全文获取类型
收费全文 | 1150篇 |
免费 | 43篇 |
专业分类
电工技术 | 8篇 |
化学工业 | 172篇 |
金属工艺 | 14篇 |
机械仪表 | 15篇 |
建筑科学 | 47篇 |
矿业工程 | 2篇 |
能源动力 | 10篇 |
轻工业 | 124篇 |
水利工程 | 11篇 |
石油天然气 | 1篇 |
无线电 | 66篇 |
一般工业技术 | 104篇 |
冶金工业 | 450篇 |
原子能技术 | 5篇 |
自动化技术 | 164篇 |
出版年
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 11篇 |
2020年 | 17篇 |
2019年 | 18篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 24篇 |
2015年 | 13篇 |
2014年 | 26篇 |
2013年 | 51篇 |
2012年 | 29篇 |
2011年 | 60篇 |
2010年 | 39篇 |
2009年 | 49篇 |
2008年 | 54篇 |
2007年 | 41篇 |
2006年 | 39篇 |
2005年 | 32篇 |
2004年 | 45篇 |
2003年 | 26篇 |
2002年 | 30篇 |
2001年 | 27篇 |
2000年 | 17篇 |
1999年 | 26篇 |
1998年 | 36篇 |
1997年 | 29篇 |
1996年 | 35篇 |
1995年 | 21篇 |
1994年 | 31篇 |
1993年 | 24篇 |
1992年 | 29篇 |
1991年 | 10篇 |
1990年 | 26篇 |
1989年 | 21篇 |
1988年 | 10篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 18篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1974年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有1193条查询结果,搜索用时 15 毫秒
11.
The effectiveness of overlearning in enhancing performance has been acknowledged by researchers within the training community for years. In spite of this general consensus, the empirical basis for this claim is often not clear. This article presents a meta-analysis of the effects of overlearning on retention. Results indicate that overlearning produces a significant effect on retention of moderate overall magnitude and that the effect of overlearning on retention is moderated by the degree of overlearning, type of task, and length of retention period. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
12.
13.
This study proposes a new interactive multicriteria method for determining the best levels of the decision variables needed to optimize a stochastic computer simulation with multiple response variables. The method, called the Pairwise Comparison Stochastic Cutting Plane (PCSCP) method, combines good features from interactive multiple objective mathematical programming and response surface methodology. The major characteristics of the PCSCP method are: (1) it interacts progressively with the decision-maker (DM) to obtain her preferences, (2) it uses experimental design to explore the decision space adequately while reducing the burden on the DM, and (3) it uses the preference information provided by the DM and the sampling error in the responses to reduce the decision space. The mechanics of the method are illustrated with a numerical example. Some computational studies evaluating the method are also reported. 相似文献
14.
Egg activation at fertilization in the sea urchin results in the exocytosis of approximately 15,000 cortical granules that are docked at the plasma membrane. Previously, we reported that several integral membrane proteins modeled in the SNARE hypothesis, synaptotagmin, VAMP, and syntaxin, in addition to a small GTPase of the ras superfamily, rab3, were present on cortical granules (Conner, S., Leaf, D., and Wessel, G., Mol. Reprod. Dev. 48, 1-13, 1997). Here we report that rab3 is associated with cortical granules throughout oogenesis, during cortical granule translocation, and while docked at the egg plasma membrane. Following cortical granule exocytosis, however, rab3 reassociates with a different population of vesicles, at least some of which are of endocytic origin. Because of its selective association with cortical granules in eggs and oocytes, we hypothesize that rab3 functions in cortical granule exocytosis. To test this hypothesis, we used a strategy of interfering with rab3 function by peptide competition with its effector domain, a conserved region within specific rab types. We first identified the effector domain sequence in Lytechinus variegatus eggs and find the sequence 94% identical to the effector domain of rab3 in Stronglocentrotus purpuratus. Then, with synthetic peptides to different regions of the rab3 protein, we find that cortical granule exocytosis is inhibited in eggs injected with effector domain peptides, but not with peptides from the hypervariable region or with a scrambled effector peptide. Additionally, effector-peptide-injected eggs injected with IP3 are blocked in their ability to exocytose cortical granules, suggesting that the inhibition is directly on the membrane fusion event and not the result of interference with the signal transduction mechanism leading to calcium release. We interpret these results to mean that rab3 functions in the regulation of cortical granule exocytosis following vesicle docking. 相似文献
15.
16.
17.
Measures of mixing for laminar flow are developed from basic principles of continuum mechanics for infinitesimal rates of stretch. The entire analysis is performed from the basis of the eigenvalues and principal directions of the appropriate flow tensors. Measuring the rate of line growth, where the line marks the interface between two miscible fluids, in terms of the major eigenvalue provides a direct measure of the maximum rate of mixing. Two efficiency measures for mixing are derived in terms of the eigenvalues and their directions. The creation efficiency of the magnitude of the major eigenvalue as a function of the energy input into the flow field is evaluated. The orientation of the interface to the principal direction qualifies the mixing efficiency in laminar flow. The new theory is used to analyze two-dimensional and three-dimensional channels. The results demonstrate not only the continuum measures for mixing but also extend our present understanding on mixing and provide future directions. 相似文献
18.
Méndez RO Bueno K Campos N López D Wyatt CJ Ortega MI 《Archivos latinoamericanos de nutrición》2005,55(2):187-193
Developing countries diets are based on a variety of plant foods that often are the main suppliers of important amounts of iron (Fe) and zinc (Zn). The objectives of this study were 1) to measure the total and dialyzable amounts of Fe and Zn in foods from Northern Mexico (Sonora) and from Southern Mexico (Oaxaca) and 2) to evaluate the effect of meat content of diets on the dialyzable amount of Fe and Zn. Methods to calculate the total dialyzable amount of Fe and Zn, were those of the AOAC and of Shen et al. Total Fe in e northern Mexican foods went from 0.78 +/- 0.0 to 11.59 +/- to 0.03 mg/ 100g (dry weight, DW); in southern Mexican foods the same micronutrient amounts were 0.86 +/- 0.18 to 8.8 +/- 0.57 mg/100 g (BS). Total Zn values were 0.91 +/- 0.00 to 13.58 +/- 0.05 mg/100 g (DW) in Sonora, and 0.64 +/- 0.18 to 20.80 +/- 0.33 mg/100 g (DW) in Oaxaca. In northern Mexico, foods dialyzable Fe had values from 0.1 +/- 0.04% to 10.6 +/- 0.36% and for Zn from 4.0 +/- 0.21% to 55.32 +/- 0.14%. Meanwhile, the range of values of dialyzable Fe for foods from Oaxaca were from 0.22 +/- 0.06% to 9.40 +/- 0.14% for and from 2.41 +/- 0.26% to 54.27 +/- 1.49% for dialyzable Zn. The average value for dialyzable Fe was higher in the foods that contained meat or meat products (p= 0.001). 相似文献
19.
A flow cell was used for the in situ ESR monitoring of the state and reactivity of chromium ions in Cr-ZSM-5. Calcination of Cr(NO3)3/NH4-ZSM-5 in air at 500°C is accompanied by migration of chromium ions inside the zeolitic channels and stabilization ofisolated Cr5+ cations near lattice A13+ ions. Calcination of Cr-ZSM-5 at 750°C leads to a gradual disappearance of the isolated Cr5+ cations and formation of -Cr2O3 microcrystals. All the Cr5+ cations are accessible to gas-phase molecules: O2 strongly broadens the dipole-dipole signal; H2O sorption increases the local crystal field symmetry; admission of CCl4 results in a small change of the Cr5+ local coordination; strongly stabilized complexes on Cr-ZSM-5 are observed upon sorption of either NO or NO2. The sorption of C2H6 on Cr-ZSM-5 at 20°C is accompanied by a gradual reduction of the Cr5+ sites. At 500°C in [C3H6 + O2 + He] flow, even at a large excess of oxidant, the reduction of a noticeable part of Cr5+ ions takes place. At 400°C, in the same gas mixtures, a deeper reduction of Cr5+ occurs. Closer to stoichiometric conditions, in a [C3H6 + NO + He] flow with 120% excess of oxidant the Cr5+ is completely reduced at 500°C. The oxidation of propene is accompanied by coke deposition on the surface of the catalyst. The implications of the results are discussed. 相似文献
20.
Karl D. Hammond Geoffrey A. Tompsett Scott M. Auerbach W. Curtis Conner 《Journal of Porous Materials》2007,14(4):409-416
We present a non-destructive, reusable apparatus with which to measure physical adsorption isotherms of intact porous membranes.
We developed a two-piece sample container to make reliable sorption measurements of porous membranes, the properties of which
may differ from those of powders due to crystal intergrowth. This novel system employs a resealable container that can be
immersed in a cryogenic bath, into which tubular, planar, or other porous membranes and films may be placed. Detailed sorption
isotherms, including high-resolution adsorption in the low pressure (micropore-filling) region, are shown for MFI-type zeolite
membranes grown on two types and configurations of α-alumina support. 相似文献