全文获取类型
收费全文 | 2657篇 |
免费 | 90篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 12篇 |
综合类 | 1篇 |
化学工业 | 242篇 |
金属工艺 | 55篇 |
机械仪表 | 95篇 |
建筑科学 | 18篇 |
能源动力 | 77篇 |
轻工业 | 124篇 |
水利工程 | 4篇 |
石油天然气 | 4篇 |
无线电 | 237篇 |
一般工业技术 | 274篇 |
冶金工业 | 1442篇 |
原子能技术 | 32篇 |
自动化技术 | 135篇 |
出版年
2024年 | 2篇 |
2023年 | 25篇 |
2022年 | 25篇 |
2021年 | 55篇 |
2020年 | 34篇 |
2019年 | 32篇 |
2018年 | 48篇 |
2017年 | 56篇 |
2016年 | 56篇 |
2015年 | 46篇 |
2014年 | 72篇 |
2013年 | 101篇 |
2012年 | 97篇 |
2011年 | 99篇 |
2010年 | 72篇 |
2009年 | 70篇 |
2008年 | 76篇 |
2007年 | 37篇 |
2006年 | 45篇 |
2005年 | 39篇 |
2004年 | 52篇 |
2003年 | 42篇 |
2002年 | 27篇 |
2001年 | 21篇 |
2000年 | 26篇 |
1999年 | 60篇 |
1998年 | 491篇 |
1997年 | 288篇 |
1996年 | 177篇 |
1995年 | 84篇 |
1994年 | 75篇 |
1993年 | 81篇 |
1992年 | 11篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 25篇 |
1988年 | 23篇 |
1987年 | 29篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1978年 | 2篇 |
1977年 | 22篇 |
1976年 | 43篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2752条查询结果,搜索用时 15 毫秒
41.
Formal Proofs for the Security of Signcryption 总被引:2,自引:0,他引:2
Signcryption is an asymmetric cryptographic method that provides simultaneously both message confidentiality and unforgeability
at a low computational and communication overhead. In this paper we propose realistic security models for signcryption, which
give the attacker power to choose both messages/signcryptexts as well as recipient/sender public keys when accessing the signcryption/unsigncryption
oracles of attacked entities. We then show that Zheng's original signcryption scheme is secure in our confidentiality model
relative to the Gap Diffie-Hellman problem and is secure in our unforgeability model relative to a Gap version of the discrete
logarithm problem. All these results are shown in the random oracle model. 相似文献
42.
Two percept-genetic methods, the Meta-Contrast Technique (MCT) and the Serial Afterimage Test (AI), were used to study adaptive aspects of perception in a group of 37 subjects suffering from manifest anxiety. The perceptual processes laid bare by these methods reflected not only anxiety but also defensive formations. MCT and AI correlated with each other in these respects and, when combined, correlated with rated symptoms. In accordance with the theory behind percept-genetic methods, anxiety signs appearing late in the test serials were more likely to correspond to manifest symptoms than signs which appeared early. The AI test scores seemed to reflect a difference between anxiety experienced as an inherent quality of life and anxiety as a foreign force struggling for dominance. 相似文献
43.
The activated coagulation time (ACT) test is technically simple, inexpensive, and commercially available and provides a rapid, accurate assessment of canine whole blood clotting time. The medium ACT for 72 normal dogs ranging in age from 6 monhts to 11 years was 75 seconds, with a range of from less than 60 seconds to 125 seconds and a mean of 77.5 seconds. Significant difference in the ACT due to sex or age of the animals tested was not found. 相似文献
44.
Based on the hitherto published population data of the human red cell PGM1 and acid phosphatase polymorphisms, the geographical distributions of their gene frequencies were analyzed. As far as the acid phosphatase alleles are concerned, a marked geographical gradient was found as the Pa and Pb alleles showed significant correlations with the mean annual temperatures of the various human biotopes (Pa:r = -0.706; Pb:r = +0.812). Against that, the world distribution of the PGM1 alleles did not show a comparable correlation (PGM1 1:R = +0.063; PGM2 1:R = -0.063). The possible reasons for the distribution pattern of the acid phosphatase alleles are discussed. 相似文献
45.
Vivek K. Bajpai Ajay Sharma Kwang‐Hyun Baek 《International Journal of Food Science & Technology》2013,48(11):2300-2305
This study investigated the antibacterial mechanism of action of the seed essential oil of Eleutherococcus senticosus (ESEO) against foodborne pathogenic bacteria. Preliminarily, the ESEO (1000 μg disc?1) showed potential antibacterial effect as diameter of inhibition zones (12.0 ± 0.2–37.0 ± 2.0 mm) against the tested foodborne pathogens. The MIC and MBC values of ESEO against the tested bacteria were found in the range of 125–500 and 500–1000 μg mL?1, respectively. At MIC concentration, the ESEO had potential inhibitory effect on the cell viability of the tested pathogens. In addition, SEM analysis showed the inhibitory effect of ESEO as confirmed by considerable morphological alterations on the cell wall of B. cereus ATCC 13061 and E. coli O157:H7 ATCC 43889. Moreover, the ESEO revealed its mode of action against foodborne pathogens on membrane integrity as confirmed by release of extracellular ATP, 260‐nm absorbing materials and leakage of potassium ions. These findings confirm that the ESEO can be used as a potential antibacterial agent in food industry to inhibit the growth of various foodborne pathogens. 相似文献
46.
Changho Lee Daeseok Han Byoungmok Kim Namin Baek Byung‐Kee Baik 《International Journal of Food Science & Technology》2013,48(5):984-991
Anthocyanin‐rich acetone extracts of barley grain of four hulless pigmented genotypes were investigated to determine their potential as functional food ingredients. The purple barley cultivar contained 11 anthocyanins, whereas only one anthocyanin, peonidin derivative, was observed in blue, black and yellow barley. The total anthocyanin content of pigmented barley genotypes ranged from 3.2 to 678.5 mg kg?1 in whole grain and from 4.5 to 1654.6 mg kg?1 in bran. The purple barley bran extract gave the highest DPPH radical scavenging capacity, superoxide radical scavenging capacity and total antioxidant activity. The half maximal inhibitory concentration (IC50) of angiotensin I‐converting enzyme (ACE) of anthocyanin‐rich extract of purple barley grain and bran was 8.77 and 4.54 mg mL?1, respectively. Purple barley appears to have great potential uses for the promotion of human health and development of nutraceuticals and functional foods. 相似文献
47.
Slowly digestible sweetpotato flour: Preparation by heat-moisture treatment and characterization of physicochemical properties 总被引:2,自引:0,他引:2
Ji Hong Ahn Hye Rim Baek Kyung Mi Kim Gui Jung Han Jun Bong Choi Yang Kim Tae Wha Moon 《Food science and biotechnology》2013,22(2):383-391
The preparation and physicochemical characteristics of sweetpotato flour with increased slowly digestible starch (SDS) fraction were investigated under various heat-moisture treatment (HMT) conditions. The optimum conditions for preparing slowly digestible sweetpotato flour established using response surface methodology were moisture content of 22%, temperature of 103°C, and treatment time of 5.8 h. The highest SDS content in heat-moisture treated sweetpotato flour was 57.6%. The relative crystallinity of heat-moisture treated sweetpotato flour decreased, but the X-ray diffraction pattern maintained the A-type. The DSC of the heatmoisture treated flour showed a decreased gelatinization temperature range and gelatinization enthalpy compared with native one. The viscosity profiles and values changed significantly with HMT, resulting in a higher pasting temperature, decrease of the viscosity values, and no breakdown. It indicates that heat-moisture treated sweetpotato flour is more stable at high temperatures and shear rates than native one. 相似文献
48.
Cui En-Ji Song Na-Young Shrestha Sabina Chung In-Sik Kim Ji-Young Jeong Tae-Sook Baek Nam-In 《Food science and biotechnology》2012,21(2):619-624
Six flavonoid glycosides were isolated from the n-butanol fraction of cowpea seeds (Vigna sinensis K.) through silica gel (SiO2) and octadecyl silica gel (ODS) column chromatographies. Based on their chemical structures determined via interpretation
of spectroscopic data including NMR, MS, and IR, the compounds were identified as kaempferol 3-O-β-d-sophoroside (1), quercetin 3-O-β-d-sophoroside (2), isoquercitrin (3), hyperin (4), catechin 7-O-β-d-glucopyranoside (5), and quercetin 3-O-β-Dglucopyranosyl( 1→6)-O-β-d-galactopyranoside (6). This is the first report of the isolation of these flavonoids from this plant. Among these flavonoids, compound 2, 5, and 6 significantly inhibited LDL oxidation exhibiting 96.0±0.1 (IC50: 3.9 μM), 96.8±1.7 (IC50: 2.9 μM), and 97.4±0.1% (IC50: 3.5 μM) inhibition, respectively, at a concentration of 40 μM. 相似文献
49.
Three-year atmospheric monitoring of organochlorine pesticides and polychlorinated biphenyls in polar regions and the South Pacific 总被引:4,自引:0,他引:4
XAD-2 resin based passive air samplers (PAS) were deployed for three one-year periods at the Korean polar and South Pacific research stations at Ny-?lesund (2005-2009), King George Island (2005-2007), and Chuuk (2006-2009) to investigate long-range transport, local sources, and temporal trends of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). The highest hexachlocyclohexane (HCH) concentration (35.2-78.9 pg·m(-3)) over the entire sampling period was detected at Ny-?lesund, in the Arctic. α-HCH was the dominant OCP (31.1-67.1 pg·m(-3)), contributing about 50% of the total OCP load. Additionally, a high and consistent α/γ-HCH ratio was observed at Ny-?lesund. HCHs might reach Arctic sites more easily than other OCPs from surrounding countries through long-range atmospheric transport (LRAT). Interestingly, high levels of the current-use OCP endosulfan-particularly endosulfan-I--were detected at almost all sampling sites, including in Antarctica, ranging 12.2-88.5, 17.7-130, and ND-59.7 pg·m(-3) at King George Island, Ny-?lesund, and Chuuk, respectively. Specific OCP and PCB patterns, such as low trans/cis-chlordane ratios and a prevalence of lighter PCB congeners, were observed in all three regions (excepting one site at Ny-?lesund and one site in the South Pacific affected by local sources) during all sampling periods. This indicates that these Polar and remote South Pacific sites are mainly influenced by LRAT. Over the entire sampling period, a decreasing trend of HCHs (α- and γ-HCH) and an increasing trend of endosulfan-I were observed at the Ny-?lesund sites. 相似文献
50.
Khan MA Lee HJ Lee WS Kim HS Kim SB Park SB Baek KS Ha JK Choi YJ 《Journal of dairy science》2008,91(3):1140-1149
Ruminal parameters, rumen development, nutrient digestibilities, and N utilization were estimated in Holstein calves fed starch from different sources. Ground corn, ground barley, ground wheat, and crimped oats were used to formulate 4 isostarch (25% of starter dry matter) pelleted diets. These diets were randomly allocated to calves (16 calves per treatment, 8 female and 8 male) and fed ad libitum along with mixed grass hay throughout the experiment. Ruminal contents and blood were sampled at d 35, 50, and 70 of age to estimate ruminal parameters and plasma β-hydroxybutyrate, respectively. At d 70, twenty-four male calves (6/treatment) were randomly selected, euthanized, and forestomach weight, papillae length (PL), papillae width (PW), rumen wall thickness (RWT), and papillae concentration were measured. At d 63, twenty-four female calves (6/treatment) were randomly selected and moved to metabolism stalls to estimate total tract apparent nutrient digestibilities and N utilization. Female calves were given 2 wk for adaptation to experimental facilities and then total collections of feces and urine were made from d 77 to 84 of age. Ruminal pH at d 35 of age was higher in calves fed corn and oat diets than in those fed barley and wheat diets. Ruminal pH at d 50 and 70 of age was the lowest in calves on barley diets followed by those on oat and wheat diets and then by those on the corn diet. Ruminal total volatile fatty acid concentrations at d 35 of age were greatest in calves fed corn or wheat diets followed by those fed barley and oat diets. Calves on corn and wheat diets maintained greater ruminal volatile fatty acids concentrations at d 50 and 70 of age. Ruminal ammonia, acetate, propionate, butyrate, and blood β-hydroxybutyrate concentrations were also greater in calves on the corn and wheat diets. Full and empty weights of forestomach, PL, PW, RWT, and papillae concentrations were greater in calves on corn and wheat diets. Daily average intake of nutrients (dry matter, crude protein, neutral detergent fiber, starch, Ca, and P) was greater in calves fed corn and wheat diets than in those fed barley and oat diets. Starch source did not influence the total tract apparent digestibilities of nutrients in calves. Daily N retention (g/d) was greatest on the corn diet followed by the wheat diet and then the barley and oat diets. In conclusion, calves on a corn diet have greater ruminal capacity to accommodate feed bulk. More physically and metabolically functional rumens in calves on corn and wheat diets probably resulted in greater feed consumption and N retention. 相似文献