全文获取类型
收费全文 | 706篇 |
免费 | 13篇 |
国内免费 | 5篇 |
专业分类
化学 | 457篇 |
晶体学 | 4篇 |
力学 | 24篇 |
数学 | 91篇 |
物理学 | 148篇 |
出版年
2022年 | 11篇 |
2021年 | 9篇 |
2019年 | 10篇 |
2018年 | 20篇 |
2017年 | 24篇 |
2016年 | 17篇 |
2015年 | 12篇 |
2014年 | 24篇 |
2013年 | 46篇 |
2012年 | 38篇 |
2011年 | 32篇 |
2010年 | 22篇 |
2009年 | 28篇 |
2008年 | 29篇 |
2007年 | 30篇 |
2006年 | 24篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 13篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 18篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 11篇 |
1973年 | 11篇 |
1972年 | 9篇 |
1971年 | 9篇 |
1967年 | 4篇 |
1957年 | 7篇 |
1954年 | 5篇 |
1936年 | 4篇 |
排序方式: 共有724条查询结果,搜索用时 78 毫秒
61.
62.
The concept of squeezing of the electromagnetic field is investigated in fundamental mode in fifth harmonic generation with the approximation |gt|2?1, where g is coupling constant and t, the interaction time between waves during the process. It has been found that squeezing occurs in amplitude, amplitude-squared, amplitude-cubed and fourth-order amplitude states of the field for selective phase values of field amplitude of fundamental mode. The dependence of squeezing on the photon number has also been investigated and found to be sub-Poissonian in nature. The signal to noise ratio has been studied in different order. It is found that the signal to noise ratio is higher in lower order. 相似文献
63.
64.
65.
An efficient [4+2] cyclization of N-methylanilines with maleimides to afford tetrahydroquinolines using N-hydroxyphthalimide as a metal-free and cheap organophotoredox catalyst is reported. The protocol involves C(sp3)H activation of N-methylanilines for the formation of α-amino radical without an oxidant at room temperature. The present method describes an easy preparation of tricyclic heterocycles in good to excellent yields under mild reaction conditions. 相似文献
66.
Ranjeet Kumar J. R. Yadav D. D. Rao Lal Chand 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(3):785-788
Bioassay technique is used for the estimation of actinides present in the body based on their excretion rate through body
fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure.
Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by
alpha spectrometry requires pre-concentration of large volumes of urine. This paper deals with standardization of analytical
method for the determination of Pu-isotopes in urine samples using anion exchange resin and 236Pu tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of plutonium along
with calcium phosphate. Separation of Pu was carried out by Amberlite, IRA-400, anion exchange resin. Pu-fraction was electrodeposited
and activity estimated using tracer recovery by alpha spectrometer. Twenty routine urine samples of radiation workers were
analyzed and consistent radiochemical tracer recovery was obtained in the range 74–96% with a mean and standard deviation
of 85 and 6% respectively. 相似文献
67.
Polyaniline nanotube (PANI-NT) based films have been fabricated onto indium-tin-oxide (ITO) coated glass plates via electrophoretic technique. These PANI-NT/ITO electrodes have been utilized for covalent immobilization of cholesterol oxidase (ChOx) using glutaraldehyde (Glu) as cross-linker. Structural, morphological and electrochemical characterization of PANI-NT/ITO electrode and ChOx/Glu/PANI-NT/ITO bioelectrode have been done using FT-IR spectroscopy, SEM, electrochemical impedance spectroscopy and cyclic voltammetry techniques. Response studies of the ChOx/Glu/PANI-NT/ITO bioelectrode have been carried out using both linear sweep voltammetry and UV-Visible spectrophotometry. The results of the biosensing studies reveal that this bioelectrode can be used to detect cholesterol in wide detection range of 25-500 mg/dL with high sensitivity of 3.36 mA mg(-1) dL and fast response time of 30 s at pH 7.4. This bioelectrode exhibits very low value of Michaelis-Menten constant of 1.18 mM indicating enhanced interactions between cholesterol and ChOx immobilized onto this nanostructured PANI matrix. 相似文献
68.
In the present communication we have reviewed some inverted type equations of state for solids under high pressures. An inverted
equation of state (EOS) gives volume as a function of pressure for a solid under isothermal conditions. We have considered
various equations of state proposed by earlier workers which express volume as a function of pressure. Expressions for bulk
modulus and its pressure derivatives based on such EOSs are obtained and reported here. It is emphasized here that the high
pressure derivative properties are very sensitive to the forms of equations of state representing volume-pressure relationships.
We have also studied the thermoelastic properties of solids based on pressure derivatives of bulk modulus. Applications have
been extended in the present review article to the solids which are metals as well as non-metals including geophysical minerals
present in the lower mantle and core of the Earth. 相似文献
69.
The reactions of dimethyltin dichloride with nitrogen and sulfur donor ligands derived by condensation of S‐benzyldithiocarbazate with indol‐3‐carboxylaldehyde, thiophene‐2‐aldehyde and furfuraldehyde have been investigated in 1:1 and 1:2 molar ratios in anhydrous alcohol. These ligands act as mononegatively charged bidentate species and coordinate to the central tin(IV) atom through the thiosulfur by proton exchange with the azomethine nitrogen. The newly synthesized complexes have been characterized by elemental analysis, conductance measurements and molecular weight determinations. The mode of bonding and the geometry of the complexes have been suggested on the basis of infrared, electronic and 1H, 13C and 119Sn NMR spectroscopy, and probable structures have been assigned to these complexes. A few representative ligands and their tin(IV) complexes have also been screened for their antifungal and antibacterial activities and found to be quite active in this respect. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
70.
M. Lal 《Il Nuovo Cimento D》1986,7(4):551-558
Summary In the present work the axially symmetric thermal-stress distribution in an infinite elastic solid containing an annular crack
under torsion has been studied. The problem is reduced to triple integral equations which in their turn are reduced to simultaneous
algebraic equations by using Hankel transform technique. The quantities of physical interest have also been computed and illustrated
graphically for different values of the inner and outer radius of the crack.
Riassunto In questo lavoro si studia la distribuzione a simmetria assiale dello stress termico in un solido elastico infinito che contiene un crack annulare sotto torsione. Il problema è ridotto alle equazioni integrali triple che per contro sono ridotte ad equazioni algebriche simul tanee usando la tecnica di trasformazione di Hankel. Sono state calcolate ed illustrate graficamente per valori differenti del raggio interno ed esterno del crack anche le quantità di interesse fisico.
Резюме В работе исследуется аксиально симметричное распределение термических напряжений в бесконечном упрутом твердом теле, содержащем кольцевые трещины при кручении. Рассматриваемая проблема сводится к интегральным уравнениям с тройными интегралами, которые, в свою очередь, сводятся к совместным алгебраическим уравнениям, испрльзуя технику преобразований Ганкеля. Вычисляются величины, представляющие физический интерес. Полученные величины иллюстрируются графически для различных значений внутреннего и внешнего радиусов трещин.相似文献