全文获取类型
收费全文 | 42903篇 |
免费 | 15127篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 797篇 |
综合类 | 7篇 |
化学工业 | 18643篇 |
金属工艺 | 386篇 |
机械仪表 | 827篇 |
建筑科学 | 1910篇 |
矿业工程 | 10篇 |
能源动力 | 1036篇 |
轻工业 | 7892篇 |
水利工程 | 322篇 |
石油天然气 | 63篇 |
无线电 | 7210篇 |
一般工业技术 | 12394篇 |
冶金工业 | 1158篇 |
原子能技术 | 42篇 |
自动化技术 | 5342篇 |
出版年
2024年 | 18篇 |
2023年 | 91篇 |
2022年 | 275篇 |
2021年 | 646篇 |
2020年 | 1612篇 |
2019年 | 3355篇 |
2018年 | 3321篇 |
2017年 | 3597篇 |
2016年 | 4139篇 |
2015年 | 4139篇 |
2014年 | 4135篇 |
2013年 | 5345篇 |
2012年 | 3045篇 |
2011年 | 2799篇 |
2010年 | 2922篇 |
2009年 | 2772篇 |
2008年 | 2363篇 |
2007年 | 2152篇 |
2006年 | 1829篇 |
2005年 | 1534篇 |
2004年 | 1493篇 |
2003年 | 1433篇 |
2002年 | 1355篇 |
2001年 | 1159篇 |
2000年 | 1116篇 |
1999年 | 512篇 |
1998年 | 150篇 |
1997年 | 136篇 |
1996年 | 91篇 |
1995年 | 57篇 |
1994年 | 57篇 |
1993年 | 59篇 |
1992年 | 50篇 |
1991年 | 36篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 19篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 19篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 19篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
251.
Polyurethane acrylate anionomer (PUAA)/silica composite gels were prepared by the sol‐gel reaction of tetraethoxysilane (TEOS) and methacryloxypropyl trimethoxysilane (MPTS) incorporated to PUAA gels by using a swelling method. The formation and structure of composites were confirmed by FTIR, X‐ray diffraction, and SEM. As a result, we found that silica components in composites are located within the ionic domains of their gels and interacted with PUAA via hydrogen bonding. This drastically enhanced the mechanical properties of the composites. Mechanical properties are also improved by MPTS, because MPTS improves the dispersibility and adhesion of silica components in PUAA/silica composite gels. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2327–2334, 2002 相似文献
252.
Provision of Quality‐of‐Service (QoS) guarantees is an important and challenging issue in the design of integrated‐services
packet networks. Call admission control is an integral part of the challenge and is closely related to other aspects of networks
such as service models, scheduling disciplines, traffic characterization and QoS specification. In this paper we provide a
theoretical framework within which call admission control schemes with multiple statistical QoS guarantees can be constructed
for the Generalized Processor Sharing (GPS) scheduling discipline. Using this framework, we present several admission control
schemes for both session‐based and class‐based service models. The theoretical framework is based on recent results in the
statistical analysis of the GPS scheduling discipline and the theory of effective bandwidths. Both optimal schemes and suboptimal
schemes requiring less computational effort are studied under these service models. The QoS metric considered is loss probability.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
253.
M Andrea 《Canadian Metallurgical Quarterly》1993,103(10):1177-1178
254.
Birthe Mller Jose Luis Molina‐Cano Lars Munck 《Journal of the Institute of Brewing》2002,108(3):294-302
In earlier studies concerning vigour, where subsamples are heat‐treated before germination there was found heat‐sensitive as well as heat‐resistant barley samples. The vigour model developed by Ellis and Roberts and further developed at Carlsberg, could only describe the heat‐sensitive barleys. Seventeen samples of the “Alexis” variety grown widely in Europe were collected from the EBC trials in 1994 in order to see if heat resistance in barley was influenced by different growing conditions. We found both heat‐sensitive samples following the vigour model as well as pronounced heat‐resistant samples, but these were not divided according to growing conditions. The germination curves dependent on heat treatment and germination time were evaluated by Principal Component Analysis (PCA). Heat‐resistant barley samples could be differentiated from heat‐sensitive samples already after ½ h of heat treatment at 68°C (12% moisture) and after 3 days of germination. The barley samples were analysed with regard to malting quality. The PCA evaluation of the data divided the samples according to growing location, mainly due to differences in protein and β‐glucan. However, the malting analyses could not describe the differences in heat resistance and sensitivity of the barleys. The biochemical background of the heat resistance found is discussed on the basis of literature. Our findings should give an experimental basis for exploiting a biochemical principle for heat resistance, which is formed during grain filling and consumed during storage and germination. 相似文献
255.
Jun‐Sik Kim Maenghyo Cho 《International journal for numerical methods in engineering》2002,55(11):1323-1343
A finite element based on the efficient higher‐order zig‐zag theory with multiple delaminations is developed. The bending part of the formulation is constructed from the concept of DKQ element. Unlike conventional elements, a developed element has its reference in the bottom surface which simplifies zig‐zag terms on formulation. Exact patch solutions are developed on elements which have the bottom reference system. The present element passes proper bending patch tests in the arbitrary mesh configurations in isotropic materials. Zig‐zag formulation is adopted to model laminated plates with multiple delaminations. To assess the accuracy and efficiency of the present element based on higher‐order zig‐zag theory with multiple delaminations, the linear buckling problem of laminated plates with multiple delaminations has been analysed. The results have been compared with three‐dimensional elasticity solutions. The present element works as an efficient tool for analysing the behaviour of the laminated composites with multiple delaminations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
256.
We have isolated a mutant which exhibits partial constitutivity for a -specific gene expression in α cells. The wild-type gene was cloned and demonstrated to be allelic to the STE13 gene, which encodes the dipeptidyl aminopeptidase involved in processing of the α-factor prepropheromone. Thus, the mating defect of the ste13 mutations in α cells may result both from the production of incompletely processed α-factor and from the increased expression of a -specific genes. The STE13 open reading frame of 931 amino acids contains a putative membrane-spanning segment near its amino terminus and is 31% identical to a second yeast dipeptidyl aminopeptidase (DAP2). A null mutant of STE13 has been constructed: it is viable and sporulation-proficient. The sequence has been deposited in the GenBank data library under Accession Number L21944. 相似文献
257.
The primary problem in concentrating phosphoric acid is due to fouling on the tube‐side of the heat exchangers of the evaporator units. Scaling on the heat transfer surfaces occurs because of high supersaturation of phosphoric acid liquor with respect to calcium sulphate. A review of the existing literature reveals that no information is available on heat transfer and on crystallization fouling of industrial phosphoric acid solutions. In this investigation, the solubility of different calcium sulphate types in phosphoric acid solution was studied and its dependency on acid concentration and temperature was investigated. A large number of fouling experiments were carried out in a side‐stream of a phosphoric acid plant at different flow velocities, surface temperatures and concentrations to determine the mechanisms, which control the deposition process. After identifying the effects of operational parameters on the deposition process, a model was developed for prediction of fouling resistances. The reaction of calcium sulphate crystallization followed a second order rate with respect to the supersaturation. The activation energy evaluated for the surface reaction of the deposit formation was found to be 57 kJ/mol. The predicted fouling resistances were compared with the experimental data. Quantitative and qualitative agreement between measured and predicted fouling rates is good. 相似文献
258.
259.
A series of polyurethane microcapsules containing a phase change material (PCM) of n‐octadecane was successfully synthesized by an interfacial polymerization in aqueous styrene‐maleic anhydride (SMA) dispersion with diethylene triamine (DETA) as a chain extender reacting with toluene‐2,4‐diisocyanate (TDI). The average diameter of microPCMs is in the range of 5–10 μm under the stirring speed of 3000–4000 rpm. Optical and SEM morphologies of microPCMs had ensured that the shell was regularly fabricated with the influence of SMA. FTIR results confirmed that the shell material was polyurethane and the SMA chains associated on core material reacted with TDI forming a part of shell material. The shell thickness was decreasing in the range of 0.31–0.55 μm with the molar ratio of DETA/TDI from 0.84 to 1.35 and the weight of core material increasing from 40 to 80% (wt %). By controlling the weight ratio of PCM as 40, 50, 60, 70, and 80% in microPCMs, it was found using DSC that the Tm and Tc of microPCMs were in the range of 29.8–31.0oC and 21.1–22.0°C and an obvious phase change had been achieved nearly the same temperature range of that of PCM. The results from release curves of microPCM samples prepared by 1.4, 1.7, and 2.0 g of SMA indicated the release properties were affected by the amount of the dispersant, which attributed to the emulsion effect and shell polymerization structure. The above results suggest that the shell structure of microPCMs can be controlled and the properties of microPCMs determined by shell will perform proper practical usage. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4996–5006, 2006 相似文献
260.