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   9172篇
  免费   534篇
  国内免费   19篇
耳鼻咽喉   95篇
儿科学   286篇
妇产科学   278篇
基础医学   1342篇
口腔科学   371篇
临床医学   776篇
内科学   1632篇
皮肤病学   406篇
神经病学   793篇
特种医学   310篇
外国民族医学   3篇
外科学   1330篇
综合类   87篇
一般理论   3篇
预防医学   549篇
眼科学   96篇
药学   459篇
中国医学   6篇
肿瘤学   903篇
  2021年   119篇
  2020年   64篇
  2019年   102篇
  2018年   147篇
  2017年   90篇
  2016年   164篇
  2015年   199篇
  2014年   230篇
  2013年   297篇
  2012年   449篇
  2011年   494篇
  2010年   264篇
  2009年   281篇
  2008年   412篇
  2007年   470篇
  2006年   425篇
  2005年   428篇
  2004年   390篇
  2003年   388篇
  2002年   399篇
  2001年   232篇
  2000年   215篇
  1999年   193篇
  1998年   101篇
  1997年   117篇
  1996年   80篇
  1995年   60篇
  1994年   71篇
  1992年   106篇
  1991年   135篇
  1990年   126篇
  1989年   122篇
  1988年   130篇
  1987年   117篇
  1986年   116篇
  1985年   124篇
  1984年   80篇
  1983年   60篇
  1982年   69篇
  1979年   85篇
  1978年   70篇
  1977年   78篇
  1975年   57篇
  1974年   66篇
  1973年   78篇
  1972年   74篇
  1971年   78篇
  1970年   81篇
  1969年   62篇
  1968年   76篇
排序方式: 共有9725条查询结果,搜索用时 31 毫秒
1.
2.
3.
Antioxidant preservatives prolong the quality of food and ensure the nutritional adequacy, palatability and safety of many processed foods and beverages. Effects of sodium sulfite (E221) and sorbic acid (E200) were investigated in human peripheral blood mononuclear cells (PBMC) which were purified from blood of healthy donors. Cells were stimulated with the mitogen phytohaemagglutinin in vitro, which induces proliferation of T-cells and the production of Th1-type cytokines like interferon-γ. The latter triggers enzyme indoleamine (2,3)-dioxygenase, which degrades tryptophan, and GTP cyclohydrolase I, which leads to increased neopterin production, in monocyte-derived macrophages. Sodium sulfite and sorbic acid suppressed both these biochemical changes in a dose-dependent way (P < 0.01 at 1 mM sodium sulfite and 50 mM sorbic acid). Data demonstrate a suppressive influence of sodium sulfite and sorbic acid on the activated Th1-type immune response.  相似文献   
4.
BACKGROUND: Endothelin, a peptide with strong vasoconstrictive and mitogenic properties, has been found to increase after cardiac transplantation. We therefore assessed the association between its precursor peptide, big endothelin-1, and intimal hyperplasia and coronary flow reserve after heart transplantation. METHODS: Thirty-five patients without hemodynamically significant coronary artery disease after heart transplantation were investigated: Average peak flow velocity in the left anterior descending artery (LAD) was assessed by intracoronary Doppler at baseline as well as after injection of adenosine; coronary flow reserve was calculated as a ratio of both and was corrected for patient age and baseline average peak flow velocity. Lumen, intima + media and total vessel area were measured by intracoronary ultrasound. The plasma concentration of big endothelin-1 in venous blood was determined by radioimmunoassay. RESULTS: Patients with elevated big endothelin-1 levels (>2 fmol/ml) tended to have a decreased corrected coronary flow reserve (2.60 +/- 0.9 vs 3.21 +/- 1.0, p = 0.078). They also had a significantly larger intima + media area (5.82 +/- 2.9 vs 2.37 +/- 2.9 mm(2), p = 0.004) and total vessel area (18.36 +/- 5.8 vs 12.81 +/- 4.8 mm(2), p = 0.012) than those with normal plasma concentrations. CONCLUSIONS: Our study suggests an association between elevated big endothelin-1 plasma levels and the development of intimal hyperplasia and reduction of coronary flow reserve after cardiac transplantation.  相似文献   
5.
BACKGROUND: The problems associated with rectal surgery are frequently discussed with no reference being made to the distance of the tumor from the anal verge. This study examined the effect of the location of the tumor on early postoperative results. PATIENTS AND METHODS: This was a multicenter study involving 75 German hospitals and 3756 patients, of whom 1463 had rectal carcinoma. On the basis of the location of the tumor (distance from the anal verge), four groups were distinguished: <4, 4-7.9, 8-11.9, and 12-16 cm. RESULTS: Resection and abdominoperineal resection rates and the incidence of postoperative complications depended on the location of the tumor. Significantly higher resection rates and fewer specific complications, and a significant reduction in overall postoperative morbidity were found with tumor locations more than 8 cm from the anal verge. The highest anastomotic leak rate was observed with anastomoses less than 7 cm from the anal verge. The logistic regression showed that the distance of the tumor from the anal verge is an independent variable for the development of an anastomotic leak. CONCLUSIONS: Early results are greatly affected by the location of the rectal carcinoma. This applies to both abdominoperineal resection rates and specific postoperative complications, such as anastomotic leak rate and operation morbidity in general.  相似文献   
6.
7.
Spinal Ewing's sarcomas are rare and cause problems in differential diagnosis. The radiologic, nuclear medicine and CT findings in two children with histologically proven Ewing's sarcoma are presented and problems in differential diagnosis discussed. Biopsy should be done early.  相似文献   
8.
PURPOSE: To compare commercial treatment-planning systems (TPS) for inverse planning (IP) and to assess constraint variations for specific IMRT indications. MATERIAL AND METHODS: For IP, OTP, XiO and BrainSCAN were used and step-and-shoot intensity-modulated radiotherapy (IMRT) delivery was assumed. Based on identical constraints, IP was performed for a prostate, head and neck, brain, and gynecologic case. IMRT plans were compared in terms of conformity/homogeneity, dose-volume histograms (DVHs), and delivery efficiency. For ten patients each of a class of indications, constraint variations were evaluated. RESULTS: IMRT plans were comparable concerning minimum target dose, homogeneity, conformity, and maximum doses to organs at risk. Larger differences were seen in dose gradients outside the target, monitor units, and segment number. Using help structures proved efficient to shape isodoses and to reduce segmentation workload. For IMRT class solutions, IP constraint variations depended on anatomic site. CONCLUSION: IP systems requiring doses as input and having objective functions based on physical parameters had a very similar performance. Constraint templates can be established for a class of IMRT indications.  相似文献   
9.
The value of a long-term treatment with clonazepam in the prophylaxis of affective disorder is discussed controversially in the scientific literature. Altogether there are only a few reports on the use of this compound as a mood stabilizer, most of them describing patients suffering from bipolar affective disorder. The aim of this investigation was to evaluate clonazepam as a phase prophylactic medication in affective disorder. We conducted a retrospective chart review in 34 out-patients of our lithium clinic (15 suffering from unipolar depression, 15 from bipolar disorder, four from schizoaffective disorder), who had been treated with clonazepam as a long-term medication. Clonazepam was either given as monotherapy, or as in the case of lithium non-responders, as adjunctive therapy. Patients with unipolar depression had significantly (P=0.026) less depressive episodes after initiation of treatment with clonazepam. Patients with bipolar disorder did not benefit from this therapy. Neither manic/hypomanic phases nor depressive episodes were reduced in this group of patients. Interestingly, clonazepam also reduced affective phases in our four schizoaffective patients on a trend level. Our results indicate that patients with unipolar depression may benefit from a maintenance treatment with clonazepam. Due to methodological limitations our results need to be replicated in controlled double-blind randomized clinical trials.  相似文献   
10.
Mechanical airway obstruction secondary to retropharyngeal bleeding is rare. In most cases such a complication is described after head and neck trauma. Complicating factors include anticoagulant therapy, tumour, aneurysm, infection or major cervical spine injury. A precise initial diagnosis is necessary to avoid a life-threatening situation. Lateral X-ray and computed tomography is essential for safe management. Treatment depends upon size of the haematoma as well as the clinical course of the patient. Smaller haematomas may be observed. Lager haematomas and those that fail to reabsorb should undergo drainage.   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