全文获取类型
收费全文 | 10903篇 |
免费 | 740篇 |
国内免费 | 27篇 |
专业分类
电工技术 | 275篇 |
综合类 | 36篇 |
化学工业 | 2453篇 |
金属工艺 | 354篇 |
机械仪表 | 386篇 |
建筑科学 | 307篇 |
矿业工程 | 39篇 |
能源动力 | 392篇 |
轻工业 | 1349篇 |
水利工程 | 73篇 |
石油天然气 | 52篇 |
武器工业 | 1篇 |
无线电 | 1147篇 |
一般工业技术 | 2455篇 |
冶金工业 | 580篇 |
原子能技术 | 97篇 |
自动化技术 | 1674篇 |
出版年
2023年 | 98篇 |
2022年 | 114篇 |
2021年 | 310篇 |
2020年 | 254篇 |
2019年 | 237篇 |
2018年 | 429篇 |
2017年 | 411篇 |
2016年 | 467篇 |
2015年 | 352篇 |
2014年 | 506篇 |
2013年 | 978篇 |
2012年 | 695篇 |
2011年 | 824篇 |
2010年 | 623篇 |
2009年 | 562篇 |
2008年 | 480篇 |
2007年 | 412篇 |
2006年 | 303篇 |
2005年 | 282篇 |
2004年 | 207篇 |
2003年 | 224篇 |
2002年 | 204篇 |
2001年 | 210篇 |
2000年 | 156篇 |
1999年 | 131篇 |
1998年 | 245篇 |
1997年 | 198篇 |
1996年 | 157篇 |
1995年 | 117篇 |
1994年 | 125篇 |
1993年 | 104篇 |
1992年 | 77篇 |
1991年 | 83篇 |
1990年 | 61篇 |
1989年 | 64篇 |
1988年 | 48篇 |
1987年 | 37篇 |
1986年 | 42篇 |
1985年 | 65篇 |
1984年 | 78篇 |
1983年 | 68篇 |
1982年 | 63篇 |
1981年 | 66篇 |
1980年 | 66篇 |
1979年 | 51篇 |
1978年 | 40篇 |
1977年 | 47篇 |
1976年 | 54篇 |
1975年 | 34篇 |
1973年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
21.
Soo Jin Kim Wha Young Lee Yeungho Park Wansoo Huh Young Gwan Ko 《Polymer Engineering and Science》2003,43(5):1011-1017
Supported zirconcene catalysts on a new support, MgO, were prepared and tested in ethylene polymerization. Three types of impregnation methods were employed to find an optimum supporting method for MgO. The direct impregnation of Cp2ZrCl2 on MgO showed low metal loading and polymerization activity, while the catalyst had a higher metal loading and polymerization activity when MgO was treated with methylaluminoxane (MAO) before supporting. Treatment of MgO with MAO during the supporting step invoked two types of catalytic sites, which was evidenced by the bimodal molecular weight distribution of the polymer products. MgO is considered to have potential as a support for metallocenes. 相似文献
22.
A key performance parameter of a manufacturing network or supply chain is its cycle time; the time that a typical item spends in the network. A previous simulation study on a semiconductor assembly and test facility showed that cycle times could be reduced by having smooth input and service rates. This suggested that there is a “cycle time principle” that, for a system with a specified throughput or input rate, the shortest cycle times are obtained when the input and service rates do not vary over time. We prove that this principle is true for the M/G/1 and M/M/s queueing systems and Jackson networks. The analysis involves establishing several results on the concavity of waiting time probabilities and the convexity of expected waiting times and queue lengths, as functions of input and service rates. These results also have natural uses in other optimization problems. 相似文献
23.
I. Budić-Leto T. Lovrić J. Gajdoš Kljusurić I. Pezo U. Vrhovšek 《European Food Research and Technology》2006,222(3-4):397-402
Identification of anthocyanins in the wine made of the Croatian autochthonous grape variety of Babić (Vitis vinifera L.) was carried out and their profile was determined by means of high-performance liquid chromatography with diode array
and mass spectrometric detection. Dependence of anthocyanins content and profile on maceration treatment conditions was investigated.
Statistically significant differences of anthocyanins concentration in wines Babić produced by various maceration treatments
were confirmed by the use of multivariate analysis of variances. The investigation results indicated that the maceration temperature
exerts higher influence on anthocyanins concentration than the duration of maceration. In addition, on the basis of anthocyanin
composition and using different multivariate statistical analyses, differentiation of wines Babić according to maceration
treatments was procured. 相似文献
24.
This letter presents our investigation for the effect of symbol timing errors in orthogonal frequency-division multiple access (OFDMA) uplink systems. We express the symbol timing errors between users as the symbol timing misalignments with respect to the desired user. Then, we derive an explicit expression of the signal-to-noise ratio (SNR) as a function of the maximum value of the symbol timing misalignments. Analyses and simulation results show that, to achieve an SNR of 20 dB, the maximum value of the symbol timing misalignments must be less than the cyclic prefix duration plus 6.25% of the useful symbol duration. Based on the resulting SNR degradation, we evaluate the SNR gain with guard subcarriers in order to mitigate the effect of the symbol timing misalignments. 相似文献
25.
Conflicting results have been reported in literature about the influence of beta-adrenergic stimulation on the fast cardiac sodium current (INa+). To elucidate these mechanisms in multicellular preparations we used the loose-patch-clamp technique to evaluate the effect of the beta-adrenergic agonist isoproterenol 1-1000 nmol/l. Isoproterenol enhanced INa+ at all membrane potentials by elevation of the maximal available INa+ . Only at the high concentration of 1 micromol/l was INa+ slightly depressed after depolarizing conditioning clamps. The most marked increase of the maximal available INa+ was 30+/-9% after application of 100 nmol/l isoproterenol. To learn about the mechanisms in view of sodium channel modulation we combined isoproterenol with the sodium channel blocker lidocaine (47 micromol/l). Under these circumstances the effects of both drugs were completely independent. This investigation shows clearly that low concentrations of isoproterenol increase INa+ in multicellular preparations by a gating-independent mechanism. 相似文献
26.
Anna Hać 《Journal of Network and Systems Management》1994,2(1):49-62
This paper analyzes the performance of a switching architecture. The performance measures include the elapsed time of packet transfer and the waiting time to begin transfer. The architecture is partitioned depending on the type of network used and the expected traffic in the network. Every partition has a switch with a buffer that can absorb surges of bursty traffic within the network partition. The buffer size depends on the type of the network and incoming traffic. The partition size depends on the network bandwidth, network traffic, packet size and buffer size. Examples of different networks are used to show the applications of the model. The results show that the elapsed time of packet switch transfer depends exponentially on the number of partitions in the network. 相似文献
27.
Summary Both preferential adsorption coefficient λ and intrinsic viscosity [η] for poly (di-o-alkylphenyl methacrylates) /Tetrahydrofuran
(THF)/water have been determined. The results are discussed in relation to the steric effect of the ortho-substituent groups
on the aromatic ring. 相似文献
28.
Ohne Zusammenfassung
VDI 相似文献
29.
30.