全文获取类型
收费全文 | 1498篇 |
免费 | 92篇 |
专业分类
电工技术 | 21篇 |
化学工业 | 302篇 |
金属工艺 | 57篇 |
机械仪表 | 31篇 |
建筑科学 | 61篇 |
矿业工程 | 2篇 |
能源动力 | 51篇 |
轻工业 | 105篇 |
水利工程 | 3篇 |
无线电 | 185篇 |
一般工业技术 | 264篇 |
冶金工业 | 196篇 |
原子能技术 | 15篇 |
自动化技术 | 297篇 |
出版年
2023年 | 20篇 |
2022年 | 28篇 |
2021年 | 61篇 |
2020年 | 30篇 |
2019年 | 37篇 |
2018年 | 50篇 |
2017年 | 56篇 |
2016年 | 64篇 |
2015年 | 38篇 |
2014年 | 46篇 |
2013年 | 80篇 |
2012年 | 115篇 |
2011年 | 116篇 |
2010年 | 74篇 |
2009年 | 83篇 |
2008年 | 102篇 |
2007年 | 72篇 |
2006年 | 49篇 |
2005年 | 43篇 |
2004年 | 33篇 |
2003年 | 32篇 |
2002年 | 18篇 |
2001年 | 16篇 |
2000年 | 17篇 |
1999年 | 20篇 |
1998年 | 58篇 |
1997年 | 36篇 |
1996年 | 20篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 9篇 |
1973年 | 4篇 |
1972年 | 3篇 |
排序方式: 共有1590条查询结果,搜索用时 31 毫秒
71.
Quentin Lequy Mathieu Bouchard Guy Desaulniers Fran?ois Soumis Beyime Tachefine 《Journal of Scheduling》2012,15(2):239-251
In some companies such as large retail stores, the employees perform different activities (e.g., cashier or clerk in a specific
department) to respond to a customer demand for each activity that varies over the planning horizon and must be fulfilled
as soon as possible. For a given time period, this demand translates into an ideal number of employees required for the corresponding
activity. During a work shift, an employee can be assigned to several activities that are interruptible at any time and subject
to operational constraints (required skills, minimum and maximum assignment durations). Given work shifts already assigned
to the employees, the multi-activity assignment problem (MAAP) consists of assigning activities to the shifts such that the
activity demands are satisfied as best as possible over the planning horizon. In this paper, we propose three integer programming
models for the MAAP and develop various heuristics based on mathematical programming techniques. Computational results obtained
on randomly generated MAAP instances show that a heuristic column generation method embedded into a rolling horizon procedure
provides the best results in general. 相似文献
72.
Lna Saint Macary Myrtil L. Kahn Claude Estourns Pierre Fau David Trmouilles Marise Bafleur Philippe Renaud Bruno Chaudret 《Advanced functional materials》2009,19(11):1775-1783
Conditions for the elaboration of nanostructured varistors by spark plasma sintering (SPS) are investigated, using 8‐nm zinc oxide nanoparticles synthesized following an organometallic approach. A binary system constituted of zinc oxide and bismuth oxide nanoparticles is used for this purpose. It is synthesized at room temperature in an organic solution through the hydrolysis of dicyclohexylzinc and bismuth acetate precursors. Sintering of this material is performed by SPS at various temperatures and dwell times. The determination of the microstructure and the chemical composition of the as‐prepared ceramics are based on scanning electron microscopy and X‐ray diffraction analysis. The nonlinear electrical characteristics are evidenced by current–voltage measurements. The breakdown voltage of these nanostructured varistors strongly depends on grain sizes. The results show that nanostructured varistors are obtained by SPS at sintering temperatures ranging from 550 to 600 °C. 相似文献
73.
Virginie Boscher Renaud Helleboid Thierry Lasuye Bernard Stasik Gérard Riess 《Polymer International》2009,58(10):1209-1216
BACKGROUND: Poly[(vinyl alcohol)‐co‐(vinyl acetate)] (PVA) copolymers obtained by partial hydrolysis of poly(vinyl acetate) are currently used as industrial stabilizers in the suspension polymerization of vinyl chloride monomer (VCM). Their molecular characteristics, mainly the average degree of hydrolysis (DH ) and average degree of polymerization (DPw ), have a major influence on the monomer droplet size and the properties of the final poly(vinyl chloride) resin. RESULTS: The average droplet size and size distribution of chlorobutane/water emulsions, as a model system for VCM/water emulsions, were studied using acoustic attenuation spectroscopy on‐line with an agitated laboratory reactor. The emulsions were stabilized by PVA with DH values between 73 and 88 mol% and DPw values between 450 and 2500. The effects of agitation speed, stirring time and concentration of the PVA copolymers were investigated. An attempt was made to correlate the interfacial tension and the droplet size. CONCLUSION: On‐line acoustic spectroscopy appears to be a suitable technique for the real‐time control of the droplet size of monomer suspensions. The advantages and limitations of the technique are outlined. The validity and the application limits of the commonly cited correlation between the droplet size and the Weber number are established for polymeric surfactant‐stabilized emulsions. Copyright © 2009 Society of Chemical Industry 相似文献
74.
We present an active optical synthetic aperture-imaging system. A phase-step digital holographic setup is used as a wavefront sensor in the far field. The overlap of the holograms enables the estimation and compensation of their relative positions and phase with a speckle cross-correlation algorithm. Experimental results on a short-range synthetic aperture setup at 633 nm are presented that are based on 128 x 128 holograms. The synthesis is executed in one direction by means of rotation of the object. Test images show a significant gain of resolution in the synthesis direction. Processing errors are estimated through experiment. Random processing errors of a synthetic pupil composed of 33 merged holograms are negligible, but biases induced by unknown optical aberrations ofthe reference wave induce defocusing and astigmatism. 相似文献
75.
76.
Shawn E. Gano John E. Renaud Jay D. Martin Timothy W. Simpson 《Structural and Multidisciplinary Optimization》2006,32(4):287-298
Many optimization methods for simulation-based design rely on the sequential use of metamodels to reduce the associated computational burden. In particular, kriging models are frequently used in variable fidelity optimization. Nevertheless, such methods may become computationally inefficient when solving problems with large numbers of design variables and/or sampled data points due to the expensive process of optimizing the kriging model parameters in each iteration. One solution to this problem would be to replace the kriging models with traditional Taylor series response surface models. Kriging models, however, were shown to provide good approximations of computer simulations that incorporate larger amounts of data, resulting in better global accuracy. In this paper, a metamodel update management scheme (MUMS) is proposed to reduce the cost of using kriging models sequentially by updating the kriging model parameters only when they produce a poor approximation. The scheme uses the trust region ratio (TR-MUMS), which is a ratio that compares the approximation to the true model. Two demonstration problems are used to evaluate the proposed method: an internal combustion engine sizing problem and a control-augmented structural design problem. The results indicate that the TR-MUMS approach is very effective; on the demonstration problems, it reduced the number of likelihood evaluations by three orders of magnitude compared to using a global optimizer to find the kriging parameters in every iteration. It was also found that in trust region-based method, the kriging model parameters need not be updated using a global optimizer—local methods perform just as well in terms of providing a good approximation without affecting the overall convergence rate, which, in turn, results in a faster execution time. 相似文献
77.
78.
According to earlier work, excited electronic states, despite their very small concentrations in wide-gap systems, might be involved in the initiation of energetic materials. To get further insight into the non-adiabatic electronic behaviour under intense mechanical perturbations, a simple approach is suggested, using finite clusters as models for materials. Preliminary calculations are carried out for isolated clusters undergoing vibrations. Electronic populations in excited states obtained from these simulations are much larger than expected on the basis of statistical mechanics. Therefore, an extension of the present scheme to the canonical NVT ensemble would be desirable. 相似文献
79.
80.
F Tesson P Richard P Charron B Mathieu C Cruaud L Carrier O Dubourg N Lautié M Desnos A Millaire R Isnard AA Hagege JB Bouhour M Bennaceur B Hainque P Guicheney K Schwartz M Komajda 《Canadian Metallurgical Quarterly》1998,12(6):385-392
The effects of two progestogen-only pills containing either 75 microgram desogestrel (DSG) or 30 microgram levonorgestrel (LNG) on hemostasis were investigated in a double-blind, randomized, controlled study of seven treatment cycles in 78 healthy women. DSG reduced factor VII activity (p < 0.05) and prothrombin fragment 1+2 (p < 0.05) and increased protein S (p < 0.001). LNG reduced factor VII activity (p < 0.01) and plasminogen activity (p < 0.01) and increased tissue-plasminogen activator (t-PA) (p < 0.05). At the end of the post-treatment cycle with DSG, protein S (p < 0.01) and t-PA (p < 0.05) were increased and plasminogen activity was decreased (p < 0.05), whereas with LNG, t-PA was increased (p < 0.001) and prothrombin fragment 1+2 (p < 0.05) and plasminogen activity (p < 0.001) were decreased. Between-group comparisons revealed higher values for DSG regarding the anticoagulatory parameter protein S at cycle 7 (p < 0.01) and post-treatment assessments (p < 0.05), and the fibrinolytic parameter plasmin-antiplasmin complex was higher with DSG at cycle 7 (p < 0.05) and at post-treatment (p < 0.05). Both preparations had comparable and potentially favorable effects of hemostasis, and may offer suitable hormonal contraception to women with a personal or family history of venous thromboembolic diseases. 相似文献