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   1069篇
  免费   70篇
电工技术   14篇
综合类   1篇
化学工业   281篇
金属工艺   11篇
机械仪表   13篇
建筑科学   23篇
矿业工程   1篇
能源动力   16篇
轻工业   150篇
水利工程   4篇
石油天然气   5篇
无线电   61篇
一般工业技术   167篇
冶金工业   243篇
原子能技术   8篇
自动化技术   141篇
  2024年   2篇
  2023年   14篇
  2022年   4篇
  2021年   66篇
  2020年   28篇
  2019年   23篇
  2018年   54篇
  2017年   42篇
  2016年   55篇
  2015年   44篇
  2014年   46篇
  2013年   65篇
  2012年   54篇
  2011年   52篇
  2010年   52篇
  2009年   43篇
  2008年   43篇
  2007年   40篇
  2006年   27篇
  2005年   22篇
  2004年   26篇
  2003年   12篇
  2002年   18篇
  2001年   14篇
  2000年   2篇
  1999年   12篇
  1998年   83篇
  1997年   48篇
  1996年   33篇
  1995年   20篇
  1994年   14篇
  1993年   18篇
  1992年   6篇
  1991年   5篇
  1990年   7篇
  1988年   6篇
  1984年   4篇
  1982年   3篇
  1981年   3篇
  1979年   1篇
  1977年   8篇
  1976年   5篇
  1975年   1篇
  1974年   1篇
  1973年   3篇
  1972年   1篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1966年   1篇
排序方式: 共有1139条查询结果,搜索用时 31 毫秒
991.

Purpose  

To study the in vivo effect of intratracheal administration of lipopolysaccharide (LPS) in mice by magnetic resonance imaging (MRI) and to investigate the correlation with ex vivo histological evaluation of lung inflammation and oedema.  相似文献   
992.
This paper presents the results of a laboratory scale investigation on the remediation of a soil contaminated by a mixture of organic compounds using a two‐step process consisting of stripping and biofiltration. The biofilter was packed with the soil under examination in order to use autochthonous microorganisms. To assess the effects of both temperature and superficial velocity of the air stream on process performance different sets of experimental tests were carried out at two air temperatures (50 and 80 °C), and at two superficial air velocities (41.0 and 82.0 m h?1), corresponding to apparent air residence times in the biofilter column of 38 and 19 s respectively. The stripping rate proves to be inversely correlated with the soil–water partitioning coefficient, while no evident correlation was found with the Henry coefficient. It can therefore be concluded that soil–water partitioning is limited by mass transfer while air–water partitioning reaches equilibrium. Temperature influences both stripping rate in the stripping column and degradation capacity in the biofilter. A stripping temperature of 80 °C combined with a biofiltration temperature of 34 °C provides the best process performance. Copyright © 2007 Society of Chemical Industry  相似文献   
993.
The effect of administering the thiol modulating agent buthionine sulfoximine (BSO) in conjunction with alkylating chemotherapy was investigated in vivo in the mouse KHT sarcomas and bone marrow stem cells. Tumour response to treatment was assessed by an in vivo to in vitro excision assay and bone marrow survival was determined in vitro by CFU-GM. Glutathione (GSH) depletion and recovery kinetics were determined at various times after treatment using high performance liquid chromatography (HPLC) techniques. Following a single 2.5 mmol kg-1 dose of BSO, tumour GSH reached a nadir of approximately 40% of control 12-16 h after treatment. Bone marrow GSH was depleted to approximately 45% of control 4-8 h after treatment but recovered to normal by 16 h. When a range of doses of CCNU, mitomycin C, cyclophosphamide or melphalan (MEL) were given 16 h after mice were exposed to a 2.5 mmol kg-1 dose of BSO, only the antitumour efficacy of MEL was effectively enhanced (by a factor of approximately 1.4). This BSO-MEL combination appeared to be selective for the tumour as the bone marrow toxicity was not increased beyond that seen for MEL alone. Since increasing the administered dose of BSO neither increased the extent of thiol depletion in the tumour nor enhanced the antitumour efficacy of MEL, three other protocols for delivering the thiol depletor were explored. BSO was given either as multiple 2.5 mmol kg-1 doses administered at 6 or 16 h intervals or continuously at a concentration of 30 mM supplied in the animals' drinking water. Both multi-dose BSO pretreatments were found to increase both the antitumour efficacy and normal tissue toxicity of MEL such that no advantage compared to the single dose combination was achieved. In contrast, maintaining the thiol depletor in the drinking water led to an approximately 1.7-fold increase in the antitumour efficacy of MEL without any corresponding increase in bone marrow stem cell toxicity. For the various pretreatment strategies it was possible, in all cases, to account for the presence or absence of a net therapeutic benefit on the basis of the tumour and bone marrow GSH depletion and recovery kinetics.  相似文献   
994.
995.
The p53 tumor suppressor gene has been found to be altered in almost all human solid tumors, whereas K-ras gene mutations have been observed in a limited number of human cancers (adenocarcinoma of colon, pancreas, and lung). Studies of mutational inactivation for both genes in the same patient's sample on non-small-cell lung cancer have been limited. In an effort to perform such an analysis, we developed and compared methods (for the mutational detection of p53 and K-ras gene) that represent a modified and universal protocol, in terms of DNA extraction, polymerase chain reaction (PCR) amplification, and nonradioisotopic PCR-single-strand conformation polymorphism (PCR-SSCP) analysis, which is readily applicable to either formalin-fixed, paraffin-embedded tissues or frozen tumor specimens. We applied this method to the evaluation of p53 (exons 5-8) and K-ras (codon 12 and 13) gene mutations in 55 cases of non-small-cell lung cancer. The mutational status in the p53 gene was evaluated by radioisotopic PCR-SSCP and compared with PCR-SSCP utilizing our standardized nonradioisotopic detection system using a single 6-microns tissue section. The mutational patterns observed by PCR-SSCP were subsequently confirmed by PCR-DNA sequencing. The mutational status in the K-ras gene was similarly evaluated by PCR-SSCP, and the specific mutation was confirmed by Southern slot-blot hybridization using 32P-labeled sequence-specific oligonucleotide probes for codons 12 and 13. Mutational changes in K-ras (codon 12) were found in 10 of 55 (18%) of non-small-cell lung cancers. Whereas adenocarcinoma showed K-ras mutation in 33% of the cases at codon 12, only one mutation was found at codon 13. As expected, squamous cell carcinoma samples (25 cases) did not show K-ras mutations. Mutations at exons 5-8 of the p53 gene were documented in 19 of 55 (34.5%) cases. Ten of the 19 mutations were single nucleotide point mutations, leading to amino acid substitution. Six showed insertional mutation, and three showed deletion mutations. Only three samples showed mutations of both K-ras and p53 genes. We conclude that although K-ras and p53 gene mutations are frequent in non-small-cell lung cancer, mutations of both genes in the same patient's samples are not common. We also conclude that this universal nonradioisotopic method is superior to other similar methods and is readily applicable to the rapid screening of large numbers of formalin-fixed, paraffin-embedded or frozen samples for the mutational analysis of multiple genes.  相似文献   
996.
BACKGROUND AND OBJECTIVE: To compare the efficacy of ProME(Epidoxorubicin)CE-CytaBOM (PE-C) and ProMI(Idarubicin)CE-CytaBOM (PI-C) in the treatment of adult patients with aggressive non Hodgkin's lymphoma in a multicenter randomized controlled trial performed by 18 centers of the Italian Lymphoma Study Group (GISL). DESIGN AND METHODS: One hundred and twenty-eight and 122 patients were randomly assigned to receive either 6 courses of PE-C or PI-C, respectively. Some patients achieving complete remission with induction therapy participated in another randomized study comparing no further therapy versus maintenance therapy consisting of four blocks of two drugs. RESULTS: The rate of CRs was 62% and 64% for patients treated with PE-C and PI-C, respectively (p = 0.51). The 5-year relapse-free survival was 60% for PE-C and 53% for PI-C (p = 0.29). The estimated relapse-free disease survival rates at 4 years were 75% for patients in the consolidation group and 57% for those in the observation group (p = 0.11). Patients alive in first complete remission 4 years after study entry were estimated to be 39% in the PE-C arm and 38% in the PI-C arm (p = 0.90). The 3-year and 5-year estimated survival rates were 61% and 55% for the PE-C group and 56% and 47% for the PI-C group (p = 0.26). Fatal toxicities occurred in 7 patients (2.9%) with active disease and in 4 patients (1.7%) in complete remission. Stage (p = 0.04), bulky disease (p = 0.02), serum LDH (p = 0.0006), serum albumin (p = 0.0051), hemoglobin (p = 0.0011), performance status (p = 0.0001), International prognostic index (p < 0.0001) and the index proposed by the French group G.E.L.A. (p < 0.0001) were of prognostic value. In a multivariate analysis (Cox regression model) alternatively IPI alone or G.E.L.A. index plus performance status emerged as independent prognostic factors. INTERPRETATION AND CONCLUSIONS: The present study indicates that epirubicin and idarubicin in a combined chemotherapy regimen, have similar activities. The toxic profile also indicates the safety of both anthracyclines at the dosages employed, suggesting their possible dose escalation in a combined chemotherapy setting. PE-C and PI-C were both effective and feasible regimens in an outpatient setting, with acceptable cardiovascular toxicity. The trend toward a better outcome in patients undergoing consolidation therapy after the achievement of a complete remission, warrants further investigation.  相似文献   
997.
Smoking-related death and disability rates for women have risen sharply recently. Despite lower smoking cessation success rates for women using behavioral therapies, data are limited on whether specific pharmacological therapies are equally efficacious in men and women. Using meta-analytic techniques, we examined whether significant differences in therapeutic efficacy of nicotine replacement therapy (NRT) for smoking cessation exist by sex. Out of the 31 randomized clinical trials of NRT that met inclusion criteria, 11 contributed to the analysis. The odds ratios for NRT vs. placebo were derived from each trial separately by sex for males and females, and these ratios were combined to give a pooled estimate of the effect of sex in response to NRT. NRT was effective at all time points in men (< 6 months: OR = 2.05, 95% CI= 1.61-2.60; 6 months: OR = 1.98, 95% CI = 1.51-2.60; 12 months: OR = 1.86, 95% CI = 1.39-2.50) and women (< 6 months: OR = 2.09, 95% CI = 1.65-2.65; 6 months, OR = 1.52, 95% CI = 1.17-1.98; 12 months: OR = 1.63, 95% CI = 1.22-2.18). At all time points, no significant difference was observed between sexes (< 6 months: OR = .97, 95% CI = .69-1.36; 6 months: OR = 1.33, 95% CI = .91-1.95; 12 months: OR = 1.21, 95% CI = .79-1.84). The results of this meta-analysis do not support the hypothesis that NRT has higher therapeutic efficacy for men than women.  相似文献   
998.
T Riccò  A Pavan  F Danusso 《Polymer》1975,16(9):685-689
Dynamic mechanical properties of a series of ABS (acrylonitrile-butadiene-styrene) resins, having a constant rubber basis grafted to different extents, were studied in the temperature range ?120° to 20°C. The observed viscoelastic transition of the rubbery phase shows two main effects: the amplitude of the transition and the transition temperature decrease as the degree of grafting increases. The grafted component had been prepared by graft copolymerization of butadiene rubber in emulsion with different comonomers/rubber ratios. Both the dynamic effects observed on ABS are discussed in terms of structure variations induced by the change of the grafting condition.  相似文献   
999.
1000.
Catalysts for the selective oxidation of isobutane to methacrylic acid, based on ammonium salts of phosphorus/molybdenum Keggin-type polyoxometalates, were prepared by precipitation of a lacunary precursor at pH 4.0, and by calcination of the precipitate at 350 °C in air. The thermal treatment led to the transformation of the lacunary polyoxometalate into (NH4)3PMo12 O40. This procedure yielded a catalyst that was active, but poorly selective, from the beginning of its reaction time, since the active sites were generated during the calcination, and thus during the transformation of the lacunary precursor into the Keggin compound. Nevertheless, for the reaction under isobutane-rich conditions, the catalyst exhibited an initial period during which the progressive reduction of the polyoxometalate led to an improvement of the selectivity to methacrylic acid. An alternative method to develop a partially reduced compound was by preparation of a Sb3+-doped polyoxometalate. A solid-state redox reaction between Sb3+ and Mo6+ occurred in the Keggin framework during the calcination of the precursor. With this procedure, a catalyst was obtained, which did not require the preliminary equilibration, and which therefore was active and selective from the beginning of its reaction time. Furthermore, the catalyst was found to be surprisingly very active under isobutane-lean conditions.  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