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81.
Gerald Giester 《Monatshefte für Chemie / Chemical Monthly》1991,122(4):229-234
Summary The crystal structure of synthetic Cu3SeO4(OH)4 was determined by single crystal X-ray methods:a=8.382 (2) Å,b=6.087 (1) Å,c=12.285 (2) Å,V=626.8 Å3,Z=4, space group Pnma,R=0.026,R
w
=0.021 for 1255 independent reflections (sin / 0.8 Å–1). The crystal structure is isotypic to that of the mineral antlerite, Cu3SO4(OH)4. The copper atoms are Jahn-Teller distorted with Cu[4+2]O6 polyhedra forming triple chains along [010]. These chains are linked via SeO4 tetrahedra and weak hydrogen bonds to a framework structure.
Die Kristallstruktur von synthetischem Cu3SeO4(OH)4
Zusammenfassung Die Kristallstruktur von synthetischem Cu3SeO4(OH)4 wurde mittels Einkristall-Röntgenmethoden ermittelt:a=8.382 (2) Å,b=6.087 (1) Å,c=12.285 (2) Å,V=626.8 Å3,Z=4, Raumgruppe Pnma,R=0.026,R w =0.021 für 1255 unabhängige Reflexe (sin / 0.8 Å–1). Die Kristallstruktur ist isotyp mit der des Minerals Antlerit, Cu3SO4(OH)4. Die Kupferatome sind Jahn-Teller-verzerrt, die Cu[4+2]O6 Polyeder bilden Dreierketten entlang [010]. Diese Ketten sind über SeO4-Tetraeder und schwache Wasserstoffbrücken zu einer Gerüststruktur verbunden.相似文献
82.
Variants of the hc ligase ribozyme, which catalyzes ligation of the 3' end of an RNA substrate to the 5' end of the ribozyme, were utilized to evolve a ribozyme that catalyzes ligation reactions on an external RNA template. The evolved ribozyme catalyzes the joining of an oligonucleotide 3'-hydroxyl to the 5'-triphosphate of an RNA hairpin molecule. The ribozyme can also utilize various substrate sequences, demonstrating a largely sequence-independent mechanism for substrate recognition. The ribozyme also carries out the ligation of two oligonucleotides that are bound at adjacent positions on a complementary template. Finally, it catalyzes addition of mononucleoside 5'-triphosphates onto the 3' end of an oligonucleotide primer in a template-dependent manner. The development of ribozymes that catalyze polymerase-type reactions contributes to the notion that an RNA world could have existed during the early history of life on Earth. 相似文献
83.
A total synthesis of phomactin A (1) based on a Cr(II)/Ni(II) macrocyclisation from the aldehyde vinyl iodide 11, leading to 12, followed by elaboration of the epoxyketone 16, which then undergoes spontaneous pyran-hemiacetal formation on deprotection, is described. 相似文献
84.
FTIR-RAIRS and ATR techniques are shown to provide a powerful means of investigating the molecular behaviour responsible for the pyroelectric properties of organic monolayer assemblies on silicon and aluminised glass. Spectral changes, associated with either proton transfer or head group rearrangement, are well correlated with the level of pyroelectric response for two different devices. The technique promises to be extremely important for the elucidation of the microscopic properties of molecular electronic devices. 相似文献
85.
Prof. Joseph P. Michael Prof. Gerald Pattenden 《Angewandte Chemie (International ed. in English)》1993,32(1):1-23
The marine environment is a seemingly inexhaustible treasury of organisms whose secondary metabolites bear witness to the lavishness and inventiveness with which nature is able to manipulate molecular architecture. But to what purpose are these diverse and often grotesque compounds produced? This review is founded on the premise that some of them may be involved in the uptake and transport of metal ions present in the aquatic milieu. Many metabolites produced by terrestrial organisms are known to act as ionophores, but the case for similar behavior by their marine counterparts is far hazier. Notwithstanding the relative abundance of certain metal ions in the oceans, and of metabolite structures possessing features that should facilitate the chelation of metal ions, few attempts to establish a connection between these two phenomena have been reported. We have whittled down the voluminous literature of natural products derived from marine sources to expose a core of observations and speculations germane to our premise. These facts and fantasies are evaluated in this review. A mere handful of metal-containing complexes has actually been isolated; furthermore, attempts to prepare such complexes in vitro are rare, and spectroscopic evidence for metal–metabolite interactions, whether in vivo or in vitro, is not common. Only with the vanadium-sequestering tunichromes does a logical (but by no means complete) picture begin to emerge. In several other cases, the plausibility of metal chelation, though mooted by authors, remains unsupported by experimental evidence. However, continuing efforts to obtain structural, and particularly conformational, information on the metabolites by means of X-ray crystallography, nuclear magnetic resonance spectroscopy, and molecular mechanics calculations would seem to provide the key to a rational approach to this neglected topic. On the basis of recent studies dealing with such structural aspects, we present a selection of candidate compounds, some of which are the targets of our own synthetic attentions, whose potential for binding to metal cations merits further research. 相似文献
86.
Gerald Giester 《Monatshefte für Chemie / Chemical Monthly》1989,120(8-9):661-666
Summary Single crystal X-ray data of the hydrothermally grown new phase Li2Cu3(SeO3)2(SeO4)2 were measured with a four-circle diffractometer up to sin /=0.81 Å–1 [I2/a,Z=4,V=1175.5 Å3,a=16.293(6),b=5.007(2),c=14.448(6) Å, = 94.21(1)°]. The structure was determined by direct and Fourier methods and refined toR=0.034,R
w
=0.027 for 2 086 independent reflections.Cu(1)[4+1]O5 forms a tetragonal pyramid, Cu(2)[4 + 2]O6 is a strongly elongated octahedron. The Li atom is surrounded by four O atoms forming a distorted tetrahedron. Se(IV)O3 and Se(VI)O4 groups are in accordance to literature, mean Se-O bond lengths are 1.714 and 1.644 Å.
Die Kristallstruktur von Li2Cu3(SeO3)2(SeO4)2
Zusammenfassung Einkristall-Röntgendaten der hydrothermal gezüchteten neuen Phase Li2Cu3(SeO3)2(SeO4)2 wurden mit einem Vierkreisdiffraktometer im Bereich bis zu sin /=0.81 Å–1 gemessen [I2/a,Z=4,V=1175.5 Å3,a=16.293(6),b=5.007(2),c=14.448(6) Å, =94.21(1)°]. Die Kristallstruktur wurde mittels direkter und Fourier-Methoden bestimmt und für 2 086 unabhängige Reflexe zuR=0.034,R w =0.027 verfeinert.Cu(1)[4+1]O5 bildet eine tetragonale Pyramide, Cu(2)[4+2]O6 ist ein stark verlängertes Oktaeder. Das Li-Atom ist von vier O-Atomen in Gestalt eines verzerrten Tetraeders umgeben. Die Se(IV)O3-und Se(VI)O4-Gruppen entsprechen der Literatur, die mittleren Se-O-Abstände betragen 1.714 und 1.644 Å.相似文献
87.
Mohammad Reza Ganjali Morteza HosseiniFatemeh Basiripour Mehran JavanbakhtOmid Reza Hashemi Majid Faal RastegarMojtaba Shamsipur Gerald.W Buchanen 《Analytica chimica acta》2002,464(2):181-186
A novel selective membrane electrode for determination of ultra-trace amount of lead was prepared. The PVC membrane containing N,N′-dimethylcyanodiaza-18-cown-6 (DMCDA18C6) directly coated on a graphite electrode, exhibits a Nernstian response for Pb2+ ions over a very wide concentration range (from 1.0×10−2 to 1.0×10−7 M) with a limit of detection of 7.0×10−8 M (∼14.5 ppb). It has a fast response time of ∼10 s and can be used for at least 2 months without any major deviation in potential. The electrode revealed very good selectivity with respect to all common alkali, alkaline earth, transition and heavy metal ions. The proposed sensor was used as an indicator electrode in potentiometric titration of lead ions and in determination of lead in edible oil, human hair and water samples. The proposed sensor was found to be superior to the best Pb2+-selective electrodes reported in terms of detection limit and selectivity coefficient. 相似文献
88.
Gerald Giester 《Monatshefte für Chemie / Chemical Monthly》1992,123(11):957-963
Summary The crystal structure of the hydrothermally synthesized compound Fe(SeO2OH) (SeO4) · H2O was determined by single crystal diffraction methods:a=8.355(2) Å,b=8.696(2) Å,c=9.255(2) Å, =93.72(1)°,V=670.95 Å3;Z=4, space group P21/c,R=0.029,R
w=0.027 for 2430 independent reflections (sin /0.76 Å–1). Isolated FeO5(H2O)-octahedra share five corners with [SeO2OH] and [SeO4] groups to form sheets parallel to (100). These sheets are interconnected via hydrogen bonds only.
Die Kristallstruktur von Fe(SeO2OH)(SeO4)·H2O
Zusammenfassung Die Kristallstruktur der hydrothermal dargestellten Verbindung Fe(SeO2OH) (SeO4)·H2O wurde mittels Einkristallbeugungsmethoden bestimmt:a=8.355(2) Å,b=8.696(2) Å,c=9.255(2) Å, =93.72(1)°,V=670.95 Å3;Z=4, Raumgruppe P21/c,R=0.029,R w=0.027 für 2 430 unabhängige Reflexe (sin / 0.76 Å–1). Isolierte FeO5(H2O)-Oktaeder teilen fünf Ecken mit [SeO2OH]- und [SeO4]-Gruppen, wobei sie Schichten parallel (100) bilden. Diese Schichten sind nur über Wasserstoffbrücken miteinander verbunden.相似文献
89.
Cornelissen C Erker G Kehr G Fröhlich R 《Dalton transactions (Cambridge, England : 2003)》2004,(23):4059-4063
Treatment of the complexes [(C(5)H(4)PR(2))(2)Zr(CH(3))(2)](b: R = isopropyl; c: R = cyclohexyl) with the reagent HIr(CO)(PPh(3))(3) (2b) yield the heterobimetallic complexes [mu-C(5)H(4)PR(2))(2)(H(3)C-Zr-Ir(CO)(PPh(3)))] (4b, 4c) with evolution of methane. The reaction of the -PPh(2) substituted analogue with initially yields an intermediate [(H(3)C)(2)Zr(mu-C(5)H(4)PPh(2))(2)Ir(H)(CO)(PPh(3))] 5a, that still contains both methyl groups at zirconium and does not contain a metal-metal bond. At room temperature, the intermediate reacts further with methane formation to eventually yield the (Zr-Ir) complex 4a. The corresponding [mu-C(5)H(4)PR(2))(2)(H(3)C-Zr-Rh(CO)(PPh(3)))] complexes 3a (R = Ph) and 3b (R = isopropyl) react cleanly with isopropyl alcohol to liberate methane and yield the corresponding [mu-C(5)H(4)PR(2))(2)(Me(2)CHO-Zr-Rh(CO)(PPh(3)))] products (7a, 7b). Carefully monitoring the reaction of with Me(2)CHOH by NMR revealed that the Zr-Rh functionality is attacked first to give the intermediate [Me(Me(2)CHO)Zr([micro sign]-C(5)H(4)PR(2))(2)Rh(H)(CO)(PPh(3))] (6b). This intermediate then reacts further to cleave off methane and re-form the (Zr-Rh) metal-metal bond to yield the product 7b. The tetrametallic mu-oxo-(Zr-Rh) metallocene derivate 11a was obtained starting from the (Zr-Rh) complex 3a and it was characterized by X-ray diffraction. It may be that this reaction is also initiated by H-OH addition to the [Zr-Rh] metal-metal bond. 相似文献
90.