全文获取类型
收费全文 | 2742篇 |
免费 | 60篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 174篇 |
综合类 | 2篇 |
化学工业 | 569篇 |
金属工艺 | 108篇 |
机械仪表 | 48篇 |
建筑科学 | 38篇 |
矿业工程 | 1篇 |
能源动力 | 116篇 |
轻工业 | 240篇 |
水利工程 | 4篇 |
石油天然气 | 2篇 |
无线电 | 220篇 |
一般工业技术 | 440篇 |
冶金工业 | 555篇 |
原子能技术 | 56篇 |
自动化技术 | 237篇 |
出版年
2023年 | 12篇 |
2022年 | 40篇 |
2021年 | 54篇 |
2020年 | 27篇 |
2019年 | 33篇 |
2018年 | 57篇 |
2017年 | 48篇 |
2016年 | 58篇 |
2015年 | 35篇 |
2014年 | 70篇 |
2013年 | 147篇 |
2012年 | 104篇 |
2011年 | 146篇 |
2010年 | 85篇 |
2009年 | 116篇 |
2008年 | 134篇 |
2007年 | 87篇 |
2006年 | 80篇 |
2005年 | 94篇 |
2004年 | 82篇 |
2003年 | 80篇 |
2002年 | 64篇 |
2001年 | 65篇 |
2000年 | 46篇 |
1999年 | 75篇 |
1998年 | 194篇 |
1997年 | 135篇 |
1996年 | 101篇 |
1995年 | 63篇 |
1994年 | 71篇 |
1993年 | 59篇 |
1992年 | 33篇 |
1991年 | 21篇 |
1990年 | 15篇 |
1989年 | 29篇 |
1988年 | 16篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 33篇 |
1984年 | 14篇 |
1983年 | 21篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 24篇 |
1976年 | 20篇 |
1975年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有2810条查询结果,搜索用时 109 毫秒
31.
An aerodynamic structure of a laminar boundary layer over a flat plate with uniform fuel injection from the flat plate and with diffusion flame is investigated numerically. Elliptic type conservation equations are used to take into account the pressure variation within the boundary layer. Velocities and the pressure are solved numerically by SIMPLER algorithm. One step irreversible chemical reaction of methane is assumed. An Arrhenius type chemical reaction rate model is assumed and the pre-exponential factor is varied from 1.0 × 1012 to 1.0 × 1030 m3/(kg s) as a parameter of the reactivity in order to elucidate the effect of the reactivity on the structure of the boundary layer. When the chemical reaction is very fast, the leading edge of the reaction zone reaches the flat plate. As the chemical reaction rate is decreased with a decrease in the pre- exponential factor, the leading edge of the reaction zone parts from the flat plate and it shifts downstream. The fuel is injected in front of the leading edge of the reaction zone, where the air is dominant, and the oxygen penetrates into the fuel dominant zone through the region between the leading edge and the flat plate. As a consequence, a premixed gas is formed around the leading edge of the reaction zone. The premixed gas seems to react in the region apart from the main visible flame.Part of this work was presented at ICCM 86, Tokyo, Japan, May 25–29, 1986 相似文献
32.
In this paper we analyze the average-case performance of the Modified Harmonic algorithm for on-line bin packing. We first analyze the average-case performance for arbitrary distribution of item sizes over (0,1]. This analysis is based on the following result. Letf
1 andf
2 be two linear combinations of random variables {N
i
}
i=1
k
where theN
i
's have a joint multinomial distribution for eachn=
i=1
k
,N
i
. LetE(f
1) O andE(f
2) 0. Then limn
E(max(f
1,f
2
))/n = lim
n
max(E(f
1),E(f
2))/n. We then consider the special case when the item sizes are uniformly distributed over (0,1]. For specific values of the parameters, the Modified Harmonic algorithm turns out to be better than the other two linear-time on-line algorithms—Next Fit and Harmonic—in both the worst case as well as the average case. We also obtain optimal values for the parameters of the algorithm from the average-case standpoint. For these values of the parameters, the average-case performance ratio is less than 1.19. This compares well with the performance ratios 1.333. and 1.2865. of the Next Fit algorithm and the Harmonic algorithm, respectively. 相似文献
33.
In this paper we analyze the average-case performance of the Modified Harmonic algorithm for on-line bin packing. We first analyze the average-case performance for arbitrary distribution of item sizes over (0,1]. This analysis is based on the following result. Letf 1 andf 2 be two linear combinations of random variables {N i } i=1 k where theN i 's have a joint multinomial distribution for eachn=σ i=1 k ,N i . LetE(f 1) ≠ O andE(f 2)≠ 0. Then limn →∞E(max(f 1,f 2 ))/n = lim n →∞ max(E(f 1),E(f 2))/n. We then consider the special case when the item sizes are uniformly distributed over (0,1]. For specific values of the parameters, the Modified Harmonic algorithm turns out to be better than the other two linear-time on-line algorithms—Next Fit and Harmonic—in both the worst case as well as the average case. We also obtain optimal values for the parameters of the algorithm from the average-case standpoint. For these values of the parameters, the average-case performance ratio is less than 1.19. This compares well with the performance ratios 1.333. and 1.2865. of the Next Fit algorithm and the Harmonic algorithm, respectively. 相似文献
34.
Numerical solutions of the singular integral equations in the crack analysis using the body force method 总被引:1,自引:1,他引:0
In this paper, numerical solutions of the singular integral equations of the body force method in the crack problems are discussed. The stress fields induced by two kinds of displacement discontinuity are used as fundamental solutions. Then, the problem is formulated as a hypersingular integral equation with the singularity of the form r
2. In the numerical calculation, two kinds of unknown functions are approximated by the products of the fundamental density function and the Chebyshev polynomials. As examples, the stress intensity factors of the oblique edge crack, kinked crack, branched crack and zig-zag crack are analyzed. The calculation shows that the present method gives accurate results even for the extremely oblique edge crack and kinked crack with extremely short bend which has been difficult to analyze by the previous method using the approximation by the products of the fundamental density function and the stepped functions etc. 相似文献
35.
36.
Kazunori Ueda 《New Generation Computing》1987,5(1):29-44
This paper presents a technique for compiling a Horn-clause program intended for exhaustive search into a GHC (Guarded Horn Clauses) program. The technique can be viewed also as a transformation technique for Prolog programs which compiles away the ‘bagof’ primitive and non-determinate bindings. The class of programs to which our technique is applicable is shown with a static checking algorithm; it is nontrivial and could be extended. An experiment on a compiler-based Prolog system showed that our technique improved the efficiency of exhaustive search by 6 times for a permutation generator program. This compilation technique is important also in that it exploits the AND-parallelism of GHC for parallel search. 相似文献
37.
Sean R. Tachibana Longteng Tang Liangdong Zhu Yuka Takeda Keiji Fushimi Yoshibumi Ueda Takahiro Nakajima Yuto Kuwasaki Moritoshi Sato Rei Narikawa Chong Fang 《International journal of molecular sciences》2021,22(10)
Cyanobacteriochromes (CBCRs) are promising optogenetic tools for their diverse absorption properties with a single compact cofactor-binding domain. We previously uncovered the ultrafast reversible photoswitching dynamics of a red/green photoreceptor AnPixJg2, which binds phycocyanobilin (PCB) that is unavailable in mammalian cells. Biliverdin (BV) is a mammalian cofactor with a similar structure to PCB but exhibits redder absorption. To improve the AnPixJg2 feasibility in mammalian applications, AnPixJg2_BV4 with only four mutations has been engineered to incorporate BV. Herein, we implemented femtosecond transient absorption (fs-TA) and ground state femtosecond stimulated Raman spectroscopy (GS-FSRS) to uncover transient electronic dynamics on molecular time scales and key structural motions responsible for the photoconversion of AnPixJg2_BV4 with PCB (Bpcb) and BV (Bbv) cofactors in comparison with the parent AnPixJg2 (Apcb). Bpcb adopts the same photoconversion scheme as Apcb, while BV4 mutations create a less bulky environment around the cofactor D ring that promotes a faster twist. The engineered Bbv employs a reversible clockwise/counterclockwise photoswitching that requires a two-step twist on ~5 and 35 picosecond (ps) time scales. The primary forward Pfr → Po transition displays equal amplitude weights between the two processes before reaching a conical intersection. In contrast, the primary reverse Po → Pfr transition shows a 2:1 weight ratio of the ~35 ps over 5 ps component, implying notable changes to the D-ring-twisting pathway. Moreover, we performed pre-resonance GS-FSRS and quantum calculations to identify the Bbv vibrational marker bands at ~659,797, and 1225 cm−1. These modes reveal a stronger H-bonding network around the BV cofactor A ring with BV4 mutations, corroborating the D-ring-dominant reversible photoswitching pathway in the excited state. Implementation of BV4 mutations in other PCB-binding GAF domains like AnPixJg4, AM1_1870g3, and NpF2164g5 could promote similar efficient reversible photoswitching for more directional bioimaging and optogenetic applications, and inspire other bioengineering advances. 相似文献
38.
Dr. Daisuke Fujiwara Kousuke Mihara Ryo Takayama Yusuke Nakamura Prof. Mitsuhiro Ueda Prof. Takeshi Tsumuraya Prof. Ikuo Fujii 《Chembiochem : a European journal of chemical biology》2021,22(24):3406-3409
Conformationally constrained peptides hold promise as molecular tools in chemical biology and as a new modality in drug discovery. The construction and screening of a target-focused library could be a promising approach for the generation of de novo ligands or inhibitors against target proteins. Here, we have prepared a protein kinase-focused library by chemically modifying helix-loop-helix (HLH) peptides displayed on phage and subsequently tethered to adenosine. The library was screened against aurora kinase A (AurA). The selected HLH peptide Bip - 3 retained the α-helical structure and bound to AurA with a KD value of 13.7 μM. Bip - 3 and the adenosine-tethered peptide Bip - 3 - Adc provided IC50 values of 103 μM and 7.7 μM, respectively, suggesting that Bip - 3 - Adc bivalently inhibited AurA. In addition, the selectivity of Bip - 3 - Adc to several protein kinases was tested, and was highest against AurA. These results demonstrate that chemical modification can enable the construction of a kinase-focused library of phage-displayed HLH peptides. 相似文献
39.
Thronsen Elisabeth Mørkeseth Hanne Marioara Calin D. Minakuchi Kazuhiro Katsumi Tetsuya Marthinsen Knut Matsuda Kenji Holmestad Randi 《Metallurgical and Materials Transactions A》2022,53(9):3296-3310
Metallurgical and Materials Transactions A - The effect of 0.03 and 0.08 at. pct Fe additions on the formation of secondary phases in an Al–1.1Mg–0.5Cu–0.3Si at. pct alloy was... 相似文献
40.
New polylactide/layered silicate nanocomposites. 5. Designing of materials with desired properties 总被引:2,自引:0,他引:2
Suprakas Sinha RayKazunobu Yamada Masami Okamoto Youhei FujimotoAkinobu Ogami Kazue Ueda 《Polymer》2003,44(21):6633-6646
Understanding the structure/property relationship in polymer/layered silicate nanocomposites is of great importance in designing materials with desired properties. In order to understand these relations, a series of polylactide (PLA)/organically modified layered silicate (OMLS) nanocomposites have been prepared using a simple melt extrusion technique. Four different types of OMLS have been used for the preparation of nanocomposites, three were modified with functionalized ammonium salts while fourth one was a phosphonium salt modified OMLS. The structure of the nanocomposites in the nanometer scale was characterized by using wide-angle X-ray diffraction and transmission electron microscopic observations. Using four different types of layered silicates modified with four different types of surfactants, the effect of OMLS in nanocomposites was investigated by focusing on four major aspects: structural analysis, thermal properties and spherulite morphology, materials properties, and biodegradability. Finally, we draw conclusions about the structure/property relationship in the case of PLA/OMLS nanocomposites. 相似文献