全文获取类型
收费全文 | 11086篇 |
免费 | 1146篇 |
国内免费 | 44篇 |
专业分类
电工技术 | 29篇 |
综合类 | 208篇 |
化学工业 | 1444篇 |
金属工艺 | 106篇 |
机械仪表 | 123篇 |
建筑科学 | 99篇 |
矿业工程 | 77篇 |
能源动力 | 634篇 |
轻工业 | 7450篇 |
水利工程 | 46篇 |
石油天然气 | 638篇 |
无线电 | 154篇 |
一般工业技术 | 683篇 |
冶金工业 | 51篇 |
原子能技术 | 18篇 |
自动化技术 | 516篇 |
出版年
2024年 | 137篇 |
2023年 | 519篇 |
2022年 | 760篇 |
2021年 | 826篇 |
2020年 | 791篇 |
2019年 | 753篇 |
2018年 | 579篇 |
2017年 | 639篇 |
2016年 | 694篇 |
2015年 | 608篇 |
2014年 | 725篇 |
2013年 | 577篇 |
2012年 | 589篇 |
2011年 | 547篇 |
2010年 | 462篇 |
2009年 | 350篇 |
2008年 | 124篇 |
2007年 | 364篇 |
2006年 | 272篇 |
2005年 | 281篇 |
2004年 | 85篇 |
2003年 | 174篇 |
2002年 | 201篇 |
2001年 | 216篇 |
2000年 | 141篇 |
1999年 | 127篇 |
1998年 | 62篇 |
1997年 | 32篇 |
1996年 | 57篇 |
1995年 | 31篇 |
1994年 | 31篇 |
1993年 | 27篇 |
1992年 | 27篇 |
1991年 | 34篇 |
1990年 | 22篇 |
1989年 | 22篇 |
1988年 | 57篇 |
1987年 | 138篇 |
1986年 | 115篇 |
1985年 | 40篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
《Fuel》2006,85(14-15):2195-2201
The solids formed in the systems containing copper in different oxidation states, in the presence and absence of hexanoic acid and dodecanethiol, together and separately, at room temperature, were studied. The experiments were performed in a mineral oil matrix, free of sulfur compounds and metals; a diesel oil matrix; and the reagents alone, without any matrix. The deposits formed were analyzed by elemental analysis (EA), infrared spectroscopy (IR), thermogravimetric analysis (TGA) and total copper by inductively coupled plasma-optical emission spectrometry (ICP-OES), for their identification and determination of the probable structures. In samples containing both hexanoic acid and dodecanethiol, when there is copper(I), anhydrous copper(II) hexanoate is preferentially formed, but in samples of copper(II), copper(II) mercaptate is formed first. In samples of metallic copper in mineral oil matrix, no deposit formations occur. In all cases in which deposits were formed, they were the same as in diesel oil matrix. 相似文献
53.
《Materials Letters》2007,61(4-5):1020-1022
Metallic silver has been prepared by direct hydrogen reduction of Ag2S in basic slurry under hydrothermal conditions. The XRD pattern and SEM micrographs of the reaction product are given. Metallic silver was predominant in the reduction product obtained by using ZnO as additive and PdCl2 as catalyst at 220 °C, pH 12.0 and 2–3 MPa of partial hydrogen pressure for 4 h. 相似文献
54.
《Food Control》2007,18(6):713-715
The Cold Chain has always played an important role in food safety within the global market. The Canadian government has recognized it has an important role in the food continuum. In partnership with industry, national voluntary enhanced food safety systems, based on Codex Alimentarius (HACCP) principles, are being developed within Canada. These efforts will contribute towards food safety and will build confidence in foodstuffs grown, prepared and sold at all levels of trade and abroad. 相似文献
55.
《Environmental Modelling & Software》2007,22(7):987-999
The project goal was to loosely couple the SWAT model and the QUAL2E model and compare their combined ability to predict total phosphorus (TP) and NO3-N plus NO2-N yields to the ability of the SWAT model with its completely coupled water quality components to predict TP and NO3-N plus NO2-N yields from War Eagle Creek watershed in Northwest Arkansas. Model predictions were compared using a statistical approach to identify significant differences between the two modeling methods. Results from two variations of the Pearson product-moment correlation (p < 0.05) indicated that correlation coefficients and regression slopes for the two data sets were not significantly different. This implies that neither modeling method was significantly better in predicting monthly TP and NO3-N plus NO2-N yields from the watershed. Additionally, no significant differences were present between predicted outputs of the SWAT model with instream components active compared with when instream components were inactive, indicating a need for further testing and refinement of the SWAT algorithms simulating instream processes. We can further infer that the instream processes available in SWAT may not be enhancing its predictive abilities as far as simulating instream components. 相似文献
56.
Yong-Seo Park Seong-Gook Kang Alma Leticia Martinez Ayala Olga Martín-Belloso Shela Gorinstein 《LWT》2006,39(7):748-755
Fresh persimmons were subjected to two different processes: sun-drying during 1 month and dehydration at 60 °C during 12 h. To assess the effect of this process on nutritional and health-related properties of persimmons dietary fibers, minerals, trace elements, polyphenols and the total radical scavenging activities (TRSAs) were determined before and after processing. It was found that the contents of dietary fibers, minerals and trace elements in fresh and dried persimmons fruits were comparable. Total polyphenols in fresh persimmons was higher than in dried fruits (1.3 vs. 0.9 and 0.8 mg/100 g FW, respectively) and percentage of inhibition was higher than in dried fruits (70% vs. 59% and 55% and 58% vs. 53% and 46% for 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) [ABTS] radicals, respectively (P>0.05 in all cases). In conclusion: (1) the differences in the contents of dietary fibers, minerals and trace elements in fresh and dried persimmons are not significant; (2) the contents of polyphenols and the level of the TRSA are higher in fresh persimmons than in dried fruits; however, both variables are also high in dried persimmons; (3) when fresh fruits are not available, proper dried persimmons could be used as a valuable substitute. 相似文献
57.
《Mathematics and computers in simulation》2006,71(2):121-130
An information criterion-based model selection method is proposed for monitoring unit root and multiple structural changes. In this method, a battery of possible models is considered by changing the integration order (I(0) or I(1)) and the combinations of change points. Next, the best model is selected from among alternative models via a modified Bayesian information criterion (BIC). Accordingly, on the basis of the selected model, the process that generates the observed time series is determined. The BIC is modified in order to adjust the frequency count of incorrectly selecting stationary models via the conventional BIC. The simulation results of monitoring unit root and structural change suggest that the proposed method outperforms the conventional hypothesis testing method in terms of detection accuracy and detection speed. Furthermore, the empirical results suggest that the proposed method exhibits better performances with regard to detection stability and forecastability. 相似文献
58.
59.
《Journal of Network and Computer Applications》2012,35(3):892-904
Security infrastructure is one of the most challenging tasks in the development, integration and deployment of Grid middlewares. Even though the Grid community addresses the security issue through public key infrastructures (PKI) to support mutual authentication using X.509 certificates, maintaining X.509 credentials is not that easy for non-IT-experts, and has proved to be an obstacle for a more wide deployment of Grid technologies. The identity federation is an increasingly popular technology that can facilitate cross-domain single sign-on without requiring the users to maintain any credentials additional to their own institutional accounts. We believe that utilizing identity federation for Grid middlewares is a promising path for the Grid technology to get more widely used. This paper describes a single sign-on infrastructure developed as a part of the NorduGrid ARC (Advanced Resource Connector) Grid middleware. It adopts the identity federation standard (SAML), as well as other Web Service standards. It focuses on a single sign-on solution at the middleware level for users to access Grids by only using their frequently used accounts, without being bothered to maintain X.509 credentials. Users can use their username/password only to access Grids developed in ARC middleware, as well as access Grids developed in other middlewares that requires users to provide X.509 certificates. Moreover, the single sign-on for workflow-like Grid applications (in which intermediate entities act on behalf of users) is also supported. As an important aspect of single sign-on, authorization is also considered by implementing an attribute-based authorization using SAML standard. In addition, the performance of single sign-on solution is measured. We identify performance limitations of security-related services inside this solution, and analyse the ways to avoid the limitations. To our knowledge, the work presented in this paper is the first evaluated implementation that utilizes identity federation for Grid usage on the middleware level. 相似文献
60.
Ning Wang Jun Chen Qi Zhou Lianzhou Jiang Liqi Wang Yingjie Dai Dianyu Yu Walid Elfalleh 《European Journal of Lipid Science and Technology》2021,123(6):2000091
Crude wax extracted from rice bran oil (RBO) is used to improve the oleogel properties and oxidative stability of RBO. The effect of crude rice bran wax (CrBW) on the formation characteristics and oxidative stability of oleogels is discussed. The results show that oleogels can be formed with 7.0 wt% CrBW at 20 °C. As the concentration of CrBW increases from 7.0 to 11.0 wt%, the hardness and solid fat content (SFC) of the oleogels increase significantly, and the oleogels are primarily β' crystals. Moreover, oleogel crystals formed with 5 and 7 wt% CrBW are flocculent; when the amount included is 9%, the oleogel crystals are transformed into long dendrites, and the density rises. After 90 days of storage at 20 °C, the peroxide value of oleogels formed with 9.0 wt% CrBW slowly rises from 3.21 to 6.52 mmol kg−1. Practical Applications: Oleogels prepared here by CrBW and RBO are an innovative structural lipid without trans fats. Useful information on the rich fats and nutrients in CrBW is provided, which reduces the production cost and improves the industrial production capacity. 相似文献