全文获取类型
收费全文 | 73416篇 |
免费 | 8487篇 |
国内免费 | 5006篇 |
专业分类
电工技术 | 6195篇 |
技术理论 | 5篇 |
综合类 | 5929篇 |
化学工业 | 10293篇 |
金属工艺 | 4316篇 |
机械仪表 | 5093篇 |
建筑科学 | 6227篇 |
矿业工程 | 2585篇 |
能源动力 | 2193篇 |
轻工业 | 5410篇 |
水利工程 | 1831篇 |
石油天然气 | 3525篇 |
武器工业 | 947篇 |
无线电 | 9447篇 |
一般工业技术 | 7392篇 |
冶金工业 | 2764篇 |
原子能技术 | 1039篇 |
自动化技术 | 11718篇 |
出版年
2024年 | 477篇 |
2023年 | 1439篇 |
2022年 | 2948篇 |
2021年 | 4166篇 |
2020年 | 3095篇 |
2019年 | 2314篇 |
2018年 | 2563篇 |
2017年 | 2870篇 |
2016年 | 2492篇 |
2015年 | 3812篇 |
2014年 | 4744篇 |
2013年 | 5448篇 |
2012年 | 6457篇 |
2011年 | 6641篇 |
2010年 | 5909篇 |
2009年 | 5450篇 |
2008年 | 5149篇 |
2007年 | 4564篇 |
2006年 | 3888篇 |
2005年 | 3102篇 |
2004年 | 2035篇 |
2003年 | 1340篇 |
2002年 | 1205篇 |
2001年 | 921篇 |
2000年 | 788篇 |
1999年 | 716篇 |
1998年 | 444篇 |
1997年 | 387篇 |
1996年 | 337篇 |
1995年 | 281篇 |
1994年 | 225篇 |
1993年 | 153篇 |
1992年 | 109篇 |
1991年 | 102篇 |
1990年 | 66篇 |
1989年 | 51篇 |
1988年 | 51篇 |
1987年 | 30篇 |
1986年 | 23篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 22篇 |
1979年 | 16篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1959年 | 14篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Lei Liu Ying Kong Hong Xu Jin P. Li Jin X. Dong Zhi Lin 《Microporous and mesoporous materials》2008,115(3):624-628
A three-dimensional zinc phosphate compound with DFT topology, designated as ZnPO4-EU1, has been synthesized by an ionothermal approach from the system HF-ZnO–P2O5-choline chloride-imidazolidone. Ethylenediamine, derived from decomposition of the imidazolidone component of the deep-eutectic solvent (DES) itself, is delivered to the synthesis and serves as an appropriate template for ZnPO4-EU1. Experiments in which the synthesis conditions were varied showed that ZnPO4-EU1 may be prepared over a wide molar ratio of P/Zn = 0.55–13.0. Powder X-ray diffraction patterns have been obtained at intervals to track the crystallization process of this material. The experimental data show that Zn3(PO4)2 · 4H2O (a dense phase) was first isolated from the DES after reaction for 1 h. Subsequently, the pure phase of ZnPO4-EU1 was obtained with increasing crystallization time from 12 h to 72 h. The experimental results show that the nucleation and crystallization take place with relatively low levels of solvent degradation, demonstrating that zinc phosphate with a three-dimensional framework can be synthesized by in situ generation of an appropriate template using an unstable DES at high temperatures (150–200 °C). 相似文献
13.
A high-power and high-repetition-rate passively Q -switched ytterbium-doped single-mode double-clad fiber laser was built using a Cr4+:YAG saturable absorber (SA). Two different SAs with initial transmissions of Tomicron = 30% and Tomicron = 50% were studied. At the maximum coupled pump power of 9.8 W, an output power of 4.7 W, pulse duration of 143 ns, pulse repetition rate of 253 KHz, pulse energy of 18.5 muJ, and slope efficiency of 49% were obtained with the Tomicron = 30% SA. 相似文献
14.
Alia-Klein Nelly; Goldstein Rita Z.; Tomasi Dardo; Zhang Lei; Fagin-Jones Stephanie; Telang Frank; Wang Gene-Jack; Fowler Joanna S.; Volkow Nora D. 《Canadian Metallurgical Quarterly》2007,7(4):735
Reports an error in "What is in a word? No versus Yes differentially engage the lateral orbitofrontal cortex" by Nelly Alia-Klein, Rita Z. Goldstein, Dardo Tomasi, Lei Zhang, Stephanie Fagin-Jones, Frank Telang, Gene-Jack Wang, Joanna S. Fowler and Nora D. Volkow (Emotion, 2007[Aug], Vol 7[3], 649-659). The supplemental materials link should appear as follows: http://dx.doi.org/10.1037/1528-3542.7.3.649.supp. (The following abstract of the original article appeared in record 2007-11660-018.) The words "No" and "Yes" are involved in conditioning to prohibit or encourage behavior, respectively. The authors, therefore, hypothesized that these words would be attributed to endogenous valence, activating neuronal circuits involved with valence and emotional control. Functional MRI (fMRI) at 4 Tesla was used to record regional brain activity while participants were exposed to emphatic vocalizations of the words. Results showed that No and Yes were associated with opposite brain-behavior responses; while No was negatively valenced, produced slower response times, and evoked a negative signal in the right lateral orbitofrontal cortex (OFC), Yes was positively valenced, produced faster response times, and evoked a positive signal in a contiguous region of the OFC. Attribution of negative valence to No and trait anger control were associated with increased responsivity of the OFC to No. Inasmuch as sensitivity to the prohibitive command No develops during childhood through interaction with primary caregivers as the first social objects, our findings may implicate the lateral OFC in the neurobiology of emotion regulation and subsequent social development. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
15.
16.
已往库存论中的决策模型,它是把现实过程用数学的方法进行分析,得到决策值,但不能看到决策的过程,不能反映出现实生活中的不确定性、动态性。运用Delphi 7.0和SQL server 2000对销售过程进行了动态仿真,利用Newsboy模型的推广(S,s)订购策略来监控库存并做出决策,这样就体现出此过程的不确定性、动态性;且举出了一个仿真商品销售的实例,对其中的一些关键技术,如何仿真、算法的实现等进行了阐述。 相似文献
17.
18.
关于彩色火焰蜡烛的研制 总被引:1,自引:0,他引:1
本文阐述了利用焰色反应的原理研制彩色火焰蜡烛,着重分析并解决了在研制工作中出现的几个技术关键,如主燃剂的选取、蜡烛成型和强度、发色剂的选择与用量等. 相似文献
19.
氯化铁催化合成富马酸二甲酯 总被引:9,自引:0,他引:9
氯化铁可代替硫酸催化酯化反应,探讨了氯化铁催化合成富马酸二甲酯的条件,操作简便,反应温和,无腐蚀,减少了污染与产品纯化。 相似文献
20.