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   1656篇
  免费   29篇
  国内免费   3篇
电工技术   8篇
综合类   2篇
化学工业   150篇
金属工艺   10篇
机械仪表   9篇
建筑科学   34篇
矿业工程   2篇
能源动力   34篇
轻工业   114篇
水利工程   4篇
石油天然气   3篇
无线电   64篇
一般工业技术   105篇
冶金工业   1053篇
原子能技术   7篇
自动化技术   89篇
  2022年   13篇
  2021年   18篇
  2020年   12篇
  2019年   12篇
  2018年   21篇
  2017年   17篇
  2016年   12篇
  2015年   7篇
  2014年   19篇
  2013年   43篇
  2012年   35篇
  2011年   21篇
  2010年   21篇
  2009年   15篇
  2008年   23篇
  2007年   24篇
  2006年   32篇
  2005年   31篇
  2004年   23篇
  2003年   23篇
  2002年   25篇
  2001年   16篇
  2000年   20篇
  1999年   37篇
  1998年   274篇
  1997年   161篇
  1996年   117篇
  1995年   61篇
  1994年   64篇
  1993年   65篇
  1992年   18篇
  1991年   16篇
  1990年   19篇
  1989年   10篇
  1988年   24篇
  1987年   23篇
  1986年   15篇
  1985年   20篇
  1984年   13篇
  1983年   7篇
  1982年   18篇
  1981年   14篇
  1980年   17篇
  1979年   17篇
  1978年   10篇
  1977年   41篇
  1976年   78篇
  1975年   11篇
  1968年   5篇
  1960年   5篇
排序方式: 共有1688条查询结果,搜索用时 0 毫秒
1.
2.
Recent concern regarding lidocaine neurotoxicity has prompted efforts to find alternatives to lidocaine spinal anesthesia. Small-dose dilute bupivacaine spinal anesthesia yields a comparably rapid recovery profile but may provide insufficient anesthesia. By exploiting the synergism between intrathecal opioids and local anesthetics, it may be possible to augment the spinal anesthesia without prolonging recovery. Fifty patients undergoing ambulatory surgical arthroscopy were randomized into two groups receiving spinal anesthesia with 3 ml 0.17% bupivacaine in 2.66% dextrose without (Group I) or with (Group II) the addition of 10 microg fentanyl. Median block levels reached T7 and T8, respectively (P = not significant [NS]). Mean times to two-segment regression, S2 regression, time out of bed, time to urination, and time to discharge were 53 vs 67 min (P < 0.01), 120 vs 146 min (P < 0.05), 146 vs 163 min (P = NS), 169 vs 177 min (P = NS), and 187 vs 195 min (P = NS) respectively. Motor blockade was similar between groups, but sensory blockade was significantly more intense in Group II (P < 0.01). Six of 25 blocks failed in Group I, whereas none failed in Group II. The addition of 10 microg fentanyl to spinal anesthesia with dilute small-dose bupivacaine intensifies and increases the duration of sensory blockade without increasing the intensity of motor blockade or prolonging recovery to micturition or street fitness. IMPLICATIONS: Concerns about the neurotoxicity of lidocaine have prompted efforts to find alternatives to lidocaine spinal anesthesia. We studied 50 patients undergoing ambulatory surgical arthroscopy and found that although small-dose bupivacaine alone is inadequate for this procedure, the addition of fentanyl makes it reliable.  相似文献   
3.
4.
BACKGROUND: Some clinical studies suggest that a combination of an H1- and H2-antagonist may be effective in the prophylaxis of allergic reactions. OBJECTIVE: The efficacy of pretreatment with an H1/H2-antagonist combination, H1-antagonist alone, or placebo in the prophylaxis of local and systemic adverse reactions to specific immunotherapy with Hymenoptera venom was compared. METHODS: In a prospective, randomized, double-blind, placebo-controlled study, 121 patients with Hymenoptera venom allergy were treated with rush immunotherapy and pretreatment with one of the following: 120 mg of terfenadine plus 300 mg of ranitidine, 120 mg of terfenadine alone, or placebo. The incidence of unwanted systemic adverse and local reactions was recorded for up to 50 weeks. RESULTS: In seven patients (6%), six in the placebo group and one in the terfenadine group, systemic side effects required cessation of therapy (p = 0.005). Subjective symptoms occurred in four patients (10%) in the terfenadine plus ranitidine group and in three patients (7%) in the terfenadine group. Regarding local reactions, significantly fewer patients treated with a combination of terfenadine and ranitidine and with terfenadine alone as compared with placebo had severe local symptoms of erythema (29%, 29%, and 49%), edema (24%, 18%, and 41%), and pruritus (13%, 11%, and 31%) at week 1 (p < 0.05). This therapeutic benefit was limited to the first 4 weeks of treatment. Treatment with a combination of terfenadine and ranitidine was not superior to treatment with terfenadine alone. CONCLUSIONS: Pretreatment with H1-antihistamines with or without H2-antihistamines significantly reduced local and systemic adverse reactions to immunotherapy with Hymenoptera venom and may therefore be helpful in the management of immunotherapy.  相似文献   
5.
Strains of the gastrointestinal species Lactobacillus reuteri were electrotransformed with plasmid constructs containing the endo-1,3-1,4-beta-glucanase gene (bglM) of Bacillus macerans. The enzyme was expressed and secreted by the lactobacilli. A plasmid construct containing the bglM gene lacking its promoter was derived and was demonstrated to be useful as a promoter probe vector.  相似文献   
6.
BACKGROUND/AIMS: The aim of the study was to assess the impact factor of HCV and HGV in fulminant hepatic failure. METHODS: The 5'-untranslated regions of HCV RNA and HGV RNA and a segment of the core antigen sequence of HBV were amplified after extracting the nucleic acids from snap-frozen tissue aliquots from explanted livers of 26 consecutive patients undergoing orthotopic liver transplantation for fulminant hepatic failure preoperatively diagnosed as either autoimmune (n=2), HAV/HBV (n=8), toxic (n=4) or aetiologically unknown (n=12). RESULTS: HCV RNA was detected in five of 26 (19.2%) livers with fulminant hepatic failure. All five HCV RNA-positive livers belonged to the group of non-toxic, non-autoimmune liver failure (n=20), three of them were found in the group of liver failure with unknown aetiology (n=12) and two in the group of HBV-associated liver failure (n=7), making an HCV incidence of 25%, 25% and 28.6%, in the different groups, respectively. HGV RNA was detected in 10 of 17 (58.8%) explants and in all four groups of fulminant hepatic failure as defined preoperatively. HBV DNA was identified in six livers of 26 patients (23.1%) with fulminant hepatic failure. Neither HCV RNA nor HBV DNA was detected in the livers of patients with toxic or autoimmune fulminant hepatic failure. CONCLUSIONS: These results indicate that HBV and HCV, but not HGV, play an aetiologic role in fulminant hepatic failure. HCV-positive cases were concentrated either in the group of otherwise unexplained fulminant hepatic failure or in the group of HBV fulminant hepatic failure. HGV-positive cases, on the other hand, were found within all four preoperatively defined groups, indicating a role as cofactor rather than as single aetiologic agent.  相似文献   
7.
The present study was carried out to investigate the biochemical and morphological changes in the liver after ligation of the hepatic artery (HA) in the presence and in the absence of extrahepatic cholestasis (EHC). The study was conducted on 100 rats divided into four groups of 25 animals each: group 1, sham operation; group 2, hepatic artery ligation (HAL); group 3, bile duct ligation (BDL); and group 4, HAL plus BDL. All animals were sacrificed 7 days after surgery when total bilirubin and fractions, alkaline phosphatase (AP), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured in serum and on the inner hepatocyte mitochondrial membrane (IHMM); the incidence of necrosis and the volume fractions of vessels, bile ducts and hepatocytes in the liver were also determined. HAL reduces the relative volumes of bile ducts, with no changes in levels of bilirubin and fractions, AP, ALT, AST and IHMM, but HAL associated with EHC reduces duct proliferation and the liver becomes more vulnerable to necrosis. In conclusion, the normal liver depends on HA flow and this dependence is more evident in the presence of EHC.  相似文献   
8.
Np‐Bromophenylmaleimide (BrPMI) does not polymerize in solution by conventional free radical mechanism. However, it readily polymerized in bulk when mixed with a free radical initiator and heated in a microwave oven for 7–8 min. Copolymerization of ethyl methacrylate or butyl methacrylate with BrPMI was conducted in dioxane. The copolymers were characterized by IR and 1H NMR spectroscopy and gel permeation chromatography. The monomer reactivity ratios were calculated by a non‐linear least‐square analysis. Thermal analysis indicated a great improvement in thermal stability of the copolymers compared with the methacrylate homopolymers. BrPMI was also polymerized in bulk in the DSC pan, which allowed the calculation of the activation energy of its polymerization. Copyright © 2003 Society of Chemical Industry  相似文献   
9.
10.
Initiating events leading to the accumulation of malignant ascites in the peritoneal cavity were investigated in two syngeneic transplantable murine ascites-producing tumors, MOT mouse ovarian tumor and the TA3/St mammary carcinoma. The transport of two tracers, 125I-labeled human serum albumin (125I-HSA) and 51Cr-labeled red blood cells (51Cr-RBC), into and out of the peritoneal cavity was studied at early times after i.p. tumor cell injection, prior to abundant fluid accumulation, and at intervals of 5 to 360 min after i.v. or i.p. tracer injection. Tracer influx and efflux rates were estimated from the mass of tracer passing into or out of the peritoneal cavity following a bolus injection of tracer into either the blood or the peritoneal cavity. Efflux of 125I-HSA from the peritoneal cavity was markedly reduced (3- to 5-fold) within 1 day of i.p. injection of either type of tumor cell. Significantly reduced efflux preceded any increase in tumor cell number and by itself did not induce peritoneal fluid accumulation. 125I-HSA tracer influx from plasma to peritoneal fluid did not increase detectably until 5 to 7 days after tumor cell injection, when the tumor cell number had increased by 10- to 100-fold. Only at relatively late stages of ascites tumor growth, when the flow rate into the peritoneal cavity had increased relative to the flow rate out of the peritoneum, was there net peritoneal fluid accumulation. Thus, increased influx, in addition to impaired efflux, were required for malignant ascites accumulation. Following i.p. injection, the efflux rates of 125I-HSA always exceeded those of 51Cr-RBC, even in ascites tumor-bearing animals. Furthermore, 125I-HSA tracer disappeared from the peritoneal cavity more rapidly than it appeared in the plasma, suggesting that 125I-HSA moves more rapidly through the channels by which 51Cr-RBC egress from the peritoneum (primarily diaphragmatic lymphatics) and/or has access to additional pathways not open to 51Cr-RBC. Finally, flow rates into and out of the blood and peritoneum were used to obtain kinetic parameters that characterized tracer transport: k1, the rate constant for tracer transport from the blood to the peritoneum; k2, the rate constant for tracer transport from the peritoneal cavity to the blood; and k6, the rate constant for tracer transport from the peritoneal cavity to surrounding interstitial tissue.(ABSTRACT TRUNCATED AT 400 WORDS)  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