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排序方式: 共有816条查询结果,搜索用时 46 毫秒
1.
László Lőrincz Máté Zsemberi György Bánsághi Tamás Sohajda Edit Székely 《化学工程与技术》2018,41(7):1466-1472
Chiral molecules, especially enantiomers and diastereomers of purity > 99 %, present a significant market share within the chemical, pharmaceutical, and flavor industries. Antisolvent precipitations, both batch and semicontinuous operations to serve the current trends in flow chemistry were demonstrated to be environmentally benign and efficient tools in achieving high optical purities. Although salts are known to be insoluble in supercritical CO2, instabilities of the nascent salts were detected and applied for increasing efficiency. Diastereomeric excess values of the crystalline products exceeded 99 % in maximum of three consecutive steps both by repeated resolution with half molar equivalent of the amine to the acid and by direct recrystallization of the salts. 相似文献
2.
We determine the exact power of two-prover interactive proof systems introduced by Ben-Or, Goldwasser, Kilian, and Wigderson (1988). In this system, two all-powerful noncommunicating provers convince a randomizing polynomial time verifier in polynomial time that the inputx belongs to the languageL. We show that the class of languages having tow-prover interactive proof systems is nondeterministic exponential time.We also show that to prove membership in languages inEXP, the honest provers need the power ofEXP only.The first part of the proof of the main result extends recent techniques of polynomial extrapolation used in the single prover case by Lund, Fortnow, Karloff, Nisan, and Shamir.The second part is averification scheme for multilinearity of a function in several variables held by an oracle and can be viewed as an independent result onprogram verification. Its proof rests on combinatorial techniques employing a simple isoperimetric inequality for certain graphs: 相似文献
3.
4.
O Biurrun Unzúe A Morelló Castro J Traserra Parareda 《Canadian Metallurgical Quarterly》1997,48(5):363-374
Palatopharyngeal surgery is a therapeutic option for obstructive Sleep Apnea Syndrome (OSAS). This operation is based on the assumption that the soft palate is the principal apneogenic area of the upper airways. The effectiveness of palatopharyngeal surgery and of correcting nasal obstruction (co-adjuvant factor of SAOS), when present, was evaluated. Thirty patients were selected by cephalometry for surgery (3 women, 27 men; age 45.3 +/- 7.5 years). The success rate was 60%, which justifies the inclusion of surgery as a useful option for treating SAOS. 相似文献
5.
OBJECTIVE: To know the variability in the interpretation (normal/pathological) of posteroanterior view chest radiograph and the associated factors between a medical primary care community and a Gold Standard (GS) from 3 reference radiologists. DESIGN: Crossover study. SETTING: Primary care. Teaching health centers of Elche. METHODS: Interobserver percentage agreement (IPA) and Kappa statistic (K) were used to analyse the interobserver agreement (IA) between the GS and every of the participants in interpretation of 100 radiographs. Intraobserver variability was assessed with a second review. Using uni and multivariant analysis some possibly associated factors were studied. RESULTS: Overall IPA and K were 71.3% (CI 95%: 69.2-73.3) and 0.41 (CI 95%: 0.36-0.46) respectively. Time employed in radiographs reading and time passed after medicine studies finished were independently and significantly associated to higher and lower interobserver agreement results respectively, whereas recent professional experience, permanent job and age were not associated. Professional training is the variable that most explain the inter and intraobserver variability. CONCLUSIONS: Overall IA is acceptable. The IA showed by the participants trained under the MIR system is good but the IA achieved by the rest of participants is not acceptable. It is necessary a training which increase the clinical competence, as it does MIR training. 相似文献
6.
The resistance to chemical attack of low water to binder ratio pastes containing silica fume was studied by soaking small paste disks in three different pH controlled solutions, with or without sodium chloride, for periods of up to three months. The pastes were made using water to binder ratios of 0,25 and 0,38. The three solutions in which the paste disks were soaked were the following: 3% NaCl (by weight) at a pH level of 8,5,0% NaCl at 8,5, and 0% NaCl at 4,5. After three months of exposure, the results show that the pH level of the aggressive solution is the most important factor controlling the durability of cement pastes subjected to chemical attack. The total porosity and the depth of decalcification was found to increase with the decrease of the pH level. It was also found that the3water to binder ratio does not significantly affect the deterioration processes, but only influences the kinetics of these processes. The decrease of the water to binder ratio reduces significantly the rate of deterioration. Chloroaluminate crystals were observed only in the cement pastes having a water to binder ratio of 0,38. 相似文献
7.
Castelló E Perna V Wenzel J Borzacconi L Etchebehere C 《Water science and technology》2011,64(11):2265-2273
This study investigated the microbial community developed in a UASB reactor for hydrogen production and correlated it to reactor performance. The reactor was inoculated with kitchen waste compost and fed with raw cheese whey at two organic loading rates, 20 gCOD/Ld and 30 gCOD/Ld. Hydrogen production was very variable, using an OLR of 30 gCOD/Ld averaged 1.0 LH(2)/Ld with no methane produced under these conditions. The hydrogen yield was also very variable and far from the theoretical. This low yield could be explained by selection of a mixed fermentative population with presence of hydrogen producing organisms (Clostridium, Ruminococcus and Enterobacter) and other non-hydrogen producing fermenters (Lactobacillus, Dialister and Prevotella). The molecular analysis of the raw cheese whey used for feeding revealed the presence of three predominant organisms that are affiliated with the genera Buttiauxella (a low-yield hydrogen producer) and Streptococcus (a lactic acid-producing fermenter). Although these organisms did not persist in the reactor, the continuous addition of these fermenters could decrease the reactor's hydrogen yield. 相似文献
8.
Nowadays, the use of Radio Frequency Identification (RFID) systems in industry and stores has increased. Nevertheless, some
of these systems present privacy problems that may discourage potential users. Hence, high confidence and effient privacy
protocols are urgently needed. Previous studies in the literature proposed schemes that are proven to be secure, but they
have scalability problems. A feasible and scalable protocol to guarantee privacy is presented in this paper. The proposed
protocol uses elliptic curve cryptography combined with a zero knowledge-based authentication scheme. An analysis to prove
the system secure, and even forward secure is also provided.
This work is supported by the Generalitat de Catalunya under Grant No. FIC 2007FIC 00880, and the projects of the Spanish
MCyT MTM2007-66842-C02-02 and TIN2006-15662-C02-02. 相似文献
9.
Dworschák E Barna E Gergely A Czuczy P Hóvári J Kontraszti M Gaál O Radnóti L Bíró G Kaltenecker J 《Meat science》1995,39(1):79-86
A new pig genotype of Hungarian Large White (75%) × Mangalica (pig with curly bristles, 25%) was used in the experiments. The experimental group was kept in a farming system under strictly natural circumstances until a body weight of 120 kg was attained. Neither antibiotics nor yield-increasing hormones were given to this group. The control group was kept in the usual large-scale farming conditions until body weight of 120 kg was attained. In most cases, protein, zinc, and copper levels and, in some cases, iron levels were significantly higher in some major cuts (neck-end (Boston-butt), loin, ham) of the 'free-range' pigs (n = 12) in comparison with the control animals kept in large-scale farming conditions. There was, on average, 15% less cholesterol in the muscles and 30% less cholesterol in the liver and less linoleic acid in all tissues of 'free-range' pigs than in the control group. There was less fat, but the amount of thiamin and riboflavin in the liver of the naturally kept pigs was twice that in the controls. In respect of TBA-reactive compounds, there were no significant differences between the two groups, but superoxide dismutase (SOD) showed significantly higher activities in all cuts from pigs kept in a large-scale farming system. This may be the effect of a higher level of linoleic acid in the fat. 相似文献
10.
The emergence of novel radio techniques enables the application of advantageous revolutionary spectrum policies. An important body of research has appeared about possible frequency management schemes, but none of them proposes solutions that meet every related criteria. In this paper we present our work on dynamic spectrum allocation and pricing that offers a distributed mechanism design, well-suited to practical employment issues. Our model handles interference effects without any restricting assumptions, provides universal scalable and incentive-compatible allocation and pricing mechanisms. We provide both analytical and numerical evaluation of the proposed framework, and in either case we prove this latter to be a suitable approach to efficient and flexible spectrum utilization. 相似文献