全文获取类型
收费全文 | 83927篇 |
免费 | 972篇 |
国内免费 | 406篇 |
专业分类
电工技术 | 774篇 |
综合类 | 2318篇 |
化学工业 | 11503篇 |
金属工艺 | 4781篇 |
机械仪表 | 3023篇 |
建筑科学 | 2163篇 |
矿业工程 | 564篇 |
能源动力 | 1112篇 |
轻工业 | 3607篇 |
水利工程 | 1271篇 |
石油天然气 | 347篇 |
无线电 | 9278篇 |
一般工业技术 | 16319篇 |
冶金工业 | 2657篇 |
原子能技术 | 256篇 |
自动化技术 | 25332篇 |
出版年
2023年 | 14篇 |
2022年 | 25篇 |
2021年 | 30篇 |
2020年 | 22篇 |
2019年 | 34篇 |
2018年 | 14478篇 |
2017年 | 13391篇 |
2016年 | 9971篇 |
2015年 | 611篇 |
2014年 | 242篇 |
2013年 | 210篇 |
2012年 | 3145篇 |
2011年 | 9424篇 |
2010年 | 8284篇 |
2009年 | 5549篇 |
2008年 | 6771篇 |
2007年 | 7773篇 |
2006年 | 118篇 |
2005年 | 1208篇 |
2004年 | 1126篇 |
2003年 | 1170篇 |
2002年 | 537篇 |
2001年 | 98篇 |
2000年 | 176篇 |
1999年 | 59篇 |
1998年 | 53篇 |
1997年 | 30篇 |
1996年 | 47篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1992年 | 17篇 |
1991年 | 24篇 |
1988年 | 10篇 |
1969年 | 25篇 |
1968年 | 43篇 |
1967年 | 34篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1964年 | 11篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1961年 | 18篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
Kang-Yi Lien Chien-Ju Liu Yi-Chien Lin Pao-Lin Kuo Gwo-Bin Lee 《Microfluidics and nanofluidics》2009,6(4):539-555
This study presents a new magnetic bead-based microfluidic platform, which integrates three major modules for rapid leukocytes
purification, genomic DNA (gDNA) extraction and fast analysis of genetic gene. By utilizing microfluidic technologies and
magnetic beads conjugated with CD15/45 antibodies, leukocytes in a human whole blood sample can be first purified and concentrated, followed by extraction of gDNA
utilizing surface-charge switchable, DNA-specific, magnetic beads in the lysis solution. Then, specific genes associated with
genetic diseases can be amplified by an on-chip polymerase chain reaction (PCR) process automatically. The whole pretreatment
process including the leukocytes purification and gDNA extraction can be performed in an automatic fashion with the incorporation
of the built bio-separators consisting of microcoils array within less than 20 min. The detection of single nucleotide polymorphism
(SNP) genotyping of methylenetetra-hydrofolate reductase (MTHFR) C677T region associated with an increased risk of genetic
diseases was further performed to demonstrate the capability of the proposed system. The extracted gDNA can be transported
into a micro PCR chamber for on-chip fast nucleic acid amplification of detection genes with minimum human intervention. Hence,
the developed system may provide a powerful automated platform for pretreatment of human leukocytes, gDNA extraction and fast
analysis of genetic gene. 相似文献
992.
We present two algorithms that are near optimal with respect to the number of inversions present in the input. One of the
algorithms is a variation of insertion sort, and the other is a variation of merge sort. The number of comparisons performed
by our algorithms, on an input sequence of length n that has I inversions, is at most . Moreover, both algorithms have implementations that run in time . All previously published algorithms require at least comparisons for some c > 1.
M. L. Fredman was supported in part by NSF grant CCR-9732689. 相似文献
993.
Ryszard Janicki 《Acta Informatica》2008,45(4):279-320
The paper deals with the foundations of concurrency theory. We show how structurally complex concurrent behaviours can be
modelled by relational structures
(X, ¨, \sqsubset){(X, \diamondsuit, \sqsubset)} , where X is a set (of event occurrences), and ¨{\diamondsuit} (interpreted as commutativity) and
\sqsubset{\sqsubset} (interpreted as weak causality) are binary relations on X. The paper is a continuation of the approach initiated in Gaifman and Pratt (Proceedings of LICS’87, pp 72–85, 1987), Lamport
(J ACM 33:313–326, 1986), Abraham et al. (Semantics for concurrency, workshops in computing. Springer, Heidelberg, pp 311–323,
1990) and Janicki and Koutny (Lect Notes Comput Sci 506:59–74, 1991), substantially developed in Janicki and Koutny (Theoretical
Computer Science 112:5–52, 1993) and Janicki and Koutny (Acta Informatica 34:367–388, 1997), and recently generalized in Guo
and Janicki (Lect Notes Comput Sci 2422:178–191, 2002) and Janicki (Lect Notes Comput Sci 3407:84–98, 2005). For the first
time the full model for the most general case is given. 相似文献
994.
In this paper, the variations of both subunitary polar factors and Hermitian positive semidefinite polar factors in the polar decomposition are studied. New perturbation bounds of both polar factors are given without the restriction that A and its perturbed matrix à have the same rank. These improve recent results. 相似文献
995.
We introduce general sequences of linear operators obtained from classical approximation processes which are useful in the
approximation of the resolvent operators of the generators of suitable C
0-semigroups. The main aim is the representation of the resolvent operators in terms of classical approximation operators.
Work performed under the auspices of PRIN 2006–07 “Kolmogorov equations” (coordinator G. Da Prato) 相似文献
996.
Anti-reflective (AR) boundary conditions (BC) have been introduced recently in connection with fast deblurring algorithms,
both in the case of signals and images. Here we extend such BCs to d dimensions (d ≥ 1) and we study in detail the algebra induced by the AR-BCs, with strongly symmetric point spread functions (PSF), both
from a structural and computational point of view. The use of the re-blurring idea and the computational features of the AR-algebra
allow us to apply Tikhonov-like techniques within O(n
d
log(n)) arithmetic operations, where n
d
is the number of pixels of the reconstructed object. Extensive numerical experimentation concerning 2D images and strongly
symmetric PSFs confirms the effectiveness of our proposal.
相似文献
997.
998.
Crumb rubber is preliminarily mixed with asphalt in wet process to produce ductile and elastic asphalt rubber (AR), which has been extensively used in high performance bituminous mixtures for road pavement. Epoxy asphalt is a thermosetting polymer modified asphalt with excellent performance and has been widely applied on the pavement of steel bridge decks. Epoxy asphalt rubber (EAR) was prepared by mixing AR with the epoxy (EP). The effect of AR concentration on the phase-separated morphology, viscosity, thermal stability and mechanical properties of the neat EP were compared with that of asphalt. Laser scanning confocal microscopy observations revealed that AR particles disperse in the continuous epoxy phase with co-continuous phase-separated structures in EARs with 40 and 50 wt% AR. However, the phase inverts to continuous asphalt structures with dispersed spherical and co-continuous epoxy phase as AR concentration reaches 60 wt%. The addition of AR increases the viscosity of the neat EP. The thermal stability of the neat EP is improved with the incorporation of AR. The presence of AR decreases the tensile strength of the neat EP, while the elongation at break of the neat EP increases with the increase of AR concentration. The viscosity and mechanical properties of EAR with 50 wt% AR completely satisfy the technical requirement of hot-mix epoxy asphalt binder for steel bridge deck pavements. 相似文献
999.
This paper investigates the effect of microwave curing on the bond strength of steel reinforcement in concrete repair. Pull-out tests on plain mild steel reinforcement bars embedded in four repair materials in 100 mm cube specimens were performed to determine the interfacial bond strength. The porosity and pore structure of the matrix at the steel interface, which influence the bond strength, were also determined. Test results show that microwave curing significantly reduces the bond strength of plain steel reinforcement. The reduction relative to normally cured (20 °C, 60% RH) specimens is between 21 and 40% with low density repair materials and about 10% for normal density cementitious mortars. The corresponding compressive strength of the matrix also recorded similar reduction and microwave curing resulted in increased porosity at the interface transition zone of the steel reinforcement. A unique relationship exists between bond strength and both compressive strength and porosity of all matrix materials. Microwave curing reduced shrinkage but despite the wide variation in the shrinkage of the repair mortars, its effect on the bond strength was small. The paper provides clear correlations between the three parameters (compressive strength, bond strength and porosity), which are common to both the microwave and conventionally cured mortars. Therefore, bond-compressive strength relationships used in the design of reinforced concrete structures will be also valid for microwave cured elements. 相似文献
1000.
The diffusion coefficient \(D_{{{\text{O}}_{2} }}\), the porosity and the pore structure of mortars produced with a Portland cement and a range of blended cements containing limestone powder, microsilica, portlandite or slag were measured in the non-carbonated and the carbonated state. Additionally, the setup for measuring O2 diffusion was adapted to measure also the CO2 diffusion of the carbonated mortars. The diffusion coefficient \(D_{{{\text{O}}_{2} }}\) and the total porosity were increased in the mortars containing microsilica and slag, while they were decreased in the other mortars due to carbonation. Invariably, the pore structure became coarser in all samples. The relationship between diffusion coefficients \(D_{{{\text{O}}_{2} }}\) and \(D_{{{\text{CO}}_{2} }}\) in the carbonated mortars was always linear, with \(D_{{{\text{O}}_{2} }}\) systematically higher by factor of 1.37. As this factor broadly agrees with what was found in the scant literature about CO2 diffusion, it could be used for estimating \(D_{{{\text{CO}}_{2} }}\) of carbonated mortar and concrete based on measurements of O2 diffusion. 相似文献