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   2823篇
  免费   198篇
  国内免费   46篇
耳鼻咽喉   37篇
儿科学   122篇
妇产科学   72篇
基础医学   291篇
口腔科学   166篇
临床医学   319篇
内科学   448篇
皮肤病学   67篇
神经病学   180篇
特种医学   384篇
外科学   210篇
综合类   58篇
一般理论   3篇
预防医学   225篇
眼科学   49篇
药学   216篇
  1篇
中国医学   14篇
肿瘤学   205篇
  2022年   17篇
  2021年   28篇
  2020年   24篇
  2019年   26篇
  2018年   47篇
  2017年   69篇
  2016年   130篇
  2015年   64篇
  2014年   63篇
  2013年   98篇
  2012年   83篇
  2011年   98篇
  2010年   71篇
  2009年   100篇
  2008年   79篇
  2007年   103篇
  2006年   67篇
  2005年   101篇
  2004年   84篇
  2003年   101篇
  2002年   91篇
  2001年   82篇
  2000年   80篇
  1999年   82篇
  1998年   95篇
  1997年   93篇
  1996年   69篇
  1995年   68篇
  1994年   48篇
  1993年   56篇
  1992年   55篇
  1991年   44篇
  1990年   44篇
  1989年   60篇
  1988年   39篇
  1987年   68篇
  1986年   51篇
  1985年   38篇
  1984年   39篇
  1983年   29篇
  1982年   27篇
  1981年   20篇
  1980年   20篇
  1979年   23篇
  1977年   26篇
  1975年   22篇
  1974年   28篇
  1971年   20篇
  1970年   22篇
  1968年   18篇
排序方式: 共有3067条查询结果,搜索用时 0 毫秒
51.
BACKGROUND: The impact of anesthetic choice on postoperative mortality and morbidity has not been determined with certainty. METHODS: The authors evaluated the effect of type of anesthesia on postoperative mortality and morbidity in a retrospective cohort study of consecutive hip fracture patients, aged 60 yr or older, who underwent surgical repair at 20 US hospitals between 1983 and 1993. The primary outcome was defined as death within 30 days of the operative procedure. The secondary outcomes were postoperative 7-day mortality, postoperative myocardial infarction, postoperative pneumonia, postoperative congestive heart failure, and postoperative change in mental status. Numerous comorbid conditions were controlled for individually and by several comorbidity indices using logistic regression. RESULTS: General anesthesia was used in 6,206 patients (65.8%) and regional anesthesia in 3,219 patients (3,078 spinal anesthesia and 141 epidural anesthesia). The 30-day mortality rate in the general anesthesia group was 4.4%, compared with 5.4% in the regional anesthesia group (unadjusted odds ratio = 0.80; 95% confidence interval = 0.66-0.97). However, the adjusted odds ratio for general anesthesia increased to 1.08 (0.84-1.38). The adjusted odds ratios for general anesthesia versus regional anesthesia for the 7-day mortality was 0.90 (0.59-1.39) and for postoperative morbidity outcomes were as follows: myocardial infarction: adjusted odds ratio = 1.17 (0.80-1.70); congestive heart failure: adjusted odds ratio = 1.04 (0.80-1.36); pneumonia: adjusted odds ratio = 1.21 (0.87-1.68); postoperative change in mental status: adjusted odds ratio = 1.08 (0.95-1.22). CONCLUSIONS: The authors were unable to demonstrate that regional anesthesia was associated with better outcome than was general anesthesia in this large observational study of elderly patients with hip fracture. These results suggest that the type of anesthesia used should depend on factors other than any associated risks of mortality or morbidity.  相似文献   
52.
53.
PURPOSE: The clinical objective of this trial was to evaluate gefitinib in patients with metastatic colorectal cancer that had progressed despite prior treatment. Serial tumor biopsies were performed when possible and analyzed for activation of the epidermal growth factor receptor (EGFR) signaling pathway. Serial serum samples were measured for amphiregulin and transforming growth factor-alpha (TGFalpha). PATIENTS AND METHODS: One hundred fifteen patients were randomly assigned to receive gefitinib 250 or 500 mg orally once a day. One hundred ten patients were assessable for clinical efficacy. Biologic evaluation was performed on paired tumor samples from 28 patients and correlated with clinical outcome. RESULTS: Median progression-free survival was 1.9 months (95% CI, 1.8 to 2.1 months) and 4-month progression-free survival rate was 13% +/- 5%. One patient achieved a radiographic partial response (RR = 1%; 95% CI, 0.01% to 5%). Median survival was 6.3 months (95% CI, 5.1 to 8.2 months). The most common adverse events were skin rash, diarrhea, and fatigue. In the biopsy cohort, expression of total or activated EGFR, activated Akt, activated MAP-kinase, or Ki67 did not decrease following 1 week of gefitinib. However, a trend toward decreased post-treatment levels of activated Akt and Ki67 was observed in patients with a PFS higher than the median, although these did not reach the .05 level of significance. CONCLUSION: Gefitinib is inactive as a single agent in patients with previously treated colorectal cancer. In tumor samples, gefitinib did not inhibit activation of its proximal target, EGFR. Trends were observed for inhibition of downstream regulators of cellular survival and proliferation in patients achieving longer progression-free survival.  相似文献   
54.
55.
氯地滴眼液的含量测定   总被引:4,自引:0,他引:4  
目的:采用HPLC法测定氯地滴眼液中氯霉素和地塞米松磷酸钠的含量。方法:色谱分析条件:ODS柱作分析柱,流动相为甲醇/水体系,0 ̄8min使用40%甲醇,8 ̄16min使用60%甲醇,流速1ml/min,0 ̄9min240nm紫外检测,:二组分分离良好。各组各组性关系良好,平均回收率氯霉素99.8%(RSD=1.2%,n=5),地塞米松磷酸钠99.4%(RSD=0.7%,n=5),结论:该法用于氯  相似文献   
56.
Cell cultures of THUJA OCCIDENTIALIS L. were found to biosynthesize various mono- and diterpenes when grown on B5-medium. The identification of the constituents was achieved mainly by capillary GLC-MS using fused silica columns and E.I.-mass spectrometry. Monoterpenes of the menthane type were only isolated from the culture medium whereas diterpenes were found in the cell extracts. Thujaplicin derivatives, monoterpenes of an irregular type, were detected in the medium as well as in the cells. Major differences were found between the terpene composition of the cell culture extracts and those from THUJA leaves. The cell cultures accumulated some compounds which are presently unknown as constituents of THUJA plants. On the other hand, the cultures were evidently unable to synthesize the thujone type of monoterpenes.  相似文献   
57.
C Y Lowder  A J Berlin  W A Cox  J F Hahn 《Ophthalmology》1986,93(10):1351-1354
Benign osteoblastoma is a rare, solitary, vascular, osteoid-producing tumor that is rich in osteoblasts. This is the first report of a case of osteoblastoma of the orbit not contiguous with a sinus cavity.  相似文献   
58.
59.
60.
OBJECTIVES: We sought to perform a preliminary comparison of signal-to-noise ratio (SNR) and image quality for magnetic resonance imaging (MRI) of the pancreas at 1.5 and 3 T. MATERIALS AND METHODS: Two imaging cohorts were studied using a T2-weighted, single-shot fast spin-echo pulse sequence and a T1-weighted, fat-suppressed 3D gradient-echo pulse sequence. In the first cohort, 4 subjects were imaged using identical imaging parameters before and after contrast administration at 1.5 and 3.0 T. The SNR was quantified for the pancreas as well as for the liver, spleen, and muscle. In a second cohort of 12 subjects in whom the receiver bandwidth was adjusted for field strength, SNR measurements and qualitative rankings of image quality were performed. RESULTS: In the study cohort using identical imaging parameters at both magnetic field strengths, the mean (SD) ratios of SNR at 3.0 to 1.5 T of the single-shot fast spin-echo images for the pancreas, liver, spleen, and muscle were 1.63 (0.39), 1.82 (0.39), 1.45 (0.18), 2.01 (0.16), respectively. For the precontrast fat-suppressed 3D gradient-echo sequence, the corresponding ratios were 1.28 (0.29), 1.26 (0.30), 1.16 (0.27), and 1.76 (0.45), respectively; for the arterial phase, the corresponding ratios were 2.02 (0.28), 1.60 (0.42), 1.47 (0.26), and 1.94 (0.32), respectively; and for the delayed postcontrast phase, the corresponding ratios were 1.63 (0.51), 2.01 (0.25), 1.66 (0.06), and 2.31 (0.47), respectively. The SNR benefit of 3.0 T was significantly greater on contrast-enhanced as compared with noncontrast T1-weighted 3D gradient-echo images. In the second study cohort, SNR was superior at 3.0 T, although the use of a reduced readout bandwidth at 1.5 T substantially diminished the advantage of the higher field system. With qualitative comparison of images obtained at the 2 magnetic field strengths, the fat-suppressed 3D gradient-echo images obtained at 3.0 T were preferred, whereas the single shot fast spin-echo images obtained at 1.5 T were preferred because of better signal homogeneity. CONCLUSIONS: Our results in a small cohort of volunteers and patients demonstrate a marked improvement in SNR at 3.0 T compared with 1.5 T (by a factor of 2 in some cases) when identical imaging parameters were used. The SNR advantage at 3.0 T is diminished but persists when the receiver bandwidth is adjusted for magnetic field strength. The results suggest that 3.0 T may offer promise for improved body MRI, although further technical development to optimize SNR and improve signal homogeneity will be needed before its full potential can be achieved.  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