全文获取类型
收费全文 | 5664篇 |
免费 | 232篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 93篇 |
综合类 | 27篇 |
化学工业 | 1557篇 |
金属工艺 | 106篇 |
机械仪表 | 101篇 |
建筑科学 | 337篇 |
矿业工程 | 24篇 |
能源动力 | 120篇 |
轻工业 | 446篇 |
水利工程 | 36篇 |
石油天然气 | 3篇 |
无线电 | 357篇 |
一般工业技术 | 1208篇 |
冶金工业 | 661篇 |
原子能技术 | 42篇 |
自动化技术 | 791篇 |
出版年
2023年 | 38篇 |
2022年 | 31篇 |
2021年 | 91篇 |
2020年 | 75篇 |
2019年 | 72篇 |
2018年 | 88篇 |
2017年 | 100篇 |
2016年 | 149篇 |
2015年 | 109篇 |
2014年 | 172篇 |
2013年 | 263篇 |
2012年 | 244篇 |
2011年 | 351篇 |
2010年 | 268篇 |
2009年 | 271篇 |
2008年 | 268篇 |
2007年 | 260篇 |
2006年 | 255篇 |
2005年 | 214篇 |
2004年 | 185篇 |
2003年 | 153篇 |
2002年 | 124篇 |
2001年 | 94篇 |
2000年 | 100篇 |
1999年 | 111篇 |
1998年 | 178篇 |
1997年 | 116篇 |
1996年 | 116篇 |
1995年 | 85篇 |
1994年 | 81篇 |
1993年 | 84篇 |
1992年 | 83篇 |
1991年 | 59篇 |
1990年 | 67篇 |
1989年 | 60篇 |
1988年 | 69篇 |
1987年 | 61篇 |
1986年 | 54篇 |
1985年 | 47篇 |
1984年 | 56篇 |
1983年 | 42篇 |
1982年 | 48篇 |
1981年 | 50篇 |
1980年 | 35篇 |
1979年 | 34篇 |
1978年 | 36篇 |
1977年 | 39篇 |
1976年 | 41篇 |
1975年 | 41篇 |
1973年 | 29篇 |
排序方式: 共有5909条查询结果,搜索用时 15 毫秒
51.
Wolfgang Schwack Gudrun Kopf 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1992,195(3):250-253
Summary In order to examine the photostability of the insecticide propoxur (2-isopropoxyphenyl-N-methylcarbamate) in the field model experiments with organic solvents were performed. Photodegradation (>280 nm) of propoxur was found to be more efficient in isopropanol solution than in the presence of cyclohexane or cyclohexene. Photolysis in isopropanol and cyclohexane mainly resulted in formation of isopropylphenyl ether. As a trace component 2-isopropoxyphenol was detected. In the presence of cyclohexene on the other hand photomineralisation was found to be the main degradation pathway.
Dedicated to Professor Dr. H. Niebergall on the occasion of his 65th birthday 相似文献
Photoabbau des Carbamat-Insecticides Propoxur
Zusammenfassung Zur Voruntersuchung der Photostabilität des Insecticides Propoxur (2-Isopropoxyphenyl-N-methylcarbamat) im Freiland wurden Modellexperimente in organischen Lösungsmitteln durchgeführt. Der Photoabbau (>280 nm) von Propoxur verlief in Isopropanol deutlich schneller als in Cyclohexan oder Cyclohexen. Bei Bestrahlung in Isopropanol und Cyclohexan entstand als Hauptprodukt Isopropylphenylether, daneben Spuren von 2-Isopropoxyphenol. Dagegen erfolgte in Cyclohexen der Abbau hauptsächlich über eine Photomineralisierung.
Dedicated to Professor Dr. H. Niebergall on the occasion of his 65th birthday 相似文献
52.
Wolfgang Sachse A. N. Netravali A. Richard Baker 《Journal of Nondestructive Evaluation》1992,11(3-4):251-261
In the single-fiber-composite (SFC) test, a fiber imbedded in a matrix is loaded in tension, resulting in a fragmentation of the fiber. In the conventional version of this test, the final fiber fragmentation length distribution is used with a micro-mechanical model to determine the average fiber/matrix interfacial shear stress. In the enhanced version of this test, one also determines the applied stress at each fiber fracture, and from this, one can evaluate the strength of the fiber at short gage lengths. In our measurement system, we utilize an acoustic emission (AE) technique to detect the fiber fractures and to locate the fiber breaks and so determine both the fiber failure stresses as well as the fiber fragmentation lengths while the test is in progress. Critical to the success of this test is a broadband AE system that utilizes point-like AE sensors, procedures for evaluatingin situ, the wavespeed of the first wave arrival and signal processing techniques for determining the arrival time of this signal as precisely as possible for a broad range of wave shapes. Here we describe the application of such an enhanced SFC test procedure to investigate the failure of a Nicalon fiber in an epoxy matrix. 相似文献
53.
Wolfgang Schmid und Werner Grosch 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1986,182(5):407-412
Zusammenfassung Die Aromastoffe wurden aus Kirschsaft isoliert durch simultane Destillation/Extraktion (Extrakt I) und durch Destillation in Vakuum mit anschließender Extraktion des Destillates (Extrakt II). Die beiden Extrakte wurden entsäuert, fraktioniert und durch HRGC analysiert. Die chemischen Strukturen wurden nur von den Aromastoffen analysiert, die im Sniffing-port nach der HRGC-Trennung zu erkennen waren. Identifiziert wurden 28 Aromastoffe im Extrakt I und 18 im Extrakt II; 16 davon enthielt auch Extrakt I. Beim Abriechen der schrittweise verdünnten Extrakte im Sniffing-port wurden in beiden Extrakten dieselben sieben Verbindungen mit den höchsten Aromawerten gefunden: Benzaldehyd, Linalool, Hexanal, 2(E)-Hexanal, Phenylacetaldehyd, 2(E),6(Z)-Nonadienal und Eugenol. Extrakt I enthielt zusätzlich einen fruchtigen Aromastoff unbekannter Struktur mit hohem Aromawert.
Identification of highly aromatic volatile flavour compounds from cherries (Prunus cerasus L.)
Summary The flavour compounds were isolated from cherry juice by simultaneous distillation/extraction (extract I) and also by vacuum distillation followed by extraction of the condensate (extract II). Both extracts were freed from the acids, fractionated and then analyzed by HRGC. The chemical structures of only the flavour compounds detectable at the sniffing-port of the HRGC-effluent were determined. 28 Flavour compounds were identified in extract I; 18 in extract II of which 16 occurred also in extract I. Sniffing the stepwise diluted extracts I and II revealed the same seven compounds with the highest aroma values: benzaldehyde, linalool, hexanal, 2(E)-hexanal, phenylacetaldehyde, 2(E),6(Z)-nonadienal and eugenol. Extract I contained in addition a flavour compound of high aroma value, whose structure is unknown.相似文献
54.
Wolfgang Schmid und Werner Grosch 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1986,183(1):39-44
Zusammenfassung Sieben Aromastoffe, isoliert durch Destillation im Vakuum aus Sauer- und Süßkirschprodukten, wurden vergleichend analysiert. In den frisch gepreßten Säften aus je fünf Sorten Sauer- und Süßkirschen wurden große Konzentrationsunterschiede (gm/l) gefunden: Benzaldehyd (18–393), Linalool (0,5–1,7), Hexanal (0,3–54,7), 2(E)-Hexenal (2,4220), 2(E),6(Z)-Nonadienal (0,1–2,4), Phenylacetaldehyd (2,1–5,6) und Eugenol (1,0–22,2). Die Benzaldehydkonzentration zeigte die höchste Korrelation zur Erkennungsschwelle für den Kirschgeruch der Säfte. Bei der Herstellung von Konfitüren veränderte sich die Zusammensetzung der Aromastoffe: Benzaldehyd und Linalool nahmen um den Faktor 7 bzw. 13 zu; Hexanal, 2(E)-Hexenal sowie Phenylacetaldehyd nahmen stark ab. Der Anstieg von Benzaldehyd und Linalool, der auch bei der simultanen Destillation/Extraktion der Säfte auftrat, beruht auf einer Hydrolyse entsprechender Glykoside, die durch eine Hitzebehandlung stark beschleunigt wird.
Quantitative analysis of the volatile flavour compounds having high aroma values from sour (Prunus cerasus L.) and sweet (Prunus apium L.) cherry juices and jams
Summary The analysis results for seven of the aroma compounds obtained by vacuum distillation from sweet and sour cherry products were compared. The freshly pressed juices from 5 varieties of sour and 5 varieties of sweet cherries showed great differences in concentrations (g/1): benzaldehyde (18–393), linalool (0.5–1.7), hexanal (0.3–54.7), 2(E)-hexenal (2.4–220), 2(E),6(Z)-nonadienal (0.1–2.4), phenylacetaldehyde (2.1–5.6) and eugenol (1.0–22.2). The benzaldehyde content of the juices showed the highest correlation to the recognition threshold of the cherry aroma note. The cherry jam showed a drastic change in the aroma composition: benzaldehyde and linalool increased greatly (7 and 13-times, respectively), while hexanal, 2(E)-hexenal and phenylacetaldehyde strongly decreased. The increase in benzaldehyde and linalool, which was also observed during simultaneous distillation/extraction of the juices, is caused by the hydrolysis of the corresponding glycosides during the heat treatments.相似文献
55.
In the present investigation it has been shown exemplarily for an austenite microstructure containing carbonitrides that the specific restraining force of a grain boundary due to the distribution of precipitates can be described by a modified Orowan's law, so that the grain boundary movement is considered to be analogous to the dislocation movement. This is achieved by using a modified restraining force Fr (corresponding to the cubic geometry of the particles), a detailed thermodynamic analysis of the precipitates (in this case, carbonitrides) and selected relation for the interparticle spacing La. The specific restraining force and the interparticle spacing depend on temperature within the austenite range. Each temperature is attached to a couple (Fr/La). The plot Fr against shows straight lines for each steel and from their average slope, a shear module G' of grain boundaries, which is about 64300 N·cm?2, is obtained. Hence, it is possible to describe the specific restraining force of a grain boundary with the help of Orowan's law or as it is conventionally done by using Zener's modell. At a critical temperature T*, which is different for each steel, the specific restraining force is equal to the driving force of the grain boundary. The corresponding values of La are also different for each steel and the steel which is the most resistant to grain coarsening is allowed to have the greatest value of La which still retains the capacity of impeding grain coarsening. 相似文献
56.
57.
Oliver Schmutzler Sebastian Graf Nils Behm Wael Y. Mansour Florian Blumendorf Theresa Staufer Christian Krnig Dina Salah Yanan Kang Jan N. Peters Yang Liu Neus Feliu Wolfgang J. Parak Anja Burkhardt Elisabetta Gargioni Sabrina Gennis Sharah Chandralingam Finn Heg Wolfgang Maison Kai Rothkamm Florian Schulz Florian Grüner 《International journal of molecular sciences》2021,22(7)
Quantitative cellular in vitro nanoparticle uptake measurements are possible with a large number of different techniques, however, all have their respective restrictions. Here, we demonstrate the application of synchrotron-based X-ray fluorescence imaging (XFI) on prostate tumor cells, which have internalized differently functionalized gold nanoparticles. Total nanoparticle uptake on the order of a few hundred picograms could be conveniently observed with microsamples consisting of only a few hundreds of cells. A comparison with mass spectroscopy quantification is provided, experimental results are both supported and sensitivity limits of this XFI approach extrapolated by Monte-Carlo simulations, yielding a minimum detectable nanoparticle mass of just 5 pg. This study demonstrates the high sensitivity level of XFI, allowing non-destructive uptake measurements with very small microsamples within just seconds of irradiation time. 相似文献
58.
59.
Luis Fernando Crdoba Wolfgang M.H. Sachtler Consuelo Montes de Correa 《Applied catalysis. B, Environmental》2005,56(4):269-277
A series of sulfated zirconia supported Pd/Co catalysts was synthesized by the sol–gel method and examined for NOx reduction by methane. The NO conversion increased up to a Co/S ratio of 0.43, and then decreased at a higher Co loading (Co/S = 0.95). Sulfate content was also essential for obtaining high selectivity to molecular nitrogen. A catalyst loaded with 0.06 wt.% Pd, 2.1 wt.% Co and 2.1 wt.% S (Pd/Co-SZ-2) exhibited remarkable performance under lean conditions and displayed stability in a long-term durability test using a synthetic reaction mixture containing 10% water vapor. This catalyst exhibited the highest sulfur retention most probably as cobalt sulfide. Besides, the catalytic oxidation of NO to NOy groups was confirmed by FT-IR, in agreement with the general mechanism for the SCR of NO by hydrocarbons. In the absence of oxygen in the feed stream, the catalyst was highly active for NO reduction with methane. IR stretching bands assigned to N2O and adsorbed nitro groups were identified upon adsorbing NO on Pd/Co-SZ-2. This indicates that under rich conditions disproportionation of NO to N2O and NO2 occurs and confirms that the formation of NO2 species is an essential step for NO reduction by CH4. 相似文献
60.
The effect of specific β‐nucleation on morphology and mechanical behavior of isotactic polypropylene
The commercial grade of isotactic polypropylene was modified by a specific β‐nucleating agent in a broad concentration range. The supermolecular structure of the specimens prepared by injection molding was characterized by X‐ray scattering and correlated with mechanical behavior. It was found that at a critical nucleant concentration of 0.03 wt % the content of the β‐modification virtually reaches a saturation level. With further addition of the nucleant, the β‐phase content increases only slightly. The long period passes through a distinct maximum at the same nucleant concentration. This singularity in structure remarkably correlates with a minimum of the yield stress and maxima of strain at break and fracture toughness. Such general behavior is also reflected in the correlation between the β‐phase concentration and fracture toughness profiles along the injection‐molded bars. It is suggested that in the critically nucleated material an optimum thickness of the amorphous interlayer with connecting chains between the β‐crystallites is established, rendering the material the highest possible ductility and toughness. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1174–1184, 2002 相似文献