全文获取类型
收费全文 | 16342篇 |
免费 | 806篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 153篇 |
综合类 | 11篇 |
化学工业 | 4050篇 |
金属工艺 | 299篇 |
机械仪表 | 316篇 |
建筑科学 | 565篇 |
矿业工程 | 27篇 |
能源动力 | 540篇 |
轻工业 | 2780篇 |
水利工程 | 152篇 |
石油天然气 | 55篇 |
无线电 | 753篇 |
一般工业技术 | 2567篇 |
冶金工业 | 2106篇 |
原子能技术 | 95篇 |
自动化技术 | 2699篇 |
出版年
2024年 | 39篇 |
2023年 | 146篇 |
2022年 | 497篇 |
2021年 | 620篇 |
2020年 | 398篇 |
2019年 | 444篇 |
2018年 | 676篇 |
2017年 | 640篇 |
2016年 | 694篇 |
2015年 | 470篇 |
2014年 | 660篇 |
2013年 | 1102篇 |
2012年 | 1000篇 |
2011年 | 1124篇 |
2010年 | 809篇 |
2009年 | 807篇 |
2008年 | 716篇 |
2007年 | 667篇 |
2006年 | 506篇 |
2005年 | 454篇 |
2004年 | 354篇 |
2003年 | 324篇 |
2002年 | 300篇 |
2001年 | 213篇 |
2000年 | 208篇 |
1999年 | 196篇 |
1998年 | 795篇 |
1997年 | 486篇 |
1996年 | 353篇 |
1995年 | 208篇 |
1994年 | 172篇 |
1993年 | 170篇 |
1992年 | 66篇 |
1991年 | 71篇 |
1990年 | 59篇 |
1989年 | 56篇 |
1988年 | 51篇 |
1987年 | 46篇 |
1986年 | 47篇 |
1985年 | 49篇 |
1984年 | 39篇 |
1983年 | 37篇 |
1982年 | 41篇 |
1981年 | 51篇 |
1980年 | 42篇 |
1979年 | 17篇 |
1978年 | 21篇 |
1977年 | 46篇 |
1976年 | 74篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
The problem of on‐line estimation of the conversion and composition evolutions in a pressurized batch copolymer reactor with temperature and pressure measurements was addressed. The estimation model consisted of mass and energy balances with a pressure equation built from phase‐equilibrium considerations. The application of a nonlinear geometric estimation approach yielded the underlying solvability condition with physical meaning, a straightforward estimator construction, and a conventional‐like tuning procedure. The resulting barocalorimetric estimator was an on‐line dynamic measurement processor with a model‐based predictor and a measurement‐driven corrector, and whose implementation did not require the polymerization rates and heat‐transfer coefficient function dependencies. The technique was tested with a representative laboratory styrene–butadiene system. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 475–482, 2005 相似文献
122.
J.-M. Giraudon A. Elhachimi F. Wyrwalski S. Siffert A. Aboukaïs J.-F. Lamonier G. Leclercq 《Applied catalysis. B, Environmental》2007,75(3-4):157-166
Calcined and reduced catalysts Pd/LaBO3 (B = Co, Fe, Mn, Ni) were used for the total oxidation of toluene. Easiness of toluene destruction was found to follow the sequence based on the T50 values (temperature at which 50% of toluene is converted): Pd/LaFeO3 > Pd/LaMnO3+δ > Pd/LaCoO3 > Pd/LaNiO3. In order to investigate the activation process (calcination and reduction) in detail, the reducibility of the samples was evaluated by H2-TPR on the calcined catalysts. Additionally, characterization of the Pd/LaBO3 (B = Co, Fe) surface was carried out by X-ray photoelectron spectroscopy (XPS) at each stage of the global process, namely after calcination, reduction and under catalytic reaction at either 150 or 200 °C for Pd/LaFeO3 and either 200 or 250 °C for LaCoO3. The different results showed that palladium oxidized entities were totally reduced after pre-reduction at 200 °C for 2 h (2 L/h, 1 °C/min). As LaFeO3 was unaffected by such a treatment, for the other perovskites, the cations B are partially reduced as B3+ (B = Mn) or B2+ even to B0 (B = Co, Ni). In the reactive stream (0.1% toluene in air), Pd0 reoxidized partially, more rapidly over Co than Fe based catalysts, to give a Pd2+/Pd4+ and Pd0/Pd2+/Pd4+ surface redox states, respectively. Noticeably, reduced cobalt species are progressively oxidized on stream into Co3+ in a distorted environment. By contrast, only the lines characteristic of the initial perovskite lattice were detected by XRD studies on the used catalysts. The higher activity performance of Pd/LaFeO3 for the total oxidation of toluene was attributed here to a low temperature of calcination and to a remarkable high stability of the perovskite lattice whatever the nature of the stream which allowed to keep a same palladium dispersion at the different stages of the process and to resist to the oxidizing experimental conditions. On the contrary, phase transformations for the other perovskite lattices along the process were believed to increase the palladium particle size responsible of a lower activity. 相似文献
123.
Student academic underachievement is a concern of paramount importance in Europe, where around 15% of the students in the last high school courses do not achieve the minimum knowledge academic requirement. In this paper, we propose a model based on a system of differential equations to study the dynamics of the students’ academic performance in the German region of the North Rhine-Westphalia. This approach is supported by the idea that both good and bad study habits, are a mixture of personal decisions and influence of classmates. This model allows us to forecast the student academic performance by means of confidence intervals over the next few years. 相似文献
124.
Spectral preconditioners are based on the fact that the convergence rate of the Krylov subspace methods is improved if the eigenvalues of the smallest magnitude of the system matrix are ‘removed’. In this paper, two preconditioning strategies are studied to solve a set of linear systems associated with the numerical integration of the time-dependent neutron diffusion equation. Both strategies can be implemented using the matrix–vector product as the main operation and succeed at reducing the total number of iterations needed to solve the set of systems. 相似文献
125.
Maria Augusta de Luca Taís Espíndola Machado Renan Beretta Notti Marly Maldaner Jacobi 《应用聚合物科学杂志》2004,92(2):798-803
Hybrid materials were synthesized from epoxidized (68, 43, or 14%) styrene–butadiene rubber (SBR) and the hydrolysis product of tetraethoxysilane (TEOS) in situ under ultrasonic irradiation. The products were characterized with thermal analysis (differential scanning calorimetry and thermogravimetric analysis), stress–strain tests, scanning electron microscopy (including energy‐dispersive spectrometry), and swelling in tetrahydrofuran and water. The most transparent were those prepared from SBR with the highest degree of epoxidation, whereas those obtained from less epoxidized SBR and with larger amounts of TEOS showed distinct phases that could be considered two hybrid phases (one rich in TEOS and another rich in SBR). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 798–803, 2004 相似文献
126.
Short syntheses of (Z)-7-dodecen-1-yl acetate, (Z)-7-tetradecen-1-yl acetate, (Z)-9-dodecen-1-yl acetate, and (Z)-9-tetradecen-1-yl acetate from 7-hydroxyheptanal and 9-oxononanoic acid precursors obtained by oxidative cleavage of easily available aleuritic acid are reported. The key step in these syntheses is a stereoselective Wittig reaction between aldehyde and alkyl-phosphonium salt. Wittig-Horner type reaction of 7-hydroxyheptanal and diethyl cyanomethylphosphonate gave the ,-unsaturated nitrile derivative which after protection of the hydroxyl group was reduced to the corresponding aldehyde. Wittig reaction of the latter, followed by acetylation, completed the synthesis of (E,Z)-7,9-dodecadien-1-yl acetate, the sex pheromone of the European grapevine mothLobesia botrana Schiff. 相似文献
127.
Jesú s Guardiola Soler Juan J. Prieto Marqu s M nica Garcí a Ruiz Guadalupe Ramos Caicedo 《Chemical Engineering Communications》2003,190(3):285-298
The purpose of the present work is to demonstrate the reliability of a digital image processing technique. A CCD (Charge Coupled Device) is used to perform an investigation on the bubble properties of a 2D gas-solid fluidized bed, and the aim of this study is to establish a criterion in order to reject all images that could not be interpreted as bubbles. This may lead to an alteration of the information obtained. The two-dimensional fluidized bed is 20 cm wide and at least 20 cm high, and the field of view of the camera is 12.54 cm wide and 12.99 cm high. In this way, bubbles could be totally or partially placed into this field of view so that a partial image of a bubble could be analyzed as a whole bubble. With this calibration, a geometric decision criterion for the rejection of nonbubble images was developed. 相似文献
128.
The isotopic exchange has been studied between catalyst radiosulfur and H2S, formed in thiophene hydrodesulfurization (HDS) (named S-displace) on alumina supported molybdena, on CoMoOx, PdMoOx, PtMoOx and on silica–alumina supported NiWOx. S-displace was compared with radiosulfur exchange data between catalyst radiosulfur and gas phase H2S (Sexc) determined previously. The extent of Sexc was higher than that of the S-displace for Mo, CoMo in and NiW, whereas the extent of S-displace from PdMoO and PtMoO was
significantly higher, than that of Sexc. Thiophene HDS product distribution data are discussed in terms of increased C=C hydrogenation and C–C hydrogenolysis activity,
explained by increasing H2S production with longer circulation time of the thiophene/H2 mixture, The C1/C3<1 ratios among C4-hydrogenolysis products indicate some coke formation. The decrease of thiophene HDS activity is presumably a consequence
of increasing site-blocking with the formation of more H2S and coke with longer duration of thiophene treatment. 相似文献
129.
The job-shop scheduling problem with operators is a very interesting problem that generalizes the classic job-shop problem in such a way that an operation must be algorithm to solve this problem considering makespan minimization. The genetic algorithm uses permutations with repetition to encode chromosomes and a schedule generation scheme, termed OG&T, as decoding algorithm. This combination guaranties that at least one of the chromosomes represents and optimal schedule and, at the samhat machines and operators are idle while an operation is available to be processed. To improve the quality of the schedules for large instances, we use Lamarckian evolution and modify the OG&T algorithm to further reduce the idle time of the machines and operators, in this case at the risk of leaving all optimal schedules out of the search space. We conducted a large experimental study showing that these improvements allow the genetic algorithm to reach high quality solutions in very short time, and so it is quite competitive with the current state-of-the-art methods. 相似文献
130.
José Sánchez-Sánchez Félix Escrig Pallarés Maria Teresa Rodríguez-León 《Nexus Network Journal》2014,16(1):135-150
Sometimes the complex structures of nature inspire human constructions. Gothic construction has shown that forces can cross space along intricate paths that may even be arbitrary if correctly dimensioned. In some way, ribbed structures are like trees where the branches conduct forces instead of sap; they operate as branches and trunks descending by fractal ways. Here we discuss reciprocal tree-like fractal structures and the difficulty in their design and erection and solutions for constructive details, as well as the possible analytical questions and automatic generation by means of proper software. The results are shown in the design of the Natural Interpretation Centre in Melilla where we have proposed two connected trees like shown at figures included below. 相似文献