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941.
A system was devised that enables quantitative, ligand-dependent exponential amplification for various ligands that can be recognized by an RNA aptamer. The aptamer is linked to an RNA enzyme that catalyzes the joining of two oligonucleotide substrates. The product of this reaction is another RNA enzyme that undergoes self-sustained replication at constant temperature, increasing in copy number exponentially. The concentration of the ligand determines the amount of time required for the replication products to reach a threshold concentration. A standardized plot of time to threshold versus ligand concentration can be used to determine the concentration of ligand in an unknown sample. This system is analogous to quantitative polymerase chain reaction (PCR), linking rare recognition events to subsequent exponential amplification, but unlike PCR can be applied to the quantitative detection of non-nucleic acid ligands. 相似文献
942.
Wang J Zhou J Donaldson GP Nakayama S Yan L Lam YF Lee VT Sintim HO 《Journal of the American Chemical Society》2011,133(24):9320-9330
The cyclic dinucleotide c-di-GMP is a master regulator of bacterial virulence and biofilm formation. The activations of c-di-GMP metabolism proteins, diguanylate cyclases (DGCs) and phosophodiesterases (PDEs), usually lead to diametrically opposite phenotypes in bacteria. Analogues of c-di-GMP, which can selectively modulate the activities of c-di-GMP processing proteins, will be useful chemical tools for studying and altering bacterial behavior. Herein we report that a conservative modification of one of the phosphate groups in c-di-GMP with a bridging sulfur in the phosphodiester linkage affords an analogue called endo-S-c-di-GMP. Computational, NMR (including DOSY), and CD experiments all reveal that, unlike c-di-GMP, endo-S-c-di-GMP does not readily form higher aggregates. The lower propensity of endo-S-c-di-GMP to form aggregates (as compared to that of c-di-GMP) is probably due to a higher activation barrier to convert from the "open" conformer (where the two guanines are on opposite faces) to the "closed" conformer (where the two guanines are on the same face). Consequently, endo-S-c-di-GMP has selectivity for proteins that bind monomeric but not dimeric c-di-GMP, which form from the "closed" conformer. For example, endo-S-c-di-GMP can inhibit the hydrolysis of c-di-GMP by RocR (a PDE enzyme that binds monomeric c-di-GMP) but did not bind to Alg44 (a PilZ protein) or regulate WspR (a DGC enzyme that has been shown to bind to dimeric c-di-GMP). This work demonstrates that selective binding to different classes of c-di-GMP binding proteins could be achieved by altering analogue conformer populations (conformational steering). We provide important design principles for the preparation of selective PDE inhibitors and reveal the role played by the c-di-GMP backbone in c-di-GMP polymorphism and binding to processing proteins. 相似文献
943.
Motion, deformation and aggregation of two cells in a microchannel by dielectrophoresis 总被引:1,自引:0,他引:1
The dynamic behavior of two cells in a microchannel subject to a nonuniform electric field is simulated numerically by a two-fluid model in the present work. Owing to the presence of nonuniform electric field, usually the cells are polarized and then the dielectrophoresis occurs. The dielectrophoretic force induces the movement and deformation of cells in the microchannel. Meanwhile, the cell membrane develops a mechanical force to resist the cell deformation. In addition, the intercellular interaction becomes dominant when the cell-cell distance is short enough such that an intercellular force is generated. The three forces are taken into account in the two-fluid model to characterize the dynamic behavior of cells. In order to validate the present model, the cell deformation is calculated and compared with the experimental results published previously, where a quantitative agreement is achieved. It is demonstrated by simulations that the cell conductivity mainly determines the motion and deformation of cells at low frequency. Instead of the cell conductivity however, the cell permittivity plays a critical and leading role at high frequency. These phenomena are consistent with the experimental observations. Furthermore, the intercellular interaction may cause the change in the dynamic behavior of cells. 相似文献
944.
Lam MP Lau E Siu SO Ng DC Kong RP Chiu PC Yeung WS Lo C Chu IK 《Electrophoresis》2011,32(21):2930-2940
In this paper, we describe an online combination of reversed‐phase/reversed‐phase (RP–RP) and porous graphitic carbon (PGC) liquid chromatography (LC) for multicomponent analysis of proteomics and glycoproteomics samples. The online RP–RP portion of this system provides comprehensive 2‐D peptide separation based on sequence hydrophobicity at pH 2 and 10. Hydrophilic components (e.g. glycans, glycopeptides) that are not retained by RP are automatically diverted downstream to a PGC column for further trapping and separation. Furthermore, the RP–RP/PGC system can provide simultaneous extension of the hydropathy range and peak capacity for analysis. Using an 11‐protein mixture, we found that the system could efficiently separate native peptides and released N‐glycans from a single sample. We evaluated the applicability of the system to the analysis of complex biological samples using 25 μg of the lysate of a human choriocarcinoma cell line (BeWo), confidently identifying a total of 1449 proteins from a single experiment and up to 1909 distinct proteins from technical triplicates. The PGC fraction increased the sequence coverage through the inclusion of additional hydrophilic sequences that accounted for up to 6.9% of the total identified peptides from the BeWo lysate, with apparent preference for the detection of hydrophilic motifs and proteins. In addition, RP–RP/PGC is applicable to the analysis of complex glycomics samples, as demonstrated by our analysis of a concanavalin A‐extracted glycoproteome from human serum; in total, 134 potentially N‐glycosylated serum proteins, 151 possible N‐glycosylation sites, and more than 40 possible N‐glycan structures recognized by concanavalin A were simultaneously detected. 相似文献
945.
By employing the vacuum ultraviolet (VUV) laser velocity-map imaging (VMI) photoelectron scheme to discriminate energetic photoelectrons, we have measured the VUV-VMI-threshold photoelectrons (VUV-VMI-TPE) spectra of propargyl radical [C(3)H(3)(X?(2)B(1))] near its ionization threshold at photoelectron energy bandwidths of 3 and 7 cm(-1) (full-width at half-maximum, FWHM). The simulation of the VUV-VMI-TPE spectra thus obtained, along with the Stark shift correction, has allowed the determination of a precise value 70 156 ± 4 cm(-1) (8.6982 ± 0.0005 eV) for the ionization energy (IE) of C(3)H(3). In the present VMI-TPE experiment, the Stark shift correction is determined by comparing the VUV-VMI-TPE and VUV laser pulsed field ionization-photoelectron (VUV-PFI-PE) spectra for the origin band of the photoelectron spectrum of the X?(+)-X? transition of chlorobenzene. The fact that the FWHMs for this origin band observed using the VUV-VMI-TPE and VUV-PFI-PE methods are nearly the same indicates that the energy resolutions achieved in the VUV-VMI-TPE and VUV-PFI-PE measurements are comparable. The IE(C(3)H(3)) value obtained based on the VUV-VMI-TPE measurement is consistent with the value determined by the VUV laser PIE spectrum of supersonically cooled C(3)H(3)(X?(2)B(1)) radicals, which is also reported in this article. 相似文献
946.
Dual optical sensor for oxygen and temperature based on the combination of time domain and frequency domain techniques 总被引:1,自引:0,他引:1
In measuring specific conditions in the real world, there are many situations where both the oxygen concentration and the temperature have to be determined simultaneously. Here we describe a dual optical sensor for oxygen and temperature that can be adapted for different applications. The measurement principle of this sensor is based on the luminescence decay times of the oxygen-sensitive ruthenium complex tris-4,7-diphenyl-1,10-phenanthroline ruthenium(III) [Rudpp] and the temperature-sensitive europium complex tris(dibenzoylmethane) mono(5-amino-1,10-phenanthroline)europium(III) [Eudatp]. The excitation and emission spectra of the two luminophores overlap significantly and cannot be discriminated in the conventional way using band pass filters or other optical components. However, by applying both the frequency and time domain techniques, we can separate the signals from the individual decay time of the complexes. The europium complex is entrapped in a poly(methyl methacrylate) (PMMA) layer and the ruthenium complex is physically adsorbed on silica gel and incorporated in a silicone layer. The two layers are attached to each other by a double sided silicone based tape. The europium sensing film was found to be temperature-sensitive between 10 and 70 °C and the ruthenium oxygen-sensitive layer can reliably measure between 0 and 21% oxygen. 相似文献
947.
S. AlluriH. Feng M. LivingsL. Samp D. BiswasT.W. Lam E. LobkovskyA.K. Ganguly 《Tetrahedron letters》2011,52(30):3945-3948
A convenient enantioselective synthesis of 3-asymmetrically substituted oxindoles is reported. Compound (2) prepared by radical cyclisation of (1) was used for the synthesis of racemic and enantiomerically pure 3-asymmetrically substituted oxindoles. Desulfurisation of (2) using Raney Ni yielded the racemate (5). Addition of (S)-1-phenylethanol to compound (2) yielded the diastereoisomer (21) the structure of which was determined using X-ray crystallography. Using a sequence of steps (21) was converted to the enantiomer (8). The enantiomer (9) was similarly prepared from (2) using (R)-1-phenylethanol. 相似文献
948.
949.
Henry Lam Jose Blanchet Damian Burch Martin Z. Bazant 《Journal of Theoretical Probability》2011,24(4):895-927
Classical Edgeworth expansions provide asymptotic correction terms to the Central Limit Theorem (CLT) up to an order that
depends on the number of moments available. In this paper, we provide subsequent correction terms beyond those given by a
standard Edgeworth expansion in the general case of regularly varying distributions with diverging moments (beyond the second).
The subsequent terms can be expressed in a simple closed form in terms of certain special functions (Dawson’s integral and
parabolic cylinder functions), and there are qualitative differences depending on whether the number of moments available
is even, odd, or not an integer, and whether the distributions are symmetric or not. If the increments have an even number
of moments, then additional logarithmic corrections must also be incorporated in the expansion parameter. An interesting feature
of our correction terms for the CLT is that they become dominant outside the central region and blend naturally with known
large-deviation asymptotics when these are applied formally to the spatial scales of the CLT. 相似文献
950.
This paper describes the fabrication and evaluation of a high-frequency (40 MHz) transducer based on lead-free piezoceramics for ultrasonic imaging. The transducer with an aperture size of 0.9 mm has been fabricated using barium strontium zirconate titanate ((Ba0.95Sr0.05)(Zr0.05Ti0.95)O3, abbreviated as BSZT) ceramics. The lead-free BSZT has a piezoelectric d33 coefficient of 300 pC/N and an electromechanical coupling factor kt of 0.45. High-frequency ultrasound transducers were fabricated and a bandwidth of 76.4% has been achieved with an insertion loss of −26 dB. Applications in high resolution biological and medical imaging could be possible with this lead-free material. 相似文献