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   12993篇
  免费   361篇
  国内免费   1篇
  2021年   114篇
  2020年   95篇
  2019年   121篇
  2018年   263篇
  2017年   233篇
  2016年   314篇
  2015年   334篇
  2014年   409篇
  2013年   546篇
  2012年   531篇
  2011年   548篇
  2010年   349篇
  2009年   256篇
  2008年   394篇
  2007年   430篇
  2006年   403篇
  2005年   404篇
  2004年   345篇
  2003年   388篇
  2002年   312篇
  2001年   281篇
  2000年   233篇
  1999年   178篇
  1998年   94篇
  1992年   238篇
  1991年   232篇
  1990年   182篇
  1989年   217篇
  1988年   234篇
  1987年   238篇
  1986年   219篇
  1985年   252篇
  1984年   202篇
  1983年   166篇
  1980年   83篇
  1979年   234篇
  1978年   158篇
  1977年   136篇
  1976年   135篇
  1975年   170篇
  1974年   269篇
  1973年   260篇
  1972年   253篇
  1971年   248篇
  1970年   258篇
  1969年   246篇
  1968年   192篇
  1967年   196篇
  1966年   173篇
  1965年   129篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
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   
102.
Summary Wistar rats were injected intraperitoneally with 2-(14C)deoxyglucose and their thymuses were processed for thaw-mount autoradiography after 5, 10 or 35 min. Highest levels of radioactivity were demonstrated in the thymic medulla (5-fold higher than in the cortex). Scanning of autoradiograms for regional differences in grain densities indicated particularly intense glucose utilization in the cortico-medullary zone. Differences in glucose utilization between individual thymic zones seem to reflect differences in cellular composition, i. e., ratio of stroma cells to thymocytes.Dedicated to Professor Dr. T.H. Schiebler on the occasion of his 65th birthday  相似文献   
103.
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   
104.
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   
105.
Normal endothelin 1/2 levels and their correlation with age were evaluated. For clinical application of the endothelin 1/2 RIA test, optimum storage conditions were investigated. Plasma endothelin 1/2 (ET) levels were measured in 36 healthy blood donors, mostly males, of mean age 36 +/- 8 years, subdivided into three age groups: 17-30, 31-40 and above 40 years old. The mean normal ET levels in the three age groups, and corresponding standard deviations, were: 0.58 +/- 0.19, 0.62 +/- 0.31, and 0.80 +/- 0.28 fmol/ml, respectively. The mean ET level for the whole normal population was 0.66 +/- 0.28 fmol/ml. Only differences between mean ET levels for the first and last groups were statistically significant (p < 0.05). Differences between mean ET levels in smokers (53% of total population) and non-smokers, women and men, irrespective of age, were found not to be statistically significant. At this stage of our work, we conclude that other factors than age alone play a role in enhancing ET levels above the age of 41 years. In our study of optimum storage conditions for endothelin 1/2, we found that after one week of storage at -24 degrees C the mean level of ET measured in frozen plasma dropped to 85% of the initial activity, while after the same period the respective decrease in ET activity in frozen extracts was 49%. Over the next two weeks, ET levels in plasma and extracts dropped to 57% and 32% of "zero time" activities, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
106.
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   
107.
Summary Each of the two ovaries ofCatajapyx aquilonaris is composed of seven segmentally (metamerically) arranged ovarioles. The two lateral oviducts that join and bear ovarioles extend throughout the abdomen. In the ovariole three regions can be recognized: the terminal filament, the germarium and the vitellarium. The terminal filaments do not fuse with each other but attach separately (by means of muscle fibres) to the closest lobes of the fat body. Germ cells in the germarium are not joined by intercellular bridges and do not form clusters. Thus the ovarioles ofC. aquilonaris are interpreted as being primarily panoistic. The results obtained support the hypothesis that both dipluran subgroups (Campodeina and Japygina) do not form a monophyletic unit.  相似文献   
108.
The aim of the study was to find out whether vasopressin (AVP) modifies hypotensive and heart rate accelerating effects of atrial natriuretic peptide (ANP) in normotensive (WKY) and spontaneously hypertensive (SHR) conscious rats. The effect of i.v. administration of 1; 2 and 4 micrograms of ANP on blood pressure (MP) and heart rate (HR) was compared during i.v. infusion of 0.9% NaCl (NaCl), NaCl+AVP (1.2 ng kg-1 min-1) and NaCl+dEt2AVP (V1 receptors antagonist, 0.5 microgram kg-1 min-1). AVP increased MP in SHR and WKY and decreased HR in SHR. V1 antagonist decreased MP and increased HR only in SHR. In SHR ANP decreased MP and increased HR during NaCl, AVP and V1 antagonist infusion. In WKY these effects were observed only during AVP administration. In each experimental situation hypotension and tachycardia induced by ANP were greater in SHR than in WKY. In both strains ANP induced changes in MP and HR were enhanced during AVP in comparison to NaCl infusion. V1 antagonist did not modify effects of ANP in WKY and SHR. The results indicate that ANP abolishes hypertensive response induced by blood AVP elevation and that the basal levels of endogenous vasopressin acting through V1 receptors does not interfere with hypotensive action of ANP neither in WKY nor in SHR.  相似文献   
109.
An effect of Aminosteril-Hepa intravenous infusions or plasmapheresis on selected amino acids, ammonia, alpha-aminonitrogen serum levels and serum GGTP activity was analysed in 28 patients with liver cirrhosis with and without hepatic encephalopathy. The patients were given protein controlled dietary treatment. It was found, that plasmapheresis exerted more potent effect on previously elevated ammonia and serum alpha-aminonitrogen levels as well as serum GGTP activity than intravenous infusions of Aminosteril-Hepa. It was clearly seen in patients with liver cirrhosis without hepatic encephalopathy. Aminosteril-Hepa intravenous infusions decreased serum glutamine levels to higher degree than plasmapheresis. Both types of therapy have had no significant effect on serum phenylalanine, tyrosine, and tryptophan levels in all patients.  相似文献   
110.
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   
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