全文获取类型
收费全文 | 58650篇 |
免费 | 5916篇 |
国内免费 | 3764篇 |
专业分类
电工技术 | 3924篇 |
综合类 | 5343篇 |
化学工业 | 8399篇 |
金属工艺 | 3956篇 |
机械仪表 | 4234篇 |
建筑科学 | 6126篇 |
矿业工程 | 3203篇 |
能源动力 | 2111篇 |
轻工业 | 3942篇 |
水利工程 | 1761篇 |
石油天然气 | 2881篇 |
武器工业 | 577篇 |
无线电 | 6199篇 |
一般工业技术 | 7436篇 |
冶金工业 | 3979篇 |
原子能技术 | 1114篇 |
自动化技术 | 3145篇 |
出版年
2024年 | 199篇 |
2023年 | 916篇 |
2022年 | 1623篇 |
2021年 | 1980篇 |
2020年 | 2027篇 |
2019年 | 1748篇 |
2018年 | 1581篇 |
2017年 | 2004篇 |
2016年 | 2125篇 |
2015年 | 2199篇 |
2014年 | 3464篇 |
2013年 | 3418篇 |
2012年 | 4022篇 |
2011年 | 4429篇 |
2010年 | 3372篇 |
2009年 | 3468篇 |
2008年 | 3165篇 |
2007年 | 3849篇 |
2006年 | 3564篇 |
2005年 | 2962篇 |
2004年 | 2584篇 |
2003年 | 2251篇 |
2002年 | 1972篇 |
2001年 | 1563篇 |
2000年 | 1436篇 |
1999年 | 1072篇 |
1998年 | 872篇 |
1997年 | 761篇 |
1996年 | 680篇 |
1995年 | 559篇 |
1994年 | 506篇 |
1993年 | 399篇 |
1992年 | 309篇 |
1991年 | 250篇 |
1990年 | 215篇 |
1989年 | 184篇 |
1988年 | 129篇 |
1987年 | 87篇 |
1986年 | 56篇 |
1985年 | 44篇 |
1984年 | 46篇 |
1983年 | 33篇 |
1982年 | 27篇 |
1981年 | 16篇 |
1980年 | 25篇 |
1979年 | 26篇 |
1965年 | 9篇 |
1961年 | 8篇 |
1959年 | 16篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Tang Helen H. Y.; McNally Gavan P.; Richardson Rick 《Canadian Metallurgical Quarterly》2007,121(6):1421
The authors studied the role of gamma-aminobutyric acid (GABA) in 2 types of forgetting of fear in the developing rat. One type of forgetting studied was that observed after an intermediate retention interval (the "Kamin effect"); the other type studied was that observed after a longer interval (infantile amnesia). Rats were given pairings of an auditory conditioned stimulus with shock, and learned fear was assessed by freezing. Forgetting at an intermediate retention interval (1 hr) was not alleviated by the GABAA receptor partial inverse agonist FG7142 (0, 1, 5, or 10 mg/kg), whereas forgetting at a longer retention interval (48 hr) was alleviated. These results suggest that in the developing rat, forgetting observed at different retention intervals is mediated by different physiological mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
92.
The effect of ductile crack growth on the near tip stress field in two different specimen geometries has been investigated. For homogeneous specimens it is observed that the peak stress level increases with ductile crack growth. The effect is most pronounced up to about 1 mm of crack growth. For low and intermediate hardening there is a significant effect of specimen size on the stress level. In case of mismatch in yield stress, the simulations show that the increase in stress level in the material with the lower yield stress is of a similar magnitude as is the case for stationary cracks. In case of ductile crack growth deviation from the original crack plane occurs, the highest stresses are still found close to the interface, and not in front of the current crack tip. 相似文献
93.
Toshihiko Hoshide Junpei Fujita 《Journal of Materials Engineering and Performance》2008,17(5):627-632
Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction
for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based
on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual
stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison
of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated
by using the proposed procedure. 相似文献
94.
Morten
rregaard Nielsen 《时间序列分析杂志》2005,26(2):279-304
Abstract. We consider semiparametric estimation in time‐series regression in the presence of long‐range dependence in both the errors and the stochastic regressors. A central limit theorem is established for a class of semiparametric frequency domain‐weighted least squares estimates, which includes both narrow‐band ordinary least squares and narrow‐band generalized least squares as special cases. The estimates are semiparametric in the sense that focus is on the neighbourhood of the origin, and only periodogram ordinates in a degenerating band around the origin are used. This setting differs from earlier studies on time‐series regression with long‐range dependence, where a fully parametric approach has been employed. The generalized least squares estimate is infeasible when the degree of long‐range dependence is unknown and must be estimated in an initial step. In that case, we show that a feasible estimate which has the same asymptotic properties as the infeasible estimate, exists. By Monte Carlo simulation, we evaluate the finite‐sample performance of the generalized least squares estimate and the feasible estimate. 相似文献
95.
J Schlipf 《Bulletin of Materials Science》1989,12(3-4):185-193
A model for propagating deformation bands is developed, based on a mechanical equation of state and on evolution equations
for the structure parameters. It is shown that, contrary to normal deformation, it is necessary to discriminate between global
parameters which depend solely on time elapsed and local parameters which are functions of the strain history. Correspondingly,
two sets of equations are presented, one describing the development of the global parameters in the course of time, the other
giving the evolution of the local state parameters in the course of deformation, i.e. as a function of strain. Measurable
quantities derived from the first set are the load serrations and the band velocity, while the second set yields the flow
stress and the strain profile of the propagating band. 相似文献
96.
The dynamics of a thin liquid film falling down a uniformly heated wall is studied. The model introduced by Kalliadasis et al. [J. Fluid Mech. 475 (2003) 377] for the same problem is revisited and its deficiencies, namely the prediction of a critical
Reynolds number with 20% error, cured. For the energy equation a high-order Galerkin projection in terms of polynomial test
functions is developed. It is shown that not only does this more refined formulation correct the critical Reynolds number,
but it also gives, with an appropriate expansion close to criticality, the long-wave theory. Bifurcation diagrams for permanent
solitary waves are constructed and compared with the solution branches obtained from different models. It is shown that, in
all cases, the long-wave theory exhibits limit points and branch multiplicity, while the other models predict the continuing
existence of solitary waves. Time-dependent computations show that the free surface and interfacial temperature approach a
train of coherent structures that resemble the infinite-domain stationary solitary pulses. 相似文献
97.
98.
99.
介绍了池27井实施机抽排水工艺取得累计排水13 334.4m3的明显效果.分析了五次检泵的原因.提出了对池27井机抽排水的四点认识. 相似文献
100.
Jiang Minhong Gu Zhengfei Cheng Gang 《中国稀土学报(英文版)》2005,23(6):723-723
Polymer matrix RE-Fe giant magnetostrictire composite (GMPC) was prepared using bonding and magnetic field forming technique, and magnetostriction of samples was measured for different compressive stress. The experimental results show thai there is certain compressive effect in GMPC. And the influence of compressive stress on magnetostriction of sample was investigated. It offers essential reference for application and device design of GMPC. 相似文献