全文获取类型
收费全文 | 6618篇 |
免费 | 283篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 74篇 |
综合类 | 7篇 |
化学工业 | 1540篇 |
金属工艺 | 107篇 |
机械仪表 | 148篇 |
建筑科学 | 334篇 |
矿业工程 | 9篇 |
能源动力 | 226篇 |
轻工业 | 559篇 |
水利工程 | 63篇 |
石油天然气 | 26篇 |
武器工业 | 2篇 |
无线电 | 589篇 |
一般工业技术 | 1117篇 |
冶金工业 | 935篇 |
原子能技术 | 35篇 |
自动化技术 | 1147篇 |
出版年
2023年 | 67篇 |
2022年 | 108篇 |
2021年 | 174篇 |
2020年 | 125篇 |
2019年 | 128篇 |
2018年 | 183篇 |
2017年 | 159篇 |
2016年 | 192篇 |
2015年 | 161篇 |
2014年 | 226篇 |
2013年 | 409篇 |
2012年 | 370篇 |
2011年 | 431篇 |
2010年 | 328篇 |
2009年 | 371篇 |
2008年 | 354篇 |
2007年 | 370篇 |
2006年 | 263篇 |
2005年 | 254篇 |
2004年 | 204篇 |
2003年 | 184篇 |
2002年 | 157篇 |
2001年 | 105篇 |
2000年 | 113篇 |
1999年 | 107篇 |
1998年 | 109篇 |
1997年 | 114篇 |
1996年 | 85篇 |
1995年 | 102篇 |
1994年 | 87篇 |
1993年 | 65篇 |
1992年 | 66篇 |
1991年 | 31篇 |
1990年 | 47篇 |
1989年 | 66篇 |
1988年 | 49篇 |
1987年 | 38篇 |
1986年 | 51篇 |
1985年 | 58篇 |
1984年 | 45篇 |
1983年 | 54篇 |
1982年 | 36篇 |
1981年 | 35篇 |
1980年 | 33篇 |
1979年 | 27篇 |
1978年 | 20篇 |
1977年 | 17篇 |
1976年 | 28篇 |
1975年 | 31篇 |
1974年 | 22篇 |
排序方式: 共有6918条查询结果,搜索用时 15 毫秒
11.
12.
Véronique Baroghel-Bouny Patrick Belin Matthias Maultzsch Dominique Henry 《Materials and Structures》2007,40(8):759-781
Within the framework of the evaluation and the prediction of chloride-induced corrosion risks, simple and rapid AgNO3 spray tests can be proposed for various issues. This paper forms the first part of a series. In this first part, the Maultzsch
procedure (spraying of 0.1-N AgNO3 solution + K2CrO4) as well as the procedure based on the use of a sole AgNO3 solution have been investigated on a broad range of concretes. These procedures have also been compared to the Collepardi
procedure (spraying of 0.1-N AgNO3 + fluoresceine). The feasibility of these colorimetric techniques on saturated specimens cast in laboratory, after non-steady-state
diffusion tests carried out in various conditions, is discussed. In addition, the results obtained from applying such spray
tests in field conditions on cores drilled out from various RC test specimens exposed to a marine environment (tidal zone)
and to a road and cold environment (freezing-thawing cycles and spraying of deicing salts) are presented. Colorimetric methods
have in particular been applied here to the assessment of the average chloride penetration depth and of its evolution versus
time (kinetics). Moreover, the detection threshold of these techniques has been investigated in various environments. The
possible sources of discrepancy on the results have been analysed. 相似文献
13.
14.
The purpose of this paper is the modelling of the mechanical behaviour of an elastomeric material, through detailed experimental and numerical procedures, specific to large strains. The experimental technique is based on in-plane kinematics measurements using a speckle extensometer, from which the whole two-dimensional field of in-plane displacements is obtained by a digital image processing [Polymer (2002)]. This part of the work concerns the identification of the constitutive equation for a carbon black natural rubber (NR) vulcanizate. We start by quoting some theoretical considerations relative to rubber elasticity and stress-softening effect, which is the counterpart of the filler reinforcement. Then, we describe the experimental procedure and present data for both non-preconditioned and preconditioned samples. Next, the identification of the constitutive law parameters using a minimization algorithm is driven. Finally, we present the validation of the constitutive model, by its implementation into the finite element code SYSTUS and the numerical simulation of the response of a double edge notched tensile (DENT) specimen. 相似文献
15.
The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH4 traces under lean-burn conditions was studied in the presence or the absence of water or H2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H2S-poisoned Pd/Al2O3 catalyst was studied by TPD in O2/He. Poisoning species decompose above 873 K as SO2 and O2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H2S-poisoned Pd/Al2O3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested. 相似文献
16.
Patrick N. Troy 《Housing Studies》1992,7(3):216-233
This paper sets out the development of four main threads of housing policy in New South Wales from the latter part of the 19th century through the first 40 years of the 20th century. Following a discussion of the social and political circumstances and debate surrounding government policy regarding landlord/tenant relations, housing quality and supply, and owner occupancy, it concludes that policy evolution is irregular and a product of the exigencies of the political process. It also suggests that although government policy did little to improve the housing situation for the underprivileged, there was nevertheless a growing acceptance by both Labor and conservative parties of the increased need for government intervention in the housing market. 相似文献
17.
The Republicans took control of both houses of Congress in November of 1994 for the 1st time in 42 yrs. Although the magnitude of the Clinton Administration's proposed Health Security Act may well have triggered fears of overcontrol, it is clear that the delivery of psychological care will be changed dramatically by the combined forces of federal and state health reform. R. J. Resnick, President of the American Psychological Association, has appointed the Task Force on Education and Training for Work in Organized Delivery Systems to look at how psychological health care is provided in the new and evolving systems, and to examine how current training programs prepare new psychologists to practice in and around organized health care systems. Dr. Resnick is similarly concerned about standardization of training, training in nontraditional areas of competence, and increased federal recognition and funding of training in psychology. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
18.
An important aspect of the vehicle routing problem (VRP) that has been largely overlooked is the use of satellite facilities to replenish vehicles during a route. When possible, satellite replenishment allows the drivers to continue making deliveries until the close of their shift without necessarily returning to the central depot. This situation arises primarily in the distribution of fuels and certain retail items. When demand is random, optimizing customer routes a priori may result in significant additional costs for a particular realization of demand. Satellite facilities are one way of safeguarding against unexpected demand. This paper presents a branch and cut methodology for solving the VRP with satellite facilities subject to capacity and route time constraints. We begin with a mixed-integer linear programming formulation and then describe a series of valid inequalities that can be used to cut off solutions to the linear programming relaxation. Several separation heuristics are then outlined that are used to generate the cuts. Embedded in the methodology is a VRP heuristic for finding good feasible solutions at each stage of the computations. Results are presented for a set of problems derived from our experience with a leading propane distributor. 相似文献
19.
20.
The theory of energy-weighted acquisition (EWA) in nuclear medicine imaging is outlined, and a system that implements EWA is described. EWA reduces the effects of scattered radiation by allowing events of all energies to contribute to image formation, processing each energy with its own short-range spatial filter. This approach implements short-range energy-dependent filtering with an image buffer called a weighted acquisition module, providing scatter reduction with controllable noise and resolution properties. The system's response to point sources and planar distributions of radioactivity embedded in radiation-scattering media have been measured. EWA is compared to conventional energy-window acquisition, showing that the EWA approach provides improved image contrast 相似文献