全文获取类型
收费全文 | 40853篇 |
免费 | 2825篇 |
国内免费 | 1007篇 |
专业分类
电工技术 | 1600篇 |
技术理论 | 4篇 |
综合类 | 1557篇 |
化学工业 | 7449篇 |
金属工艺 | 1786篇 |
机械仪表 | 2061篇 |
建筑科学 | 1803篇 |
矿业工程 | 761篇 |
能源动力 | 1511篇 |
轻工业 | 2710篇 |
水利工程 | 475篇 |
石油天然气 | 1024篇 |
武器工业 | 148篇 |
无线电 | 6332篇 |
一般工业技术 | 6456篇 |
冶金工业 | 3040篇 |
原子能技术 | 451篇 |
自动化技术 | 5517篇 |
出版年
2024年 | 110篇 |
2023年 | 520篇 |
2022年 | 961篇 |
2021年 | 1354篇 |
2020年 | 1068篇 |
2019年 | 930篇 |
2018年 | 1083篇 |
2017年 | 1124篇 |
2016年 | 1066篇 |
2015年 | 1224篇 |
2014年 | 1674篇 |
2013年 | 2472篇 |
2012年 | 2419篇 |
2011年 | 2815篇 |
2010年 | 2186篇 |
2009年 | 2288篇 |
2008年 | 2279篇 |
2007年 | 2035篇 |
2006年 | 1793篇 |
2005年 | 1468篇 |
2004年 | 1284篇 |
2003年 | 1345篇 |
2002年 | 1559篇 |
2001年 | 1309篇 |
2000年 | 947篇 |
1999年 | 816篇 |
1998年 | 1123篇 |
1997年 | 814篇 |
1996年 | 655篇 |
1995年 | 550篇 |
1994年 | 434篇 |
1993年 | 379篇 |
1992年 | 278篇 |
1991年 | 236篇 |
1990年 | 245篇 |
1989年 | 221篇 |
1988年 | 187篇 |
1987年 | 168篇 |
1986年 | 140篇 |
1985年 | 135篇 |
1984年 | 113篇 |
1983年 | 84篇 |
1982年 | 76篇 |
1981年 | 64篇 |
1980年 | 82篇 |
1979年 | 53篇 |
1978年 | 61篇 |
1977年 | 63篇 |
1976年 | 82篇 |
1975年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Byeong Il Noh Tae Kyung Yoon Byung Hyun Moon Jong Hyun Kim 《Korean Journal of Chemical Engineering》1995,12(1):18-22
Multicomponent mass transfer accompanied by instantaneous chemical reactions in a small drop has been modeled and simulated
for the case where two different solutes diffuse from a continuous phase into the drop and react rapidly with a third reactant
in the drop. The computational results obtained by Galerkin’s finite element method are reported in terms of concentration
profiles, the locations of reaction front, the cumulative mass flux, and the enhancement factor. The effects of physical parameters,
such as diffusivities of the solutes and the reactant, the interfacial concentration of solutes, and the relative amount of
the reactant, on the calculated quantities are discussed. 相似文献
122.
123.
Wen-Chau Liu Lih-Wen Laih Shiou-Ying Cheng Wen-Lung Chang Wei-Chou Wang Jing-Yuh Chen Po-Hung Lin 《Electron Devices, IEEE Transactions on》1998,45(2):373-379
In this paper, a new multiple negative-differential-resistance (MNDR) device based on a metal-insulator-semiconductor-insulator-metal (MISIM)-like structure with step-compositional InxGa1-x As quantum wells has been fabricated and demonstrated. The interesting MNDR phenomena are found in the current-voltage (I-V) characteristics of this device. At room temperature, the triple switching behaviours and quadruple stable operation states are obtained. In addition, the sixfold switching behaviors and a staircase-shaped I-V characteristic are observed at -105°C. A sequential carrier accumulation at InGaAs subwells and the potential lowering process are used to qualitatively explain the interesting MNDR phenomena. From the experimental results, it is shown that the studied device has good potential in multiple-valued logic applications 相似文献
124.
SR Marengo RA Sikes P Anezinis SM Chang LW Chung 《Canadian Metallurgical Quarterly》1997,19(3):165-175
The effects of the composition of bacteriological growth media on the light output in a chemiluminometric assay of beta-galactosidase in Escherichia coli using 1,2-dioxetane substrates has been studied. In this assay a basic conflict exists between conditions that promote optimal bacterial growth and those conducive to maximal chemiluminescence. Common medium ingredients such as yeast or beef extract, protein hydrolysates and lactose suppress light emission and/or lead to high backgrounds. Quenching of light emission is probably partly due to light absorption by medium ingredients such as oxgall, and partly to interference with the reaction triggering the chemiluminescent process. Elevated backgrounds are caused by the presence of high concentrations of protein hydrolysates, which interact with the alkali in the accelerator solution. Only two purposely developed media, i.e. ILM and Colicult are shown to reconcile the requirements of growth support with that of optimal luminescent properties. 相似文献
125.
从冷却曲线上相变段倾角最小原则出发,研究了新型激冷剂的配比与热分析法检测铸铁成分精度的关系,实验结果表明,能使相变段倾角最小的成分配比,也能提高对铸铁成分的热分析和检测精度。 相似文献
126.
127.
GIS技术与微机制图 总被引:1,自引:0,他引:1
地理信息系统(GIS)随着信息社会的发展愈发显示出强大的生命力。本文简要叙述GIS的重要作用及其发展进程中涌出出来的四个设计模型,总结了运用GIS国产软件平台MAPGIS制作遥感地质构造解译图的工作步骤和技术方法。 相似文献
128.
Ten groups of 14 immunosuppressed NMRI-mice (nu/nu) were raised and kept under germ-reduced conditions. The control animals were fed a germ-reduced diet, nine other groups received the same diet with selegiline (CAS 14611-51-9, Deprenyl) or lipoic acid (thioctic acid, CAS 62-46-4) admixed at various amounts. The 50% survival rate, the total life span of each group and the areas under the curves were determined to evaluate life expectancy as compared to the controls. The racemate of lipoic acid at high dosage (350 mg/kg body weight) reduced the life span significantly. The S(-)-enantiomer of lipoic acid (75 mg/kg body weight) increased the 50% survival rate, whereas the physiologic R(+)-enantiomer (9 mg/kg body weight) expanded the total life span of its group. Alteration of only one out of three parameters was not considered significant. All other groups except for one did not differ from controls: only animals which obtained 75 micrograms selegiline per kg of body weight and per day exerted increased life expectancies by all three parameters. This group exhibited also in statistical evaluation a significantly (p < 0.05) prolongated survival time up to about 200% as compared to the control animals. 相似文献
129.
We examined the molecular mechanism of metronidazole resistance by constructing a lambda-Zap II phagemid expression library with genomic DNA from a metronidazole-resistance strain of Helicobacter pylori. Twenty-two clones were found to have elevated MTZ resistances in XLOLR strain of E. coli. Phagemids belonging to the twenty two clones were extracted and then retransformed into the XLOLR strain of E. coli. After MTZ selection, five clones could confer metronidazole resistance consistently. According to Southern hybridization and DNA sequencing, the five clones contained a same locus, recA. In addition, transforming the five clones into BL21 strain of E. coli produced a higher resistance to MTZ. Interestingly, electroporation of one of the five phagemid clones into two MTZ sensitive H. pylori yielded MTZ resistant strains. Comparing amino acid sequence in MTZ resistant with sensitive isolates revealed two point mutations at this locus. Above results suggest that mutation in recA may be associated with metronidazole resistance of H. pylori. 相似文献
130.