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   1898篇
  免费   17篇
  国内免费   1篇
电工技术   12篇
综合类   2篇
化学工业   57篇
金属工艺   1篇
机械仪表   18篇
建筑科学   31篇
能源动力   6篇
轻工业   18篇
水利工程   3篇
石油天然气   4篇
无线电   74篇
一般工业技术   53篇
冶金工业   1566篇
原子能技术   1篇
自动化技术   70篇
  2022年   4篇
  2021年   3篇
  2020年   4篇
  2018年   12篇
  2017年   5篇
  2016年   5篇
  2015年   12篇
  2014年   6篇
  2013年   22篇
  2012年   18篇
  2011年   15篇
  2010年   18篇
  2009年   16篇
  2008年   22篇
  2007年   19篇
  2006年   20篇
  2005年   10篇
  2004年   14篇
  2003年   18篇
  2002年   7篇
  2001年   9篇
  2000年   17篇
  1999年   45篇
  1998年   450篇
  1997年   292篇
  1996年   178篇
  1995年   113篇
  1994年   82篇
  1993年   95篇
  1992年   13篇
  1991年   14篇
  1990年   25篇
  1989年   20篇
  1988年   17篇
  1987年   14篇
  1986年   10篇
  1985年   11篇
  1983年   4篇
  1982年   6篇
  1981年   14篇
  1980年   23篇
  1978年   4篇
  1977年   61篇
  1976年   134篇
  1975年   4篇
  1973年   1篇
  1972年   3篇
  1965年   1篇
  1959年   1篇
  1955年   2篇
排序方式: 共有1916条查询结果,搜索用时 0 毫秒
991.
PURPOSE: To report the successful coil embolization of a true gluteal artery aneurysm and review therapeutic options for this rare condition. METHODS AND RESULTS: A ruptured superior gluteal artery aneurysm in a symptomatic 80-year-old man was successfully thrombosed by embolization using a combination of Gianturco coils and helical platinum microcoils. Six-month computed tomography demonstrated persistent thrombosis of the aneurysm and resolution of the perivascular blood. CONCLUSIONS: This report offers support for the use of catheter-based techniques as an alternative to standard surgical repair of gluteal artery aneurysms.  相似文献   
992.
In this paper, we report more information on the important role of the aldehyde group in the sarcin/ricin domain of 28S rRNA in rat liver ribosome. We find D-amino acids, amino acid derivatives having free amino group and two polyamines can also partially restore the activity of cinnamomin-inactivated ribosomes. However, amino acid derivatives and a tripeptide with blocked amino group cannot. Neither sodium borohydride nor the L-amino acids can restore the activity of ribosomes inactivated by alpha-sarcin. These data demonstrate that partial restoration of the activity of the inactivated ribosome is indeed the result of the blockage of the aldehyde group. It reaches the conclusion that emergence of the active aldehyde group in the sarcin/ricin domain of 28S rRNA is one of factors that inactivate the ribosome for protein synthesis.  相似文献   
993.
Thirty adult dogs with chronic generalized demodicosis were treated with oral administration of milbemycin oxime (0.52 to 3.8 mg/kg of body weight, q 24 h). Results of skin scrapings were used to determine whether administration of milbemycin should be continued or discontinued. Dogs that were free of clinical signs of demodicosis 12 months after administration of milbemycin was discontinued were considered cured. Sixteen dogs were cured, 5 dogs were never cleared of mites, and 9 dogs were cleared of mites, but relapsed after administration of milbemycin was discontinued. Adverse effects of milbemycin were rare and transient.  相似文献   
994.
The clinical course and prognosis of familial hypertrophic cardiomyopathy (HCM) are different according to the type of mutation in the genes for sarcomere proteins. It has been disputed that a mutation, which occurs at a functionally important region in the sarcomere proteins, may increase the penetrance and expressivity of the disease. We searched for a causative mutation in an HCM family, which is characterized by early expression of clinical phenotype, high incidence of sudden death at young ages, and progressive heart failure in adults. Among the 32 family members in 4 generations, 13 were affected; 4 died suddenly before age 16, 2 children have already had full expression of the cardiac hypertrophy, and other adults have either progressive heart failure or poor left ventricular systolic functions. PCR-SSCP (polymerase chain reaction-single strand confirmation polymorphism) analysis of genomic DNAs isolated from peripheral blood leukocytes of the family members identified a Gly716Arg mutation in the cardiac beta-myosin heavy chain gene, which was cosegregated with the clinical phenotype. The mutation is localized near a functionally important site of the myosin heavy chain, the 2 active thiols, which contribute to the adenosine triphosphatase activity of myosin S1. This family provides further evidence that the mutation, which occurs at a functionally important site of the myosin heavy chain, is associated with the high penetrance and early expression of HCM.  相似文献   
995.
1. To investigate the effects of clozapine, an atypical antipsychotic, on the cloned mu-, delta- and kappa-opioid receptors and G-protein-activated inwardly rectifying K+ (GIRK) channel, we performed the Xenopus oocyte functional assay with each of the three opioid receptor mRNAs and/or the GIRK1 mRNA. 2. In the oocytes co-injected with either the delta- or kappa-opioid receptor mRNA and the GIRK1 mRNA, application of clozapine induced inward currents which were attenuated by naloxone, an opioid-receptor antagonist, and blocked by Ba2+, which blocks the GIRK channel. Since the opioid receptors functionally couple to the GIRK channel, these results indicate that clozapine activates the delta- and kappa-opioid receptors and that the inward-current responses are mediated by the GIRK channel. The action of clozapine at the delta-opioid receptor was more potent and efficacious than that at the kappa-opioid receptor. In the oocytes co-injected with the mu-opioid receptor and GIRK1 mRNAs, application of clozapine (100 microM) did not induce an inward current, suggesting that clozapine could not activate the mu-opioid receptor. 3. Application of clozapine caused a reduction of the basal inward current in the oocytes injected with the GIRK1 mRNA alone, but caused no current response in the uninjected oocytes. These results indicate that clozapine blocks the GIRK channel. 4. To test the antagonism of clozapine for the mu- and kappa-opioid receptors, we applied clozapine together with each selective opioid agonist to the oocytes co-injected with either the mu- or kappa-opioid receptor mRNA and the GIRK1 mRNA. Each of the peak currents induced by each selective opioid agonist together with clozapine was almost equal to the responses to a selective opioid agonist alone. These results indicate that clozapine has no significant antagonist effect on the mu- and kappa-opioid receptors. 5. We conclude that clozapine acts as a delta- and kappa-agonist and as a GIRK channel blocker. Our results suggest that the efficacy and side effects of clozapine under clinical conditions may be partly due to activation of the delta-opioid receptor and blockade of the GIRK channel.  相似文献   
996.
Small ruminants are very important livestock species in the English-speaking Caribbean. Total populations for the Caribbean region are approximately 677,000 goats and 281,000 sheep. Although the primary purpose of sheep and goats is meat production for local consumption, the animals are also a source of emergency income. Production systems are generally characterised as small-scale and low-input, and few breeding or productivity records are kept. Although intra-regional trade does occur between Caribbean countries, there is insufficient production for extra-regional trade. The Caribbean countries collectively have a very favourable animal health situation, which is maintained by strict import restrictions on livestock. Zoonotic diseases are relatively rare, with the exception of leptospirosis. The most important public health risk relates to the slaughter of small ruminants in small, unregulated butcheries which do not have acceptable standards of hygiene. In addition, meat is often transported or sold under unhygienic conditions. Recommendations are made for the reduction of these risks.  相似文献   
997.
The growth of retinal axons was investigated in different regions of the optic chiasm in C57 pigmented mouse embryos aged embryonic day 13 (E13) to E15. Individual retinal axons and their growth cones were labelled anterogradely by DiI and imaged using a confocal imaging system. In aldehyde-fixed embryos, retinal growth cones display a simple form in the optic nerve and become more complex in morphology in the chiasm. The complex form is particularly prominent in those axons that turn to the ipsilateral tract in the premidline region of chiasm. Moreover, complex growth cones are also commonly found in axons in the postmidline chiasm, which are markedly different in morphology from those axons in the premidline region, suggesting that the postmidline chiasm contains a novel environment for the pathfinding of retinal axons. In another experiment, the dynamic growth of retinal axons is studied in a brain slice preparation of the living retinofugal pathway. Retinal axons show an intermittent growth across the premidline and postmidline chiasm. Extensive remodelling of growth cone form followed by a shift in growth direction is commonly seen during the pause periods, indicating that signals that guide axon growth across the chiasm are not restricted to the midline, but are laid down throughout the chiasm. Moreover, dramatic changes in axon trajectory are noted first at the premidline chiasm where the uncrossed axons segregate from the crossed axons, and second at the postmidline chiasm where specific sorting of retinal axons according to their position in the dorsal ventral retinal axis and their ages are known to take place. These results show that there are two distinct environments, separated by the midline in the chiasm, where axons show different responses to local guidance cues and develop the distinct fibre orders.  相似文献   
998.
An acidic 1,2-alpha-mannosidase from fungus, Aspergillus saitoi (now designated Aspergillus phoenicis), is highly specific for 1,2-alpha-mannosidic linkage in the high-mannose type oligosaccharide at pH 5.0. The predicted amino acid sequence of several peptide regions, including aspartic acid and glutamic acid, bears striking similarities to 1,2-alpha-mannosidases from fungi, yeast and mouse. Active site determination of the enzyme expressed in Saccharomyces cerevisiae cells was performed by site-directed mutagenesis. Substitutions of Asp-269 to Glu and of the Glu-residues, Glu-273, Glu-411, Glu-414 and Glu-474, to Asp altered the drastic decrease of specific activities with Man alpha 1-2Man-OMe and Man9-GlcNAc2-PA as substrates and shifted the optimal pH of the mutant enzymes. From the present results, Asp-269 is probably in the ionized COO- form, whereas one of four glutamic acid residues, probably Glu-411, is the un-ionized COOH form according to the analogy of a plausible mechanism for lysozyme catalysis. It is assumed that three glutamic acid residues, Glu-273, Glu-414, and Glu-474, are probably binding sites of substrate.  相似文献   
999.
OBJECTIVES: Multi-Frequency Bioelectrical Impedance Analysis (MFBIA) is a quick, simple, and inexpensive method to assess body fluid compartments. This study aimed at determining the validity of MFBIA in detecting clinically relevant changes of fluid balance in geriatric patients. DESIGN: A prospective, observational study. SETTING: The 22-bed Geriatric Department of the University Hospital Nijmegen. PARTICIPANTS: Hospitalized patients were eligible if they did not have a pacemaker, were not suffering from terminal illnesses, and did not have psychogeriatric diseases likely to interfere with capacity to consent or comply. During a 16-months period, 218 patients were admitted, of whom 78 patients were eligible and 53 consented to participate. MEASUREMENTS: Each subject's fluid balance was diagnosed twice a week as dehydrated, overhydrated, or euvolemic, based on standardized physical examination, laboratory tests, and weight evaluation. Changes in fluid balance were quantified by measuring total body water (TBW) and extracellular fluid (ECF) applying deuterium- and bromide-dilution techniques. Impedance at 1, 5, 50, and 100 kHz and body weight were measured daily. Sensitivity and Guyatt's responsiveness indexes of MFBIA in detecting dehydration and overhydration were determined. RESULTS: In total, 1071 MFBIA measurements were performed, during which 14 transitions from dehydration to euvolemia and 13 transitions from overhydration to euvolemia were monitored. Rehydration of dehydrated patients caused an increase in TBW and ECF of 3.4 +/- 1.8 L and 1.9 +/- 1.9 L, respectively, which resulted in significant decreases in impedance of 133 +/- 67 omega at 1 kHz and 93 +/- 61 omega at 100 kHz (P = .001). Treatment of overhydrated patients caused a TBW and ECF loss of 3.8 +/- 4.2 L and 3.1 +/- 3.8 L, respectively, which resulted in significant increases in impedance of 104 +/- 72 omega at 1 kHz and 81 +/- 68 omega at 100 kHz (P < .001). Sensitivity of a single MFBIA in diagnosing dehydration and overhydration was 14% and 17%, respectively. Responsiveness indexes of weighing and MFBIA for dehydration and overhydration were similar at all frequencies and greater than one. CONCLUSION: The sensitivity of a single impedance measurement in detecting dehydration and overhydration was low. However, responsiveness of serial measurements to intra-individual changes in fluid balance was good. Therefore, this noninvasive technique may be used in clinical practice to improve monitoring fluid balance in geriatric patients, especially when daily weighing is difficult.  相似文献   
1000.
An alternative method of uniting small diameter vessels to obtain tissue union while limiting the thrombogenic effect of suture placement at a vessel anastomosis involves the use of a thrombin based fibrin glue as a surgical sealant. This investigation addresses whether the in vitro application of a thrombin based glue (TG), or batroxobin glue (BG), a non-thrombin based glue made with the snake venom enzyme batroxobin, alters intravascular platelet deposition (PD) or cleaves blood fibrinogen, as measured by fibrinopeptide A (FPA) production, when the respective glue is applied to the external surface of an intact human placental artery or an artery with an anastomosis. When TG was applied to the adventitial surface of an intact vessel or an anastomosis (n = 7) of control and experimental vessels, there was a significant increase in intraluminal platelet deposition, an effect not realized with BG (n = 12, intact vessel TG p = 0.01, BG p = 0.66, anastomosis TG p <0.01, BG p <0.01). Both TG and BG significantly increased FPA levels when human whole blood was perfused through both intact vessels or vessels containing an anastomosis when compared to control vessels (intact vessel TG and BG p <0.01, anastomosis TG and BG p <0.01). Labelled thrombin studies document the rapid passage of thrombin through an intact vessel wall or vessels with an anastomosis when TG was applied to the adventitial surface of the vessel. The data suggest that TG and BG are drug delivery systems for their respective enzymes that either pass through or transfer a message across not only a surgically created anastomosis, but also an intact vessel wall.  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