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91.
Microwave transitions up to J = 53 in the ground vibrational state of deuterothioformaldehyde, CD2S, were studied between 8 and 40 GHz. A detailed centrifugal distortion analysis yields accurate constants for comparison with force field values. The isotopic species 13CH2S, CH234S, CH233S, 13CD2S, CD234S, and CD233S were studied in natural abundance. Accurate average zero-point structures were determined for both CD2S and CH2S: Changes in the zero-point geometry for deuterium substitution were established. Quadrupole fine structure arising from the 33S nucleus has been measured in CH233S and CD233S. Analysis gives the following coupling constants (for both molecules) as χaa = ?11.7 and χbb - χcc = 88.1 MHz. The dipole moment of CD2S was measured to be 1.6588(8)D and an accurate comparison with CH2S was made; the ratio of dipole moments was found to be 1.0062(4). The spectroscopic and bonding properties of CH2S will be compared with formaldehyde and other molecules. 相似文献
92.
Ignatov SK Rees NH Tyrrell BR Dubberley SR Razuvaev AG Mountford P Nikonov GI 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(20):4991-4999
The titanocene silyl hydride complexes [Ti(Cp)2(PMe3)(H)(SiR3)] [SiR3=SiMePhCl (6), SiPh2Cl (7), SiMeCl2 (8), SiCl3 (9)] were prepared by HSiR3 addition to [Ti(Cp)2(PMe3)2] and were studied by NMR and IR spectroscopy, X-ray diffraction (for 6, 8, and 9), and DFT calculations. Spectroscopic and structural data established that these complexes exhibit nonclassical Ti-H-Si-Cl interligand hypervalent interactions. In particular, the observation of silicon-hydride coupling constants J(Si,H) in 6-9 in the range 22-40 Hz, the signs of which we found to be negative for 8 and 9, is conclusive evidence of the presence of a direct Si-H bond. The analogous reaction of [Ti(Cp)2(PMe3)2] with HSi(OEt)3 does not afford the expected classical silyl hydride complex [Ti(Cp)2(PMe3)(H)[Si(OEt)3]], and instead NMR-silent titanium (apparently TiIII) complex(es) and the silane redistribution product Si(OEt)4 are formed. The structural data and DFT calculations for the compounds [Ti(Cp)2(PMe3)(H)(SiR3)] show that the strength of interligand hypervalent interactions in the chlorosilyl complexes decreases as the number of chloro groups on silicon increases. However, in the absence of an Si-bound electron-withdrawing group trans to the Si-H moiety, a silane sigma complex is formed, characterized by a long Ti-Si bond of 2.658 A and short Si-H contact of 1.840 A in the model complex [Ti(Cp)2(PMe3)(H)(SiMe3)]. Both the silane sigma complexes and silyl hydride complexes with interligand hypervalent interactions exhibit bond paths between the silicon and hydride atoms in Atoms in Molecules (AIM) studies. To date a classical titanocene phosphane silyl hydride complex without any Si-H interaction has not been observed, and therefore titanocene silyl hydrides are, depending on the nature of the R groups on Si, either silane sigma complexes or compounds with an interligand hypervalent interaction. 相似文献
93.
Bis(fluoroalkyl)acrylic and methacrylic phosphate monomers, their polymers and some of their properties 总被引:1,自引:0,他引:1
Christopher M. Timperley Robert E. Arbon Michael Bird Stuart A. Brewer Malcolm W. Parry David J. Sellers Colin R. Willis 《Journal of fluorine chemistry》2003,121(1):23-31
Ten fluoromonomers of structure (RFO)2P(O)OCH2CH2OC(O)CRCH2 were made in 30-64% yield by treating the chloridates (RFO)2P(O)Cl with HOCH2CH2OC(O)CRCH2 in chloroform in the presence of triethylamine [RF=CF3CH2, C2F5CH2, C3F7CH2, C4F9CH2, C4F9CH2CH2 or C6F13CH2CH2; R H or Me]. The chloromonomer (CCl3CH2O)2P(O)OCH2CH2OC(O)CHCH2 was obtained analogously in 29% yield. Polymerisation of the acrylate monomers, but not the methacrylate monomers, could be effected using α-azoisobutyronitrile as a radical initiator. Acrylic polymers having CF3CH2O, CCl3CH2O and C6F13CH2CH2O side-chains were obtained as translucent rubbers. Specimens of cotton fabric were treated with solutions of the polymers, and average water and oil repellency ratings measured. Fabric coated with the polymer with the C6F13CH2CH2O side-chain afforded protection from penetration of the test liquids. Treated fabrics were subjected to the limiting oxygen index (LOI) test according to BS EN ISO 4589-2 (1999): this test determines the point at which a material just burns in a volumetric flow of oxygen and nitrogen. The treated fabrics were more fire-resistant (LOI 22-29%) than the untreated fabric (LOI 18%). Fabric coated with the CCl3CH2O-based polymer can be considered fire-retardant (LOI 29%). The fluoromonomers were tested for anti-acetylcholinesterase activity and were found to be poor enzyme inhibitors; they are predicted to possess low acute toxicity. 相似文献
94.
van der Gucht J Besseling NA Cohen Stuart MA 《Journal of the American Chemical Society》2002,124(21):6202-6205
The effects of supramolecular equilibrium polymers on surface forces are studied by both a phenomenological Landau type analysis and a molecular model based on a Bethe-Guggenheim approximation. We point out that surface forces brought about by equilibrium polymers may be completely different from what can be found with "ordinary" polymers. The new feature is the role of inversion (a)symmetry or "directionality" of the associating unit molecules ("monomers"). Symmetric B-B monomers (where B denotes a self-complementary binding group) give rise to nondirectional chains and lead to attractive forces between similar surfaces. Asymmetric A-D monomers (where A and D denote complementary acceptor and donor groups, respectively) produce directional chains and can cause strong repulsion. The range of the attractive force has a maximum at intermediate concentration, while the range of the repulsive force increases over the whole concentration range. 相似文献
95.
Spring DR Krishnan S Blackwell HE Schreiber SL 《Journal of the American Chemical Society》2002,124(7):1354-1363
Diversity-oriented synthesis of structurally complex and diverse small molecules can be used as the first step in a process to explore cellular and organismal pathways. The success of this process is likely going to be dependent on advances in the synthesis of small molecules having natural product-like structures in an efficient and stereoselective manner. The development, scope, and mechanism of the oxidation of organocuprates was investigated and exploited in the atropdiastereoselective synthesis of biaryl-containing medium rings (9-, 10-, and 11-membered rings). The methodology was performed on high-capacity, large polystyrene beads by metalating aryl bromides with i-PrBu(2)MgLi, followed by transmetalating with CuCN x 2LiBr and then oxidizing with 1,3-dinitrobenzene, and was used in a diversity-oriented synthesis of biaryl-containing medium rings (library total theoretical maximum 1412 members). The high capacity beads were arrayed into 384-well plates and, using a process optimized during the development of a one bead/one stock solution technology platform, converted into arrays of stock solutions, with each stock solution containing largely one compound. These stock solutions were used in numerous phenotypic and protein-binding assays. The process described outlines a pathway that we feel will contribute to a comprehensive and systematic chemical approach to exploring biology (chemical genetics). 相似文献
96.
The syntheses of the proposed structures of hachijodine B 1, ikimine B 2 and niphatesine D 3 from S-citronellol are described. Our results suggest that the gross structures of hachijodine B and niphatesine D are correct, but that ikimine B was incorrectly assigned. We have also established that the previous absolute stereochemical assignment for niphatesine D is unreliable. 相似文献
97.
Frank Javor Gerald F. Thomas Stuart M. Rothstein 《International journal of quantum chemistry》1977,11(1):59-71
The goodness of the local fit of an approximate wave-function, \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \psi $\end{document}, to the exact function, ψ0, is \documentclass{article}\pagestyle{empty}\begin{document}$ |\tilde \psi - \psi _0 | $\end{document}. From this quantity the global accuracy of \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \psi $\end{document} is defined and a “working supposition” is presented, which quantitatively relates the global accuracy to the accuracy of expectation values. Two criteria based on the accuracy of the reduced local energy and the density respectively, are presented as alternatives to \documentclass{article}\pagestyle{empty}\begin{document}$ |\tilde \psi - \psi _0 | $\end{document}. The relative global accuracies of eight wave-functions for H2 are determined using the two criteria. The ‘working supposition’ is applied and predictions are made concerning the relative accuracies of the expectation values of the following operators: z2, r2, x2 + y2, 3z2 ?; r2, ξ, r, r, and EL (the reduced local energy). The success rate is high (>90%) except for those operators which are sensitive to interelectron coordinates or derivatives of the wave-function. 相似文献
98.
Wendt-Pienkowski E Huang Y Zhang J Li B Jiang H Kwon H Hutchinson CR Shen B 《Journal of the American Chemical Society》2005,127(47):16442-16452
Fredericamycin (FDM) A, a pentadecaketide featuring two sets of peri-hydroxy tricyclic aromatic moieties connected through a unique chiral spiro carbon center, exhibits potent cytotoxicity and has been studied as a new type of anticancer drug lead because of its novel molecular architecture. The fdm gene cluster was localized to 33-kb DNA segment of Streptomyces griseus ATCC 49344, and its involvement in FDM A biosynthesis was proven by gene inactivation, complementation, and heterologous expression experiments. The fdm cluster consists of 28 open reading frames (ORFs), encoding a type II polyketide synthase (PKS) and tailoring enzymes as well as several regulatory and resistance proteins. The FDM PKS features a KSalpha subunit with heretofore unseen tandem cysteines at its active site, a KSbeta subunit that is distinct phylogenetically from KSbeta of hexa-, octa-, or decaketide PKSs, and a dedicated phosphopantetheinyl transferase. Further study of the FDM PKS could provide new insight into how a type II PKS controls chain length in aromatic polyketide biosynthesis. The availability of the fdm genes, in vivo characterization of the fdm cluster in S. griseus, and heterologous expression of the fdm cluster in Streptomyces albus set the stage to investigate FDM A biosynthesis and engineer the FDM biosynthetic machinery for the production of novel FDM A analogues. 相似文献
99.
Andrew J. Smith Daniela Dimitrova Jude N. Arokianathar Kenneth F. Clark Darren L. Poole Stuart G. Leach John A. Murphy 《Chemical science》2020,11(45):12364
The combination of potassium tert-butoxide and triethylsilane is unusual because it generates multiple different types of reactive intermediates simultaneously that provide access to (i) silyl radical reactions, (ii) hydrogen atom transfer reactions to closed shell molecules and to radicals, (iii) electron transfer reductions and (iv) hydride ion chemistry, giving scope for unprecedented outcomes. Until now, reactions with this reagent pair have generally been explained by reference to one of the intermediates, but we now highlight the interplay and competition between them.The combination of potassium tert-butoxide and triethylsilane provides simultaneous access to multiple reactive intermediates, radicals, H-atom donors, hydride donors and electron donors, giving scope for unprecedented reaction outcomes. 相似文献
100.
Stuart Lipsitz Garrett Fitzmaurice Debajyoti Sinha Nathanael Hevelone Jim Hu Louis L. Nguyen 《Journal of computational and graphical statistics》2017,26(3):734-737
Medical studies increasingly involve a large sample of independent clusters, where the cluster sizes are also large. Our motivating example from the 2010 Nationwide Inpatient Sample (NIS) has 8,001,068 patients and 1049 clusters, with average cluster size of 7627. Consistent parameter estimates can be obtained naively assuming independence, which are inefficient when the intra-cluster correlation (ICC) is high. Efficient generalized estimating equations (GEE) incorporate the ICC and sum all pairs of observations within a cluster when estimating the ICC. For the 2010 NIS, there are 92.6 billion pairs of observations, making summation of pairs computationally prohibitive. We propose a one-step GEE estimator that (1) matches the asymptotic efficiency of the fully iterated GEE; (2) uses a simpler formula to estimate the ICC that avoids summing over all pairs; and (3) completely avoids matrix multiplications and inversions. These three features make the proposed estimator much less computationally intensive, especially with large cluster sizes. A unique contribution of this article is that it expresses the GEE estimating equations incorporating the ICC as a simple sum of vectors and scalars. 相似文献