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   13219篇
  免费   706篇
  国内免费   39篇
耳鼻咽喉   187篇
儿科学   277篇
妇产科学   261篇
基础医学   2104篇
口腔科学   263篇
临床医学   1157篇
内科学   2653篇
皮肤病学   278篇
神经病学   1460篇
特种医学   690篇
外国民族医学   1篇
外科学   1461篇
综合类   102篇
预防医学   553篇
眼科学   656篇
药学   1129篇
中国医学   64篇
肿瘤学   668篇
  2022年   52篇
  2021年   169篇
  2020年   115篇
  2019年   142篇
  2018年   178篇
  2017年   150篇
  2016年   213篇
  2015年   279篇
  2014年   338篇
  2013年   503篇
  2012年   687篇
  2011年   721篇
  2010年   419篇
  2009年   425篇
  2008年   733篇
  2007年   804篇
  2006年   748篇
  2005年   751篇
  2004年   755篇
  2003年   737篇
  2002年   679篇
  2001年   221篇
  2000年   210篇
  1999年   234篇
  1998年   174篇
  1997年   150篇
  1996年   127篇
  1995年   118篇
  1994年   110篇
  1993年   116篇
  1992年   135篇
  1991年   130篇
  1990年   122篇
  1989年   139篇
  1988年   114篇
  1987年   114篇
  1986年   96篇
  1985年   125篇
  1984年   105篇
  1983年   81篇
  1982年   87篇
  1981年   93篇
  1980年   71篇
  1979年   107篇
  1978年   77篇
  1977年   81篇
  1976年   59篇
  1975年   77篇
  1974年   60篇
  1973年   63篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Background: Pain on injection of propofol in children has been reported to be as high as 30-80%. The reason for the pain is assumed to be the aqueous phase of the propofol emulsion. Therefore, for the first time, this study tested the hypothesis that dilution of propofol to a 0.5% emulsion might reduce the incidence of pain during propofol injection.

Methods: The study design was prospective, monocenter, double-blind, and randomized. Sixty-four children aged 2-6 yr were scheduled to receive 0.5% or 1.0% propofol in a medium-chain-triglyceride/long-chain-triglyceride emulsion. Incidence and intensity of pain were assessed by spontaneous expressions of pain and withdrawal of the arm. In a subgroup of 21 children, serum triglyceride levels were measured before and 3 and 20 min after induction. Adverse events were recorded.

Results: Amounts of propofol required until loss of eyelash reflex were 4.40 +/- 1.01 mg/kg for 0.5% propofol and 4.31 +/- 0.86 mg/kg for 1.0% propofol. Percentages of children who showed at least one pain reaction were 23.3% in the 0.5% propofol group and 70.0% in the 1.0% propofol group (P < 0.001). Serum triglycerides were higher in the 0.5% propofol group 3 and 20 min after injection (251.7 vs. 148.8 mg/dl; P = 0.001 and 135.5 vs. 75.5 mg/dl; P = 0.03). Adverse events or complications did not occur.  相似文献   

72.
(18)F-FDG PET is the most accurate noninvasive modality for staging mediastinal lymph nodes in lung cancer. Besides using visual image interpretation, some institutions use standardized uptake value (SUV) measurements in lymph nodes. Mostly, an SUV of 2.5 is used as the cutoff, but this choice was never deduced from respective studies. Receiver operating characteristic (ROC) analyses demonstrated that SUV thresholds of more than 4 resulted in the highest accuracy. But these high cutoffs imply high false-negative rates (FNRs). The aim of our evaluation was to determine an optimal SUV threshold and to compare its diagnostic performance with the results of visual interpretation. METHODS: This retrospective study included 95 patients with suspected lung cancer who underwent mediastinoscopy/mediastinal lymphadenectomy after (18)F-FDG PET (90-150 min after 250 MBq of (18)F-FDG). Maximum SUV was measured in 371 lymph node regions biopsied afterward and visually interpreted using a 6-level score (- - - through + + +). Diagnostic performance was assessed by ROC analysis. FNR and false-positive rate (FPR), the sum of both error rates (FNR + FPR), and diagnostic accuracy were plotted against a hypothetical SUV threshold to determine the optimum SUV threshold. RESULTS: SUVs in metastatic lymph nodes were higher (mean +/- SD, 7.1 +/- 4.5; range, 1.4-26.9; n = 70) than in tumor-free lymph node stations (2.4 +/- 1.7; range, 0.6-14.9; n = 301; P < 0.01). Inflammatory lymph nodes exhibited slightly increased SUVs (2.7 +/- 2.0; range, 0.8-14.9; n = 146). The plot of error rates featured a minimum of the sum FNR + FPR for an SUV of 2.5. With increasing SUV threshold, the FPR decreased most prominently up to that value whereas a continuous rise of FNR was noticed. Highest diagnostic accuracy was achieved with an SUV of 4.5. The areas under the ROC curves demonstrated that visual interpretation tends to be more accurate than SUV quantification (visual, 0.930 +/- 0.022; SUV, 0.899 +/- 0.025; P = 0.241). Using an SUV of 2.5 as the threshold, the resulting sensitivity, specificity, and negative predictive value were 89%, 84%, and 96%, respectively. CONCLUSION: For mediastinal staging, the choice of an SUV of 2.5 as the threshold is justified because FNR + FPR is minimized. The resulting high negative predictive value of 96% allows the omission of mediastinoscopy in patients with negative mediastinal findings on (18)F-FDG PET images. For the experienced observer, visual analysis should be relied on primarily, with calculation of the SUV used, at most, as a secondary aid. For the less experienced observer, the SUV may be of greater value.  相似文献   
73.
74.
75.
This study examines the correlation between development of expressed emotion (EE) in relatives and course of illness of 99 DSM-III schizophrenic patients. Patients whose relatives were high EE at baseline and at the 2nd CFI approximately 20 months later had a poor prognosis at the very outset of the study and an unfavourable course of illness. They had a higher rehospitalisation rate, more symptoms, lower psychosocial assessment, and a poorer 2-year and even 8-year outcome. Patients from families with a fluctuating EE or a consistently low EE had better courses. Expessed emotion is therefore a valid predictor not only of symptomatic relapses, but also of other important aspects of schizophrenia. The connection between EE index and course of illness seerns not to be simply reactive or causal, but complex and non-uniform.  相似文献   
76.
Forced-choice testing provides evidence of malingering.   总被引:1,自引:0,他引:1  
Assessment of motivation using forced-choice testing is described and illustrated with case reports. Two injured workers with protracted disability complained of numbness and loss of sensation in their fingers. Each patient received a forced-choice, multiple-choice finger graphesthesia test, with a 0.5 probability of guessing correctly on each item. Both patients performed significantly below the chance level, indicating that they had deliberately provided wrong answers. One patient did not exaggerate until the difficulty level of the task was enhanced. Forced-choice testing, particularly with enhancement of difficulty levels, is proposed as a specific measure to detect faked poor performance. Identification of malingering reduces the risk of iatrogenic damage. The subjective complaints of malingerers must be viewed with skepticism.  相似文献   
77.
Summary When only plastidic features are considered, it is difficult to distinguish between monophyletic and polyphyletic xenogenous origins of plastids. We suggest that a direct comparison of nuclear and plastidic sequence-similarity pattern will help to solve this problem. The D1 amino acid sequence of six major groups of photosynthetic eukaryotes and of the two groups of photosynthetic prokaryotes are now available, including the psbA-gene product from Bumilleriopsis filiformis, which is the first molecular sequence reported for a xanthophycean alga. Evidence is provided for an independent and polyphyletic origin of plastids from five out of the six major taxa of photosynthetic eukaryotes. This conclusion is reached by comparing a plastid-based pattern of D1 similarity with a nucleus-based similarity pattern published recently. Furthermore, the availability of D1 sequences from five eukaryotic algae led to a re-evaluation of the taxonomic position of Prochlorothrix.  相似文献   
78.
[GlyA21,ArgB31,ArgB32]insulin (HOE 901) represents a biosynthetic human insulin analogue that, due to its isoelectric point, precipitates at neutral tissue pH leading to a retarded absorption rate and a corresponding longer duration of action. In the present investigation we have evaluated the growth promoting and metabolic activity of this analogue in muscle tissue using exponentially growing H9c2 cardiac myoblasts and adult rat ventricular cardiomyocytes. Equilibrium binding studies of 125I-labelled IGF-I (insulin-like growth factor I) to differentiating myoblasts revealed the presence of 7×103 IGF-I receptors per cell. In contrast, no specific binding of insulin could be detected. Competition binding experiments showed a slightly higher affinity of HOE 901 for the IGF-I receptor when compared to regular human insulin with IC50 (half-inhibitory concentration) values of 70 and 101 nM, respectively. However, the supermitogenic insulin analogue [AspB10]insulin competed significantly more efficiently for IGF-I binding (IC50: 44 nM). Maximum growth promoting activity of the peptides was then determined in serum-starved myoblasts by an incubation with the peptides (5×10−7 M) for 16 h in the presence of [3H]thymidine. [AspB10]Insulin produced a stimulation of DNA synthesis (about 3-fold) which was comparable to the effect of IGF-I and significantly (P<0.005) higher than the effect of HOE 901 with the latter being essentially equipotent to native insulin. Comparable results were obtained at lower concentrations of the peptides (10−9 to 10−8 M). Metabolic activity of HOE 901 was determined by measuring the dose-dependent stimulation of 3-O-methylglucose transport in adult cardiomyocytes. Maximum transport stimulation was identical for insulin and HOE 901 with EC50 (half-effective concentration) values of 0.7×10−10 and 1.9×10−9 M, respectively. We concluded that the IGF-I receptor-mediated growth promoting activity of HOE 901 in muscle cells and the maximal metabolic activity of this analogue are not different from those of native human insulin. It is suggested that differential interaction with IGF-I receptors significantly contributes to the action profile of insulin analogues.  相似文献   
79.
80.
Besides of four pica cases (eating of dirt, paper, cotton, oakum, sand, lime, chalk) the authors report on a girl with trichophagia. The treatment of choice in pica consists in a sufficient supply of iron. The authors suggest that the intravenously administered iron acts on some centers of the central nervous system.  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