全文获取类型
收费全文 | 18426篇 |
免费 | 525篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 244篇 |
综合类 | 9篇 |
化学工业 | 3673篇 |
金属工艺 | 286篇 |
机械仪表 | 311篇 |
建筑科学 | 1105篇 |
矿业工程 | 109篇 |
能源动力 | 512篇 |
轻工业 | 1407篇 |
水利工程 | 158篇 |
石油天然气 | 204篇 |
武器工业 | 1篇 |
无线电 | 1093篇 |
一般工业技术 | 2897篇 |
冶金工业 | 4323篇 |
原子能技术 | 165篇 |
自动化技术 | 2472篇 |
出版年
2022年 | 139篇 |
2021年 | 215篇 |
2020年 | 171篇 |
2019年 | 223篇 |
2018年 | 267篇 |
2017年 | 260篇 |
2016年 | 319篇 |
2015年 | 238篇 |
2014年 | 388篇 |
2013年 | 1108篇 |
2012年 | 670篇 |
2011年 | 876篇 |
2010年 | 680篇 |
2009年 | 667篇 |
2008年 | 873篇 |
2007年 | 878篇 |
2006年 | 698篇 |
2005年 | 726篇 |
2004年 | 569篇 |
2003年 | 578篇 |
2002年 | 512篇 |
2001年 | 334篇 |
2000年 | 303篇 |
1999年 | 313篇 |
1998年 | 361篇 |
1997年 | 331篇 |
1996年 | 308篇 |
1995年 | 340篇 |
1994年 | 276篇 |
1993年 | 308篇 |
1992年 | 279篇 |
1991年 | 166篇 |
1990年 | 239篇 |
1989年 | 287篇 |
1988年 | 215篇 |
1987年 | 219篇 |
1986年 | 216篇 |
1985年 | 268篇 |
1984年 | 262篇 |
1983年 | 230篇 |
1982年 | 219篇 |
1981年 | 217篇 |
1980年 | 172篇 |
1979年 | 191篇 |
1978年 | 181篇 |
1977年 | 179篇 |
1976年 | 152篇 |
1975年 | 181篇 |
1974年 | 168篇 |
1973年 | 135篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
921.
Summary A sequence of tasks that must be performed on a sequential database can be scheduled in various ways. Schedules will differ with respect to the number of accesses made to peripheral storage devices and the amount of memory space consumed by buffers. Buffer requirements are discussed for task schedules that avoid accesses to peripherals storing the sequential database. The relationship between certain thrifty scheduling policies and loop jamming, a standard code optimization technique, is also identified. Application to UNIX pipelines and to file processing is discussed.This work is supported in part by NSF Grant MCS-8003340 and MCS-8103605. Schneider is also supported by a Faculty Development Grant from IBM Corporation 相似文献
922.
Valencia Richard R.; Henderson Ronald W.; Rankin Richard J. 《Canadian Metallurgical Quarterly》1985,77(3):323
Examined the relative contributions of several family status variables (child and parental language, parental schooling attainment and location, and SES), a family constellation variable (family size), and the Henderson Environmental Learning Process Scale (HELPS) to the prediction of cognitive performance among 140 Mexican-American preschool children (aged 38–71 mo) from low-income backgrounds. Ss were administered the McCarthy Scales of Childrens' Abilities (MSCA). A factor analysis of the family status and constellation variables produced 3 factors. The General Cognitive Index (GCI) of the MSCA was predicted by multiple regression procedures. The 3 status/constellation factors and HELPS served as independent variables. As hypothesized, the best predictor of GCI was HELPS. A Language/Schooling factor made an additional significant contribution to the explained variance. The theoretical and practical implications of including proximal as well as distal background variables in future research on relations between family characteristics and intellectual performance are discussed. (43 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
923.
Abstract. Time series analysts have begun to consider the applicability of nonlinear models. In order for nonlinear models to be accepted by practitioners, practicai tests must be avilable to test for the presence of nonlinearity in both raw time series and in the residuals from fitted models. A diagnostic test, based on the bispectrum, for the presence of nonlinear serial dependence in these time series is investigated here using artificial data. Detection of such nonlinear dependence is taken to indicate that nonlinear modelling methods are necessary. The theory behind the test is reviewed and simulations driven by pseudorandom numbers are presented for a variety of models and sample sizes. The simulations indicate that the test has substantial power for many models. In addition, theoretical and empirical results are presented which show that the bispectral diagnostic test is equally powerful for both the source series and for the fitting errors from a line& model. Thus, while the test is suitable for use as a diagnostic test on the fitting errors of linear time series models, prior linear modeling of the time series is not required. 相似文献
924.
925.
Prolonged alcohol (ethanol) consumption leads to the development of alcohol tolerance and cross-tolerance to some benzodiazepines and barbiturates. In contrast, rats undergoing alcohol withdrawal are sensitized to the anticonvulsant effects of the endogenous GABA(A) receptor modulator, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP). Alterations in endogenous, cerebral cortical levels of 3alpha,5alpha-THP during alcohol withdrawal could contribute to the observed sensitization to 3alpha,5alpha-THP. Therefore, this study investigated plasma and brain levels of 3alpha,5alpha-THP, progesterone, and corticosterone during alcohol dependence and withdrawal in the rat. Plasma corticosterone, progesterone (a precursor of 3alpha,5alpha-THP) and 3alpha,5alpha-THP levels were unchanged in alcohol-dependent animals. Cerebral cortical levels of 3alpha,5alpha-THP decreased in dependent male animals, but not in dependent female rats. During alcohol withdrawal, plasma corticosterone and progesterone levels increased in male, but not female rats. However, neither plasma nor cerebral cortical 3alpha,5alpha-THP levels were altered from control levels in male or female rats during alcohol withdrawal. Plasma and brain levels of 3alpha,5alpha-THP were markedly higher in female compared with male rats. Cerebral cortical levels of 3alpha,5alpha-THP during the diestrus phase of the estrus cycle were approximately 4 to 6 ng/g, a concentration that may approach physiological relevance. These findings suggest that sensitization to 3alpha,5alpha-THP during alcohol withdrawal is not mediated by elevations in brain levels of endogenous 3alpha,5alpha-THP in male or female rats. However, elevations in circulating corticosterone and progesterone levels during ethanol withdrawal in male rats may underlie gender differences in allopregnanolone sensitivity during ethanol withdrawal. 相似文献
926.
DV Serreze SA Fleming HD Chapman SD Richard EH Leiter RM Tisch 《Canadian Metallurgical Quarterly》1998,161(8):3912-3918
Nonobese diabetic (NOD) mice genetically deficient in B lymphocytes (NODJg mu(null)) are resistant to T cell-mediated autoimmune insulin-dependent diabetes mellitus (IDDM). Ig infusions from diabetic NOD donors did not abrogate IDDM resistance in NODJg mu(null) mice. However, T cell responses to the candidate pancreatic beta cell autoantigen glutamic acid decarboxylase (GAD), but not the control Ag keyhole limpet hemocyanin, were eliminated in NODJg mu(null) mice. To initially test whether they contribute to IDDM as APC, NOD B lymphocytes were transferred into NODJg mu(null) recipients. B lymphocytes transferred into unmanipulated NODJg mu(null) recipients were rejected by MHC class I-restricted T cells. Stable T and B lymphocyte repopulation was achieved in irradiated NODJg mu(null) mice reconstituted with syngeneic bone marrow admixed with NOD B lymphocytes. IDDM susceptibility was restored in NODJg mu(null) mice reconstituted with syngeneic marrow plus B lymphocytes, but not with syngeneic marrow only. T cell responses to GAD were restored only in NODJg mu(null) mice reconstituted with syngeneic marrow plus B lymphocytes. Hence, B lymphocytes appear to contribute to IDDM in NOD mice as APC with a preferential ability to present certain beta cell Ags such as GAD to autoreactive T cells. 相似文献
927.
Bowers Jeffrey S.; Vigliocco Gabriella; Haan Richard 《Canadian Metallurgical Quarterly》1998,24(6):1705
A series of experiments assessed masked priming for letters and words that are visually similar (SIM) and dissimilar (DIS) in upper- and lowercase formats. For letters, robust DIS priming was obtained in a naming task, but this priming did not extend to a variety of non-naming tasks. For words, robust DIS priming was obtained in both naming and non-naming tasks. SIM letter and word priming extended to all tasks, but the effects were generally small for letters. The restricted set of conditions for DIS letter priming suggests that this priming is mediated by phonological-articulatory processes, and the generality of DIS word priming argues that abstract orthographic codes mediate these effects. Consistent with this conclusion, priming between homophones (for both letters and words) was found in a naming task, but little word homophone priming was obtained in a lexical decision task. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
928.
Hartmut Logemann Richard Rebarber 《Mathematics of Control, Signals, and Systems (MCSS)》1996,9(2):123-151
It has been observed that for many stable feedback systems, the introduction of arbitrarily small time-delays into the loop causes instability. In this paper we present a systematic treatment of this phenomenon for a large class of boundary control systems which allows for in-span control. Our approach is based on a combination of input-output methods and modal analysis. We give a number of sufficient conditions for robustness/nonrobustness of closed-loop input-output stability with respect to delays. Our framework includes a large class of ill-posed systems, i.e., systems whose open-loop transfer function is unbounded on any right half-plane. We then analyze the relationship between the poles of the transfer function and the exponential modes of the underlying boundary-value problem to derive internal stability properties from external ones.This work was supported by the British Council/DAAD (ARC project 464), by the Human Capital and Mobility programme (Project number CHRX-CT93-0402), by the National Science Foundation (Grant DMS-9206986) and by NATO (Grant CRG 950179). 相似文献
929.
RA Nugent M Murphy ST Schlachter CJ Dunn RJ Smith ND Staite LA Galinet SK Shields DG Aspar KA Richard 《Canadian Metallurgical Quarterly》1993,36(1):134-139
Vinylidenebisphosphonic acid tetraethyl ester (1) and diazo ketones 7a-1 in ether at 22 degrees C yield pyrazoline bisphosphonate tetraethyl esters 8a-1 in moderate to good yield. These compounds were evaluated in animal models of arthritis: rat adjuvant-induced polyarthritis (AIP) and murine antigen-induced arthritis (AIA) and a murine model of chronic inflammation, the delayed type hypersensitivity granuloma reaction (DTH-GRA). (5-Benzoyl-2,4-dihydro-3H-pyrazol-3-ylidene)-bisphosphonic acid tetraethyl ester (8a), and [5-(3-fluorobenzoyl)-2,4-dihydro-3H-pyraxol-3-ylidene]- bisphosphonic acid tetraethyl ester (8d) significantly inhibited the arthritis models, AIP (15 mg/kg) and AIA (25 mg/kg), as well as the DTH-GRA (25 mg/kg). Conversion of 8a to the corresponding bisphosphonic acid, 10a, resulted in loss of activity. Compounds with alkyl substituents on the pyrazoline nitrogen, 9a-d, were inactive in the DTH-GRA. These results show that 8a and 8d have novel antiinflammatory activity and are capable of inhibiting chronic arthritis and inflammation in animals. Such compounds might be useful in man for treating chronic tissue injury associated with arthropathies such as inflammatory joint disease as well as other chronic inflammatory diseases. 相似文献
930.
Richard Wood 《河流研究与利用》1988,2(3):471-477
Integrated river basin management has been the backcloth against which river regulation has been practiced in England and Wales for the past 14 years. Its success is reviewed and the forthcoming changes in legislation are critically examined. A number of problems facing the emergent National Rivers Authority are discussed. The need for co-operation rather than conflict is advocated wherever environment is to be protected and when competing pressures impact on river resources. A number of technical issues remain unresolved and the need for continuing work is recognized. 相似文献