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121.
The transverse polarization of forward Λ hyperons produced in high-energy p–A collisions is expected to display an extremum at a transverse momentum around the saturation scale. This was first observed within the context of the McLerran–Venugopalan model which has an x -independent saturation scale. The extremum arises due to the kt-odd nature of the polarization-dependent fragmentation function, which probes approximately the derivative of the dipole scattering amplitude. The amplitude changes most strongly around the saturation scale, resulting in a peak in the polarization. We find that the observation also extends to the more realistic case in which the saturation scale Qs is x-dependent. Since a range of x and therefore Qs values is probed at a given transverse momentum and rapidity, this result is a priori not expected. Moreover, the measurement of Λ polarization over a range of xF values actually provides a direct probe of the x-dependence of the saturation scale. This novel feature is demonstrated for typical LHC kinematics and for several phenomenological models of the dipole scattering amplitude. We show that although the measurement will be challenging, it may be feasible at LHC. The situation at RHIC is not favorable, because the peak will likely be at too low transverse momentum of the Λ to be a trustworthy measure of the saturation scale. 相似文献
122.
The general form of the anisotropy parameter of the expansion for Bianchi type-III metric is obtained in the presence of a
single diagonal imperfect fluid with a dynamically anisotropic equation of state parameter and a dynamical energy density
in general relativity. A special law is assumed for the anisotropy of the fluid which reduces the anisotropy parameter of
the expansion to a simple form (D μ H-2V-2{\Delta\propto H^{-2}V^{-2}}, where Δ is the anisotropy parameter, H is the mean Hubble parameter and V is the volume of the universe). The exact solutions of the Einstein field equations, under the assumption on the anisotropy
of the fluid, are obtained for exponential and power-law volumetric expansions. The isotropy of the fluid, space and expansion
are examined. It is observed that the universe can approach to isotropy monotonically even in the presence of an anisotropic
fluid. The anisotropy of the fluid also isotropizes at later times for accelerating models and evolves into the well-known
cosmological constant in the model for exponential volumetric expansion. 相似文献
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126.
Base hydrolysis of bis-bipyridylplatinum(II) occurs via a 1:1 intermediate adduct with hydroxide ion. The equilibrium constants for this 1:1 addition of hydroxide inwater to complex ions [PtL2]2+, where L=one of theisoelectronic set 2,2-bipyridyl (bpy); 2,2- bipyrazine (bpz); 3,3-bipyridazine (bpdz) and 2,2- bipyrimidine (bpym) are respectively (as log10K at 25°C): 4.23; 4.59; 3.82; 6.14. This result is rationalized in terms of addition at the 6–position of the ligand. 相似文献
127.
The reaction has been studied spectrophotometrically monitoring the absorbance in the 240–400 nm wavelength range. The spectra of the reactants, intermediates, and products in this system are overlapping; thus special programs [ 1 , 2 ] have been used (and tested) to unravel the kinetics and mechanism of the reaction. The stoichiometry of the reaction in excess hypochlorous acid is S4O62− + 7HOCl + 3H2O → 4SO42− + 7Cl− + 13H+. Various experiments are presented to show that—in excess tetrathionate—the reaction produces a light‐absorbing intermediate identified as S2O3Cl−. The intermediate slowly hydrolyzes into sulfur and sulfate and it yields pentathionate in excess tetrathionate. The rate‐determining steps and their rate constants are The further oxidation of S2O42− and SO32− by HOCl to sulfate are fast processes. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 395–402, 2000 相似文献
128.
A novel method for cobalt preconcentration by cloud point extraction with on-line phase separation in a PTFE knotted reactor and further determination by electrothermal atomic absorption spectrometry (ETAAS) is proposed. The cloud point system was formed in the presence of non-ionic micelles of polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) and it was retained on the inner walls of a knotted reactor (KR). The surfactant rich-phase was removed from the knotted reactor with 75 microL of methanol acidified with 0.8 mol L(-1) nitric acid, directly into the dosing hole of the L'Vov graphite tube. An enrichment factor of 15 was obtained with a preconcentration time of 60 s, with respect to the direct determination of cobalt by ETAAS in aqueous solutions. The value of the detection limit for the preconcentration of 5 mL of sample solution was 10 ng L(-1). The precision, expressed as the relative standard deviation (R.S.D.), for 10 replicate determinations at 0.5 microg L(-1) Co level was 4.5%. Verification of the accuracy was carried out by analysis of a standard reference material (NIST SRM 1640e "Trace elements in natural water"). The method was successfully applied to the determination of cobalt in drinking water samples. 相似文献
129.
Hernández C Fernández M Quejido AJ Sánchez DM Morante R Martín R 《Analytica chimica acta》2006,571(2):279-287
Isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) analysis has been applied to the determination of tin in a fly ash sample supplied by the EC Joint Research Centre (Ispra, Italy). The proposed procedure includes the silica gel/phosphoric acid technique for tin thermal ionisation activation and a strict heating protocol for isotope ratio measurements. Instrumental mass discrimination factor has been previously determined measuring a natural tin standard solution. Spike solution has been prepared from 112Sn-enriched metal and quantified by reverse isotope dilution analysis. Two sample aliquots were spiked and tin was extracted with 4.5 M HCl during 25 min ultrasound exposure time. Due to the complex matrix of this fly ash material, a two-step purification stage using ion-exchange chromatography was required prior TIMS analysis. Obtained results for the two sample-spike blends (10.11 ± 0.55 and 10.50 ± 0.64 μmol g−1) are comparable, both value and uncertainty. Also a good reproducibility is observed between measurements. The proposed ID-TIMS procedure, as a primary method and due to the lack of fly ash reference materials certified for tin content, can be used to validate more routine methodologies applied to tin determination in this kind of samples. 相似文献
130.
Bibal C Santini CC Chauvin Y Vallée C Olivier-Bourbigou H 《Dalton transactions (Cambridge, England : 2003)》2008,(21):2866-2870
A new family of hydroxytris(pentafluorophenyl)borate anions [B(C6F5)3OH](-) associated with organic and aprotic cations c+ (imidazolium, pyrrolidinium and phosphonium) has been prepared by a general one-pot synthesis that implies the chloride borate analogues [B(C6F5)3Cl](-)[c]+. The [c]+[B(C6F5)3OH](-) salts have been isolated and fully characterized. The borate anion [B(C6F5)3OH](-) has been shown to protonate the Zr-Me bond in the Cp2ZrMe2 complex forming CH4 and the first published example of anionic [Cp2Zr(Me)OB(C6F5)3](-) species. Standard spectroscopic methods demonstrate the covalent character of the Zr metal center and the anionic character of the boron atom. This protonolysis methodology using [B(C6F5)3OH](-) anion affords a new route for the incorporation of a covalently bonded anionic functionality on organometallic complexes. This provides a new way to immobilize transition metal complexes in ionic liquids. 相似文献