全文获取类型
收费全文 | 40279篇 |
免费 | 3892篇 |
国内免费 | 2175篇 |
专业分类
电工技术 | 2752篇 |
技术理论 | 1篇 |
综合类 | 3609篇 |
化学工业 | 6300篇 |
金属工艺 | 2410篇 |
机械仪表 | 2515篇 |
建筑科学 | 3007篇 |
矿业工程 | 1278篇 |
能源动力 | 1142篇 |
轻工业 | 3099篇 |
水利工程 | 927篇 |
石油天然气 | 1754篇 |
武器工业 | 511篇 |
无线电 | 4214篇 |
一般工业技术 | 4250篇 |
冶金工业 | 2783篇 |
原子能技术 | 547篇 |
自动化技术 | 5247篇 |
出版年
2024年 | 160篇 |
2023年 | 582篇 |
2022年 | 1060篇 |
2021年 | 1533篇 |
2020年 | 1157篇 |
2019年 | 968篇 |
2018年 | 1047篇 |
2017年 | 1083篇 |
2016年 | 963篇 |
2015年 | 1543篇 |
2014年 | 1818篇 |
2013年 | 2227篇 |
2012年 | 2610篇 |
2011年 | 2738篇 |
2010年 | 2616篇 |
2009年 | 2566篇 |
2008年 | 2487篇 |
2007年 | 2471篇 |
2006年 | 2405篇 |
2005年 | 2012篇 |
2004年 | 1555篇 |
2003年 | 1465篇 |
2002年 | 1682篇 |
2001年 | 1431篇 |
2000年 | 992篇 |
1999年 | 897篇 |
1998年 | 905篇 |
1997年 | 683篇 |
1996年 | 593篇 |
1995年 | 467篇 |
1994年 | 345篇 |
1993年 | 311篇 |
1992年 | 197篇 |
1991年 | 126篇 |
1990年 | 106篇 |
1989年 | 95篇 |
1988年 | 80篇 |
1987年 | 44篇 |
1986年 | 26篇 |
1985年 | 28篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 21篇 |
1981年 | 13篇 |
1980年 | 24篇 |
1979年 | 7篇 |
1977年 | 55篇 |
1976年 | 97篇 |
1961年 | 7篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
镶嵌在CaF2介质中纳米Cu团簇微观结构的研究 总被引:2,自引:0,他引:2
利用磁控溅射产生金属Cu团簇,同时蒸发CaF2介质,将Cu团簇包埋在CaF2介质中,团簇大小可通过改变溅射气压控制,用TEM研究了嵌埋团簇的结构,分析结果表明:Cu团簇呈三角状多晶结构,团簇大小为10 ̄70nm,基质CaF2晶体也为多晶结构,Cu团簇的晶格常数在包埋状态下发生了膨胀,膨胀率大约在16%左右。 相似文献
132.
133.
AN Reshetilov DA Efremov PV Iliasov AM Boronin NI Kukushskin RV Greene TD Leathers 《Canadian Metallurgical Quarterly》1998,13(7-8):795-799
Amperometric biosensors register oxygen depletion in response to analyte catabolism, and thus are limited by the availability of dissolved oxygen. Microbial sensors containing immobilized cells of Gluconobacter oxydans were hyperoxygenated to 400% of control levels and the effects on sensor responses to glucose were determined. Oxygenated perfluorodecalin (a completely fluorinated organic substance) was as effective in hyperoxygenation as direct sparging with O2, increasing sensor base medium oxygen concentrations from 9.3 to 37 mg/l. Hyperoxygenation enhanced maximal biosensor response amplitudes, particularly at high cell loading densities. Maximal response rates were also improved, although less dramatically. Results suggest that hyperoxygenation may be a new general approach for modulating biosensor responses. 相似文献
134.
用于生产甲基丙烯酸的杂多酸催化剂的研究 总被引:4,自引:0,他引:4
以异丁烯为原料的两段直接氧化生产甲基丙烯酸最新工艺有许多优点。其技术关键在于研制出高效的甲基丙烯醛选择性氧化催化剂。本文报道P-Mo-As-Cu杂多化合物催化剂的组成、制备条件对催化剂活性的影响。经优化后获得高选择性、高活性的二段氧化催化剂,其甲基丙烯酸收率达60%以上。 相似文献
135.
136.
Y. Ohshima H.S. Ahn M. Aoki S. Awa M. Fukushima H. Hayashii X.Q. Hu T.W. Hur S. Igarashi H. Ikeda H.C. Jeong K. Kaneyuki D.Y. Kim S.K. Kim A. Kuzmin M.H. Lee S. Noguchi A. Ochi H. Sagawa N. Sato N. Sugiyama K. Tamai T. Tanimori N. Toomi T.J. Wang K. Watanabe Y. Watanabe X.C. Zhong Y.C. Zhu 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,380(3):517-523
We studied the performance of a prototype electromagnetic calorimeter for the BELLE detector at the KEK proton synchrotron for an energy range of 0.25–3.5 GeV. The prototype consisted of an array of 6 × 5 CsI(Tl) crystals with 30 cm length (16.2 radiation lengths) and about 6 cm × 6 cm cross section. The scintillation light of each CsI(Tl) crystal was read out by two large-area PIN photodiodes and charge-sensitive preamplifiers attached at the rear face of the crystal. We measured the energy and position resolution for electrons and the e/π separation for two sets of matrix configurations: one corresponded to the center and the other to the edge of the barrel calorimeter. The overall performance measured by the test proves that the prototype calorimeter is satisfactory for the use in the BELLE detector. 相似文献
137.
EA.hy 926 cells, a human endothelial cell line, show characteristics of differentiated endothelial cells. The cells express saturable binding of apo E-free 125I-high density lipoprotein3 (HDL3). Bmax increased from 71 to 226 ng HDL3 bound/mg cell protein after cholesterol loading of the confluent endothelial cells with cationized low density lipoprotein (LDL). The affinity did not change after cholesterol enrichment (Kd was 37 micrograms HDL3 protein/ml for control cells and 31 micrograms/ml for loaded cells). Incubation of cholesterol-loaded EA.hy 926 cells with native HDL and LDL had different effects on cellular cholesterol levels. Incubation with HDL decreased both esterified and unesterified cellular cholesterol, but LDL did not change total cellular cholesterol. However, LDL tended to increase cellular cholesteryl esters, with a concomitant decrease of unesterified cellular cholesterol. Incubation of endothelial cells with both HDL and LDL also resulted in decreased total cellular cholesterol levels. These data show that cationized LDL-loaded human endothelial EA.hy 926 cells can be used to study the net transport of cellular cholesterol to HDL, the first step in reverse cholesterol transport. 相似文献
138.
139.
Antisense oligodeoxynucleotides were used to determine whether alterations in the expression of N-methyl-D-aspartate (NMDA) receptor subunit mRNA are responsible for developmental changes in the sensitivity of receptors to agonists and antagonists. Xenopus laevis oocytes were injected with mRNA prepared from neonatal and adult rat cerebral cortex, and the effects of agonists and antagonists were determined under voltage-clamp conditions. Glycine-site antagonists like 7-chlorokynurenate and glutamate-site antagonists like CGP-39653 were more potent at NMDA receptors expressed from mRNA from adult rat cerebral cortex than those expressed from mRNA from 1-day-old rat. NMDA receptors from 1-day-old rat cerebral cortex were more sensitive to activation by glycine than were receptors from adult rat cerebral cortex. 7-Chlorokynurenate and CGP-39653 were more potent inhibitors of responses seen with heteromeric NR1/NR2A receptors than with NR1/ NR2B receptors. Conversely, heteromeric NR1/NR2B receptors were more sensitive to activation by glycine than were NR1/NR2A receptors. We previously described a delay in the expression of the NR2A subunit in developing rat brain. Anti-sense oligodeoxynucleotides were used to determine whether the delayed expression of the NR2A subunit underlies changes in pharmacological properties observed during development. The properties of receptors seen when adult brain mRNA was coinjected with antisense oligodeoxynucleotides against the NR2A subunit were similar to those found in receptors from 1-day-old rat brain. These data suggest that changes in the sensitivity of NMDA receptors to antagonists and to glycine seen during development are a result of alterations in the expression of different species of NR2 subunit mRNA. 相似文献
140.
Summary We consider a circular cylindrical membrane subjected to longitudinal extension and twist. The associated equilibrium deformation is considered to be axisymmetric and the analysis is based on a direct two-dimensional formulation. Wrinkling of the membrane is taken into account in an approximate way by introducing arelaxed strain energy function derived from the neo-Hookean strain energy for isotropic elastic solids. Analytical formulae for wrinkled parts of the membrane are used to corroborate the results of a numerical treatment of the full boundary value problem.Dedicated to the memory of A. C. Pipkin 相似文献