全文获取类型
收费全文 | 2773篇 |
免费 | 91篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 37篇 |
化学工业 | 579篇 |
金属工艺 | 92篇 |
机械仪表 | 54篇 |
建筑科学 | 140篇 |
矿业工程 | 25篇 |
能源动力 | 64篇 |
轻工业 | 246篇 |
水利工程 | 18篇 |
石油天然气 | 13篇 |
无线电 | 168篇 |
一般工业技术 | 455篇 |
冶金工业 | 591篇 |
原子能技术 | 41篇 |
自动化技术 | 347篇 |
出版年
2022年 | 23篇 |
2021年 | 30篇 |
2020年 | 26篇 |
2019年 | 33篇 |
2018年 | 38篇 |
2017年 | 45篇 |
2016年 | 45篇 |
2015年 | 50篇 |
2014年 | 64篇 |
2013年 | 192篇 |
2012年 | 93篇 |
2011年 | 121篇 |
2010年 | 114篇 |
2009年 | 88篇 |
2008年 | 117篇 |
2007年 | 118篇 |
2006年 | 113篇 |
2005年 | 83篇 |
2004年 | 96篇 |
2003年 | 92篇 |
2002年 | 64篇 |
2001年 | 50篇 |
2000年 | 51篇 |
1999年 | 52篇 |
1998年 | 76篇 |
1997年 | 59篇 |
1996年 | 55篇 |
1995年 | 35篇 |
1994年 | 39篇 |
1993年 | 47篇 |
1992年 | 41篇 |
1991年 | 25篇 |
1990年 | 25篇 |
1989年 | 27篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 29篇 |
1985年 | 36篇 |
1984年 | 38篇 |
1983年 | 25篇 |
1982年 | 21篇 |
1981年 | 36篇 |
1980年 | 21篇 |
1979年 | 23篇 |
1978年 | 26篇 |
1977年 | 31篇 |
1976年 | 29篇 |
1975年 | 22篇 |
1974年 | 25篇 |
1972年 | 19篇 |
排序方式: 共有2870条查询结果,搜索用时 15 毫秒
91.
92.
Carl J. Stacy 《应用聚合物科学杂志》1986,32(3):3959-3969
Poly(phenylene sulfide) (PPS) has been characterized using a novel high temperature gel permeation chromatograph (GPC). Samples were injected in slurry form at ambient temperature, and redissolved by an in-line precolumn heater at 250°C. A viscometer consisting of a capillary tube with inlet and outlet taps connected to a sensitive differential pressure transducer was used as sole detector, with deflections converted to concentration using the column calibration. Columns and viscometer were operated at 210°C. Universal calibration was carried out using intrinsic viscosity/molecular weight relations for polystyrene and PPS, determined by light scattering. Satisfactory operation was confirmed by agreement between intrinsic viscosity calculated from GPC with independently measured values, and comparisons with melt flow data. Samples of PPS tested were found to be of relatively narrow distribution, with Mw/Mn typically less than two. 相似文献
93.
A number of studies have modeled flow and mixing of granular materials using the discrete element method (DEM). In an attempt to reduce computational costs, many of these DEM studies model particles larger than the actual particle size without investigating the implications of this assumption. Using DEM, the influence of the modeled particle size on flow and mixing in a bladed granular mixer is studied. The predicted flow microdynamics, including mixing rates, are strongly dependent on the particle diameter. The effect of particle size on macroscopic advective flow also is significant, particularly for dilute flow regions. These results suggest that the influence of particle size needs to be taken into consideration when using larger particles in DEM mixing simulations. To guide scale‐up efforts, particle‐size‐based scaling relationships for several key flow measurements are presented. © 2014 American Institute of Chemical Engineers AIChE J, 61: 46–57, 2015 相似文献
94.
Gilbert D. Nessim Matteo Seita Desirée L. Plata Kevin P. O’Brien A. John Hart Eric R. Meshot Christopher M. Reddy Philip M. Gschwend Carl V. Thompson 《Carbon》2011,49(3):804-810
Despite significant progress in carbon nanotube (CNT) synthesis by thermal chemical vapor deposition (CVD), the factors determining the structure of the resulting carbon filaments and other graphitic nanocarbons are not well understood. Here, we demonstrate that gas chemistry influences the crystal structure of carbon filaments grown at low temperatures (500 °C). Using thermal CVD, we decoupled the thermal treatment of the gaseous precursors (C2H4/H2/Ar) and the substrate-supported catalyst. Varying the preheating temperature of the feedstock gas, we observed a striking transition between amorphous carbon nanofibers (CNFs) and crystalline CNTs. These results were confirmed using both a hot-wall CVD system and a cold-wall CVD reactor. Analysis of the exhaust gases (by ex situ gas chromatography) showed increasing concentrations of specific volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) that correlated with the structural transition observed (characterized using high-resolution transmission electron microscopy). This suggests that the crystallinity of carbon filaments may be controlled by the presence of specific gas phase precursor molecules (e.g., VOCs and PAHs). Thus, direct delivery of these molecules in the CVD process may enable selective CNF or CNT formation at low substrate temperatures. The inherent scalability of this approach could impact many promising applications, especially in the electronics industry. 相似文献
95.
In high-rate algal ponds, the grazing activity of rotifers such as Brachionus rubens or B. calyciflorus often leads to a replacement of Scenedesmus species by Micractinium pusillum. In contrast to many other green microalgae including Scenedesmus, Micractinium pusillum with fully developed spines (setae) cannot be eaten by Brachionus. Ecological conditions for population shifts between Scenedesmus and Micractinium are, therefore, interpreted as a response of the rotifers rather than being due to physiological properties of the algae. Another effect of rotifer grazing on the microbial flora of high-rate ponds is the development of large stable flocs consisting of bacteria and microalgae. 相似文献
96.
Carl E. Baum 《International Journal of Numerical Modelling》1988,1(4):175-188
The asymptotic form, for high frequencies, of the equations of propagation on a nonuniform N-conductor transmission line is considered. Under the assumption of perfect conditions in uniform, isotropic media, all N propagation velocities are the same, but the characteristic impedance matrix is allowed to vary with position along the line. Closed-form solutions are obtained for some cases of interest. 相似文献
97.
There are many multi-stage optimization problems that are not easily solved through any known direct method when the stages are coupled. For instance, the problem of planning a vehicle's control sequence to negotiate obstacles and reach a goal in minimum time is investigated. The vehicle has a known mass, and the controlling forces have finite limits. A genetic programming technique is developed that finds admissible control trajectories that tend to minimize the vehicle's transit time through the obstacle field. The immediate application is that of a space robot that must rapidly traverse around two or three dimensional structures via application of a rotating thruster or non-rotating on-off thrusters. (An air-bearing floor test-bed for such vehicles is located at the Marshal Space Flight Center in Huntsville, Alabama.) It appears that the developed method is applicable to a general set of optimization problems in which the cost function and the multi-dimensional multi-state system can be any non-linear functions that are continuous in the operating regions. Other applications include: the planning of optimal navigation pathways through a traversability graph, the planning of control input for underwater maneuvering vehicles which have complex control state-space relationships, the planning of control sequences for milling and manufacturing robots, the planning of control and trajectories for automated delivery vehicles, and the optimization of control for racing vehicles and athletic training in slalom sports. 相似文献
98.
99.
Terrence B. Lindemer Theodore M. Besmann Carl E. Johnson 《Journal of Nuclear Materials》1981,100(1-3):178-226
This paper considers the phase equilibria of alkali metal oxides and their combinations with other oxides relevant to nuclear fuels, fission products, and structural materials. The other oxides include those of the lanthanides, the actinides, iron, nickel, aluminum, silicon, as well as those of periodic table groups IIA, IVB, VB, VIB, and VIA. The alkali metal halides, chalcogenides, and hydroxides are also included. Techniques are developed to permit calculation of phase equilibria and Ellingham diagrams in ternary and higher-order systems. These techniques include estimation of previously unknown 298.15 K values of the enthalpies of formation and the entropies of many compounds. 相似文献