全文获取类型
收费全文 | 2834篇 |
免费 | 18篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
综合类 | 6篇 |
化学工业 | 29篇 |
金属工艺 | 2篇 |
机械仪表 | 6篇 |
建筑科学 | 3篇 |
能源动力 | 19篇 |
轻工业 | 31篇 |
水利工程 | 1篇 |
无线电 | 21篇 |
一般工业技术 | 45篇 |
冶金工业 | 2676篇 |
原子能技术 | 2篇 |
自动化技术 | 10篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 6篇 |
2011年 | 7篇 |
2010年 | 7篇 |
2009年 | 8篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 2篇 |
2000年 | 2篇 |
1999年 | 106篇 |
1998年 | 873篇 |
1997年 | 501篇 |
1996年 | 333篇 |
1995年 | 169篇 |
1994年 | 139篇 |
1993年 | 179篇 |
1992年 | 12篇 |
1991年 | 22篇 |
1990年 | 27篇 |
1989年 | 32篇 |
1988年 | 19篇 |
1987年 | 23篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1980年 | 29篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 49篇 |
1976年 | 99篇 |
1975年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有2853条查询结果,搜索用时 15 毫秒
101.
Enrico Maccallini Theodoros Tsoufis Salvatore La Rosa Gennaro Chiarello Vincenzo Formoso Raffaele G. Agostino 《Carbon》2010,48(12):3434-3445
Fe-Co bimetallic catalysts supported on MgO were studied for the catalytic chemical vapor deposition growth of carbon nanotubes (CNTs). Different wt.% metal loadings were investigated at various deposition temperatures and times. Characterization of the products involved thermal analysis (DTA-TGA), X-ray diffraction, spectroscopy (Raman, UPS, EELS and STS) and microscopy (SEM, TEM and STM) techniques. It was found that the metal content is critical, not only to the yield and the structural quality of the synthesized carbon nanotubes, but it can be also used to tune the desired type of synthesized nanotubes. Lower (2 wt.%) loadings of Fe-Co catalysts favor the formation of single- and/or double-wall CNTs for deposition time and temperature 30 min and 800 °C, respectively. Thermal analysis and Raman measurements showed that these thin CNTs were synthesized at high amounts (CNT-per-catalyst wt.% of more than 100%), exhibiting high graphitization degree with only traces of by-products (mainly amorphous carbon) among them. Microscopy results revealed the formation of CNTs bundles, consisting of individual nanotubes with less than 2 nm outer diameter, while additional energy loss measurements pointed out that the deposited CNTs are mainly single wall. Higher (10 wt.%) Fe-Co loadings resulted to the formation of multi-wall CNTs. 相似文献
102.
103.
随着半导体制造业的不断发展,对现场浓度测量的需求也不断增加。化学品浓度细微变化都会对晶圆缺陷等级造成不良影响,最为重要的是会对产量产生影响。另外,减少液态化学品废弃物流,使其对环境的影响最小化面临着不断增长的压力。 相似文献
104.
105.
JJ Fins FG Miller CA Acres MD Bacchetta LL Huzzard BD Rapkin 《Canadian Metallurgical Quarterly》1999,17(1):6-15
The contributions of the various ulnar-innervated muscles of the hand to the hypothenar compound muscle action potential (CMAP) were estimated by directly stimulating individual muscles and by analyzing CMAP shape changes resulting from manipulations that changed individual muscle lengths. The results show that the first peak of the negative phase of the hypothenar CMAP comes from the hypothenar muscles, but that the second peak is due to a large volume-conducted potential from the interosseous muscles. The interosseous contribution affects both the amplitude and the area of the CMAP, and makes these parameters sensitive to changes in the configuration of the fingers and the temperature gradient in the hand. To reduce the interosseous contribution, a "balanced reference" consisting of two reference electrodes, one over each tendon, is proposed. 相似文献
106.
R Wikaningrum J Highton A Parker M Coleman PA Hessian PJ Roberts-Thompson MJ Ahern MD Smith 《Canadian Metallurgical Quarterly》1998,41(10):1783-1797
OBJECTIVE: To investigate the production of proinflammatory cytokines and expression of cell adhesion molecules in the rheumatoid nodule. METHODS: Cytokine content (tumor necrosis factor alpha [TNFalpha], interleukin-1beta [IL-1beta], and IL-1 receptor antagonist [IL-1Ra]), at the messenger RNA (mRNA) and protein levels, and cell adhesion molecule expression were studied in 16 rheumatoid nodules and 6 synovial membranes. RESULTS: Macrophages in the rheumatoid nodules contained TNFalpha, IL-1beta, and IL-1Ra mRNA and protein, particularly in perivascular cells of the stroma and in the palisading layer. All cell adhesion molecules studied were expressed in both the rheumatoid nodules and synovial membranes, with increased expression of E-selectin in the rheumatoid nodule compared with the synovial membrane, and with the absence of vascular cell adhesion molecule 1 expression on cells of the palisading layer in the rheumatoid nodule. CONCLUSION: The presence of similar proinflammatory cytokines and cell adhesion molecules in the rheumatoid nodule and synovial membrane suggests that similar pathogenic processes result in the chronic inflammation and tissue destruction in these lesions. 相似文献
107.
T cell recognition typically involves both the engagement of a specific T cell receptor with a peptide/major histocompatibility complex (MHC) and a number of accessory interactions. One of the most important interactions is between the integrin lymphocyte function-associated antigen 1 (LFA-1) on the T cell and intracellular adhesion molecule 1 (ICAM-1) on an antigen-presenting cell. By using fluorescence video microscopy and an ICAM-1 fused to a green fluorescent protein, we find that the elevation of intracellular calcium in the T cell that is characteristic of activation is followed almost immediately by the rapid accumulation of ICAM-1 on a B cell at a tight interface between the two cells. This increased density of ICAM-1 correlates with the sustained elevation of intracellular calcium in the T cell, known to be critical for activation. The use of peptide/MHC complexes and ICAM-1 on a supported lipid bilayer to stimulate T cells also indicates a major role for ICAM-1/LFA-1 in T cell activation but, surprisingly, not for adhesion, as even in the absence of ICAM-1 the morphological changes and adhesive characteristics of an activated T cell are seen in this system. We suggest that T cell antigen receptor-mediated recognition of a very small number of MHC/peptide complexes could trigger LFA-1/ICAM-1 clustering and avidity regulation, thus amplifying and stabilizing the production of second messengers. 相似文献
108.
DH Vandorpe BE Shmukler L Jiang B Lim J Maylie JP Adelman L de Franceschi MD Cappellini C Brugnara SL Alper 《Canadian Metallurgical Quarterly》1998,273(34):21542-21553
We have cloned from murine erythroleukemia (MEL) cells, thymus, and stomach the cDNA encoding the Ca2+-gated K+ (KCa) channel, mIK1, the mouse homolog of hIK1 (Ishii, T. M., Silvia, C., Hirschberg, B., Bond, C. T., Adelman, J. P., and Maylie, J. (1997) Proc. Natl. Acad. Sci.(U. S. A. 94, 11651-11656). mIK1 mRNA was detected at varied levels in many tissue types. mIK1 KCa channel activity expressed in Xenopus oocytes closely resembled the Kca of red cells (Gardos channel) and MEL cells in its single channel conductance, lack of voltage-sensitivity of activation, inward rectification, and Ca2+ concentration dependence. mIK1 also resembled the erythroid channel in its pharmacological properties, mediating whole cell and unitary currents sensitive to low nM concentrations of both clotrimazole (CLT) and its des-imidazolyl metabolite, 2-chlorophenyl-bisphenyl-methanol, and to low nM concentrations of iodocharybdotoxin. Whereas control oocytes subjected to hypotonic swelling remained swollen, mIK1 expression conferred on oocytes a novel, Ca2+-dependent, CLT-sensitive regulatory volume decrease response. Hypotonic swelling of voltage-clamped mIK1-expressing oocytes increased outward currents that were Ca2+-dependent, CLT-sensitive, and reversed near the K+ equilibrium potential. mIK1 mRNA levels in ES cells increased steadily during erythroid differentiation in culture, in contrast to other KCa mRNAs examined. Low nanomolar concentrations of CLT inhibited proliferation and erythroid differentiation of peripheral blood stem cells in liquid culture. 相似文献
109.
RT D'Aquila L Sutton A Savara MD Hughes VA Johnson 《Canadian Metallurgical Quarterly》1998,177(6):1549-1553
Mechanisms underlying the delay in dominance of syncytium-inducing (SI) phenotype HIV-1 (human immunodeficiency virus type 1) in vivo are unknown. Both random mutational events and selective pressures operative only late in the disease process have been suggested to underlie the shift from CCR5 to alternative coreceptor usage. Among the moderately advanced patients who entered AIDS Clinical Trials Group protocol 241, SI viral phenotype was more common among CCRS/delta(ccr5) heterozygotes (7/7, 100%) than among CCR5/CCR5 homozygotes (29/88, 33%; P < .001, Fisher's exact test). Other characteristics did not differ at study entry by CCR5 genotype, including median CD4 cell counts, plasma RNA levels, and infectious HIV-1 titers in circulating cells. These data indicate that CCR5/delta(ccr5) heterozygosity, which decreases cell-surface levels of CCR5 available to serve as an HIV-1 entry coreceptor, is a selective pressure for evolution of T cell line-tropic viruses that use an alternative coreceptor. 相似文献
110.
A new faster paradigm to measure the duration of auditory sensory memory, as indexed by mismatch negativity (MMN) suppression to stimuli presented at increasing inter-stimulus intervals (ISI), is proposed. Trains of three stimuli were delivered at very short ISI (300 ms). The inter-train interval varied according to the memory probe interval (MPI) tested. Trains started randomly with a deviant or standard stimulus (50% each), with their event-related brain potentials subtracted to obtain the MMN. The new paradigm provided MMNs identical to the conventional one at MPIs of 0.4 and 4.0 s in young subjects, and revealed MMN suppression when the MPI was increased to 5.0 s in older subjects. The new paradigm estimates auditory sensory memory duration in one-third the time of conventional MMN. 相似文献