全文获取类型
收费全文 | 709415篇 |
免费 | 9879篇 |
国内免费 | 1920篇 |
专业分类
电工技术 | 12964篇 |
综合类 | 707篇 |
化学工业 | 105051篇 |
金属工艺 | 31356篇 |
机械仪表 | 23208篇 |
建筑科学 | 16420篇 |
矿业工程 | 4330篇 |
能源动力 | 18077篇 |
轻工业 | 56123篇 |
水利工程 | 8034篇 |
石油天然气 | 14950篇 |
武器工业 | 53篇 |
无线电 | 78093篇 |
一般工业技术 | 144124篇 |
冶金工业 | 130162篇 |
原子能技术 | 15177篇 |
自动化技术 | 62385篇 |
出版年
2021年 | 6245篇 |
2020年 | 4549篇 |
2019年 | 5858篇 |
2018年 | 15047篇 |
2017年 | 15242篇 |
2016年 | 13398篇 |
2015年 | 7287篇 |
2014年 | 11742篇 |
2013年 | 30165篇 |
2012年 | 19809篇 |
2011年 | 29945篇 |
2010年 | 24630篇 |
2009年 | 26257篇 |
2008年 | 26560篇 |
2007年 | 27559篇 |
2006年 | 19185篇 |
2005年 | 19680篇 |
2004年 | 17934篇 |
2003年 | 17587篇 |
2002年 | 16072篇 |
2001年 | 15893篇 |
2000年 | 14769篇 |
1999年 | 15414篇 |
1998年 | 39394篇 |
1997年 | 27646篇 |
1996年 | 21186篇 |
1995年 | 15879篇 |
1994年 | 13869篇 |
1993年 | 13739篇 |
1992年 | 9994篇 |
1991年 | 9579篇 |
1990年 | 9267篇 |
1989年 | 8991篇 |
1988年 | 8458篇 |
1987年 | 7520篇 |
1986年 | 7486篇 |
1985年 | 8324篇 |
1984年 | 7777篇 |
1983年 | 7011篇 |
1982年 | 6536篇 |
1981年 | 6588篇 |
1980年 | 6399篇 |
1979年 | 6303篇 |
1978年 | 6091篇 |
1977年 | 7161篇 |
1976年 | 9095篇 |
1975年 | 5375篇 |
1974年 | 5056篇 |
1973年 | 5235篇 |
1972年 | 4368篇 |
排序方式: 共有10000条查询结果,搜索用时 100 毫秒
991.
F Douaud N Le Roch J Renault R Havouis M Vaultier JP Moulinoux N Seiler 《Canadian Metallurgical Quarterly》1997,12(8):621-633
Several dimethylsilane tetramines [homologs of spermine with an Si(CH3)2 group in the central carbon chain], a carbon analog of the dimethylsilane tetramines [containing C(CH3)2 instead of Si(CH3)2] and a dimethylsilane hexamine were studied with regard to their cytotoxic activity and their ability to interact with double-stranded DNA. All polyamine analogs exerted cytostatic effects to several cell lines at micromolar concentrations. Their ability to condense DNA was comparable to and their ability to displace ethidium bromide from binding to DNA was superior to that of spermine. Their cytostatic effect was not correlated with the depletion of cellular spermidine concentrations. It is suggested that the new polyamine analogs act mainly by displacing spermidine from binding sites which are essential for the promotion of cell growth. 相似文献
992.
Photonic networks based on the optical path concept and wavelength division multiplexing (WDM) technology require unique operation, administration, and maintenance (OAM) functions. In order to realize the required OAM functions, the optical path network must support an effective management information transfer method. The method that superimposes a pilot tone on the optical signal appears very interesting for optical path overhead transfer. The pilot tone transmission capacity is determined by the carrier to noise ratio which depends on the power spectral density of the optical signal. The pilot tone transmission capacity of an optical path network employing WDM technology is elucidated; 4.5 kb/s transmission can be realized when the pilot tone modulation index is set at 3% 相似文献
993.
A dental student developed swelling of the lips and peri-oral urticaria, immediately after placement of a dental rubber dam during a chairside demonstration of clinical dentistry. A provisional diagnosis of a Type I hypersensitivity reaction to natural rubber latex was made and an appointment organised for specialist investigations. The student reported an atopic history and allergy to peanuts. A Radioallergosorbent Test (RAST), to measure Ig-E antibodies to latex, was positive. The dental student was given advice concerning the avoidance of natural rubber latex. Dental staff must be aware of potentially serious reactions to natural rubber latex in the dental surgery. 相似文献
994.
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
995.
996.
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
997.
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
998.
999.
George V. Eleftheriades Gabriel M. Rebeiz 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(10):1925-1946
In this paper, an efficient implementation of the spectral domain moment technique is presented for computing the self and mutual coupling between slot antennas on a dielectric half-space. It is demonstrated that by the proper selection of the weighting functions in the method of moments, the analytic evaluation or simplification of the transverse moment integrals is enabled. This results into a significant reduction of the required computational labor. The method is then utilized in order to provide design data for the self and mutual admittances between two slot antennas on a dielectric substrate lens in the case of fused quartz (∈ r =3.80), crystal quartz (∈ r =4.53), silicon (∈ r =11.9) and GaAs (∈ r =12.8). The presented technique and associated results are useful when designing twin slot quasi-optical receivers, imaging arrays, phased arrays or power-combining arrays of slot elements at millimeter-wave frequencies. 相似文献
1000.