全文获取类型
收费全文 | 38066篇 |
免费 | 3598篇 |
国内免费 | 66篇 |
专业分类
耳鼻咽喉 | 380篇 |
儿科学 | 1180篇 |
妇产科学 | 776篇 |
基础医学 | 5271篇 |
口腔科学 | 661篇 |
临床医学 | 4762篇 |
内科学 | 6764篇 |
皮肤病学 | 431篇 |
神经病学 | 4290篇 |
特种医学 | 1086篇 |
外科学 | 5201篇 |
综合类 | 766篇 |
一般理论 | 23篇 |
预防医学 | 4356篇 |
眼科学 | 739篇 |
药学 | 2428篇 |
中国医学 | 33篇 |
肿瘤学 | 2583篇 |
出版年
2023年 | 198篇 |
2022年 | 309篇 |
2021年 | 745篇 |
2020年 | 420篇 |
2019年 | 737篇 |
2018年 | 846篇 |
2017年 | 592篇 |
2016年 | 600篇 |
2015年 | 724篇 |
2014年 | 990篇 |
2013年 | 1599篇 |
2012年 | 2290篇 |
2011年 | 2224篇 |
2010年 | 1159篇 |
2009年 | 1129篇 |
2008年 | 1956篇 |
2007年 | 1965篇 |
2006年 | 1863篇 |
2005年 | 1747篇 |
2004年 | 1761篇 |
2003年 | 1652篇 |
2002年 | 1480篇 |
2001年 | 961篇 |
2000年 | 970篇 |
1999年 | 818篇 |
1998年 | 446篇 |
1997年 | 383篇 |
1996年 | 379篇 |
1995年 | 340篇 |
1994年 | 306篇 |
1993年 | 339篇 |
1992年 | 674篇 |
1991年 | 662篇 |
1990年 | 615篇 |
1989年 | 631篇 |
1988年 | 594篇 |
1987年 | 603篇 |
1986年 | 554篇 |
1985年 | 539篇 |
1984年 | 432篇 |
1983年 | 382篇 |
1982年 | 283篇 |
1981年 | 247篇 |
1980年 | 233篇 |
1979年 | 380篇 |
1978年 | 210篇 |
1977年 | 211篇 |
1976年 | 237篇 |
1974年 | 257篇 |
1973年 | 240篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
981.
7-Chloro-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine S,S-dioxide (IDRA 21), a congener of aniracetam, potently abates pharmacologically induced cognitive impairments in patas monkeys. 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Proceedings of the National Academy of Sciences of the United States of America》网站下载免费的PDF全文](/ch/ext_images/free.gif)
D M Thompson A Guidotti M DiBella E Costa 《Proceedings of the National Academy of Sciences of the United States of America》1995,92(17):7667-7671
We report here on the ability of IDRA 21 and aniracetam, two negative allosteric modulators of glutamate-induced DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor desensitization, to attenuate alprazolam-induced learning deficit in patas monkeys working in a complex behavioral task. In one component of a multiple schedule (repeated acquisition or "learning"), patas monkeys acquired a different four-response chain each session by responding sequentially on three keys in the presence of four discriminative stimuli (geometric forms or numerals). In the other component (performance) the four-response chain was the same each session. The response chain in each component was maintained by food presentation under a fixed-ratio schedule. When alprazolam (0.1 or 0.32 mg/kg p.o.) was administered alone, this full allosteric modulator of gamma-aminobutyric acid type A (GABAA) receptors produced large decreases in the response rate and accuracy in the learning component of the task. IDRA 21 (3 or 5.6 mg/kg p.o.) and aniracetam (30 mg/kg p.o.) administered 60 min before alprazolam, having no effect when given alone, antagonized the large disruptive effects of alprazolam on learning. From dose-response studies, it can be estimated that IDRA 21 is approximately 10-fold more potent than aniracetam in antagonizing alprazolam-induced learning deficit. We conclude that IDRA 21, a chemically unrelated pharmacological congener of aniracetam, improves learning deficit induced in patas monkeys by the increase of GABAergic tone elicited by alprazolam. Very likely IDRA 21 exerts its behavioral effects by antagonizing AMPA receptor desensitization. 相似文献
982.
Stockwell DH Woo P Jacobson BC Remily R Syngal S Wolf J Farraye FA 《The American journal of gastroenterology》2003,98(8):1875-1880
OBJECTIVES: Women who participate in screening for breast cancer are more likely to participate in screening for colorectal cancer. We studied such a motivated group of women to identify predictors of, and barriers to, participation in colorectal cancer screening by endoscopy. METHODS: We distributed surveys to 551 women > or = 50 yr of age while they were awaiting mammography at four sites in and around Boston, MA from June to September, 2000. The 40-question survey assessed knowledge, attitudes, and beliefs about, and behaviors toward, breast and colorectal cancer screening. Regression models were used to determine factors associated with having had sigmoidoscopy or colonoscopy. RESULTS: Seventy-nine percent of the women completed all or part of the survey. Half (221/438) reported ever having had sigmoidoscopy or colonoscopy. Of these, 93% did so at the recommendation of their primary care provider. Factors associated with participation in endoscopic screening included compliance with annual fecal occult blood testing, a family history of colorectal cancer, and indifference toward the gender of the doctor performing the endoscopy. CONCLUSIONS: Women undergoing mammography overwhelmingly cite the recommendation of their primary care provider as the reason for participating in colorectal cancer screening by endoscopy. Women who preferred a female endoscopist were less likely to have been screened. Whenever possible, primary care providers should offer women the choice of a female endoscopist for colorectal cancer screening. 相似文献
983.
Xiang Z Zhao Y Mitaksov V Fremont DH Kasai Y Molitoris A Ries RE Miner TL McLellan MD DiPersio JF Link DC Payton JE Graubert TA Watson M Shannon W Heath SE Nagarajan R Mardis ER Wilson RK Ley TJ Tomasson MH 《Blood》2008,111(9):4809-4812
Somatic mutations in JAK2 are frequently found in myeloproliferative diseases, and gain-of-function JAK3 alleles have been identified in M7 acute myeloid leukemia (AML), but a role for JAK1 in AML has not been described. We screened the entire coding region of JAK1 by total exonic resequencing of bone marrow DNA samples from 94 patients with de novo AML. We identified 2 novel somatic mutations in highly conserved residues of the JAK1 gene (T478S, V623A), in 2 separate patients and confirmed these by resequencing germ line DNA samples from the same patients. Overexpression of mutant JAK1 did not transform primary murine cells in standard assays, but compared with wild-type JAK1, JAK1T478S, and JAK1V623A expression was associated with increased STAT1 activation in response to type I interferon and activation of multiple downstream signaling pathways. This is the first report to demonstrate somatic JAK1 mutations in AML and suggests that JAK1 mutations may function as disease-modifying mutations in AML pathogenesis. 相似文献
984.
To assess the effects of acute cardioselective beta blockade on ventilatory function in patients with COPD and active cardiac disorders, 50 patients were studied during intravenous infusion of esmolol. All patients had an obstructive ventilatory component on baseline pulmonary function testing, and 58 percent had a significant bronchodilator response to inhaled albuterol. Esmolol infusion (8 to 24 mg/min) produced large decreases in heart rate (84 +/- 2 to 69 +/- 2 beats/min, p less than 0.01) and SBP (124 +/- 3 to 106 +/- 3 mm Hg, p less than 0.01). Despite this marked hemodynamic response, there was no significant group effect of beta blockade on pulmonary function. No patient experienced dyspnea or wheezing with acute esmolol infusion; however, three patients (6 percent) developed asymptomatic decreases of FEV1. It is concluded that acute beta blockade with esmolol can be achieved in patients with COPD and cardiac disorders with little risk of bronchospasm. 相似文献
985.
Kasper Korsholm Jesper Møller Jensen Bjarne Linde Nørgaard Athanasios Samaras Jacqueline Saw Sergio Berti Apostolos Tzikas Jens Erik Nielsen-Kudsk 《JACC: Cardiovascular Interventions》2021,14(1):83-93
ObjectivesThis study aimed to investigate cardiac computed tomography (CT) and transesophageal echocardiography (TEE) peridevice leak (PDL) assessments, and the clinical relevance of PDL.BackgroundPDL assessment is integral during follow-up after left atrial appendage (LAA) occlusion. Comparative studies of TEE and cardiac CT are sparse, and the clinical relevance of PDL is uncertain.MethodsThis was a single-center observational study of consecutive patients undergoing LAA occlusion with Amplatzer devices (Amplatzer Cardiac Plug/Amulet) between 2010 and 2018 (N = 415). Patients with both 8-week CT and TEE were included for analysis (n = 346). Images were analyzed by blinded investigators (K.K. and A.S.). PDL on cardiac CT was classified from grade 1 to 3, based on PDL at the device disc, device lobe, and LAA contrast patency. Primary clinical outcome was a composite of ischemic stroke, transient ischemic attack, systemic embolism, or all-cause death.ResultsPDL was present in 110 patients (32%) by TEE, with 29 (8%) >3 mm. By cardiac CT, 210 patients (61%) had PDL at the disc, with contrast patency in 204 patients (59%). A grade 3 PDL (gap at disc, lobe, and LAA contrast patency) was present in 63 patients (18%). Bland-Altman analysis showed poor agreement between CT and TEE for leak sizing. CT and TEE detected PDL was not significantly associated with worse outcome, hazard ratio: 1.82 (95 % confidence interval: 0.95 to 3.50); p = 0.07 and hazard ratio: 1.43 (95% confidence interval: 0.74 to 2.76); p = 0.28, respectively.ConclusionsPDL occurrence is substantially higher with CT compared with TEE, with a large discrepancy between modalities in leak quantification. A novel CT-based classification is proposed, yet PDL was not associated with worse clinical outcome. 相似文献
986.
M Friedman C E Thoresen J J Gill D Ulmer L H Powell V A Price B Brown L Thompson D D Rabin W S Breall 《American heart journal》1986,112(4):653-665
One thousand thirteen post myocardial infarction patients were observed for 4.5 years to determine whether their type A (coronary-prone) behavior could be altered and the effect such alteration might have on the subsequent cardiac morbidity and mortality rates of these individuals. Eight hundred sixty-two of these individuals were randomly assigned either to a control section of 270 participants who received group cardiac counseling or an experimental section of 592 participants who received both group cardiac counseling and type A behavioral counseling. The remaining 151 patients, serving as a "comparison group," did not receive group counseling of any kind. Using the "Intention-to-Treat" principle, we observed markedly reduced type A behavior at the end of 4.5 years in 35.1% of participants given cardiac and type A behavior counseling compared with 9.8% of participants given only cardiac counseling. The cumulative 4.5-year cardiac recurrence rate was 12.9% in the 592 participants in the experimental group that received type A counseling. This recurrence rate was significantly less (p less than 0.005) than either the recurrence rate (21.2%) observed in the 270 participants in the control group or the recurrence rate (28.2%) in those of the comparison group not receiving any special treatment. After the first year, a significant difference in number of cardiac deaths between the experimental and control participants was observed during the remaining 3.5 years of the study. Overall, the results of this study demonstrate for the first time, within a controlled experimental design, that altering type A behavior reduces cardiac morbidity and mortality in post infarction patients. 相似文献
987.
Richard H. Turnage Frederic E. Eckhauser Aaron I. Vinik William E. Strodel Norman W. Thompson Anne Smid David Smid 《Journal of gastrointestinal cancer》1988,3(6):477-489
Summary Cystic neoplasms of the pancreas (CNP) are rare lesions that can be difficult to diagnose preoperatively. Twenty patients
with cystic neoplasms of the pancreas including five microcystic adenomas, six benign mucinous cystic neoplasms, three malignant
mucinous cystic neoplasms, two solid and papillary epithelial neoplasms, and four cystic neuroendocrine tumors were treated
at a single institution between 1962 and 1987. The average duration of symptoms prior to diagnosis was 10 months. Five patients
were asymptomatic. Forty percent of patients presented with an abdominal mass. Plain abdominal x-rays and UGI barium contrast
studies were never diagnostic. Ultrasonography, computerized tomography (CT) and visceral angiography aided in the correct
diagnosis in 28%, 36%, and 75% of patients studied, respectively. Overall a correct diagnosis was made preoperatively in only
35% of patients. Twelve of 13 patients were correctly diagnosed at laparotomy with intraoperative biopsy. Without biopsy the
mass was misdiagnosed at laparotomy in five of six cases.
CNP must be suspected inany patients who present with an upper abdominal mass with or without abdominal pain and no history of pancreatitis. CT may be
diagnostic in up to one third of cases and should be obtained routinely to demonstrate the proximity of the lesion to other
structures. Visceral angiography should also be obtained prior to operation. A generous incisional biopsy should be obtained
of all pancreatic cysts that are not to be resected. 相似文献
988.
989.
Amorosi SL Tsilimingras K Thompson D Fanikos J Weinstein MC Goldhaber SZ 《The American journal of cardiology》2004,93(4):509-511
Patients on long-term anticoagulation who require interruption of therapy for surgery may receive "bridging therapy" with continuous-infusion unfractionated heparin or low-molecular-weight heparin (LMWH). We estimated the costs of bridging therapy with: (1) LMWH self-administered at home, (2) LMWH administered by a nurse to patients at home, and (3) continuous-infusion unfractionated heparin in the hospital. For surgeries requiring an overnight stay, bridging costs are estimated to be 672, 933, and 3,816 US dollars, respectively, for each of these strategies. 相似文献
990.
Pacheco FJ Servin J Dang D Kim J Molinaro C Daniels T Brown-Bryan TA Imoto-Egami M Casiano CA 《Arthritis and rheumatism》2005,52(7):2133-2145
OBJECTIVE: Autoantibodies to DNA topoisomerase I (topo I) are associated with diffuse systemic sclerosis (SSc), appear to be antigen driven, and may be triggered by cryptic epitopes exposed during in vivo topo I fragmentation. These autoantibodies recognize topo I and fragments of this autoantigen generated during apoptosis and necrosis. We undertook this study to determine whether lysosomal cathepsins are involved in topo I fragmentation during necrosis. METHODS: Topo I cleavage during necrosis was assessed by immunoblotting of lysates from L929 fibroblasts exposed to tumor necrosis factor alpha (TNFalpha) and the broad caspase inhibitor Z-VAD-FMK, and by immunoblotting of lysates from endothelial cells treated with HgCl2. Purified topo I and L929 nuclei were incubated with cathepsins B, D, G, H, and L, and topo I cleavage was detected by immunoblotting. The intracellular localization of cathepsin L activity and topo I in necrotic cells was examined using fluorescence microscopy. RESULTS: Treatment of L929 cells with TNFalpha and Z-VAD-FMK induced caspase-independent cell death with necrotic morphology. This cell death involved topo I cleavage into fragments of approximately 70 kd and 45 kd. This cleavage profile was reproduced in vitro by cathepsins L and H and was inhibited by the cathepsin L inhibitor Z-FY-CHO. During necrosis, cathepsin L activity diffused from lysosomes into the cytoplasm and nucleus, whereas topo I partially relocalized to the cytoplasm. Z-FY-CHO delayed necrosis and partially blocked topo I cleavage. The topo I cleavage fragments were also detected in necrotic endothelial cells and recognized by SSc sera containing anti-topo I antibodies. CONCLUSION: These results implicate cathepsins, particularly cathepsin L, in the cleavage of topo I during necrosis. This cleavage may generate potentially immunogenic fragments that could trigger anti-topo I immune responses in SSc. 相似文献