全文获取类型
收费全文 | 696440篇 |
免费 | 10951篇 |
国内免费 | 2202篇 |
专业分类
电工技术 | 12480篇 |
综合类 | 679篇 |
化学工业 | 102574篇 |
金属工艺 | 25534篇 |
机械仪表 | 20083篇 |
建筑科学 | 17417篇 |
矿业工程 | 2703篇 |
能源动力 | 19674篇 |
轻工业 | 64490篇 |
水利工程 | 6576篇 |
石油天然气 | 10849篇 |
武器工业 | 41篇 |
无线电 | 82641篇 |
一般工业技术 | 132903篇 |
冶金工业 | 137434篇 |
原子能技术 | 12756篇 |
自动化技术 | 60759篇 |
出版年
2021年 | 5981篇 |
2020年 | 4433篇 |
2019年 | 5615篇 |
2018年 | 9450篇 |
2017年 | 9286篇 |
2016年 | 9853篇 |
2015年 | 6973篇 |
2014年 | 11572篇 |
2013年 | 32672篇 |
2012年 | 18833篇 |
2011年 | 26409篇 |
2010年 | 20681篇 |
2009年 | 23196篇 |
2008年 | 23981篇 |
2007年 | 23602篇 |
2006年 | 21008篇 |
2005年 | 19171篇 |
2004年 | 18393篇 |
2003年 | 18170篇 |
2002年 | 17175篇 |
2001年 | 17416篇 |
2000年 | 16122篇 |
1999年 | 17225篇 |
1998年 | 43978篇 |
1997年 | 30700篇 |
1996年 | 23365篇 |
1995年 | 17596篇 |
1994年 | 15316篇 |
1993年 | 15003篇 |
1992年 | 10754篇 |
1991年 | 10102篇 |
1990年 | 9727篇 |
1989年 | 9295篇 |
1988年 | 8764篇 |
1987年 | 7547篇 |
1986年 | 7397篇 |
1985年 | 8546篇 |
1984年 | 7926篇 |
1983年 | 7056篇 |
1982年 | 6614篇 |
1981年 | 6774篇 |
1980年 | 6342篇 |
1979年 | 6119篇 |
1978年 | 5794篇 |
1977年 | 6990篇 |
1976年 | 9097篇 |
1975年 | 4999篇 |
1974年 | 4677篇 |
1973年 | 4887篇 |
1972年 | 3896篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In order to observe the transport ability of peritoneum to small molecular substances, peritoneal equilibration test (PET) was performed in 52 CAPD patients. By analysing the relationship between peritoneal transport function and dialysis adequacy, we found the average urea KT/V and Cr were significantly lower in high and low transport groups (n = 6 and n = 2) than in high average and low average groups (n = 35 and n = 9). According to the results of PET, we adjusted the dialysis program of 11 patients and the dialysis adequacy was markedly improved. We concluded that PET was helpful for selecting and adjusting CAPD program, and discussed some questions which should be payed more attention in PET operation. 相似文献
992.
993.
994.
J Nesvera M Pátek J Hochmannová Z Abrhámová V Becvárová M Jelínkova J Vohradsky 《Canadian Metallurgical Quarterly》1997,179(5):1525-1532
The complete nucleotide sequence (4,826 bp) of the cryptic plasmid pGA1 from Corynebacterium glutamicum was determined. DNA sequence analysis revealed four putative coding regions (open reading frame A [ORFA], ORFA2, ORFB, and ORFC). ORFC was identified as a rep gene coding for an initiator of plasmid replication (Rep) according to the high level of homology of its deduced amino acid sequence with the Rep proteins of plasmids pSR1 (from C. glutamicum) and pNG2 (from Corynebacterium diphtheriae). This function was confirmed by deletion mapping of the minimal replicon of pGA1 (1.7 kb) which contains only ORFC. Deletion derivatives of pGA1 devoid of ORFA exhibited significant decreases in the copy number in C. glutamicum cells and displayed segregational instability. Introduction of ORFA in trans into the cells harboring these deletion plasmids dramatically increased their copy number and segregational stability. The ORFA gene product thus positively influences plasmid copy number. This is the first report on such activity associated with a nonintegrating bacterial plasmid. The related plasmids pGA1, pSR1, and pNG2 lacking significant homology with any other plasmid seem to be representatives of a new group of plasmids replicating in the rolling-circle mode. 相似文献
995.
The biased percolation model is proposed for investigating device degradation and failure associated with the generation of defects due to local Joule heating. The degradation processes of a thin conducting or semiconducting film is monitored by a set of relevant indicators, such as: the evolution of damage pattern, the current distribution, the film resistance and its fluctuations, the defect concentration, the film lifetime, etc. The conductor-insulator (CI) and conductor-superconductor (CS) like degradation processes are considered. The results can be used to propose non-destructive indicators to test the reliability of samples and to interpret the corresponding experiments. 相似文献
996.
Le C.T.C. Ishimaru A. Kuga Y. Yea J.-H. 《Geoscience and Remote Sensing, IEEE Transactions on》1998,36(1):61-71
The polarimetric angular memory effect is applied to obtain the average topographic height of a rough surface. This novel effect improves the height sensitivity while maintaining a good degree of correlation between the sensors. By using a reference flat surface, the interferometric phase is linearly related to the mean topographic height. The combination of angular memory and wideband frequency interferometry (AMFI) is realized and offers a means to design a robust interferometric system. Extension of the technique to the pulse scattering problem is studied through the two-frequency mutual coherence function, and its time-domain transform provides an equivalent way to obtain the mean topographic height by combining both spatial and temporal diversity. Millimeter-wave (MMW) experiments are conducted with rough surfaces of different statistics and scattering media of different types (gravel, sand, and rough surfaces) to prove the effectiveness of the technique 相似文献
997.
Li Wang ping Mechanics Department Huazhong University of Science Technology Wuhan P.R.China Yeo K.S. Khoo B.C. Mechanical Production Engineering Department National University of Singapore 《水动力学研究与进展(B辑)》1999,(3)
1. INTRODUCTIONThemaingoalofthispaperistoexplorethepossibilitytolearnmoreaboutthemechanismofturbulentboundarylayerflowinteractionsanditseffectsoncompliantwallperformance.Therearecertainprerequisiteconditionstofurtherthestudyonthemechanism,i.e.theco… 相似文献
998.
999.
Approaches to using visual language in a cultural context can be placed on a continuum, with global (universal) on one end and culture-focused on the other. Each approach reveals contrasting assumptions about three central design issues: perception, aesthetics and pragmatics. The global approach is characterized by attempts to invent an objective, universal visual language or to define such a language through perceptual principles and empirical research. The culture-focused perspective is founded on the principle that visual communication is intimately bound to experience and hence can function only within a given cultural context, to which designers must be sensitive. While the modernist, universal approach has been losing ground to the postmodern, culture-focused approach, the two complement each other in a variety of ways and, depending on the rhetorical situation, offer pragmatic benefits and drawbacks 相似文献
1000.
The robust Schur stability of a polynomial with uncertain coefficients will be investigated. A formula for the stability radius of a Schur polynomial is established. The result is the counterpart of [1] for linear discrete-time systems 相似文献