全文获取类型
收费全文 | 8202篇 |
免费 | 292篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 75篇 |
综合类 | 5篇 |
化学工业 | 1549篇 |
金属工艺 | 166篇 |
机械仪表 | 176篇 |
建筑科学 | 450篇 |
矿业工程 | 14篇 |
能源动力 | 246篇 |
轻工业 | 793篇 |
水利工程 | 116篇 |
石油天然气 | 32篇 |
无线电 | 622篇 |
一般工业技术 | 1477篇 |
冶金工业 | 1567篇 |
原子能技术 | 66篇 |
自动化技术 | 1147篇 |
出版年
2023年 | 36篇 |
2022年 | 74篇 |
2021年 | 115篇 |
2020年 | 95篇 |
2019年 | 108篇 |
2018年 | 131篇 |
2017年 | 147篇 |
2016年 | 153篇 |
2015年 | 147篇 |
2014年 | 213篇 |
2013年 | 461篇 |
2012年 | 378篇 |
2011年 | 465篇 |
2010年 | 325篇 |
2009年 | 370篇 |
2008年 | 491篇 |
2007年 | 406篇 |
2006年 | 354篇 |
2005年 | 363篇 |
2004年 | 283篇 |
2003年 | 275篇 |
2002年 | 244篇 |
2001年 | 152篇 |
2000年 | 120篇 |
1999年 | 157篇 |
1998年 | 260篇 |
1997年 | 184篇 |
1996年 | 186篇 |
1995年 | 139篇 |
1994年 | 136篇 |
1993年 | 113篇 |
1992年 | 98篇 |
1991年 | 76篇 |
1990年 | 86篇 |
1989年 | 103篇 |
1988年 | 61篇 |
1987年 | 70篇 |
1986年 | 68篇 |
1985年 | 84篇 |
1984年 | 80篇 |
1983年 | 70篇 |
1982年 | 64篇 |
1981年 | 63篇 |
1980年 | 46篇 |
1979年 | 57篇 |
1978年 | 49篇 |
1977年 | 51篇 |
1976年 | 59篇 |
1975年 | 44篇 |
1974年 | 33篇 |
排序方式: 共有8501条查询结果,搜索用时 765 毫秒
11.
12.
13.
Marginal costs of electricity vary by time and location. In the past, researchers attributed the variations to factors related to electricity generation and transmission. These authors, however, have not analyzed possible variations in marginal distribution capacity costs (MDCC). The objectives of this paper are:
- 1. (i) to show that large MDCC variations are due to the dispersion in distribution capital expenditures by time and space,
- 2. (ii) to propose a method for quantifying the area- and time-specific MDCC in the presence of lumpy investments, and
- 3. (iii) to compare our MDCC estimates to those commonly used in the electric utility industry.
14.
Dynamic mechanical properties have been investigated for interpenetrating-network systems based on polyol-cured polyurethanes (PU) and 2 to 1 n-butyl acrylate-n-butyl methacrylate (Ac) networks. The systems were formed simultaneously (SIN) from all of the precursors and reactants for both networks in the same vessel, and sequentially (SIPN) by swelling a precured PU with the reactants that will form the Ac network. If the Ac network is formed after gelation of the PU, the IPNs are transparent and appear to have single T (tan δmax) between those of the homonetworks; visible-phase separation occurs if the Ac is intentionally polymerized prior to PU gelation. Damping curves were lower and broader and the T (tan δmax) and rubber moduli were higher for the SIN than for the SIPN systems. Up to 65 percent Ac, the T (tan δmax) data for both SIN and SIPN fit the Gordon-Taylor equation if a T (tan δmax) for the Ac homonetwork 7°C higher than observed is used, suggesting a higher crosslink density for the Ac network under these conditions. The differences in properties of the SIN and SIPN are assumed to be dependent on sample homogeneity and upon the presence of a tin catalyst in the SIN preparation. This can result in limited Ac-network formation and consequent phase separation before PU gelation has occurred, and the catalyst may also increase the extent of interaction, such as grafting or hydrogen-bond formation between the networks. 相似文献
15.
Letters to the editor 总被引:1,自引:0,他引:1
16.
We report here observational results demonstrating that a three-station network of properly distributed VLBI observatories can routinely determine UT1 with a formal standard error of ±0.05 ms of time, in an observing period of 24 h. We also report the results of a three-month series of daily observing sessions of only 1-h duration with a single interferometer, which produced estimates of UT1 with standard errors of ±0.1 ms. The UT1 values obtained from the 1-h observing sessions track smoothly between the points of the 24-h time series, and the combined time series shows that it is not unusual for UT1 to vary by 1-2 ms in periods of several days. Preliminary results of reprocessing the 24-h observing sessions in 2-h segments suggest that variations of 0.4 ms may occur on time scales of only 6-8 h. 相似文献
17.
Brian M. Louie Thomas Franaszek Tina Pho Wen Yen Chiu David S. Soong 《应用聚合物科学杂志》1985,30(9):3841-3856
Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate. 相似文献
18.
L.D. Bozano B.W. Kean M. Beinhoff K.R. Carter P.M. Rice J.C. Scott 《Advanced functional materials》2005,15(12):1933-1939
Non‐volatile solid‐state memory cells based on composites of metal nanoparticles and polymers are embedded in organic semiconducting host materials. This paper presents data from a wide range of materials and device structures and shows that the switching phenomenon is commonly observed. 相似文献
19.
Jon T. Carter Paul E. Krajewski Ravi Verma 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(11):77-81
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive
applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect
of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General
Motors Corporation is reviewed. 相似文献
20.
Todd M. Alam Joshua U. Otaigbe Dave Rhoades Gregory P. Holland Brian R. Cherry Paul G. Kotula 《Polymer》2005,46(26):12468-12479
Nanostructured polymer blends prepared via anionic ring opening polymerizations of cyclic monomers in the presence of a pre-made polymer melt exhibit a number of special properties over traditional polymer blends and homopolymers. Here, we report on a simple and versatile method of in situ polymerization of macrocyclic carbonates in the presence of a maleic anhydride polypropylene (mPP) matrix and a surface-active compatibilizer (i.e. PC grafted onto a mPP backbone generated in situ) to yield a micro- and nanostructured polymer blends consisting of a polycarbonate (PC) minor phase, and a polypropylene (PP) major phase. By varying the processing conditions and concentration of the macrocyclic carbonate it was possible to reduce the size of the PC dispersions to an average minor diameter of 150 nm. NMR and TEM characterizations indicate that the PC dispersions do not influence crystal content in the PP phase. Overall, the results point to a simple strategy and versatile route to new polymeric materials with enhanced benefits. 相似文献