全文获取类型
收费全文 | 9160篇 |
免费 | 531篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 127篇 |
综合类 | 23篇 |
化学工业 | 1825篇 |
金属工艺 | 185篇 |
机械仪表 | 204篇 |
建筑科学 | 425篇 |
矿业工程 | 37篇 |
能源动力 | 131篇 |
轻工业 | 1279篇 |
水利工程 | 40篇 |
石油天然气 | 12篇 |
无线电 | 609篇 |
一般工业技术 | 2366篇 |
冶金工业 | 1139篇 |
原子能技术 | 73篇 |
自动化技术 | 1217篇 |
出版年
2023年 | 112篇 |
2022年 | 49篇 |
2021年 | 163篇 |
2020年 | 137篇 |
2019年 | 123篇 |
2018年 | 296篇 |
2017年 | 308篇 |
2016年 | 338篇 |
2015年 | 245篇 |
2014年 | 318篇 |
2013年 | 599篇 |
2012年 | 403篇 |
2011年 | 473篇 |
2010年 | 396篇 |
2009年 | 404篇 |
2008年 | 466篇 |
2007年 | 423篇 |
2006年 | 306篇 |
2005年 | 254篇 |
2004年 | 204篇 |
2003年 | 213篇 |
2002年 | 185篇 |
2001年 | 180篇 |
2000年 | 144篇 |
1999年 | 133篇 |
1998年 | 420篇 |
1997年 | 263篇 |
1996年 | 219篇 |
1995年 | 128篇 |
1994年 | 127篇 |
1993年 | 99篇 |
1992年 | 46篇 |
1991年 | 72篇 |
1990年 | 53篇 |
1989年 | 62篇 |
1988年 | 63篇 |
1987年 | 57篇 |
1986年 | 59篇 |
1985年 | 112篇 |
1984年 | 82篇 |
1983年 | 53篇 |
1982年 | 51篇 |
1981年 | 50篇 |
1980年 | 53篇 |
1979年 | 34篇 |
1978年 | 43篇 |
1977年 | 35篇 |
1976年 | 59篇 |
1973年 | 33篇 |
1925年 | 44篇 |
排序方式: 共有9692条查询结果,搜索用时 15 毫秒
1.
2.
ABSTRACT The concept of digital game-based learning (DGBL) evolves rapidly together with technological enhancements of virtual reality (VR) and smart phones. However, the mental workload (MWL) that VR-training applications demand and motivational qualities originating from user experience (UX) should be identified in order to create effective and enjoyable training/learning challenges that fit with individual users’ capabilities. This study examined the effects of reality-based interaction (RBI) and VR on measures of student motivation and MWL, in a mental arithmetic game for secondary school pupils. In a randomised controlled trial with sixty school children, a mental arithmetic game was tested with three different interaction and two different presentation methods – VR RBI, VR head-mounted-display tapping and tablet flick-gesture. Results found a significant effect of RBI on MWL but no differences in enjoyment of training were found between VR-experience and tablet training-experience. In fact, adding the gaming-context to the mental arithmetic task created an enjoyable, motivating experience regardless of presentation or interaction-style. 相似文献
3.
4.
5.
6.
Antti Voss Niko Hänninen Mohammad Pour-Ghaz Marko Vauhkonen Aku Seppänen 《Materials and Structures》2018,51(3):68
The development of visualizing tools to monitor unsaturated moisture flow in cement-based materials is of great importance, as most degradation processes in cement-based materials are connected to and take place in the presence moisture. This paper investigates the ability of electrical capacitance tomography (ECT) to image two-dimensional (2D) unsaturated moisture flow in cement-based materials. In ECT, the electrical permittivity distribution within an object is reconstructed based on measured capacitances between electrodes attached on the object’s surface. In a series of experiments, mortar specimens with and without discrete cracks were imaged with ECT during a 2D moisture ingress. The results show that ECT is able to monitor the evolution of the moisture flow, and to approximate the shape and position of the moisture front. These findings indicate that ECT is a viable method for monitoring and visualizing 2D unsaturated moisture flow in cement-based materials in the presence and absence of discrete cracks. 相似文献
7.
Kurjenniemi Janne Hämäläinen Seppo Ristaniemi Tapani 《Wireless Personal Communications》2003,27(4):337-351
In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out. 相似文献
8.
Björn Täljsten 《International Journal of Fracture》1996,82(3):253-266
This paper presents the use of fracture mechanics for the plate bonding technique. Plates of steel or carbon-fibre reinforced
plastic are bonded with an epoxy adhesive to rectangular concrete prisms and loaded in shear up to failure, what is normally
known in fracture mechanics as mode II failure. In this special application a linear and a nonlinear approach are presented.
The nonlinear equation derived for a realistic shear-deformation curve can only be used for numerical calculations. However,
for simplified shear-deformation curves, the derived formula can be solved analytically. Results from tests, which are compared
with the theory, are also presented. 相似文献
9.
S Schaefer H Hussein GR Gershony JC Rutledge CT Kappagoda 《Canadian Metallurgical Quarterly》1997,45(9):536-541
BACKGROUND: Intensive risk factor reduction in patients with dyslipidemias and coronary atherosclerosis has been shown to result in alterations in coronary artery morphology and reduced clinical events. However, the impact of such interventions in populations with relatively normal levels of low-density lipoproteins (LDL) is unclear. METHODS: To test the hypothesis that intensive risk factor reduction results in angiographic regression in patients with only mildly elevated levels of LDL, 14 patients with angiographically proven coronary atherosclerosis were entered into the University of California Davis Coronary Artery Disease Regression Program and intensively treated with pharmacologic and nonpharmacologic interventions for 2 years. Quantitative angiography was performed prior to and after 2 years of therapy to determine changes in coronary artery diameter. RESULTS: As a result of this program, dietary fat intake was reduced by 58% and LDL fell from 120 +/- 7 mg/dL to 104 +/- 6 mg/dL (p = 0.05). The average diameter of the measured arterial locations (including all 53 stenoses and 292 nondiscrete regions) on study entry was 2.74 +/- 0.05 mm. After 24 months, there was a net increase in arterial diameter (regression) of +0.05 +/- 0.04 mm to 2.81 +/- 0.05 mm (p = 0.01). While there was no significant change in the average diameter of discrete stenoses, all 8 lesions > or = 50% initial diameter narrowing regressed, with a mean diameter change of + 0.2 mm. Conversely, only 1 of 8 mild lesions < or = 20% regressed, while 4 progressed. Intermediate lesions (20% to 50%, n = 37) had balanced progression and regression. CONCLUSIONS: When examined as a continuous variable, there was a significant linear correlation between initial lesion severity (% stenosis) and the extent of regression (mm). Therefore, risk factor reduction (dietary therapy, exercise, psycho-social counseling, and lipid lowering therapy) in patients with only mild dyslipidemia results in angiographic regression of more severe lesions (> 50% initial stenosis), but does not prevent progression of mild lesions (< 20%). These findings demonstrate that intensive risk factor reduction in patients with only mild elevation of lipids beneficially influences the morphology of the most severe lesions. 相似文献
10.
E La Hey J de Vries CT Langerhorst GS Baarsma A Kijlstra 《Canadian Metallurgical Quarterly》1993,116(3):327-340
After reviewing the records of 111 patients with Fuchs' heterochromic iridocyclitis, we studied the therapy and prognosis of secondary glaucoma in 30 of these 111 patients (27%) who had glaucoma or could be considered glaucoma suspects. Maximal medical therapy was unsuccessful in 22 of the 30 patients (73%). Surgical intervention (mostly trabeculectomies, half with 5-fluorouracil) successfully controlled intraocular pressure (< or = 21 mm Hg with or without medication) in 13 of the 18 operated-on patients (72%) after a mean follow-up of 26 months. All successfully operated-on patients retained a visual acuity of 20/80 or better. We had favorable results, possibly because of modern surgical techniques (use of 5-fluorouracil, sodium hyaluronate) or earlier surgical intervention, or both. 相似文献