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   2726篇
  免费   6篇
  国内免费   2篇
电工技术   7篇
综合类   1篇
化学工业   65篇
金属工艺   4篇
机械仪表   8篇
建筑科学   12篇
矿业工程   1篇
能源动力   12篇
轻工业   48篇
水利工程   7篇
无线电   24篇
一般工业技术   57篇
冶金工业   2444篇
原子能技术   2篇
自动化技术   42篇
  2024年   9篇
  2023年   7篇
  2022年   10篇
  2021年   12篇
  2020年   12篇
  2019年   12篇
  2018年   6篇
  2017年   15篇
  2016年   7篇
  2015年   10篇
  2014年   9篇
  2013年   30篇
  2012年   19篇
  2011年   19篇
  2010年   7篇
  2009年   9篇
  2008年   9篇
  2007年   12篇
  2006年   8篇
  2005年   6篇
  2004年   7篇
  2003年   14篇
  2002年   5篇
  2001年   5篇
  2000年   8篇
  1999年   64篇
  1998年   825篇
  1997年   439篇
  1996年   291篇
  1995年   158篇
  1994年   113篇
  1993年   153篇
  1992年   15篇
  1991年   21篇
  1990年   21篇
  1989年   22篇
  1988年   19篇
  1987年   26篇
  1986年   23篇
  1985年   16篇
  1983年   6篇
  1982年   12篇
  1981年   8篇
  1980年   19篇
  1978年   3篇
  1977年   52篇
  1976年   153篇
  1975年   3篇
  1971年   1篇
  1955年   2篇
排序方式: 共有2734条查询结果,搜索用时 0 毫秒
31.
Converting available biomass from municipal, agricultural and forest wastes to bio-methanol can result in significant environmental and economic benefits. Keeping these benefits in mind, one plausible scenario discussed here is the potential to produce energy using bio-methanol in five states of the western United States. In this scenario, the bio-methanol produced is from different biomass sources and used as a substitute for fossil fuels in energy production. In the U.S. West, forest materials are the dominant biomass waste source in Idaho, Montana, Oregon and Washington, while in California, the greatest amount of available biomass is from municipal wastes. Using a 100% rate of substitution, bio-methanol produced from these sources can replace an amount equivalent to most or all of the gasoline consumed by motor vehicles in each state. In contrast, when bio-methanol powered fuel cells are used to produce electricity, it is possible to generate 12–25% of the total electricity consumed annually in these five states.As a gasoline substitute, bio-methanol can optimally reduce vehicle C emissions by 2–29 Tg of C (23–81% of the total emitted by each state). Alternatively, if bio-methanol supported fuel cells are used to generate electricity, from 2 to 32 Tg of C emissions can be avoided. The emissions avoided, in this case, could equate to 25–32% of the total emissions produced by these particular western states when fossil fuels are used to generate electricity. The actual C emissions avoided will be lower than the estimates here because C emissions from the methanol production processes are not included; however, such emissions are expected to be relatively low. In general, there is less carbon emitted when bio-methanol is used to generate electricity with fuel cells than when it is used as a motor vehicle fuel.In the state of Washington, thinning “high-fire-risk” small stems, namely 5.1–22.9 cm diameter trees, from wildfire-prone forests and using them to produce methanol for electricity generation with fuel cells would avoid C emissions of 3.7–7.3 Mg C/ha. Alternatively, when wood-methanol produced from the high-fire-risk wood is used as a gasoline substitute, 3.3–6.6 Mg C/ha of carbon emissions are avoided. If these same “high-fire-risk” woody stems were burned during a wildfire 7.9 Mg C/ha would be emitted in the state of Washington alone. Although detailed economic analyses of producing methanol from biomass are in its infancy, we believe that converting biomass into methanol and substituting it for fossil-fuel-based energy production is a viable option in locations that have high biomass availability.  相似文献   
32.
In the preliminary phase of this study, a selective isolation medium was developed. Using the new medium, 24 strains of Bacillus Spp. that elevate tomato juice pH were isolated from garden soil or natural vegetative materials. Two jars of home-canned, water-bathed tomatoes contained sporeformers which produced noneffervescent spoilage. All strains were morphologically and physiologically different from 2 flat-sour strains of B. coagulans and B. licheniformis strains, but similar to a previous isolate from home-canned, spoiled green beans that elevated pH. The new medium may have future applications in isolation and enumeration of other acidurics including yeast-like microorganisms.  相似文献   
33.
34.
35.
36.
The cytoplasm of the iris--ciliary body of the rabbit contains a receptor capable of specifically binding dexamethasone. This binding protein has a high affinity for dexamethasone (average KD = 2.0 X 10(-8) M), a low capacity (average 4.8 X 10(-13) mol of steroid bound per milligram of protein), and extreme heat sensitivity; it exhibits a pattern of competition virtually identical to that obtained with glucocorticoid receptors from other tissues and shows characteristic physicochemical behavior in various salt concentrations. The demonstration of a specific dexamethasone receptor in the iris--ciliary body provides the first direct biochemical evidence that these tissues may function as a target organ for glucocorticoids.  相似文献   
37.
38.
39.
The conformations of two synthetic pentapeptides with antimicrobial activity and their 4-fluorophenylalanine (Pff)-containing analogues (ArXArXAr-NH(2); Ar=Phe, Pff; X=Lys, Arg) have been studied. NMR experiments carried out both in aqueous fluoroalcohol solutions and SDS micelles permitted their interactions with membrane-like environments to be explored. WaterLOGSY experiments and Mn(2+)-based paramagnetic probes were also applied to assess their orientations with respect to the SDS micelles. In addition, pulse-field gradient (PFG) diffusion NMR spectroscopy studies were conducted, under different experimental conditions (i.e., concentration, temperature) to characterize the possible changes in the peptides' aggregation states as a putative critical factor for their antimicrobial activity. Finally, molecular dynamics simulations on a variety of conformations showed the intrinsic flexibility of these peptides in both aqueous solutions and membrane-mimetic systems.  相似文献   
40.
The mating pathway of Saccharomyces cerevisiae is widely used as a model system for G protein-coupled receptor-mediated signal transduction. Following receptor activation by the binding of mating pheromones, G protein betagamma subunits transmit the signal to a MAP kinase cascade, which involves interaction of Gbeta (Ste4p) with the MAP kinase scaffold protein Ste5p. Here, we identify residues in Ste4p required for the interaction with Ste5p. These residues define a new signaling interface close to the Ste20p binding site within the Gbetagamma coiled-coil. Ste4p mutants defective in the Ste5p interaction interact efficiently with Gpa1p (Galpha) and Ste18p (Ggamma) but cannot function in signal transduction because cells expressing these mutants are sterile. Ste4 L65S is temperature-sensitive for its interaction with Ste5p, and also for signaling. We have identified a Ste5p mutant (L196A) that displays a synthetic interaction defect with Ste4 L65S, providing strong evidence that Ste4p and Ste5p interact directly in vivo through an interface that involves hydrophobic residues. The correlation between disruption of the Ste4p-Ste5p interaction and sterility confirms the importance of this interaction in signal transduction. Identification of the Gbetagamma coiled-coil in Ste5p binding may set a precedent for Gbetagamma-effector interactions in more complex organisms.  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