全文获取类型
收费全文 | 9250篇 |
免费 | 969篇 |
国内免费 | 493篇 |
专业分类
电工技术 | 1687篇 |
综合类 | 1052篇 |
化学工业 | 1264篇 |
金属工艺 | 119篇 |
机械仪表 | 255篇 |
建筑科学 | 1158篇 |
矿业工程 | 286篇 |
能源动力 | 696篇 |
轻工业 | 424篇 |
水利工程 | 635篇 |
石油天然气 | 285篇 |
武器工业 | 52篇 |
无线电 | 339篇 |
一般工业技术 | 1230篇 |
冶金工业 | 274篇 |
原子能技术 | 24篇 |
自动化技术 | 932篇 |
出版年
2024年 | 44篇 |
2023年 | 177篇 |
2022年 | 304篇 |
2021年 | 346篇 |
2020年 | 369篇 |
2019年 | 328篇 |
2018年 | 310篇 |
2017年 | 390篇 |
2016年 | 377篇 |
2015年 | 358篇 |
2014年 | 569篇 |
2013年 | 631篇 |
2012年 | 597篇 |
2011年 | 608篇 |
2010年 | 453篇 |
2009年 | 548篇 |
2008年 | 494篇 |
2007年 | 637篇 |
2006年 | 556篇 |
2005年 | 481篇 |
2004年 | 364篇 |
2003年 | 333篇 |
2002年 | 248篇 |
2001年 | 226篇 |
2000年 | 182篇 |
1999年 | 152篇 |
1998年 | 107篇 |
1997年 | 101篇 |
1996年 | 93篇 |
1995年 | 50篇 |
1994年 | 42篇 |
1993年 | 31篇 |
1992年 | 31篇 |
1991年 | 24篇 |
1990年 | 25篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 25篇 |
1984年 | 13篇 |
1983年 | 19篇 |
1982年 | 6篇 |
1980年 | 7篇 |
1977年 | 1篇 |
1972年 | 1篇 |
1966年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 971 毫秒
11.
12.
13.
14.
《IIE Transactions》2007,39(9):879-898
We study an inventory system that consists of two demand classes. The orders in the first class need to be satisfied immediately, whereas the orders in the second class are to be filled in a given demand lead time. The two classes are also of different criticality. For this system, we propose a policy that rations the non-critical orders. Under a one-for-one replenishment policy with backordering and for Poisson demand arrivals for both classes, we first derive expressions for the service levels of both classes. The service level for the critical class is an approximation, whereas the service level for the non-critical class is exact. We then conduct a computational study to show that our approximation works reasonably, the benefits of rationing can be substantial, and the incorporation of demand lead time provides more value when the demand class with demand lead time is the critical class. The research is motivated by the spare parts service system of a major capital equipment manufacturer that faces two types of demand. For this company, the critical down orders need to be satisfied immediately, while the less critical maintenance orders can be satisfied after a fixed demand lead time. We conduct a case study with 64 representative parts and show that significant savings (as much as 14% on inventory on hand) are possible through incorporation of demand lead times and rationing. 相似文献
15.
D.H.R. Price J.A. Sharp 《International Journal of Electrical Power & Energy Systems》1985,7(3):131-137
Peak demand forecasts obtained from six different univariate forecasting methods, under a range of conditions, were used to drive a capacity acquisition model of a large electrical supply system; and the resulting physical and financial performance of the model was observed for each set of forecasts. The results obtained are discussed in the context of their implications for the choice of load forecasting method used in capacity acquisition planning by a power supply undertaking. 相似文献
16.
Molecular dynamics simulations are used to investigate polymer networks made by either end-linking or randomly crosslinking a melt of linear precursor chains. The resulting network structures are very different, since end-linking leads to nearly ideal monodisperse networks, while random crosslinking leads to polydisperse networks, characterized by an exponential strand length distribution. Networks with average strand length 20 and 100 were generated. These networks were used to study the effects of disorder in the network connectivity on observables averaged either over the entire network or selected sub-structures. Heterogeneities in the randomly crosslinked networks cause significant differences in the localization of monomers, however, neither the localization of crosslinks nor the microscopic strain response are significantly affected. Compared to end-linked networks, randomly crosslinked networks have a slightly increased tube diameter, and as a result a slightly decreased shear modulus, but otherwise identical stress-strain behavior. For the investigated systems, we conclude that the microscopic strain response, tube diameter, and stress-strain relation are all insensitive to the heterogeneities due to the linking process by which the network were made. 相似文献
17.
18.
In this paper, we study a three-dimensional axisymmetric boundary-value problem of a slender cylinder composed of a nonlinearly elastic material subjected to an axial force. Starting from the field equations, after a transformation and proper scalings, we identify a small variable and two small parameters, which characterize the present problem. Then, by an approach involving compound series-asymptotic expansions, a nonlinear ODE is derived, which governs the axial strain (the first-term in the series expansion). By imposing the zero radial displacement conditions at two ends, we manage to get the analytical solution of the axial strain, from which all other physical quantities can be deduced and thus the three-dimensional displacement field can be determined. Graphical results are presented, which show that there are two boundary layers near the two ends while the middle part is in a state of almost uniform extension. The asymptotic structure of the analytical solution is derived, which offers clear explanations to the structure of the deformed configuration and shows that the thickness of both boundary layers is of the order of the radius. We also point out the relevance of the present results to the St. Venant’s problem. In particular, we obtain the explicit uniformly-valid exponentially small error term, when the obtained deformed configuration is compared to the configuration of a uniform extension. 相似文献
19.
G. MENEGHETTI P. LAZZARIN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(2):95-106
The paper presents an expression useful to estimate the notch stress intensity factor (NSIF) from finite element analyses carried out by using a mesh pattern with a constant element size. The evaluation of the NSIF from a numerical analysis of the local stress field usually requires very refined meshes and then large computational effort. The usefulness of the presented expression is that (i) only the elastic peak stress numerically evaluated at the V‐notch tip is needed and no longer the whole stress–distance set of data; (ii) the adopted meshes are rather coarse if compared to those necessary for the evaluation of the whole local stress field. The proposed expression needs the evaluation of a virtual V‐notch tip radius, i.e. the radius which would produce the same elastic peak stress than that calculated by FEM at the sharp V‐notch tip by means of a given mesh pattern. Once such a radius has been theoretically determined for a given geometry, the expression can be applied in a wide range of notch depths and opening angles. 相似文献
20.
Quirk Stuart W.; Subramanian Lakshmi; Hoerger Michael 《Canadian Metallurgical Quarterly》2007,116(3):624
The socioemotional functioning of schizophrenic and schizotypic individuals is marked by withdrawal, poor organization, and limited emotional displays. Such behavioral tendencies and lack of social enjoyment in schizotypy could be linked to the relative situational demands or role ambiguity inherent in specific social activities. To determine whether high-schizotypy individuals prefer more clearly role-defined social activities (e.g., visiting relatives) to more ambiguous, novel situations (e.g., going alone to a party), the authors gathered reports from 52 high-schizotypy and 60 low-schizotypy individuals on their enjoyment and frequency of engaging in social situations varying in relative situational demand. Parallel reports were obtained from knowledgeable others. Group × Situational Demand interactions revealed the hypothesized pattern of reduced frequency and enjoyment ratings for ambiguous or novel situations by the high-schizotypy participants in both self and others' reports. Groups were more comparable in their reported frequency and enjoyment of less ambiguous situations. Results suggest the importance of situational demands in the socioemotional experience and behavioral withdrawal in schizotypy. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献