全文获取类型
收费全文 | 1363篇 |
免费 | 29篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 8篇 |
化学工业 | 176篇 |
金属工艺 | 8篇 |
机械仪表 | 15篇 |
建筑科学 | 35篇 |
矿业工程 | 2篇 |
能源动力 | 18篇 |
轻工业 | 80篇 |
水利工程 | 9篇 |
石油天然气 | 6篇 |
无线电 | 77篇 |
一般工业技术 | 187篇 |
冶金工业 | 668篇 |
原子能技术 | 4篇 |
自动化技术 | 101篇 |
出版年
2022年 | 10篇 |
2021年 | 16篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 18篇 |
2017年 | 17篇 |
2016年 | 16篇 |
2015年 | 14篇 |
2014年 | 14篇 |
2013年 | 34篇 |
2012年 | 27篇 |
2011年 | 48篇 |
2010年 | 34篇 |
2009年 | 20篇 |
2008年 | 53篇 |
2007年 | 40篇 |
2006年 | 35篇 |
2005年 | 39篇 |
2004年 | 22篇 |
2003年 | 33篇 |
2002年 | 22篇 |
2001年 | 35篇 |
2000年 | 21篇 |
1999年 | 40篇 |
1998年 | 174篇 |
1997年 | 112篇 |
1996年 | 73篇 |
1995年 | 50篇 |
1994年 | 29篇 |
1993年 | 41篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 23篇 |
1989年 | 12篇 |
1988年 | 29篇 |
1987年 | 14篇 |
1986年 | 19篇 |
1985年 | 8篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1977年 | 16篇 |
1976年 | 40篇 |
1974年 | 4篇 |
1971年 | 7篇 |
1970年 | 8篇 |
1969年 | 5篇 |
1961年 | 4篇 |
排序方式: 共有1394条查询结果,搜索用时 10 毫秒
31.
Under oxygen-rich conditions in H2 + NO + O2 mixtures, Pd/V2O5/Al2O3 catalysts are active and highly selective (~80%) for NOx reduction to N2. In situ DRIFT spectroscopy and reactor data show that the system operates via formation of NHx species on the highly dispersed V2O5 component. Both NH3 and NH4 + are formed, with the latter dominant. The role of the palladium component is also discussed. 相似文献
32.
33.
Felix Amissah Shalina Taylor Randolph Duverna Lambert T. Ayuk‐Takem Nazarius S. Lamango 《European Journal of Lipid Science and Technology》2011,113(11):1321-1331
Polyisoprenylation is a set of secondary modifications involving proteins whose aberrant activities are implicated in cancers and degenerative disorders. The last step of the pathway involves an ester‐forming polyisoprenylated protein methyl transferase‐ and hydrolytic polyisoprenylated methylated protein methyl esterase (PMPMEase)‐catalyzed reactions. Omega‐3 and omega‐6 PUFAs have been linked with antitumorigeneis and tumorigenesis, respectively. PUFAs are structurally similar to the polyisoprenyl groups and may interfere with polyisoprenylated protein metabolism. It was hypothesized that PUFAs may be more potent inhibitors of PMPMEase than their more polar oxidative metabolites, the prostaglandins. As such, the relative effects of PUFAs and prostaglandins on PMPMEase could explain the association between cyclooxygenase‐2 (COX‐2) expression in tumors, the chemopreventive effects of the non‐steroidal anti‐inflammatory (NSAIDs) COX‐2 inhibitors and PUFAs. PUFAs such as AA, EPA, and DHA inhibited PMPMEase activity with Ki values of 0.12–3.7 µM. The most potent prostaglandin was 63‐fold less potent than AA. The PUFAs were also more effective at inducing neuroblastoma cell death at physiologically equivalent concentrations. The lost PMPMEase activity in AA‐treated degenerating cells was restored by incubating the lysates with COX‐1 or COX‐2. PUFAs may thus be physiological regulators of cell growth and could owe these effects to PMPMEase inhibition. Practical applications: Some PUFAs have been widely reported to have anticancer benefits. However, the molecular mechanisms for these effects are not well understood. The findings in the current paper appear to suggest that inhibition of PMPMEase may underlie their effects. They also imply that the expression of COX‐2 in various tumors may serve to convert the PUFAs into significantly less inhibitory prostaglandins. From these findings, AA and the other PUFAs, rather than being substrates for the synthesis of tumorigenic agents may actually contribute in suppressing cell proliferation. This being congruent with the lower cancer risks associated with long term use of anti‐inflammatory agents, the practical implications will likely include the nutritional and/or therapeutic management of cancer with the goal of maintaining suitable levels of the fatty acids in tissues. 相似文献
34.
Mathilde Pfiffer Jean‐Louis Longuet Christine Labrugère Evelyne Fargin Bruno Bousquet Marc Dussauze Sébastien Lambert Philippe Cormont Jérôme Néauport 《Journal of the American Ceramic Society》2017,100(1):96-107
In this work, the polishing‐induced contamination layer at the fused silica optics surface was studied with various interface analysis techniques: Secondary Ion Mass Spectroscopy (SIMS), Electron Probe Microanalysis (EPMA), X‐Ray Photoelectron Spectroscopy (XPS), and Inductively Coupled Plasma—Optical Emission Spectroscopy (ICP‐OES). Samples were prepared using an MRF polishing machine and cerium‐based slurry. The cerium and iron penetration and concentration were measured in the surface out of defects. Cerium is embedded at the surface in a 60 nm layer and concentrated at 1200 ppmw in this layer while iron concentration falls down at 30 nm. Spatial distribution and homogeneity of the pollution were also studied in the scratches and bevel using SIMS and EPMA techniques. We saw evidence that surface defects, such as scratches, are specific places that hold the pollutants. This overconcentration is also observed in the chamfer. These new insights into the polishing‐induced contamination of fused silica optics and it repartition have been obtained using various characterization methods. Advantages and disadvantages of each one are discussed. 相似文献
35.
Styrene undergoes efficient epoxidation to styrene epoxide on the Cu{111} surface. At the optimum condition (Θo = 0.03 ML) ∼20% of the styrene is converted to the epoxide with almost 100% selectivity. Comparison with Ag{111} shows that the epoxidation activity and selectivity of Cu greatly exceed those of Ag. Incipient oxidation of the Cu{111} surface does not suppress the adsorption of styrene, but the oxidised metal is catalytically inert. Submonolayer amounts of Cs enhance styrene uptake and increase conversion to the epoxide without adversely affecting epoxidation selectivity. This effect is due to inhibition of Cu oxidation by Cs. Our findings are discussed in the light of current understanding of Ag‐catalysed alkene epoxidation. This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
36.
A ${\text{Pd/}}\gamma {\text{ - Al}}_{\text{2}} {\text{O}}_{\text{3}}$ membrane supported on a macroporous $\alpha {\text{ - Al}}_{\text{2}} {\text{O}}_{\text{3}}$ tube was prepared by sol–gel processing and used in the partial hydrogenation of acetylene and 1,3-butadiene. The average pore diameter of the ${\text{Pd/}}\gamma {\text{ - Al}}_{\text{2}} {\text{O}}_{\text{3}}$ membrane was 3.6 nm. The gases were separated by Knudsen diffusion. The activity and selectivity of the ${\text{Pd/}}\gamma {\text{ - Al}}_{\text{2}} {\text{O}}_{\text{3}}$ membrane was compared to that of ${\text{Pd/}}\gamma {\text{ - Al}}_{\text{2}} {\text{O}}_{\text{3}}$ catalysts used in a conventional packed bed reactor. The highest selectivity to the partially hydrogenated products occurred when the reactant was premixed with H2 and was passed through the membrane wall. 相似文献
37.
38.
Geoffray Labar Cédric Bauvois Dr. Franck Borel Dr. Jean‐Luc Ferrer Dr. Johan Wouters Prof. Didier M. Lambert Prof. 《Chembiochem : a European journal of chemical biology》2010,11(2):218-227
2‐Arachidonoylglycerol plays a major role in endocannabinoid signaling, and is tightly regulated by the monoacylglycerol lipase (MAGL). Here we report the crystal structure of human MAGL. The protein crystallizes as a dimer, and despite structural homologies to haloperoxidases and esterases, it distinguishes itself by a wide and hydrophobic access to the catalytic site. An apolar helix covering the active site also gives structural insight into the amphitropic character of MAGL, and likely explains how MAGL interacts with membranes to recruit its substrate. Docking of 2‐arachidonoylglycerol highlights a hydrophobic and a hydrophilic cavity that accommodate the lipid into the catalytic site. Moreover, we identified Cys201 as the crucial residue in MAGL inhibition by N‐arachidonylmaleimide, a sulfhydryl‐reactive compound. Beside the advance in the knowledge of endocannabinoids degradation routes, the structure of MAGL paves the way for future medicinal chemistry works aimed at the design of new drugs exploiting 2‐arachidonoylglycerol transmission. 相似文献
39.
Ruth U Barbante C Bigler M Delmonte B Fischer H Gabrielli P Gaspari V Kaufmann P Lambert F Maggi V Marino F Petit JR Udisti R Wagenbach D Wegner A Wolff EW 《Environmental science & technology》2008,42(15):5675-5681
To improve quantitative interpretation of ice core aeolian dust records, a systematic methodological comparison was made. This involved methods for water-insoluble particle counting (Coulter counter and laser-sensing particle detector), soluble ion analysis (ion chromatography and continuous flow analysis), elemental analysis (inductively coupled plasma mass spectroscopy at pH 1 and after full acid digestion), and water-insoluble elemental analysis (proton induced X-ray emission). Antarctic ice core samples covering the last deglaciation from the EPICA Dome C (EDC) and the EPICA Dronning Maud Land (EDML) cores were used. All methods correlate very well among each other, but the ratios of glacial age to Holocene concentrations, which are typically a factor approximately 100, differ between the methods by up to a factor of 2 with insoluble particles showing the largest variability. The recovery of ICP-MS measurements depends on the digestion method and is differentfor different elements and during different climatic periods. EDC and EDML samples have similar dust composition, which suggests a common dust source or a common mixture of sources for the two sites. The analyzed samples further reveal a change of dust composition during the last deglaciation. 相似文献
40.
An explanation for the effect of inoculum size on MIC and the growth/no growth interface 总被引:1,自引:0,他引:1
The inoculum effect (IE) is the phenomenon observed where changes in the inoculum size used in an experiment alters the outcome with respect to, for example, the minimum inhibitory concentration of an antimicrobial or the growth/no growth boundary for a given set of environmental conditions. Various hypotheses exist as to the cause of the IE such as population heterogeneity and quorum sensing, as well as the null hypothesis - that it is artefactual. Time to detection experiments (TTD) were carried out on different initial inoculum sizes of several bacterial species (Aeromonas hydrophila, Enterobacter sakazakii, Salmonella Poona, Escherichia coli and Listeria innocua) when challenged with different pH and with combined pH and sodium acetate. Data were modelled using a modification to a Gamma model (Lambert and Bidlas 2007, Int. J. Food Microbiology 115, 204-213), taking into account the inoculum size dependency on the TTD obtained under ideal conditions. The model suggests that changes in minimum inhibitory concentration (MIC) or in the growth-no growth boundary with respect to inoculum size are due to using a smaller or larger inoculum (i.e. is directly related to microbial number) and is not due to other, suggested, phenomena. The model used further suggests that the effect of a changing inoculum size can be modelled independently of any other factor, which implies that a simple 1 to 2-day experiment measuring the TTD of various initial inocula can be used as an adjunct to currently available models. 相似文献