全文获取类型
收费全文 | 306883篇 |
免费 | 33385篇 |
国内免费 | 11156篇 |
专业分类
电工技术 | 15120篇 |
技术理论 | 24篇 |
综合类 | 16838篇 |
化学工业 | 61447篇 |
金属工艺 | 16038篇 |
机械仪表 | 17495篇 |
建筑科学 | 21788篇 |
矿业工程 | 8518篇 |
能源动力 | 8075篇 |
轻工业 | 23254篇 |
水利工程 | 4986篇 |
石油天然气 | 19146篇 |
武器工业 | 1987篇 |
无线电 | 35176篇 |
一般工业技术 | 44397篇 |
冶金工业 | 16332篇 |
原子能技术 | 3510篇 |
自动化技术 | 37293篇 |
出版年
2024年 | 1136篇 |
2023年 | 4197篇 |
2022年 | 7461篇 |
2021年 | 10615篇 |
2020年 | 9366篇 |
2019年 | 9622篇 |
2018年 | 10550篇 |
2017年 | 11767篇 |
2016年 | 11388篇 |
2015年 | 13834篇 |
2014年 | 16521篇 |
2013年 | 20183篇 |
2012年 | 19141篇 |
2011年 | 20087篇 |
2010年 | 18154篇 |
2009年 | 17289篇 |
2008年 | 16438篇 |
2007年 | 15772篇 |
2006年 | 15816篇 |
2005年 | 13579篇 |
2004年 | 9880篇 |
2003年 | 8849篇 |
2002年 | 8330篇 |
2001年 | 7431篇 |
2000年 | 7320篇 |
1999年 | 7424篇 |
1998年 | 5830篇 |
1997年 | 4816篇 |
1996年 | 4512篇 |
1995年 | 3762篇 |
1994年 | 3043篇 |
1993年 | 2183篇 |
1992年 | 1774篇 |
1991年 | 1463篇 |
1990年 | 1174篇 |
1989年 | 1022篇 |
1988年 | 775篇 |
1987年 | 579篇 |
1986年 | 542篇 |
1985年 | 463篇 |
1984年 | 429篇 |
1983年 | 391篇 |
1982年 | 384篇 |
1981年 | 353篇 |
1978年 | 385篇 |
1977年 | 357篇 |
1976年 | 383篇 |
1974年 | 406篇 |
1973年 | 388篇 |
1972年 | 363篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
951.
Ibuprofen is a well-known nonsteroidal anti-inflammatory drug, which can interact with lipid membranes. In this paper, the interaction of ibuprofen with bilayer lipid membrane was studied by UV-vis spectroscopy, cyclic voltammetry and AC impedance spectroscopy. UV-vis spectroscopy data indicated directly that ibuprofen could interact with lipid vesicles. In electrochemical experiments, ibuprofen displayed a biphasic behavior on bilayer lipid membrane supported on a glassy carbon electrode. It could stabilize the lipid membrane in low concentration, while it induced defects formation, even removed off bilayer lipid membrane from the surface of the electrode with increasing concentration. The mechanism about the interaction between ibuprofen and supported bilayer lipid membrane was discussed. 相似文献
952.
Huang L. Chew K. A. Thilakawardana S. Liu Y. Moessner K. Tafazolli R. 《Broadcasting, IEEE Transactions on》2006,52(4):492-504
Recently, an upsurge of interest has been observed in providing multimedia on-demand (MoD) services to mobile users over wireless networks. Nevertheless, due to the rapidly varying nature of mobile networks and the scarcity of radio resources, the commercial implementation is still limited. This paper presents an efficient group-based multimedia-on-demand (GMoD) service model over multicast-enabled wireless infrastructures, where users requesting the same content are grouped and served simultaneously with a single multicast stream. The grouping is fulfilled through a process named "batching". An analytical model is derived to analyse a timeout-based batching scheme with respect to the tradeoff between user blocking probability and reneging probability. Based on the deduced analytical model, an optimal timeout-based batching scheme is proposed to dynamically identify the optimal tradeoff point that maximizes the system satisfaction ratio given a particular system status. The proposed scheme is evaluated by means of simulation and compared with two basic batching schemes (timeout-based, size-based), and two hybrid ones (combined-for-profit, combined-for-loss). The simulation results demonstrate the proposed approach can ensure significant gains in terms of user satisfaction ratio, with low reneging and blocking probabilities 相似文献
953.
2006年,一场百年不遇的特大干旱袭击了四川省21个市、州的139个县(市、区)。据统计,干旱造成全省作物受旱188.52万hm^2,成灾116.55万hm^2,绝收27.73万hm^2,造成农业直接经济损失87.7亿元,有443.6万人出现临时饮水困难。为抗御干旱,四川水利经受了一次严峻的考验,作为四川水利的重要组成部分,已有2260多年历史的都江堰水利也同样经历了一个酷热的夏天。 相似文献
954.
Nonisothermal thermogravimetry differential scanning calorimetry (TG‐DSC) mounting is intensively used for the determination of kinetic parameters and reaction heat along the chemical transformation of a solid. Nevertheless, when tests are performed with heating rates as high as those encountered in industrial processes, e.g., several tens of K min–1, there is great uncertainty in the knowledge of the exact sample temperature. In this work, a method to derive a simple mathematical expression is proposed and fully described in order to calculate the real sample temperature throughout a temperature‐ramped test on a commercial apparatus. The furnace temperature and the heat flow signals were used, together with the crucible specific heat and the heating rate. A number of validation tests were performed to derive similar reaction rates for a reference. First‐order kinetic reactions were presented and reconciled over a large range of heating rates from 3 to 50 K min–1. 相似文献
955.
Rafael Gallego Lucia Comino Alberto Ruiz‐Cabello 《International journal for numerical methods in engineering》2006,66(12):1913-1933
In this paper, the material constant sensitivity boundary integral equation is presented, and its numerical solution proposed, based on boundary element techniques. The formulation deals with plane problems with general rectilinear anisotropy. Expressions for the computation of sensitivities for displacements, tractions, strains and stresses are derived, both for boundary and interior points. The sensitivities can be computed with respect to the bulk material properties or to the properties of part of the domain (inclusions, coatings, etc.). To assess the accuracy of the proposed approach, the computed results are compared to analytical ones derived from exact solutions obtained by complex potential theory, when possible, or finite difference derivatives otherwise. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
956.
957.
958.
959.
960.
A series of new o‐phenylenediamine (OPD)/o‐phenetidine (PHT) copolymers with partly phenazine‐like structures has been successfully synthesized at three polymerization temperatures by chemically oxidative polymerization in four different polymerization media. The molecular structures and properties of the resulting OPD/PHT polymers were investigated by IR, UV–vis and high‐resolution 1H NMR spectroscopies, and DSC, in order to ascertain the effect of reaction temperature, comonomer ratio and acid medium. The copolymerization mechanism of OPD with PHT monomers has been proposed. It is found that the statistical OPD/PHT copolymer obtained at a temperature of 118 °C has a higher degree of polymerization than that obtained at 12–17 °C. The OPD content in the copolymers calculated from NMR spectroscopic analysis is higher than that in the feed OPD content, whereas the OPD content calculated from element analysis is slightly lower than the feed OPD content. It can be predicted that denitrogenation takes place in the OPD units during the polymerization process at OPD/PHT molar ratios of 90/10 and 100/0. These OPD/PHT copolymers exhibit a much better solubility than the OPD homopolymer, hence suggesting an incorporation of PHT units into the phenazine structure of the homopolymer. The thermal behavior of the copolymers was also studied. Copyright © 2004 Society of Chemical Industry 相似文献