全文获取类型
收费全文 | 108593篇 |
免费 | 9418篇 |
国内免费 | 5157篇 |
专业分类
电工技术 | 6699篇 |
技术理论 | 11篇 |
综合类 | 7483篇 |
化学工业 | 17956篇 |
金属工艺 | 6242篇 |
机械仪表 | 7054篇 |
建筑科学 | 8010篇 |
矿业工程 | 2880篇 |
能源动力 | 3196篇 |
轻工业 | 7401篇 |
水利工程 | 1957篇 |
石油天然气 | 5723篇 |
武器工业 | 917篇 |
无线电 | 13272篇 |
一般工业技术 | 13824篇 |
冶金工业 | 4840篇 |
原子能技术 | 1412篇 |
自动化技术 | 14291篇 |
出版年
2024年 | 493篇 |
2023年 | 1768篇 |
2022年 | 3162篇 |
2021年 | 4474篇 |
2020年 | 3283篇 |
2019年 | 2817篇 |
2018年 | 3104篇 |
2017年 | 3528篇 |
2016年 | 3370篇 |
2015年 | 4453篇 |
2014年 | 5536篇 |
2013年 | 6719篇 |
2012年 | 7099篇 |
2011年 | 7730篇 |
2010年 | 6793篇 |
2009年 | 6318篇 |
2008年 | 6330篇 |
2007年 | 5923篇 |
2006年 | 5814篇 |
2005年 | 4994篇 |
2004年 | 3616篇 |
2003年 | 3308篇 |
2002年 | 3572篇 |
2001年 | 3022篇 |
2000年 | 2650篇 |
1999年 | 2455篇 |
1998年 | 1999篇 |
1997年 | 1677篇 |
1996年 | 1545篇 |
1995年 | 1273篇 |
1994年 | 1072篇 |
1993年 | 767篇 |
1992年 | 587篇 |
1991年 | 454篇 |
1990年 | 354篇 |
1989年 | 285篇 |
1988年 | 236篇 |
1987年 | 133篇 |
1986年 | 120篇 |
1985年 | 75篇 |
1984年 | 59篇 |
1983年 | 43篇 |
1982年 | 44篇 |
1981年 | 34篇 |
1980年 | 24篇 |
1979年 | 14篇 |
1976年 | 14篇 |
1975年 | 7篇 |
1959年 | 6篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
A multi-channel continuous toxicity monitoring system developed in our laboratory, based on two-stage mini-bioreactors, was successfully implemented in the form of computer-based data acquisition. The multi-channel system consists of a series of a two-stage minibioreactor systems connected by a fiber optic probe to a luminometer, and uses genetically engineered bioluminescent bacteria for the detection of the potential toxicity from the soluble chemicals. This system can be stably and continuously operated due to the separation of the culture reactor from the test reactor and accomplish easy and long-term monitoring without system shut down by abrupt inflows of severe polluting chemicals. Four different recombinant bioluminescent bacteria were used in different channels so that the modes of the samples toxicities can be reasonably identified and evaluated based upon the response signature of each channel. The bioluminescent signatures were delivered from four channels by switching one at once, while the data is automatically logged to an IBM compatible computer. We also achieved the enhancement of the system through the manipulation of the dilution rate and the use of thermo-lux fusion strains. Finally, this system is now being implemented to a drinking water reservoir and river for remote sensing as an early warning system. 相似文献
12.
Y. K. Cheung W. G. Jin O. C. Zienkiewicz 《International journal for numerical methods in engineering》1991,32(1):63-78
The application of the Trefftz method for calculating wave forces on offshore structures is presented. Indirect and direct formulations using complete and non-singular systems of Trefftz functions for the Helmholtz equation are posed in this paper. An effective technique using different interpolation functions for the velocity potential and wave force are suggested to improve the computational accuracy of the wave force. The numerical examples show that the present method is highly efficient and accurate. 相似文献
13.
14.
15.
Effects of surfactant/silica and silica/cerium ratios on the characteristics of mesoporous Ce-MCM-41
Se Ho Park Bo Yune Song Tai Gyu Lee 《Journal of Industrial and Engineering Chemistry》2008,14(2):261-264
Using the surfactant CTMABr (cetyltrimethyl ammonium bromide) and cerium(IV) sulfate, mesoporous Ce-MCM-41 molecular sieves were produced under a hydrothermal condition with various surfactant/silica (surfactant/Si) and silica/cerium (Si/Ce) ratios. Changes to the structural traits caused by changing the molar ratios of both surfactant/Si and Si/Ce were investigated. XRD (X-ray diffraction), FT-IR (fourier transform infrared spectroscopy), and SEM (scanning electro microscopy) were used for the characterization of prepared mesoporous samples. Among the tested molar ratios, surfactant/Si ratio of 0.5 and 0.2 showed highest values of d1 0 0 and intensity, respectively, for the Si-MCM-41. XRD analysis also identified a quintessential hexagonal structure of Ce-MCM-41 for the Si/Ce molar ratio higher than 40 (maintaining the surfactant/Si ratio at 0.2). When cerium content was increased to have the Si/Ce molar ratio of 20, the hexagonal structure of Ce-MCM-41 was collapsed due to the structural stress of substituted cerium. FT-IR results confirmed calcination of Ce-MCM-41 and the incorporation of Ce4+ ions of cerium sulfate into the silica surface with proper removal of the surfactant. Rod-like shape with rounded edges of the prepared Ce-MCM-41 samples was identified by SEM. These results suggest surfactant/Si ratio of 0.2 and Si/Ce ratio of 40 for the production of Ce-MCM-41 with the highest level of crystallinity. 相似文献
16.
17.
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
18.
Dae-Son Kim Hyun-Young Oh Hong-Yeop Song 《Communications Letters, IEEE》2008,12(3):203-205
In parallel-architecture turbo codes, the constituent interleavers must avoid memory collision. This paper proposes a collision-free interleaver structure composed of a Latin square (LS) and pre-designed interleavers. Our proposed interleavers can be easily optimized for various information block sizes and for various degrees of parallelism. Their performances were evaluated by computer simulation. 相似文献
19.
Many approaches have been proposed to enhance software productivity and reliability. These approaches typically fall into three categories: the engineering approach, the formal approach and the knowledge-based approach. But the optimal gain in software productivity cannot be obtained if one relies on only one of these approaches. This paper describes the work in knowledge-based software engineering conducted by the authors for the past 10 years. The final goal of the research is to develop a paradigm for software engineering which integrates the three approaches mentioned above. A knowledge-based tool which can support the whole process of software development is provided in this paper. 相似文献
20.
In this paper we design an experiment which can be depicted as a simple scenario, a very limited 'world'. In this world, there are an actor that can pursue a project and an observer that is keeping its eyes on the actor. We try to show in the experiment that the observer can to some degree understand the actor based on its knowledge and some metaphors, i.e. understand what the actor is doing and why. As the conclusion of this experiment, we try to show some features of 'understanding'. These are (1) that 'understanding' has to be based on some preliminary knowledge; (2) that 'understanding' is a process of incremental learning; (3) that, as for symbolic systems, some metaphors are necessary for mapping real entities into concepts in mind. 相似文献