全文获取类型
收费全文 | 32943篇 |
免费 | 991篇 |
国内免费 | 66篇 |
专业分类
电工技术 | 366篇 |
综合类 | 35篇 |
化学工业 | 6788篇 |
金属工艺 | 858篇 |
机械仪表 | 621篇 |
建筑科学 | 1839篇 |
矿业工程 | 247篇 |
能源动力 | 1016篇 |
轻工业 | 2762篇 |
水利工程 | 335篇 |
石油天然气 | 207篇 |
武器工业 | 2篇 |
无线电 | 2149篇 |
一般工业技术 | 5194篇 |
冶金工业 | 6641篇 |
原子能技术 | 322篇 |
自动化技术 | 4618篇 |
出版年
2022年 | 196篇 |
2021年 | 386篇 |
2020年 | 332篇 |
2019年 | 399篇 |
2018年 | 488篇 |
2017年 | 506篇 |
2016年 | 520篇 |
2015年 | 463篇 |
2014年 | 736篇 |
2013年 | 2132篇 |
2012年 | 1240篇 |
2011年 | 1590篇 |
2010年 | 1169篇 |
2009年 | 1258篇 |
2008年 | 1436篇 |
2007年 | 1467篇 |
2006年 | 1256篇 |
2005年 | 1172篇 |
2004年 | 1052篇 |
2003年 | 1023篇 |
2002年 | 1031篇 |
2001年 | 634篇 |
2000年 | 615篇 |
1999年 | 575篇 |
1998年 | 599篇 |
1997年 | 499篇 |
1996年 | 604篇 |
1995年 | 546篇 |
1994年 | 532篇 |
1993年 | 534篇 |
1992年 | 486篇 |
1991年 | 321篇 |
1990年 | 438篇 |
1989年 | 424篇 |
1988年 | 379篇 |
1987年 | 425篇 |
1986年 | 382篇 |
1985年 | 515篇 |
1984年 | 491篇 |
1983年 | 443篇 |
1982年 | 464篇 |
1981年 | 445篇 |
1980年 | 353篇 |
1979年 | 365篇 |
1978年 | 329篇 |
1977年 | 307篇 |
1976年 | 268篇 |
1975年 | 318篇 |
1974年 | 243篇 |
1973年 | 279篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Schmidt Frank L.; Law Kenneth; Hunter John E.; Rothstein Hannah R.; Pearlman Kenneth; McDaniel Michael 《Canadian Metallurgical Quarterly》1993,78(1):3
Using a large database, this study examined 3 refinements of validity generalization procedures: (1) a more accurate procedure for correcting the residual standard deviation (SD) for range restriction to estimate SDp, (2) use of r? instead of study-observed rs in the formula for sampling error variance, and (3) removal of non-Pearson rs. The 1st procedure does not affect the amount of variance accounted for by artifacts. The addition of the 2nd and 3rd procedures increased the mean percentage of validity variance accounted for by artifacts from 70 to 82%, a 17% increase. The cumulative addition of all 3 procedures decreased the mean SDp estimate from .150 to .106, a 29% decrease. Six additional variance-producing artifacts were identified that could not be corrected for. In light of these it was concluded that the obtained estimates of mean SDp and mean validity variance accounted for were consistent with the hypothesis that the true mean SDp value is close to zero. These findings provide further evidence against the situational specificity hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
Andrzej Banaszuk Andrzej Święch John Hauser 《Mathematics of Control, Signals, and Systems (MCSS)》1996,9(3):207-241
We study the problem of approximating one-dimensional nonintegrable codistributions by integrable ones and apply the resulting
approximations to approximate feedback linearization of single-input systems. The approach derived in this paper allows a
linearizable nonlinear system to be found that is close to the given system in a least-squares (L
2) sense. A linearly controllable single-input affine nonlinear system is feedback linearizable if and only if its characteristic
distribution is involutive (hence integrable) or, equivalently, any characteristic one-form (a one-form that annihilates the
characteristic distribution) is integrable. We study the problem of finding (least-squares approximate) integrating factors
that make a fixed characteristic one-form close to being exact in anL
2 sense. A given one-form can be decomposed into exact and inexact parts using the Hodge decomposition. We derive an upper
bound on the size of the inexact part of a scaled characteristic one-form and show that a least-squares integrating factor
provides the minimum value for this upper bound. We also consider higher-order approximate integrating factors that scale
a nonintegrable one-form in a way that the scaled form is closer to being integrable inL
2 together with some derivatives and derive similar bounds for the inexact part. This allows a linearizable nonlinear system
that is close to the given system in a least-squares (L
2) sense together with some derivatives to be found. The Sobolev embedding techniques allow us to obtain an upper bound on
the uniform (L
∞) distance between the nonlinear system and its linearizable approximation.
This research was supported in part by NSF under Grant PYI ECS-9396296, by AFOSR under Grant AFOSR F49620-94-1-0183, and by
a grant from the Hughes Aircraft Company. 相似文献
104.
105.
106.
Schmitter-Edgecombe Maureen; Marks William; Fahy John F. 《Canadian Metallurgical Quarterly》1993,7(2):136
The 2-process theory of semantic priming (J. H. Neely, 1977; M. I. Posner and C. R. Snyder, 1975) was used to determine the maintenance of automatic processes after severe closed head injury (CHI) and to determine whether processes that demand attention suffer a deficit. Ss with severe CHI (N?=?18,?>?2 yrs postinjury) and 18 matched control Ss completed a lexical decision task in which a category prime was followed by a target. Automatic and attentional priming were determined by orthogonally varying prime–target relatedness, expectancy, and stimulus onset asynchrony. Although the CHI Ss had slower reaction times (RTs) overall, there were no significant group differences in the magnitude of either the automatic or attentional component of semantic priming. The present results indicate the integrity of semantic processes and normal semantic priming in long-term patients with severe CHI. The results are discussed in relation to an attentional resource hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
107.
108.
Bond Gary R.; Dietzen Laura L.; McGrew John H.; Miller Larry D. 《Canadian Metallurgical Quarterly》1995,40(2):75
Tested the hypothesis that Ss with severe mental illnesses would achieve better vocational outcomes with an accelerated approach to supported employment (AASE), as compared to gradual approaches (GA) with prevocational training. 86 Ss (mean age 35.1 yrs) with a diagnosis of a serious mental illness, were randomly assigned to either the AASE, or the GA, which included a minimum of 4 mo prevocational training. Data were obtained on indicators of vocational outcomes over 2 yrs, and for a limited number of Ss (n=36), during the 4th yr of inception into the program. Initially, only 5% of Ss preferred prevocational training. After 1 yr, AASE Ss showed better outcomes for a range of indicators, including achievement of competitive employment, duration of employment and mean earnings. During the 4th yr, 59% of these Ss were competitively employed, as compared to only 6% of GA Ss. Rehabilitation is more effective using AASE than GA. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
109.
Single-assignment and functional languages have value semantics that do not permit side-effects. This lack of side-effects makes automatic detection of parallelism and optimization for data locality in programs much easier. However, the same property poses a challenge in implementing these languages efficiently. This paper describes an optimizing compiler system that solves the key problem of aggregate copy elimination. The methods developed rely exclusively on compile-time algorithms, including interprocedural analysis, that are applied to an intermediate data flow representation. By dividing the problem into update-in-place and build-in-place analysis, a small set of relatively simple techniques—edge substitution, graph pattern matching, substructure sharing and substructure targeting—was found to be very powerful. If combined properly and implemented carefully, the algorithms eliminate unnecessary copy operations to a very high degree. No run-time overhead is imposed on the compiled programs. 相似文献
110.
Traditional homogenization techniques are not useful when the microstructural scale of a material is of the same order of magnitude as the structural scale of a component. Such is the case for many textile composites. Since discrete modeling of the microstructure throughout a component is prohibitively expensive, continuum finite elements are needed which account for the microstructure within a single element. This paper describes a simple substructuring technique for formulating these special elements. 相似文献