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   12980篇
  免费   1361篇
  国内免费   15篇
耳鼻咽喉   168篇
儿科学   306篇
妇产科学   394篇
基础医学   1791篇
口腔科学   276篇
临床医学   1276篇
内科学   2446篇
皮肤病学   275篇
神经病学   867篇
特种医学   565篇
外科学   1855篇
综合类   335篇
一般理论   7篇
预防医学   1299篇
眼科学   363篇
药学   798篇
中国医学   6篇
肿瘤学   1329篇
  2021年   174篇
  2019年   186篇
  2018年   164篇
  2017年   147篇
  2016年   144篇
  2015年   183篇
  2014年   287篇
  2013年   415篇
  2012年   569篇
  2011年   545篇
  2010年   340篇
  2009年   301篇
  2008年   533篇
  2007年   547篇
  2006年   551篇
  2005年   557篇
  2004年   563篇
  2003年   560篇
  2002年   475篇
  2001年   413篇
  2000年   424篇
  1999年   422篇
  1998年   167篇
  1997年   152篇
  1996年   137篇
  1995年   131篇
  1994年   117篇
  1993年   111篇
  1992年   287篇
  1991年   291篇
  1990年   273篇
  1989年   247篇
  1988年   260篇
  1987年   234篇
  1986年   213篇
  1985年   232篇
  1984年   185篇
  1983年   201篇
  1982年   136篇
  1981年   119篇
  1980年   129篇
  1979年   173篇
  1978年   128篇
  1977年   120篇
  1976年   133篇
  1975年   128篇
  1974年   121篇
  1973年   132篇
  1972年   101篇
  1971年   102篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Seventy-nine patients with moderate to severe left ventricular dysfunction who underwent aortocoronary bypass grafting between 1971 and 1977 had follow-up heart catheterization at a mean interval of 3 years. Thirty-three patients (42%) had angiographic improvement in left ventricular function at follow-up and 18 (25%) had a decrease in left ventricular end-diastolic pressure. Fifty-eight patients (73%) had improvement in angina of at least one New York Heart Association class at follow-up. There was no correlation between late improvement in left ventricular function and improvement in angina. Improvement in left ventricular function did not correlate with preoperative indices of severity of coronary disease or with indices of completeness of surgical repair.  相似文献   
22.
The behavior of the free acid and ammonium salt of maduramicin towards heat and alcohols is examined. In refluxing lower alcohols the free acid material is decarboxylated. In addition a bisketal decarboxylated compound as well as an A-ring monoketal decarboxylated derivative are formed. Heating the ammonium salt of the ionophores in suspension in water, or dissolved in inert solvents such as heptane or xylene can cause decarboxylation as well as concomitant dehydration of the F-ring. Reaction of dansyl chloride with the free acid of maduramicin can cause dehydration of the B-ring under very mild conditions.  相似文献   
23.
24.
OBJECTIVE. Our objective was to study the imaging findings in patients who had gastric and duodenal obstruction as a long-term complication of cholangiocarcinoma and to determine if the obstruction was associated with radiation therapy. MATERIALS AND METHODS. Between 1973 and 1989, 96 patients had either curative resection or palliative stenting for cholangiocarcinoma involving the hepatic duct bifurcation. Sixty-three (66%) also received adjuvant radiation therapy ranging from 4960 to 7220 rad (cGy). Gastric outlet or duodenal obstruction or both developed subsequently in seven of the 63 patients treated with radiation therapy. Radiographic studies, including upper gastrointestinal series and CT, and medical and surgical records for these seven patients were retrospectively reviewed. RESULTS. Upper gastrointestinal series in the seven patients with obstruction showed narrowing of the lumen, deformity and enlargement of gastric and duodenal mucosal folds, and delayed gastric emptying. CT performed in five of the seven patients showed thickening of the wall of the gastric antrum and small bowel and retained food and fluid within the stomach. All seven patients required gastrojejunostomy; at surgery, dense adhesions and fibrosis were found, and it was not evident whether the obstruction was due to the tumor or to radiation fibrosis. However, because this complication was seen only after radiotherapy, it was presumed to be radiation fibrosis. CONCLUSION. Our experience suggests that radiation therapy increases the risk of postoperative gastric and duodenal obstruction in patients undergoing surgery for cholangiocarcinoma.  相似文献   
25.
Cholesterol intakes in Britain have been re-estimated by analysing Total Diet samples taken in 1991 and from 1993 National Food Survey records. The Total Diet samples contained only 284 mg/day compared with 319 mg/day in 1987 and 337 mg/day in 1981, while the National Food Survey showed intakes had fallen to 238 mg/day from 259 mg/day in 1990 and 405 mg/day in 1970-75. More details of the intakes by adults in 1986/87 are given, and compared with the results from the other methods. Daily intakes of eight phytosterols were also estimated, the main ones being β-sitosterol, campesterol, stigmasterol and 57-stigmastenol whose intakes were 104, 49, 10 and 4 mg/day, respectively, in 1991. These intakes had increased since 1981, reflecting the rising consumption of vegetable oils.  相似文献   
26.
Fat absorption from two different premature infant formulas and one full-term formula containing three different fat blends was investigated in two groups of premature infants. The first group of nine infants (gestational age, 29.1 +/- 0.88 weeks; postnatal age, 3.13 +/- 0.71 weeks) was fed alternately for 1 week each SMA preterm formula containing either high levels (50%) of medium-chain triglycerides (MCT) (6:0, 8:0, and 10:0) or high levels (86%) of long-chain triglycerides (LCT) (greater than or equal to C12). Except for fat blends, the formulas were otherwise identical. The second group of 11 infants (gestational age, 30.5 +/- 0.77 weeks, studied at a postnatal age of 4.33 +/- 0.91 weeks) was fed for 1 week a full-term infant formula, S-26, containing 98% LCT. Fat absorption (studied during a 3-day fat balance period) was similar irrespective of fat blend: 89.08 +/- 2.37% during feeding of preterm SMA, 50% MCT; 87.0 +/- 3.81% during feeding of preterm SMA, 86% LCT; and 83.00 +/- 2.89% during feeding of S-26, 98% LCT. Weight gain (grams per day) and increase in length (centimeters per day) were 23.2 +/- 1.7, 21.20 +/- 1.7, and 14.28 +/- 2.9, and 0.17 +/- 0.06, 0.16 +/- 0.04, and 0.22 +/- 0.07 during feeding of the three fat blends, respectively. Lipase activity levels in fasting gastric aspirates were higher during feeding of the LCT than the MCT formula. The possible stimulation of gastric lipase secretion secondary to long-chain fatty acid stimulation of cholecystokinin secretion might be related to the efficient digestion of formula fat, irrespective of triglyceride-fatty acid chain length.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
27.
Magnetic resonance (MR) imaging may be a noninvasive method for assessing perfusion of vascularized bone grafts placed for treatment of avascular necrosis. One proximal femur of seven beagles was devascularized, with insertion of a vascularized fibular graft. MR imaging at 1 week (seven dogs) and 6 weeks (five dogs) after surgery included pre- and postcontrast spin-echo sequences, unenhanced twodimensional time-of-flight (TOF) vascular imaging, and dynamic gradient-echo imaging during infusion of gadolinium. Relative signal intensity values of selected regions obtained from the dynamic gradientecho images were plotted as percent enhancement versus time. In the operated hip, MR imaging did not show enhancement in six of seven femoral heads and greater trochanters at 1 week after surgery, with similar results after 6 weeks. MR imaging of fibular grafts 6 weeks after surgery showed an initial rapid increase in enhancement and a subsequent slower increase in five of five dogs, although no enhancement was seen in six of seven dogs at 1 week. These findings contrasted with a rapid initial increase in enhancement followed by slow decline in non-operated hips. Two-dimensional TOP imaging did not show the vascular pedicle of the graft in any dog. Findings of radionuclide bone scanning performed 1 week after surgery were consistent with devascularization of the operated femur and fibular graft. However, tetracycline distribution and histologic findings confirmed the viability of five of five grafts within the devascularized femurs 6 weeks after surgery. Thus, dynamic contrast-enhanced MR imaging at 6 weeks after surgery is valuable for assessing vascular bone graft perfusion, while similar imaging at 1 week may suggest otherwise.  相似文献   
28.
Surgical resection for metastatic melanoma to the lung   总被引:5,自引:0,他引:5  
From 1971 through December 1986, the courses of 47 patients who underwent thoracotomy for pulmonary metastases from melanoma were retrospectively reviewed to determine the efficacy of this approach in the management of selected patients with melanoma. The overall five-year survival rate was 25% (median survival, 19 months). Thirty-eight patients were free of disease following thoracotomy. These patients fared significantly better than those who had residual disease following thoracotomy, with a five-year survival rate of 31% (median survival, 24 months) compared with 0% (median survival, six months). Survival was not influenced by the addition of adjuvant therapy or duration of time before the development of metastases (less than 12 months vs greater than or equal to 12 months). In selected patients with melanoma metastatic to the lung, thoracotomy with complete excision of the metastatic deposits results in improved survival and should be considered the treatment of choice.  相似文献   
29.
We report a case of a patient with CF who had a long history of recurrent distal intestinal obstruction syndrome. She had been treated with conventional treatment including gastrografin, n-acetyl cysteine, Klean prep and Picolax. She underwent a modified antegrade continence enema procedure. She currently irrigates her conduit every 2-3 days. She has had no further symptoms of distal intestinal obstruction syndrome.  相似文献   
30.
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