全文获取类型
收费全文 | 1372篇 |
免费 | 26篇 |
国内免费 | 3篇 |
专业分类
化学 | 831篇 |
晶体学 | 24篇 |
力学 | 41篇 |
数学 | 131篇 |
物理学 | 374篇 |
出版年
2024年 | 8篇 |
2023年 | 9篇 |
2022年 | 25篇 |
2021年 | 30篇 |
2020年 | 43篇 |
2019年 | 42篇 |
2018年 | 35篇 |
2017年 | 30篇 |
2016年 | 43篇 |
2015年 | 34篇 |
2014年 | 44篇 |
2013年 | 90篇 |
2012年 | 78篇 |
2011年 | 81篇 |
2010年 | 68篇 |
2009年 | 58篇 |
2008年 | 76篇 |
2007年 | 54篇 |
2006年 | 44篇 |
2005年 | 36篇 |
2004年 | 23篇 |
2003年 | 20篇 |
2002年 | 25篇 |
2001年 | 9篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1987年 | 7篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 11篇 |
1978年 | 16篇 |
1977年 | 19篇 |
1976年 | 26篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 13篇 |
1972年 | 7篇 |
1958年 | 7篇 |
排序方式: 共有1401条查询结果,搜索用时 15 毫秒
41.
Amit Verma 《Physics letters. A》2010,374(8):1009-1020
A generalized notion of higher order nonclassicality (in terms of higher order moments) is introduced. Under this generalized framework of higher order nonclassicality, conditions of higher order squeezing and higher order subpoissonian photon statistics are derived. A simpler form of the Hong-Mandel higher order squeezing criterion is derived under this framework by using an operator ordering theorem introduced by us in [A. Pathak, J. Phys. A 33 (2000) 5607]. It is also generalized for multi-photon Bose operators of Brandt and Greenberg. Similarly, condition for higher order subpoissonian photon statistics is derived by normal ordering of higher powers of number operator. Further, with the help of simple density matrices, it is shown that the higher order antibunching (HOA) and higher order subpoissonian photon statistics (HOSPS) are not the manifestation of the same phenomenon and consequently it is incorrect to use the condition of HOA as a test of HOSPS. It is also shown that the HOA and HOSPS may exist even in absence of the corresponding lower order phenomenon. Binomial state, nonlinear first order excited squeezed state (NLESS) and nonlinear vacuum squeezed state (NLVSS) are used as examples of quantum state and it is shown that these states may show higher order nonclassical characteristics. It is observed that the Binomial state which is always antibunched, is not always higher order squeezed and NLVSS which shows higher order squeezing does not show HOSPS and HOA. The opposite is observed in NLESS and consequently it is established that the HOSPS and HOS are two independent signatures of higher order nonclassicality. 相似文献
42.
Self-assembling behaviour of block copolymers and their ability to evade the immune system through polyethylene oxide stealth
makes it an attractive candidate for drug encapsulation. Micelles formed by polyethylene oxide-polypropylene oxide- polyethylene
oxide triblock copolymers (PEO-PPO-PEO), pluronic P123, have been employed for encapsulating the anti-cancer drug doxorubicin
hydrochloride. The binding affinity of doxorubicin within the micelle carrier is enhanced through complex formation of drug
and anionic surfactant, aerosol OT (AOT). Electrostatic binding of doxorubicin with negatively charged surfactants leads to
the formation of hydrophobic drug-surfactant complexes. Surfactant-induced partitioning of the anti-cancer drug into nonpolar
solvents such as chloroform is investigated. SANS measurements were performed on pluronic P123 micelles in the presence of
drug-surfactant complex. No significant changes in the structure of the micelles are observed upon drug encapsulation. This
demonstrates that surfactant- drug complexes can be encapsulated in block copolymer micelles without disrupting the structure
of aggregates.
相似文献
43.
K. Kuperkar L. Abezgauz D. Danino G. Verma P. A. Hassan V. K. Aswal D. Varade P. Bahadur 《Pramana》2008,71(5):1003-1008
A highly viscoelastic worm-like micellar solution is formed in hexadecyltrimethylammonium bromide (CTAB) in the presence of
sodium nitrate (NaNO3). A gradual increase in micellar length with increasing NaNO3 was assumed from the rheological measurements where the zero-shear viscosity (η
0) versus NaNO3 concentration curve exhibits a maximum. However, upon increase in temperature, the viscosity decreases. Changes in the structural
parameters of the micelles with addition of NaNO3 were inferred from small angle neutron scattering measurements (SANS). The intensity of scattered neutrons in the low q region was found to increase with increasing NaNO3 concentration. This suggests an increase in the size of the micelles and/or decrease of intermicellar interaction with increasing
salt concentration. Analysis of the SANS data using prolate ellipsoidal structure and Yukawa form of interaction potential
between micelles indicate that addition of NaNO3 leads to a decrease in the surface charge of the ellipsoidal micelles which induces micellar growth. Cryo-TEM measurements
support the presence of thread-like micelles in CTAB and NaNO3.
相似文献
44.
Electron diffraction data have been used as a constraint in the determination of force field for Tl2F2 having planar rhombic structure. The L-F approximation method, recently given by us, has also been applied to evaluate force
constants for thallous halide dimers,e.g. T12F2 and T12Cl2. The results have been compared with the available experimental data in order to check the validity of the present work.
It is concluded that non-bond experimental mean amplitudeU
1...Tl for Tl2F2 is capable of fixing the force field and L-F approximation gives reasonably good force fields for the two thallous halide
dimers now under study. 相似文献
45.
46.
47.
Physics of Atomic Nuclei - The reaction mechanism for the decay of the hot and rotating compound system $${}^{88}$$ Mo $${}^{*}$$ formed in $${}^{48}\textrm{Ti}+^{40}$$ Ca reaction and the time for... 相似文献
48.
Salwinder Singh Dhaliwal Vivek Sharma Arvind Kumar Shukla Vibha Verma Manmeet Kaur Yashbir Singh Shivay Shahida Nisar Ahmed Gaber Marian Brestic Viliam Barek Milan Skalicky Peter Ondrisik Akbar Hossain 《Molecules (Basel, Switzerland)》2022,27(4)
Globally, many developing countries are facing silent epidemics of nutritional deficiencies in human beings and animals. The lack of diversity in diet, i.e., cereal-based crops deficient in mineral nutrients is an additional threat to nutritional quality. The present review accounts for the significance of biofortification as a process to enhance the productivity of crops and also an agricultural solution to address the issues of nutritional security. In this endeavor, different innovative and specific biofortification approaches have been discussed for nutrient enrichment of field crops including cereals, pulses, oilseeds and fodder crops. The agronomic approach increases the micronutrient density in crops with soil and foliar application of fertilizers including amendments. The biofortification through conventional breeding approach includes the selection of efficient genotypes, practicing crossing of plants with desirable nutritional traits without sacrificing agricultural and economic productivity. However, the transgenic/biotechnological approach involves the synthesis of transgenes for micronutrient re-translocation between tissues to enhance their bioavailability. Soil microorganisms enhance nutrient content in the rhizosphere through diverse mechanisms such as synthesis, mobilization, transformations and siderophore production which accumulate more minerals in plants. Different sources of micronutrients viz. mineral solutions, chelates and nanoparticles play a pivotal role in the process of biofortification as it regulates the absorption rates and mechanisms in plants. Apart from the quality parameters, biofortification also improved the crop yield to alleviate hidden hunger thus proving to be a sustainable and cost-effective approach. Thus, this review article conveys a message for researchers about the adequate potential of biofortification to increase crop productivity and nourish the crop with additional nutrient content to provide food security and nutritional quality to humans and livestock. 相似文献
49.
Poonam Singh U.P. Verma Per Jensen 《Journal of Physics and Chemistry of Solids》2011,72(12):1414-1418
The structural, electronic and optical properties of HgAl2Se4 are investigated using the full potential linear augmented plane wave method based on density functional theory. The calculated structural parameters using LDA are in excellent agreement with the available experimental result. The obtained energy band gap (2.24 eV) using EV-GGA approximation is in excellent agreement with experimental data (2.20 eV). Variation in the energy band gap as a function of the unit cell lattice parameter has been studied. The optical properties show a considerable anisotropy, which makes this compound very useful for various linear–nonlinear optical devices. 相似文献
50.
S. Lal R. Raghavan T. N. Rangaswamy B. V. Sreekantan A. Subramanian S. D. Verma S. C. Tonwar R. H. Vatcha 《Proceedings Mathematical Sciences》1971,73(4):170-178
Detailed features of extremely collimated nuclear interactions induced by cosmic ray particles in carbon and brass (belonging to group I as classified in Part I of this series of papers) are presented. These extremely collimated nuclear interactions seem to be preferentially induced by pions rather than by nucleons; also the relative frequency of these seems to be less when brass is used as target compared to the case with carbon as target. The distribution of multiplicities of secondary particles emitted in the forward direction show certain regularities in the case of interactions induced by charged primaries. Observations on the γ-rays associated with these events give support to the interpretation that in these inelastic collisions pions are produced in pairs in the forward direction with low transverse momentum. It is suggested that such a low energy di-pion system could be the same as found in the so-called ABC effect. 相似文献