全文获取类型
收费全文 | 805篇 |
免费 | 24篇 |
国内免费 | 2篇 |
专业分类
化学 | 512篇 |
力学 | 37篇 |
数学 | 138篇 |
物理学 | 144篇 |
出版年
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 21篇 |
2017年 | 7篇 |
2016年 | 20篇 |
2015年 | 14篇 |
2014年 | 15篇 |
2013年 | 20篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 16篇 |
2009年 | 17篇 |
2008年 | 35篇 |
2007年 | 22篇 |
2006年 | 16篇 |
2005年 | 22篇 |
2004年 | 14篇 |
2003年 | 13篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 17篇 |
1976年 | 11篇 |
1975年 | 6篇 |
1974年 | 11篇 |
1973年 | 12篇 |
1970年 | 7篇 |
1967年 | 8篇 |
1936年 | 7篇 |
1933年 | 6篇 |
1930年 | 6篇 |
1909年 | 7篇 |
1884年 | 7篇 |
排序方式: 共有831条查询结果,搜索用时 15 毫秒
1.
2.
Tatyana Kovshova Nadezhda Osipova Anna Alekseeva Julia Malinovskaya Alexey Belov Andrey Budko Galina Pavlova Olga Maksimenko Shakti Nagpal Svenja Braner Harshvardhan Modh Vadim Balabanyan Matthias G. Wacker Svetlana Gelperina 《Molecules (Basel, Switzerland)》2021,26(4)
Targeted delivery of doxorubicin still poses a challenge with regards to the quantities reaching the target site as well as the specificity of the uptake. In the present approach, two colloidal nanocarrier systems, NanoCore-6.4 and NanoCore-7.4, loaded with doxorubicin and characterized by different drug release behaviors were evaluated in vitro and in vivo. The nanoparticles utilize a specific surface design to modulate the lipid corona by attracting blood-borne apolipoproteins involved in the endogenous transport of chylomicrons across the blood–brain barrier. When applying this strategy, the fine balance between drug release and carrier accumulation is responsible for targeted delivery. Drug release experiments in an aqueous medium resulted in a difference in drug release of approximately 20%, while a 10% difference was found in human serum. This difference affected the partitioning of doxorubicin in human blood and was reflected by the outcome of the pharmacokinetic study in rats. For the fast-releasing formulation NanoCore-6.4, the AUC0→1h was significantly lower (2999.1 ng × h/mL) than the one of NanoCore-7.4 (3589.5 ng × h/mL). A compartmental analysis using the physiologically-based nanocarrier biopharmaceutics model indicated a significant difference in the release behavior and targeting capability. A fraction of approximately 7.310–7.615% of NanoCore-7.4 was available for drug targeting, while for NanoCore-6.4 only 5.740–6.057% of the injected doxorubicin was accumulated. Although the targeting capabilities indicate bioequivalent behavior, they provide evidence for the quality-by-design approach followed in formulation development. 相似文献
3.
Amit Kumar Trevor Janes Subrata Chakraborty Prosenjit Daw Niklas vonWolff Raanan Carmieli Yael Diskin‐Posner David Milstein 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(11):3411-3415
We report a C?C bond‐forming reaction between benzyl alcohols and alkynes in the presence of a catalytic amount of KOtBu to form α‐alkylated ketones in which the C=O group is located on the side derived from the alcohol. The reaction proceeds under thermal conditions (125 °C) and produces no waste, making the reaction highly atom efficient, environmentally benign, and sustainable. Based on our mechanistic investigations, we propose that the reaction proceeds through radical pathways. 相似文献
4.
5.
Svenja M. Ackermann Dirk W. Lachenmeier Thomas Kuballa Birk Schütz Manfred Spraul Mirko Bunzel 《Magnetic resonance in chemistry : MRC》2019,57(9):579-588
Both the German and European organic food markets are growing fast, and there is also a rising demand for organic chicken eggs. Consumers are willing to pay higher prices for organic eggs produced in an animal-appropriate environment considering animal welfare. Strict labelling requirements do not prevent chicken eggs from being a subject of food fraud. Conventionally produced (barn/free-range) eggs can easily be mislabeled as organic eggs. Especially because the demand for organically produced chicken eggs is likely to exceed supply in the future, mislabeling appears to be a realistic scenario. Therefore, there is a need for analytical methods that are suitable to classify eggs as being either conventionally or organically produced. Nuclear magnetic resonance (NMR) spectroscopy in combination with multivariate data analysis is a suitable tool to screen eggs according to the different systems of husbandry. Sample preparation is based on a fat extraction method, which was optimised for application to freeze-dried egg yolk. Samples were analysed using typical q-NMR parameters. A nontargeted approach was used for the analysis of the 1H NMR data. Principal component analysis (PCA) was applied followed by a linear discriminant analysis (PCA-LDA) and Monte Carlo cross-validation. In total, 344 chicken eggs (214 barn/free-range eggs and 130 eggs from organic farms), most of them originating from Germany, were used to build and validate the prediction model. The results showed that the prediction model allowed for the correct classification of about 93% of the organic eggs. 相似文献
6.
Oxidative Addition of Haloheteroarenes to Palladium(0): Concerted versus SNAr‐Type Mechanism 下载免费PDF全文
Prof. Bert U. W. Maes Dr. Stefan Verbeeck Dr. Tom Verhelst Audrey Ekomié Niklas von Wolff Dr. Guillaume Lefèvre Dr. Emily A. Mitchell Prof. Anny Jutand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7858-7865
The kinetics of the oxidative additions of haloheteroarenes HetX (X=I, Br, Cl) to [Pd0(PPh3)2] (generated from [Pd0(PPh3)4]) have been investigated in THF and DMF and the rate constants have been determined. In contrast to the generally accepted concerted mechanism, Hammett plots obtained for substituted 2‐halopyridines and solvent effects reveal a reaction mechanism dependent on the halide X of HetX: an unprecedented SNAr‐type mechanism for X=Br or Cl and a classical concerted mechanism for X=I. These results are supported by DFT studies. 相似文献
7.
8.
Summary Birefringence and orientation angle of solutions of Polyox WSR 301 in the concentration range of 50 to 1350 ppm have been measured up to 8000 s–1. A few marked differences with ordinary flexible polymers have been evidenced: (i) a very low value of the extinction angle at high shear rate, which could be attributed to an unusually high molecular weight; (ii) the independence of this angle on the concentration, which is due to the variation of the flexibility with the concentration, as shown by the study of the concentration dependence of the segmental optical anisotropy; (iii) the concentration dependence of the elongation shows a plateau value forc 150 ppm, which may come from a concentration dependent and reversible association process, as shown from reduced viscosity measurements.
With 5 figures 相似文献
Zusammenfassung Es wurden die Doppelbrechung und der Orientierungswinkel von Polyox-WSR 301-Lösungen im Konzentrationsbereich 50–1350 ppm bis zu Schergeschwindigkeiten von 8000 s–1 gemessen. Dabei wurden einige ausgeprägte Unterschiede gegenüber normalen flexiblen Polymeren gefunden: (i) ein sehr niedriger Wert des Auslöschwinkels, was auf ein ungewöhnlich hohes Molekulargewicht schließen läßt: (ii) die Unabhängigkeit dieses Winkels von der Konzentration, was von einer Änderung der Flexibilität mit der Konzentration herrührt, wie sie durch die Untersuchung der Konzentrationsabhängigkeit der optischen Anisotropie der Segmente aufgezeigt wird; (iii) die Existenz eines Plateaus in der Konzentrationsabhängigkeit der Streckung beic 150 ppm, welches auf einen konzentrationsabhängigen reversiblen Assoziationsvorgang hindeutet, der auch durch Messung der reduzierten Viskosität nahegelegt wird.
With 5 figures 相似文献
9.
As part of an EEC Science Stimulation programme on extensional viscosity two major conferences were organised on the subject. The second of these was devoted to the results obtained on a standard fluid, M 1. The data obtained in shear flow was remarkably consistent from laboratory to laboratory. Extensional flow results presented quite a different picture. Using a series of nonequilibrium techniques such as the spinline rheometer, opposing jet, falling drop and converging flow, extensional viscosity results were obtained which differed by as much as two to three orders of magnitude. Nevertheless, it was apparent that consistancy did exist between similar techniques. It is in the context of this information that the measurements described below have been made.The shear and extensional flow properties of partially ionised polyacrylamide in solution at concentrations ranging from 5 ppm were measured. The method of solution preparation was found to have a profound effect on the behaviour of the solutions in shear flow. The influence of salt concentration and pH was investigated and is discussed in the context of molecular shape in solution.Extensional flow measurements, using the spinline rheometer, show that the solutions are strongly strain thickening even at concentrations as low as 5 ppm. These results are considered in the light of polymer entanglement and association in the strong flow field.Delivered as a Keynote Lecture at the Golden Jubilee Conference of the British Society of Rheology and Third European Rheology Conference, Edinburgh, 3–7 September, 1990. 相似文献
10.
Summary The flow curves of SBR-1500 containing increasing amounts of tread powder and of glass powder of different grain sizes were taken by means of aGöttfert High-Pressure-Capillary-Rheometer. Up to a certain extrusion pressure of about 300 bar the flow rate decreases with increasing filler concentration. In this pressure range the characteristic filler influence upon the flow behaviour was estimated from the relative viscosity.At extrusion pressures higher than 300 bar, however, the flow curves intersect and an increase of the flow rate with increasing filler concentration is observed. Possible reasons for this peculiar behaviour are discussed.
Paper presented at the Annual Conference of the German Rheologists in Berlin, April 28–30, 1975.
With 8 figures 相似文献
Zusammenfassung Die Fließgeschwindigkeit von SBR-1500, dem steigende Mengen von Reifenmehl oder Glaspulver zugesetzt waren, wurde mit Hilfe desGöttfert-Hochdruck-Kapillar-Rheometers HKR 2000 als Funktion des Extrusionsdruckes bei 120°C ermittelt. Die Fließgeschwindigkeit nahm im Bereich kleiner Extrusionsdrücke mit steigender Füllstoffkonzentration ab. Bei Drücken um 300 bar und höher stieg die Fließgeschwindigkeit mit steigender Füllstoffkonzentration plötzlich an. Die Gründe für dieses unerwartete Verhalten werden diskutiert.
Paper presented at the Annual Conference of the German Rheologists in Berlin, April 28–30, 1975.
With 8 figures 相似文献