全文获取类型
收费全文 | 68014篇 |
免费 | 7441篇 |
国内免费 | 3750篇 |
专业分类
电工技术 | 5684篇 |
技术理论 | 8篇 |
综合类 | 5156篇 |
化学工业 | 10039篇 |
金属工艺 | 4264篇 |
机械仪表 | 4328篇 |
建筑科学 | 5599篇 |
矿业工程 | 2383篇 |
能源动力 | 2058篇 |
轻工业 | 4380篇 |
水利工程 | 1619篇 |
石油天然气 | 3424篇 |
武器工业 | 807篇 |
无线电 | 8002篇 |
一般工业技术 | 7547篇 |
冶金工业 | 2866篇 |
原子能技术 | 924篇 |
自动化技术 | 10117篇 |
出版年
2024年 | 377篇 |
2023年 | 1345篇 |
2022年 | 2805篇 |
2021年 | 3674篇 |
2020年 | 2755篇 |
2019年 | 2100篇 |
2018年 | 2413篇 |
2017年 | 2627篇 |
2016年 | 2406篇 |
2015年 | 3385篇 |
2014年 | 4028篇 |
2013年 | 4717篇 |
2012年 | 5292篇 |
2011年 | 5606篇 |
2010年 | 4781篇 |
2009年 | 4471篇 |
2008年 | 4290篇 |
2007年 | 3914篇 |
2006年 | 3662篇 |
2005年 | 3012篇 |
2004年 | 2028篇 |
2003年 | 1482篇 |
2002年 | 1346篇 |
2001年 | 1063篇 |
2000年 | 1018篇 |
1999年 | 949篇 |
1998年 | 705篇 |
1997年 | 567篇 |
1996年 | 584篇 |
1995年 | 414篇 |
1994年 | 340篇 |
1993年 | 248篇 |
1992年 | 210篇 |
1991年 | 120篇 |
1990年 | 105篇 |
1989年 | 80篇 |
1988年 | 77篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 29篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1976年 | 9篇 |
1975年 | 3篇 |
1959年 | 9篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
本文叙述了我国管道业面临的市场机遇和受到天然气价格等因素的制约以及进口钢管的挑战。建议中国管道业应适当发展ERW610机组和UOE机组的高质量产品;在钢板上宜以X70级为主,设备潜力可向X80级为目标而努力。 相似文献
52.
53.
从油气勘探、开发投资的特性出发,正确选择投资绩效评价指标,是保证评价科学性以及进行中外对比研究的前提条件。 相似文献
54.
采用P型InP衬底新月型结构制备了1.48μm大功率激光器,该激光器与单模光纤耦合输出功率大于40mW。 相似文献
55.
56.
Li Xi Zuoyan Peng Wei Fan Kui Guo Gu Jianmin Muyu Zhao Wu Guoqiang 《Materials Science and Engineering: B》1996,40(2-3):147-152
SrMgxTi1 - xO3 nanocrystals (x = 0.1–0.6) were synthesized by the stearic acid gel method. Powder samples were characterized by X-ray diffraction and X-ray photoelectron (XP) spectroscopy. The results showed that the lattice parameter a and the O 1s XP spectrum changed not only with the Mg content x but also with the grain size d of the samples. The conductivity of a thick film specimen fabricated on an aluminium oxide wafer was investigated in a nitrogen—oxygen atmosphere. 相似文献
57.
Retroviral display of antibody fragments; interdomain spacing strongly influences vector infectivity 总被引:1,自引:0,他引:1
S Ager BH Nilson FJ Morling KW Peng FL Cosset SJ Russell 《Canadian Metallurgical Quarterly》1996,7(17):2157-2164
Five different single-chain antibody fragments (scFv) against human cell-surface antigens were displayed on murine ecotropic retroviral vectors by fusing them to the Moloney SU envelope glycoprotein. The spacing between the scFv and the SU glycoprotein was varied by fusing the scFv to residue +7 or to residue +1 of Moloney SU and by inserting linker sequences of different lengths between the domains. All of the chimeric envelopes were efficiently incorporated into vector particles and could bind to human cells through their displayed antibody fragments, but did not infect them. The spacing between the scFvs and the SU glycoproteins had no significant effect on the efficiency of envelope expression or viral incorporation and did not affect the binding properties of the chimeric envelopes, nor did it influence the efficiency of targeted gene delivery to human cells by scFv-displaying vectors. However, on murine fibroblasts the infectivity of vectors incorporating the chimeric envelopes was strongly influenced by the length of the interdomain spacer. The titers were very low when the single-chain antibodies were fused through a tripeptide linker to SU residue +7 and were greatly enhanced (up to 10(5)-fold) when they were fused to SU residue +1 through a heptapeptide linker. These results point to the importance of steric interactions between the domains of chimeric envelope glycoproteins and may have implications for retroviral vector design for human gene therapy. 相似文献
58.
59.
We present a method that is useful in the estimate and assessment of heat capacity data. The approach is based on an analysis of the logarithmic average of the phonon frequencies. In this quantity, that may be easily derived from experimental data on the vibrational entropy, the influence of atomic masses can be exactly accounted for even in polyatomic solids. Our method is applied to Li2O, Na2O, K2O, Rb2O, and Cs2O. In particular, literature data for K2O are critically examined. 相似文献
60.
A conjugative aminoglycoside resistance plasmid pST2 has been isolated from Escherichia coli K-12 14R525, which was mated with a clinical isolate of Salmonella typhimurium S24. A novel resistance gene of aminoglycoside 6'-N-acetyltransferase[AAC(6')] was cloned from plasmid pST2 on a 1,393 kilobase (kb) of SphI-SalI fragment into vector pACYC184 and pUC18. This novel AAC(6') gene in plasmid pST2 acetylated kanamycin, amikacin, dibekacin, tobramycin, gentamicin, netilmicin, and sisomicin. The complete nucleotide sequence of the novel AAC(6') gene and its neighboring sequences were also determined. Minicell experiments detected only one protein of 24.7 kilodaltons (kDa) translated from an open reading frame of the 618 base pairs (bp) gene. 相似文献