全文获取类型
收费全文 | 1612篇 |
免费 | 24篇 |
专业分类
电工技术 | 18篇 |
化学工业 | 334篇 |
金属工艺 | 14篇 |
机械仪表 | 33篇 |
建筑科学 | 69篇 |
矿业工程 | 13篇 |
能源动力 | 47篇 |
轻工业 | 174篇 |
水利工程 | 10篇 |
石油天然气 | 6篇 |
无线电 | 69篇 |
一般工业技术 | 257篇 |
冶金工业 | 462篇 |
原子能技术 | 14篇 |
自动化技术 | 116篇 |
出版年
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 13篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 20篇 |
2013年 | 76篇 |
2012年 | 25篇 |
2011年 | 43篇 |
2010年 | 34篇 |
2009年 | 41篇 |
2008年 | 51篇 |
2007年 | 45篇 |
2006年 | 56篇 |
2005年 | 39篇 |
2004年 | 35篇 |
2003年 | 42篇 |
2002年 | 41篇 |
2001年 | 21篇 |
2000年 | 24篇 |
1999年 | 46篇 |
1998年 | 106篇 |
1997年 | 69篇 |
1996年 | 50篇 |
1995年 | 30篇 |
1994年 | 33篇 |
1993年 | 33篇 |
1992年 | 20篇 |
1991年 | 10篇 |
1990年 | 25篇 |
1989年 | 25篇 |
1988年 | 27篇 |
1987年 | 29篇 |
1986年 | 21篇 |
1985年 | 23篇 |
1984年 | 36篇 |
1983年 | 25篇 |
1982年 | 25篇 |
1981年 | 27篇 |
1980年 | 34篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 24篇 |
1976年 | 29篇 |
1975年 | 18篇 |
1974年 | 14篇 |
1973年 | 19篇 |
1972年 | 12篇 |
1968年 | 10篇 |
排序方式: 共有1636条查询结果,搜索用时 15 毫秒
1.
MA Nowak AL Lloyd GM Vasquez TA Wiltrout LM Wahl N Bischofberger J Williams A Kinter AS Fauci VM Hirsch JD Lifson 《Canadian Metallurgical Quarterly》1997,71(10):7518-7525
Mathematical modeling of viral replication dynamics, based on sequential measurements of levels of virion-associated RNA in plasma during antiretroviral treatment, has led to fundamental new insights into human immunodeficiency virus type 1 pathogenesis. We took advantage of the simian immunodeficiency virus (SIV)-infected macaque model to perform detailed measurements and mathematical modeling during primary infection and during treatment of established infection with the antiretroviral drug (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA). The calculated clearance half-life for productively infected cells during resolution of the peak viremia of primary infection was on the order of 1 day, with slightly shorter clearance half-lives calculated during PMPA treatment. Viral reproduction rates upon discontinuation of PMPA treatment after 2 weeks were approximately twofold greater than those obtained just prior to initiation of treatment in the same animals, likely reflecting accumulation of susceptible target cells during treatment. The basic reproductive ratio (R0) for the spread of SIV infection in vivo, which represents the number of productively infected cells derived from each productively infected cell at the beginning of infection, was also estimated. This parameter quantifies the extent to which antiviral therapy or vaccination must limit the initial spread of virus to prevent establishment of chronic disseminated infection. The results thus provide an important guide for efforts to develop vaccines against SIV and, by extension, human immunodeficiency virus. 相似文献
2.
Malloy B.A. Lloyd E.L. Soffa M.L. 《Parallel and Distributed Systems, IEEE Transactions on》1994,5(5):498-508
A new approach is given for scheduling a sequential instruction stream for execution “in parallel” on asynchronous multiprocessors. The key idea in our approach is to exploit the fine grained parallelism present in the instruction stream. In this context, schedules are constructed by a careful balancing of execution and communication costs at the level of individual instructions, and their data dependencies. Three methods are used to evaluate our approach. First, several existing methods are extended to the fine grained situation. Our approach is then compared to these methods using both static schedule length analyses, and simulated executions of the scheduled code. In each instance, our method is found to provide significantly shorter schedules. Second, by varying parameters such as the speed of the instruction set, and the speed/parallelism in the interconnection structure, simulation techniques are used to examine the effects of various architectural considerations on the executions of the schedules. These results show that our approach provides significant speedups in a wide-range of situations. Third, schedules produced by our approach are executed on a two-processor Data General shared memory multiprocessor system. These experiments show that there is a strong correlation between our simulation results, and these actual executions, and thereby serve to validate the simulation studies. Together, our results establish that fine grained parallelism can be exploited in a substantial manner when scheduling a sequential instruction stream for execution “in parallel” on asynchronous multiprocessors 相似文献
3.
An investigation into the effects of pressure (helium gas) on the isothermal fluid behavior includes: (1) the effect of pressure on the rate of melting and coking as evidenced by the rate constants k(melt) and k(coke); (2) the effect of pressure on the energies of activation of melting and coking; (3) the effects of pressure on the characteristic times; (4) the effects of pressure on the maximum isothermal fluidity. Results from the effects of pressure on k(melt) revealed that it was generally the high total sulfur, low nitrogen, low reactives/mineral matter ratio, medium rank coals which show the greatest increase in k(melt), whereas the highest rank coals show the least decrease in k(coke). The energies of activation of melting and coking were not significantly affected by pressure. The investigation also reveals increases or decreases in the respective times of softening, maximum fluidity, resolidification and total time of fluid behavior under isothermal pressurized conditions. There appears the possibility that these shifts may be rank dependent. Additionally, the lower rank coals show the largest relative increase in their fluidities when subjected to pressure. Empirical relationships were derived in order to quantitatively predict the maximum isothermal fluidity for most (fluid) coals at a given pressure. 相似文献
4.
The technique of analytical pyrolysis has been used to characterize 40 similar mid-rank western Kentucky coals of widely differing ASTM Gieseler plasticity. Certain pyrolysis/g.c. variables were shown to correlate well with both ASTM Gieseler and isothermal plasticity. Highly plastic coals were shown to exhibit certain characteristic peaks in the 450 °C pyrogram which were absent in the pyrogram of the non-plastic coals. Two coals, representing the two extremes in plasticity, were selected for further study. After extraction with solvents such as DMF the characteristic peaks were absent in the 450 °C pyrogram of the extraction residue of the highly plastic coal. These peaks were also shown to decrease with increasing severity of air oxidation of the plastic coal. This technique appears to be a useful tool for the analysis of mid-rank plastic coals and supports the view that the substances contained in the bitumen fraction of these coals are involved in the development of the plastic state. 相似文献
5.
6.
This article describes the application, at the team and individual level, of findings from the positive psychology research. An overview of this research is presented focusing on several areas generally included in the positive psychology domain: flow, appreciative inquiry, the broaden and build theory, and other strategies for increasing the experience of positive emotions and the identification and deployment of strengths. The authors propose that these applications show promise in consulting psychology engagements and may have merit when utilized by practitioners themselves. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
International migrations: A framework for directing research. 总被引:1,自引:0,他引:1
Current, large-scale, cross-cultural migrations offer promising research targets for the study of human adaptations. The opportunities for such research, however, remain substantially unused in the mainstream of psychology. The purpose here is to provide a framework encompassing components of the migration experience to aid such research. Contextual factors in the sending and receiving societies impinge on the components of the migration experience: social networks, SES, and culture. The components, treated as intertwining transitional experiences in migration, should be juxtaposed in research to examine their effects. Gender and age mediate the effects. The framework aims to benefit research that implicates, directly or heuristically, the experiences of persons exposed to rapid sociocultural change and the consequences of such changes in their lives. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
9.
PA Cabrera S Parietti G Haran U Benavidez S Lloyd G Perera S Valledor MA Gemmell T Botto 《Canadian Metallurgical Quarterly》1996,26(1):79-83
Forced thinking is an incompletely understood and rarely described epileptic aura. We studied three patients with forced thinking from left frontal lesions, two neoplastic and one vascular. All three experienced repetitive, intrusive thoughts at the onset of seizures. Their forced thinking was associated with the desire to vocalize, orobuccal movements, and speech arrest. The episodes occurred with other ictal manifestations and responded to antiseizure therapy. These patients suggest that epileptic forced thinking is a heterogeneous phenomenon; forced thinking from left frontal lesions is a manifestation of expressive language and is distinct from experiential thoughts arising from temporal limbic foci. 相似文献
10.
David Lloyd Suzie Morrell Helle N. Carlsen Hans Degn Phillip E. James Christopher C. Rowlands 《Yeast (Chichester, England)》1993,9(8):825-833
Saccharomyces cerevisiae HSc was grown with ethanol at concentrations up to 10% (v/v). The immediate effects of additions of externally added ethanol on CO2 production and O2 consumption of washed organisms were studied by stopped-flow membrane inlet quadrupole mass spectrometry. Fermentative activities of organisms grown with ethanol (0–5% v/v) showed similar sensitivities to inhibition by ethanol, whereas those grown with 10% (v/v) ethanol had become protected and were markedly less sensitive. The fluidity of subcellular membrane fractions was measured by determination of the temperature dependence of the rotational order parameter of the spin label 5-doxyl stearic acid (free radical) by electron spin resonance. Mitochondria prepared from yeasts grown with 0, 7 and 9% (v/v) ethanol showed similar overall fluidity, although differences in temperature-dependent behaviour indicate altered lipid composition or lateral phase separations. On the other hand the microsomal fraction from organisms grown with 9% ethanol showed a remarkable increase in fluidity. These data suggest that the protective effects of growth with ethanol near the limit of tolerance on fermentative activities may arise from altered plasma membrane fluidity properties. 相似文献