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   5571篇
  免费   391篇
  国内免费   21篇
耳鼻咽喉   68篇
儿科学   113篇
妇产科学   45篇
基础医学   720篇
口腔科学   110篇
临床医学   593篇
内科学   1287篇
皮肤病学   135篇
神经病学   432篇
特种医学   366篇
外科学   829篇
综合类   27篇
一般理论   5篇
预防医学   349篇
眼科学   210篇
药学   351篇
中国医学   5篇
肿瘤学   338篇
  2023年   37篇
  2022年   83篇
  2021年   144篇
  2020年   84篇
  2019年   138篇
  2018年   174篇
  2017年   131篇
  2016年   159篇
  2015年   196篇
  2014年   225篇
  2013年   316篇
  2012年   423篇
  2011年   451篇
  2010年   260篇
  2009年   227篇
  2008年   329篇
  2007年   340篇
  2006年   354篇
  2005年   309篇
  2004年   264篇
  2003年   289篇
  2002年   237篇
  2001年   78篇
  2000年   73篇
  1999年   57篇
  1998年   48篇
  1997年   38篇
  1996年   26篇
  1995年   23篇
  1994年   22篇
  1993年   15篇
  1992年   36篇
  1991年   42篇
  1990年   30篇
  1989年   24篇
  1988年   32篇
  1987年   23篇
  1986年   16篇
  1985年   18篇
  1984年   20篇
  1983年   19篇
  1982年   9篇
  1981年   11篇
  1979年   11篇
  1978年   9篇
  1977年   9篇
  1974年   16篇
  1973年   10篇
  1972年   13篇
  1970年   9篇
排序方式: 共有5983条查询结果,搜索用时 15 毫秒
51.
Host cell proteases such as TMPRSS2 are critical determinants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) tropism and pathogenesis. Here, we show that antithrombin (AT), an endogenous serine protease inhibitor regulating coagulation, is a broad-spectrum inhibitor of coronavirus infection. Molecular docking and enzyme activity assays demonstrate that AT binds and inhibits TMPRSS2, a serine protease that primes the Spike proteins of coronaviruses for subsequent fusion. Consequently, AT blocks entry driven by the Spikes of SARS-CoV, MERS-CoV, hCoV-229E, SARS-CoV-2 and its variants of concern including Omicron, and suppresses lung cell infection with genuine SARS-CoV-2. Thus, AT is an endogenous inhibitor of SARS-CoV-2 that may be involved in COVID-19 pathogenesis. We further demonstrate that activation of AT by anticoagulants, such as heparin or fondaparinux, increases the anti-TMPRSS2 and anti-SARS-CoV-2 activity of AT, suggesting that repurposing of native and activated AT for COVID-19 treatment should be explored.  相似文献   
52.
This study examined the effect of a pharmacologically induced rightward shift in the partial pressure of oxygen at which 50% of hemoglobin is saturated (P50) on outcome from transient focal cerebral ischemia in the rat. Halothane anesthetized rats (n=20 per group) were given saline or a single 15-min infusion of 150 mg/kg RSR13 (2-[4-[[3,5-dimethylanilino) carbonyl]methyl]phenoxy]-2-methylproprionic acid) intravenously before or 30 min after onset of 75 min of middle cerebral artery filament occlusion (MCAO). Seven days later, severity of hemiparesis and cerebral infarct size were examined. RSR13 alone did not significantly improve outcome. Conscious normothermic rats (n=12 per group) were also given RSR13 (150 mg/kg) or 0.9% NaCl intravenously and subjected to 75 min of MCAO with 7 days of recovery. Again, RSR13 alone did not significantly reduce infarct size or improve neurologic score. A dose-response curve for dizocilpine (MK-801) was then constructed in conscious normothermic rats subjected to 75 min of MCAO. Dizocilpine (0.5 mg/kg i.v.) caused a 90% reduction in mean infarct size while 0.25 mg/kg reduced infarct size by 48%. Other rats were then subjected to 75 min of MCAO after being given dizocilpine (0.25 mg/kg i.v.; n=18) or RSR13 (150 mg/kg i.v. )+dizocilpine (0.25 mg/kg i.v.; n=15). RSR13+dizocilpine resulted in smaller cortical infarct volume (8+/-14 mm3 vs. 34+/-37 mm3, p<0.02) and total cerebral infarct volume (46+/-28 mm3 vs. 81+/-60 mm3, p<0. 05) compared to dizocilpine alone, respectively. We conclude that a pre-ischemic peak increase in P50 of approximately 25 mmHg alone is insufficient to reduce focal ischemic injury, but may be advantageous when used in conjunction with other neuroprotective agents.  相似文献   
53.
Organizational commitment on the part of nursing home employees can be a determinant of service quality. Proper design of health care jobs and clarity of roles make employees feel more dedicated to their jobs, enable them to do their jobs well, and enhance family members' evaluations of nursing home care. When management develops a dynamic, interactive, high-quality environment, nursing home employees feel encouraged to report shortcomings without fear because they are involved in the process.  相似文献   
54.
Steffen T  Tsantrizos A  Aebi M 《Spine》2000,25(9):1077-1084
STUDY DESIGN: A human cadaveric study on the compressive strength of different lumbar interbody fusion implants and endplate preparation techniques was performed. OBJECTIVES: To assess the axial compressive strength of an implant with peripheral endplate contact as opposed to full surface contact, and to assess whether removal of the central bony endplate affects the axial compressive strength. SUMMARY OF BACKGROUND DATA: The compressive strength of interbody fusion constructs has been compared between implants and bone grafts. Neither implant design nor endplate preparation has been shown to affect strength. Removal of the central bony endplate for bone grafts was noted to improve graft incorporation but also to facilitate subsidence. METHODS: A total of 44 vertebrae were tested in four experimental groups by combining two interbody implants (full-surface vs peripheral surface support) with two endplate preparation techniques (intact bony endplate vs removal of the central bony endplate). Specimens were tested to ultimate compressive failure using a 50 N/second ramped load. Yield strength and ultimate compressive strength were compared between groups using two-factor analysis of covariance. A P value less than 0.05 was considered significant. Stepwise linear regressions assessed the predictive power of age, bone mineral content, and the implant's normalized endplate coverage on yield strength and ultimate compressive strength. RESULTS: Neither implant design nor endplate preparation technique affected yield strength or ultimate compressive strength. Age, bone mineral content, and the normalized endplate coverage were strong predictors of yield strength (P < 0. 0001; r2 = 0.459) and ultimate compressive strength (P < 0.0001; r2 = 0.510). CONCLUSIONS: An implant with only peripheral support resting on the apophyseal ring offers axial mechanical strength similar to that of an implant with full support. Neither supplementary struts nor a solid implant face has any additional mechanical advantage, but reduces graft-host contact area. Removal of the central bony endplate is recommended because it does not affect the compressive strength and promotes graft incorporation.  相似文献   
55.
Fifty patients with impingement syndrome refractory to long-term conservative treatment were randomized to three treatment groups. All patients received an injection of 10 ml 0.5% bupivacaine, in group 1 without corticosteroid, in group 2 with crystalline corticosteroid and in group 3 with lipoid corticosteroid. Treatment in group 1 had to be stopped because of inefficacy. In groups 2 and 3 favorable results were achieved in 19 out of 40 patients.
Résumé  50 patients avec conflit sous-aeromial, qui ne montraient pas d’amélioration après un long traitement conservatif récevaient une injection dans la bourse subacromiale. Le premier groupe récevait une injection contenant un anaesthétique local pur, groupe 2 une mixture d’anaesthétique avec des corticostéroides cristalins et groupe 3 avec des corticostéroides lipoides. Le traitement du groupe 1 devait être arrété cause d’inificacité. 19 de 40 patients du groupe 2 et 3 montraient une amélioration après 6 mois.


Accepted: 6 January 2000  相似文献   
56.
57.
PURPOSE: To evaluate the predictive accuracy of the Palliative Prognostic (PaP) score in patients with advanced cancer under the care of an oncologist. PATIENTS AND METHODS: The PaP score was calculated in 100 consecutive patients with advanced cancer hospitalized under the care of a medical or radiation oncologist at a university teaching hospital in Australia. The attending oncologist predicted the survival duration for the purpose of the scoring. The positive predictive value of the PaP score was evaluated. Survival analysis was performed to compare the survival of the three prognostic groups. RESULTS: Assessable survival data were available for 98 patients. The overall median survival was 12 weeks (interquartile range, 7 to 25 weeks). The PaP score divided the heterogeneous patient sample into three isoprognostic groups related to the chance of surviving 1 month, with 64 patients in group A (> 70% chance), 32 patients in group B (30% to 70% chance), and four patients in group C (< 30% chance). The estimated median survival of the three groups was 17 weeks (95% CI, 12 to 26 weeks), 7 weeks (95% CI, 4 to 12 weeks), and less than 1 week (95% CI, < 1 to 3 weeks), respectively. These survival differences were highly significant (log-rank test of trend, chi1(2) = 25.65; P < .0001). The 1-month survival of the groups was 97%, 59%, and 25%, respectively. CONCLUSION: When oncologists' survival estimates are used, the PaP score is able to identify accurately three isoprognostic patient groups, irrespective of the cancer type. The PaP score may help reduce the uncertainty of formulating a prognosis in patients with advanced cancer.  相似文献   
58.
PURPOSE: The human ELAV (embryonic lethal abnormal vision)-like protein HuR stabilizes a certain group of cellular mRNAs that contain AU-rich elements in their 3'-untranslated region. Cell culture studies have shown that the mRNA of cyclooxygenase (COX)-2 can be stabilized by HuR. EXPERIMENTAL DESIGN: To investigate a possible contribution of dysregulation of mRNA stability to the progression of cancer and to overexpression of COX-2, we studied expression of HuR in 208 primary breast carcinomas by immunohistochemistry. RESULTS: There were two different staining patterns of HuR in tumor tissue of breast carcinomas: nuclear expression was seen in 61% of cases; and an additional cytoplasmic expression was seen in 30% of cases. Expression of HuR was significantly associated with increased COX-2 expression; this association was particularly significant for cytoplasmic HuR expression (P < 0.0005). We further observed a significant association of cytoplasmic (P = 0.002) or nuclear HuR (P = 0.027) expression with increased tumor grade. Only 13% of the grade 1 carcinomas showed cytoplasmic expression of HuR, compared with 46% of the grade 3 carcinomas. There was no significant correlation between HuR expression and other clinicopathological parameters such as histological type, tumor size, or nodal status as well as patient survival. CONCLUSIONS: Our results suggest that overexpression of HuR in tumor tissue may be part of a regulatory pathway that controls the mRNA stability of several important targets in tumor biology, such as COX-2. Based on our results, additional studies are necessary to investigate whether HuR might be a potential target for molecular tumor therapy.  相似文献   
59.
PURPOSE: Mannan-binding lectin-associated serine protease 2 (MASP-2) is a plasma protein involved in inflammatory processes. MASP-2 circulates in complex with the protein mannan-binding lectin (MBL) or ficolins, and is activated to recruit the complement system when MBL binds to its targets. The level of MASP-2 is genetically determined, and the aim of the present study was to evaluate the effect of MASP-2 levels on postoperative infection, recurrence and survival. EXPERIMENTAL DESIGN: MASP-2 concentrations were determined in serum from 605 patients collected before elective resection for primary colorectal cancer. The primary end points were postoperative infection, time to any recurrence, and time to death. The median time of follow-up was 7.9 years. RESULTS: MASP-2 levels were not correlated to postoperative infections (P = 0.49). High MASP-2 levels significantly correlated with recurrent cancer disease [P = 0.03; hazard ratio (HR) = 1.4; 95% confidence interval (CI), 1.0-2.0] and with poor survival (P = 0.0005; HR = 1.4; 95% CI, 1.2-1.7). Multivariate statistical analysis, including age, gender, Dukes' stage of disease, tumor localization, and postoperative pneumonia, showed that the MASP-2 level had an independent prognostic value in the patients (P = 0.0001; HR = 1.5; 95% CI, 1.2-1.8). CONCLUSION: In the cohort of patients with colorectal cancer investigated, MASP-2 concentration in serum proved to be an independent prognostic marker with high MASP-2 levels predicting recurrence and poor survival. Postoperative infection could not be shown to be associated with MASP-2 levels.  相似文献   
60.
PURPOSE: The L1 adhesion molecule (CD171) is overexpressed in human ovarian and endometrial carcinomas and is associated with bad prognosis. Although expressed as a transmembrane molecule, L1 is released from carcinoma cells in a soluble form. Soluble L1 is present in serum and ascites of ovarian carcinoma patients. We investigated the mode of L1 cleavage and the function of soluble L1. EXPERIMENTAL DESIGN: We used ovarian carcinoma cell lines and ascites from ovarian carcinoma patients to analyze soluble L1 and L1 cleavage by Western blot analysis and ELISA. RESULTS: We find that in ovarian carcinoma cells the constitutive cleavage of L1 proceeds in secretory vesicles. We show that apoptotic stimuli like C2-ceramide, staurosporine, UV irradiation, and hypoxic conditions enhance L1-vesicle release resulting in elevated levels of soluble L1. Constitutive cleavage of L1 is mediated by a disintegrin and metalloproteinase 10, but under apoptotic conditions multiple metalloproteinases are involved. L1 cleavage occurs in two types of vesicles with distinct density features: constitutively released vesicles with similarity to exosomes and apoptotic vesicles. Both types of L1-containing vesicles are present in the ascites fluids of ovarian carcinoma patients. Soluble L1 from ascites is a potent inducer of cell migration and can trigger extracellular signal-regulated kinase phosphorylation. CONCLUSIONS: We suggest that tumor-derived vesicles may be an important source for soluble L1 that could regulate tumor cell function in an autocrine/paracrine fashion.  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