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   13397篇
  免费   388篇
  国内免费   1篇
  13786篇
  2021年   130篇
  2020年   105篇
  2019年   133篇
  2018年   288篇
  2017年   252篇
  2016年   350篇
  2015年   370篇
  2014年   432篇
  2013年   585篇
  2012年   564篇
  2011年   590篇
  2010年   372篇
  2009年   279篇
  2008年   416篇
  2007年   431篇
  2006年   438篇
  2005年   410篇
  2004年   325篇
  2003年   364篇
  2002年   319篇
  2001年   282篇
  2000年   230篇
  1999年   182篇
  1998年   91篇
  1992年   237篇
  1991年   229篇
  1990年   185篇
  1989年   221篇
  1988年   237篇
  1987年   242篇
  1986年   220篇
  1985年   251篇
  1984年   205篇
  1983年   169篇
  1980年   87篇
  1979年   241篇
  1978年   156篇
  1977年   137篇
  1976年   136篇
  1975年   172篇
  1974年   270篇
  1973年   261篇
  1972年   253篇
  1971年   248篇
  1970年   258篇
  1969年   248篇
  1968年   192篇
  1967年   197篇
  1966年   173篇
  1965年   130篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
The severe strain of potato spindle tuber viroid (s-PSTV) as well as chrysanthemum stunt (CSV) and cucumber pale fruit (CPFV) viroids were found to be transmitted through seed and pollen of the tomato cvs. Rutgers and Najwcze?niejszy. Plants pollinated with a pollen infected with any of these three viroids became systematically infected. Plant, fruit and seed symptoms of viroid infection were noted on sap- and pollen-inoculated plants and the yield of these plants was reduced. Tomato cv. Rutgers plants grown from infected seeds were symptomless although all three viroids were detected in these plants by bioassay and by electrophoresis on 5% polyacrylamide gel. When DNA complementary to s-PSTV RNA was used for a direct viroid detection in seed samples by spot hybridization technique it hybridized not only with s-PSTV RNA but also with CSV RNA as well as with CPFV RNA.  相似文献   
73.
The present work has a twofold aim: 1. To ascertain whether the stimulative influence of peripheral nerve grafts on injured hippocampal neurons depends on the time lapse after transection and; 2. To examine whether the mentioned effect runs parallel to the time-dependent changes of proteins contents and composition in the submicrosomal fraction from transected rat sciatic nerves. Fluorescence microscope examination revealed that FITC-HRP labeled cells extending their neurites into the implanted peripheral nerve segments were particularly numerous among the hippocampal neurons when 7- and 35-day-old predegenegated distal stumps were used as grafts. Discontinuous SDS-slab polyacrylamide gel electrophoresis of submicrosomal fraction proteins obtained from distal stumps of rat sciatic nerves was performed at the 7, 14, 21 and 35 days after transection. Among the obtained protein fractions the most interesting seem to be the ones of 47 and 54 kDa, which reached maximal levels at the 7th day and the 50 kDa fraction with a maximum at the 35th experimental day. It is possible that the growth promoting power of the employed grafts depends on the presence of proper proteins.  相似文献   
74.
Majority of pituitary tumours secrete one of the named hormones: PRL, GH, ACTH, proopiomelanocortine, alpha and beta subunit of TSH, LH, and FSH. Some of those tumours secrete two or more hormones. The aim of this study was to determine the effect of bromocriptine (Parlodel MR and LAR) upon secretion of hormones and tumour size in 10 patients with mixed pituitary tumours. In all patients pituitary and peripheral hormones, CT scan and visual fields were examined before and after treatment with bromocriptine: Parlodel MR and LAR. Bromocriptine treatment decreased PRL secretion in all 10 patients; GH--in all 6 in whom it was increased; TSH--in 2, FSH--in 2 and alpha-subunit in all 6 in whom they were increased. In 5 patients treatment resulted in shrinkage of the tumour mass by 20 to 35%. In all examined subjects clinical improvement was achieved. Our results demonstrate that bromocriptine (Parlodel MR and LAR) is very effective and well tolerated in the treatment of patients with mixed pituitary tumours particularly those with hyperprolactinemia.  相似文献   
75.
Hypopituitarism can be a result of various lesions of hypothalamus, pituitary stalk, or of the pituitary gland itself. The aim of the study was to assess the value of CT and MRI examinations in determination of the cause of hypopituitarism. Seventeen patients with hypopituitarism (9 women and 8 men) aged 22 to 61 years have been examined. In three cases growth deficiency was observed, 4 women had galactorrhoea, 4 patients had diabetes insipidus, 16 patients had supra-adrenal insufficiency, 14 had signs of hypogonadism and 10 hypothyroidism. In each case plasma concentrations of LH, FSH, PRL, TSH, alpha-subunit, ACTH before and after appropriate stimulation with TRH, metoclopramid, LH-RH, GRF or metyrapon were determined with RIA. Every patient was examined both with CT and MRI (0.5 T Toshiba MRT 50a). All 17 patients had abnormal MR images of hypothalamo-pituitary area, while only 10 of them had abnormalities in their CT scans. In remaining 7 patients the MRI revealed: three cases of congenital malformation of hypophyseal stalk, two cases of empty sella, one posttraumatic lesion of the stalk and one case of granulomatous infiltration of the stalk. We found MRI superior to CT in establishing the case of hypopituitarism.  相似文献   
76.
An effect of cimetidine on ECG records has been investigated in a group of 40 patients with gastric or duodenal ulcers and coexisting circulatory disorders. For this purpose ECG has been recorded with Holter's technique (Medilog 2000) together with ECG-recording using high amplifying technique. An intravenous injection of 200 mg of cimetidine produced in some of patients inhibition of the sinus rhythm atrio-ventricular conduction disturbances as well as changes in the end phase of ECG ventricular image. The authors suggest, that intravenous administration of cimetidine to patients with cardiac diseases should be monitored with ECG recording.  相似文献   
77.
78.
Phagocytic index and rosette test E have been determined in 50 patients, including 15 with diffuse peritonitis and the noncomplicated diffuse peritonitis, 20 patients with septic complications, and 15 patients who underwent abdominal surgery. It was found, that phagocytic index is decreased in all patients after abdominal surgery. The most marked decrease of this index was found in patients with complicated peritonitis. It still decreases in the course of peritonitis and increases in the reference group. The marked decrease in the number of T-cells was observed in complicated peritonitis during the whole period of follow-up while it normalizes in case of noncomplicated peritonitis as in the reference group. Using the tests under study it was possible to assess cell-mediated immunity which is depressed in peritonitis. The tests enable also the prediction of septic complications of peritonitis.  相似文献   
79.
Activity of methemoglobin reductase was studied in human red cells treated with methylguanidine and guanidinosuccinic acid in concentrations similar to those in plasma of patients with chronic renal failure. Enzyme activity was measured with Richterich technique following an incubation at 37 degrees C for three hours. Results have shown that methylguanidine in concentration of 5.4 x 10(-5) mol/l decreases activity of methemoglobin reductase in human red cells on average by 13.9%. Higher concentrations potentiate this effect. Similar changes in methemoglobin reductase activity were noted after introduction of guanidine-succinic acid into the mixture. This agent in concentration 5.6 x 10(-5) mol/l inhibited activity of the tested enzyme by 34.2% on average. Combined methylguanidine in concentration of 5.4 x 10(-5) mol/l and guanidine-succinic acid in concentration of 2.8 x 10(-5) mol/l inhibited methemoglobin reductase activity by 33.0% on average. It may be suggested, that methylguanidine and guanidine-succinic acid being low molecular uremic toxins may significantly decrease methemoglobin reductase activity in red cells of patients with chronic renal failure.  相似文献   
80.
An average follow-up period of 16 patients was 28 months following an implantation of the artificial aortic valve for its insufficiency. In 10 operated patients who were able to continue their occupation exercise tolerance increased by two classes, according to NYHA. Blood pressure gradient decreased significantly from 61.8 to 37.5 mmHg, cardiac volume index decreased from 639 to 602 ml/m2. Echocardiographically measured muscle mass of the left ventricle, end-diastolic and end-systolic volumes, and the left atrial dimensions decreased significantly following surgery. A significance of the relation of the left ventricle volume to its mass <4 as a prognostic factor in aortic valve replacement has also been confirmed.  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