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51.
Vikas Mittal 《Colloid and polymer science》2010,288(6):621-630
Hybrid organic–inorganic latex particles are synthesized to combine the beneficial properties of the constituents which thus
lead to synergistic improvement in the properties. The properties of hybrid particles are dependent on the successful hybridization
process, thus controlling or tuning of such processes by effective characterization is immensely important. Analytical ultracentrifugation
provides these characterization possibilities owing to its high statistical capability and ability to characterize multiple
parameters. The use of different detection methodologies can help in generating valuable information on the overall size and
density distributions of the particles. Apart from that, it is also possible to quantify the presence of any free polymer
and inorganic particles in the hybrid latex which would affect the properties of hybrid latexes. By following the densities
of the pure and hybrid particles, it is also possible to quantify the amounts of the constituent phases in the hybrid particles.
The density gradients generated in preparative ultracentrifugation also provide additional possibilities for the characterization
of the hybrid particles which have densities higher than the measurable range in the analytical ultracentrifuge. Evolution
of hybrid particles can also be studied as a function of time. It also provides advantage of separation of the various fractions
for further characterization. 相似文献
52.
Vinod Chhokar Meenakshi Sangwan Vikas Beniwal Kiran Nehra Kaur S. Nehra 《Applied biochemistry and biotechnology》2010,160(8):2256-2264
Tannase from Aspergillus awamori MTCC 9299 was purified using ammonium sulfate precipitation followed by ion-exchange chromatography. A purification fold
of 19.5 with 13.5% yield was obtained. Temperature of 30 °C and pH of 5.5 were found optimum for tannase activity. The effects
of metals and organic solvents on the activity of tannase were also studied. Metal ions Mg+2, Mn+2, Ca+2, Na+, and K
+
stimulated the tannase activity, while Cu+2, Fe+3, and Co+2 acted as inhibitors of the enzyme. The addition of organic solvents like acetic acid, isoamylalcohol, chloroform, isopropyl
alcohol, and ethanol completely inhibited the enzyme activity. However, butanol and benzene increased the enzyme activity. 相似文献
53.
R. Andrew Sims Christina C.C. Willis Timothy S. McComb Vikas Sudesh Menelaos K. Poutous Martin Richardson 《Optics Communications》2011,284(7):1988-739
Output beams from three independently frequency-stabilized thulium master-oscillator power-amplifier fiber laser systems were spectrally combined using a plane-ruled metal diffraction grating. Two laser channels were frequency-stabilized with guided mode resonance filters and the third was stabilized using a plane-ruled metal diffraction grating. The systems had output wavelengths between 1984 and 2015 nm, each with a spectral width of 100-450 pm and output powers between 40-120 W. The combined beam had powers up to 49 W and was 32% efficient with respect to the launched pump power. 相似文献
54.
The modal dispersion characteristics of EM waves in a new unconventional plasma loaded doubly clad waveguide having a shape of the lemniscates of Bernoulli-type core cross-section have been studied analytically. The proposed waveguide has three parts namely the core with slighter high index, the inner cladding with plasma and the outer cladding with air. Now using the necessary orthogonal coordinates for the proposed structure and imposing the boundary conditions under the weak guidance condition, the modal characteristics equation has been obtained considering variations in plasma width and plasma frequency, the dispersion curves and cutoff frequencies have been obtained and presented in this paper. It is noted that as the width of plasma layer increases, the cutoff frequency also increases considerably in all considered cases. This shows that using plasma width as a new parameter we can control any particular mode on our wish. 相似文献
55.
Vikas 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(3):551-561
Evolution of the helium atom in a strong time-dependent (TD) magnetic field
(B) of strength up to 1011 G is investigated through a quantum fluid
dynamics (QFD) based current-density functional theory (CDFT). The
TD-QFD-CDFT computations are performed through numerical solution of a
single generalized nonlinear Schr?dinger equation employing vector
exchange-correlation potentials and scalar exchange-correlation density
functionals that depend both on the electronic charge-density and the
current-density. The results are compared with that obtained from a
B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical
constraints but employing only scalar exchange-correlation potential
dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a
particular TD magnetic field-strength, yields electronic charge- and
current-densities as well as exchange-correlation potential resembling with
that obtained from the time-independent studies involving static
(time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge-
and current-densities along with the exchange-correlation potential and
energy differ significantly from that obtained using B-TD-QFD-DFT approach,
particularly at field-strengths >109 G, representing dynamical effects
of a TD field. The work concludes that when a helium atom is subjected to a
strong TD magnetic field of order >109 G, the conventional TD-DFT
based approach differs “dynamically” from the CDFT based approach under
similar computational constraints. 相似文献
56.
Pawan Kumar R. PrasadR.K. Dwivedi H.K. Singh 《Journal of magnetism and magnetic materials》2011,323(21):2564-2568
A comparative study of the out-of-plane anisotropic magnetoresistance (AMR) in single crystalline and polycrystalline thin films of phase separated manganite Nd0.51Sr0.49MnO3 has been carried out. On-axis DC magnetron sputtering was used to deposit the single crystalline films (30 and 100 nm in thickness) on single crystal (0 0 1) LaAlO3 (LAO) and polycrystalline films (100 nm) on (1 0 0) Yttrium-stabilized ZrO2 (YSZ) substrates. The in-plane and out-of-plane magnetotransport properties of these films differ significantly. A large low field AMR is observed in all the films. AMR shows a peak below the insulator-metal transition temperature in the single crystalline films, while the same increases monotonically in the polycrystalline film. Relatively larger low field AMR (∼20% at T=78 K and H=1.7 kOe) in the polycrystalline films suggests the dominance of the shape anisotropy. 相似文献
57.
Vikas Jain A.K. Nayak P.K. Vijayan D. Saha R.K. Sinha 《Experimental Thermal and Fluid Science》2010,34(6):776-787
Natural circulation as a mode of heat removal is being considered as a prominent passive feature in the innovative nuclear reactor designs, particularly in boiling-water-reactors, due to its simplicity and economy. However, boiling natural circulation system poses many challenges to designer due to occurrence of various kinds of instabilities such as excursive instability, density wave oscillations, flow pattern transition instability, geysering and metastable states in parallel channels. This problem assumes greater significance particularly at low-pressures i.e. during startup, where there is great difference in the properties of two phases. In light of this, a parallel channel loop has been designed and installed that has a geometrical resemblance to the pressure-tube-type boiling-water-reactor, to investigate into the behavior of boiling natural circulation. The loop comprises of four identical parallel channels connected between two common plenums i.e. steam drum and header. The recirculation path is provided by a single downcomer connected between steam drum and header. Experiments have been conducted over a wide range of power and pressures (1–10 bar). Two distinct unstable zones are observed with respect to power i.e. corresponding to low power (Type-I) and high power (Type-II) with a stable zone at intermediate powers. The nature of oscillations in terms of their amplitude and frequency and their evolution for Type-I and Type-II instabilities are studied with respect to the effect of heater power and pressure. This paper discusses the evolution of unstable and stable behavior along with the nature of flow oscillation in the channels and the effect of pressure on it. 相似文献
58.
It is emphasized that any equation of state (EOS) based on the generalized Lennard-Jones potential or the Mie potential, suffers
from two main shortcomings as pointed out by Stacey and Davis [2]. One of the shortcomings viz. the problem related to imaginary numbers for the exponents in the potential function, has been removed recently by Jiuxun
[11] by using a relationship between the exponents. However, the modified EOS obtained by Jiuxun suffers from the second shortcoming
viz. it gives lower values for −B
0
B″0, an important equation of state parameter related to the second pressure derivative of the bulk modulus. Values of B
0
B″0 obtained by Jiuxun are not consistent with those reported by Stacey and Davis.
相似文献
59.
Generalizing earlier results of [1], we analyze here the spherically symmetric gravitational collapse of a matter cloud with a general form of matter for the formation of a naked singularity. It is shown that this is related basically to the choice of initial data to the Einstein field equations, and would therefore occur in generic situations from regular initial data within the general context considered here, subject to the matter satisfying the weak energy condition. The condition on initial data which leads to the formation of black hole is also characterized. 相似文献
60.
Quantitative determination of isoquinoline alkaloids and chlorogenic acid in Berberis species using ultra high performance liquid chromatography with hybrid triple quadrupole linear ion trap mass spectrometry 下载免费PDF全文
Awantika Singh Vikas Bajpai Sunil Kumar Kamal Ram Arya Kulwant Rai Sharma Brijesh Kumar 《Journal of separation science》2015,38(12):2007-2013
Berberis species are well known and used extensively as medicinal plants in traditional medicine. They have many medicinal values attributable to the presence of alkaloids having different pharmacological activities. In this study, a method was developed and validated as per international conference on harmonization guidelines using ultra high performance liquid chromatography with hybrid triple quadrupole‐linear ion trap mass spectrometry operated in the multiple reaction monitoring mode for nine bioactive compounds, including protoberberine alkaloids, aporphine alkaloids and chlorogenic acid. This method was applied in different plant parts of eight Berberis species to determine variations in content of nine bioactive compounds. The separation was achieved on an ACQUITY UPLC CSH? C18 column using a gradient mobile phase at flow rate 0.3 mL/min. Calibration curves for all the nine analytes provided optimum linear detector response (with R2 ≥0.9989) over the concentration range of 0.5–1000 ng/mL. The precision and accuracy were within RSDs ≤2.4 and ≤2.3%, respectively. The results indicated significant variation in the total contents of the nine compounds in Berberis species. 相似文献