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   1945篇
  免费   5篇
电工技术   4篇
综合类   1篇
化学工业   70篇
金属工艺   5篇
机械仪表   21篇
建筑科学   22篇
矿业工程   1篇
能源动力   8篇
轻工业   91篇
水利工程   7篇
无线电   15篇
一般工业技术   53篇
冶金工业   1606篇
原子能技术   14篇
自动化技术   32篇
  2019年   4篇
  2017年   5篇
  2014年   5篇
  2013年   24篇
  2012年   9篇
  2011年   15篇
  2010年   13篇
  2009年   14篇
  2008年   14篇
  2007年   17篇
  2006年   9篇
  2005年   15篇
  2004年   8篇
  2003年   8篇
  2002年   6篇
  2001年   6篇
  2000年   8篇
  1999年   62篇
  1998年   573篇
  1997年   307篇
  1996年   172篇
  1995年   100篇
  1994年   71篇
  1993年   119篇
  1992年   18篇
  1991年   20篇
  1990年   16篇
  1989年   15篇
  1988年   15篇
  1987年   13篇
  1986年   16篇
  1985年   17篇
  1984年   4篇
  1983年   7篇
  1982年   8篇
  1981年   8篇
  1980年   15篇
  1979年   5篇
  1978年   9篇
  1977年   33篇
  1976年   65篇
  1975年   8篇
  1974年   11篇
  1973年   6篇
  1972年   5篇
  1971年   11篇
  1970年   5篇
  1969年   7篇
  1968年   5篇
  1967年   6篇
排序方式: 共有1950条查询结果,搜索用时 15 毫秒
101.
102.
Forty-three homozygous (SS) female sickle cell anemic patients with a history of at least one painful crisis per month and desiring a reversible contraceptive were administered DMPA/3 months or Microgynon monthly. A third group of 16 surgically sterilized patients served as control. Patients were followed for 1 year to assess possible effects of the contraceptives on the patients' painful crises. No changes were observed in any of the groups in the hematological parameters. At the end of the study, 70% of the patients receiving DMPA were pain-free and only 16% of those still reporting painful crises rated them as intense. Patients receiving Microgynon also had an amelioration of the painful crises, although at a lower rate; after 12 months, 45.5% still experienced some crises. Although less marked than in the other groups, 50.5% of the control patients also reported an improvement of their painful crisis, which may be a result of closer medical care.  相似文献   
103.
New antimalarial drugs are urgently needed. The use of short courses of the new antimalarial drug artemether as monotherapy has been limited by secondary malaria episodes following parasite clearance. Therefore, a new antimalarial drug, CGP 56697, has been developed, which combines artemether with a longer-acting antimalarial agent, benflumetol. A safety trial was undertaken in 60 Gambian children 1-6 years old with uncomplicated Plasmodium falciparum malaria. All children treated with CGP 56697 cleared their parasites 72 h after the start of treatment. No neurologic, cardiac, or other adverse reactions were observed. Second episodes of falciparum malaria were recorded in 16 (27%) of the children. Second infections were more frequent during the rainy season than during the dry season. Molecular epidemiologic studies suggested that 12 of the 14 second episodes of malaria in children treated with CGP 56697 were due to new infections. CGP 56697 proved to be a safe and effective antimalarial drug in African children.  相似文献   
104.
Two species of Pseudomonas capable of utilizing nitroglycerin (NG) as a sole nitrogen source were isolated from NG-contaminated soil and identified as Pseudomonas putida II-B and P. fluorescens I-C. While 9 of 13 laboratory bacterial strains that presumably had no previous exposure to NG could degrade low concentrations of NG (0.44 mM), the natural isolates tolerated concentrations of NG that were toxic to the lab strains (1.76 mM and higher). Whole-cell studies revealed that the two natural isolates produced different mixtures of the isomers of dinitroglycerol (DNG) and mononitroglycerol (MNG). A monomeric, flavin mononucleotide-containing NG reductase was purified from each natural isolate. These enzymes catalyzed the NADPH-dependent denitration of NG, yielding nitrite. Apparent kinetic constants were determined for both reductases. The P. putida enzyme had a Km for NG of 52 +/- 4 microM, a Km for NADPH of 28 +/- 2 microM, and a Vmax of 124 +/- 6 microM x min(-1), while the P. fluorescens enzyme had a Km for NG of 110 +/- 10 microM, a Km for NADPH of 5 +/- 1 microM, and a Vmax of 110 +/- 11 microM x min(-1). Anaerobic titration experiments confirmed the stoichiometry of NADPH consumption, changes in flavin oxidation state, and multiple steps of nitrite removal from NG. The products formed during time-dependent denitration reactions were consistent with a single enzyme being responsible for the in vivo product distributions. Simulation of the product formation kinetics by numerical integration showed that the P. putida enzyme produced an approximately 2-fold molar excess of 1,2-DNG relative to 1,3-DNG. This result could be fortuitous or could possibly be consistent with a random removal of the first nitro group from either the terminal (C-1 and C-3) positions or middle (C-2) position. However, during the denitration of 1,2-DNG, a 1.3-fold selectivity for the C-1 nitro group was determined. Comparable simulations of the product distributions from the P. fluorescens enzyme showed that NG was denitrated with a 4.6-fold selectivity for the C-2 position. Furthermore, a 2.4-fold selectivity for removal of the nitro group from the C-2 position of 1,2-DNG was also determined. The MNG isomers were not effectively denitrated by either purified enzyme, which suggests a reason why NG could not be used as a sole carbon source by the isolated organisms.  相似文献   
105.
A randomized double-blind controlled trial was undertaken to study the efficacy of a cow udder ointment versus petroalatum alone. A total of 30 patients participated in the study. Sixteen patients completed the trial with 8 of 9 patients improving in the active group and 6 of 7 patients improving in the placebo group. This difference was not statistically significant. The use of a cow udder ointment for psoriasis cannot be supported, particularly with the potential for side effects.  相似文献   
106.
Serum apolipoproteins (apo) B and AI were measured in a probability sample of the noninstitutionalized US civilian population, ages > or = 4 years, which included non-Hispanic whites, non-Hispanic blacks, and Mexican-Americans. Apo B concentrations were the same in males and females, lower in black males than in other males, low in childhood (approximately 0.80 g/L) and increasing to approximately 1.2 g/L in adults, and higher in younger women on hormones. Apo AI was higher in females than males, higher in blacks than in others, remained constant from childhood to adulthood (approximately 1.35 g/L) in males, but increased with age (approximately 1.30 g/L to approximately 1.55 g/L) in females, and was higher in women taking hormones. These are the first national probability estimates of apo B and apo AI in the US and are referable to the WHO-IFCC First International Reference Materials for apo AI and B.  相似文献   
107.
COTS software products are increasingly becoming standard components for building integrated information systems. At the same time, the growth of electronic trading, turbulent market conditions, and a project-style approach to business have created a demand for information systems that can be rapidly adapted to changing business process demands. However, the ongoing development of COTS products is unpredictable as their developers and source code are rarely available. Flexible information systems use COTS components because they cost-effectively supply required component functionality. A software architecture can capture a system design as a set of interacting components and capture the role of COTS software in "implementing" certain components.  相似文献   
108.
Sociotechnical interventions in large organizations pose multiple challenges for consulting psychologists. The nature of this intervention was technical (a reengineered human resources information system) but had social, workplace impact in both its execution and its outcomes. The key issue of organizational support for an intervention of this magnitude is discussed. This case study describes the theoretical framework for the intervention, the implementation model, and the unforeseen critical junctures in the project, plus it addresses the lessons learned by a consulting group of industrial/organizational psychologists in implementing this long-term, large-scale project. A discussion of implications for both theory and practice concludes the article. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
109.

Background  

Ingestion of carbohydrate (CHO) and protein (PRO) following intense exercise has been reported to increase insulin levels, optimize glycogen resynthesis, enhance PRO synthesis, and lessen the immuno-suppressive effects of intense exercise. Since different forms of CHO have varying glycemic effects, the purpose of this study was to determine whether the type of CHO ingested with PRO following resistance-exercise affects blood glucose availability and insulin levels, markers of anabolism and catabolism, and/or general immune markers.  相似文献   
110.
The CTFA Evaluation of Alternatives Program is an evaluation of the relationship between data from the Draize primary eye irritation test and comparable data from a selection of promising in vitro eye irritation tests. In Phase III, data from the Draize test and 41 in vitro endpoints on 25 representative surfactant-based personal care formulations were compared. As in Phase I and Phase II, regression modelling of the relationship between maximum average Draize score (MAS) and in vitro endpoint was the primary approach adopted for evaluating in vitro assay performance. The degree of confidence in prediction of MAS for a given in vitro endpoint is quantified in terms of the relative widths of prediction intervals constructed about the fitted regression curve. Prediction intervals reflect not only the error attributed to the model but also the material-specific components of variation in both the Draize and the in vitro assays. Among the in vitro assays selected for regression modeling in Phase III, the relationship between MAS and in vitro score was relatively well defined. The prediction bounds on MAS were most narrow for materials at the lower or upper end of the effective irritation range (MAS = 0-45), where variability in MAS was smallest. This, the confidence with which the MAS of surfactant-based formulations is predicted is greatest when MAS approaches zero or when MAS approaches 45 (no comment is made on prediction of MAS > 45 since extrapolation beyond the range of observed data is not possible). No single in vitro endpoint was found to exhibit relative superiority with regard to prediction of MAS. Variability associated with Draize test outcome (e.g. in MAS values) must be considered in any future comparisons of in vivo and in vitro test results if the purpose is to predict in vivo response using in vitro data.  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