全文获取类型
收费全文 | 357557篇 |
免费 | 28887篇 |
国内免费 | 15736篇 |
专业分类
电工技术 | 21007篇 |
技术理论 | 45篇 |
综合类 | 25454篇 |
化学工业 | 59825篇 |
金属工艺 | 20837篇 |
机械仪表 | 22526篇 |
建筑科学 | 27773篇 |
矿业工程 | 11706篇 |
能源动力 | 9747篇 |
轻工业 | 24081篇 |
水利工程 | 6786篇 |
石油天然气 | 23510篇 |
武器工业 | 2808篇 |
无线电 | 38894篇 |
一般工业技术 | 39398篇 |
冶金工业 | 18588篇 |
原子能技术 | 3659篇 |
自动化技术 | 45536篇 |
出版年
2024年 | 1474篇 |
2023年 | 5578篇 |
2022年 | 9916篇 |
2021年 | 13851篇 |
2020年 | 10488篇 |
2019年 | 8562篇 |
2018年 | 9889篇 |
2017年 | 11113篇 |
2016年 | 10171篇 |
2015年 | 13936篇 |
2014年 | 17515篇 |
2013年 | 20976篇 |
2012年 | 22792篇 |
2011年 | 25269篇 |
2010年 | 22323篇 |
2009年 | 21119篇 |
2008年 | 20718篇 |
2007年 | 19748篇 |
2006年 | 20123篇 |
2005年 | 17704篇 |
2004年 | 11993篇 |
2003年 | 10718篇 |
2002年 | 9921篇 |
2001年 | 8843篇 |
2000年 | 8797篇 |
1999年 | 9410篇 |
1998年 | 7195篇 |
1997年 | 6145篇 |
1996年 | 5822篇 |
1995年 | 4792篇 |
1994年 | 3892篇 |
1993年 | 2625篇 |
1992年 | 2077篇 |
1991年 | 1571篇 |
1990年 | 1234篇 |
1989年 | 996篇 |
1988年 | 831篇 |
1987年 | 524篇 |
1986年 | 412篇 |
1985年 | 258篇 |
1984年 | 207篇 |
1983年 | 164篇 |
1982年 | 128篇 |
1981年 | 76篇 |
1980年 | 97篇 |
1979年 | 43篇 |
1978年 | 17篇 |
1977年 | 23篇 |
1976年 | 28篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
同等功率和照射时间条件下,在14只家兔大脑皮质运用伊文思蓝染料和超微结构观察方法进行血脑屏障改变的研究。结果表明:CO_2激光作用十分表浅,且激光作用后的水肿层血脑屏障改变是可逆的。 相似文献
962.
Bo PanD-Y Shang B.Q. Li H.C. de Groh 《International Journal of Heat and Mass Transfer》2002,45(1):125-144
Numerical modeling and analyses are presented of magnetic damping of g-jitter driven fluid flow and its effect on the solutal striation in a simplified Bridgman-Stockbarger crystal growth system under microgravity. The model development is based on the finite element solution of the momentum, energy and solute transport equations under g-jitter conditions in the presence of an external magnetic field. The numerical model is verified by comparison with analytical solutions obtained for a simple parallel plate channel flow driven by g-jitter in a transverse magnetic field. Simulations are carried out to study the behavior of convective flow and solutal transport induced by the combined g-jitter and magnetohydrodynamic forces. Both the idealized single frequency g-jitter force and the real g-jitter perturbation taken during space flight are considered. Results indicate that an applied magnetic field can effectively damp the velocity caused by g-jitter and help to reduce the time variation of solute redistribution. A stronger applied field is more effective in suppressing the convective flows and hence reducing concentration variation. It is found that g-jitter driven flows have the same oscillation period as the driving force with or without the applied field. However, an applied magnetic field shortens the transient period over which the flow field evolves into a quasi-steady state time harmonic oscillation after g-jitter sets in. The flow intensity increases with an increase in g-jitter magnitude but decreases with an increase in the applied field strength. The reduced convection in the liquid pool by the applied magnetic field results in a reduction of the concentration oscillation. The magnetic field is very useful in suppressing the spiking velocities that are induced by the spikes in the real g-jitter data. The damping effect is more pronounced if the magnetic field is switched on before the onset of g-jitter disturbances. 相似文献
963.
本文介绍用Turbo Pascal 5.0在3~+网上运行的DBASEⅢplus网络数据库中进行图形处理的技术. 相似文献
964.
965.
云南锰矿资源丰富,具有品位高、低磷低铁、易选等特点。文章概述了斗南、鹤庆、建水等锰矿的选矿科研进展情况,三个锰矿均可采用强磁选或磁-重选流程选别,可提高品位8—12%;精矿含锰可达33—35%,锰回收率在80%以上的好结果。 相似文献
966.
常减压蒸饱装置几起典型硫腐蚀事例分析 总被引:1,自引:1,他引:0
随着高(含)硫原油加工量的增加,硫腐蚀事故也时有发生。通过对常减压装置硫腐蚀事例进行分析,指出合理的混炼比,加强“一脱三注”管理,材料升级和实施腐蚀监测是防止腐蚀事故发生的有效措施。 相似文献
967.
Provision of Quality‐of‐Service (QoS) guarantees is an important and challenging issue in the design of integrated‐services
packet networks. Call admission control is an integral part of the challenge and is closely related to other aspects of networks
such as service models, scheduling disciplines, traffic characterization and QoS specification. In this paper we provide a
theoretical framework within which call admission control schemes with multiple statistical QoS guarantees can be constructed
for the Generalized Processor Sharing (GPS) scheduling discipline. Using this framework, we present several admission control
schemes for both session‐based and class‐based service models. The theoretical framework is based on recent results in the
statistical analysis of the GPS scheduling discipline and the theory of effective bandwidths. Both optimal schemes and suboptimal
schemes requiring less computational effort are studied under these service models. The QoS metric considered is loss probability.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
968.
The thermal stability and formation range of amorphous Al100-xLn5Nix (x = 3, 5, 9, 13, 17, 21, 23) alloys were studied by
differential scanning calorimetry and X-ray diffraction techniques. The microhardness, Hv, of these Al–RE–Ni alloys was measured.
The experimental results show that toughness was adversely affected by increase in the nickel content. The atomic size factor
was applied to explain the formation mechanism of aluminium-based amorphous alloys by the atomic clusters model. The minimum
concentration of nickel in Al–RE–Ni alloys results from the effective atomic volume difference of the nickel and aluminium
atoms.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
969.
Jun Xiang Ge Si Fan Li Yi Yuan Chen 《Journal of Infrared, Millimeter and Terahertz Waves》1991,12(7):811-818
In this paper, a new kind of solid-state quasi-optical power combiner is presented. It consists of two or more singlecavity multiple-device power combiners and a Fabry-Perot cavity. The experimenal results using six Gunn diodes at X-band show that the total output power is higher than 400 mW, the total combining efficiency is as high as 83%, and the frequency stability is better than 10?5. 相似文献
970.
A Saleem N Ibrahim M Patel XG Li E Gupta J Mendoza P Pantazis EH Rubin 《Canadian Metallurgical Quarterly》1997,57(22):5100-5106
Camptothecins are a new class of anticancer drugs that target DNA topoisomerase I; current efforts are directed toward elucidating optimal combinations of these drugs with other antineoplastic agents. A rationale for the use of sequential therapy involving the combination of camptothecins with topoisomerase II-targeting drugs, such as etoposide, has arisen from observations of increased topoisomerase II protein levels in cell lines resistant to camptothecin. In an effort to understand potential mechanisms of resistance to this strategy, we developed a U-937 cell subline, denoted RERC, that is capable of surviving exposure to sequential topoisomerase poisoning. The RERC cells are 200-fold resistant to camptothecin, 8-fold resistant to etoposide, and 10-fold hypersensitive to cisplatin compared to the parental U-937 cells. Biochemical analyses indicate that the resistant phenotype involves alterations in both topoisomerase I and topoisomerase IIalpha. Topoisomerase I catalytic activity in the resistant cells is similar to that of the parental line but is resistant to camptothecin. Moreover, the resistant cells express a single mRNA species of topoisomerase I that codes for a mutation in codon 533. In addition, topoisomerase IIalpha protein levels are decreased 10-fold in the resistant line, coincident with a two-fold decrease in the expression of topoisomerase IIalpha mRNA. Collectively, these results indicate that resistance to sequential topoisomerase poisoning may involve a reduction in total cellular topoisomerase activity. 相似文献