全文获取类型
收费全文 | 22933篇 |
免费 | 2456篇 |
国内免费 | 1217篇 |
专业分类
电工技术 | 1587篇 |
技术理论 | 2篇 |
综合类 | 1582篇 |
化学工业 | 3672篇 |
金属工艺 | 1207篇 |
机械仪表 | 1488篇 |
建筑科学 | 1824篇 |
矿业工程 | 679篇 |
能源动力 | 614篇 |
轻工业 | 2174篇 |
水利工程 | 394篇 |
石油天然气 | 1151篇 |
武器工业 | 227篇 |
无线电 | 2758篇 |
一般工业技术 | 2896篇 |
冶金工业 | 873篇 |
原子能技术 | 259篇 |
自动化技术 | 3219篇 |
出版年
2024年 | 113篇 |
2023年 | 511篇 |
2022年 | 951篇 |
2021年 | 1262篇 |
2020年 | 938篇 |
2019年 | 774篇 |
2018年 | 827篇 |
2017年 | 921篇 |
2016年 | 873篇 |
2015年 | 1070篇 |
2014年 | 1337篇 |
2013年 | 1578篇 |
2012年 | 1828篇 |
2011年 | 1818篇 |
2010年 | 1606篇 |
2009年 | 1421篇 |
2008年 | 1408篇 |
2007年 | 1312篇 |
2006年 | 1100篇 |
2005年 | 883篇 |
2004年 | 628篇 |
2003年 | 485篇 |
2002年 | 413篇 |
2001年 | 407篇 |
2000年 | 342篇 |
1999年 | 387篇 |
1998年 | 273篇 |
1997年 | 251篇 |
1996年 | 185篇 |
1995年 | 144篇 |
1994年 | 128篇 |
1993年 | 88篇 |
1992年 | 61篇 |
1991年 | 52篇 |
1990年 | 38篇 |
1989年 | 34篇 |
1988年 | 23篇 |
1987年 | 31篇 |
1986年 | 18篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1968年 | 2篇 |
1959年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
超低碳奥氏体不锈钢00Cr18Ni10还原脱磷研究 总被引:1,自引:0,他引:1
在 2 5kg真空感应炉上用镁钙合金对超低碳奥氏体不锈钢 0 0Cr18Ni10进行了还原脱磷试验。通过充入工业纯氩使炉内压力为 6 6 .6 6kPa和精炼时的反应温度 14 5 0~ 15 0 0℃ ,加入镁钙合金 5 0kg t和助熔剂CaF2 11kg t,可使精炼后 0 0Cr18Ni10的磷含量进一步降低到 (5 0~ 6 0 )× 10 - 6 ,钢中氧、硫含量分别稳定降到(4~ 6 )× 10 - 6 和 15× 10 - 6 。 相似文献
82.
Ching‐Nan Chuang Liang Chao Ying‐Jie Huang Tar‐Hwa Hsieh Hung‐Yi Chuang Shu‐Chi Lin Ko‐Shan Ho 《应用聚合物科学杂志》2008,107(6):3917-3924
The synthesis of a p‐toluidine/formaldehyde (PTF) resin was performed, and the effects of the molar ratio of the individual monomers and the polymerization conditions on the structure of the PTF resin were studied. Fourier transform infrared and 13C‐NMR spectra were used to characterize the PTF. Wide‐angle X‐ray diffraction patterns revealed the crystalline structures of various PTFs. Polarized optical microscopy revealed that the molar ratio of the monomers had a strong effect on the crystalline morphologies. A longer polymerization time turned out a polymer with a higher intrinsic viscosity and molecular weight, which led to differences in the proton conductivity. All of the PTFs showed a higher proton conductivity than a commercial Nafion membrane at 90–100°C and 0% relative humidity. The proton conductivity of the PTF series could be improved by sulfonation with sulfuric acid and could be maintained after blending with polyurethane. Pure methanol could be used as a fuel source because of the insolubility and nonwetting properties of PTF in methanol to increase the output current density for a PTF membrane electrode assembly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
83.
84.
85.
86.
87.
随着单井蒸汽吞吐周期的增加,加剧了油层纵向和平面上的非均质性。汽驱井组油层存在高渗透带或孔道,注入蒸汽上升,从稠油顶部跨越,会出现越顶现象,造成提早汽窜,注蒸汽驱的波及效率进一步降低。针对此问题,开发了稠油注汽井用高温调剖封窜剂。室内研究结果表明,研制的高温调副封窜剂HD、HT具有较好的高温成胶性能和强度。现场应用孤东油田的9口井,有效8口,有效率88.9%,累计增油726.8t。 相似文献
88.
DP Kiel RH Myers LA Cupples XF Kong XH Zhu J Ordovas EJ Schaefer DT Felson D Rush PW Wilson JA Eisman MF Holick 《Canadian Metallurgical Quarterly》1997,12(7):1049-1057
Previous studies of the vitamin D receptor (VDR) polymorphisms and bone mineral density (BMD) have suggested that there may be differences in calcium absorption among groups of women with different VDR genotypes, and that the association may be stronger in younger women. To investigate the association between the VDR polymorphisms and BMD, this study was undertaken in the Framingham Study Cohort and a group of younger volunteers. Subjects from the Framingham Study (ages 69-90 years) included those who underwent BMD testing and who had genotyping for the VDR alleles (n = 328) using polymerase chain reaction methods and restriction fragment length polymorphisms with BsmI (B absence, b presence of cut site). A group of younger volunteer subjects (ages 18-68) also underwent BMD testing and VDR genotyping (n = 94). In Framingham Cohort subjects with the bb genotype, but not the Bb or BB genotypes, there were significant associations between calcium intake and BMD at five of six skeletal sites, such that BMD was 7-12% higher in those with dietary calcium intakes greater than 800 mg/day compared with those with intakes < 500 mg/day. The data also suggested that BMD was higher in persons with the bb genotype only in the group with calcium intakes above 800 mg/day. No significant differences were found in the Framingham Cohort for age-, sex-, and weight-adjusted BMD at any skeletal site between those with the BB genotype and those with the bb genotype regardless of 25-hydroxyvitamin D levels or country of origin. In the younger volunteers, BMD of the femoral neck was 5.4% higher (p < 0.05) in the bb genotype group compared with the BB group and 11% higher (p < 0.05) in males with the bb genotype compared with the BB group. There were no significant differences at the lumbar spine. In this study, the association between calcium intake and BMD appeared to be dependent upon VDR genotype. The findings of an association between dietary calcium intake and BMD only in the bb genotype group suggests that the VDR genotype may play a role in the absorption of dietary calcium. Studies that do not consider calcium intake may not detect associations between VDR genotype and BMD. In addition, the association between VDR alleles and BMD may become less evident in older subjects. 相似文献
89.