全文获取类型
收费全文 | 7482篇 |
免费 | 397篇 |
国内免费 | 54篇 |
专业分类
电工技术 | 142篇 |
综合类 | 26篇 |
化学工业 | 1931篇 |
金属工艺 | 124篇 |
机械仪表 | 220篇 |
建筑科学 | 284篇 |
矿业工程 | 6篇 |
能源动力 | 505篇 |
轻工业 | 738篇 |
水利工程 | 79篇 |
石油天然气 | 118篇 |
无线电 | 714篇 |
一般工业技术 | 1223篇 |
冶金工业 | 352篇 |
原子能技术 | 84篇 |
自动化技术 | 1387篇 |
出版年
2024年 | 25篇 |
2023年 | 157篇 |
2022年 | 325篇 |
2021年 | 424篇 |
2020年 | 311篇 |
2019年 | 351篇 |
2018年 | 435篇 |
2017年 | 376篇 |
2016年 | 376篇 |
2015年 | 250篇 |
2014年 | 342篇 |
2013年 | 684篇 |
2012年 | 387篇 |
2011年 | 529篇 |
2010年 | 396篇 |
2009年 | 338篇 |
2008年 | 302篇 |
2007年 | 234篇 |
2006年 | 205篇 |
2005年 | 155篇 |
2004年 | 131篇 |
2003年 | 126篇 |
2002年 | 113篇 |
2001年 | 67篇 |
2000年 | 74篇 |
1999年 | 50篇 |
1998年 | 79篇 |
1997年 | 43篇 |
1996年 | 49篇 |
1995年 | 42篇 |
1994年 | 36篇 |
1993年 | 47篇 |
1992年 | 36篇 |
1991年 | 33篇 |
1990年 | 30篇 |
1989年 | 21篇 |
1988年 | 35篇 |
1987年 | 31篇 |
1986年 | 23篇 |
1985年 | 18篇 |
1984年 | 27篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 17篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1976年 | 20篇 |
1975年 | 19篇 |
排序方式: 共有7933条查询结果,搜索用时 31 毫秒
951.
Tests have been performed to assess feasibility of using the impact-echo method (IEM) and ultrasonic pulse velocity method (UPVM) in detecting flaws and evaluating their depths on the early stage of a concrete structure's service life. Five reinforced concrete (RC) slabs of grades 25, 30, 40, and 50 with fabricated voids at known locations were studied on the 3rd, 7th, 14th, and 28th day. The results were compared to estimate the accuracy of both methods and their efficiency. Both methods detected flaws in the tested samples on the early stages of their operation. Depth measurements of flaws by IEM, however, are more accurate. Results of our tests indicate that both methods can be used in determining depths of flaws in concrete and in performing on-site tests. The accuracy of both methods proved to be better in tests of stronger concretes, and the detection probability ranged from 51.81 to 99.8% after aging during 3 to 28 days under full load, respectively. 相似文献
952.
The spectrophotometric assay of 2,4-dienoyl coenzyme A (CoA) reductase (EC 1.1.1.34) was modified to improve the linearity
and sensitivity of this method. 5-Phenyl-2,4-pentadienoyl-CoA, which has an absorbance maximum at 340 nm with an extinction
coefficient of 44,300 M−1 cm−1, was synthesized and used as substrate. This compound is reduced by nicotinamide adenine dinucleotide phosphate (NADPH)-dependent
2,4-dienoyl-CoA reductase to 5-phenyl-3-pentenoyl-CoA. When a tissue homogenate serves as an enzyme source, the product is
further metabolized by Δ3Δ2-enoyl-CoA isomerase (EC 5.3.3.8) to 5-phenyl-2-pentenoyl-CoA, which is hydrated to 5-phenyl-3-hydroxypentanoyl-CoA by enoyl-CoA
hydratase (EC 4.2.1.17). The modified assay method, which measures the decrease in absorbance at 340 nm due to the reduction
of 5-phenyl-2,4-pentadienoyl-CoA and the oxidation of NADPH, is linear for a longer period of time and is twice as sensitive
as the conventional assay with 2,4-decadienoyl-CoA as substrate. 相似文献
953.
Fatma S. D. Harb Mohamed M. El Nady Janette S. Basta 《Petroleum Science and Technology》2003,21(9):1583-1600
Physical and specific geochemical analyses are used in detail for the petroleum geochemical studies to permit the correlation of six crude oil samples from Western Desert Egypt. Different analytical techniques, including liquid chromatographic separation, gas chromatography, and gas chromatography-mass spectrometry (GC-MS), were used to characterize the oil samples. The oils were identified using oil characterization parameters including specific gravity (°API), sulfur content, distribution of n-alkanes, carbon preference index (CPI), pristane/phytane ratio, isoprenoid/n-alkane ratios, and detailed biological marker analysis. All these parameters showed that the studied oil samples are correlated with each other, where they are similar in their oil type maturation and source depositional environments. 相似文献
954.
The authors used lexical decision in a dichotic listening situation and measured identity priming across channels to explore whether unattended stimuli can be processed lexically. In 6 experiments, temporal synchronization of prime and target words was manipulated, and acoustic saliency of the unattended prime was varied by embedding it in a carrier sentence or in babble speech. When the prime was acoustically salient, a cross-channel priming effect emerged, and participants were aware of the prime. When the prime was less salient, no identity priming was found, and participants failed to notice the prime. Saliency was manipulated in ways that did not degrade the prime. Results are inconsistent with models of late filtering, which predict equal priming irrespective of prime saliency. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
955.
Experiments were conducted on electrodeposited (ED) nanocrystalline (nc) Ni with an average initial grain size of about 20 nm
at 393 K to study the shape of the creep curves. In addition, microstructure was examined by means of transmission electron
microscopy (TEM). The results show that the creep curves are characterized by the presence of a well-defined steady-state
stage. An examination of the microstructure indicates that while grain growth occurs during deformation, the grain size attains
a constant value once steady state creep is approached. A comparison between grain size measurements obtained by the TEM technique
and those obtained via the X-ray diffraction method shows that the use of the latter method may lead to an underestimation
of the value of the average grain size. 相似文献
956.
Maxime Wack Ahmed Nait-Sidi-Moh Sid Lamrous Nathanael Cottin 《Artificial Intelligence and Law》2006,14(3):161-175
Legal information certification and secured storage combined with documents electronic signature are of great interest when
digital documents security and conservation are in concern. Therefore, these new and evolving technologies offer powerful
abilities, such as identification, authentication and certification. The latter contribute to increase the global security
of legal digital archives conservation and access. However, currently used cryptographic and hash coding concepts cannot intrinsically
enclose cognitive information about both the signer and the signed content. Indeed, an evolution of these technologies may
be necessary to achieve full text researches within hundreds or thousands of electronically signed documents. This article
aims at describing a possible model along with associated processes to create and make use of these new electronic signatures
called “meaningful electronic signatures” as opposed to traditional electronic signatures based on bit per bit computation. 相似文献
957.
V Ratanatharathorn C Karanes J Uberti LG Lum MM de Planque KR Schultz S Cronin ME Dan A Mohamed M Hussein 《Canadian Metallurgical Quarterly》1993,81(8):2194-2199
Preparative regimens containing busulfan (BU) followed by allogeneic bone marrow transplantation (BMT) were used in 27 consecutive patients with myelodysplastic syndromes (MDS). The median age was 33 years (range, 4 to 54). Ten were female and 17 male. Sixteen patients had primary MDS, 11 other patients had antecedent hematologic diseases or developed MDS after cytotoxic and/or radiation therapy. Six patients had leukemic transformation and received antileukemic therapy before BMT. Pre-BMT cytogenetic studies showed complex chromosomal abnormalities in 13 patients, a simple abnormality in 5 patients, and normal chromosome in 8 patients. Three BU-based preparative regimens were used: 1 patient received BU 4 mg/kg orally (PO) daily for 4 days and cyclophosphamide (CY) 50 mg/kg intravenously (IV) daily for 4 days (BUCY-4); 24 patients received BU 4 mg/kg PO daily for 4 days, cytosine arabinoside (ara-C) 2 g/m2 IV every 12 hours for 4 doses, and CY 60 mg/kg IV daily for 2 days (BAC); and 2 patients with preceding Fanconi anemia received BU 2 mg/kg PO daily for 4 days followed by total lymphoid irradiation of 5 Gy. Seventeen of 27 patients are alive with no evidence of disease. Ten patients have died: 2 from hepatic veno-occlusive disease, 3 from sepsis, 1 from a cerebral bleed, 1 from a massive gastrointestinal (GI) bleed associated with acute graft-versus-host disease, 1 from hemolytic uremic syndrome with adult respiratory distress syndrome, 1 from bronchiolitis obliterans, and the only patient who did not engraft died from acute myeloid leukemia. Regimen-related toxicities (RRT) include GI tract (diarrhea, 14; stomatitis, 11), liver (9), cardiac (1), and skin (5). Patients who received a genotypically matched marrow graft had a significantly better disease-free survival (DFS) than patients who received a nongenotypic marrow graft (P = .02). The Kaplan-Meier analysis projects an overall DFS of 56% +/- 13% and 78% +/- 10% for patients who received a genotypically matched marrow graft. With the exception of a child who did not engraft, there was no relapse of MDS or leukemia. Excellent DFS, acceptable RRT, and the ease of administration are advantages of this regimen. 相似文献
958.
Mohamed N. Rahaman Lutgard C. De Jonghe May-Ying Chu 《Journal of the American Ceramic Society》1988,71(5):237-C
A thin cylindrical powder compact (3-mm diameter by 20-mm) with a nominal composition of YBa2 Cu3 Ox was sintered in a static temperature gradient of 25°C/mm in air for 12 h. The temperature at the hot end of the sample was maintained at 940°±5°C. Considerable mass transport and chemical demixing occurred along the length of the sample. The results are consistent with the formation of a liquid phase at the hot end of the sample, transport of the liquid down the temperature gradient, and the formation of different eutectic compositions along the length of the sample. The implications for processing high-Tc superconductors in the system Y-Ba-Cu-O are discussed. 相似文献
959.
Adams Kong Author Vitae King-Hong Cheung Author Vitae Author Vitae Mohamed Kamel Author Vitae Author Vitae 《Pattern recognition》2006,39(7):1359-1368
As a result of the growing demand for accurate and reliable personal authentication, biometric recognition, a substitute for or complement to existing authentication technologies, has attracted considerable attention. It has recently been reported that, along with its variants, BioHashing, a new technique that combines biometric features and a tokenized (pseudo-) random number (TRN), has achieved perfect accuracy, having zero equal error rates (EER) for faces, fingerprints and palmprints. There are, however, anomalies in this approach. These are identified in this paper, in which we systematically analyze the details of the approach and conclude that the claim of having achieved a zero EER is based upon an impractical hidden assumption. We simulate the claimants’ experiments and find that it is not possible to achieve their reported performance without the hidden assumption and that, indeed, the results are worse than when using the biometric alone. 相似文献
960.
Mohamed M. Omar 《Food chemistry》1984,15(1):19-29
The physical state of the protein in Ras cheese has been followed by TEM and SEM in parallel with the chemical changes during maturation. The microstructure of young Ras cheese, by TEM, consists of casein micelles joined to form an open network, with some clustering of the micelles that appear, by SEM, as thin fibres aggregated into cross-linked elongated strands. At higher magnification, the casein fibres appear folded to include cavities.With further maturation to 4 months, the cheese matrix changed considerably by dissociation of the casein micelles to form a more homogeneous structure of sub-micelles, as seen by TEM, whilst SEM micrographs indicated that some protein fibres still existed.The protein breakdown, the accumulation of free amino acids and the liberation of free fatty acids in Ras cheese increased during maturation by decomposition of paracasein and cheese fat.Ras cheese is characterized as a compact body but can be viewed as an extensive inter-connection between the casein sheets in a cheese matrix and by a sharp flavour attributed to free glutamic acid and the presence of butyric, caprylic and caproic (free volatile) fatty acids. 相似文献