全文获取类型
收费全文 | 877篇 |
免费 | 43篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 6篇 |
化学工业 | 242篇 |
金属工艺 | 13篇 |
机械仪表 | 26篇 |
建筑科学 | 34篇 |
能源动力 | 35篇 |
轻工业 | 153篇 |
水利工程 | 7篇 |
无线电 | 58篇 |
一般工业技术 | 125篇 |
冶金工业 | 85篇 |
原子能技术 | 15篇 |
自动化技术 | 123篇 |
出版年
2023年 | 7篇 |
2022年 | 32篇 |
2021年 | 44篇 |
2020年 | 25篇 |
2019年 | 20篇 |
2018年 | 22篇 |
2017年 | 24篇 |
2016年 | 29篇 |
2015年 | 19篇 |
2014年 | 35篇 |
2013年 | 44篇 |
2012年 | 46篇 |
2011年 | 59篇 |
2010年 | 37篇 |
2009年 | 36篇 |
2008年 | 48篇 |
2007年 | 33篇 |
2006年 | 38篇 |
2005年 | 30篇 |
2004年 | 19篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 17篇 |
2000年 | 16篇 |
1999年 | 22篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 15篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 4篇 |
1990年 | 9篇 |
1989年 | 3篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1968年 | 2篇 |
排序方式: 共有922条查询结果,搜索用时 31 毫秒
1.
Mireia Castejn-Vilatersana Magda Faijes Antoni Planas 《International journal of molecular sciences》2021,22(6)
The health benefits of human milk oligosaccharides (HMOs) make them attractive targets as supplements for infant formula milks. However, HMO synthesis is still challenging and only two HMOs have been marketed. Engineering glycoside hydrolases into transglycosylases may provide biocatalytic routes to the synthesis of complex oligosaccharides. Lacto-N-biosidase from Bifidobacterium bifidum (LnbB) is a GH20 enzyme present in the gut microbiota of breast-fed infants that hydrolyzes lacto-N-tetraose (LNT), the core structure of the most abundant type I HMOs. Here we report a mutational study in the donor subsites of the substrate binding cleft with the aim of reducing hydrolytic activity and conferring transglycosylation activity for the synthesis of LNT from p-nitrophenyl β-lacto-N-bioside and lactose. As compared with the wt enzyme with negligible transglycosylation activity, mutants with residual hydrolase activity within 0.05% to 1.6% of the wild-type enzyme result in transglycosylating enzymes with LNT yields in the range of 10–30%. Mutations of Trp394, located in subsite -1 next to the catalytic residues, have a large impact on the transglycosylation/hydrolysis ratio, with W394F being the best mutant as a biocatalyst producing LNT at 32% yield. It is the first reported transglycosylating LnbB enzyme variant, amenable to further engineering for practical enzymatic synthesis of LNT. 相似文献
2.
Pedro Ideia Lorenzo Degli Esposti Carla Caseiro Miguel Alessio Adamiano Michele Iafisco Paula C. Castilho 《International Journal of Applied Ceramic Technology》2021,18(1):235-243
The conversion of food industry by-products to compounds with high added value is nowadays a significant topic, for social, environmental, and economic reasons. In this paper, calcium phosphate-based materials were obtained from black scabbardfish (Aphanopus carbo) bones and grey triggerfish (Balistes capriscus) skin, which are two of the most abundant fish by-products of Madeira Island. Different calcination temperatures between 400 and 1000°C were employed. Materials obtained from calcination of bones of black scabbard fish were composed by homogeneous mixtures of hydroxyapatite (Ca10(PO4)6(OH)2, HAp) and β-tricalcium phosphate (β-Ca3(PO4)2, β-TCP). Because of the high biocompatibility of HAp and the good resorbability of β-TCP, these natural biphasic materials could be very relevant in the field of biomaterials, as bone grafts. The ratio between HAp and β-TCP in the biphasic compound was dependent on the calcination temperature. Differently, the material obtained from skin of grey triggerfish contained HAp as the main phase, together with small amounts of other mineral phases, such as halite and rhenanite, which are known to enhance osteogenesis when used as bone substitutes. In both cases, the increase of calcination temperature led to an increase in the particles size with a consequent decrease in their specific surface area. These results demonstrate that from the fish by-products of the most consumed fishes in Madeira Island it is possible to obtain bioceramic materials with tunable composition and particle morphology, which could be promising materials for the biomedical field. 相似文献
3.
4.
Penedo Frank J.; Dahn Jason R.; Gonzalez Jeffrey S.; Molton Ivan; Carver Charles S.; Antoni Michael H.; Roos Bernard A.; Schneiderman Neil 《Canadian Metallurgical Quarterly》2003,22(2):220
This study evaluated relations among optimism, perceived stress management skills (PSMS), and positive mood in 46 men who had surgical treatment for localized prostate cancer. The authors found that optimism, PSMS, and positive mood scores were positively correlated. Positive mood was unrelated to demographic and disease-related control variables. In a hierarchical regression model controlling for PSMS, the relationship between optimism and positive mood became nonsignificant, whereas PSMS remained a correlate of positive mood. Results suggest that the relationship between optimism and positive mood may be mediated by belief in being able to use stress management techniques effectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
5.
6.
7.
Esterling Brian A.; Antoni Michael H.; Kumar Mahendra; Schneiderman Neil 《Canadian Metallurgical Quarterly》1993,12(2):132
Investigated the relationship of individual differences in repressive coping styles with differences in antibody titer to Epstein-Barr (EB) viral capsid antigen in a normal, healthy college population made up of people previously exposed to EB. Each of 54 1st-yr undergraduates completed a battery of physical-status questions and items pertaining to potential behavioral immunomodulatory confounds, along with the Taylor Manifest Anxiety Scale and the Marlowe-Crowne Social Desirability Scale. Ss reporting high and middle levels of anxiety had higher antibody titers to EB, suggesting poorer immune control over the latent virus, as compared with the low-anxious group. Similarly, high-defensive Ss had higher antibody titers than their low-defensive counterparts, and neither group differed from the middle group. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
9.
Katarzyna Jasieniecka-Gazarkiewicz Kamil Demski Satinder K. Gidda Sylwia Kliska Janusz Niedojado Ida Lager Anders S. Carlsson Elena A. Minina Robert T. Mullen Peter V. Bozhkov Sten Stymne Antoni Bana 《International journal of molecular sciences》2021,22(6)
Arabidopsis thaliana possesses two acyl-CoA:lysophosphatidylethanolamine acyltransferases, LPEAT1 and LPEAT2, which are encoded by At1g80950 and At2g45670 genes, respectively. Both single lpeat2 mutant and double lpeat1 lpeat2 mutant plants exhibit a variety of conspicuous phenotypes, including dwarfed growth. Confocal microscopic analysis of tobacco suspension-cultured cells transiently transformed with green fluorescent protein-tagged versions of LPEAT1 or LPEAT2 revealed that LPEAT1 is localized to the endoplasmic reticulum (ER), whereas LPEAT2 is localized to both Golgi and late endosomes. Considering that the primary product of the reaction catalyzed by LPEATs is phosphatidylethanolamine, which is known to be covalently conjugated with autophagy-related protein ATG8 during a key step of the formation of autophagosomes, we investigated the requirements for LPEATs to engage in autophagic activity in Arabidopsis. Knocking out of either or both LPEAT genes led to enhanced accumulation of the autophagic adaptor protein NBR1 and decreased levels of both ATG8a mRNA and total ATG8 protein. Moreover, we detected significantly fewer membrane objects in the vacuoles of lpeat1 lpeat2 double mutant mesophyll cells than in vacuoles of control plants. However, contrary to what has been reported on autophagy deficient plants, the lpeat mutants displayed a prolonged life span compared to wild type, including delayed senescence. 相似文献
10.
The inhibition of squalene-hopene cyclase (SHC) (E.C. 5.4.99.-), an enzyme of bacterial membranes catalyzing the formation
of pentacyclic sterol-like triterpenes, was studied by using different classes of compounds originally developed as inhibitors
of oxidosqualene cyclase (OCS) (E.C. 5.4.99.7), the enzyme of eukaryotes responsible for the formation of tetracyclic precursors
of sterols. The mechanism of cyclization of squalene by SHC, beginning with a protonation of the 2,3 double bond by an acidic
residue of the enzyme, followed by a series of electrophilic additions of the carbocationic intermediates to the double bonds,
is similar to the mechanism of cyclization of 2,3-oxidosqualene by OSC. The inhibitors studied included: (i) analogs of the
carbocationic intermediates formed during cyclization, such as aza-analogs of squalene and 2,3-oxidosqualene; (ii) affinity-labeling
inhibitors bearing a methylidene reactive group; and (iii) vinyldioxidosqualenes and vinylsulfide derivatives of the substrates.
Comparison of the results obtained with the two enzymes, SHC and OSC, showed that many of the most effective inhibitors of
OSC were also able to inhibit SHC, while some derivatives acted as specific inhibitors. Differences could be easily explained
on the basis of the different substrate specificity of the two enzymes. 相似文献