全文获取类型
收费全文 | 313229篇 |
免费 | 3891篇 |
国内免费 | 719篇 |
专业分类
电工技术 | 6241篇 |
综合类 | 562篇 |
化学工业 | 47692篇 |
金属工艺 | 10371篇 |
机械仪表 | 8909篇 |
建筑科学 | 8078篇 |
矿业工程 | 865篇 |
能源动力 | 8715篇 |
轻工业 | 31598篇 |
水利工程 | 2568篇 |
石油天然气 | 3709篇 |
武器工业 | 8篇 |
无线电 | 39924篇 |
一般工业技术 | 58921篇 |
冶金工业 | 56776篇 |
原子能技术 | 5469篇 |
自动化技术 | 27433篇 |
出版年
2021年 | 2438篇 |
2019年 | 2262篇 |
2018年 | 3734篇 |
2017年 | 3563篇 |
2016年 | 3706篇 |
2015年 | 2625篇 |
2014年 | 4594篇 |
2013年 | 14576篇 |
2012年 | 7596篇 |
2011年 | 10407篇 |
2010年 | 8117篇 |
2009年 | 9354篇 |
2008年 | 9800篇 |
2007年 | 9730篇 |
2006年 | 8612篇 |
2005年 | 7968篇 |
2004年 | 7847篇 |
2003年 | 7567篇 |
2002年 | 7405篇 |
2001年 | 7585篇 |
2000年 | 7235篇 |
1999年 | 7582篇 |
1998年 | 17691篇 |
1997年 | 12868篇 |
1996年 | 10126篇 |
1995年 | 7902篇 |
1994年 | 7226篇 |
1993年 | 6919篇 |
1992年 | 5307篇 |
1991年 | 5080篇 |
1990年 | 4948篇 |
1989年 | 4796篇 |
1988年 | 4689篇 |
1987年 | 3894篇 |
1986年 | 4011篇 |
1985年 | 4724篇 |
1984年 | 4282篇 |
1983年 | 4028篇 |
1982年 | 3604篇 |
1981年 | 3768篇 |
1980年 | 3462篇 |
1979年 | 3421篇 |
1978年 | 3228篇 |
1977年 | 3820篇 |
1976年 | 4852篇 |
1975年 | 2781篇 |
1974年 | 2660篇 |
1973年 | 2675篇 |
1972年 | 2215篇 |
1971年 | 1964篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Several off-the-shelf animation software packages provide extensive capabilities, obviating the need for studios to develop their own software, except for highly specialized effects and interfaces. These capabilities make it feasible for a university to educate students in animation production without years of software development. The author discusses The UTS School of Cinema-Television and The USC Computer Animation Laboratory in particular 相似文献
992.
Thermal stratification, cycling, and striping phenomena have drawn much attention recently because of the incidents at several nuclear plants that raised significant safety concerns. The concerns due to these phenomena relate to thermal fatigue in branch pipes connected to the main coolant piping. Nuclear utility industry is addressing the issue with the aim to understand the mechanisms that lead to fatigue in nominally stagnant piping systems near the reactor coolant piping. Two key results from this effort are described in this paper. First, tests to investigate the interaction between the main coolant piping and the stagnant attached lines by turbulence penetration are described and a working correlation is obtained. Turbulence penetration into unisolable lines, or the transport of turbulence into stagnant piping from the reactor coolant system (RCS) line, represents a mechanism for carrying hot RCS water into regions filled with cold water. The possibility of stratification of the two fluids (and the resultant thermal stresses) is the reason for developing an understanding of the turbulence penetration process. Secondly, results of an evaluation to develop a loading definition for thermal striping are included. Based on this testing several important conclusions relating to fatigue in nominally static reactor coolant systems are reached. 相似文献
993.
R. T. Coupe 《欧洲信息系统杂志》1994,3(1):28-36
There is a common belief that CASE software enhances developer productivity and the quality of applications software. However, though the few empirical studies of the impact of CASE have produced inconclusive findings, they do indicate an absence of appreciable productivity gains. There is a need to determine the extent to which CASE products are worth their cost, and this paper focuses on the key methodological issues involved in assessing the cost-effectiveness of CASE products. Existing studies of the impact of CASE software have considered developers' perceptions, but have not considered system users' perceptions nor used software metrics to assess applications software. It is also rare for the characteristics of the development environments and other factors that have an important bearing on the productivity and quality of software to be investigated. In this paper, perceptual and objective measurement, and the different ways of designing the research and of accessing the population of CASE users, are outlined and evaluated. While the aim is to establish the most appropriate research design and measurement approaches for determining the value of CASE tools, the conclusions are also relevant to the assessment of the impact of other new software technologies. 相似文献
994.
Impact modeling with smooth particle hydrodynamics 总被引:1,自引:0,他引:1
Smooth Particle Hydrodynamics (SPH) is a new computational technique well suited to computation of hypervelocity impact phenomena. This paper reviews the characteristics, philosophy, and a bit of the derivation of the method. As illustrations of the technique, several test case computations and several application computations are shown. 相似文献
995.
G Licata R Scaglione G Avellone G Parrinello G Merlino S Corrao 《Canadian Metallurgical Quarterly》1993,12(4):326-330
OBJECTIVE: To determine the effect on oxygen saturation of instilling a saline bolus into artificial airways prior to suctioning, as measured by pulse oximeter. DESIGN: Quasi-experimental, single-case, counterbalanced design. SETTING: The surgical, medical and coronary intensive care units of a federal, teaching medical center. SUBJECTS: Subjects were 40 men, more than 40 years old, in need of intensive care nursing and mechanical ventilation. INTERVENTIONS: Subjects were suctioned as needed for 24 hours. A 5-mL saline bolus was instilled every other time the subject was suctioned. Outcome measurements were done immediately before and after suctioning and at 1-minute intervals for 5 minutes after suctioning. MAIN OUTCOME MEASURES: Noninvasive oxygen saturation values. RESULTS: The instillation of a saline bolus was found to have an adverse effect on oxygen saturation that worsened over time. Significant changes in oxygen saturation as a result of saline bolus instillation were found at 2,3,4 and 5 minutes after instillation. CONCLUSIONS: These results indicate that instilling saline prior to suctioning has an adverse effect on oxygen saturation. These results support the recommendation that the practice of instilling saline prior to suctioning should be abandoned as a routine procedure. More study is needed to investigate whether a specific group of patients may actually benefit from this procedure. 相似文献
996.
The validity and reliability of two factor structures of the Mental Adjustment to Cancer (MAC) scale for assessing coping style was assessed by examining the relationship between the subscales, psychological distress, and quality of life (QOL) among Stage II and Stage IV breast cancer patients in four phases. First, MANOVAs assessed differences in coping, distress, and QOL across disease stages. Second, for each MAC factor structure, canonical correlation analyses assessed the relationship between coping styles, distress, and QOL, for each disease-stage group separately. Third, structural equation modeling (SEM) assessed the relationship among coping styles, distress, and QOL for all participants. Finally, the internal consistency of both MAC factor structures was assessed using Chronbach's alpha. The results were as follows: (1) significant differences across disease stages were found for coping styles using either the Watson or the Schwartz MAC subscales, but there were no differences in levels of distress or QOL; (2) for both MAC factor structures, coping style was found to be highly related to emotional distress and QOL, however, the strengths of the correlations between individual coping styles and distress/QOL indicators varied across disease stages; (3) SEM indicated that coping style was significantly related to distress and QOL when stage of disease was not considered, and that coping style and indicators of distress/QOL are separate, but highly correlated factors, as opposed to a single latent construct; and, (4) the Watson MAC subscales showed slightly better internal consistency than the Schwartz MAC subscales. Taken together, these findings highlight: (i) the validity of both MAC factor structures for clinical and research use with American breast cancer patients; (ii) the role of coping style as a mediator between disease stage and psychological distress and QOL; and, (iii) the need for refinement of certain Watson and Schwartz subscales. 相似文献
997.
I Contreras R San-Millán A Agustín-Barrasa J Pontón G Quindós 《Canadian Metallurgical Quarterly》1996,136(1):17-20
A clinical study was carried out in an attempt to assess the efficacy of a newly designed electric toothbrush compared to a conventional manual toothbrush using the American Dental Association's protocol for evaluating toothbrushes. An Oral-B 35 manual toothbrush, which served as the control, was compared to the Plaq & White125 electric toothbrush. Examinations were performed by two calibrated examiners at baseline, day 15 and day 30. Examinations included the gingival index, plaque index and bleeding index. Mean indices were calculated and compared between the two brushes using the repeated measures multiple analysis of variance. No statistically significant differences between the mean indices on the three examination days were observed following the use of the manual or the electric toothbrushes. The results of this study demonstrate that the electric toothbrush was numerically more effective than the manual toothbrush in reducing supragingival plaque levels, either before or after brushing, at each examination date compared to baseline plaque values. However, this difference was not statistically significant. This and other findings concluded that the Plaq & White toothbrush is comparable to the control ADA-accepted toothbrush. 相似文献
998.
All-optical networks without switches are considered where the signals are routed based on wavelength only. 2 square root (M log/sub 2/( square root (2)M)) wavelengths are shown to be sufficient to build an M*M nonblocking connector without switches and without wavelength changers.<> 相似文献
999.
1000.
The performance of batch and continuous fluidized solids dryers has been modeled, with allowance for diffusional moisture transport in the dense phase particles and for interstitial gas-to-particle mass transfer within the dense phase, as well as for interphase exchange resistance between gas bubbles and the dense phase. Two types of boundary conditions are employed. Variations of the bed temperature and product moisture content in the bed with time are predicted numerically under various batch drying conditions. Exit product moisture contents, bed temperatures and outlet air humidities are also predicted for continuous drying at various mean residence times. The model can be used for homogeneous as well as bubbling fluidized bed drying. It can be used for a wide range of materials, including cereal grains and granular synthetic polymeric materials. 相似文献