全文获取类型
收费全文 | 15954篇 |
免费 | 234篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 189篇 |
综合类 | 4篇 |
化学工业 | 2007篇 |
金属工艺 | 361篇 |
机械仪表 | 338篇 |
建筑科学 | 523篇 |
矿业工程 | 62篇 |
能源动力 | 306篇 |
轻工业 | 1219篇 |
水利工程 | 90篇 |
石油天然气 | 118篇 |
无线电 | 1510篇 |
一般工业技术 | 2340篇 |
冶金工业 | 5588篇 |
原子能技术 | 159篇 |
自动化技术 | 1397篇 |
出版年
2021年 | 101篇 |
2019年 | 102篇 |
2018年 | 135篇 |
2017年 | 101篇 |
2016年 | 95篇 |
2015年 | 107篇 |
2014年 | 224篇 |
2013年 | 573篇 |
2012年 | 304篇 |
2011年 | 407篇 |
2010年 | 336篇 |
2009年 | 336篇 |
2008年 | 451篇 |
2007年 | 439篇 |
2006年 | 433篇 |
2005年 | 388篇 |
2004年 | 325篇 |
2003年 | 362篇 |
2002年 | 309篇 |
2001年 | 322篇 |
2000年 | 316篇 |
1999年 | 407篇 |
1998年 | 1593篇 |
1997年 | 993篇 |
1996年 | 707篇 |
1995年 | 471篇 |
1994年 | 438篇 |
1993年 | 442篇 |
1992年 | 283篇 |
1991年 | 254篇 |
1990年 | 263篇 |
1989年 | 221篇 |
1988年 | 222篇 |
1987年 | 208篇 |
1986年 | 201篇 |
1985年 | 255篇 |
1984年 | 208篇 |
1983年 | 208篇 |
1982年 | 203篇 |
1981年 | 183篇 |
1980年 | 203篇 |
1979年 | 128篇 |
1978年 | 135篇 |
1977年 | 263篇 |
1976年 | 364篇 |
1975年 | 135篇 |
1974年 | 125篇 |
1973年 | 107篇 |
1972年 | 80篇 |
1970年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Thomas R. Savage Fernando Almeida-Trasvina Ehecatl A. del-Rio Chanona Robin Smith Dondga Zhang 《American Institute of Chemical Engineers》2021,67(11):e17358
With liquefied natural gas becoming increasingly prevalent as a flexible source of energy, the design and optimization of industrial refrigeration cycles becomes even more important. In this article, we propose an integrated surrogate modeling and optimization framework to model and optimize the complex CryoMan Cascade refrigeration cycle. Dimensionality reduction techniques are used to reduce the large number of process decision variables which are subsequently supplied to an array of Gaussian processes, modeling both the process objective as well as feasibility constraints. Through iterative resampling of the rigorous model, this data-driven surrogate is continually refined and subsequently optimized. This approach was not only able to improve on the results of directly optimizing the process flow sheet but also located the set of optimal operating conditions in only 2 h as opposed to the original 3 weeks, facilitating its use in the operational optimization and enhanced process design of large-scale industrial chemical systems. 相似文献
3.
4.
5.
Lihua Lou Weijie Yu Ronald J. Kendall Ernest Smith Seshadri S. Ramkumar 《应用聚合物科学杂志》2020,137(30):49213
A tensile properties testing study was conducted to understand the influence of thickness, cross-head speed (speed of testing), gauge length (GL; specimen test length), and sample shape on important tensile properties of polyvinyl alcohol (PVA) nanofiber webs. The effects of each testing parameter on load at break, extension at break, Young's modulus, and tensile stress–strain curve of PVA nanofiber webs are analyzed. The Welch two sample t-tests show the significant difference among tested data. Using interaction plots, two-way analysis of variance, and margin mean plots, the interaction effects among testing parameters have been analyzed. Of all the factors, cross-head speed, the interaction among GL, and sample thickness (GL: Thickness) and the interaction among GL, testing speed and sample thickness (GL: Speed: Thickness) have significant influence on the tensile properties of PVA nanofiber webs. Moreover, the hypothesized model of mechanism of tensile strain–stress curve of PVA nanofiber webs has been proposed. Based on the model, the tensile strain–stress curve can be split into three stages: linear elastic, partial break up, and complete breakage. This study will provide a better understanding of tensile testing parameters' effects and their interaction effects on the tensile properties of nanowebs. 相似文献
6.
Sawao Honda Shinobu Hashimoto Benoît Nait-Ali David S. Smith Yusuke Daiko Yuji Iwamoto 《Journal of the American Ceramic Society》2022,105(10):6335-6344
Porous alumina with a highly textured microstructure was fabricated by pulse electric current sintering (PECS) using alumina platelets. Highly oriented porous alumina with a porosity of 3%–50% was obtained by a pressure-controlled method of PECS. The properties of the highly textured porous alumina were measured in two directions. The nitrogen gas permeance and thermal conductivity at room temperature were higher in the direction along the platelet length due to the higher continuity of pores and the connectivity of alumina platelets, respectively. The anisotropy of the thermal conductivity at room temperature was investigated and explained by the effect of grain size of platelets as well as morphology and orientation of pores. The bending strength was higher with the loading direction along the platelet thickness. The thermal shock strength was clearly different in the two directions. The difference in the thermal shock strength was investigated by the measurement of properties and thermal stress analysis. 相似文献
7.
Dr. Li Di Prof. Per Artursson Dr. Alex Avdeef Prof. Leslie Z. Benet Prof. J. Brian Houston Dr. Manfred Kansy Edward H. Kerns Prof. Hans Lennernäs Dr. Dennis A. Smith Prof. Kiyohiko Sugano 《ChemMedChem》2020,15(20):1862-1874
Passive permeability is a key property in drug disposition and delivery. It is critical for gastrointestinal absorption, brain penetration, renal reabsorption, defining clearance mechanisms and drug-drug interactions. Passive diffusion rate is translatable across tissues and animal species, while the extent of absorption is dependent on drug properties, as well as in vivo physiology/pathophysiology. Design principles have been developed to guide medicinal chemistry to enhance absorption, which combine the balance of aqueous solubility, permeability and the sometimes unfavorable compound characteristic demanded by the target. Permeability assays have been implemented that enable rapid development of structure-permeability relationships for absorption improvement. Future advances in assay development to reduce nonspecific binding and improve mass balance will enable more accurately measurement of passive permeability. Design principles that integrate potency, selectivity, passive permeability and other ADMET properties facilitate rapid advancement of successful drug candidates to patients. 相似文献
8.
David J. Lawrence Brianna L. Smith Cameron D. Collard Keyton A. Elliott Kyle L. Fakhoury Jeffery D. Mangold Anna N. Soyka 《International Journal of Hydrogen Energy》2021,46(2):1642-1655
Monolithically-integrated tandem photoanodes were fabricated on substrates consisting of epitaxial n-GaAs1-xPx (x ? 0.32) grown on n+-GaAs wafers. A p+-n junction photovoltaic (PV) cell was first formed by zinc diffusion into the n-GaAs0.68P0.32 from a deposited ZnO coating. After diffusion the ZnO serves as a transparent electrical contact to the resulting p+-GaAs0.68P0.32 surface layer. Transparent, conducting SnO2:F provides chemical and mechanical protection for the ZnO and the underlying PV cell, and it electrically connects this cell to a top BiVO4 photocatalyst layer. In some photoanodes, a WO3 thin film was interposed between the SnO2:F and BiVO4. All oxide coatings were produced by ultrasonic spray pyrolysis except WO3, which was spin coated. Unassisted (unbiased) solar water splitting was achieved, with a solar-to-hydrogen efficiency approaching 2%, without addition of any co-catalyst to the BiVO4 surface. This work can provide insights to other researchers regarding scalable, low cost approaches for the planar monolithic integration of oxide photoanode materials with PV cells to create new tandem devices. 相似文献
9.
Smith J. David; Beran Michael J.; Redford Joshua S.; Washburn David A. 《Canadian Metallurgical Quarterly》2006,135(2):282
Although researchers are exploring animals' capacity for monitoring their states of uncertainty, the use of some paradigms allows the criticism that animals map avoidance responses to error-causing stimuli not because of uncertainty monitored but because of feedback signals and stimulus aversion. The authors addressed this criticism with an uncertainty-monitoring task in which participants completed blocks of trials with feedback deferred so that they could not associate reinforcement signals to particular stimuli or stimulus-response pairs. Humans and 1 of 2 monkeys were able to make cognitive, decisional uncertainty responses that were independent of feedback or reinforcement history within a task. This finding unifies the comparative literature on uncertainty monitoring. The dissociation of performance from reinforcement has theoretical implications, and the deferred-feedback technique has many applications. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
Daeyoung Kim Ingram M.A. Smith W.W. Jr. 《Antennas and Propagation, IEEE Transactions on》2003,51(8):1740-1749
RF modulated backscatter (RFMB), also known as modulated radar cross section or sigma modulation, is a RF transmission technique useful for short-range, low-data-rate applications, such as nonstop toll collection, electronic shelf tags, freight container identification and chassis identification in automobile manufacturing, that are constrained to have extremely low power requirements. The small-scale fading observed on the backscattered signal has deeper fades than the signal from a traditional one-way link of the same range in the same environment because the fading on the backscattered signal is the product of the fading on the off-board-generated carrier times the fading on the reflected signal. This paper considers the continuous wave (CW) type of RFMB, in which the interrogator transmitter and receiver antennas are different. This two-way link also doubles the path loss exponent of the one-way link. This paper presents the cumulative distribution functions for the measured small-scale fading and the measured path loss for short ranges in an indoor environment at 2.4 GHz over this type of link. 相似文献