全文获取类型
收费全文 | 979篇 |
免费 | 34篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 130篇 |
金属工艺 | 6篇 |
机械仪表 | 11篇 |
建筑科学 | 49篇 |
矿业工程 | 2篇 |
能源动力 | 10篇 |
轻工业 | 101篇 |
水利工程 | 9篇 |
石油天然气 | 1篇 |
无线电 | 28篇 |
一般工业技术 | 93篇 |
冶金工业 | 395篇 |
原子能技术 | 4篇 |
自动化技术 | 175篇 |
出版年
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 10篇 |
2020年 | 16篇 |
2019年 | 18篇 |
2018年 | 18篇 |
2017年 | 18篇 |
2016年 | 23篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 43篇 |
2012年 | 30篇 |
2011年 | 53篇 |
2010年 | 30篇 |
2009年 | 35篇 |
2008年 | 49篇 |
2007年 | 36篇 |
2006年 | 32篇 |
2005年 | 29篇 |
2004年 | 39篇 |
2003年 | 25篇 |
2002年 | 24篇 |
2001年 | 26篇 |
2000年 | 14篇 |
1999年 | 20篇 |
1998年 | 17篇 |
1997年 | 26篇 |
1996年 | 29篇 |
1995年 | 17篇 |
1994年 | 28篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 6篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有1017条查询结果,搜索用时 15 毫秒
11.
12.
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
13.
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
14.
宋继萍 《中国生物制品学杂志》2007,20(9):681-684,687
目的评估免疫细胞素Hu14.18-IL-2对黑色素瘤病人体内免疫作用。方法33位黑色素瘤病人用一种人源化抗神经节苷脂GD-2的单抗与IL-2融合的免疫细胞素进行治疗,按每天0.8、1.6、3.2、4.8、6.0、7.5 mg/m2静脉滴注,连续3 d为一疗程,病情稳定或缓解后,在第5周接受第2疗程治疗。观察病人外周血单核淋巴细胞抗体依赖的细胞毒性、自然杀伤细胞活性、IL-2的体外增殖以及IL-2可溶性受体的变化。结果Hu14.18-IL-2能诱导病人淋巴细胞的吞噬作用,增强外周血中自然杀伤细胞的杀伤能力和数目,使血清中IL-2受体复合体的可溶性受体α链水平上升。结论免疫细胞素Hu14.18-IL-2对黑色素瘤病人具有免疫激活作用。 相似文献
15.
A comparison of bending strength between adhesive and steel reinforced concrete with steel only reinforced concrete 总被引:1,自引:0,他引:1
Cracking of brittle cementitious composites subjected to excessive loading causes a potential reduction in material performance. Steel bars or metal fibers typically act as tensile reinforcing in concrete composites to increase the material's structural capacity in bending and to delay or prevent matrix cracking.The goal of this research is to determine whether the performance in bending strength and material integrity of a typically reinforced cementitious composite may be improved through the release of “healing” chemicals, such as adhesives, from hollow fibers into cracks induced by loading in addition to the metal reinforcing. Adhesive-filled repair fibers are intended to break immediately upon cracking in the concrete thereby activating the healing process with the release of a sealing or adhering substance. This self-repair occurs whenever and wherever cracks are generated. 相似文献
16.
James N. Seiber Paul M. Tuskes Lincoln P. Brower Carolyn J. Nelson 《Journal of chemical ecology》1980,6(2):321-339
Adult monarch butterflies,Danaus plexippus L. (Lepidoptera: Danaidae), store only some of the cardenolides present in the larval milkweed (Asclepiadaceae) host. Feeding known doses of individual cardenolides to 4th instar monarch larvae led to more efficient larval tissue incorporation at low doses than at high ones, and favored storage of cardenolide glycosides over genins. A qualitative regulation also occurs during larval feeding; calactin and calotropin were stored as such but uscharidin was rapidly converted to a mixture of calactin and calotropin which were the forms stored by the larvae. Two genins, uzarigenin and digitoxigenin, were stored by larvae as polar cardenolide metabolites.Research supported by National Science Foundation grants DEB 7514266 and DEB 7514266-AO2 (U.C. Davis) and DEB 7514265 (Amherst College). 相似文献
17.
Terry Carolyn J.; Blake Colin C. F. 《Protein engineering, design & selection : PEDS》1992,5(6):505-510
The structure of cleaved thyroxine-binding globulin (TBG) hasbeen modelled on the crystal structure of cleaved 1-antitrypsin(a member of the serine proteinase inhibitor, serpin, superfamily)based on the high sequence homology exhibited by the two proteins.Particular attention was paid to the identification and modelledcharacteristics of the thyroxine binding site. The primary aimof the study was to compare the site qualitatively with thecrystallographically determined binding site of transthyretin,the other major transporter of thyroxine, in an attempt to explainthe higher binding affinity of the site compared with the knownthyrox ine binding site in transthyretin (1010 versus 108 M1).The proposed binding site shares some similar characteristicswith the transthyretin binding site but also includes a clusterof aromatic residues which are entirely absent in transthyretin.It is proposed that this might account for the substantial differencein binding affinities. 相似文献
18.
Zirconia and yttria films were sputter deposited onto unheated fused silica substrates using a metal target and rare gas-oxygen discharges. Double-beam spectrophotometry was used to measure the transmission and reflection as a function of incident photon energy, E , from which the absorption coefficient, α( E ), was calculated. An indirect interband transition at E i = 4.70 eV and two direct interband transitions at E g1 = 5.17 eV and E g2 = 5.93 eV occur in monoclinic zirconia. Two direct interband transitions at E g1 = 5.07 eV and E g2 = 5.73 eV occur in cubic yttria. The absorption edge structure is modified when unusual phases, such as tetragonal zirconia, and zirconia and yttria with no longrange crystallographic order, are present. 相似文献
19.
J. Richard Hall Carolyn A. L. Westerdahl Andrew T. Devine Michael J. Bodnar 《应用聚合物科学杂志》1969,13(10):2085-2096
Polyethylene, polypropylene, poly(vinyl fluoride) (Tedlar), polystyrene, nylon 6, poly(ethylene terephthalate) (Mylar), polycarbonate, cellulose acetate butyrate, and a poly(oxymethylene) copolymer were treated with activated helium and with activated oxygen. Mechanical strengths of adhesive-bonded specimens prepared from treated and from untreated coupons were compared. Polyethylene (PE) and polypropylene (PP) showed the greatest increases in bond strength. Oxygen and helium were both effective with polyethylene, but polypropylene showed no improvement when treated with activated helium. The results with excited helium parallel the effects of ionizing radiation on these two polymers, as does the appearance of unsaturation bands in the infrared (965 cm?1 in PE, and 887 and 910 cm?1 in PP). Active nitrogen produced excellent bond strength with polyethylene but not with polypropylene. Of the remaining polymers examined, Tedlar, polystyrene, and nylon 6 showed the greatest improvement in bondability after treatment, and Mylar showed moderate improvement. Polycarbonate, cellulose acetate butyrate, and the poly(oxymethylene) copolymer gave approximately two-fold increases in lap-shear bond strength. In several cases, significant differences in response to time of treatment and type of excited gas were found. 相似文献
20.
Yuepu Guo Rodrigo Oliveira Spínola Carolyn Seaman 《Empirical Software Engineering》2016,21(1):159-182
Technical debt is a metaphor for delayed software maintenance tasks. Incurring technical debt may bring short-term benefits to a project, but such benefits are often achieved at the cost of extra work in future, analogous to paying interest on the debt. Currently technical debt is managed implicitly, if at all. However, on large systems, it is too easy to lose track of delayed tasks or to misunderstand their impact. Therefore, we have proposed a new approach to managing technical debt, which we believe to be helpful for software managers to make informed decisions. In this study we explored the costs of the new approach by tracking the technical debt management activities in an on-going software project. The results from the study provided insights into the impact of technical debt management on software projects. In particular, we found that there is a significant start-up cost when beginning to track and monitor technical debt, but the cost of ongoing management soon declines to very reasonable levels. 相似文献