全文获取类型
收费全文 | 1972篇 |
免费 | 75篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 22篇 |
综合类 | 4篇 |
化学工业 | 377篇 |
金属工艺 | 71篇 |
机械仪表 | 37篇 |
建筑科学 | 31篇 |
矿业工程 | 4篇 |
能源动力 | 52篇 |
轻工业 | 76篇 |
水利工程 | 7篇 |
石油天然气 | 5篇 |
无线电 | 296篇 |
一般工业技术 | 526篇 |
冶金工业 | 231篇 |
原子能技术 | 15篇 |
自动化技术 | 305篇 |
出版年
2023年 | 26篇 |
2022年 | 34篇 |
2021年 | 58篇 |
2020年 | 45篇 |
2019年 | 46篇 |
2018年 | 65篇 |
2017年 | 71篇 |
2016年 | 65篇 |
2015年 | 45篇 |
2014年 | 66篇 |
2013年 | 128篇 |
2012年 | 80篇 |
2011年 | 88篇 |
2010年 | 76篇 |
2009年 | 79篇 |
2008年 | 74篇 |
2007年 | 70篇 |
2006年 | 54篇 |
2005年 | 40篇 |
2004年 | 46篇 |
2003年 | 53篇 |
2002年 | 46篇 |
2001年 | 29篇 |
2000年 | 31篇 |
1999年 | 33篇 |
1998年 | 58篇 |
1997年 | 34篇 |
1996年 | 45篇 |
1995年 | 32篇 |
1994年 | 45篇 |
1993年 | 30篇 |
1992年 | 26篇 |
1991年 | 21篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 22篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 18篇 |
1977年 | 21篇 |
1976年 | 14篇 |
1973年 | 7篇 |
1968年 | 6篇 |
排序方式: 共有2059条查询结果,搜索用时 15 毫秒
1.
Vancha Harish Effi Haque Magdalena
miech Hiroaki Taniguchi Sarah Jamieson Devesh Tewari Anupam Bishayee 《International journal of molecular sciences》2021,22(9)
Xanthohumol (XH) is an important prenylated flavonoid that is found within the inflorescence of Humulus lupulus L. (Hop plant). XH is an important ingredient in beer and is considered a significant bioactive agent due to its diverse medicinal applications, which include anti-inflammatory, antimicrobial, antioxidant, immunomodulatory, antiviral, antifungal, antigenotoxic, antiangiogenic, and antimalarial effects as well as strong anticancer activity towards various types of cancer cells. XH acts as a wide ranging chemopreventive and anticancer agent, and its isomer, 8-prenylnaringenin, is a phytoestrogen with strong estrogenic activity. The present review focuses on the bioactivity of XH on various types of cancers and its pharmacokinetics. In this paper, we first highlight, in brief, the history and use of hops and then the chemistry and structure–activity relationship of XH. Lastly, we focus on its prominent effects and mechanisms of action on various cancers and its possible use in cancer prevention and treatment. Considering the limited number of available reviews on this subject, our goal is to provide a complete and detailed understanding of the anticancer effects of XH against different cancers. 相似文献
2.
Kamalesh Pal Amitava Mukherjee Md. Motin Seikh Parthasarathi Bera Arup Gayen 《Ceramics International》2021,47(10):14798-14808
Synthesis of nanocrystalline pristine and Mn-doped calcium copper titanate quadruple perovskites, CaCu3?xMnxTi4?xMnxO12 (x = 0, 0.5, and 1.0) by modified citrate solution combustion method has been reported. Powder X-ray diffraction patterns attest the phase purity of the perovskite materials. Average particle sizes of all the materials obtained from the Scherrer's formula are in the range of 55–70 nm. The specific surface areas for all the perovskites obtained from BET isotherms are found to be low as expected for the condensed oxide systems and fall in the range of 13–17 m2 g?1. Transmission electron microscopy studies show a reduction in particle size of CaCu3Ti4O12 with increase in Mn doping. Ca and Ti are present in +2 and +4 oxidation states in all the materials as demonstrated by X-ray photoelectron spectroscopy analyses. Cu2+ gets reduced in CaCu3Ti4O12 with higher Mn content. Mn is observed to be present only in +3 oxidation state. All the materials have been examined to be active in CO oxidation as well as H2 production from methanol steam reforming. CaCu3Ti4O12 with ~14 at.% Mn is found to show best catalytic activities among these materials. A comprehensive analysis of the catalytic activities of these perovskites toward CO oxidation and H2 production from MSR reveal the cooperative activity of copper-manganese in the doped perovskites and it is more effective at lower manganese content. 相似文献
3.
4.
A fiber optic ring network, such as fiber distributed data interface (FDDI), can be operated over multiple wavelengths on its existing fiber plant consisting of point-to-point fiber links. Using wavelength division multiplexing (WDM) technology, FDDI nodes can be partitioned to operate over multiple subnetworks, with each subnetwork operating independently on a different wavelength, and inter-subnetwork traffic forwarding performed by a bridge. For this multiwavelength version of FDDI, which we refer to as wavelength distributed data interface (WDDI), we examine the necessary upgrades to the architecture of a FDDI node, including its possibility to serve as a bridge. The main motivation behind this study is that, as network traffic scales beyond (the single-wavelength) FDDI's information-carrying capacity, its multiwavelength version, WDDI, can gracefully accommodate such traffic growth. A number of design choices exist in constructing a good WDDI network. Specifically, we investigate algorithms using which, based on prevailing traffic conditions, partitioning of nodes into subnetworks can be performed in an optimized fashion. Our algorithms partition the nodes into subrings, such that the total traffic flow in the network and/or the network-wide average packet delay is minimized 相似文献
5.
Probability (P) of equipment failure consequent upon stress exceeding built-in strength has been estimated assuming a bivariate normal stress-strength distribution. The UMVUE of P when parameters other than the means are known has been derived. An alternative estimator based on maximum likelihood estimates has been proposed in the case when all the five parameters are unknown. Asymptotic variances of both these estimators have been worked out. Some relevant numerical computations have also been reported. 相似文献
6.
7.
A computer method for the calculation of the phase shift due to optically injected carriers in an InP avalanche transit time diode has been suggested using the numerically simulated negative resistance profiles in the depletion layer of the diode. The results show that the phase shift due to hole injection is larger than that due to electron injection which explains the pronounced effect of photogenerated hole leakage current in modulating the microwave properties of InP diodes 相似文献
8.
Mechanical properties of polypropylene-g-poly(methacrylic acid) fibers, prepared by graft copolymerization of methacrylic acid onto polypropylene fiber using simultaneous gamma ray irradiation technique, were evaluated. In general, an improvement in the mechanical behavior of the polypropylene fiber by grafting was observed. Denier and initial modulus of the fiber showed a linear increase with the percent graft, and elongation showed an opposite trend. The results have been explained in terms of reinforcing effect of poly(methacrylic acid) grafts and reduction in the segmental mobility of the polymeric chains. Tenacity also increases up to certain graft level, beyond which a sharp decrease occurs, probably due to the influence on the compactness of the macromolecular chains with the further grafting. 相似文献
9.
10.