全文获取类型
收费全文 | 623篇 |
免费 | 33篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 31篇 |
综合类 | 2篇 |
化学工业 | 109篇 |
金属工艺 | 16篇 |
机械仪表 | 25篇 |
建筑科学 | 18篇 |
矿业工程 | 13篇 |
能源动力 | 44篇 |
轻工业 | 13篇 |
水利工程 | 4篇 |
石油天然气 | 3篇 |
无线电 | 49篇 |
一般工业技术 | 134篇 |
冶金工业 | 111篇 |
原子能技术 | 16篇 |
自动化技术 | 69篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 16篇 |
2020年 | 14篇 |
2019年 | 8篇 |
2018年 | 33篇 |
2017年 | 20篇 |
2016年 | 21篇 |
2015年 | 12篇 |
2014年 | 20篇 |
2013年 | 27篇 |
2012年 | 41篇 |
2011年 | 37篇 |
2010年 | 22篇 |
2009年 | 24篇 |
2008年 | 29篇 |
2007年 | 16篇 |
2006年 | 18篇 |
2005年 | 8篇 |
2004年 | 13篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 29篇 |
1997年 | 15篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1982年 | 3篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 4篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1962年 | 4篇 |
排序方式: 共有657条查询结果,搜索用时 31 毫秒
71.
72.
The virion host shutoff (vhs) function of herpes simplex virus induces degradation of host mRNAs at early times and rapid turnover of viral mRNAs throughout infection. Previous studies have shown that disruption of the UL41 gene abrogates vhs activity, but have not determined whether the UL41 polypeptide is the direct inducer of mRNA degradation or whether it is the only virion component required for this activity. In this paper we report that transfection of cells with UL41 inhibits expression of a cotransfected CAT reporter gene and that the inhibition is not dependent upon other viral genes. Inhibition of CAT expression was due to UL41-dependent reduction of CAT mRNA levels. UL41 alleles encoding polypeptides that lacked vhs activity during virus infections exhibited a similar lack of activity in transfected cells. The results indicate that the UL41 polypeptide is the direct inducer of host mRNA degradation following virus infection and that it is the only virion component directly required for this activity. A 382-amino-acid nonsense polypeptide missing the last 107 residues of UL41 lacked inhibitory activity, but was packaged into virions, while a 343-amino-acid nonsense polypeptide lacked both inhibitory activity and the ability to be packaged. 相似文献
73.
J Anderson L Phan R Cuesta BA Carlson M Pak K Asano GR Bj?rk M Tamame AG Hinnebusch 《Canadian Metallurgical Quarterly》1998,12(23):3650-3662
Gcd10p and Gcd14p are essential proteins required for the initiation of protein synthesis and translational repression of GCN4 mRNA. The phenotypes of gcd10 mutants were suppressed by high-copy-number IMT genes, encoding initiator methionyl tRNA (tRNAiMet), or LHP1, encoding the yeast homolog of the human La autoantigen. The gcd10-504 mutation led to a reduction in steady-state levels of mature tRNAiMet, attributable to increased turnover rather than decreased synthesis of pre-tRNAiMet. Remarkably, the lethality of a GCD10 deletion was suppressed by high-copy-number IMT4, indicating that its role in expression of mature tRNAiMet is the essential function of Gcd10p. A gcd14-2 mutant also showed reduced amounts of mature tRNAiMet, but in addition, displayed a defect in pre-tRNAiMet processing. Gcd10p and Gcd14p were found to be subunits of a protein complex with prominent nuclear localization, suggesting a direct role in tRNAiMet maturation. The chromatographic behavior of elongator and initiator tRNAMet on a RPC-5 column indicated that both species are altered structurally in gcd10Delta cells, and analysis of base modifications revealed that 1-methyladenosine (m1A) is undetectable in gcd10Delta tRNA. Interestingly, gcd10 and gcd14 mutations had no effect on processing or accumulation of elongator tRNAMet, which also contains m1A at position 58, suggesting a unique requirement for this base modification in initiator maturation. 相似文献
74.
The paper evaluates the thermodynamical, economical and environmental characteristics of a cogeneration system composed of a gas turbine and a waste heat boiler (system A). Two other systems for increasing power generating efficiency are also evaluated, namely systems B and C, which are constructed by incorporating a regenerative cycle and a dual fluid cycle, respectively, into system A. It has been estimated that system C satisfies an environmental constraint that the nitrogen oxide density exhausted should be less than 100 parts in 106, and that systems A and B also satisfy this constraint if a small amount of steam is injected into the combustor. The power generating efficiencies of systems A and B, in this case, and that of system C have been estimated to be 33.5%, 38.5% and 41.2%, respectively; i.e. the efficiencies of systems B and C can be improved noticeably compared with that of system A. The economics of these systems have also been evaluated based on the value of a profit index, and the systems are all estimated to be economically viable under the conditions assumed. As a result, it has been shown that it is possible to construct cogeneration systems with satisfactory characteristics of both environmental protection and profitability if system A is used in districts where the heat demand is large, system C in districts where the heat demand is small, and system B in districts with intermediate heat demand. 相似文献
75.
76.
Heuristical job allocation in a flexible manufacturing system 总被引:1,自引:1,他引:0
T. S. Chan H. A. Pak 《The International Journal of Advanced Manufacturing Technology》1986,1(2):69-90
Two heuristic algorithms are presented for solving the scheduling problem in a statically loaded Flexible Manufacturing System
(FMS). The heuristics goal is to minimise the total cost resulting from the tardiness of jobs. Using the same heuristics,
an iterative method is proposed to find an optimal makespan and the average lead time. Modifications required to handle the
case of a dynamically loaded FMS are then presented. Simulation results show that the developed heuristics appear to out perform
the other published techniques used in obtaining the schedules associated with minimum makespan, minimum average lead time
and minimum cost of tardiness. Finally, the simulation of the dynamic case shows that the algorithms could be implemented
locally on each station for the scheduling calculation. 相似文献
77.
Technique for suppression of pattern dependence in a semiconductor-optical-amplifier wavelength converter 总被引:1,自引:0,他引:1
D. Mahgerfteh Pak Cho J. Goldhar G.L. Burdge 《Photonics Technology Letters, IEEE》1997,9(12):1583-1585
Wavelength converters that employ cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs) are limited in bit rate by the amplifier's pattern dependent response. We substantially suppress this pattern dependence by converting the phase modulation at the data transitions to amplitude modulation using a fiber grating filter. We use this technique to obtain error-free wavelength conversion of 10-Gb/s nonreturn-to-zero (NRZ) data using an SOA that showed an error floor at 10/sup -5/ bit-error rate (BER) when used alone. 相似文献
78.
79.
80.
H. Andrew Grebe Han-Ryong Pak Marc A. Meyers 《Metallurgical and Materials Transactions A》1985,16(5):761-775
Ballistic impact experiments were conducted on 12.5 mm thick commercial purity titanium and Ti-6 pct Al-4 pct V alloy plates
using steel “stepped” projectiles with 10.5 mm diameter. The impact velocities varied between 578 m per second and 846 m per
second, and a flash X-ray technique was used to determine projectile velocity and to assure the normality of impact. The microstructural
damage mechanisms associated with impact (shear band formation, shock wave propagation, and dynamic fracture) were analyzed
by optical, and scanning and transmission electron microscopy. Elliptical and spherical cavities were observed along the bands.
Microindentation hardness differences between the bands and adjacent regions were slight for the targets; for the projectiles,
the hardness in the band was significantly lower than that of surrounding regions. Observation of the fractured regions along
the bands showed unique features indicating possible melting. Transmission-electron microscopy of a shear band in titanium
revealed microcrystalline features (∼0.3 μm diameter) with poorly defined grain boundaries.
Formerly Graduate Student, Department of Metallurgical and Materials Engineering, New Mexico Institute of Mining and Technology,
Socorro, NM 87801 相似文献