全文获取类型
收费全文 | 10188篇 |
免费 | 811篇 |
国内免费 | 215篇 |
专业分类
电工技术 | 452篇 |
技术理论 | 1篇 |
综合类 | 492篇 |
化学工业 | 2048篇 |
金属工艺 | 342篇 |
机械仪表 | 514篇 |
建筑科学 | 609篇 |
矿业工程 | 217篇 |
能源动力 | 310篇 |
轻工业 | 1143篇 |
水利工程 | 144篇 |
石油天然气 | 461篇 |
武器工业 | 52篇 |
无线电 | 852篇 |
一般工业技术 | 1268篇 |
冶金工业 | 726篇 |
原子能技术 | 60篇 |
自动化技术 | 1523篇 |
出版年
2024年 | 39篇 |
2023年 | 148篇 |
2022年 | 259篇 |
2021年 | 423篇 |
2020年 | 309篇 |
2019年 | 311篇 |
2018年 | 340篇 |
2017年 | 362篇 |
2016年 | 350篇 |
2015年 | 367篇 |
2014年 | 512篇 |
2013年 | 716篇 |
2012年 | 652篇 |
2011年 | 734篇 |
2010年 | 600篇 |
2009年 | 554篇 |
2008年 | 526篇 |
2007年 | 508篇 |
2006年 | 510篇 |
2005年 | 377篇 |
2004年 | 285篇 |
2003年 | 257篇 |
2002年 | 235篇 |
2001年 | 231篇 |
2000年 | 196篇 |
1999年 | 199篇 |
1998年 | 271篇 |
1997年 | 200篇 |
1996年 | 145篇 |
1995年 | 118篇 |
1994年 | 99篇 |
1993年 | 77篇 |
1992年 | 38篇 |
1991年 | 32篇 |
1990年 | 24篇 |
1989年 | 24篇 |
1988年 | 27篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 22篇 |
1982年 | 14篇 |
1981年 | 5篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 5篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Molecular dynamics (MD) simulations of-Al2O3, using a pairwise additive interaction potential of Pauling's type with four different radii for aluminum atoms, were analysed in order to determine the influence of the radius on the modification of coordination numbers of A1 relative to the ideal structure, at two different temperatures of 300 and 1500 K. It is found that the best choice is the radius of penta-coordinated aluminum, reproducing structural and vibrational properties of the compound in excellent agreement with experimentally observed properties. 相似文献
122.
123.
Zhong-Ni Wang Gan-Zuo Li Jian-Hai Mu Wen-Xia Zhang 《Journal of surfactants and detergents》2002,5(4):391-396
The interaction and synergism of some polyoxyethylenated fatty alcohol ether (POE) nonionic surfactants (C12E2, C12E3, C10E5, C10E7, where Cx indicates number of carbon atoms in the chain and Ey indicates number of oxyethylene glycol ethers) with trioxyethylenated dodecyl sulfonate (C12E3S) in mixed monolayer formation at the surface and in mixed micelle formation in aqueous solutions were studied at 25 and
40°C by calculating interaction parameters (βα, βM) from surface tension-concentration data by use of Rosen's equations based on the nonideal solution theory. All the systems
investigated adapt reasonably well to the nonideal model, with negative values of βσ and βM (where M means micelle and σ refers to the air-liquid interface) indicating a favorable interaction between the mixed surfactants.
Either at a monolayer or in a mixed micelle, the attractive interaction becomes stronger when the alkyl chain in the POE surfactant
is longer, i.e., when the POE becomes more hydrophobic. The interaction increases in the order C10E7<C10E5<C12E3, C12E2. For the two C10E
n
(n= 5,7)/C12E3S systems, as temperature increases from 25 to 40°C, the interaction increases in a mixed micelle, but it decreases in a mixed
monolayer. Synergism in mixed micelle formation exists for C12E3S/C10E
n
mixtures when X1
M
, the mole fraction of POE in a mixed micelle, is ≈0.4–0.8, whereas synergism does not occur in the systems of C12E3S/C12E
m
due to the large difference between CMC1 and CMC2, i.e., large |In(C
1
M
/C
2
M
)| value (where CMC=critical micelle concentration). The degree of synergism in mixed micelle formation is temperature independent
and is 0.23, 0.18, and close to zero for C10E5/C12E3S, C10E7/C12E3S, and C12E
m
(m=2,3)/C12E3S systems, respectively. Synergism in surface tension reduction effectiveness occurs in C12E3S/C12E2 and C12E3S/C12E3 systems. The mole fractions of POE in the solution phase are 0.302 and 0.333 for the two mixtures at the point of maximum
synergism. 相似文献
124.
Jose Saldana Julián Fernández-Navajas José Ruiz-Mas Eduardo Viruete-Navarro Luis Casadesus 《Multimedia Tools and Applications》2014,71(3):1823-1856
First Person Shooters are a genre of online games in which users demand a high interactivity, because the actions and the movements are very fast. They usually generate high rates of small packets which have to be delivered to the server within a deadline. When the traffic of a number of players shares the same link, these flows can be aggregated in order to save bandwidth. Certain multiplexing techniques are able to merge a number of packets, in a similar way to voice trunking, creating a bundle which is transmitted using a tunnel. In addition, the headers of the original packets can be compressed by means of standard algorithms. The characteristics of the buffers of the routers which deliver these bundled packets may have a strong influence on the network impairments (mainly delay, jitter and packet loss) which determine the quality of the game. A subjective quality estimator has been used in order to study the mutual influence of the buffer and multiplexing techniques. Taking into account that there exist buffers which size is measured in terms of bytes, and others measured in packets, both kinds of buffers have been tested, using different sizes. Traces from real game parties have been merged in order to obtain the traffic of 20 simultaneous players sharing the same Internet access. The delay and jitter produced by the buffer of the access router have been obtained using simulations. In general, the quality is expected to be reduced as the background traffic grows, but the results show an anomalous region in which the quality rises with the background traffic amount. Small buffers present better subjective quality results than bigger ones. When the total traffic amount gets above the available bandwidth, the buffers measured in bytes add to the packets a fixed delay, which grows with buffer size. They present a jitter peak when the offered traffic is roughly the link capacity. On the other hand, buffers which size is measured in packets add a smaller delay, but they increase packet loss for gaming traffic. The obtained results illustrate the need of knowing the characteristics of the buffer in order to make the correct decision about traffic multiplexing. As a conclusion, it would be interesting for game developers to identify the behaviour of the router buffer so as to adapt the traffic to it. 相似文献
125.
The different melting temperatures of N‐methyl morpholine N‐oxide (NMMO) hydrates in the cellulose–NMMO hydrate solution may be explained by the rather different crystal structures of NMMO hydrates, which are determined by the amount of the hydrates. The preparative process of cellulose–NMMO hydrate solution may result in cellulose structural change from cellulose I to cellulose II, depending on the amount of the hydrate. Mixtures of cellulose and NMMO hydrate in a blender was changed from the granules to slurry with increasing mixing time at 60–70°C, which is below the melting point of the NMMO hydrate. In the case of 15 wt % cellulose–NMMO hydrate granules, which were made by mixing for 20 min, the melting points of various NMMO hydrates were obtained as 77.8°C (n = 0.83), 70.2°C (n = 0.97), and 69.7°C (n = 1.23), respectively, depending on the hydrate number. However, the melting points of cellulose–NMMO hydrate slurry and solution were shifted lower than those of cellulose granules, while the mixing time of slurry and solution are 25 and 35 min, respectively. These melting behaviors indicate instantaneous liquefaction of the NMMO hydrate and the diffusion of the NMMO hydrate into cellulose during mixing in a blender. When cellulose was completely dissolved in NMMO hydrate, the crystal structure of cellulose showed only cellulose II structure. In the cellulose–NMMO products of granules or slurry obtained by high‐speed mixing, which is a new preparation method, they still retained the original cellulose I structure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1687–1697, 2004 相似文献
126.
Fabrication and characterization of PFSI/ePTFE composite proton exchange membranes of polymer electrolyte fuel cells 总被引:1,自引:0,他引:1
PFSI/ePTFE composite proton exchange membranes were fabricated by impregnating perfluorosulfonic acid resin (PFSI resin, Nafion) into chemically modified expanded PTFE (ePTFE) matrix. Chemical modification of sodium-naphthalene treatment and N-methylol acrylamide (NMA) grafting decreased the contact angle of the as-received ePTFE from 125 ± 0.5° to 67 ± 0.5°, effectively converting the as-received hydrophobic ePTFE to a hydrophilic ePTFE matrix. The composite membrane fabricated with the hydrophilic ePTFE have higher impregnated PFSI loading, much lower porosity and better PTFE/PFSI interface contact, as compared to the composite membranes with the as-received ePTFE. This leads to much lower gas permeability and significantly improves the durability under an accelerated dry/wet cycle test. The fuel cell made from the PFSI/ePTFE composite membranes with hydrophilic ePTFE showed superior performance as compared to that with the composite membrane made from the as-received ePTFE and Nafion 211 membrane. 相似文献
127.
灭多威在棉花及土壤中降解动态及残留量研究 总被引:6,自引:0,他引:6
按生产上常规用量,每亩喷施20%灭多威乳油60毫升防治二代棉铃虫,施药后7天在棉叶上及14天在土壤中其降解率分别为98.81%及88.09%;半衰期分别的1.56天及4.98天。防治二、三、四代棉铃虫,按有效剂量施药6次,有效成分72克/亩,棉籽和土壤中的最大残留量分别为0.023及0.084微克/克;再加大50%用量,有效成分108克/亩,最大残留量仅为0.034及0.214微克/克。结果表明,灭多威在棉叶上及土壤中降解较迅速,常规用量下,对棉籽及土壤污染较轻。 相似文献
128.
129.
果酸脂质体的制备、检测及应用 总被引:3,自引:0,他引:3
以大豆卵磷脂为包封材料 ,用反相蒸发法制备果酸脂质体。并用透射电子显微镜表征了其形态结构 ,证实其直径在1 0 0纳米~ 2 0 0纳米之间。研究了果酸浓度对包封率 ,稳定剂浓度对脂质体稳定性的影响。结果表明 ,果酸浓度为 0 .3mg/ml时可以得到较好的包封率 ,丙二醇的适宜浓度是 5 % -1 5 % ,最终将脂质体应用于化妆品中 ,并证明是可行的 相似文献
130.
Rgia Maria Cordeiro Brito Alzir Azevedo Batista Javier Ellena Eduardo E. Castellano Izaura Cirino Nogueira Digenes Luiz Gonzaga de Frana Lopes Jackson Rodrigues de Sousa Ícaro de Sousa Moreira 《Inorganic chemistry communications》2007,10(12):1515-1517
The cis-[Ru(dppb)(Me-bipy)(NCS)2], dppb = 1,4-bis (diphenylphosphino)butane, Me-bipy = 4,4′-dimethyl-2,2′-bipyridine, and NCS = thiocyanate, was synthesized and characterized by spectroscopic and electrochemical techniques and its structure was determined by crystal X-ray analysis. The crystal structure reveals that the coordination geometry around the Ru(II) center is distorted octahedron where two molecules of thiocyanate are bonded to the ruthenium through nitrogen atom in cis orientation. The half-wave formal potential value E1/2 = 0.8 V (versus Ag/AgCl) observed is considerable higher than that for the cis-[RuCl2(dppb)(Me-bipy)] complex, E1/2 = 0.6 V (versus Ag/AgCl), well illustrating the strong π-acceptor effect the NCS ligand toward the backbonding interaction with the Ru(II) metal center. The MLCT absorption bands of the thiocyanate complex present a higher molar absorptivity (about 12%) compared with the cis-[RuCl2(dppb)(Me-bipy)] complex, in the same experimental conditions. These properties make the complex potentially promising for the photosensitization process. 相似文献