全文获取类型
收费全文 | 415568篇 |
免费 | 6502篇 |
国内免费 | 1519篇 |
专业分类
电工技术 | 7900篇 |
综合类 | 530篇 |
化学工业 | 62548篇 |
金属工艺 | 14465篇 |
机械仪表 | 12066篇 |
建筑科学 | 11903篇 |
矿业工程 | 964篇 |
能源动力 | 11202篇 |
轻工业 | 43992篇 |
水利工程 | 3369篇 |
石油天然气 | 2085篇 |
武器工业 | 36篇 |
无线电 | 55765篇 |
一般工业技术 | 77008篇 |
冶金工业 | 75117篇 |
原子能技术 | 5593篇 |
自动化技术 | 39046篇 |
出版年
2021年 | 2820篇 |
2019年 | 2526篇 |
2018年 | 3943篇 |
2017年 | 3987篇 |
2016年 | 4253篇 |
2015年 | 3561篇 |
2014年 | 5884篇 |
2013年 | 19478篇 |
2012年 | 10384篇 |
2011年 | 14881篇 |
2010年 | 11458篇 |
2009年 | 13051篇 |
2008年 | 14059篇 |
2007年 | 14438篇 |
2006年 | 12949篇 |
2005年 | 12146篇 |
2004年 | 11683篇 |
2003年 | 11377篇 |
2002年 | 11002篇 |
2001年 | 11214篇 |
2000年 | 10361篇 |
1999年 | 10844篇 |
1998年 | 24080篇 |
1997年 | 17648篇 |
1996年 | 13949篇 |
1995年 | 11011篇 |
1994年 | 9811篇 |
1993年 | 9377篇 |
1992年 | 7138篇 |
1991年 | 6800篇 |
1990年 | 6409篇 |
1989年 | 6117篇 |
1988年 | 5870篇 |
1987年 | 4898篇 |
1986年 | 4843篇 |
1985年 | 5982篇 |
1984年 | 5607篇 |
1983年 | 4834篇 |
1982年 | 4498篇 |
1981年 | 4449篇 |
1980年 | 4211篇 |
1979年 | 4081篇 |
1978年 | 3771篇 |
1977年 | 4548篇 |
1976年 | 6097篇 |
1975年 | 3115篇 |
1974年 | 3011篇 |
1973年 | 2890篇 |
1972年 | 2318篇 |
1971年 | 2003篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
This paper presents a novel matrix unit cell scheduler (MUCS) for input-buffered asynchronous transfer mode (ATM) switches. The MUCS concept originates from a heuristic strategy that leads to an optimal solution for cell scheduling. Numerical analysis indicates that input-buffered ATM switches scheduled by MUCS can utilize nearly 100% of the available link bandwidth. A transistor-level MUCS circuit has been designed and verified using HSPICE. The circuit features a regular structure, minimal interconnects, and a low transistor count. HSPICE simulation indicates that using 2-μm CMOS technology, the MUCS circuit can operate at clock frequency of 100 MHz 相似文献
994.
The vast majority of recombinant polytropic murine leukemia viruses (MuLVs) generated in mice after infection by ecotropic MuLVs can be classified into two major antigenic groups based on their reactivities to two monoclonal antibodies (MAbs) termed Hy 7 and 516. These groups very likely correspond to viruses formed by recombination of the ecotropic MuLV with two distinct sets of polytropic env genes present in the genomes of inbred mouse strains. We have found that nearly all polytropic MuLVs identified in mice infected with a substrain of Friend MuLV (F-MuLV57) are reactive with Hy 7, whereas mice infected with Moloney MuLV (Mo-MuLV) generate major populations of both Hy 7- and 516-reactive polytropic MuLVs. We examined polytropic MuLVs generated in NFS/N mice after inoculation with Mo-MuLV-F-MuLV57 chimeras to determine which regions of the viral genome influence this difference between the two ecotropic MuLVs. These studies identified a region of the MuLV genome which encodes the nucleocapsid protein and a portion of the viral protease as the only region that influenced the difference in polytropic-MuLV generation by Mo-MuLV and F-MuLV57. 相似文献
995.
The combination of the techniques of expert systems and neural networks has the potential of producing more powerful systems, for example, expert systems able to learn from experience. In this paper, we address the combinatorial neural model (CNM), a kind of fuzzy neural network able to accommodate in a simple framework the highly desirable property of incremental learning, as well as the usual capabilities of expert systems. We show how an interval-based representation for membership grades makes CNM capable of reasoning with several types of uncertainty: vagueness, ignorance, and relevance commonly found in practical applications. In addition, we show how basic functions of expert systems such as inference, inquiry, censorship of input information, and explanation may be implemented. We also report experimental results of the application of CNM to the problem of deforestation monitoring of the Amazon region using satellite images 相似文献
996.
997.
M Fornerod J van Deursen S van Baal A Reynolds D Davis KG Murti J Fransen G Grosveld 《Canadian Metallurgical Quarterly》1997,16(4):807-816
The oncogenic nucleoporin CAN/Nup214 is essential in vertebrate cells. Its depletion results in defective nuclear protein import, inhibition of messenger RNA export and cell cycle arrest. We recently found that CAN associates with proteins of 88 and 112 kDa, which we have now cloned and characterized. The 88 kDa protein is a novel nuclear pore complex (NPC) component, which we have named Nup88. Depletion of CAN from the NPC results in concomitant loss of Nup88, indicating that the localization of Nup88 to the NPC is dependent on CAN binding. The 112 kDa protein is the human homologue of yeast CRM1, a protein known to be required for maintenance of correct chromosome structure. This human CRM1 (hCRM1) localized to the NPC as well as to the nucleoplasm. Nuclear overexpression of the FG-repeat region of CAN, containing its hCRM1-interaction domain, resulted in depletion of hCRM1 from the NPC. In CAN-/- mouse embryos lacking CAN, hCRM1 remained in the nuclear envelope, suggesting that this protein can also bind to other repeat-containing nucleoporins. Lastly, hCRM1 shares a domain of significant homology with importin-beta, a cytoplasmic transport factor that interacts with nucleoporin repeat regions. We propose that hCRM1 is a soluble nuclear transport factor that interacts with the NPC. 相似文献
998.
Laura M. Haas Michael J. Carey Miron Livny Amit Shukla 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(3):241-256
In this paper, we re-examine the results of prior work on methods for computing ad hoc joins. We develop a detailed cost model for predicting join algorithm performance, and we use the model to develop cost formulas
for the major ad hoc join methods found in the relational database literature. We show that various pieces of “common wisdom” about join algorithm
performance fail to hold up when analyzed carefully, and we use our detailed cost model to derive op
timal buffer allocation schemes for each of the join methods examined here. We show that optimizing their buffer allocations
can lead to large performance improvements, e.g., as much as a 400% improvement in some cases. We also validate our cost model's
predictions by measuring an actual implementation of each join algorithm considered. The results of this work should be directly
useful to implementors of relational query optimizers and query processing systems.
Edited by M. Adiba. Received May 1993 / Accepted April 1996 相似文献
999.
1000.
Bartolo A. Clymer B.D. Burgess R.C. Turnbull J.P. 《Signal Processing, IEEE Transactions on》1998,46(8):2243-2248
A new method of implementing efficient FIR filters is presented. It involves approximation of an equiripple FIR by a rounding operation and application of the derived impulse response by a simple recursive equation. The technique is extremely efficient for lowpass, highpass, bandpass, and bandstop filters with sharp transitions and low edge frequencies 相似文献