全文获取类型
收费全文 | 518462篇 |
免费 | 6054篇 |
国内免费 | 1417篇 |
专业分类
电工技术 | 10091篇 |
综合类 | 734篇 |
化学工业 | 76646篇 |
金属工艺 | 18291篇 |
机械仪表 | 15004篇 |
建筑科学 | 12916篇 |
矿业工程 | 1657篇 |
能源动力 | 14467篇 |
轻工业 | 47107篇 |
水利工程 | 4375篇 |
石油天然气 | 6433篇 |
武器工业 | 21篇 |
无线电 | 67393篇 |
一般工业技术 | 98897篇 |
冶金工业 | 98754篇 |
原子能技术 | 9607篇 |
自动化技术 | 43540篇 |
出版年
2021年 | 4060篇 |
2019年 | 3728篇 |
2018年 | 6271篇 |
2017年 | 6212篇 |
2016年 | 6399篇 |
2015年 | 4358篇 |
2014年 | 7628篇 |
2013年 | 23727篇 |
2012年 | 12418篇 |
2011年 | 17153篇 |
2010年 | 13611篇 |
2009年 | 15659篇 |
2008年 | 16414篇 |
2007年 | 16254篇 |
2006年 | 14511篇 |
2005年 | 13180篇 |
2004年 | 12916篇 |
2003年 | 12862篇 |
2002年 | 12288篇 |
2001年 | 12781篇 |
2000年 | 12026篇 |
1999年 | 12791篇 |
1998年 | 31703篇 |
1997年 | 22493篇 |
1996年 | 17437篇 |
1995年 | 13355篇 |
1994年 | 12093篇 |
1993年 | 11779篇 |
1992年 | 8613篇 |
1991年 | 8270篇 |
1990年 | 8068篇 |
1989年 | 7761篇 |
1988年 | 7538篇 |
1987年 | 6347篇 |
1986年 | 6437篇 |
1985年 | 7343篇 |
1984年 | 6629篇 |
1983年 | 6306篇 |
1982年 | 5781篇 |
1981年 | 5862篇 |
1980年 | 5500篇 |
1979年 | 5319篇 |
1978年 | 4951篇 |
1977年 | 6021篇 |
1976年 | 7941篇 |
1975年 | 4281篇 |
1974年 | 4136篇 |
1973年 | 4065篇 |
1972年 | 3480篇 |
1971年 | 2979篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Piquemal F.P.M. Trapon G.R. Geneves G.P.J. 《IEEE transactions on instrumentation and measurement》1996,45(6):918-922
AC measurements of the longitudinal resistance, Rxx, of a quantum Hall effect (QHE) sample have been made in a frequency range from 10 Hz to 10 kHz. The results show no frequency effect on the minimum value of Rxx corresponding to the quantum numbers i=2 and i=4, within the measurement resolution of 0.5 mΩ. Therefore, the influence of frequency on the value of the quantized Hall resistance, RH, should not exceed a few parts in 109 . Some unwanted effects detected during the development of the resistance bridge have been pointed out 相似文献
952.
R. G. Cox 《Journal of Engineering Mathematics》1996,30(1-2):177-213
It is demonstrated how the hydrodynamic force and moment of force acting on a solid sphere may be calculated when it is placed at rest at an arbitrary position in a two dimensional flow at zero Reynolds number in which the region of flow is bounded by either an undeformable planar free surface or by a plane solid wall. The results so obtained are used to calculate the motion of a freely moving solid sphere in an asymmetric vortex in the presence of an underformable free surface. It is seen that the sphere, depending on the direction of the undisturbed flow, will either spiral into or out of the vortex. This implies that when a dilute suspension of such spherical particles undergoes such a vortex motion in the presence of the free surface, the vortex will either fill up with particles from the surrounding flow or become devoid of particles.Deceased, July 31, 1995 相似文献
953.
A melt-extraction technique, using a sharpened molybdenum wheel, has been used to produce fine oxide ceramic fibres. Wetting of the molybdenum wheel by molten ceramic is a key parameter in the melt-extraction process. Two types of fibre are generally obtained, depending on the extraction speed. At very low wheel speed, fine and uniform fibres of high quality are produced. However, when the wheel speed exceeds a critical velocity, Rayleigh waves are formed on the free surface of the fibres. Moreover, the average fibre thickness first increases with the wheel velocity, then passes through a maximum, decreasing at high velocity. This thickness variation is discussed in terms of both surface tension and viscosity of the liquid ceramics. 相似文献
954.
The calculations of the first paper suggesting phase separation in the Hubbard model [2] are performed under modern computer facilties for the one and three-band Hubbard model. High-temperature approximations for specific heat and static correlation functions are obtained. The latter show, at these high temperatures, no tendency to phase separate in the same way as in the cited paper because our spin parallel nearest-neighbor charge correlation function is negative for all doping values. The spin antiparallel correlation function has positive and negative values for different doping regimes.Extension of this work to higher levels of iterations and to other correlation functions is in progress. 相似文献
955.
Cellular solid structures with unbounded thermal expansion 总被引:1,自引:0,他引:1
R. Lakes 《Journal of Materials Science Letters》1996,15(6):475-477
956.
R. Knockaert I. Doghri Y. Marchal T. Pardoen F. Delannay 《International Journal of Fracture》1996,81(4):383-399
Double-edge notched (DENT) steel plates were pulled until complete fracture and several experimental observations were made (using profilometry and scanning electron microscopy). The essential work of fracture (EWF) model was found to be well verified. Numerical simulations—up to the maximum load only—of some experiments were performed using the finite element method (FEM), and incorporating geometric and material non-linearities (large deformation elasto-plasticity). Some experimental measurements were compared with the corresponding numerical computations and excellent agreement was found. 相似文献
957.
R. C. Moreton 《Drug development and industrial pharmacy》1996,22(1):11-23
The future for tablet excipients is reviewed from a number of viewpoints: new materials, formulation development, quality, regulatory aspects, logistics, and production. The field of excipients is changing rapidly in response to economic, regulatory, and scientific pressures. As our understanding of drug delivery improves, so will the demands we place on excipients and on their quality, both chemical and functional. In order to fully optimize drug delivery systems, a better understanding of excipients and their properties and limitations is required. The materials science approach to the study of excipients will help to increase our understanding of excipients and how best to use them. But excipients are only one part of the very complex mechanism whereby new medicinal products are brought to the marketplace. It is important that the processes of formulation design and development are properly integrated to obtain optimized drug delivery systems as early as possible. Developments in related fields such as manufacturing technology, logistics, and analytical techniques will also influence the field of excipients. 相似文献
958.
Pharmacodynamic Comparison of a Nasal Formulation of Verapamil and Intravenous and Oral Dosage Forms
The nasal route has been shown to be effective for the administration of numerous drugs in order to improve drug bioavailability. A nasal gel of verapamil hydrochloride was formulated and evaluated pharmacodynamically in humans, using electrocardiographic results, with comparison to oral and IV routes. Seven volunteers were involved in the study and the pharmacodynamic parameters were evaluated statistically. Experimental nasal gel showed similar pharmacodynamic results with the intravenous route, which is a hint to the reduction in verapamilinduced first-pass metabolism. However, oral route of administration showed a tendency of less efficacy. No reasonable effect of verapamil could be obtained with the placebo group. 相似文献
959.
960.
N. Satou A. Morikawa K. Ohmoto H. Urabe H. Shintani K. Wakasa M. Yamaki 《Journal of materials science. Materials in medicine》1996,7(12):749-752
This study was designed to evaluate the bacterial adhesion to five types of experimental composite-based resins and a commercial composite resin used as a control. Physicochemical surface characteristics of composite resins with and without an artificial saliva coating were measured. The relationship between the numbers of adhering cells (Streptococcus sanguis, S. mutans and S. sobrinus) and surface characteristics was analysed. The values of contact angles and the number of adhering cells were small with saliva coating. S. sanguis ATCC 10557 showed a positive correlation (r=0.835, p<0.05) with the contact angles of uncoated resins, whereas no relationship was observed for saliva-coated resins. With S. mutans Ingbritt the cell numbers adhering to resins correlated strongly (p<0.01) with the values of zeta potential of resins for either saliva coated or uncoated. Electrical repulsion forces had a strong contribution to adherence of cells such as S. mutans and S. sobrinus which show a high absolute zeta potential. 相似文献