全文获取类型
收费全文 | 141083篇 |
免费 | 24195篇 |
国内免费 | 5481篇 |
专业分类
电工技术 | 7752篇 |
技术理论 | 7篇 |
综合类 | 7669篇 |
化学工业 | 33343篇 |
金属工艺 | 6224篇 |
机械仪表 | 7499篇 |
建筑科学 | 9867篇 |
矿业工程 | 2660篇 |
能源动力 | 3809篇 |
轻工业 | 14472篇 |
水利工程 | 2471篇 |
石油天然气 | 5439篇 |
武器工业 | 966篇 |
无线电 | 19427篇 |
一般工业技术 | 23412篇 |
冶金工业 | 4835篇 |
原子能技术 | 1247篇 |
自动化技术 | 19660篇 |
出版年
2024年 | 462篇 |
2023年 | 1819篇 |
2022年 | 3564篇 |
2021年 | 5121篇 |
2020年 | 4796篇 |
2019年 | 5802篇 |
2018年 | 6101篇 |
2017年 | 6636篇 |
2016年 | 6838篇 |
2015年 | 8197篇 |
2014年 | 9222篇 |
2013年 | 11167篇 |
2012年 | 9683篇 |
2011年 | 10032篇 |
2010年 | 9510篇 |
2009年 | 8596篇 |
2008年 | 8271篇 |
2007年 | 7563篇 |
2006年 | 7207篇 |
2005年 | 6126篇 |
2004年 | 4732篇 |
2003年 | 4354篇 |
2002年 | 4570篇 |
2001年 | 3910篇 |
2000年 | 3414篇 |
1999年 | 2807篇 |
1998年 | 1879篇 |
1997年 | 1545篇 |
1996年 | 1404篇 |
1995年 | 1194篇 |
1994年 | 995篇 |
1993年 | 729篇 |
1992年 | 571篇 |
1991年 | 441篇 |
1990年 | 330篇 |
1989年 | 255篇 |
1988年 | 215篇 |
1987年 | 129篇 |
1986年 | 115篇 |
1985年 | 81篇 |
1984年 | 60篇 |
1983年 | 48篇 |
1982年 | 48篇 |
1981年 | 44篇 |
1980年 | 41篇 |
1979年 | 22篇 |
1978年 | 14篇 |
1976年 | 17篇 |
1975年 | 14篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The analysis of an arbitrarily inclined slot on the ground plane of a microstrip line is presented using the spectral domain approach and reciprocity theorem. Comparison of numerical results for the special case of a perpendicular slot with other available computed and measured data shows a good agreement. It is found that the impedance level can be controlled over a wide range by varying inclination angle. Results should be useful in antenna and multilayer circuit integration applications 相似文献
992.
介绍一种新型发射技术──冲压加速原理,它在仅仅利用化学能的条件下,可将弹丸加速到超过2km/s的非常规初速,加速效率很高,弹迫效率可高达30%,是一种很有发展前途的超高速发射技术。 相似文献
993.
GH Fan J Zhao YL Wu LG Lou Z Zhang Q Jing L Ma G Pei 《Canadian Metallurgical Quarterly》1998,53(4):684-690
The effects of N-methyl-D-aspartate (NMDA) on opioid receptor-mediated G protein activation were explored in neuroblastoma X glioma hybrid (NG108-15) cells. Treatment of the cells with NMDA resulted in a remarkable attenuation of [35S]guanosine-5'-O-(3-thio)triphosphate binding stimulated by [D-Pen2,D-Pen5]-enkephalin (DPDPE), a delta-opioid receptor agonist. The effects of NMDA were dose and time dependent with an IC50 value of 5 nM and could be blocked by NMDA receptor antagonists. After NMDA treatment, the DPDPE dose-response curve shifted to the right (EC50 value increased approximately 7-fold, from 6 to 40 nM), and the maximal response induced by DPDPE was reduced by approximately 60%. The effects of NMDA were reversible, and the DPDPE response could recover within 60 min. The functional responses of delta-, mu-, and kappa-opioid receptors in primarily cultured neurons also were attenuated significantly by NMDA treatment. The inhibitory effects of NMDA on opioid receptor-mediated G protein activation could be blocked by coadministration of the protein kinase C (PKC) inhibitors or by elimination of the extracellular Ca2+. Correspondingly, NMDA treatment of NG108 cells significantly elevated cellular PKC activity and stimulated Gialpha2 phosphorylation. Transient transfection into NG108-15 cells of the wild-type Gialpha2 and a mutated Gialpha2 (Ser144Ala) resulted in a 2-fold increase in DPDPE-stimulated G protein activation. The DPDPE responses were greatly inhibited by NMDA treatment in the wild-type Gialpha2-transfected cells but much less affected in the mutant Gialpha2-transfected cells. In summary, NMDA attenuates opioid receptor/G protein coupling, and this process requires activation of PKC. 相似文献
994.
995.
996.
本文通过对光存储系统出错特性的分析,研究了一些描述出错特性的主要参数,并且给出了描述出错特性的Gilbert模型及其改进型模型。 相似文献
997.
动态毛吸法测定纤维表面能 总被引:2,自引:0,他引:2
本文用浸润测定仪对玻璃纤维和Kevlar-49芳纶纤维进行了表面能测定,讨论了纤维束柱末端沾湿量的影响,提出了浸润仪测试数据的正确处理方法,求得了Kevlar-49纤维的表面能并对其色散分量和非色散分量进行了解析. 相似文献
998.
999.
1000.
Peng Dangcong Jin Qiting 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1993,58(1):89-93
The anaerobic digestion of alkaline black liquor from a cereal straw pulping mill was studied in batch (serum bottles) and continuous systems (up-flow anaerobic sludge blanket reactor—UASB). The batch digestion studies confirmed that lignin and related compounds (LRC) in the alkaline black liquor were the main inhibitory substances and could not be decomposed by anaerobic bacteria. At organic loading rates of 5–10 kg COD m?3 day?1, the UASB reactor achieved 50–60% COD removal efficiencies. Gas production was 2–3 dm3 per dm3 of alkaline black liquor. Two different sludge types were examined in the reactor: granular and cluster-like sludges. Sludge in a cluster, which involved many small granules and flocs, tended to form larger aggregates and possessed good settling ability. 相似文献