全文获取类型
收费全文 | 1565篇 |
免费 | 94篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 32篇 |
综合类 | 13篇 |
化学工业 | 324篇 |
金属工艺 | 19篇 |
机械仪表 | 29篇 |
建筑科学 | 73篇 |
矿业工程 | 8篇 |
能源动力 | 50篇 |
轻工业 | 124篇 |
水利工程 | 45篇 |
无线电 | 103篇 |
一般工业技术 | 231篇 |
冶金工业 | 86篇 |
原子能技术 | 7篇 |
自动化技术 | 517篇 |
出版年
2024年 | 3篇 |
2023年 | 21篇 |
2022年 | 56篇 |
2021年 | 90篇 |
2020年 | 42篇 |
2019年 | 35篇 |
2018年 | 60篇 |
2017年 | 52篇 |
2016年 | 62篇 |
2015年 | 46篇 |
2014年 | 71篇 |
2013年 | 66篇 |
2012年 | 93篇 |
2011年 | 156篇 |
2010年 | 71篇 |
2009年 | 60篇 |
2008年 | 56篇 |
2007年 | 125篇 |
2006年 | 21篇 |
2005年 | 143篇 |
2004年 | 128篇 |
2003年 | 82篇 |
2002年 | 15篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1976年 | 4篇 |
1974年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有1661条查询结果,搜索用时 15 毫秒
1.
The cellulose solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF) was
successfully applied as reaction medium for the synthesis of allyl cellulose by conversion of the polymer
with allyl chloride in the presence of solid NaOH. Samples with degree of substitution from 0.50 to 2.98
were accessible by varying the molar ratio anhydroglucose unit:allyl chloride:NaOH and reaction time. DMSO/TBAF
was found to be an efficient reaction medium for the preparation of highly functionalized samples from spruce
sulfite pulp with degree of polymerization of about 500 even in a scale of 50 g. The allyl cellulose samples
were characterized by means of FTIR- and NMR spectroscopy. Size exclusion chromatography revealed negligible
polymer degradation during synthesis and purification of the samples. 相似文献
2.
Cz. Woźniak 《Acta Mechanica》1989,78(1-2):81-94
Summary In this paper a new high efficiency C-O grid coupled with the potential flow solver based on the finite volume technique is given. It significantly reduces the CPU time and increases the computational efficiency. In order to improve the accuracy of traditional potential method a shock point operator is used to account for entropy correction. Some calculated results of 2D inviscid, viscous/inviscid interaction and 3D inviscid flow indicate that nonisentropic potential method produces results closer to Euler solution as well as experimental data, while its computational efforts are nearly the same as the usual isentropic potential method.With 9 Figures 相似文献
3.
Victor Chabanenko Roman Puźniak Adam Nabiałek Sergei Vasiliev Vladimir Rusakov Loh Huanqian Ritta Szymczak Henryk Szymczak Jan Jun Janusz Karpiński Vitaly Finkel 《Journal of Low Temperature Physics》2003,130(3-4):175-191
We present a study of magneto-thermal instabilities in polycrystalline MgB2 superconductor, by magnetic hysteresis loop measurements and by investigations of magnetic flux dynamics with a miniature Hall probe. Temperature and magnetic field ranges where the flux jumps may be observed have been determined. On the basis of measurements of the magnetic flux dynamics, an average magnetic diffusivity describing the process of the flux jump is estimated. This parameter is compared with the thermal and magnetic diffusivities calculated on the basis of available data for thermal conductivity, heat capacity and resistivity. It is shown that the estimated value of the field of the first flux jump is influenced significantly by the field dependence of specific heat. In order to explain the observed phenomenon, the temperature reached by the sample during the flux jump at different magnetic fields is calculated. 相似文献
4.
Processes of heat and mass exchange which take place in the course of wetting and drying of cereal grain cause internal stress, the result of which are endosperm cracks. This damage, invisible to the naked eye and difficult to detect, causes specific effects, physical as well as biological. Spring wheat grain, cv. Henika, of an initial moisture content of 10% and varied endosperm structure (vitreous and mealy), was subjected to the process of wetting, and then dried under various thermal conditions. Internal damage to grain, caused by those processes, was detected by means of X-ray techniques. The extent of damage was described by means of suitable numerical indexes. Analysis of the results obtained revealed that, irrespective of the methods of grain treatment (wetting or drying), vitreous kernels suffered more extensive damage than mealy ones. The most extensive destruction of endosperm was observed following the drying of grain of high moisture content at high temperature. 相似文献
5.
Dominik Steup 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(12):2519-2532
Starting from a SMMW-multiplier design with quasioptical output two different multiplier compounds are presented. These new multipliers consist of a quasioptical antenna array in the output circuit which acts as a tunable power combiner. The multipliers work as quadruplers with an output frequency of 600 GHz. In all constructions the pump energy is fed into the diodes by a screened waveguide network. Optimum configurations for all arrays concerning quasioptical power combining are calculated and a theoretical comparison between the different multiplying conceptions is made. Finally some characteristic measurements of the quasioptical quadruplers are illustrated. 相似文献
6.
A major task of a Web GIS (Geographic Information Systems) system is to transfer map data to client applications over the
Internet, which may be too costly. To improve this inefficient process, various solutions are available. Caching the responses
of the requests on the client side is the most commonly implemented solution. However, this method may not be adequate by
itself. Besides caching the responses, predicting the next possible requests from a client and updating the cache with responses
for those requests together provide a remarkable performance improvement. This procedure is called “prefetching” and makes
caching mechanisms more effective and efficient. This paper proposes an efficient prefetching algorithm called Retrospective
Adaptive Prefetch (RAP), which is constructed over a heuristic method that considers the former actions of a given user. The
algorithm reduces the user-perceived response time and improves user navigation efficiency. Additionally, it adjusts the cache
size automatically, based on the memory size of the client’s machine. RAP is compared with four other prefetching algorithms.
The experiments show that RAP provides better performance enhancements than the other methods. 相似文献
7.
Alexander Kutschera Ursula Schombel Dominik Schwudke Stefanie Ranf Nicolas Gisch 《International journal of molecular sciences》2021,22(6)
Lipopolysaccharide (LPS), the major component of the outer membrane of Gram-negative bacteria, is important for bacterial viability in general and host–pathogen interactions in particular. Negative charges at its core oligosaccharide (core-OS) contribute to membrane integrity through bridging interactions with divalent cations. The molecular structure and synthesis of the core-OS have been resolved in various bacteria including the mammalian pathogen Pseudomonas aeruginosa. A few core-OS structures of plant-associated Pseudomonas strains have been solved to date, but the genetic components of the underlying biosynthesis remained unclear. We conducted a comparative genome analysis of the core-OS gene cluster in Pseudomonas syringae pv. tomato (Pst) DC3000, a widely used model pathogen in plant–microbe interactions, within the P. syringae species complex and to other plant-associated Pseudomonas strains. Our results suggest a genetic and structural conservation of the inner core-OS but variation in outer core-OS composition within the P. syringae species complex. Structural analysis of the core-OS of Pst DC3000 shows an uncommonly high phosphorylation and presence of an O-acetylated sugar. Finally, we combined the results of our genomic survey with available structure information to estimate the core-OS composition of other Pseudomonas species. 相似文献
8.
Continuous size fractionation of magnetic nanoparticles by using simulated moving bed chromatography
Carsten-Rene Arlt Dominik Brekel Stefan Neumann David Rafaja Matthias Franzreb 《Frontiers of Chemical Science and Engineering》2021,15(5):1346
The size fractionation of magnetic nanoparticles is a technical problem, which until today can only be solved with great effort. Nevertheless, there is an important demand for nanoparticles with sharp size distributions, for example for medical technology or sensor technology. Using magnetic chromatography, we show a promising method for fractionation of magnetic nanoparticles with respect to their size and/or magnetic properties. This was achieved by passing magnetic nanoparticles through a packed bed of fine steel spheres with which they interact magnetically because single domain ferro-/ferrimagnetic nanoparticles show a spontaneous magnetization. Since the strength of this interaction is related to particle size, the principle is suitable for size fractionation. This concept was transferred into a continuous process in this work using a so-called simulated moving bed chromatography. Applying a suspension of magnetic nanoparticles within a size range from 20 to 120 nm, the process showed a separation sharpness of up to 0.52 with recovery rates of 100%. The continuous feed stream of magnetic nanoparticles could be fractionated with a space-time-yield of up to 5 mg/(L∙min). Due to the easy scalability of continuous chromatography, the process is a promising approach for the efficient fractionation of industrially relevant amounts of magnetic nanoparticles. 相似文献
9.
Dorota Butkiewicz Magorzata Krzeniak Agnieszka Gdowicz-Kosok Monika Giglok Magorzata Marszaek-Zeczak Rafa Suwiski 《International journal of molecular sciences》2021,22(11)
For non-small cell lung cancer (NSCLC), radiotherapy (RT) and platinum-based chemotherapy (CHT) are among the main treatment options. On the other hand, radioresistance and cytotoxic drug resistance are common causes of failure. The epidermal growth factor receptor (EGFR) plays an important role in radioresponse and therapy resistance. We hypothesized that single nucleotide polymorphisms (SNPs) in the EGFR gene might affect individual sensitivity to these treatments, and thus, therapy outcome and prognosis. The association between functional EGFR SNPs and overall (OS), locoregional recurrence-free (LFRS), and metastasis-free (MFS) survival was examined in 436 patients with unresectable NSCLC receiving RT and platinum-based CHTRT. In a multivariate analysis, the rs712830 CC homozygotes showed reduced OS in the whole group (p = 0.039) and in the curative treatment subset (p = 0.047). The rs712829 TT genotype was strongly associated with decreased LRFS (p = 0.006), and the T-C haplotype was a risk factor for locoregional recurrence in our patients (p = 0.003). The rs2227983 GG alone and in combination with rs712829 T was an indicator of unfavorable LRFS (p = 0.028 and 0.002, respectively). Moreover, significant independent effects of these SNPs on OS, LRFS, and MFS were observed. Our results demonstrate that inherited EGFR gene variants may predict clinical outcomes in NSCLC treated with DNA damage-inducing therapy. 相似文献
10.
A hybrid ab initio path integral molecular dynamics/bosonic path integral Monte Carlo simulation method has been developed, implemented and tested, which allows for the reactive simulations of molecules, clusters or complexes solvated by superfluid 4He. The simulation takes into account “on-the-fly” the electronic structure and thus the chemical reactivity of the solutes, in conjunction with the Bose–Einstein statistics, and thus the superfluid character of this peculiar solvent. This enables investigations into cryochemical reactions taking place in helium nanodroplets, such as those used in helium nanodroplet isolation (HENDI) spectroscopy. 相似文献