全文获取类型
收费全文 | 723950篇 |
免费 | 11204篇 |
国内免费 | 2460篇 |
专业分类
电工技术 | 13415篇 |
综合类 | 1327篇 |
化学工业 | 107835篇 |
金属工艺 | 28301篇 |
机械仪表 | 20785篇 |
建筑科学 | 18166篇 |
矿业工程 | 3034篇 |
能源动力 | 19153篇 |
轻工业 | 65104篇 |
水利工程 | 6913篇 |
石油天然气 | 10300篇 |
武器工业 | 44篇 |
无线电 | 82338篇 |
一般工业技术 | 134602篇 |
冶金工业 | 150320篇 |
原子能技术 | 13226篇 |
自动化技术 | 62751篇 |
出版年
2021年 | 5902篇 |
2020年 | 4245篇 |
2019年 | 5534篇 |
2018年 | 9654篇 |
2017年 | 9578篇 |
2016年 | 10424篇 |
2015年 | 7488篇 |
2014年 | 11556篇 |
2013年 | 32041篇 |
2012年 | 19706篇 |
2011年 | 27073篇 |
2010年 | 20423篇 |
2009年 | 22847篇 |
2008年 | 23587篇 |
2007年 | 23301篇 |
2006年 | 20704篇 |
2005年 | 21449篇 |
2004年 | 20056篇 |
2003年 | 19387篇 |
2002年 | 17733篇 |
2001年 | 17701篇 |
2000年 | 16003篇 |
1999年 | 17244篇 |
1998年 | 46599篇 |
1997年 | 32496篇 |
1996年 | 24872篇 |
1995年 | 18380篇 |
1994年 | 15919篇 |
1993年 | 15602篇 |
1992年 | 10932篇 |
1991年 | 10509篇 |
1990年 | 10008篇 |
1989年 | 9723篇 |
1988年 | 9224篇 |
1987年 | 8020篇 |
1986年 | 7954篇 |
1985年 | 8988篇 |
1984年 | 8316篇 |
1983年 | 7375篇 |
1982年 | 6981篇 |
1981年 | 7138篇 |
1980年 | 6762篇 |
1979年 | 6424篇 |
1978年 | 6231篇 |
1977年 | 8031篇 |
1976年 | 11274篇 |
1975年 | 5433篇 |
1974年 | 5058篇 |
1973年 | 5158篇 |
1972年 | 4250篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
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
992.
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
993.
994.
John C. Hart Gordon W. Lescinsky Daniel J. Sandin Thomas A. DeFanti Louis H. Kauffman 《The Visual computer》1993,9(7):346-355
The pipelined architecture and parallel organization of the AT&T Pixel Machine image computer are described and demonstrated with applications for the visualization of multidimensional fractals, particularly linear fractals and quaternion/ stacked Julia sets. Techniques for pushing the Pixel Machine to its peak abilities are described and apply to more recent parallel image computers as well. 相似文献
995.
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
996.
997.
Prolog/Rex represents a powerful amalgamation of the latest techniques for knowledge representation and processing, rich in semantic features that ease the difficult task of encoding heterogeneous knowledge of real-world applications. The Prolog/Rex concept mechanism lets a user represent domain entities in terms of their structural and behavioral properties, including multiple inheritance, arbitrary user-defined relations among entities, annotated values (demons), incomplete knowledge, etc. A flexible rule language helps the knowledge engineer capture human expertise and provide flexible control of the reasoning process. Additional Prolog/Rex strength that cannot be found in any other hybrid language made on top of Prolog is language level support for keeping many potentially contradictory solutions to a problem, allowing possible solutions and their implications to be automatically generated and completely explored before they are committed. The same mechanism is used to model time-states, which are useful in planning and scheduling applications of Prolog/Rex 相似文献
998.
It is well known that the effectiveness of relational database systems is greatly dependent on the efficiency of the data access strategies. For this reason, much work has been devoted to the development of new access techniques, supported by adequate access structures such as the B+trees. The effectiveness of the B +tree also depends on the data distribution characteristics; in particular, poor performance results when the data show strong key value distribution unbalancing. The aim of this paper is to present the partial index: a new access structure that is useful in such cases of unbalancing, as an alternative to the B+tree unclustered indexes. The access structures are built in the physical design phase, and at execution (or compilation) time, the optimizer chooses the most efficient access path. Thus, integration of the partial indexing technique in the design and in the optimization process are also described 相似文献
999.
We propose and evaluate a parallel “decomposite best-first” search branch-and-bound algorithm (dbs) for MIN-based multiprocessor systems. We start with a new probabilistic model to estimate the number of evaluated nodes for a serial best-first search branch-and-bound algorithm. This analysis is used in predicting the parallel algorithm speed-up. The proposed algorithm initially decomposes a problem into N subproblems, where N is the number of processors available in a multiprocessor. Afterwards, each processor executes the serial best-first search to find a local feasible solution. Local solutions are broadcasted through the network to compute the final solution. A conflict-free mapping scheme, known as the step-by-step spread, is used for subproblem distribution on the MIN. A speedup expression for the parallel algorithm is then derived using the serial best-first search node evaluation model. Our analysis considers both computation and communication overheads for providing realistic speed-up. Communication modeling is also extended for the parallel global best-first search technique. All the analytical results are validated via simulation. For large systems, when communication overhead is taken into consideration, it is observed that the parallel decomposite best-first search algorithm provides better speed-up compared to other reported schemes 相似文献
1000.
A constant-time algorithm for labeling the connected components of an N×N image on a reconfigurable network of N3 processors is presented. The main contribution of the algorithm is a novel constant-time technique for determining the minimum-labeled PE in each component. The number of processors used by the algorithm can be reduced to N/sup 2+(1/d/), for any 1⩽d⩽log N, if O(d) time is allowed 相似文献