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   36697篇
  免费   1944篇
  国内免费   976篇
  2023年   295篇
  2022年   674篇
  2021年   1137篇
  2020年   798篇
  2019年   1052篇
  2018年   1229篇
  2017年   976篇
  2016年   1338篇
  2015年   1683篇
  2014年   1965篇
  2013年   2405篇
  2012年   2500篇
  2011年   2474篇
  2010年   1427篇
  2009年   1201篇
  2008年   1487篇
  2007年   1449篇
  2006年   1388篇
  2005年   1205篇
  2004年   1027篇
  2003年   981篇
  2002年   868篇
  2001年   699篇
  2000年   633篇
  1999年   516篇
  1998年   284篇
  1997年   207篇
  1996年   217篇
  1995年   205篇
  1992年   384篇
  1991年   371篇
  1990年   305篇
  1989年   312篇
  1988年   329篇
  1987年   343篇
  1986年   285篇
  1985年   334篇
  1984年   248篇
  1983年   222篇
  1979年   276篇
  1978年   184篇
  1975年   194篇
  1974年   286篇
  1973年   279篇
  1972年   265篇
  1971年   259篇
  1970年   262篇
  1969年   255篇
  1968年   196篇
  1967年   201篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
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   
152.
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   
153.
We have previously reported two common lipoprotein lipase (LPL) gene mutations underlying LPL deficiency in the majority of 37 French Canadians (Monsalve et al., 1990. J. Clin. Invest. 86: 728-734; Ma et al., 1991. N. Engl. J. Med. 324: 1761-1766). By examining the 10 coding exons of the LPL gene in another French Canadian patient, we have identified a third missense mutation that is found in two of the three remaining patients for whom mutations are undefined. This is a G to A transition in exon 6 that results in a substitution of asparagine for aspartic acid at residue 250. Using in vitro site-directed mutagenesis, we have confirmed that this mutation causes a catalytically defective LPL protein. In addition, the Asp250----Asn mutation was also found on the same haplotype in an LPL-deficient patient of Dutch ancestry, suggesting a common origin. This mutation alters a TaqI restriction site in exon 6 and will allow for rapid screening in patients with LPL deficiency.  相似文献   
154.
K Sakai  X Y Ma  I Gordienko    D J Volsky 《Journal of virology》1991,65(11):5765-5773
Two molecularly cloned coisolates of human immunodeficiency virus type 1 (HIV-1) have been found to exhibit different phenotypes of viral expression, either rapid and cytopathic (N1T-A virus) or delayed and noncytopathic (N1T-E virus [X. Ma, K. Sakai, F. Sinangil, E. Golub, and D. J. Volsky, Virology 176:184-194, 1990]). To identify the viral genetic elements responsible for these phenotypes, we prepared reciprocal recombinants in different regions of N1T-A and N1T-E viral genomes. Infectivity experiments with the recombinant viruses revealed that the rapid/cytopathic (N1T-A-like) phenotype assorted cleanly with the V1f-coding region and Vif expression. The smallest HIV-1 DNA region that conferred the complete phenotypic switch was a 284-bp NdeI-StuI fragment within the vif open reading frame. Nucleotide sequence analysis revealed a 35-bp deletion starting at nucleotide 218 in the N1T-E vif gene. A 23-kDa Vif protein was detected by immunoblotting using Vif-specific antiserum in extracts of cells infected with N1T-A but not N1T-E virus. No detectable vif protein was found in association with sedimented particles of either virus. Cotransfection of a eucaryotic vif expression plasmid with N1T-E DNA complemented the N1T-E defect; rapid/cytopathic infection similar to that in N1T-A-transfected cells was observed. We conclude that Vif controls the rate, and consequently the cytopathic outcome, of HIV-1 infection.  相似文献   
155.
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   
156.
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   
157.
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   
158.
159.
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   
160.
An efficiency of the acute myeloblastic leukemia therapy has been assessed in 79 patients aged over 60 years. Twenty six patients out of this group have been treated with usual or reduced doses of doxorubicin and cytarabine (ADR-Ara-C) 35--low doses of cytarabine (LD Ara-C), 11-6-mercaptopurine (6 MP), and 7 patients died before chemotherapy. Complete remission in group treated with ADR-Ara-C was achieved in 23% of patients while partial remission in 42%. Median survival in this group was 5.8 months (range from 0.5 to 16 months). Percentage of the complete remissions in the group treated with LD-Ara-C was 6%, and partial remissions 40%. Median survival was 4.7 months (range from 0.5 to 14.2 months). Partial remission in 5 out of 11 patients treated with 6 MP (36%) and no complete remissions were noted. Median survival was 3.9 months. Therapy with ADR-Ara-C produced marked leucopenia and thrombocytopenia in the majority of treated patients. Vomiting, hemorrhagic complications, and bacterial infections have also been noted. These adverse reactions have been less frequent in patients treated with LD-Ara-C, and 6 MP. Ten patients (38%) treated with ADR-Ara-C and 7 patients treated with LD-Ara-C died during remission inducing therapy.  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