全文获取类型
收费全文 | 1684篇 |
免费 | 40篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 50篇 |
综合类 | 20篇 |
化学工业 | 396篇 |
金属工艺 | 21篇 |
机械仪表 | 23篇 |
建筑科学 | 109篇 |
矿业工程 | 10篇 |
能源动力 | 32篇 |
轻工业 | 177篇 |
水利工程 | 20篇 |
石油天然气 | 18篇 |
无线电 | 128篇 |
一般工业技术 | 288篇 |
冶金工业 | 261篇 |
原子能技术 | 17篇 |
自动化技术 | 156篇 |
出版年
2023年 | 15篇 |
2021年 | 21篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 22篇 |
2016年 | 16篇 |
2015年 | 25篇 |
2014年 | 38篇 |
2013年 | 88篇 |
2012年 | 58篇 |
2011年 | 86篇 |
2010年 | 52篇 |
2009年 | 65篇 |
2008年 | 69篇 |
2007年 | 70篇 |
2006年 | 60篇 |
2005年 | 47篇 |
2004年 | 53篇 |
2003年 | 32篇 |
2002年 | 40篇 |
2001年 | 17篇 |
2000年 | 28篇 |
1999年 | 20篇 |
1998年 | 26篇 |
1997年 | 22篇 |
1996年 | 17篇 |
1995年 | 25篇 |
1994年 | 21篇 |
1993年 | 21篇 |
1992年 | 19篇 |
1991年 | 30篇 |
1990年 | 23篇 |
1987年 | 23篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 27篇 |
1983年 | 22篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 17篇 |
1978年 | 23篇 |
1976年 | 14篇 |
1975年 | 19篇 |
1974年 | 27篇 |
1973年 | 20篇 |
1972年 | 26篇 |
1970年 | 20篇 |
1967年 | 14篇 |
1966年 | 15篇 |
排序方式: 共有1726条查询结果,搜索用时 406 毫秒
151.
152.
153.
Guoyu Lin Yun-Jae Kim Alfred Cornec Karl-Heinz Schwalbe 《International Journal of Fracture》1998,91(4):323-347
Ductile failure of an interleaf tension specimen consisting of a metal interleaf bonded between two elastic substrates, with
a crack located in the centre of the metal, is studied by means of detailed finite element (FE) analyses. The rate-independent
version of the Gurson model is used. This accounts for ductile failure mechanisms of micro-void nucleation, growth and coalescence
within the framework of a finite deformation plasticity theory. Also, the rapid evolution of void density due to coalescence,
which leads to ultimate failure, is considered. The effect of the interleaf thickness on failure (crack initiation and limited
amount of crack growth) is investigated. The results show that the interleaf thickness affects crack initiation only slightly.
For all specimens considered, crack initiation takes place at the crack tip. However, after crack initiation, the interleaf
thickness affects stress and strain distributions significantly. Reducing the interleaf thickness significantly increases
the load-carrying capacity. Moreover, reducing the interleaf thickness increases the maximum hydrostatic stress in the interleaf,
which is no longer developed at the crack tip but at a distance far away from the crack tip. The resulting fracture toughness
thus decreases as the interleaf thickness decreases. The shielding of the crack tip due to constrained plasticity is observed
at higher load levels for interleaf specimens.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
154.
155.
Inverse gas chromatography of alkanes has been used to assess the degree of fusion of rigid polyvinyl chloride (PVC) extrudates. The relative degree of fusion is provided by ratios of the retention volumes of the alkane probe molecules in the bulk of the PVC. This method is nonintrusive and can be used to measure degree of fusion quantitatively if a completely fused reference material can be provided. The present analysis involves evaluations of the contributions to the overall retention volume of the alkane probes, resulting from adsorption and from bulk diffusion. The diffusivity of the alkanes was clearly dependent on the processing history of the PVC extrudate. A direct variation was observed between the size of the diffusing molecules and their residence time as adsorbates on the polymer surface. © 1995 John Wiley & Sons, Inc. 相似文献
156.
This paper presents an investigation on the effects of construction loads and vibrations on typical newly poured reinforced concrete bridge decks. The main objective of this paper was to perform dynamic finite-element analyses of concrete bridge decks under construction loads and vibrations. Two types of bridges were modeled by effectively simulating the loads encountered during construction. Separate analyses were performed to simulate one truck as well as two side-by-side trucks. Additional analyses were performed to simulate the loads during construction and pouring sequence. The loads imposed by concrete mixer trucks, including the full concrete load and the load imposed by a trailer unit carrying the pump, were taken into consideration during the modeling of the bridges. The results obtained consisted of vibration modes and frequencies for each structure in addition to top and bottom stresses in each principal direction. A separate analysis was performed that took into account the sequence of pour to determine the effect of moving loads from adjacent traffic and construction loads on fresh concrete. The time history and dynamic analysis indicated that the sequence of pour has a significant effect on the deformation of the concrete at early ages. As a result, the first three mode shapes obtained by the finite-element analysis will be used to optimize sensor locations for future dynamic field testing. 相似文献
157.
42 college students who responded to an announcement for a writing therapy study were randomly assigned to 1 of 3 groups. The writing therapy group wrote letters describing their problems to a psychotherapist whose written replies contained behaviorally oriented responses. Reassuring responses were written to the problem letters of Ss in a reassurance control group. A 2nd control group was asked to count the frequency of occurrence of specific problem behaviors and mail them to the therapist, who did not reply. 10 Ss in the writing therapy group and 8 in each of the control groups completed the 4-mo treatment period. The decrease in the number of problems (as measured by the Mooney Problem Check List) was significantly greater in the writing therapy group than in the 2 control groups. Analysis of demographic data revealed that more males than females dropped out of the study, and a significantly greater proportion of the dropouts were from lower-class families. It is concluded that writing therapy may be useful and appeal to students who do not feel able to use traditional student counseling services. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
158.
In replying to H. Abikoff and P. P. Ramsey's (see record 1980-03741-001) reanalysis of some of the present authors' (see record 1978-32185-001) data from a study of the cognitive-behavioral treatment of impulsive children, it is noted that covariance is likely to increase the differences between groups, but because of a negative relationship between the measures at pretreatment and follow-up, covariance reduced the group differences. A central clinical question—whether cognitive-behavioral interventions can result in treatment generalization—is considered; some recent evidence indicates supportive outcomes. (3 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
159.
This paper presents the establishment of a Bridge Rating Expert System (BRES) by using a knowledge-based computer artificial intelligent expert system for analysis and rating of existing short span prestressed concrete highway bridges. The rating methods considered were: Inventory Rating, Operation Rating, Rating Factor Rating and Sufficiency Rating. A strength rating is based on the evaluation of existing prestressed concrete bridges in accordance with the American Association of State Highway Transportation Officials (AASHTO) specifications, and inventory rating for all bridges according to the Federal Highway Administration (FHWA) guide for the Structure Inventory and Appraisal of the Nation's Bridges. The parameters considered were bridge type, dead loads, type of vehicle loading, bridge dimensions and cross-section, material properties, reinforcement details, and existing physical condition of the bridge. The results show that, through its runtime rule controller, user interface and linkage mechanisms, the BRES is a friendly user system for rating highway bridges. In addition, the EXSYSP shell provides an effective tool for other possible applications in civil engineering practice. 相似文献
160.
George E. Myers Alfred W. Christiansen Robert L. Geimer Robert A. Follensbee James A. Koutsky 《应用聚合物科学杂志》1991,43(2):237-250
Two different phenol–formaldehyde (PF) resole resins are serving as models in a study aimed at establishing the effects of moisture, temperature, pressure, and time on resin cure and bonding during the pressing of wood flakeboard. This phase of the program had two goals: first, to characterize the two resins in terms of their structure and chemistry during synthesis, aging, and cure—using viscosity measurement, gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and dynamic mechanical analysis (DMA); second, to make a preliminary evaluation of the utility of DSC, FTIR, and DMA for measuring the degree of resin cure. The two resins differed significantly in relative amounts of hydroxymethyl groups and methylene linkages (NMR), in molecular weight and its distribution (GPC), and in reaction rate (as measured by viscosity, DSC, FTIR, or DMA). The degree of cure developed during constant heating rate DSC scans was calculated for a series of maximum DSC temperatures from both the loss in hydroxymethyl groups (FTIR) and the decrease in available exothermic heat (DSC). Agreement between the two methods was quite good, considering the inherent difficulties in quantifying infrared data. For comparison, the degree of cure developed during constant heating rate DMA scans was calculated for a series of maximum DMA temperatures from both the increase in storage modulus (DMA) and the decrease in exothermic heat (DSC after rewetting). Samples that apparently achieved complete cure in the DMA still exhibited significant residual cure potential in the DSC. We attribute the lower apparent cure in the DMA to loss of moisture from samples during the DMA scan, with consequent loss in plasticization and molecular mobility. 相似文献