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   44400篇
  免费   2846篇
  国内免费   255篇
耳鼻咽喉   382篇
儿科学   1291篇
妇产科学   1200篇
基础医学   5884篇
口腔科学   934篇
临床医学   4458篇
内科学   9683篇
皮肤病学   879篇
神经病学   4770篇
特种医学   1493篇
外科学   5881篇
综合类   174篇
一般理论   19篇
预防医学   3249篇
眼科学   762篇
药学   2755篇
  1篇
中国医学   84篇
肿瘤学   3602篇
  2024年   53篇
  2023年   472篇
  2022年   613篇
  2021年   1795篇
  2020年   1056篇
  2019年   1484篇
  2018年   1698篇
  2017年   1189篇
  2016年   1336篇
  2015年   1542篇
  2014年   2120篇
  2013年   2640篇
  2012年   3913篇
  2011年   3901篇
  2010年   1972篇
  2009年   1841篇
  2008年   3110篇
  2007年   2999篇
  2006年   2701篇
  2005年   2673篇
  2004年   2231篇
  2003年   1995篇
  2002年   1766篇
  2001年   225篇
  2000年   157篇
  1999年   229篇
  1998年   301篇
  1997年   222篇
  1996年   198篇
  1995年   180篇
  1994年   154篇
  1993年   121篇
  1992年   84篇
  1991年   75篇
  1990年   62篇
  1989年   41篇
  1988年   39篇
  1987年   34篇
  1986年   31篇
  1985年   31篇
  1984年   38篇
  1983年   19篇
  1982年   39篇
  1981年   24篇
  1980年   21篇
  1979年   9篇
  1978年   12篇
  1977年   11篇
  1976年   8篇
  1972年   8篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
91.
OBJECTIVE: It is not well established whether the blood flow of arterial composite Y-grafts can efficiently respond to the flow demand of the coronary system early postoperatively. The aim of this study was to evaluate if soon after the operation, arterial composite Y-grafts can increase blood flow in response to an increase in myocardial oxygen consumption (MVO2). METHODS: Twenty-seven patients who received complete arterial myocardial revascularization using the left internal thoracic artery (LITA) and the radial artery (RA) as composite Y-graft gave their consent to a pre-discharge coronary angiography and intravascular flow velocity measurements using a Doppler guide wire. Flow measurements were performed in the LITA main stem, the distal LITA and the RA, both at rest and during atrial pacing at the 85% of the patient age-predicted maximum. The heart rate-systolic blood pressure product was considered as an indirect index of MVO2. Hyperemic flow was determined after injection of adenosine. The flow reserve (FR) was defined as the ratio of blood flow during maximal hyperemia (Qmax) to baseline flow (Qbasal). RESULTS: Atrial pacing increased MVO2 significantly (P<0.000). None of the patients developed ischemic S-T segment modifications or complained of chest pain. Q(basal) increased significantly in the LITA main stem (P=0.001), distal LITA (P=0.041) and RA (P=0.004) while Qmax did not change significantly. As a consequence, the FR decreased in the LITA main stem (P=0.002), distal LITA (P<0.000) and RA (P<0.000) but was not completely exhausted. CONCLUSIONS: Soon after the operation, arterial composite Y-grafts can significantly increase blood flow in response to conditions of increased MVO2, keeping normal the myocardial O2 supply-to-demand ratio.  相似文献   
92.
Apolipoprotein E (apoE, protein; APOE, gene) is the major lipid-transport protein in the brain and plays an important role in modulating the outcome and regenerative processes after acute brain injury. The aim of the present study was to determine if gene transfer of the epsilon3 form of APOE improves outcome in a murine model of transient focal cerebral ischaemia. Mice received an intrastriatal injection of vehicle, a second-generation adenoviral vector containing the green fluorescent protein gene (Ad-GFP) or a vector containing the APOE epsilon3 gene (Ad-APOE) 3 days before 60 mins focal ischaemia. Green fluorescent protein expression was observed in cells throughout the striatum and subcortical white matter indicating successful gene transfer and expression. ApoE levels in the brain were significantly increased after Ad-APOE compared with Ad-GFP or vehicle treatment. Ad-APOE treatment reduced the volume of ischaemic damage by 50% compared with Ad-GFP or vehicle treatment (13+/-3 versus 29+/-4 versus 27+/-5 mm(3)). The extent of postischaemic apoE immunoreactivity was enhanced in Ad-APOE compared with Ad-GFP or vehicle treated mice. These results show the ability of APOE gene transfer to markedly improve outcome after cerebral ischaemia and suggest that modulating apoE levels may be a potential strategy in human stroke therapy.  相似文献   
93.

Background  

Long-term morphofunctional outcome may vary widely in surgical anterior left ventricular wall restoration, suggesting variability in post-surgical remodeling similar to that observed following acute myocardial infarction. The aim of this pilot study was to demonstrate that surgical restoration obtained with a particular shape of endoventricular patch leads to steady morphofunctional ventricular improvement when geometry, volume and residual akinesia can be restored as normal as possible.  相似文献   
94.
Parvalbumin 3 is an Abundant Ca2+ Buffer in Hair Cells   总被引:3,自引:0,他引:3  
Ca2+ signaling serves distinct purposes in different parts of a hair cell. The Ca2+ concentration in stereocilia regulates adaptation and, through rapid transduction-channel reclosure, underlies amplification of mechanical signals. In presynaptic active zones, Ca2+ mediates the exocytotic release of afferent neurotransmitter. At efferent synapses, Ca2+ activates the K+ channels that dominate the inhibitory postsynaptic potential. A copious supply of diffusible protein buffer isolates the three signals by restricting the spread of free Ca2+ and limiting the duration of its action. Using cDNA subtraction and a gene expression assay based on in situ hybridization, we detected abundant expression of mRNAs encoding the Ca2+ buffer parvalbumin 3 in bullfrog saccular and chicken cochlear hair cells. We cloned cDNAs encoding this protein from the corresponding inner-ear libraries and raised antisera against recombinant bullfrog parvalbumin 3. Immunohistochemical labeling indicated that parvalbumin 3 is a prominent Ca2+-binding protein in the compact, cylindrical hair cells of the bullfrog's sacculus, and occurs as well in the narrow, peanut-shaped hair cells of that organ. Using quantitative Western blot analysis, we ascertained that the concentration of parvalbumin 3 in saccular hair cells is approximately 3 mM. Parvalbumin 3 is therefore a significant mobile Ca2+ buffer, and perhaps the dominant buffer, in many types of hair cell. Moreover, parvalbumin 3 provides an early marker for developing hair cells in the frog, chicken, and zebrafish.  相似文献   
95.
96.
SUMMARY. I have examined the function of silence - its possible role and meanings - in the psychoanalytic encounter. I have argued that silence is complementary to words in general, and to analytic free-associations in particular, and that silence in the patient is often more than just the expression of his resistance.
It could be useful to consider the silent space within a session as a sort of container of words -words that, for complex, over-determined, unconscious reasons cannot be uttered. I have insisted on the significance of analytic silences and warned against responding to them either through a retaliatory silence or through a flood of premature interpretations. These inadequate reactions often stem from the analyst's own anxiety evoked in him by the patient's silence.
Anxiety and silence are closely connected. Each silence is a compromise formation, concealing the unconscious fantasy from which it originates, while expressing a conscious one, often related to the transference situation. It is the task of the analyst to listen to his patient's silences in order to help him understand their meanings.  相似文献   
97.
Patients with Taylor-type focal cortical dysplasia (TTFCD) generally present with medically intractable epilepsy and impaired neurological and/or intellectual functioning. Surgery usually proves to be the only treatment approach leading to control of seizures. We describe a 17-year-old girl with TTFCD who exhibited a very long period of seizure remission. Combined clinical and neuroimaging findings were compatible with a diagnosis of a balloon cell-subtype TTFCD. As for the clinical course, partial motor seizures began at one year of age and ceased at five: our patient has had no seizure recurrence over a 12-year-follow-up. Moreover, throughout the 15-year follow-up, neurological examinations and cognitive abilities always remained within normal limits. Neuropsychological assessment clearly showed no impairments in executive functions: planning abilities, working memory, attention and impulse control, or constructive aspects of motor coordination. The predominant deficits pertained to verbal abilities in the context of borderline intellectual performances. To our knowledge, this case report documents the longest duration of seizure remission in a patient with TTFCD, thus emphasizing the possible benign course of such dysplastic lesions which usually have a poor prognosis, leading to early surgical treatment.  相似文献   
98.
Abstract: Background : In response to rising cesarean rates, it is reasonable for health care organizations to look to a managed care model as a means of controlling further rate increases. However, little conclusive evidence exists to support this solution. We undertook a study of the Department of Defense health care beneficiary population to assess the impact of enrollment in TRICARE Prime, the Department's managed care health plan, on cesarean delivery rates. Methods : Pooled hospital discharge records from 1999–2002 for live, singleton births were analyzed to calculate primary and repeat cesarean rates for TRICARE Prime and non‐Prime beneficiaries in the military and civilian hospitals that comprise the Department of Defense health care network. Stepwise logistic regression was used to calculate adjusted odds ratios for clinical indicators for each combination of health plan and hospital setting using theχ2difference(p < 0.05)to eliminate nonsignificant variables from the model. Total primary and repeat cesarean rates were compared with primary and repeat cesarean rates for women with no reported clinical complications to account for differences in case mix across subgroups. Statistical significance of the differences calculated for subgroups was assessed usingχ2. Results : Primary cesarean rates were significantly lower for TRICARE Prime enrollees relative to non‐Prime beneficiaries for all race subgroups and three of five age subgroups in military hospitals and four of five age subgroups in civilian hospitals. No significant differences in repeat cesarean rates were observed between Prime and non‐Prime beneficiaries within any race or age subgroup. Breech presentation followed by dystocia, fetal distress, and other complications were significant predictors for primary cesarean. Previous cesarean delivery was the leading predictor for repeat cesarean delivery. Primary and repeat cesarean rates observed for military hospitals were consistently lower than rates observed for civilian hospitals within each health plan type and age group. Conclusions : Enrollment in the managed care health plan was significantly associated with lower risk of primary cesarean delivery relative to membership in other health plans offered to Department of Defense health care beneficiaries. Repeat cesarean rates in this population varied independently of health plan type. Primary cesarean delivery was generally associated with clinical complications, whereas previous cesarean delivery was the strongest indictor for a repeat cesarean delivery. A clear explanation of reduced cesarean rates for Prime enrollees remains elusive, but it is likely that factors beyond individual practitioner decision‐making were at work.  相似文献   
99.
Human immunodeficiency virus (HIV)-associated progressive multifocal leukoencephalopathy (PML) remains a relevant clinical problem even in the era of highly active antiretroviral therapy (HAART). Aims of the study were to analyze clinical and treatment-related features and the survival probability of PML patients observed within the Italian Registry Investigative Neuro AIDS (IRINA) during a 29-month period of HAART. Intravenous drug use, the presence of focal signs, and the involvement of white matter at neuroradiology increased the risk of having PML. A reduced probability of PML was observed when meningeal signs were reported. Patients starting HAART at PML diagnosis and previously naïve for antiretrovirals showed significantly higher 1-year probability of survival (.58), compared to those continuing HAART (.24), or never receiving HAART (.00). Higher CD4 cell count were associated with a higher survival probability (.45). At multivariate analysis, a younger age, higher CD4, starting HAART at PML diagnosis, the absence of previous acquired immunodeficiency syndrome (AIDS)-defining events, and the absence of a severe neurologic impairment were all associated with a reduced hazard of death. The use of cidofovir showed a trend towards a reduced risk of death.  相似文献   
100.
Patient monitoring at the bedside is an inherently parallel job, best handled by multiple individual tasks running concurrently. Cost and diffusion considerations strongly favor the use of PC's at the bedside, but their most widespread operating system, DOS, is not built for multitasking. Hence, a software platform in C language has been prepared, allowing the intermediate programmer to easily write independent modules which will then run simultaneously without conflicts.Such a platform aims at allowing effortless sharing of data among concurrently running processes, while providing strong insulation between tasks, enough to allow multiple copies of any one task to run simultaneously unknown to each other. A cooperative, memory sharing multitasking paradigm has been chosen, which offers fine granularity of timeslicing and low execution overhead at the price of some loss in generality of design.Speed, data exchange capability and number of stackable windows are greater than with commercial packages like Windows or LabWinows. Dynamical reprioritization of tasks is built in, allowing the computerized monitor to focus its attention and resources on urgent tasks.  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