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121.
V. V. Tereshatov 《Journal of Macromolecular Science: Physics》2015,54(4):365-380
The stress–strain dependences of segmented elastomers based on polyetherurethanes, polyesterurethane ureas, and polybutadieneurethane ureas were investigated. These dependences were adequately described using the generalized approach proposed earlier by the authors for amorphous elastomers. The experimental data obtained for four series of samples with chemical cross-linking confirmed an applicability of this approach for segmented elastomers. Unlike amorphous elastomers, the effective network density value was affected not only by the density of the chemical network, but the contribution of the network formed by the hard domains also needs be taken into account. 相似文献
122.
Density functional theory (DFT) calculations of nuclear magnetic resonance (NMR) spin–spin coupling constants (SSCCs) provide an important contribution for understanding experimentally observed values. It is known that calculated SSCCs using DFT methods correlate well with those experimentally measured. Unlike most of SSCCs, in fluorine compounds, fluorine–fluorine SSCC JFF shows that the Fermi contact (FC) term is not dominant, particularly for JFF in polyfluorinated organic molecules. In order to devise a DFT approach that would correctly reproduce the variation of SSCCs within a series of fluorine compounds, we test several DFT-based approaches, using different exchange and correlation functionals. Isotropic contributions to NMR fluorine–fluorine coupling constants (FC, spin-dipolar, SD, paramagnetic spin-orbit, PSO, and diamagnetic spin-orbit, DSO) have been calculated. Results show that DFT methods give appropriate values for nJFF (n = 4 to 7), while for geminal and vicinal JFF present large deviations from experimental values. For the latter SSCCs (2JFF and 3JFF), the four contributions (FC, SD, PSO and DSO) are analysed as a function of the local and nonlocal exchange in 1,1- and 1,2-difluoroethylene. Although FC term is not dominant for these SSCCs, the variation of this contribution with exchange is remarkable. On the other hand, SD and PSO contributions can be suitably computed without and with exact exchange, respectively. 相似文献
123.
Accurate determination of both fundamental and optical gap is necessary for designing molecules relevant for organic photovoltaics. Here, we study how range-separated density functionals reproduce frontier orbital energies, HOMO (highest occupied molecular orbital)–LUMO (lowest unoccupied molecular orbital) gaps, and optical gaps for molecules relevant for organic photovoltaics. In this study, we consider 12 different range-separated density functional for computing HOMO energy, HOMO–LUMO gap, and optical gap which are compared with available experimental and reported GW values. We found that the reproduction of desired photovoltaic properties primarily depend on range separation parameter. Moreover, the tested functionals are comparable with OT-BNL functional. 相似文献
124.
The recently introduced multireference equation of motion (MR-EOM) approach is combined with a simple treatment of spin–orbit coupling, as implemented in the ORCA program. The resulting multireference equation of motion spin–orbit coupling (MR-EOM-SOC) approach is applied to the first-row transition metal atoms Cr, Mn, Fe and Co, for which experimental data are readily available. Using the MR-EOM-SOC approach, the splittings in each L-S multiplet can be accurately assessed (root mean square (RMS) errors of about 70 cm?1). The RMS errors for J-specific excitation energies range from 414 to 783 cm?1 and are comparable to previously reported J-averaged MR-EOM results using the ACESII program. The MR-EOM approach is highly efficient. A typical MR-EOM calculation of a full spin–orbit spectrum takes about 2 CPU hours on a single processor of a 12-core node, consisting of Intel XEON 2.93 GHz CPUs with 12.3 MB of shared cache memory. 相似文献
125.
126.
In this research paper, we propose a two-hop integrated radio frequency–visible light communication (RF–VLC) system which may provide a better option to transceive between the hospitals and some laboratory to transfer patient’s information. In the proposed system model, the data (such as patient’s lab test reports) is transmitted towards the amplify and forward (AF) relay mounted on the top of the hospital building via the RF channel. Further, the AF relay amplifies and converts the received information into corresponding optical signal using light emitting diodes (LED) and supporting circuitry. This optical signal is then forwarded towards the destination device (equipped with VLC transceiver), via the VLC channel. To analyse the performance of the system, we first derive the closed form analytical expressions for the cumulative distribution function (CDF) of the end-to-end (e2e) signal to noise ratio (SNR) of the system by using the moment generating function (MGF) of the SNR of the individual RF and VLC channels. Further, we use these statistical expressions to obtain the outage probability, average bit error rate (BER) and the average capacity of the system. Moreover, the asymptotic performance of the proposed system is also analysed to study the system’s behaviour at high SNR regimes. Finally, we studied the impact of the variations in channel parameters on the proposed system model performance through numerically simulated plots. 相似文献
127.
This work studies the system design for the reduced cycle-prefix (CP) orthogonal time frequency space (OTFS) modulation in which only one CP is inserted in each frame. First, a compact input–output model is established which does not need to assume that the delay and Doppler shifts are on the delay-Doppler sampling grids. Second, based on the proposed compact model, a joint precoding and equalization method is proposed for the reduced-CP OTFS modulation, which can decomposes the whole reduced-CP OTFS communication system into parallel multiple-input multiple-output (MIMO) subsystems. Hence, the computational complexity can be greatly reduced. Simulation results of the bit error rate (BER) performance of the proposed method are reported and compared with the standard method under different system parameters. 相似文献
128.
In view of the distinctive characteristics of satellite communication, the physical random access signals used in the terrestrial mobile communication system have to be modified or redesigned for the satellite communication system. In this paper, we boost the random access signal energy by repeating the short Zadoff–Chu (ZC) sequence based preamble signal used in the terrestrial system. Different long ZC sequences are used to scramble this cascaded sequence to distinguish different random access signals for multiple random access user equipments. For correlation performance optimization, properties of the roots for both the short and long ZC sequences are mathematically analyzed and derived. Finally, we illustrate how to construct a root set for these different long ZC sequences based on the obtained propositions in a practical way. This analytical framework provides a useful insight into ZC sequence-based random access signal design and performance analysis in mobile satellite communication systems. 相似文献
129.
Anton Shatskiy Konstantin D. Litasov Igor S. Sharygin Ilya A. Egonin Aleksandr M. Mironov Yuri N. Palyanov 《高压研究》2016,36(1):23-41
In order to constrain the Na2CO3–CaCO3–MgCO3 T–X diagram at 6?GPa in addition to the binary and pseudo-binary systems we conducted experiments along the Na2CO3–Ca0.5Mg0.5CO3 join. At 900–1000°C, melting does not occur and isothermal sections are presented by one-, two- and three-phase regions containing Ca-bearing magnesite, aragonite, Na2CO3 (Na2) and Na2(Ca1–0.9Mg0-0.1)3-4(CO3)4-5 (Na2Ca3-4), Na4(Ca1–0.6Mg0–0.4)(CO3)3 (Na4Ca), Na2(Ca0-0.08Mg1–0.92)(CO3)2 (Na2Mg) phases with intermediate compositions. The minimum melting point locates between 1000°C and 1100°C. This point would resemble that of three eutectics: Mgs–Na2Ca3–Na2Mg, Na2Mg–Na2Ca3–Na4Ca or Na2Mg–Na4Ca–Na2, in the compositional interval of [45Na2CO3·55(Ca0.6Mg0.4)CO3]–[60Na2CO3·40Ca0.6Mg0.4CO3]. The liquidus projection has seven primary solidification phase regions for Mgs, Dol, Arg, Na2Ca3, Na4Ca, Na2 and Na2Mg. The results suggest that extraction of Na and Ca from silicate to carbonate components has to decrease minimum melting temperature of carbonated mantle rocks to 1000–1100°C at 6?GPa and yields Na-rich dolomitic melt with a Na# (Na2O/(Na2O?+?CaO?+?MgO))?≥?28?mol%. 相似文献
130.
We have investigated the performance of a graphite–boron composite (GBC) with 3?wt % boron as a precursor for a boron-doped diamond heater in a Kawai-type apparatus at 15?GPa. We first tested a machinable cylinder of GBC sintered at 1000°C in Ar/H2 gas (99:1 molar ratio). Boron oxide (B2O3) formed during sintering frequently hindered the GBC heater from stable operation at temperatures higher than 1400°C by producing melt throughout the heater together with oxide and/or silicates. We then rinsed the GBC heater in hydrochloric acid to remove B2O3. After rinsing, we succeeded in stably generating temperatures higher than 2000°C. We also improved a molding process of different-sized GBC tubes for convenient use and tested the molded GBC heater. It was free from the B2O3 problem. The electromotive force of the W/Re thermocouple was successfully monitored up to 2400°C. 相似文献