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991.
992.
Removal of sodium on a polymer containing cryptand 221B permits rapid determination of a number of elements in biological samples by neutron activation. Sodium is retained on the polymer from EDTA solution at pH 10 and other elements are quantified in the eluate. The polymer capacity is 6.1 mg sodium per g of polymer and the sodium ions can be simply eluted with 1 M nitric acid for column re-use. Selected elements have been determined in reference samples of wheat flour, animal muscle, and oyster tissue. 相似文献
993.
The dispersion of a pulse of O(3P) atoms in flowing helium has been analyzed by a modification of Taylor's method in order to determine the diffusion coefficient. Atoms of O(3P) were produced in a flowing stream of helium by a pulsed microwave discharge of molecular oxygen. After traversing a known length of the flow tube, the arrival time distribution of the O(3P) atoms was obtained using a mass spectrometer. The value obtained for D0 at 294 K, where D0 = D[He], is (2.40 ± 0.06) × 1019 cm?1 ·s?1, which corresponds to a diffusion coefficient of (731 ± 18) cm2/s at 1 torr. In addition to D0, analysis of the arrival time distributions gives an estimate of the mean flow velocity for O atoms in helium. There was no significant difference between the value of the velocity found this way and that obtained from the mean bulk gas flow measurement. Thus for this system there is no evidence for a chromatographic effect for O(3P) atoms on the walls of the flow tube. 相似文献
994.
995.
996.
The exclusive product of thermal rearrangement of (±)-7-isopropylidene-2,3-diazabicyclo[2.2.1]hept-2-ene N-oxide (2) has been identified as the title compound (1). The compound crystallizes in the orthorhombic space group Pbca (No. 61), with a= 8.953 (2), b= 12.740 (2), c=14.446 (3) Å; Z= 8; px=1.227 g cm?3. The details of the molecular structure are not unusual, except for a long C–N distance (C(8)–N(7), 1.560 (4) Å). No significant short intermolecular contacts are observed in the crystal. 相似文献
997.
Photometric investigation of precipitation reactions, by automatically recording the changes in absorbance of a stirred suspension with titrant added, showed that end-points and reacting mole ratios are quickly and easily evaluated. Quantitative analysis in the concentration range 10-2 to 10-4M is possible with an error of about 1%. The use of breaks in titration curves to formulate intermediate reaction products is doubtful. A rapid change in the physical form of the precipitate is a limitation of the method. 相似文献
998.
Bakes M. D. Bramson M. J. Freckleton S. Roberts P. C. Ryan D. 《The Journal of the Operational Research Society》1970,21(1):45-67
This paper describes some aspects of cost effectiveness methodology and operational research as they have been applied in a system design study for a military communications system. There are two main areas of interest from an operational research point of view:(a) The attempt to use cost effectiveness analysis as an integral part of system design.(b) The development and application of new techniques (notably in stochastic network analysis and simulation) which are potentially of much wider application.There are several ways of attacking the problem of multiple objectives encountered in a cost effectiveness analysis. These are briefly described and the preferred method of a single measure of effectiveness is discussed in detail. The measure used in the communications system design study is presented and the method of evaluating it by simulation is described. The next step after evaluation of the effectiveness is optimization and here the use of the Lagrange multipliers is introduced. This method requires iteration on the values of performance parameters and their costs and this becomes very time-consuming if a simulation must be performed each time. It is here that the novel methods of analysing networks are developed. The main use of these methods of analysis, or reduction rules, has been in reducing the size and complexity of the simulations. The technique which has contributed most to the reduction in the number of simulations required to arrive at an optimum disposition of resources is a method of carrying out a sensitivity analysis based on data collected during a single simulation run. This hybrid analytical-cum-simulation technique is discussed in detail with reference to a communications system, and its application to a wider range of problems, such as probabilistic PERT, indicated. 相似文献
999.
Groups of six mongolian gerbils were exposed to two-octave (1414-5656 Hz) band noise for 1 h at 100, 110, and 120 dB SPL. Threshold shift at several frequencies was measured 0.5, 3, 6, and 12 h, and 1-28 days after exposure. Final thresholds were determined at least two months postexposure. Extensive threshold shift was observed in all groups 0.5 h after exposure (TS0.5h). Where threshold shift increased in the initial hours after exposure, such increases were correlated with eventual permanent threshold shift (PTS). Recovery of thresholds from 1-28 days after exposure was approximately exponential, and slowest at the edges of the exposure band. PTS was seen in the 110 and 120 dB SPL groups. With TS0.5h of 50 dB or less, no PTS resulted. With TS0.5h above 50-60 dB, eventual PTS increased linearly with a slope of about 1.25 PTS/TS0.5h. Cochlear damage was evaluated by light microscopy. The relationship between hair cell loss and PTS was consistent with an inner hair cell threshold about 40 dB higher than that of outer hair cells. It is suggested that recovery from noise-induced threshold shift may involve different mechanisms in the two types of hair cells. 相似文献
1000.