全文获取类型
收费全文 | 1428篇 |
免费 | 95篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 14篇 |
综合类 | 8篇 |
化学工业 | 464篇 |
金属工艺 | 35篇 |
机械仪表 | 29篇 |
建筑科学 | 61篇 |
矿业工程 | 2篇 |
能源动力 | 37篇 |
轻工业 | 124篇 |
水利工程 | 19篇 |
石油天然气 | 2篇 |
无线电 | 95篇 |
一般工业技术 | 282篇 |
冶金工业 | 120篇 |
原子能技术 | 6篇 |
自动化技术 | 228篇 |
出版年
2023年 | 18篇 |
2022年 | 45篇 |
2021年 | 43篇 |
2020年 | 35篇 |
2019年 | 54篇 |
2018年 | 43篇 |
2017年 | 45篇 |
2016年 | 49篇 |
2015年 | 36篇 |
2014年 | 73篇 |
2013年 | 94篇 |
2012年 | 69篇 |
2011年 | 114篇 |
2010年 | 77篇 |
2009年 | 60篇 |
2008年 | 68篇 |
2007年 | 66篇 |
2006年 | 62篇 |
2005年 | 54篇 |
2004年 | 39篇 |
2003年 | 44篇 |
2002年 | 25篇 |
2001年 | 18篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 21篇 |
1997年 | 21篇 |
1996年 | 18篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 14篇 |
1991年 | 6篇 |
1990年 | 12篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 5篇 |
排序方式: 共有1526条查询结果,搜索用时 0 毫秒
81.
Roland Guérin El Houssine El Ghadraoui Jean-Yves Pivan Jean Padiou Marcel Sergent 《Materials Research Bulletin》1984,19(10):1257-1270
Two new compounds Ni12Zr2P7 and Ni20Zr6P13 were synthesized in the NiZrP system by reacting the constituent elements. Ni12Zr2P7 is of the Fe12Zr2P7-type while Ni20Zr6P13 appears as a new structural type in the chemistry of transition metal phosphides. Its unit cell is hexagonal with space group P6̄ and contains one formula unit. The X-ray structure was studied from three-dimensional single-crystal counter data and was refined down to R = 0.040 for 221 independent reflections. The structure of Ni20Zr6P13 can be described as built up by two groups of three phosphorus trigonal prisms occupied by the zirconium atoms. In each group, the |ZrP6| prisms are linked together by common edges in order to generate triangular phosphorus sites occupied by nickel atoms. In addition, nickel atoms are also in tetrahedral and square-planar pyramidal phosphorus sites. A comparative study with the Fe2P- and Co4Hf2P3-type structures having the same metal/non metal ratio as in Ni12Zr2P7 and Ni20Zr6P13 is also discussed. A nearly temperature independent paramagetism and a metallic conduction deducted from magnetic and electrical measurements exhibit the metallic behavior for these new compounds. 相似文献
82.
New halide glasses based on cadmium halides as glass progenitors have been discovered. This paper describes fluoride glasses in the CdF2-BaF2-ZnF2 ternary system. Binary glasses CdxBa1?xF2 (0.45 < x < 0.52) have been obtained. The limits of the glassy area are: 5–55 % CdF2, 15–55 % BaF2, 0–60 % ZnF2. Numerous fluorides such as the alkali fluorides, AlF3, YbF3 and ThF4 may be included in the glass composition. Only thin glass samples may be prepared because of the high crystallization rate. The characteristic temperatures of the Cd0.3Ba0.4Zn0.3F2 glass are 290° C for TG, 330° C for TC and 620° C for TF. The optical transmission spectrum of a thin sample shows an extrinsic absorption band at around 9000 nm and the multiphonon IR absorption edge beyond 10500 nm. The optimization of these glasses will make them attractive materials for IR transmittance and IR optical fibres. The crystallization of the Cd0.5Ba0.5F2 glass results in two solid solutions Ba1?xCdxF2 and Cd1?xBaxF2 deriving from the fluorite structural type. Thus, cadmium fluoride glasses appear as the result of the disordering of the fluorite type structure in the same way as ZrF4-based glasses derive from the disordering of the ReO3-type structure. Both glasses may be described as the random insertion of cations into an aperiodic array of F? anions. 相似文献
83.
Hiscock Merrill; Kinsbourne Marcel; Caplan Bruce; Swanson James M. 《Canadian Metallurgical Quarterly》1979,88(1):27
Administered dichotic digit tasks requiring free report and selective listening, respectively, to 20 6–16 yr old hyperactive children. Ss received methylphenidate before 2 experimental sessions and a placebo before 2 control sessions. The stimulant did not improve free-report performance significantly; rather it facilitated or impaired performance, depending on how it affected the order in which stimuli were reported. Similarly, medication had no effect on overall selective-listening performance, but it increased the difficulty of switching attention from one ear to the other. Results demonstrate that stimulants may act to maintain selective attention and to inhibit channel switching. Listening asymmetry, that is, right-ear superiority, was influenced by task variables but not by stimulant medication. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
84.
Regelous M Turner SP Elliott TR Rostami K Hawkesworth CJ 《Analytical chemistry》2004,76(13):3584-3589
We describe a new method for the chemical separation and analysis of Pa in silicate rock samples by isotope dilution. Our new technique has the following advantages over previous methods: (a) The initial separation of Pa from the rock matrix is carried out using anionic exchange resin and HCl-HF mixtures, avoiding the need to remove F(-) quantitatively from the sample solution prior to this step, (b) Efficient ionization of Pa is achieved using a multicollector inductively coupled plasma mass spectrometer, so that smaller sample sizes and shorter measurement times are required, compared to previous methods using thermal ionization mass spectrometry or alpha spectrometry. (c) Plasma ionization requires less efficient separation of the high field strength elements from Pa, thus reducing reagent volumes, blanks, and sample preparation times. Instrumental mass fractionation can be corrected for using admixed U of known isotopic composition. Using this method, Pa concentrations can be measured to a precision of approximately 0.5% and an accuracy of approximately 1% using only a few tens of femtograms of Pa. 相似文献
85.
The molecular architecture of the GPCRs, including the dynamic set of interactions between the receptor and the ligand, is one of the key structural questions of biophysical approaches. In the present study, molecular dynamics (MD) simulations were performed on the well-validated molecular model of the vasopressin V1a receptor applying different parameters (i.e., force fields, time variation, use of constraints) in order to sample the conformational space of the endogenous ligand arginine vasopressin (AVP), to explore different putative binding modes, and to analyze the simulation results with respect to experimental data. Noteworthy, it is to mention that for the first time a model of the vasopressin receptor remained stable in a 500 ps MD simulation run under vacuo boundary conditions using the Kollman all-atom FF even though no constraints were imposed. Conclusively, we determined an optimized experimental procedure for studying the dynamics and structure-functionship of this highly important family of GPCRs: the use of MD simulations with the Kollman all-atom force-field parameters on a constrained receptor. Our simplified model may be used as a basis for structure based design of new GPCR ligands and for in silico screening of virtual combinatorial chemistry libraries. 相似文献
86.
Rohrlack T Christoffersen K Hansen PE Zhang W Czarnecki O Henning M Fastner J Erhard M Neilan BA Kaebernick M 《Journal of chemical ecology》2003,29(8):1757-1770
This paper describes the purification and characterization of microviridin J, a newly discovered metabolite of Microcystis that causes a lethal molting disruption in Daphnia spp., upon ingestion of living cyanobacterial cells. Microviridin J consists of an acetylated chain of 13 amino acids arranged in three rings and two side chains. Unlike other known isoforms of microviridin, microviridin J contains arginine that imparts a unique solution conformation characterized by proximal hydrophobic interactions between Arg and other regions of the molecule. This eventually results in the formation and stabilization of an additional ring system. Microviridin J potently inhibits porcine trypsin, bovine chymotrypsin, and daphnid trypsin-like proteases. The activity against trypsin is most likely due to Arg and its distinctive conformational interactions. Overall, the data presented for microviridin J emphasize once again the ability of cyanobacteria to produce numerous and potent environmental toxins. 相似文献
87.
A fully integrated, web-based, virtual screening platform has been developed to allow rapid virtual screening of large numbers of compounds. ORACLE is used to store information at all stages of the process. The system includes a large database of historical compounds from high throughput screenings (HTS) chemical suppliers, ATLAS, containing over 3.1 million unique compounds with their associated physiochemical properties (ClogP, MW, etc.). The database can be screened using a web-based interface to produce compound subsets for virtual screening or virtual library (VL) enumeration. In order to carry out the latter task within ORACLE a reaction data cartridge has been developed. Virtual libraries can be enumerated rapidly using the web-based interface to the cartridge. The compound subsets can be seamlessly submitted for virtual screening experiments, and the results can be viewed via another web-based interface allowing ad hoc querying of the virtual screening data stored in ORACLE. 相似文献
88.
A toolset for building the virtual enterprise 总被引:6,自引:0,他引:6
Much research has been undertaken to define what a virtual enterprise is and how it should work. This paper addresses the specific question, how a virtual enterprise can be designed to have the agility to support short-term business opportunities. A framework is presented for the organizational design and the changing business roles of the business architect who constructs the various phases of the virtual enterprises lifecycle. This infrastructure for creating virtual enterprises is referred to as the value system designer; a set of methods and tools to select partners, re-engineer business- and logistic processes and to set up an information and communication platform for the virtual enterprise. The methods and tools have been developed in two longitudial research projects TELEflow and the Virtuelle Fabrik between 1995 and 1999. Focusing on the experiences gained from numerous cases, a summary on crucial success factors for designing virtual enterprises shall be presented. Thus, this paper gives insights and applicable know-how for companies and managing engineers in their role as virtual enterprise architects, for example leaders of project consortia or joint ventures or as first-tier suppliers co-ordinating supplier (sub-) nets. 相似文献
89.
Primary amines (ammonia, methyl, propyl, octyl, octadecyl, phenyl, benzyl, phenethyl) including methyl esters of amino acids
(glycine, dl-alanine, l-valine, l-leucine, L-tyrosine, and l-methionine), and secondary amines (dimethyl, diethyl, dipropyl, diisopropyl, dioctyl, and diphenyl) attack regiospecifically
the central carbon atom of the allene system of methyl 12-keto-9,10-octadecadienoate (1) to give the corresponding lipidic enaminone derivatives (2–21) with an average yield of 77%. The E- and Z-configuration of the enaminone system of these novel lipid derivatives was confirmed
by infrared and nuclear magnetic resonance spectroscopic techniques. Primary amines furnished Z-enaminones, while secondary
amines gave E-enaminones. 相似文献
90.
Marcel Brun Author Vitae Author Vitae Jianping Hua Author Vitae Author Vitae Brent Carroll Author Vitae Author Vitae Edward R. Dougherty Author Vitae 《Pattern recognition》2007,40(3):807-824
A cluster operator takes a set of data points and partitions the points into clusters (subsets). As with any scientific model, the scientific content of a cluster operator lies in its ability to predict results. This ability is measured by its error rate relative to cluster formation. To estimate the error of a cluster operator, a sample of point sets is generated, the algorithm is applied to each point set and the clusters evaluated relative to the known partition according to the distributions, and then the errors are averaged over the point sets composing the sample. Many validity measures have been proposed for evaluating clustering results based on a single realization of the random-point-set process. In this paper we consider a number of proposed validity measures and we examine how well they correlate with error rates across a number of clustering algorithms and random-point-set models. Validity measures fall broadly into three classes: internal validation is based on calculating properties of the resulting clusters; relative validation is based on comparisons of partitions generated by the same algorithm with different parameters or different subsets of the data; and external validation compares the partition generated by the clustering algorithm and a given partition of the data. To quantify the degree of similarity between the validation indices and the clustering errors, we use Kendall's rank correlation between their values. Our results indicate that, overall, the performance of validity indices is highly variable. For complex models or when a clustering algorithm yields complex clusters, both the internal and relative indices fail to predict the error of the algorithm. Some external indices appear to perform well, whereas others do not. We conclude that one should not put much faith in a validity score unless there is evidence, either in terms of sufficient data for model estimation or prior model knowledge, that a validity measure is well-correlated to the error rate of the clustering algorithm. 相似文献