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101.
Kiran Matcha 《Tetrahedron letters》2010,51(20):2754-6476
A concise synthesis of a highly functionalized tricyclic ring system representing the CDE core of nortriterpenoid schintrilactones A and B is described using a tandem ROM-RCM of a norbornene derivative. 相似文献
102.
Kiran Matcha 《Tetrahedron letters》2010,51(52):6924-6927
Total synthesis of the furano lignan (+)-veraguensin is described. The key steps involve a diastereoselective aldol-type condensation of an ester enolate having an α-chiral center with an aromatic aldehyde and a novel isomerization of the syn vicinal substituents on the furan ring via a ring opening-ring closing protocol. 相似文献
103.
Kiran Kumar Morishetti Betty De Suan Huang Jessica Marney Yates Jianhua Ren 《Journal of the American Society for Mass Spectrometry》2010,21(4):603-614
The sequence and conformational effects on the gas-phase acidities of peptides have been studied by using two pairs of isomeric
cysteine-polyglycine peptides, CysGly3,4NH2 and Gly3,4CysNH2. The extended Cooks kinetic method was employed to determine the gas-phase acidities using a triple quadrupole mass spectrometer
with an electrospray ionization source. The ion activation was achieved via collision-induced dissociation experiments. The
deprotonation enthalpies (Δacid
H) were determined to be 323.9 ± 2.5 kcal/mol (CysGly3NH2), 319.2 ± 2.3 kcal/mol (CysGly4NH2), 333.8 ± 2.1 kcal/mol (Gly3CysNH2), and 321.9 ± 2.8 kcal/mol (Gly4CysNH2), respectively. The corresponding deprotonation entropies (Δacid
S) of the peptides were estimated. The gas-phase acidities (Δacid
G) were derived to be 318.4 ± 2.5 kcal/mol (CysGly3NH2), 314.9 ± 2.3 kcal/mol (CysGly4NH2), 327.5 ± 2.1 kcal/mol (Gly3CysNH2), and 317.4 ± 2.8 kcal/mol (Gly4CysNH2), respectively. Conformations and energetic information of the neutral and anionic peptides were calculated through simulated
annealing (Tripos), geometry optimization (AM1), and single point energy calculations (B3LYP/6-31+G(d)), respectively. Both
neutral and deprotonated peptides adopt many possible conformations of similar energies. All neutral peptides are mainly random
coils. The two C-cysteine anionic peptides, Gly3,4(Cys-H)−NH2, are also random coils. The two N-cysteine anionic peptides, (Cys-H)−Gly3,4NH2, may exist in both random coils and stretched helices. The two N-cysteine peptides, CysGly3NH2 and CysGly4NH2, are significantly more acidic than the corresponding C-terminal cysteine ones, Gly3CysNH2 and Gly4CysNH2. The stronger acidities of the former may come from the greater stability of the thiolate anion resulting from the interaction
with the helix-macrodipole, in addition to the hydrogen bonding interactions. 相似文献
104.
M.S.R.N. Kiran M. Ghanashyam Krishna K.A. Padmanabhan 《Solid State Communications》2011,151(7):561-563
Titanium nitride films of a thickness of ∼1.5 μm were deposited on amorphous and crystalline substrates by DC reactive magnetron sputtering at ambient temperature with 100% nitrogen in the sputter gas. The growth of nanostructured, i.e. crystalline nano-grain sized, films at ambient temperature is demonstrated. The microstructure of the films grown on crystalline substrates reveals a larger grain size/crystallite size than that of the films deposited on amorphous substrates. Specular reflectance measurements on films deposited on different substrates indicate that the position of the Ti-N 2s band at 2.33 eV is substrate-dependent, indicating substrate-mediated stoichiometry. This clearly demonstrates that not only structure and microstructure, but also chemical composition of the films is substrate-influenced. The films deposited on amorphous substrates display lower hardness and modulus values than the films deposited on crystalline substrates, with the highest value of hardness being 19 GPa on a lanthanum aluminate substrate. 相似文献
105.
106.
Kiran Bhaganagar Vejapong Juttijudata 《Theoretical and Computational Fluid Dynamics》2012,26(6):583-589
This brief communication quantifies the time-events that contribute to the dynamics of wall-bounded flows with rough walls. Lumley’s Proper Orthogonal Decomposition (POD) methodology has been used to extract the energetic modes of the flow. We have used the concept of entropy, a representation of lack of organization in the flow, to represent the extent of spread of turbulent kinetic energy to higher modes. The rough-wall dynamics is dominated by fast activity (short time period) propagating modes and slow activity (long time period) roll modes. A single dominant timescale has been captured for all the propagating modes in flows over smooth walls; multiple dominant timescales representing various vortex shedding events are captured for rough walls. Variable-interval time averaging technique has been used to obtain the bursting frequency. The bursting frequency of rough-wall turbulence is higher compared to smooth-wall turbulence, suggesting that roughness enhances turbulence production activity. Another insightful observation for rough walls revealed by our study is that the vortex shedding frequency of roughness elements is much higher compared to the bursting frequency of rough-wall turbulence. POD provides a straightforward method to extract the natural frequency of shed vortices due to roughness, an important dynamical activity in rough-wall turbulent boundary layers. 相似文献
107.
This paper examines the nature of classical correspondence in the case of coherent states at the level of quantum trajectories. We first show that for a harmonic oscillator, the coherent state complex quantum trajectories and the complex classical trajectories are identical to each other. This congruence in the complex plane, not restricted to high quantum numbers alone, illustrates that the harmonic oscillator in a coherent state executes classical motion. The quantum trajectories we consider are those conceived in a modified de Broglie-Bohm scheme. Though quantum trajectory representations are widely discussed in recent years, identical classical and quantum trajectories for coherent states are obtained only in the present approach. We may note that this result for standard harmonic oscillator coherent states is not totally unexpected because of their holomorphic nature. The study is extended to coherent states of a particle in an infinite potential well and that in a symmetric Poschl-Teller potential by solving for the trajectories numerically. For the Gazeau-Klauder coherent state of the infinite potential well, almost identical classical and quantum trajectories are obtained whereas for the Poschl-Teller potential, though classical trajectories are not regained, a periodic motion results as t→∞. Similar features were found for the SUSY quantum mechanics-based coherent states of the Poschl-Teller potential too, but this time the pattern of complex trajectories is quite different from that of the previous case. Thus we find that the method is a potential tool in analyzing the properties of generalized coherent states. 相似文献
108.
Mauji Ram Salim Khan Prabhakar Jha Mather A. Khan Usha Kiran Saleem Javed Malik Z. Abdin 《Chromatographia》2008,68(1-2):129-133
A simple, rapid, specific and sensitive thin layer chromatographic (TLC) method has been developed for the quantitative estimation of mevalonic acid (MVA) in leaves of medicinal plants; Artemisia annua, Psorelia corylifolia, Vinca rosea, Withania somnifera and Barleria proinites. The assay procedure involved conversion of MVA to its lactone, mevalonolactone (MVAL). Mevalonic acid was extracted from the leaf tissues of plants. Separation of MVAL was carried out on silica gel 60 F254 TLC plates using benzene:acetone (3:2) as the mobile phase. The densitometric determination of MVAL was performed at 600 nm after derivatization with anisaldehyde reagent in absorption–reflectance mode. The method was validated over the linearity range of 100–500 ng spot?1 and correlation coefficient for the calibration curve was >0.99. The average recovery of MVAL, used as internal standard, was higher than 98%. The lower limit of detection was found to be 50 ng spot?1. 相似文献
109.
Hosakere D Revanasiddappa Telangusadhushetty N Kiran Kumar 《Analytical sciences》2002,18(10):1131-1135
A simple, sensitive and rapid spectrophotometric method was developed for the determination of thallium(III) using trifluoperazine hydrochloride (TFPH). The method is based on the oxidation of TFPH by thallium(III) in a phosphoric acid medium to form a red-colored radical cation with an absorption maximum at 505 nm. Beer's law is valid over the concentration range of 0.5 - 6.5 microg ml(-1) of thallium(III). The molar absorptivity and Sandell's sensitivity of the color system are 2.14 x 10(4) l mol(-1) cm(-1) and 0.0095 microg cm(-2), respectively. The optimum reaction conditions and other analytical parameters were evaluated. The tolerance limit of the method towards various ions usually associated with thallium has been studied. The proposed method has been successfully applied to the analysis of thallium in alloys, minerals, standard reference material, water, and urine samples. 相似文献
110.
The effect of change in deuteron size on its elastic scattering from protons and alphas is investigated by varying the Hulthen
parameters of the deuteron wave function in the scattering process. The cross sections forp-d scattering, calculated in the Born approximation, are found to increase substantially at backward angles even when the deuteron
size is reduced by a small amount, whereas the shape of the angular distribution does not change significantly. For theα-d elastic scattering, interaction potential is obtained by folding the deuteron wave function and the optical potential for
nucleon-scattering. The cross sections calculated atE
d
= 13·7 MeV, shows that the first minimum around Θcm = 60° is deepend as the deuteron size is reduced, while at 52 MeV bombarding energy, the size effects are not very distinct.
These observations are useful in the interpretation of deuteron cluster knockout reactions. 相似文献