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   116462篇
  免费   9014篇
  国内免费   392篇
耳鼻咽喉   1258篇
儿科学   3064篇
妇产科学   2069篇
基础医学   16676篇
口腔科学   2575篇
临床医学   11840篇
内科学   24569篇
皮肤病学   2350篇
神经病学   12320篇
特种医学   4808篇
外国民族医学   6篇
外科学   16189篇
综合类   1416篇
一般理论   80篇
预防医学   9179篇
眼科学   1916篇
药学   7852篇
中国医学   132篇
肿瘤学   7569篇
  2023年   569篇
  2022年   1166篇
  2021年   2348篇
  2020年   1466篇
  2019年   2205篇
  2018年   2698篇
  2017年   2029篇
  2016年   2404篇
  2015年   2764篇
  2014年   3617篇
  2013年   4838篇
  2012年   7398篇
  2011年   7548篇
  2010年   4376篇
  2009年   4022篇
  2008年   6603篇
  2007年   7036篇
  2006年   6596篇
  2005年   6496篇
  2004年   6091篇
  2003年   5450篇
  2002年   5352篇
  2001年   2356篇
  2000年   2258篇
  1999年   2140篇
  1998年   1409篇
  1997年   1158篇
  1996年   945篇
  1995年   957篇
  1994年   851篇
  1993年   760篇
  1992年   1457篇
  1991年   1391篇
  1990年   1283篇
  1989年   1266篇
  1988年   1138篇
  1987年   1028篇
  1986年   1029篇
  1985年   1011篇
  1984年   837篇
  1983年   720篇
  1982年   633篇
  1981年   548篇
  1980年   461篇
  1979年   626篇
  1978年   500篇
  1977年   463篇
  1975年   427篇
  1974年   472篇
  1973年   426篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Poor results after surgery for bronchioloalveolar carcinoma.   总被引:2,自引:0,他引:2  
BACKGROUND: Bronchioloalveolar carcinoma (BAC) is suggested to be less aggressive than other types of lung cancer. To assess the option of treatment modification, actual outcome data were studied and compared with results for other types of lung cancer. METHOD: Retrospective analysis of all consecutive patients who underwent resection for stage I lung cancer in our hospital. For 18 BAC cases, histological specimens were re-evaluated and in three cases diagnosis was revised. RESULTS: In the period 1989 through 2000, 15 patients with BAC and 260 patients with other tumour types underwent surgery in our hospital. Five-year survival rates were 24 and 53%, respectively, (p = 0.01). CONCLUSIONS: Given the poor results after standard surgery, parenchyma-sparing operations do not seem justified in patients with invasive BAC.  相似文献   
52.
Effect of catalase supplementation in storage media for avulsed teeth   总被引:1,自引:0,他引:1  
Abstract – The type of liquid medium used to store avulsed teeth prior to replantation has been shown to affect the long‐term prognosis. One possibility is that some storage media contain hydrogen peroxide (H2O2) that may be toxic to periodontal ligament cells. Therefore, the aim of this study was to determine if the addition of catalase to storage media improved the prognosis of replanted dog teeth. Forty‐eight mongrel premolar roots were endodontically treated, extracted, randomly divided and placed into one of four storage media: Hank's balanced salt solution (HBSS), containing no antioxidant); Viaspan, containing the antioxidant, glutathione, or the same two media supplemented with catalase(100 U ml?1) for 1, 5, or 26 h prior to replantation. After 2 months, the dogs were euthanized and the roots histologically examined to evaluate the attachment tissues. Regardless of the storage medium used, overall healing was excellent and only 4% of the roots displayed inflammatory or replacement resorption. When roots from the different storage media were compared, those stored in HBSS were found to display the highest incidence of surface resorption (55.7%). Supplementation of HBSS with catalase resulted in a lower level of surface resorption (48.6%) that was statistically significant (P < 0.05). Roots stored in Viaspan – or + catalase displayed even lower levels of surface resorption (41.3 and 38.2%, respectively). The improvement observed with catalase‐supplemented HBSS was confined to the 45‐min incubation period; only Viaspan – or + catalase reduced surface resorption at the 5‐ and 26‐h incubations. Collectively, these data demonstrate that roots stored in media containing antioxidant activity undergo less surface resorption. These results suggest that low levels of H2O2 in storage media for avulsed teeth may adversely affect periodontal ligament cells.  相似文献   
53.
BACKGROUND: A low level of response to alcohol has been associated with both the genetic constitution of the regulatory region (SLC6A4) of the human serotonin (5-hydroxytryptamine, 5-HT) transporter (5-HTT) and with future alcohol intake and an increased risk for alcoholism. To date, all studies of relevant polymorphisms have been carried out in populations in the United States. METHODS: Data were extracted from a subset (n = 243) of a cohort of children who have been observed since birth through evaluation of the family history of alcoholism and psychosocial risk influences. At age 16 years, the response to alcohol was assessed with the Self-Rating of the Effects of Alcohol (SRE) questionnaire, and the average amount of alcohol intake per month was assessed during the prior 6 months. Additional variables that were measured included the 5-HTT genotype, externalizing behavior, and sociodemographic variables, such as gender and age. RESULTS: The level of response to alcohol was significantly lower among carriers of two long alleles of the 5-HTT regulatory region compared with carriers of one or two short alleles (Mann-Whitney U = 5225.0, p = .005). In a multiple regression analysis, the level of response to alcohol and externalizing behavior but not psychosocial factors significantly predicted the average amount of alcohol intake per month. CONCLUSIONS: This study demonstrates that, independent of the assessed psychosocial variables, the 5-HTT genotype correlated with the level of response to alcohol and predicted alcohol intake among 16-year-old adolescents.  相似文献   
54.
Much of the research on episodic memory in schizophrenia spectrum disorders has focused on memory deficits and how they relate to clinical measures such as outcome. Memory bias refers to the modulatory influence that state or trait psychopathology may exert on memory performance for specific categories of stimuli, often emotional in nature. For example, subjects suffering from depression frequently have better memory for negative stimuli than for neutral or positive ones. This dimension of memory function has received only scant attention in schizophrenia research but could provide fresh new insights into the relation between symptoms and neurocognition. This paper reviews the studies that have explored memory biases in individuals with schizophrenia. With respect to positive symptoms, we examine studies that have explored the link between persecutory delusions and memory bias for threatening information and between psychosis and a memory bias toward external source memory. Although relatively few studies have examined negative symptoms, we also review preliminary evidence indicating that flat affect and anhedonia may lead to some specific emotional memory biases. Finally, we present recent findings from our group delineating the relation between emotional valence for faces and memory bias toward novelty and familiarity, both in schizophrenia patients and in healthy control subjects. A better understanding of the biasing effects of psychopathology on memory in schizophrenia (but also on other cognitive functions, such as attention, attribution, and so forth) may provide a stronger association between positive and negative symptoms and memory function. Memory measures sensitive to such biases may turn out to be stronger predictors of clinical and functional outcome.  相似文献   
55.
1 Intravenous administration of the ganglionic nicotinic receptor agonist DMPP (1,1-dimethyl-4-phenylpiperazinium iodide) into urethane-anaesthetized rats evoked dose-dependent increases in mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA). 2 The ganglionic nicotinic receptor antagonists pentolinium and hexamethonium either alone or combined did not inhibit the increase in RSNA and MAP evoked by 50 to 200 μg kg?1 doses of DMPP. The increase in renal sympathetic nerve activity evoked by DMPP occurred as a brief burst in firing. 3 The increase in MAP, but not RSNA, evoked by DMPP in the presence of pentolinium was inhibited by the selective α1-adrenergic receptor antagonist prazosin. 4 The non-selective α-adrenoceptor and NPY receptor antagonist benextramine also inhibited the increase in MAP without inhibiting the increase in RSNA. Surprisingly, the combination of benextramine and pentolinium, or benextramine and hexamethonium, completely blocked the DMPP-evoked increase in RSNA and thus the increase in MAP. 5 The uptake1 antagonist desipramine combined with pentolinium did not affect the DMPP-evoked increases in MAP or RSNA when compared to the responses evoked in the presence of pentolinium alone. 6 Adding the selective M1 muscarinic receptor antagonist telenzepine to pentolinium and prazosin did not inhibit the increase in RSNA evoked by a 100 μg kg?1 dose of DMPP. 7 While the DMPP-evoked increase in MAP in the presence of ganglionic nicotinic receptor antagonists is primarily dependent upon activation of α1-adrenoceptors, the increase in RSNA occurs via activation of ganglionic nicotinic receptors and activation of a mechanism susceptible to blockade by benextramine.  相似文献   
56.
57.
Unilateral microinjection of the acetylcholine receptor agonist carbachol into the posterior hypothalamic nucleus evokes a pressor response in the conscious, freely moving rat. To further localize this response 3.3 or 5.5 nmol of carbachol was microinjected in a volume of 50 nl directly into and outside the region of the posterior hypothalamic nucleus. Administration of carbachol outside the posterior hypothalamic nucleus failed to evoke a change in blood pressure indicating that the carbachol-induced pressor response is mediated from the posterior hypothalamic nucleus. Since posterior hypothalamic administration of atropine completely blocks the carbachol-induced increase in blood pressure and atropine blocks the three pharmacologically identified muscarinic receptor subtypes, methylatropine and progressively more selective muscarinic antagonists were administered into the posterior hypothalamic nucleus prior to 5.5 nmol of carbachol. Microinjection of the M1/M2/M3 muscarinic antagonist methylatropine (0.19-12.5 nmol), the M1/M3 antagonist 4-DAMP (4-diphenylacetoxy-N-methylpiperidine; 0.9-3.6 nmol), the M1 antagonist pirenzepine (9.5-38 nmol), the M2 antagonist methoctramine (5.5-44 nmol), or the M3 antagonist p-F-HHSiD (para-fluoro-hexahydro-sila-difenidol; 2.1-8.3 nmol) inhibited the peak increase in mean arterial pressure and the area under the curve of the change in mean arterial pressure versus time plot in a dose-dependent manner. Log ID50s calculated for the antagonists from the dose-response curves were found to correlate significantly with the log Kis of the antagonists for the muscarinic M3 receptor subtype. These results demonstrate that the increase in mean arterial pressure evoked by microinjection of carbachol into the posterior hypothalamic nucleus is mediated by the muscarinic M3 receptor.  相似文献   
58.
We reported recently that a novel immunomodulator, 7-thia-8-oxoguanosine (7T80G)2 inhibited formation of pulmonary melanoma metastases (1), prevented against viral infection in mice (2) and potentiated the efficacy of a weakly immunogenic leukemia vaccine (3). Since certain tumor metastases and virus infected cells are targets to natural killer cells (NK cells), we now investigated whether 7T80G is capable of activating NK cells in mice using NK cell sensitive YAC-1 and B16 and NK cell insensitive P815 targets. CBA/CaJ spleen cells incubated in vitro with 7T80G at concentrations ranging from 0.005 to 0.5 mM responded with increased NK cell activity (32-62 %) compared to controls (4-8%) to YAC-1 targets. Similar levels of augmentation in NK cell activity were observed when 40-168 mg/kg of 7T80G was administered in vivo. In addition to the spleen, 7T80G activated NK cells in the bone marrow (BM), the lungs, the liver, and in peritoneal exudate cells (PE). Although 7T80G elicited activation of NK cells was observed as early as three hours after treatment, the maximal activity was observed after 24 h in the spleen; 12 h in the BM; 48 h in the lungs, and 72 h in PE. Administration of the drug by s.c, i.v., and i.p. routes all induced activition of NK cells in spleen, BM and PE. 7T80G was found to activate NK cells in seven inbred and an outbred mouse strain, suggesting that the induced cytotoxicity against allogeneic and syngeneic tumor cells is not strain specific as well as independent of MHC restriction. C3H/He, CBA/CaJ and BDF/1 displayed higher levels of increased NK cell activity, whereas AKR mice were low responders. Low concentrations of IL-2 (0.25-5 U/ml) that induce little or no NK cell activity, when used in combination with 7T80G, elicited significant enhancement of NK cell cytotoxicity. In contrast, IFN and 7T80G showed no such synergism.  相似文献   
59.
BACKGROUND: The blood flow to the acetabular fragment is of some concern in juxtaarticular pelvic osteotomies used for the treatment of hip dysplasia. No direct measurements have determined the effect of the Bernese periacetabular osteotomy (PAO) on acetabular perfusion. METHODS: Acetabular perfusion was measured by means of laser Doppler flowmetry in 10 patients undergoing a PAO for symptomatic acetabular dysplasia. During the surgical procedure, the intraosseous high energy laser Doppler reliably depicts dynamic changes of small vessel blood flow. Measurements were performed after defined surgical steps to obtain sequential information on the blood perfusion of the acetabular fragment. RESULTS: After complete separation of the acetabular fragment, nine out of 10 patients had pulsatile signals, but the blood flow (BF) significantly decreased by 77%. Corrective positioning of the fragment induced no further drop of the BF signal but a loss of pulsatility in six patients. After a recovery period of about 30 min following preliminary fixation of the fragment, reestablishment of the pulsatile signal and an increase of the BF signal was seen. At termination of the surgical procedure, five out of eight patients, who could be followed throughout the whole procedure, showed a clear pulsatile signal in the supraacetabular area. Bleeding of the supraacetabular cancellous surface could be observed in all acetabula. CONCLUSION: Despite careful preservation of soft tissues during the surgical procedure, a significant reduction of the blood flow in the supraacetabular region has been observed. Nevertheless, a pulsatile signal in more than 60% of the fragments after fragment correction and an increasing signal during the recovery period showed ongoing blood perfusion indicating reversible changes in the measured supraacetabular area. All osteotomies healed within eight weeks without showing signs of necrosis during a minimum follow up of 1 year.  相似文献   
60.
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