全文获取类型
收费全文 | 49543篇 |
免费 | 4337篇 |
国内免费 | 2120篇 |
专业分类
电工技术 | 2818篇 |
技术理论 | 7篇 |
综合类 | 3214篇 |
化学工业 | 8279篇 |
金属工艺 | 2911篇 |
机械仪表 | 3192篇 |
建筑科学 | 3525篇 |
矿业工程 | 1572篇 |
能源动力 | 1537篇 |
轻工业 | 3093篇 |
水利工程 | 773篇 |
石油天然气 | 3118篇 |
武器工业 | 464篇 |
无线电 | 5799篇 |
一般工业技术 | 6320篇 |
冶金工业 | 2406篇 |
原子能技术 | 686篇 |
自动化技术 | 6286篇 |
出版年
2024年 | 177篇 |
2023年 | 888篇 |
2022年 | 1292篇 |
2021年 | 2108篇 |
2020年 | 1606篇 |
2019年 | 1327篇 |
2018年 | 1529篇 |
2017年 | 1759篇 |
2016年 | 1569篇 |
2015年 | 2048篇 |
2014年 | 2642篇 |
2013年 | 3161篇 |
2012年 | 3330篇 |
2011年 | 3565篇 |
2010年 | 3001篇 |
2009年 | 2864篇 |
2008年 | 2842篇 |
2007年 | 2694篇 |
2006年 | 2600篇 |
2005年 | 2217篇 |
2004年 | 1560篇 |
2003年 | 1344篇 |
2002年 | 1337篇 |
2001年 | 1158篇 |
2000年 | 1158篇 |
1999年 | 1155篇 |
1998年 | 965篇 |
1997年 | 815篇 |
1996年 | 760篇 |
1995年 | 579篇 |
1994年 | 490篇 |
1993年 | 329篇 |
1992年 | 262篇 |
1991年 | 195篇 |
1990年 | 168篇 |
1989年 | 132篇 |
1988年 | 110篇 |
1987年 | 58篇 |
1986年 | 54篇 |
1985年 | 33篇 |
1984年 | 28篇 |
1983年 | 23篇 |
1982年 | 24篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1976年 | 6篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
81.
82.
带隔板底水油藏油井临界产量计算公式 总被引:25,自引:9,他引:16
本给出了带隔板底水油藏油井的监界产量计算公式,它适用于所有带隔板底水油藏的油井。 相似文献
83.
本文描述一种基于8031单片机和TC8830AF语音处理器的PC机智能语音卡,通过软硬件设计解决了PC-8031-TC8830AF结构中的通讯问题。该语音卡在进行语音的合成、编辑和播放时,仅占用极少的PC机CPU处理时间,能满足计算机系统进行实时语音合成的要求。 相似文献
84.
1 INTRODUCTIONParticlesreinforcedtitaniumalloymatrixcomposites(TMCp)havewideapplicationfieldsfortheirattractivehighspecificstreng 相似文献
85.
通过密度测定和DSC热分析,观测了超高分子量聚乙烯的辐射效应。实验结果表明:在吸收剂量0—1.13MGy范围内,密度随吸收剂量的增加而增大,熔化热和熔点也有所增加,特别是在低剂量范围内增加十分明显。以上结果都说明,超高分子量聚乙烯在辐照过程中,结晶在完善或有新的结晶形成 相似文献
86.
We predict that, for wavelength division multiplexing optical-network applications, an asymmetrically dilated configuration of a 2×2 cross-connect is significantly better in terms of overall crosstalk when the levels of the bar-port crosstalk and the cross-port crosstalk are significantly different from each other, as is the case with optical-frequency filters which utilize grating-assisted coupling. As a verification, we present a simulation study with 2×2 polarization-diversified acousto-optic tunable filters. We present a recursive method to extend the principle of asymmetric dilation to larger-size cross-connect switches, and make a recommendation for an asymmetrically dilated 4×4 cross-connect configuration 相似文献
87.
本文论述了具有透明波导结构的量子阱半导体激光器及其光集成技术的其本原理及主要优点。尤其在实现高功率窄光束输出的光集成器件方面更显出其独特的优点。 相似文献
88.
Fernandez E.B. Gudes E. Haiyan Song 《Knowledge and Data Engineering, IEEE Transactions on》1994,6(2):275-292
The integration of object-oriented programming concepts with databases is one of the most significant advances in the evolution of database systems. Many aspects of such a combination have been studied, but there are few models to provide security for this richly structured information. We develop an authorization model for object-oriented databases. This model consists of a set of policies, a structure for authorization rules, and algorithms to evaluate access requests against the authorization rules. User access policies are based on the concept of inherited authorization applied along the class structure hierarchy. We propose also a set of administrative policies that allow the control of user access and its decentralization. Finally, we study the effect of class structuring changes on authorization 相似文献
89.
我们用PEG凝胶法合成出的LiFe_5O_3纳米晶,用XRD和TEM观测其粒径和形貌。用振动样品磁强计考察其比饱和磁化强度σ_s,随粒径口变化,得到样品的σ_s随D的减小而下降。 相似文献
90.
M Sternfeld G Ming H Song K Sela R Timberg M Poo H Soreq 《Canadian Metallurgical Quarterly》1998,18(4):1240-1249
Accumulated indirect evidence suggests nerve growth-promoting activities for acetylcholinesterase (AChE). To determine unequivocally whether such activities exist, whether they are related to the capacities of this enzyme to hydrolyze acetylcholine and enhance synapse development, and whether they are associated with alternative splicing variants of AChEmRNA, we used four recombinant human AChEDNA vectors. When Xenopus laevis embryos were injected with a vector expressing the synapse-characteristic human AChE-E6, which contains the exon 6-encoded C terminus, cultured spinal neurons expressing this enzyme grew threefold faster than co-cultured control neurons. Similar enhancement occurred in neurons expressing an insertion-inactivated human AChE-E6-IN protein, containing the same C terminus, and displaying indistinguishable immunochemical and electrophoretic migration properties from AChE-E6, but incapable of hydrolyzing acetylcholine. In contrast, the nonsynaptic secretory human AChE-I4, which contains the pseudointron 4-derived C terminus, did not affect neurite growth. Moreover, no growth promotion occurred in neurons expressing the catalytically active C-terminally truncated human AChE-E4, demonstrating a dominant role for the E6-derived C terminus in neurite extension. Also, AChE-E6 was the only active enzyme variant to be associated with Xenopus membranes. However, postsynaptic length measurements demonstrated that both AChE-E6 and AChE-E4 enhanced the development of neuromuscular junctions in vivo, unlike the catalytically inert AChE-E6-IN and the nonsynaptic AChE-I4. These findings demonstrate an evolutionarily conserved synaptogenic activity for AChE that depends on its hydrolytic capacity but not on its membrane association. Moreover, this synaptogenic effect differs from the growth-promoting activity of AChE, which is unrelated to its hydrolytic capacity yet depends on its exon 6-mediated membrane association. 相似文献