全文获取类型
收费全文 | 4179篇 |
免费 | 56篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 33篇 |
综合类 | 2篇 |
化学工业 | 370篇 |
金属工艺 | 66篇 |
机械仪表 | 49篇 |
建筑科学 | 91篇 |
矿业工程 | 4篇 |
能源动力 | 39篇 |
轻工业 | 240篇 |
水利工程 | 15篇 |
石油天然气 | 6篇 |
无线电 | 349篇 |
一般工业技术 | 351篇 |
冶金工业 | 2340篇 |
原子能技术 | 51篇 |
自动化技术 | 231篇 |
出版年
2021年 | 24篇 |
2019年 | 16篇 |
2018年 | 29篇 |
2017年 | 29篇 |
2016年 | 39篇 |
2015年 | 23篇 |
2014年 | 36篇 |
2013年 | 110篇 |
2012年 | 71篇 |
2011年 | 95篇 |
2010年 | 55篇 |
2009年 | 73篇 |
2008年 | 93篇 |
2007年 | 92篇 |
2006年 | 86篇 |
2005年 | 71篇 |
2004年 | 92篇 |
2003年 | 64篇 |
2002年 | 80篇 |
2001年 | 58篇 |
2000年 | 54篇 |
1999年 | 122篇 |
1998年 | 692篇 |
1997年 | 354篇 |
1996年 | 290篇 |
1995年 | 136篇 |
1994年 | 126篇 |
1993年 | 141篇 |
1992年 | 50篇 |
1991年 | 62篇 |
1990年 | 50篇 |
1989年 | 51篇 |
1988年 | 51篇 |
1987年 | 44篇 |
1986年 | 47篇 |
1985年 | 51篇 |
1984年 | 29篇 |
1983年 | 40篇 |
1982年 | 27篇 |
1981年 | 43篇 |
1980年 | 35篇 |
1979年 | 19篇 |
1978年 | 33篇 |
1977年 | 72篇 |
1976年 | 166篇 |
1975年 | 20篇 |
1973年 | 14篇 |
1972年 | 14篇 |
1971年 | 20篇 |
1969年 | 14篇 |
排序方式: 共有4237条查询结果,搜索用时 15 毫秒
71.
The abrasive wear of rubbers is strongly affected by the filler particles dispersed in the elastomer matrix. The fillers are incorporated usually for the purposes of mechanical reinforcement and improving the conductivity of the neat resins. It is found that the wear rates of the filled silicone rubbers increase slowly with filler concentration until a critical volume fraction,v
c, is reached, at which point they increase very rapidly with increasing filler concentration. This behaviour appeared to be universal in all the filled silicones we studied, regardless of the type of filler and silicone rubber used. However the magnitude of the critical filler fraction,v
c, can be changed significantly with the filler shape, resin cross-linking density and filler surface treatments. No reasonable relationship could be found between this wear behaviour and the mechanical properties measured in a macroscopic manner. Experimental evidence suggests that the incipient cracks that lead to wear losses may start within the thin layers of highly stressed material, the damage zones, surrounding the rigid particles. A simple model taking into account the stress concentration induced by the rigid fillers shows excellent correlation between the wear rate and the damage zones volume. With this new model, the observed wear behaviours can be explained satisfactorily. 相似文献
72.
Thermal stability of polyaniline 总被引:2,自引:0,他引:2
Thermal stability data for neutral (emeraldine base) and doped polyaniline with various counter anions are reported. The emeraldine base is a highly heat-stable polymer, with thermal stability up to 420 °C. The thermal stability of doped polyaniline is dependent on the counter anion. The methane sulfonic acid doped polyaniline is stable up to 250 °C. The decomposition of the doped polyaniline is seen as a two-step process. The first step is the loss of the dopant and the second step corresponds to the decomposition of the backbone. 相似文献
73.
Utilising the methodology of content analysis, this study uses a multidisciplinary approach to define public e-procurement. Various aspects of e-procurement have been discussed from information systems, supply chain management, electronic commerce/electronic government, and public procurement to come up with an integrated definition of public e-procurement. Following this, e-procurement assimilation has been defined and its impact on procurement efficiency has been evaluated. Following the confirmatory factor analysis in structural equation modelling, dimensional level analysis in ANOVA has been undertaken for the three forms of e-procurement technologies namely e-tendering, e-catalogue management systems, and e-marketplace. The results show the positive and significant impact of the assimilation process on procurement efficiency. 相似文献
74.
75.
Completions of linear time varying singular systems of the formE(t)x(t)+F(t)x(t)=f(t) are explicitly computed using recent results on rational matrix functions. The algorithm and the theory behind it are carefully described. Computational issues are discussed.Research supported in part by the U.S. Army Research Office under DAAL03-89-D-0003, and the National Science Foundation under ECS-9012909. 相似文献
76.
C. S. Campbell 《Acta Mechanica》1994,104(1-2):65-90
Summary This paper describes measurements of the impulses that particles experience while undergoing rapid shear. These were performed with an eye towards understanding the processes that lead to particle attrition and fracture. The measurements were taken from a discrete particle computer simulation of a simple shear flow of spheres. Special attention is paid to the strongest impulses as these will do the most damage. The results indicate that the largest impulses arise, not from the mean shear flow, but from the random particle velocities that are characterized by the so-called granular temperature. Measurements of the largest impulses are presented as functions of particle properties and solid concentration. Histograms of the impulse strengths illustrate the effect of concentration and particle surface friction. Finally, geometric distributions are presented that illustrate the shear induced anisotropy in the impulse strengths. 相似文献
77.
Identifying and integrating patient and caregiver perspectives for clinical practice guidelines on the screening and management of infectious microorganisms in hemodialysis units 下载免费PDF全文
Hilary M. Miller Allison Tong David J. Tunnicliffe Denise Campbell Jule Pinter Robert J. Commons Eugene Athan Jonathan C. Craig Nicole Gilroy Julianne Green Belinda Henderson Martin Howell Rhonda L. Stuart Carolyn van Eps Muh Geot Wong Janak de Zoysa Meg J. Jardine 《Hemodialysis international. International Symposium on Home Hemodialysis》2017,21(2):213-223
78.
BK Park ES Cho JD Lee C Oh MS Lee SZ Kim SH Kim KW Cho 《Canadian Metallurgical Quarterly》1998,43(8):611-618
The effect of a naturally occurring plant phenolic constituent (the acylphloroglucinol derivative, jensenone, derived from Eucalyptus jensenii) on the food intake of two folivorous marsupials, the common ringtail (Pseudocheirus peregrinus) and the common brushtail possum (Trichosurus vulpecula) was studied. When fed diets containing varying concentrations of jensenone, both species regulated their intake of jensenone so as not to exceed a ceiling intake. This ceiling was about twice as high for common ringtails as for common brushtails from northern Australia. Southern populations of common ringtails showed greatly reduced capacities to tolerate jensenone. When common brushtails were injected (0.5 mg.kg-0.75 body mass) with ondansetron (a selective antagonist of serotonin 5HT3 receptors), they ate significantly more jensenone than animals injected with physiological saline. The same pattern was observed when common ringtails were fed diets containing both jensenone and ondansetron (0.0035 mg.g-1 wet mass of diet). Ondansetron injection had no effect on food intake when the food did not contain jensenone while the addition of higher doses of ondansetron to diets of common ringtails very slightly reduced food intakes of a non-jensenone diet. When common brushtails were given 50 mg of jensenone by gastric lavage, their average subsequent intake of dietary jensenone matched the difference between the daily threshold and the dose given, although the response of individuals was highly variable. Lavage with water alone had no effect on subsequent jensenone intake compared with the pre-dose period. We interpret these results as evidence that the antifeedant effects of jensenone and related compounds are partly mediated by serotonin action on 5HT3 receptors most likely via "nausea" to condition a food aversion. 相似文献
79.
By using the concept of transfer matrices and Bloch waves, we have derived a set of equations that provide insight into the operation of asymmetric Bragg reflectors that have been demonstrated to be useful in achieving high reflectivities in strained-material systems. These equations will be useful in the design of asymmetric mirrors and can be used to compare the trade-offs between the conventional, symmetric (quarter-wavelength), and asymmetric mirrors. 相似文献
80.
A distributed optical-fiber stress sensor whose principle of operation is based on the frequency-modulation continuous-wave technique is reported. The sensor consists of a length of birefringent fiber with a mirror attached to one end, a diode laser, and a p-i-n photodiode detector. The intensity and the location of an applied stress are determined simultaneously by detecting the amplitude and the frequency of the beat signal, which is produced by two forward-coupled mode beams. The system was found to have a reasonable spatial resolution of 0.85 m (rms error) in a sensing range of 100 m. The advantages and limitations of the sensor are also discussed. 相似文献