全文获取类型
收费全文 | 38648篇 |
免费 | 1293篇 |
国内免费 | 19篇 |
专业分类
化学 | 21645篇 |
晶体学 | 180篇 |
力学 | 830篇 |
综合类 | 1篇 |
数学 | 6460篇 |
物理学 | 10844篇 |
出版年
2023年 | 208篇 |
2021年 | 315篇 |
2020年 | 500篇 |
2019年 | 345篇 |
2018年 | 464篇 |
2017年 | 439篇 |
2016年 | 1000篇 |
2015年 | 845篇 |
2014年 | 955篇 |
2013年 | 2073篇 |
2012年 | 1644篇 |
2011年 | 1987篇 |
2010年 | 1020篇 |
2009年 | 849篇 |
2008年 | 1886篇 |
2007年 | 1838篇 |
2006年 | 1621篇 |
2005年 | 1469篇 |
2004年 | 1170篇 |
2003年 | 997篇 |
2002年 | 913篇 |
2001年 | 758篇 |
2000年 | 675篇 |
1999年 | 464篇 |
1998年 | 420篇 |
1997年 | 415篇 |
1996年 | 529篇 |
1995年 | 472篇 |
1994年 | 486篇 |
1993年 | 566篇 |
1992年 | 470篇 |
1991年 | 357篇 |
1990年 | 393篇 |
1989年 | 324篇 |
1988年 | 341篇 |
1987年 | 333篇 |
1986年 | 311篇 |
1985年 | 497篇 |
1984年 | 473篇 |
1983年 | 435篇 |
1982年 | 442篇 |
1981年 | 445篇 |
1980年 | 430篇 |
1979年 | 375篇 |
1978年 | 419篇 |
1977年 | 398篇 |
1976年 | 344篇 |
1975年 | 331篇 |
1974年 | 317篇 |
1973年 | 318篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Klika KD Imrich J Danihel I Böhm S Kristian P Hamul'aková S Pihlaja K Koch A Kleinpeter E 《Magnetic resonance in chemistry : MRC》2005,43(5):380-388
The configuration and dynamic behavior of O-allyl-S-methyl-N-(acridin-9-yl)iminothiocarbonate (1) and its S-allyl-O-methyl regioisomer (2) were studied using quantum chemical calculations and by applying a novel graphical method to scatter maps obtained from MD simulations for evaluation of an NOE-weighted internuclear distance (r(NOE)). Energy calculations indicated that the Z configuration was predominant for each compound and, further, this was supported both by the calculated chemical shifts and the r(NOE). Both N-inversion- and rotation-type transition-state structures were also calculated for the E/Z isomerization process, the results indicating that the preferred interconversion mechanism for 1 is N-inversion, but contrastingly, interconversion via rotation is equally as probable as N-inversion for 2. This supports the notion that one or the other or both pathways can be active and each system needs to be assessed on a case-by-case basis. 相似文献
992.
Griesbeck AG Heinrich T Oelgemöller M Lex J Molis A 《Journal of the American Chemical Society》2002,124(37):10972-10973
An elaborated protocol is described which allows the efficient transformation of di-, tri-, and tetrapeptides into cyclopeptides with a minimum of protection and activation chemistry using the photoinduced electron transfer initiated decarboxylation of N-phthaloyl peptides resulting in C-C coupling between the initially formed carbon radicals. 相似文献
993.
Zusammenfassung Es wird die Darstellung von 2-Sulfanilamido-4-methoxy-5-chlorpyrimidin, 2-Sulfanilamido-4-methoxy-5-jodpyrimidin sowie 4-Sulfanilamido-2-methoxy-5-chlorpyrimidin beschrieben. Die erste Verbindung wurde auf zwei voneinander unabhängigen Synthesewegen erhalten.
W. Klötzer undJ. Schantl, Mh. chem.94, 1178 (1963). 相似文献
994.
Cataldo L Dutan C Misra SK Loss S Grützmacher H Geoffroy M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(11):3463-3468
The EPR spectrum of the novel radical Mes*(CH3)P--PMes* (Mes*=2,4,6-(tBu)3C6H2) was measured in the temperature range 100-300 K, and was found to be drastically temperature dependent as a result of the large anisotropy of the 31P hyperfine tensors. Below 180 K, a spectrum of the liquid solution is accurately simulated by calculating the spectral modifications due to slow tumbling of the radical. To achieve this simulation, an algorithm was developed by extending the well-known nitroxide slow-motion simulation technique for the coupling of one electron spin to two nuclear spins. An additional dynamic process responsible for the observed line broadening was found to occur between 180 K and room temperature; this broadening is consistent with an exchange between two conformations. The differences between the isotropic 31P couplings associated with the two conformers are shown to be probably due to an internal rotation about the P--P bond. 相似文献
995.
F. Götze 《Probability Theory and Related Fields》1984,65(4):599-625
Summary Berry-Esseen results and expansions are derived for the distribution function of von Mises functionals of order r under moment conditions and conditions on the smoothness of the limit distribution.The results apply to goodness-of-fit statistics — as well as to the central limit theorem in L
2p,p2, the rate of convergence being O(n
–1) for centered balls, provided a fourth moment exists.Research sponsored in part under Office of Naval Research. Contract Number N00014-80-C-0163. 相似文献
996.
An analytical free flow capillary isotachophoresis procedure, with a discontinuous electrolyte system, for the detailed analysis of lipoproteins in human body fluids has been developed. The technique is based on prestaining whole serum lipoproteins with a lipophilic dye before separation. Human serum lipoproteins are separated into 14 well-characterized subfractions according to their electrophoretic mobility. High density lipoproteins (fraction 1 to 6) are separated into three major subpopulations, the fast migrating high density lipoprotein (HDL) subpopulation, containing mainly apo AI and phosphatidylcholine, the subpopulation with intermediate mobility, consisting of particles rich in apo AII, apo E, and C apolipoproteins, and the slowly migrating HDL subfraction, containing mainly particles rich in apo AI, apo AIV, and lecithin: cholesterol acyltransferase (LCAT) activity. The apo B containing lipoproteins (fraction 7 to 14) can be subdivided into four major functional groups. The first represents chylomicron derived particles and large triglyceride-rich very low density lipoproteins (VLDL). The second group consists of small VLDL and intermediate density lipoprotein (IDL) particles, anf the third and fourth group represent the low density lipoproteins. The isotachophoretic analysis of human serum samples obtained from patients with hyperlipoproteinemias is compatible with the classification according to the Frederickson phenotypes and reflects the respective biochemical abnormalities. Furthermore, several genetic disorders of lipid and lipoprotein metabolism like HDL deficiency syndromes, familial LCAT deficiency, Fish eye disease, hypobetalipoproteinemia and abetalipoproteinemia can be well characterized by analytical capillary iso tachophoresis. In addition to patient analysis we investigated the influence of lipid lowering drugs on the lipoprotein subfraction distribution during therapy with analytical capillary isotachophoresis. 相似文献
997.
Johansson A Abrahamsson M Magnuson A Huang P Mårtensson J Styring S Hammarström L Sun L Akermark B 《Inorganic chemistry》2003,42(23):7502-7511
The preparation of donor (D)-photosensitizer (S) arrays, consisting of a manganese complex as D and a ruthenium tris(bipyridyl) complex as S has been pursued. Two new ruthenium complexes containing coordinating sites for one (2a) and two manganese ions (3a) were prepared in order to provide models for the donor side of photosystem II in green plants. The manganese coordinating site consists of bridging and terminal phenolate as well as terminal pyridyl ligands. The corresponding ruthenium-manganese complexes, a manganese monomer 2b and dimer 3b, were obtained. For the dimer 3b, our data suggest that intramolecular electron transfer from manganese to photogenerated ruthenium(III) is fast, k(ET) > 5 x 10(7) s(-)(1). 相似文献
998.
Enzymatic resolution of beta-chloro alcohols in combination with ruthenium-catalyzed alcohol isomerization led to a successful dynamic kinetic resolution (conversion up to 99% and ee up to 97%). The efficiency of the DKR is dramatically reduced when beta-bromo alcohols are used. The presence of the bromo substituent causes decomposition of the ruthenium catalysts, which triggers the progressive deactivation of the enzyme. The synthetic utility of this procedure has been illustrated by the practical synthesis of different chiral epoxides. 相似文献
999.
13C ENDOR spectra of Cu(et2dtc)2 substituted into a single crystals of Zn(et2dtc)2 are reported. The symmetry of the incorporated guest molecule appears to be considerably influenced by the Zn(et2dtc)2 host lattice. The unexpectedly large isotropic 13C hfs coupling can be understood assuming a “transannular overlap” mechanism. 相似文献
1000.
Summary Examples are given of the application of higher-order derivative spectrophotometry to microanalytical problems, including the increase in sensitivity for estimation of Zn and Cd dithizonates and the quantitative detection of arenes, aniline and phenols. We also describe the estimation of saccharin in soft drinks, and the characterization and estimation of dyes in solution and after absorption on a thin layer of alumina. Only ng-g amounts of substance are needed.
Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980. 相似文献
Hochauflösende UV/VIS-Derivativspektrophotometrie höherer Ordnung in der Mikroanalytik
Zusammenfassung Einige Beispiele für die Anwendung der Derivativspektrophotometrie höherer Ordnung in der Mikroanalyse wurden angegeben. Im besonderen wurden die Erhöhung der Empfindlichkeit der Zn- und Cd-Dithizonat-Bestimmung, die quantitative Bestimmung von Arenen, Anilin, Phenol, die Erfassung von Saccharin in Limonaden und sowohl die Charakterisierung als auch die quantitative Bestimmung von Farbstoffen in Lösung oder adsorbiert an einer dünnen Schicht Aluminiumoxid beschrieben. Es werden nur einige Mikrogramm bis Nanogramm Substanz für die Untersuchungen benötigt.
Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980. 相似文献