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   1191篇
  免费   69篇
  国内免费   68篇
电工技术   25篇
综合类   44篇
化学工业   168篇
金属工艺   265篇
机械仪表   50篇
建筑科学   99篇
矿业工程   11篇
能源动力   39篇
轻工业   61篇
水利工程   6篇
石油天然气   68篇
武器工业   7篇
无线电   63篇
一般工业技术   103篇
冶金工业   103篇
原子能技术   23篇
自动化技术   193篇
  2024年   1篇
  2023年   9篇
  2022年   37篇
  2021年   47篇
  2020年   63篇
  2019年   29篇
  2018年   31篇
  2017年   42篇
  2016年   36篇
  2015年   30篇
  2014年   61篇
  2013年   68篇
  2012年   69篇
  2011年   84篇
  2010年   75篇
  2009年   78篇
  2008年   73篇
  2007年   73篇
  2006年   87篇
  2005年   41篇
  2004年   34篇
  2003年   36篇
  2002年   29篇
  2001年   30篇
  2000年   20篇
  1999年   14篇
  1998年   29篇
  1997年   19篇
  1996年   11篇
  1995年   12篇
  1994年   15篇
  1993年   4篇
  1992年   10篇
  1991年   7篇
  1990年   5篇
  1989年   2篇
  1988年   3篇
  1986年   2篇
  1985年   1篇
  1984年   5篇
  1983年   1篇
  1982年   1篇
  1980年   2篇
  1971年   1篇
  1951年   1篇
排序方式: 共有1328条查询结果,搜索用时 15 毫秒
91.
Lee A. Gladwin 《Cryptologia》2013,37(3):199-211
Abstract

The discovery of intercepts in the Japanese “Orange Translations” regarding the sinking of merchant ships (marus) bearing allied POWs led to the conclusion that the Joint Intelligence Center Pacific Ocean Area (JICPOA) gave latitudes and longitudes of these vessels to the Commander, Submarine Force, Pacific (ComSubPac) knowing that POWs would be killed. An examination of the “Orange Translations” reveals that most of the intercepts are from the Japanese Water Transport Code (2468) system, not the “Maru Code” (JN-11). The author concludes that while JICPOA provided ComSubPac with convoy coordinates, they were unaware of the presence of POWs on the marus.  相似文献   
92.
In 1941, the United States Navy intercepted enough Japanese naval messages to predict the attack on Pearl Harbor if the code which protected them had been solved. The messages would have disclosed that, while the Japanese government cynically conducted diplomatic negotiations with the United States, the Japanese Combined Fleet under Admiral Isoroku Yamamoto, beginning as early as September 1941, systematically prepared ships, crews, weapons, tactics, and a complicated fuel supply system for the most ambitious operation ever undertaken by the Japanese navy. Details of Japan's intentions were hidden from Navy cryptanalysts because of limited manpower resources and because all Japanese navy codes were assigned a lower priority than Japanese diplomatic codes and German submarine threat.  相似文献   
93.
David Kahn 《Cryptologia》2013,37(4):273-294
American codebreakers achieved remarkable success in solving Japanese codes, but could not prevent the surprise attack on Pearl Harbor because the Japanese never transmitted anything about the attack on the airwaves.  相似文献   
94.
Gene clusters are becoming promising tools for gene identification. The study reveals the purposive genomic distribution of genes toward higher inheritance rates of intact metabolic pathways/phenotypes and, thereby, higher fitness. The co-localization of co-expressed, co-interacting, and functionally related genes was found as genome-wide trends in humans, mouse, golden eagle, rice fish, Drosophila, peanut, and Arabidopsis. As anticipated, the analyses verified the co-segregation of co-localized events. A negative correlation was notable between the likelihood of co-localization events and the inter-loci distances. The evolution of genomic blocks was also found convergent and uniform along the chromosomal arms. Calling a genomic block responsible for adjacent metabolic reactions is therefore recommended for identification of candidate genes and interpretation of cellular functions. As a case story, a function in the metabolism of energy and secondary metabolites was proposed for Slc25A44, based on its genomic local information. Slc25A44 was further characterized as an essential housekeeping gene which has been under evolutionary purifying pressure and belongs to the phylogenetic ETC-clade of SLC25s. Pathway enrichment mapped the Slc25A44s to the energy metabolism. The expression of peanut and human Slc25A44s in oocytes and Saccharomyces cerevisiae strains confirmed the transport of common precursors for secondary metabolites and ubiquinone. These results suggest that SLC25A44 is a mitochondrion-ER-nucleus zone transporter with biotechnological applications. Finally, a conserved three-amino acid signature on the cytosolic face of transport cavity was found important for rational engineering of SLC25s.  相似文献   
95.
Abstract. This article investigates home attributes that attract residential burglars in choosing a target. These attributes are the location of the home, its physical appearance, demographic characteristics of the residents, and the security precautions present. The theoretical foundation of the empirical model is the criminal utility maximization behavior that considers costs and benefits as formulated by Becker. However, this article introduces to the model the spatial dimension of the burglar's search for a target. The incidence of burglary is the dependent variable and is measured in a dichotomy scale. The empirical analysis utilizes a survey database of burgled and non-burgled homes that was conducted by the researchers. A logit model is used for the investigation, and the effects of the explanatory variables are calculated as probabilities. The database is unique in the wealth of attributes of individual homes that are relevant to burglars'decision process.  相似文献   
96.
Eine blo? gedachte Umrissfl?che bei der Ermittlung der Geb?udeh?he muss nicht den vorgeschriebenen Nachbarabstand wahren.  相似文献   
97.
Monadic second order (MSO) logic has proved to be a useful tool in many areas of application, reaching from decidability and complexity to picture processing, correctness of programs and parallel processes. To characterize the structural borderline between decidability and undecidability is a classical research problem here. This problem is related to questions in computational complexity, especially to the model checking problem, for which many tools developed in the area of decidability have proved to be useful. For more than two decades it was conjectured in [D. Seese, The structure of the models of decidable monadic theories of graphs, Ann. Pure Appl. Logic 53 (1991) 169–195] that decidability of monadic theories of countable structures implies that the theory can be reduced via interpretability to a theory of trees.  相似文献   
98.
本文研究了M25车用(煤基)甲醇汽油在高寒地区的使用性能。试验表明,在-30℃温度下放置48h或含水0.3%时,油品均保持清亮透明无相分离,同时具有明显的抗腐蚀与抑制橡胶溶胀作用。甲醇汽油作为一种理想的清洁燃料,将成为汽车的主要替代能源。  相似文献   
99.
为了探究不同油浸变压器受火情况下的火灾动力学过程,搭建了全尺度变压器火灾实验平台,分别针对基于RAPO天然酯植物油和25号变压器油的10 kV油浸变压器开展了外部热源耐火实验。研究结果表明,在同一外部热源条件下,矿物油变压器在受火状态下9 min左右即出现猛烈的喷射火灾现象,喷射出的矿物油品同时导致了大面积的池火和流淌火灾,使得火灾进一步加剧。相比而言,植物油变压器燃烧相对平缓,在24 min左右才出现轻微的喷射火现象,但并未造成明显的火灾加剧,且实验结束后变压器周边残存大量未燃植物油。在燃烧实验中,植物油的温升速率约为0.18 ℃/s,显著低于矿物油的0.24 ℃/s,也进一步说明了植物绝缘油的安全性。从消防安全角度,植物油变压器的火灾安全性远胜于矿物油变压器,具有较好的应用前景。  相似文献   
100.
Persistent organic pollutants (POPs) encompass an array of anthropogenic organic and elemental substances and their degradation and metabolic byproducts that have been found in the tissues of exposed animals, especially POPs categorized as organohalogen contaminants (OHCs). OHCs have been of concern in the circumpolar arctic for decades. For example, as a consequence of bioaccumulation and in some cases biomagnification of legacy (e.g., chlorinated PCBs, DDTs and CHLs) and emerging (e.g., brominated flame retardants (BFRs) and in particular polybrominated diphenyl ethers (PBDEs) and perfluorinated compounds (PFCs) including perfluorooctane sulfonate (PFOS) and perfluorooctanic acid (PFOA) found in Arctic biota and humans. Of high concern are the potential biological effects of these contaminants in exposed Arctic wildlife and fish. As concluded in the last review in 2004 for the Arctic Monitoring and Assessment Program (AMAP) on the effects of POPs in Arctic wildlife, prior to 1997, biological effects data were minimal and insufficient at any level of biological organization. The present review summarizes recent studies on biological effects in relation to OHC exposure, and attempts to assess known tissue/body compartment concentration data in the context of possible threshold levels of effects to evaluate the risks. This review concentrates mainly on post-2002, new OHC effects data in Arctic wildlife and fish, and is largely based on recently available effects data for populations of several top trophic level species, including seabirds (e.g., glaucous gull (Larus hyperboreus)), polar bears (Ursus maritimus), polar (Arctic) fox (Vulpes lagopus), and Arctic charr (Salvelinus alpinus), as well as semi-captive studies on sled dogs (Canis familiaris). Regardless, there remains a dearth of data on true contaminant exposure, cause-effect relationships with respect to these contaminant exposures in Arctic wildlife and fish. Indications of exposure effects are largely based on correlations between biomarker endpoints (e.g., biochemical processes related to the immune and endocrine system, pathological changes in tissues and reproduction and development) and tissue residue levels of OHCs (e.g., PCBs, DDTs, CHLs, PBDEs and in a few cases perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonates (PFSAs)). Some exceptions include semi-field studies on comparative contaminant effects of control and exposed cohorts of captive Greenland sled dogs, and performance studies mimicking environmentally relevant PCB concentrations in Arctic charr. Recent tissue concentrations in several arctic marine mammal species and populations exceed a general threshold level of concern of 1 part-per-million (ppm), but a clear evidence of a POP/OHC-related stress in these populations remains to be confirmed. There remains minimal evidence that OHCs are having widespread effects on the health of Arctic organisms, with the possible exception of East Greenland and Svalbard polar bears and Svalbard glaucous gulls. However, the true (if any real) effects of POPs in Arctic wildlife have to be put into the context of other environmental, ecological and physiological stressors (both anthropogenic and natural) that render an overall complex picture. For instance, seasonal changes in food intake and corresponding cycles of fattening and emaciation seen in Arctic animals can modify contaminant tissue distribution and toxicokinetics (contaminant deposition, metabolism and depuration). Also, other factors, including impact of climate change (seasonal ice and temperature changes, and connection to food web changes, nutrition, etc. in exposed biota), disease, species invasion and the connection to disease resistance will impact toxicant exposure. Overall, further research and better understanding of POP/OHC impact on animal performance in Arctic biota are recommended. Regardless, it could be argued that Arctic wildlife and fish at the highest potential risk of POP/OHC exposure and mediated effects are East Greenland, Svalbard and (West and South) Hudson Bay polar bears, Alaskan and Northern Norway killer whales, several species of gulls and other seabirds from the Svalbard area, Northern Norway, East Greenland, the Kara Sea and/or the Canadian central high Arctic, East Greenland ringed seal and a few populations of Arctic charr and Greenland shark.  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