全文获取类型
收费全文 | 2362篇 |
免费 | 155篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 1055篇 |
金属工艺 | 21篇 |
机械仪表 | 41篇 |
建筑科学 | 77篇 |
矿业工程 | 5篇 |
能源动力 | 41篇 |
轻工业 | 565篇 |
水利工程 | 15篇 |
石油天然气 | 7篇 |
无线电 | 80篇 |
一般工业技术 | 293篇 |
冶金工业 | 69篇 |
原子能技术 | 6篇 |
自动化技术 | 236篇 |
出版年
2024年 | 5篇 |
2023年 | 48篇 |
2022年 | 276篇 |
2021年 | 306篇 |
2020年 | 84篇 |
2019年 | 70篇 |
2018年 | 88篇 |
2017年 | 84篇 |
2016年 | 98篇 |
2015年 | 75篇 |
2014年 | 95篇 |
2013年 | 157篇 |
2012年 | 137篇 |
2011年 | 163篇 |
2010年 | 109篇 |
2009年 | 117篇 |
2008年 | 92篇 |
2007年 | 92篇 |
2006年 | 76篇 |
2005年 | 62篇 |
2004年 | 54篇 |
2003年 | 42篇 |
2002年 | 29篇 |
2001年 | 22篇 |
2000年 | 14篇 |
1999年 | 6篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 13篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1934年 | 1篇 |
1933年 | 1篇 |
1932年 | 2篇 |
排序方式: 共有2518条查询结果,搜索用时 15 毫秒
21.
The effect of hygrothermal aging on a particle‐filled, epoxy‐based adhesive was studied using a gravimetric sorption technique. This study has explored moisture sorption characteristics as well as the associated behaviors of swelling and the depression of the glass transition temperature (Tg). We observed that the diffusion of water in this adhesive has a non‐Fickian behavior, and the depression of Tg proceeds to a definite value that is independent of the final equilibrium water content of the system. Our observations suggest that water diffuses into the polymer in a dual‐sorption mode, in which water resides in two populations. In one population, water is considered to occupy apparent free volume of the adhesive, and the second population water infiltrates polymer structure and forms hydrogen‐bonded clusters. Our results show that hygrothermal aging temperature and swelling do not alter the apparent free volume of this adhesive. We conclude that the constant value of Tg depression at saturation implies that only water in the apparent free volume is responsible for the Tg depression, whereas the swelling proceeds through the formation of hydrogen bonds in the adhesive. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1436–1444, 2003 相似文献
22.
Very long chain (VLC) PUFA of the n−6 and n−3 series are known to occur in mammalian testis. The aim of this work was to characterize
further two testicular lipid classes with VLCPUFA, cholesterol esters (CE) and total triglycerides (TG) in rat and mouse testis.
The VLCPUFA predominating in these lipids were a series of n−6 pentaenes and tetraenes with 24 to 32 carbons, including small
amounts of odd-chain PUFA, 28∶5n−6 and 24∶5n−6 prevailing in CE and TG, respectively. Most of the VLCPUFA of TG were concentrated
in a small fraction of TG, made up by 1-O-alkyl-2,3-DAG. This TG subclass was absent altogether from the TG of sexually immature testis. The TG and the CE with VLCPUFA
only occurred in testis of adult fertile animals. The proportion of VLCPUFA in total TG and CE was higher in rodents than
in other mammals. In the n−6 PUFA-rich adult mouse testis, the amounts of testicular triacylglycerols decreased significantly
after consumption of fish oil for 2 wk. Whereas 18∶2n−6 was significantly reduced, the amounts of 22∶5n−6 and longer n−6 PUFA
were less affected in all mamor testicular lipids including PC and PE, where they were unchanged. The 1-O-alkyl-2,3-DAG and their n−6 VLCPUFA were virtually unaffected by the diet. The VLCPUFA-containing molecular species of CE
and TG may represent a form of storage of cholesterol and polyenoic FA required to sustain spermatogenesis. Via chain-shortening, VLCPUFA stored in the neutral lipids may serve as precursors of the major C22 PUFA typical of cell membrane glycerophospholipids, protecting testicular cells against shifts in FA composition induced
by dietary changes. 相似文献
23.
Rajmund S. Dybczyński Marta Pyszynska Krzysztof Kulisa Anna Bojanowska-Czajka 《分离科学与技术》2020,55(7):1364-1379
ABSTRACTNew ion interaction chromatographic (IIC) method employing Kromasil 100 C18 column and tetra-n-butylammonium hydroxide (TBAOH) as an ion interaction reagent (IIR) is able to separate yttrium from Rare Earth Elements (REE) as anionic complexes with nitrilotriacetic acid (NTA). New method for the chromatographic determination of Y in REE mixture was devised and validated by the analysis of the certified reference material (CRM). Potential possibilities of the new chromatographic system for larger scale applications including macro-micro events were demonstrated. 相似文献
24.
Neurospora crassa incorporated exogenous deuterated palmitate (16∶0) and 14C-labeled oleate (18∶1Δ9) into cell lipids. Of the exogenous 18∶1Δ9 incorporated, 59% was desaturated to 18∶2Δ9,12 and 18∶3Δ9,12,15. Of the exogenous 16∶0 incorporated, 20% was elongated to 18∶0, while 37% was elongated and desaturated into 18∶1Δ9, 18∶2Δ9,12, and 18∶3Δ9,12,15. The mass of unsaturated fatty acids in phospholipid and triacylglycerol is 12 times greater than the mass of 18∶0. Deuterium
label incorporation in unsaturated fatty acids is only twofold greater than in 18∶0, indicating a sixfold preferential use
of 16∶0 for saturated fatty acid synthesis. These results indicate that the release of 16∶0 from fatty acid synthase is a
key control point that influences fatty acid composition in Neurospora. 相似文献
25.
Ingrid R. Marques Camila Silveira Monique J. L. Leite Artur M. Piacentini Cristiano Binder Marta E. R. Dotto Alan Ambrosi Marco Di Luccio Cristiane da Costa 《应用聚合物科学杂志》2021,138(24):50558
The modification of the surface characteristics after treatment with plasma in polymeric materials, such as the aging phenomenon, calls the attention of research in the area of nonthermal plasma technology. In this work, a direct treatment with dielectric-barrier discharge plasma was used on the surfaces of ultrafiltration membranes. The measurements of the contact angle with water, attenuated total reflectance accessory, zeta potential, atomic force microscopy and scanning electron microscopy-MEV were performed on the surfaces to verify changes after plasma treatment and to understand the occurrence and timing of the plasma aging effect. In the analysis of the membrane performance, hydraulic permeation and protein retention tests were performed. The results showed an improvement in wettability and hydrophilic properties in the post-treated membranes. The study of reversibility/aging of the post-plasma surface is important for research that deals with the modification of polymeric membranes. Changes in surface morphology, topography and wettability of the membranes were observed up to seven days after treatment, with a tendency to return to the initial characteristics of the membranes. 相似文献
26.
The purpose of this study is to analyze the political economy of food-water security in the water-scarce Middle East and North Africa region. The study deploys the lens of virtual water trade to determine how the region's economies have met their rising food-water requirements over the past three decades. It is shown that the region's water and food security currently depend to a considerable extent on water from outside the region, ‘embedded’ in food imports and accessed through trade. The analysis includes blue (surface and groundwater) and green water resources. 相似文献
27.
Marco Riccardi Roberto Di Pietro Marta Palanques Jorge Aguilà Vila 《Computer Networks》2013,57(2):422-435
Malware is one of the main threats to the Internet security in general, and to commercial transactions in particular. However, given the high level of sophistication reached by malware (e.g. usage of encrypted payload and obfuscation techniques), malware detection tools and techniques still call for effective and efficient solutions. In this paper, we address a specific, dreadful, and widely diffused financial malware: Zeus.The contributions of this paper are manifold: first, we propose a technique to break the encrypted malware communications, extracting the keystream used to encrypt such communications; second, we provide a generalization of the proposed keystream extraction technique. Further, we propose Cronus, an IDS that specifically targets Zeus malware. The implementation of Cronus has been experimentally tested on a production network, and its high quality performance and effectiveness are discussed. Finally, we highlight some principles underlying malware—and Zeus in particular—that could pave the way for further investigation in this field. 相似文献
28.
This paper presents an empirical evaluation of coreference resolution that covers several interrelated dimensions. The main goal is to complete the comparative analysis from the SemEval-2010 task on Coreference Resolution in Multiple Languages. To do so, the study restricts the number of languages and systems involved, but extends and deepens the analysis of the system outputs, including a more qualitative discussion. The paper compares three automatic coreference resolution systems for three languages (English, Catalan and Spanish) in four evaluation settings, and using four evaluation measures. Given that our main goal is not to provide a comparison between resolution algorithms, these are merely used as tools to shed light on the different conditions under which coreference resolution is evaluated. Although the dimensions are strongly interdependent, making it very difficult to extract general principles, the study reveals a series of interesting issues in relation to coreference resolution: the portability of systems across languages, the influence of the type and quality of input annotations, and the behavior of the scoring measures. 相似文献
29.
30.
Morphology and structure of the pollen cone and pollen grain of the Araucaria species from Argentina
The pollen cone and the pollen grain of the two Argentinean species of Araucaria are described with LM, SEM and TEM. Primordia of pollen cones are formed in April and May and reach maturity by mid-October in A. angustifolia (Bert.) O. Kuntze and by mid-November in A. araucana. (Mol.) K. Koch. Characters of the mature pollen cones and microsporophylls between both taxa are clearly differentiated. Pollen grains are spheroidal-subspheroidal, inaperturate, and asaccate with granulate exine and a subequatorial annular area that corresponds to the sexine thickness. Sculpturing consists of irregularly dispersed granules that are sometimes fused to each other (A. angustifolia) or forming microrugulae (A. araucana). Microgranules and microspinules are also present. The pollen wall ultrastructure is formed by a granular ectexine and lamellated endexine. Granular elements in A. angustifolia are more loosely disposed, form more interstices, and are gradually smaller towards the endexine than in A. araucana. To asses the probable relationships within the family, we compared the pollen grains of the two Araucaria species with those of other extant genera (Agathis, Wollemia) and also with fossil pollen (Araucariacites, Balmeiopsis, Cyclusphaera, Dilwynites) attributed to Araucariaceae. 相似文献