全文获取类型
收费全文 | 5724篇 |
免费 | 386篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 81篇 |
综合类 | 3篇 |
化学工业 | 1210篇 |
金属工艺 | 182篇 |
机械仪表 | 262篇 |
建筑科学 | 171篇 |
矿业工程 | 2篇 |
能源动力 | 297篇 |
轻工业 | 674篇 |
水利工程 | 34篇 |
石油天然气 | 17篇 |
无线电 | 818篇 |
一般工业技术 | 1165篇 |
冶金工业 | 438篇 |
原子能技术 | 41篇 |
自动化技术 | 731篇 |
出版年
2024年 | 17篇 |
2023年 | 48篇 |
2022年 | 110篇 |
2021年 | 211篇 |
2020年 | 173篇 |
2019年 | 159篇 |
2018年 | 218篇 |
2017年 | 204篇 |
2016年 | 243篇 |
2015年 | 169篇 |
2014年 | 243篇 |
2013年 | 424篇 |
2012年 | 340篇 |
2011年 | 424篇 |
2010年 | 303篇 |
2009年 | 343篇 |
2008年 | 320篇 |
2007年 | 264篇 |
2006年 | 208篇 |
2005年 | 156篇 |
2004年 | 147篇 |
2003年 | 130篇 |
2002年 | 97篇 |
2001年 | 106篇 |
2000年 | 86篇 |
1999年 | 83篇 |
1998年 | 174篇 |
1997年 | 125篇 |
1996年 | 95篇 |
1995年 | 67篇 |
1994年 | 64篇 |
1993年 | 53篇 |
1992年 | 38篇 |
1991年 | 46篇 |
1990年 | 26篇 |
1989年 | 30篇 |
1988年 | 27篇 |
1987年 | 15篇 |
1986年 | 17篇 |
1985年 | 9篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 5篇 |
1977年 | 8篇 |
1976年 | 14篇 |
1974年 | 4篇 |
1972年 | 3篇 |
排序方式: 共有6126条查询结果,搜索用时 46 毫秒
11.
12.
13.
S H Lee J H Ko J R Kim Y J Kim J J Lee C W Kim T H Lee 《Water science and technology》2006,53(4-5):115-123
The adverse effect of nitrate on the phosphate release rate in the anaerobic phase was observed and was hardly explainable with conventional EBPR process models. Four possible mechanisms were proposed including substrate competition, reduced fermentation, parallel reaction and sequential reaction. Batch experiments were designed and conducted to identify the dominant mechanism. Results showed that the sequential reaction was the only possible mechanism where only denitrification occurred if any nitrate existed in the anaerobic phase. Then the phosphate release following after the nitrate was completely removed. Nitrate inhibition effect was added into the PHA storage rate to incorporate the sequential reaction in the conventional ASM3 plus EAWAG bio-P module (ASM3 + P). Nitrate inhibition coefficient, K(I,NO,PAO) was found to be as low as 0.05 mg/L. This correlated well with experimental observation where no also meant that the anaerobic compartment of a continuous flow reactor could be seriously affected by the residual nitrate contained in the sludge recycle flow. This phenomenon caused overestimation of the phosphate uptake rate and consequently underestimation of PO4(3-) -P concentration. This problem was resolved by incorporation of a nitrate inhibition term in the ASM3 + P for more accurate simulation of the EBPR process. 相似文献
14.
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
15.
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
16.
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
17.
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
18.
In order to observe the transport ability of peritoneum to small molecular substances, peritoneal equilibration test (PET) was performed in 52 CAPD patients. By analysing the relationship between peritoneal transport function and dialysis adequacy, we found the average urea KT/V and Cr were significantly lower in high and low transport groups (n = 6 and n = 2) than in high average and low average groups (n = 35 and n = 9). According to the results of PET, we adjusted the dialysis program of 11 patients and the dialysis adequacy was markedly improved. We concluded that PET was helpful for selecting and adjusting CAPD program, and discussed some questions which should be payed more attention in PET operation. 相似文献
19.
20.
Per Johan Råsmark Čestmír Koňák Petr Štěpánek Christer Elvingson 《Polymer Bulletin》2005,54(4-5):335-342
Summary Dynamic light scattering was used to investigate the dynamics of sodium poly(styrene sulfonate) and fully neutralized poly(acrylic acid) gels as a function of the degree of swelling and weight ratio of cross-linking agent. It was shown that the collective diffusion coefficient increases with increasing degree of swelling and that the diffusion coefficient shows stronger concentration dependence than predicted by scaling arguments. For gel samples measured at the swelling equilibrium, the diffusion coefficient increases with increasing gel concentration for both gel systems. 相似文献