全文获取类型
收费全文 | 3700篇 |
免费 | 45篇 |
国内免费 | 9篇 |
专业分类
化学 | 2359篇 |
晶体学 | 14篇 |
力学 | 62篇 |
数学 | 893篇 |
物理学 | 426篇 |
出版年
2016年 | 35篇 |
2015年 | 35篇 |
2014年 | 37篇 |
2013年 | 142篇 |
2012年 | 57篇 |
2011年 | 80篇 |
2010年 | 48篇 |
2009年 | 76篇 |
2008年 | 93篇 |
2007年 | 71篇 |
2006年 | 82篇 |
2005年 | 86篇 |
2004年 | 96篇 |
2003年 | 82篇 |
2002年 | 84篇 |
2001年 | 65篇 |
2000年 | 52篇 |
1998年 | 45篇 |
1997年 | 59篇 |
1996年 | 55篇 |
1995年 | 50篇 |
1994年 | 64篇 |
1993年 | 75篇 |
1992年 | 63篇 |
1991年 | 46篇 |
1990年 | 54篇 |
1989年 | 66篇 |
1988年 | 73篇 |
1987年 | 81篇 |
1986年 | 69篇 |
1985年 | 87篇 |
1984年 | 84篇 |
1983年 | 54篇 |
1982年 | 87篇 |
1981年 | 91篇 |
1980年 | 105篇 |
1979年 | 91篇 |
1978年 | 92篇 |
1977年 | 64篇 |
1976年 | 60篇 |
1975年 | 73篇 |
1974年 | 66篇 |
1973年 | 68篇 |
1972年 | 49篇 |
1971年 | 50篇 |
1970年 | 41篇 |
1967年 | 31篇 |
1966年 | 28篇 |
1959年 | 34篇 |
1958年 | 27篇 |
排序方式: 共有3754条查询结果,搜索用时 531 毫秒
71.
In contrast to normal cells, the glycoprotein profile on epithelial tumor cells is distinctly altered. Due to an incomplete formation of the glycan side-chains resulting from a premature sialylation, additional peptide epitopes become accessible to the immune system in mucin-type glycoproteins on tumor cells. These tumor-associated structure alterations constitute the basis for a selective immunological attack on cancer cells. For the construction of immunostimulating antigens, glycopeptide partial structures from the mucins MUC1 and MUC4 carrying the tumor-associated sialyl-T(N), alpha2,6-sialyl-T and alpha2,3-sialyl-T antigens have been synthesized. Employing different linkers such as the allylic HYCRON or the fluoride-sensitive PTMSEL anchor, the antigenic glycopeptide structures were constructed on the solid phase utilizing pre-assembled glycosyl amino acid building blocks prepared in solution by convergent chemical or chemoenzymatic strategies. The proliferation of cytotoxic T cells has been induced applying a construct composed of a sialyl-T(N) MUC1-glycopeptide conjugated with a tetanus toxin T cell peptide epitope. 相似文献
72.
Wolf-Dieter Fessner Gottfried Sedelmeier Lothar Knothe Horst Prinzbach Grety Rihs Zhong-Zhi Yang Branka Kova
Edgar Heilbronner 《Helvetica chimica acta》1987,70(7):1816-1842
‘Face-to-Face’ Benzo-anellated Homologous Hypostrophenes. Syntheses, X-Ray-Structure Analyses and PE Spectra ‘Face-to-face’ Benzo-anellated homologous hypostrophenes (series M ), of interest as substrates for [6 + 6]-photocycloaddition reactions, have been synthesized. From X-ray structural analyses of 13b and 13c shortest C? C distances of 2.80(2.76)/2.71 Å and interorbital angles (ω) of 129° (128°)/130° between the benzene rings have been determined. The PE spectra are discussed in the context of transannular π,π interactions. 相似文献
73.
74.
75.
The crystal structure of the title compound has been determined from single crystal X-ray diffraction data and refined toR=0.125. The unit cell is triclinic, space group P,
(No. 2),a=5.688(1),b=5.701(1),c=8.583(1) Å, =81.32(1), =71.50(1), =67.95(1)° andZ=2. The structure consists of isolated [GeO4] tetrahedra linked together by four- and five-coordinate sodium atoms. Na4GeO4 is isostructural with Na4CoO4 (which has been described to be non-centrosymmetric and for which a centrosymmetric model is presented), K4GeO4, K4SnO4 and K4PbO4. 相似文献
76.
Horst Weitkamp und Friedhelm Korte 《Fresenius' Journal of Analytical Chemistry》1964,204(4):245-263
Zusammenfassung Die Spin-Spin-Kopplungskonstanten der olefinischen Protonen mit dem 31P sowie die Feinstruktur der 1H-NMR-Spektren sind charakteristisch für die Lage der Doppelbindung. Vielfach kann auch die Intensität der
C=C-Schwingung im IR zur Bestimmung der Doppelbindungslage benutzt werden. Massenspektren geben nur in Ausnahmefällen Hinweise, können jedoch zur exakten Bestimmung des Molekulargewichts dienen.
Die Ausführung der Untersuchungen erfolgte unter Mitarbeit von Herrn F. Dlugosch, Herrn H. Au und Fräulein R. Barth.
Herrn Dr. C. A. Reilly, Shell-Development Company, Emeryville, USA, danken wir für die Überlassung getesteter Programmkartensätze zur Berechnung der NMR-Spektren. 相似文献
Summary The spin-spin coupling constants of the olefinic protons with the phosphorus-31 as well as the fine structure of the nmr-spectra are characteristic for the position of the double bond. In the infrared, the intensity of the C=C-frequency may often serve as indication of the position of the double bond. The applicability of mass spectra is limited to a small number of compounds. They may be used, however, for an accurate determination of the molecular weight.
Die Ausführung der Untersuchungen erfolgte unter Mitarbeit von Herrn F. Dlugosch, Herrn H. Au und Fräulein R. Barth.
Herrn Dr. C. A. Reilly, Shell-Development Company, Emeryville, USA, danken wir für die Überlassung getesteter Programmkartensätze zur Berechnung der NMR-Spektren. 相似文献
77.
Friedrich Bossert Horst Meyer Egbert Wehinger 《Angewandte Chemie (International ed. in English)》1981,20(9):762-769
The aryldihydropyridines first prepared by Hantzsch almost 100 years ago have recently been found to be highly effective calcium antagonists with suitable pharmacological profiles. An illustrative example is dimethyl-l,4-dihydro-2,6-dimethyl-4-(o-nitrophenyl)pyridine-3,5-dicarboxylate (Nifedipine) which is already employed therapeutically. This substance lowers the frequency of attack of angina pectoris and reduces blood pressure. The discovery of the therapeutic activity of this class of substances initiated renewed investigation of the Hantzsch condensation and the synthesis of numerous 4-aryldihydropyridines and related compounds. Qualitative and quantitative structure/activity relationships of these substances can be deduced from their biological data. 相似文献
78.
Transient absorption spectroscopy on electronic levels of molecules in the liquid phase is governed by population kinetics as well as rotational diffusion. The goal of transient absorption experiments has been the true level kinetics free of rotation. Moreover, to extract the rotational time from transient photodichroism experiments the knowledge of true population kinetics is instrumental. Three methods for separating rotational and level kinetics are described theoretically, and one of them is performed experimentally using a repetitive picosecond spectrometer for the measurement of rotational behaviour of fluorescein 27 in solvents of different viscosity. 相似文献
79.
Roswitha Stejskal Ernst Urban Horst Völlenkle 《Monatshefte für Chemie / Chemical Monthly》1991,122(3):145-156
Summary Oxidation of isobenzofuranone1 yielded in a diastereoselective reaction epoxide2. Acidolysis of2 resulted in a mixture oftrans-glycols6 a (88%) and7 a (4%), which were separated by crystallization. The relative configuration of6 a and7 a at the chiral centers 3 a, 5, 6, and 7 a was determined by1H-NMR-spectroscopy and X-ray analysis of O-acetylated and 7 a-methylated derivatives. 相似文献
80.
Martin TC Moecks J Belooussov A Cawthraw S Dolenko B Eiden M Von Frese J Kohler W Schmitt J Somorjai R Udelhoven T Verzakov S Petrich W 《The Analyst》2004,129(10):897-901
Signatures of Bovine Spongiform Encephalopathy (BSE) have been identified in serum by means of "Diagnostic Pattern Recognition (DPR)". For DPR-analysis, mid-infrared spectroscopy of dried films of 641 serum samples was performed using disposable silicon sample carriers and a semi-automated DPR research system operating at room temperature. The combination of four mathematical classification approaches (principal component analysis plus linear discriminant analysis, robust linear discriminant analysis, artificial neural network, support vector machine) allowed for a reliable assignment of spectra to the class "BSE-positive" or "BSE-negative". An independent, blinded validation study was carried out on a second DPR research system at the Veterinary Laboratory Agency, Weybridge, UK. Out of 84 serum samples originating from terminally-ill, BSE-positive cattle, 78 were classified correctly. Similarly, 73 out of 76 BSE-negative samples were correctly identified by DPR such that, numerically, an accuracy of 94.4 % can be calculated. At a confidence level of 0.95 (alpha = 0.05) these results correspond to a sensitivity > 85% and a specificity > 90%. Identical class assignment by all four classifiers occurred in 75% of the cases while ambiguous results were obtained in only 8 of the 160 cases. With an area under the ROC (receiver operating charateristics) curve of 0.991, DPR may potentially supply a valuable surrogate marker for BSE even in cases in which a deliberate bias towards improved sensitivity or specificity is desired. To the best of our knowledge, DPR is the first and--up to now--only method which has demonstrated its capability of detecting BSE-related signatures in serum. 相似文献