全文获取类型
收费全文 | 15475篇 |
免费 | 1110篇 |
国内免费 | 1267篇 |
专业分类
电工技术 | 201篇 |
技术理论 | 1篇 |
综合类 | 1099篇 |
化学工业 | 3269篇 |
金属工艺 | 1884篇 |
机械仪表 | 408篇 |
建筑科学 | 721篇 |
矿业工程 | 193篇 |
能源动力 | 453篇 |
轻工业 | 1909篇 |
水利工程 | 155篇 |
石油天然气 | 198篇 |
武器工业 | 86篇 |
无线电 | 1308篇 |
一般工业技术 | 4574篇 |
冶金工业 | 642篇 |
原子能技术 | 136篇 |
自动化技术 | 615篇 |
出版年
2024年 | 39篇 |
2023年 | 246篇 |
2022年 | 423篇 |
2021年 | 585篇 |
2020年 | 472篇 |
2019年 | 496篇 |
2018年 | 402篇 |
2017年 | 521篇 |
2016年 | 533篇 |
2015年 | 536篇 |
2014年 | 778篇 |
2013年 | 972篇 |
2012年 | 812篇 |
2011年 | 1139篇 |
2010年 | 886篇 |
2009年 | 930篇 |
2008年 | 897篇 |
2007年 | 918篇 |
2006年 | 785篇 |
2005年 | 691篇 |
2004年 | 661篇 |
2003年 | 515篇 |
2002年 | 472篇 |
2001年 | 381篇 |
2000年 | 381篇 |
1999年 | 282篇 |
1998年 | 297篇 |
1997年 | 247篇 |
1996年 | 212篇 |
1995年 | 171篇 |
1994年 | 150篇 |
1993年 | 125篇 |
1992年 | 147篇 |
1991年 | 138篇 |
1990年 | 126篇 |
1989年 | 84篇 |
1988年 | 69篇 |
1987年 | 35篇 |
1986年 | 37篇 |
1985年 | 47篇 |
1984年 | 59篇 |
1983年 | 31篇 |
1982年 | 25篇 |
1981年 | 20篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1977年 | 13篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Charles A. Bateman Lijie Zhang Helen M. Chan Martin P. Harmer 《Journal of the American Ceramic Society》1992,75(5):1281-1283
It is experimentally observed that the peritectic reaction, 211 + liquid → 123, can be driven essentially to completion in 1 h at an undercooling of only ∽30°C. The kinetic data, together with the observed microstructures, are inconsistent with the normal mechanism of the peritectic reaction. It is proposed that the mechanism of the reaction involves dissolution of 211 particles into the liquid and precipitation of solid 123. The aligned grain structure is explained through sympathetic nucleation of new 123 grains on existing grains. 相似文献
92.
Hongyu Wang Yolande Berta Gary S. Fischman 《Journal of the American Ceramic Society》1992,75(5):1080-1084
The microstructure of silicon carbide whiskers synthesized by carbothermal reduction of silicon nitride has been studied using transmission electron microscopy. All of the whiskers examined are single crystals, and grow in the (111) crystallographic direction. Two different forms of stacking faults and microtwins were observed; in one the planar defects are normal to the whisker growth direction, and the other has the defect planes at an angle of about 70° to the growth axis, while both forms of the defects are on the [111] closed-packed planes. Without the addition of catalyst, droplets containing metallic impurities were not found at the tips of the whiskers synthesized by the present process. A core and outer regions were observed in the single-crystal whiskers, which may be evidence that the whiskers were formed by a two-stage mechanism. 相似文献
93.
149 strains of bacteria, mostly brewery contaminants able to spoil wort or beer, and 12 brewing strains of yeast (8 ale and 4 lager strains) have been screened using a well-test assay for sensitivity to the food preservative, Nisin (E234), Nisin inhibited growth of 92% of the gram-positive strains, predominantly lactic acid bacteria of the genera Lactobacillus and Pediococcus. In contrast, all 32 gram-negative strains tested, except 3 Flavobacter strains, were Nisin-resistant; in addition none of the brewing yeasts showed Nisin-sensitivity. Therefore. Nisin has potential applications in preventing spoilage of worts or beers by lactic acid bacteria. 相似文献
94.
Stephen J. Spells 《Polymer》1985,26(13):1921-1928
The chain conformation of solution-crystallized polyethylene has previously been confirmed by infra-red spectroscopy, using the CD2 bending bandshape for samples with a minority of the deuterated species1–3. The method of calculating the i.r. band profile from molecular conformational models is now developed to give a more accurate representation of doublet splittings and to include the singlet component. The CH2 bending profile is calculated for samples with a deuterated matrix, and the good agreement with experimental data indicates that the same molecular model is applicable for samples with the deuterated polymer as either guest or matrix, for identical crystallization conditions. This result implies that isotopic fractionation is unimportant under these conditions. 相似文献
95.
J G De Nobel F M Klis A Ram H Van Unen J Priem T Munnik H Van Den Ende 《Yeast (Chichester, England)》1991,7(6):589-598
To study cell-cycle-related variations in wall permeability of Saccharomyces cerevisiae, two approaches were used. First, an asynchronous culture was fractionated by centrifugal elutriation into subpopulations containing cells of increasing size. The subpopulations represented different stages of the cell cycle as judged by light microscopy. Cell wall porosity increased when these subpopulations became enriched with budded cells. Secondly, synchronous cultures were obtained by releasing MATa cells from alpha-factor induced G1-arrest. These cultures grew synchronously for at least two generations. The cell wall porosity increased sharply in these cultures, shortly before buds became visible and was maximal during the initial stages of bud growth. It decreased in cells which had completed nuclear migration and before abscission of the bud had occurred. The porosity reached its lowest value during abscission and in unbudded cells. We examined the incorporation of mannoproteins into the wall during the cell cycle. SDS-extractable mannoproteins were incorporated continuously. However, the incorporation of glucanase-extractable mannoproteins, which are known to affect cell wall porosity, showed cyclic oscillations and reached its maximum after nuclear migration. This coincided with a rapid decrease in cell wall porosity, indicating that glucanase-extractable mannoproteins might contribute to this decrease. 相似文献
96.
Arjunan Arulchakkaravarthi Rakesh Kumar Parthasarathy Santhanaraghavan Sivaramakrishnan Muralithar Rengasamy Gopalakrishanan Perumalsamy Ramasamy 《Materials Research Innovations》2002,6(5-6):273-276
Organic molecular scintillating crystals are noted for their good timing and particle discrimination process. Trans-stilbene
is one such candidate noted for its good particle detection characteristics for the past five decades. Progressive strengthening
of detection characteristics of trans-stilbene has been attempted by improving crystal perfection. A series of timing resolution
studies have been carried out for the Bridgman grown trans-stilbene crystals under different experimental conditions. The
results were compared with the previously reported values. Pulse shape discrimination process has been carried out for 241Am and 252Cf sources and good discrimination has been obtained for gamma-alpha and gamma-neutron sources from the grown organic phosphor
crystal.
Electronic Publication 相似文献
97.
Crack propagation tests were carried out on 2024-T3 sheet specimens to study the effects of omitting low-amplitude cycles from the gust-dominated TWIST load sequence (MiniTWIST) and the removal of small load ranges from the manoeuvre-dominated FALSTAFF load sequence (short FALSTAFF). In other tests high-amplitude loads of TWIST and MiniTWIST were truncated at different levels. The results are compared with data from similar test programmes, including crack initiation. Attention is paid to unstationary crack growth retardation and a transient retardation during initial crack growth started by an artificial crack. 相似文献
98.
Johan M. Thevelein 《Yeast (Chichester, England)》1994,10(13):1753-1790
99.
本文论述了局部施肥对植株地上部与地下部的影响。局部施肥促进了施肥区根系的发达 ,第一侧根与第二侧根较多 ,根的吸收表面积增多 ,根鲜重增加 ,对养分的吸收能力增强 ,但整个根系与地上部的干鲜重下降。 相似文献
100.
平面Z-型软磁铁氧体频率特性的研究 总被引:2,自引:0,他引:2
研究分析了Co2Z材料显微结构与磁性能的关系,在普通铁氧体工艺中引入预磁化处理方法,并适当控制二次再结晶现象,成功地研制出高性能的Co2Z型宽频材料,Z-型铁氧体材料的共振频率可达1.8GHz以上,截止频率在1GHz附近,起始磁导率在8-13之间,介电常数相对较低(ε'<30)。 相似文献