全文获取类型
收费全文 | 3065篇 |
免费 | 81篇 |
国内免费 | 37篇 |
专业分类
电工技术 | 108篇 |
综合类 | 197篇 |
化学工业 | 1441篇 |
金属工艺 | 35篇 |
机械仪表 | 94篇 |
建筑科学 | 291篇 |
矿业工程 | 78篇 |
能源动力 | 81篇 |
轻工业 | 62篇 |
水利工程 | 34篇 |
石油天然气 | 29篇 |
武器工业 | 63篇 |
无线电 | 111篇 |
一般工业技术 | 199篇 |
冶金工业 | 131篇 |
原子能技术 | 14篇 |
自动化技术 | 215篇 |
出版年
2023年 | 3篇 |
2022年 | 9篇 |
2021年 | 14篇 |
2020年 | 23篇 |
2019年 | 13篇 |
2018年 | 10篇 |
2017年 | 17篇 |
2016年 | 18篇 |
2015年 | 29篇 |
2014年 | 74篇 |
2013年 | 60篇 |
2012年 | 85篇 |
2011年 | 80篇 |
2010年 | 68篇 |
2009年 | 80篇 |
2008年 | 68篇 |
2007年 | 96篇 |
2006年 | 89篇 |
2005年 | 80篇 |
2004年 | 71篇 |
2003年 | 50篇 |
2002年 | 45篇 |
2001年 | 42篇 |
2000年 | 39篇 |
1999年 | 38篇 |
1998年 | 22篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 49篇 |
1994年 | 45篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 157篇 |
1984年 | 276篇 |
1983年 | 320篇 |
1982年 | 271篇 |
1981年 | 335篇 |
1980年 | 177篇 |
1979年 | 76篇 |
1978年 | 85篇 |
1977年 | 42篇 |
1976年 | 29篇 |
1975年 | 31篇 |
1974年 | 19篇 |
1973年 | 10篇 |
1964年 | 1篇 |
排序方式: 共有3183条查询结果,搜索用时 15 毫秒
1.
2.
The void fraction in a three-component randomly packed bed was calculated from the authors' model, and the calculated values were compared with published experimental data for spherical and irregularly shaped particles and with results from computer simulations. Results from the model were in good agreement with simulated and published experimental data. 相似文献
3.
《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
4.
The paper considers a generalized discrete‐time order‐replacement model for a single unit system, which is subject to random failure when in operation. Two types of discrete randomized lead times are considered for a spare unit; one is for regular (preventive) order and another is for expedited (emergency) order. The model is formulated based on the discounted cost criterion. The underlying two‐dimensional optimization problem is reduced to a simple one‐dimensional one and then the optimal ordering policy for the spare unit is characterized under two extreme conditions: (i) unlimited inventory time and (ii) zero inventory time for the spare unit. A numerical example is used to determine the optimal spare‐ordering policy numerically and to examine the sensitivity of the model parameters. 相似文献
5.
An efficient method is described for sensitivity analysis of nonlinear initial value problems, which may include algebraic equations as well as ordinary differential equations.The linearity of the sensitivity equations is utilized to solve them directly via the local Jacobian of the state equations. The method is implemented with the implicit integrator DASSL and is demonstrated on a stiff industrial reaction model. 相似文献
6.
K W Brown K C Donnelly J C Thomas P Davol B R Scott 《The Science of the total environment》1985,41(2):173-186
A chemical and biological testing protocol was employed to evaluate the mutagenic potential of the organic compounds extracted from three agricultural soils. The analytical procedures used included bioassays with Salmonella typhimurium and Aspergillus nidulans for the detection of point mutations and a gas chromatography/mass spectrometry/computer system to identify major organic constituents. The extracts of all three soils exhibited mutagenic response in the bioassays. At a dose level of 1000 micrograms per plate, the organic extract of the Bastrop clay induced 434 net revertants; while at the same dose level the Norwood sandy clay and the Sassafrass sandy loam induced 35 and 178 net revertants, respectively, in the Salmonella assay with metabolic activation. In the Aspergillus assay, the extract of the Norwood and Bastrop soils induced a positive response without metabolic activation; this effect was reduced or eliminated in the presence of metabolic activation. Chemical analysis identified a variety of initiators, promotors, inhibitors, and cocarcinogens; however, there were no mutagenic compounds identified in any of the soil extracts. The results of this combined testing protocol indicate that the agricultural soils tested had an inherent level of mutagenic activity, which was not detected by GC/MS analysis alone, and this activity may be related to the past history of agricultural practices, including biocide applications, fertilization, and cultivation. 相似文献
7.
8.
Survival of rotavirus on lettuce, radishes, and carrots was studied to evaluate the potential of rotavirus transmission by vegetables irrigated with wastewater. The vegetables were contaminated with rotavirus SA-11 and stored at 4°C and room temperature in covered and uncovered containers to simulate post harvest conditions. Virus decay rates were greater on radishes and carrots than lettuce. Decay rates of rotavirus on lettuce, radish, and carrot ranged from ?0·057 to ?0·479 (log10 pfu/day). Rotavirus SA-11 survived on lettuce, radish, and carrot for 25 to 30 days at 4°C but at room temperature survival was very different for the various vegetables varying from 5 to 25 days. Greatest survival was always observed on the lettuce. These data suggest that rotaviruses can survive long enough on contaminated vegetables as to be transmitted by this vehicle. 相似文献
9.
With the aim of optimizing the performance of Li/Li1+xV3O8 cells, several aspects of cathode preparation have been examined. The influence of synthesis technique, nature and amount of conductive additives, compacting pressure, cathode loading, and particle size, has been investigated. Furthermore, the role played by the solutions on cathode efficiency has been outlined. The formulations which perform best are based on small-sized particles blended with about 20% acetylene black and compacted at very high pressures to improve the contact between particles. Such cathodes can provide high capacities at high rates and good cycling efficiencies. The kinetic loss of capacity, observed during the first few cycles, may be alleviated by choosing solutions with high fluidity and conductivity. 相似文献
10.
The effect of methanol, acetone, formalin and glucose on the nitrification process in the packed bed reactors has been investigated. For the utilized compounds the inhibition constant Ki was determined according to Dixon's method. The determined values were as follows: methanol Ki = 116.0 mg l?1; acetone Ki = 804.2 mg l?1; formalin Ki = 61.5 mg l?1. The value of Ki for glucose has not been determined because glucose in applied concentration up to 11,325 mg l?1 had no effect on the nitrification course. 相似文献