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211.
Clauwaert K Vande Casteele S Sinnaeve B Deforce D Lambert W Van Peteghem C Van Bocxlaer J 《Rapid communications in mass spectrometry : RCM》2003,17(13):1443-1448
This article describes a simple method to perform lock mass corrected accurate mass measurements in tandem mass spectrometry (MS/MS) with a quadrupole time-of-flight (Q-TOF) mass spectrometer. The experimental approach consists of using the protonated molecule of a known compound, which is measured in a MS/MS function using low collision energy (no fragmentation), as mass calibrator. The unknown compound is acquired in MS/MS mode albeit using high collision energy. After the acquisition, the two MS/MS spectra of unknown and mass calibrator are combined, and the fragments of the unknown are lock mass corrected by using the protonated molecule of the mass calibrator. To prove this concept, 10 compounds were analyzed using this approach, the fragments interpreted and, where possible, related to structural data available in the literature. All the unequivocally assigned fragments were accurately mass measured with mass errors within appropriate limits, i.e. for m/z values <200 with a mass tolerance of 3 mDa while for m/z > 200 the mass tolerance is expressed as 10 ppm. 相似文献
212.
Norbert Kuhn Stefan Stubenrauch
Roland Boese
Dieter Bl ser 《Journal of organometallic chemistry》1992,440(3):289-296The azacyclopentadienyl compounds (2,5-C4tBu2RHN)MCl3 (M = Ti, Zr, Hf; R = H, SiMe3) have been prepared as stable solids from the lithiated pyrroles and MCl4. The π-coordination of the azacyclopentadienyl ligands, as suggested from 13 C NMR data, has been confirmed for (2,5-C4tBu2H2N)TiCl3 by an X-ray diffraction study. 相似文献
213.
Reaction of Telluriumhexafluoride and Trimethylamine, Structures of the TeF5? and SeF5? Anions The reaction of TeF6 and (CH3)3N is of the redox kind, resulting in reduction of tellurium: X-ray single crystal analysis reveals the compounds (CH3)2N? CH2? N(CH3)2+TeF5? and [(CH3)3NH+]5(TeF5?)3(HF2?)2. By comparison with published data it can be shown that this mixture is identical to previously published [(CH3)3N]2TeF6. The latter was supposed to be one of the few examples of tellurium in a coordination state of eight. (CH3)4N+TeF5? and (CH3)4N4SeF5? are obtained and their structure is investigated by single crystal x-ray methods also. The anions SF5?, SeF5? and TeF5? are discussed in terms of weak interactions. 相似文献
214.
Ulrich Ch . Fischer Paul Towner Dieter Oesterhelt 《Photochemistry and photobiology》1981,33(4):529-537
Abstract— Bacteriorhodopsin (BR) from the purple membrane of Haiobacterium halobium contains covalently bound retinal in the 13- cis and all- trans configurations. Several forms of bacteriorhodopsin are known, with different absorption maxima which are designated as BRλmax (nm). At acidic pH, BR605 is formed from BR560. The following sequence of reactions was found, which is initiated by irradiation of BR605 with red light:
An all- trans /13- cis to 9- cis isomerisation occurs in the light induced reaction BR605 ∼ BR500. BR500 seems to contain covalently bound retinal, whereas BR390 contains free retinal. By irradiation with light, BR500, BR450 and BR390 can be reconverted to BR560. 相似文献
An all- trans /13- cis to 9- cis isomerisation occurs in the light induced reaction BR605 ∼ BR500. BR500 seems to contain covalently bound retinal, whereas BR390 contains free retinal. By irradiation with light, BR500, BR450 and BR390 can be reconverted to BR560. 相似文献
215.
Dieter Oesterhelt 《Angewandte Chemie (International ed. in English)》1976,15(1):17-24
Apart from the long known visual pigments, another retinal protein complex exists in nature, viz. bacteriorhodopsin from halobacteria. In contrast to the visual pigments such as the rhodopsins, which act as light sensors in the eye, bacteriorhodopsin actually transforms light energy. This energy conversion is connected with the asymmetric incorporation of bacteriorhodopsin in the lattice structure of the purple membrane which forms patches on the cell surface of halobacteria. Alongside the chlorophyll system, the purple membrane system represents the second light energy conversion principle to be discovered in living nature. Bacteriorhodopsin acts as a light-driven proton pump or as the main component of such a pump system. Absorption of light triggers off a cycle of reactions coupled with the spatially oriented uptake and release of a proton. In the intact cell an electrochemical gradient is thus built up across the cell membrane of the bacterium in which part of the absorbed light energy is stored and which is not dependent upon redox processes as in the case of respiration or photosynthesis. This electrochemical gradient can supply the energy required for ATP synthesis in the cell; a reversible proton-translocating ATPase serves as catalyst system. 相似文献
216.
Summary Qualitative molecular orbital considerations of the complexes [5-CPV(CO)3 L] (L = substituted phosphane, SbPh3, AsPh3, CN–) suggest that s' V chemical shift parameters () obtained for these compounds should correlate with the -acceptor abilities of L. Based on observed r-values, the ligands are arranged in sequence of their -acceptor ability, which lies in the order P(OR)3 > CN– > PR'33 SbPh3 PPhF2 > P(i-Bu)3 P(NR
2
)3 > PPh3 > AsPh3 Nuclear spin-spin coupling constants J (51V-31 P), line widths H and i.r. data in the (CO) region are also presented.P(OR)3 = P(OEt)3, 4-Ethyl-l-phospha-2,6,7-trioxabicyclo[2.2.2]-octane; R = Me, n-Pr; R = Me, Et. 相似文献
217.
Uwe Klingebiel Dieter Bentmann Anton Meller 《Journal of organometallic chemistry》1978,144(3):381-388
Aminofluorsilanes are obtained by the reaction of fluorosilanes with the lithium salts of the corresponding amines. The reaction of aminofluorosilanes with butyllithium in a (2 + 2)cyclo addition reaction leads to the formation of fourmembered silicon-nitrogen ring compounds. The mechanism of the reaction is discussed, the mass, 1H and 19F NMR spectra of the compounds are reported. 相似文献
218.
HgI2 crystallizes under ambient conditions from various solvents and by sublimation into three concomitant polymorphs whose colors are red, orange, and yellow. The orange and yellow phases are metastable and transform into the red phase when touched. A phase transition from red to yellow occurs at 400 K. The reverse transition from yellow to red shows a huge hysteresis. We established that the structures of the metastable yellowM phase (determined by single‐crystal X‐ray diffraction) and the high‐temperature yellowHT phase (determined by powder synchrotron X‐ray diffraction and second‐harmonic generation) are different, albeit closely related. Both show analogous packings of I? Hg? I molecules, which are straight in the first and bent with an angle of ca. 160° in the second. The red and orange phases are tetrahedral semiconductor structures that sublime even at room temperature. The growth of the yellowM phase from 2‐chloroethanol and the kinetics of the reconstructive phase transition red to yellowHT and back were studied by optical microscopy, Raman spectroscopy in solution, luminescence, and powder synchrotron X‐ray diffraction as a function of time at various temperatures. Both yellow phases grow by accretion of HgI2 molecules, present in the solution or liberated from the red crystals, on the surface of the crystal. In contrast, the reverse transformation from yellow to red occurs in the bulk of the crystal, presumably by migration of Hg in the packing of I and subsequent rearrangement of I. The displacement parameters of Hg in both structures are considerably larger than those of I and apparently not dominated by disorder effects. 相似文献
219.
Michael Limbach Markus Lweneck JürgV. Schreiber Jens Frackenpohl Dieter Seebach Andreas Billich 《Helvetica chimica acta》2006,89(7):1427-1441
β‐Peptides and, to a certain extent, also mixed α,β‐peptides, are resistant to degradation by a variety of proteolytic enzymes that rapidly degrade natural α‐peptides. This is one of many characteristics that make β‐peptides an attractive class of compounds for drug‐discovery studies. On the other hand, modern organometallic reactions such as the Suzuki–Miyaura cross‐coupling have become standard tools in industry laboratories to derivatize side chains of α‐peptidic compounds to build up libraries of unnatural peptides. Combining both features, we prepared (4‐bromo)‐β3‐homophenylalanine derivatives 3 – 5 and 12 as precursors for Suzuki–Miyaura couplings. From these bromo compounds, we synthesized biaryl‐substituted β‐homoamino acids 6 , and analogs 13 and 15 of the anti‐AIDS drug Saquinavir. 相似文献
220.
Investigation of the Interactions of β‐Peptides with DNA Duplexes by Circular Dichroism Spectroscopy
Kenji Namoto James Gardiner Thierry Kimmerlin Dieter Seebach 《Helvetica chimica acta》2006,89(12):3087-3103
The interaction of β‐peptides with the DNA duplexes of dA20dT20 and a GCN4‐binding CRE sequence was examined. To gauge the factors that govern these interactions, two β‐pentadecapeptides, 1 and 2 , a β‐dodecapeptide, 3 , three β‐decapeptides, 4 – 6 , three β‐heptapeptides, 7 – 9 , and β‐octaarginine 10 were designed and synthesized. The β‐peptides were conceived to adopt a β‐peptide 314 helix, in which the side chains at position i and i + 3 are aligned vertically along one side of the helix. The side chains of Lys, Asn, and Arg were positioned such that potential H‐bonding sites were created for a helical conformation to interact with the base pairs of DNA. CD Analysis showed that β‐peptides 1, 2 , and 10 interacted with dA20dT20. In addition, β‐peptides 1 and 2 showed significant interaction with a DNA‐duplex 20mer containing the ATF/CREB recognition sequence for the regulatory protein GCN4. It is impossible, at this stage of the investigation, to make a safe proposal about the actual nature of the interaction of the structures(s) of the complexes, the formation of which is suggested by the CD spectra reported herein. 相似文献