全文获取类型
收费全文 | 515篇 |
免费 | 39篇 |
国内免费 | 30篇 |
专业分类
电工技术 | 3篇 |
综合类 | 32篇 |
化学工业 | 247篇 |
金属工艺 | 64篇 |
机械仪表 | 16篇 |
建筑科学 | 19篇 |
矿业工程 | 8篇 |
能源动力 | 8篇 |
轻工业 | 35篇 |
水利工程 | 5篇 |
石油天然气 | 5篇 |
武器工业 | 2篇 |
无线电 | 12篇 |
一般工业技术 | 86篇 |
冶金工业 | 31篇 |
原子能技术 | 5篇 |
自动化技术 | 6篇 |
出版年
2024年 | 4篇 |
2023年 | 12篇 |
2022年 | 17篇 |
2021年 | 24篇 |
2020年 | 20篇 |
2019年 | 17篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 18篇 |
2015年 | 20篇 |
2014年 | 22篇 |
2013年 | 42篇 |
2012年 | 23篇 |
2011年 | 34篇 |
2010年 | 12篇 |
2009年 | 27篇 |
2008年 | 11篇 |
2007年 | 19篇 |
2006年 | 31篇 |
2005年 | 24篇 |
2004年 | 14篇 |
2003年 | 21篇 |
2002年 | 13篇 |
2001年 | 15篇 |
2000年 | 6篇 |
1999年 | 12篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 4篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1957年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有584条查询结果,搜索用时 15 毫秒
1.
Mri Miczi Mria Golda Balzs Kunkli Tibor Nagy Jzsef Tzsr Jnos Andrs Mtyn 《International journal of molecular sciences》2020,21(24)
The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease-19 (COVID-19) being associated with severe pneumonia. Like with other viruses, the interaction of SARS-CoV-2 with host cell proteins is necessary for successful replication, and cleavage of cellular targets by the viral protease also may contribute to the pathogenesis, but knowledge about the human proteins that are processed by the main protease (3CLpro) of SARS-CoV-2 is still limited. We tested the prediction potentials of two different in silico methods for the identification of SARS-CoV-2 3CLpro cleavage sites in human proteins. Short stretches of homologous host-pathogen protein sequences (SSHHPS) that are present in SARS-CoV-2 polyprotein and human proteins were identified using BLAST analysis, and the NetCorona 1.0 webserver was used to successfully predict cleavage sites, although this method was primarily developed for SARS-CoV. Human C-terminal-binding protein 1 (CTBP1) was found to be cleaved in vitro by SARS-CoV-2 3CLpro, the existence of the cleavage site was proved experimentally by using a His6-MBP-mEYFP recombinant substrate containing the predicted target sequence. Our results highlight both potentials and limitations of the tested algorithms. The identification of candidate host substrates of 3CLpro may help better develop an understanding of the molecular mechanisms behind the replication and pathogenesis of SARS-CoV-2. 相似文献
2.
Diphenylzinc, alone or in combination with water and butanone as coinitiators, was used as a polymerization initiator system for a variety of lactones at varying temperatures. The resulting data indicate that the course of the polymerization is greatly influenced by the lactone structure, as well as by the molar ratio of coinitiator to diphenylzinc. When used alone, diphenylzinc exhibited high activity as an initiator in δ‐valerolactone polymerizations, although it was less efficient when used in the β‐butyrolactone and the β‐propiolactone polymerizations. Activity in the polymerization of β‐lactones was increased by adding small amounts of butanone or water. It was also observed that the diphenylzinc–butanone combination was more effective than the diphenylzinc–water mixture in the polymerizations of β‐butyrolactone and β‐propiolactone. Copyright © 2003 Society of Chemical Industry 相似文献
3.
D. SHERMAN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(1):32-40
Fracture experiments with silicon specimens in recent years have shown the need for a new approach to the analysis of rapidly propagating cracks in single crystals. Behaviour and phenomena have been revealed that fracture in these materials is rather different from the fracture of both amorphous and polycrystalline materials. We show that continuum mechanics is insufficient for analyzing crack propagation in single crystals since it is unable to consider atomistic‐scale phenomena. Accordingly, we describe basic phenomena associated with rapid crack propagation in silicon : (i) anisotropic velocity‐dependent R‐curve behaviour, as a key phenomenon dictating atomistic scale behaviour, (ii) crack deflection from one cleavage plane to another as a mesoscopic scale phenomenon in single‐crystal fracture, (iii) the Rayleigh surface wave speed as the limiting crack tip velocity is re‐examined, (vi) the lowest crack velocity in brittle crystals is examined, and finally (v) the interaction between crack path and preferred cleavage planes in single crystals is depicted. 相似文献
4.
R. RODRÍGUEZ-MARTÍN I. OCAÑA A. MARTÍN-MEIZOSO 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(7):664-670
High-strength steels are used to increase the load carrying capacity of components. However, to guarantee a safe design, it is also necessary to combine high strength with adequate fracture toughness. In this paper, fracture toughness of three high-strength steels with yield strengths ranging from 460 to 890 MPa has been studied at very low temperatures. Taking into account experimental evidence, a new mechanism of cleavage at very low temperatures is proposed. This mechanism considers the possibility of reaching the ideal strength (the stress at which the lattice of a single crystal losses its stability) in the immediate vicinity of the fatigue crack tip. Moreover, a computational model able to calculate the external load needed to produce a catastrophic failure of these steels has been developed. 相似文献
5.
6.
The heat affect zone (HAZ) is in many cases considered to be the most critical part of a weldment. In this paper, the effect of crack size and weld metal mismatch on the HAZ cleavage toughness of wide plate specimens with X-groove has been investigated by the J-Q-M theories and a simple micromechanism for cleavage fracture. Two crack sizes have been studied (a/w = 0.1 and 0.3). In the analyses, the HAZ yield strength is assumed to be higher than the base metal. For each crack size, weld metal local overmatch and local evenmatch with respect to the HAZ are considered. For a given global strain, the results indicate that weld metal overmatch and evenmatch yield the same crack tip loading in terms of J-integral for a/w = 0.3. For a/w = 0.1, overmatch gives lower crack tip loading than evenmatch. For a given crack tip loading, weld metal local evenmatch in general results in less effective crack tip loading than the overmatch. Overmatch is detrimental to HAZ toughness, but this detrimental effect becomes less significant when the crack size decreases. 相似文献
7.
8.
Various aspects on probabilistic modelling of cleavage fracture are discussed. The investigation involves consideration of
a unit cell with an explicitly modelled void. The results from this model are compared with results for the case when the
void content is accounted for in the sense of a Gurson-Tvergaard law. It is found that explicit modelling of the void can
give substantially different results for the fracture probability. The effect depends on the exponent in the assumed Weibull
distribution, the threshold stress, the constraint conditions and the hardening of the material.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
XIA Yuebo WANG Zhongguang State Key Laboratory for Fatigue Failure of Materials Institute of Metal Research Academia Sinica Shenyang China 《金属学报(英文版)》1992,5(5):330-335
SEM photos for very coarse grained and high ductile polycrystalline pure Al show followingcharacteristics:A few fracture sources are concentrated,the crack propagates in fan-shapenear them,and the fatigue striations are cyclic cleavage facets.Each striation consists of awide cleavage facet and a narrow cleavage stage.Those stages often blunt due to plasticdeformation.The fatigue striations are clear and continual,and distribute over whole zone ofstage Ⅱ crack propagation.Two kinds of fatigue striations form in different levels,areconjoined by a“twisted baked piece of pastry”band.The secondary crack along the fatiguestriations was observed frequently.Some of them have already developed into secondarymacrocracks and secondary fatigue striations were found clearly on secondary fracture sur-face.The fracture surface can be divided into two parts,initiation and propagation zone of thecrack,however,no statical-fracture zone was observed.The mechanism to form striationswas preliminarily discussed. 相似文献
10.
The cobalt(II) chloride-catalyzed oxidative cleavage of -methylstyrene with oxygen in t-BuOH gives acetophenone and formaldehyde in good yield. The competing reactions between C=C cleavage and formation of polymeric products are strongly affected by the solvent, cobalt catalyst and concentration used, as well as the reaction temperature. A free radical mechanism involving a cyclic peroxide intermediate is proposed to give the cleavage products. Oxidation of various alkenes using CoCl2/t-BuOH/O2 system shows that only activated styrenes can be oxidized effectively. The reactivity of various styrenes and their selectivity towards giving cleavage products or polymers are strongly influenced by the electronic and steric properties of the substrate. 相似文献