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   30469篇
  免费   1414篇
  国内免费   7篇
  31890篇
  2023年   185篇
  2022年   301篇
  2021年   568篇
  2020年   433篇
  2019年   525篇
  2018年   874篇
  2017年   760篇
  2016年   1030篇
  2015年   1186篇
  2014年   1395篇
  2013年   1852篇
  2012年   1780篇
  2011年   1888篇
  2010年   1175篇
  2009年   951篇
  2008年   1318篇
  2007年   1383篇
  2006年   1367篇
  2005年   1115篇
  2004年   984篇
  2003年   975篇
  2002年   830篇
  2001年   645篇
  2000年   545篇
  1999年   436篇
  1998年   235篇
  1992年   330篇
  1991年   319篇
  1990年   259篇
  1989年   276篇
  1988年   292篇
  1987年   295篇
  1986年   272篇
  1985年   296篇
  1984年   245篇
  1983年   200篇
  1979年   271篇
  1978年   185篇
  1977年   154篇
  1976年   156篇
  1975年   196篇
  1974年   281篇
  1973年   281篇
  1972年   263篇
  1971年   254篇
  1970年   265篇
  1969年   260篇
  1968年   200篇
  1967年   198篇
  1966年   179篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
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   
102.
Developing pods of pea ( Pisum sativum L. cv. Alaska no 7) were used to study the enzymes of sucrose metabolism. Acid and neutral invertase (EC 3.2.1.26). sucrose synthase (SS, EC 2.4.1.13) and sucrose phosphate synthase (SPS, EC 2.4.1.14) have been localized in the soluble fraction. Acid invertase activity was also present in the insoluble fraction and in pea ovary apoplast. In pea pods, sucrose breakdown was dominated by the invertase pathway. SS specific activity only increased at late stages of parthenocarpic pod development, while SPS did so in pods obtained by pollination. Changes in time course of invertase activities have been correlated with the growth rate of fruits induced to develop either by fertilization or by exogenous application of giberellic acid (GA), 2,4-dichloro-phenoxy acetic acid (2,4-D) or 6-benzylaminopurine (6-BAP). The soluble neutral activities might be associated with pod elongation, while the acid ones were rather related to assimilate import by the induced fruits. Application of gibberellic acid to non-pollinated ovaries significantly enhanced the soluble neutral invertase activity before any ovary outgrowth was detected (up to 2 h after treatment). Within the same period of time. GA-treated ovaries showed a decrease in the acid invertase activity of the soluble fraction and an increase of the acid invertase activity in the apopiast. preceding in time the increment of the acid invertase activity associated with the insoluble fraction. Our results suggest that the early GA response may be mediated through a promotion of processes of protein secretion.  相似文献   
103.
Twelve patients with chronic renal failure treated with repeated dialysis underwent subtotal parathyroidectomy. Histologic examination revealed hyperplasia parathyroidal adenoma in all patients. Diagnostic correlation between bone X-ray, ultrasound of parathyroid glands, calcium deposits in cornea and conjunctiva, and histological findings has been analysed. Radiological abnormalities have been noted in 8 patients (66%), parathyroid glands hyperplasia in 9 (75%), and corneal and conjunctival calcium deposits in 10 (83%) patients. These data confirm the value of techniques under study for the diagnosis of the secondary hyperparathyroidism in patients with chronic renal failure.  相似文献   
104.
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   
105.
106.
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   
107.
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   
108.
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   
109.
Summary Microbial transformations of neutral fraction (NF) and upgraded neutral fraction (UNF) of Polish tall oil byMycobacterium sp. MB 3683 were performed. Final metabolites and yields were compared to bioconversion of pure -sitosterol. Additionally, origin of a new metabolite —5-androsta-3,6,17-trione was proved by transformation of UNF in the presence of labeled -sitosterol.  相似文献   
110.
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