全文获取类型
收费全文 | 4460篇 |
免费 | 171篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 53篇 |
综合类 | 14篇 |
化学工业 | 1236篇 |
金属工艺 | 74篇 |
机械仪表 | 61篇 |
建筑科学 | 232篇 |
矿业工程 | 8篇 |
能源动力 | 90篇 |
轻工业 | 428篇 |
水利工程 | 15篇 |
石油天然气 | 5篇 |
无线电 | 295篇 |
一般工业技术 | 859篇 |
冶金工业 | 621篇 |
原子能技术 | 36篇 |
自动化技术 | 607篇 |
出版年
2023年 | 44篇 |
2022年 | 28篇 |
2021年 | 93篇 |
2020年 | 54篇 |
2019年 | 76篇 |
2018年 | 61篇 |
2017年 | 62篇 |
2016年 | 109篇 |
2015年 | 108篇 |
2014年 | 138篇 |
2013年 | 209篇 |
2012年 | 209篇 |
2011年 | 262篇 |
2010年 | 205篇 |
2009年 | 196篇 |
2008年 | 219篇 |
2007年 | 203篇 |
2006年 | 173篇 |
2005年 | 165篇 |
2004年 | 125篇 |
2003年 | 106篇 |
2002年 | 99篇 |
2001年 | 88篇 |
2000年 | 78篇 |
1999年 | 95篇 |
1998年 | 180篇 |
1997年 | 135篇 |
1996年 | 87篇 |
1995年 | 74篇 |
1994年 | 75篇 |
1993年 | 57篇 |
1992年 | 57篇 |
1991年 | 58篇 |
1990年 | 38篇 |
1989年 | 39篇 |
1988年 | 43篇 |
1987年 | 43篇 |
1986年 | 42篇 |
1985年 | 33篇 |
1984年 | 40篇 |
1983年 | 25篇 |
1982年 | 18篇 |
1981年 | 34篇 |
1980年 | 30篇 |
1979年 | 30篇 |
1978年 | 29篇 |
1977年 | 41篇 |
1976年 | 50篇 |
1975年 | 27篇 |
1974年 | 17篇 |
排序方式: 共有4634条查询结果,搜索用时 46 毫秒
71.
Roland Schmidt Ulrich Hammon Stefan Gottfried M. Bruce Welch Helmut G. Alt 《应用聚合物科学杂志》2003,88(2):476-482
The synthesis of iron(II) complexes with various tridentate di(imino)pyridine ligands and their potential as ethene oligomerization catalysts are described. The ligands are characterized by 1H‐ and 13C‐NMR spectroscopy and the complexes only by mass spectrometry due to their paramagnetism. After activation either with methylalumoxane (MAO) or with a heterogeneous cocatalyst consisting of partially hydrolyzed trimethylaluminum and silica gel, the prepared complexes proved to be good catalysts for the oligomerization of ethene. 1‐Octene, 1‐hexene, and 1‐decene were the major products, formed in very high isomeric purity (99.9 %). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 476–482, 2003 相似文献
72.
Maria Casapu Jan-Dierk Grunwaldt Marek Maciejewski Meike Wittrock Ulrich Gbel Alfons Baiker 《Applied catalysis. B, Environmental》2006,63(3-4):232-242
The formation and stability of BaAl2O4 and BaCeO3 in Pt-Ba/Al2O3 and Pt-Ba/CeO2 based NOx storage-reduction (NSR) catalysts has been investigated using kinetic measurements, X-ray diffraction, thermal analysis and X-ray absorption spectroscopy. In as-prepared state, the Ba-component in the NSR catalysts was made up of amorphous BaO and BaCO3. The formation of BaAl2O4 started above 850 °C, whereas the formation of BaCeO3 was already observed at 800 °C and was faster than that of BaAl2O4. The stability of BaAl2O4 and BaCeO3 in various liquid and gaseous atmospheres was different. BaAl2O4 was rapidly hydrated at room temperature in the presence of water and transformed to Ba(NO3)2 and γ-alumina in the presence of HNO3, whereas BaCeO3 was decomposed to much lower extent under these conditions. Interestingly, BaCeO3 was transformed to Ba(NO3)2/CeO2 in the presence of NO2/H2O at 300–500 °C. Also, the presence of CO2 led to decomposition of barium cerate, which has important consequences for the catalyst ageing under NOx-storage conditions and can be exploited for regeneration of thermally aged NSR-catalysts. 相似文献
73.
The reactions of trans-2,5-dimethoxy-4′-aminostilbene with poly(maleic anhydride-co-methylvinyl ether) and trans-2,5-dimethoxy-4′-isocyanatostilbene with poly(oxy-1,4-phenyleneisopropylidene:1,4-phenyleneoxy-2-hydroxytrimethylene) yield polymeric systems which undergo rapid crosslinking upon short exposure to ultraviolet light. The extent of photocrosslinking as a function of exposure time was determined by the decrease of the trans-stilbene ultraviolet absorption at 350 nm. 相似文献
74.
Lenssen K Jantscheff P von Kiedrowski G Massing U 《Chembiochem : a European journal of chemical biology》2002,3(9):852-858
Here we describe the first synthesis-screening approach for the identification and optimization of new cationic lipids for gene transfer in various cell lines. Combinatorial solid-phase chemistry was used to synthesize a library of new cationic lipids based on 3-methylamino-1,2-dihydroxypropane as the polar, cationic lipid part. As the nonpolar lipid part, different hydrocarbon chains were bound to the amino group of the scaffold and the amino group was further methylated to afford constantly cationic lipids. Lipids were synthesized in both configurations and as racemates, and the counter ions were also varied. By using a fully automated transfection screening method and COS-7 cells, the cationic lipid N,N-ditetradecyl-N-methyl-amino-2,3-propanediol (KL-1-14) was identified as a candidate lipid for the development of an improved transfection reagent. Screening the transfection properties of KL-1-14 in numerous combinations with the helper lipids dioleoylphosphatidylethanolamine (DOPE) and cholesterol (Chol) revealed that Chol is the most suitable helper lipid and the best KL-1-14/Chol ratio is 0.5-0.7. Compared to the standard transfection lipid N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl sulfate (DOTAP), transfection efficiency was improved by a factor of about 40. Furthermore, by using R- and S-configured KL-1-14, it could be shown that the configuration of the lipids had no significant influence on its transfection efficiency. The highest transfection efficiencies were achieved with chloride as the counter ion. The new lipofection reagent was further tested to transfect the cell lines MDA-MB-468, MCF-7, MDCK-C7, and primary dentritic cells (DC), which are important for the development of new anticancer gene therapy strategies. Even in these cells, KL-1-14/Chol (1:0.6) had improved transfection efficiencies, which were about two to four times higher than for DOTAP. 相似文献
75.
Ulrich Frank 《Software and Systems Modeling》2014,13(3):941-962
The paper presents a method for multi- perspective enterprise modeling (MEMO) and a corresponding (meta-) modeling environment. An extensive analysis of requirements for enterprise modeling serves to motivate and assess the method. The method is based on an elaborate conception of multi-perspective enterprise models and on an extensible language architecture. The language architecture is comprised of a meta modeling language and an extensible set of integrated domain-specific modeling languages (DSML). The DSML are supplemented with process models and with guidelines for their reflective use. The corresponding modeling environment integrates editors for various DSML into multi-language model editors. It includes a meta model editor which enables the convenient use, development and extension of the set of supported DSML and supports the generation of respective graphical model editors. Thus, it also serves as a foundation for method engineering. MEMO covers both software engineering as well as social, managerial and economic aspects of the firm. The presentation of MEMO is supplemented with a comparative overview of other approaches to enterprise modeling. The paper concludes bys summarizing fundamental technical, epistemological and political challenges for enterprise modeling research and discusses potential paths for future research. 相似文献
76.
Johannes Konnerth Andreas Jger Josef Eberhardsteiner Ulrich Müller Wolfgang Gindl 《应用聚合物科学杂志》2006,102(2):1234-1239
Seven different polymers used frequently as adhesives and/or matrix polymers in wood, wood composites, and natural fiber‐reinforced composites were studied by uniaxial tensile tests and nanoindentation. It was shown that the elastic modulus, the hardness, the creep factor, and the elastic‐, plastic‐, and viscoelastic work of indentation of the seven different polymers is essentially the same regardless whether the polymers were tested in the form of pure films or in situ, i.e., in an adhesive bond line with spruce wood. An excellent correlation was found between the elastic modulus measured by tensile tests and the elastic modulus measured by nanoindentation. In spite of the good correlation, the elastic modulus measured by nanoindentation is significantly higher than the elastic modulus measured by tensile tests. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1234–1239, 2006 相似文献
77.
Markert Yvonne; Koditz Jens; Ulbrich-Hofmann Renate; Arnold Ulrich 《Protein engineering, design & selection : PEDS》2003,16(12):1041-1046
The virtue of the so-called proline concept andthe charge concept for stabilizing protease-susceptibleregions of a protein structure was compared on bovine pancreaticribonuclease A. Alanine 20 and serine 21, both of whichare located in a loop that is susceptible to the unspecificproteases subtilisin Carlsberg, subtilisin BPN', proteinaseK and elastase, were replaced with proline or lysine by site-directedmutagenesis. The rate constant of proteolysis was decreasedby up to three orders of magnitude for the proline mutants dependingon the site of the mutation and the protease used. In contrast,substitution by lysine increased the proteolytic resistanceby only one order of magnitude characterizing the prolineconcept as superior to the charge concept.Although the four applied proteases are considered to be unspecific,the degree of stabilization of the ribonuclease molecule variedconsiderably, indicating the impact of individual differencesin their substrate specificity on the proteolytic resistanceand degradation pathway of the target protein. Received May 12, 2003; revised October 23, 2003; accepted October 30, 2003 相似文献
78.
Copper deposition in the presence of an organic additive (3-mercaptopropionic acid, MPA) was studied by cyclic voltammetry and in situ scanning tunneling microscopy (STM) and the results are compared to those for additive-free solutions. It is shown that underpotential deposition (upd) of copper onto a fully MPA-covered electrode produces a defect-rich substrate, but the defects are blocked by the dense organic film for bulk deposition, resulting in a low number of nuclei. A grain-refining effect of MPA, however, was found, when Cu deposition was initiated shortly after addition of MPA to the solution, i.e., for a low-coverage MPA adlayer. 相似文献
79.
Thomas Fehn Felix Kugler Beatrice Tübke Rainer Schweppe Phillip Mebert Wolfgang Krcmar Ulrich Teipel 《化学,工程师,技术》2021,93(5):771-780
Due to the growing energy requirements, the proportion of external thermal insulation composite systems (ETICS) installed has increased significantly during the past 50 years. Due to the longevity of these systems, ETICS waste is currently accumulating. Owing to the complex construction as well as a multitude of differently installed materials and substances of the past generations, there are many uncertainties and problems with the clean and low-pollutant processing of such systems. In the frame of this work, the ETICS were processed and sorted before being screened for ingredients or pollutants as well as for the purity of the recovered material fractions. 相似文献
80.
Ulrich Muschelknautz 《化学,工程师,技术》2021,93(1-2):91-107
A competitive alternative to the standard reverse flow cyclone for gas-solids separation is the uniflow cyclone. Gas and particles passing through it in only one direction, allowing a cost-effective usage in space limited applications. Comprehensive studies of uniflow cyclones have strongly improved their understanding and led to approved design criteria and calculation methods. Here it is shown that uniflow cyclones can achieve higher efficiencies per volume with a low pressure drop than standard cyclones. 相似文献