in CMRO2. This metabolic improvement afforded by EIAB in our patients has not been reported before; it suggests that long-standing hemodynamic failure may induce a metabolic depression that is still potentially reversible by surgical revascularization.  相似文献   
39.
BackgroundThe greatest risk of infectious disease undernotification occurs in settings with limited capacity to detect it reliably. World Health Organization guidance on the measurement of misreporting is paradoxical, requiring robust, independent systems to assess surveillance rigor. Methods are needed to estimate undernotification in settings with incomplete, flawed, or weak surveillance systems. This study attempted to design a tuberculosis (TB) inventory study that balanced rigor with feasibility for high-need settings.ObjectiveThis study aims to design a hybrid TB inventory study for contexts without World Health Organization preconditions. We estimated the proportion of TB cases that were not reported to the Ministry of Health in 2015. The study sought to describe TB surveillance coverage and quality at different levels of TB care provision. Finally, we aimed to identify structural-, facility-, and provider-level barriers to notification and reasons for underreporting, nonreporting, and overreporting.MethodsRetrospective partial digitalization of paper-based surveillance and facility records preceded deterministic and probabilistic record linkage; a hybrid of health facilities and laboratory census with a stratified sampling of HFs with no capacity to notify leveraged a priori knowledge. Distinct extrapolation methods were applied to the sampled health facilities to estimate bacteriologically confirmed versus clinical TB. In-depth interviews and focus groups were used to identify causal factors responsible for undernotification and test the acceptability of remedies.ResultsThe hybrid approach proved viable and instructive. High-specificity verification of paper-based records in the field was efficient and had minimal errors. Limiting extrapolation to clinical cases improved precision. Probabilistic record linkage is computationally intensive, and the choice of software influences estimates. Record absence, decay, and overestimation of the private sector TB treatment behavior threaten validity, meriting mitigation. Data management demands were underestimated. Treatment success was modest in all sectors (R=37.9%–72.0%) and did not align with treatment success reported by the state (6665/8770, 75.99%). One-fifth of TB providers (36/178, 20%) were doubtful that the low volume of patients with TB treated in their facility merited mastery of the extensive TB notification forms and procedures.ConclusionsSubnational inventory studies can be rigorous, relevant, and efficient in countries that need them even in the absence of World Health Organization preconditions, if precautions are taken. The use of triangulation techniques, with minimal recourse to sampling and extrapolation, and the privileging of practical information needs of local decision makers yield reasonable misreporting estimates and viable policy recommendations.  相似文献   
40.
Production of a new monoclonal antibody designated NCL-5D3 is described. The antibody recognizes several low molecular weight cytokeratins, in particular cytokeratin Moll number 8 as determined by immunoblotting studies, and is highly effective for immunocytochemistry using routinely processed paraffin-embedded material. Staining is enhanced by prior treatment of the sections with trypsin. Assessment using a wide variety of normal and neoplastic tissue indicates reactivity with all tissues of simple or glandular epithelial origin, and in addition with many squamous carcinomas. Thus the antibody should prove of value in diagnostic histopathology.  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