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841.
An incremental variational equation for non-linear motions of multilayer beams composed of n stiff layers and (n ? 1) soft cores is derived from the dynamic virtual work equation by an appropriate integration procedure. The kinematical hypotheses of Euler-Bernoulli and Timoshenko beam theories are used to describe the displacement fields of the stiff layers and cores respectively. An efficient solution procedure of incremental harmonic balance method type, with use of finite elements, is developed. To demonstrate its capability, some problems in free non-linear vibrations of multilayer beams are treated by using the procedure. Results are compared with those available in the literature. The effects of damping are also included in this investigation but are described in Part II [1] of this paper in which a number of undamped and damped forced non-linear vibration problems are studied. Results in the form of tables and plots are also presented and comparisons are made with those available in the literature. 相似文献
842.
843.
The emission spectrum of CrO has been investigated by Fourier transform spectroscopy in the near infrared. New weak electronic bands have been found in the 6000- to 10 000-cm?1 region, the strongest of which, near 8000 cm?1, is shown to be the (0,0) band of a 5Σ-5Π transition where the 5Π lower state is the ground state. Fifty branches have been assigned in this band, which have permitted the first detailed characterizations of quintet electronic states in the gas phase. Accurate values have now been obtained for the spin-orbit coupling and Λ-doubling intervals in the ground state (which could only be estimated in the previous laser-induced fluorescence work in the visible region by Hocking et al. [Canad. J. Phys.58, 516–533 (1980)]). The relative branch intensities are not consistent with those calculated for a pure 5Σ-5Π(a) transition, and indicate considerable spin-orbit contamination such that there are interference effects between two or more competing transition moments. It is not known whether the 5Σ excited state is 5Σ+ or 5Σ?. 相似文献
844.
D. Sculli K. C. Mok S. H. Cheung 《The Journal of the Operational Research Society》1987,38(3):233-239
This paper reports an application of vehicle-scheduling algorithms in the collection of refuse. The problem differs from classical vehicle-scheduling applications in that the tipping site and the place where the vehicles are garaged are at different locations. Several algorithms are tested in terms of total route mileage and computational loads. An improvement over the manual method of the order of 8% was obtained using average figures for refuse volume over a period of time. The results appear to be more useful in obtaining a good solution when the main problem parameters change rather than in the day-to-day routeing of vehicles. 相似文献
845.
Ma H Appel R Atoyan GS Bassalleck B Bergman DR Cheung N Dhawan S Do H Egger J Eilerts S Fischer H Herold W Issakov VV Kaspar H Kraus DE Lazarus DM Lichard P Lowe J Lozano J Majid W Menzel W Pislak S Poblaguev AA Rehak P Sher A Thompson JA 《Physical review letters》2000,84(12):2580-2583
More than 400 K+-->pi(+)&mgr;(+)&mgr;(-) events were observed in a rare K+ decay experiment at the Brookhaven Alternating Gradient Synchrotron. Normalized to the K+-->pi(+)pi(+)pi(-) decay, the branching ratio is determined to be [9.22+/-0.60(stat)+/-0. 49(syst)]x10(-8). This branching ratio and the &mgr;&mgr; mass spectrum is in very good agreement with the measurement of the K+-->pi(+)e(+)e(-) decay, but deviates significantly from the previous measurement. 相似文献
846.
847.
A stability-indicating HPLC assay has been developed for 2-{4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy}propanoic acid (XK469). XK-469 is the 7-chloro analog of herbicide Quizalofop and is currently under development as an antineoplastic agent. HPLC separation of XK469 is achieved with an ODS column using isocratic elution of an aqueous MeOH mobile phase. The assay is reproducible (RSD=0.9%), linear (r2=0.999), accurate (error=1.2%) and sensitive (LDL=1.2 ng). The HPLC separates XK469 from its forced decomposition products. Identities of the decomposition products have been elucidated. 相似文献
848.
From the very beginning organic chemistry and total synthesis have been intimately joined. In fact, one of the first things that freshmen in organic chemistry learn is how to join two molecules together to obtain a more complex one. Of course they still have a long way to go to become fully mature synthetic chemists, but they must have the primary instinct to build molecules, as synthesis is the essence of organic chemistry. With the different points of view that actually coexist in the chemical community about the maturity of the science (art, or both) of organic synthesis, it is clear that nowadays we know how to make almost all of the most complex molecules ever isolated. The primary question is how easy is it to accomplish? For the readers of papers describing the total synthesis of either simple or complex molecules, it appears that the routes followed are, most of the time, smooth and free of troubles. The synthetic scheme written on paper is, apparently, done in the laboratory with few, if any, modifications and these, essentially, seem to be based on finding the optimal experimental conditions to effect the desired reaction. Failures in the planned synthetic scheme to achieve the goal, detours imposed by unexpected reactivity, or the absence of reactivity are almost never discussed, since they may diminish the value of the work reported. This review attempts to look at total synthesis from a different side; it will focus on troubles found during the synthetic work that cause detours from the original synthetic plan, or on the dead ends that eventually may force redesign. From there, the evolution from the original route to the final successful one that achieves the synthetic target will be presented. The syntheses discussed in this paper have been selected because they contain explicit information about the failures of the original synthetic plan, together with the evolution of the final route to the target molecule. Therefore, they contain a lot of useful negative information that may otherwise be lost. 相似文献
849.
Gas–liquid flows are commonly encountered in industrial flow systems. Numerical studies have been performed to assess the performances of different population balance approaches – direct quadrature method of moments (DQMOMs), average bubble number density (ABND) model and homogeneous MUlti-SIze-Group (MUSIG) model – in tracking the changes of gas void fraction and bubble size distribution under complex flow conditions and to validate the model predictions against experimental measurements from medium- and large-sized vertical pipes. Subject to different gas injection method and flow conditions, bubble size evolution exhibited a coalescence dominant trend in the medium-sized pipe; while bubble break-up was found to be dominant in large-sized pipe. The two experiments were therefore strategically selected for carrying out a thorough examination of existing population balance models in capturing the complicated behaviour of bubble coalescence and break-up. In general, predictions of all the different population balance approaches were in reasonable agreement with experimental data. More importantly, encouraging results have been obtained in adequately capturing the dynamical changes of bubbles size due to bubble interactions and transition from wall peak to core peak gas void fraction profiles. As a compromise between numerical accuracy and computational time, DQMOM has performed rather well in capturing the essential two-phase flow structures within the medium- and large-sized vertical pipes when compared to those of ABND and homogeneous MUSIG models. From a practical perspective, the ABND model may still be considered as a more viable approach for industrial applications of gas–liquid flow systems. 相似文献
850.