全文获取类型
收费全文 | 1098篇 |
免费 | 13篇 |
国内免费 | 4篇 |
专业分类
化学 | 632篇 |
晶体学 | 15篇 |
力学 | 22篇 |
数学 | 118篇 |
物理学 | 328篇 |
出版年
2023年 | 8篇 |
2022年 | 11篇 |
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 19篇 |
2018年 | 19篇 |
2017年 | 16篇 |
2016年 | 17篇 |
2015年 | 22篇 |
2014年 | 31篇 |
2013年 | 78篇 |
2012年 | 57篇 |
2011年 | 79篇 |
2010年 | 42篇 |
2009年 | 53篇 |
2008年 | 62篇 |
2007年 | 60篇 |
2006年 | 55篇 |
2005年 | 52篇 |
2004年 | 27篇 |
2003年 | 20篇 |
2002年 | 20篇 |
2001年 | 21篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 8篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 17篇 |
1976年 | 6篇 |
1975年 | 13篇 |
1973年 | 9篇 |
排序方式: 共有1115条查询结果,搜索用时 125 毫秒
211.
Subarna Mitra Suvankar Chakraborty Krishnakumar S. R. Menon 《Applied Physics A: Materials Science & Processing》2014,117(3):1185-1190
Present report details an analysis of X-ray reflectivity (XRR) for solution processed NiO thin films on Si (100) substrates. The films were annealed at 700–1,000 °C for 1 h in air. XRR data indicated growth of SiO2 layer from ~8 nm at 700 °C to ~66 nm at 1,000 °C along with significant variation of electron density profile. X-ray photoelectron spectroscopy and X-ray diffraction studies were used as supporting studies for phase purity and oxidation states of the NiO thin films as well as interfacial SiO2 layer. 相似文献
212.
Karmakar S Choudhury M Das AS Maiti A Majumdar S Mitra C 《Natural product research》2012,26(6):500-509
This study examined the efficacy of hydroalcoholic extract of dried clove buds, which is rich in phenolic compounds namely eugenol and eugenol derivatives (precursors of flavones, isoflavones and flavonoids), on different primary and secondary osteoporotic marker changes in an ovariectomised (OVX) rat model of osteoporosis. Female Wistar rats were randomly divided into three groups: sham-operated control (A), OVX (B) and OVX plus 50% hydroalcoholic extract of dried clove buds for 4 weeks (C). Results indicated that, compared to control, serum alkaline phosphatase (AP; 48.25%, p?0.01), serum tartrate-resistant acid phosphatase (TRAP; 63.48%, p?0.01), urinary calcium (14.70%, p?0.01), urinary phosphate (50.30%, p?0.01) and urinary creatinine (122.44%, p?0.01) were significantly altered in OVX rats. All these altered responses were significantly restored (AP: 27.53%, p?0.01; TRAP: 33.51%, p?0.01; calcium: 53.15%, p?0.01; phosphate: 27.49%, p?0.01; creatinine: 46.40%, p?0.01) by supplementation with hydroalcoholic extract of dried clove buds. Results of bone density, bone mineral content, bone tensile strength and histological analysis also showed similar trend of results, which supported initial observations of this study. It is proposed that hydroalcoholic extract of dried clove buds has bone-preserving efficacy against hypogonadal osteoporosis. 相似文献
213.
An ab initio calculation has been carried out to investigate the biaxial strain ( - 10.71% < ε < 9.13%) effect on elastic, electronic and optical properties of CuAlO(2). All the elastic constants (c(11), c(12), c(13), c(33)) except c(44) decrease (increase) during tensile (compressive) strain. The band gap is found to decrease in the presence of tensile as well as compressive strain. The relative decrease of the band gap is asymmetric with respect to the sign of the strain. Significant differences between the parallel and perpendicular components of the dielectric constant and the optical properties have been observed due to anisotropic crystal structure. It is further noticed that these properties are easily tunable by strain. Importantly, the collective oscillation of the valence electrons has been identified for light polarized perpendicular to the c-axis. From calculations, it is clear that the tensile strain can enhance the hole mobility as well as the transparency of CuAlO(2). 相似文献
214.
Consider random k-circulants A k,n with n????,k=k(n) and whose input sequence {a l } l??0 is independent with mean zero and variance one and $\sup_{n}n^{-1}\sum_{l=1}^{n}\mathbb{E}|a_{l}|^{2+\delta}<\infty$ for some ??>0. Under suitable restrictions on the sequence {k(n)} n??1, we show that the limiting spectral distribution (LSD) of the empirical distribution of suitably scaled eigenvalues exists, and we identify the limits. In particular, we prove the following: Suppose g??1 is fixed and p 1 is the smallest prime divisor of g. Suppose $P_{g}=\prod_{j=1}^{g}E_{j}$ where {E j }1??j??g are i.i.d. exponential random variables with mean one. (i) If k g =?1+sn where s=1 if g=1 and $s=o(n^{p_{1}-1})$ if g>1, then the empirical spectral distribution of n ?1/2 A k,n converges weakly in probability to $U_{1}P_{g}^{1/(2g)}$ where U 1 is uniformly distributed over the (2g)th roots of unity, independent of P g . (ii) If g??2 and k g =1+sn with $s=o(n^{p_{1}-1})$ , then the empirical spectral distribution of n ?1/2 A k,n converges weakly in probability to $U_{2}P_{g}^{1/(2g)}$ where U 2 is uniformly distributed over the unit circle in ?2, independent of P g . On the other hand, if k??2, k=n o(1) with gcd?(n,k)=1, and the input is i.i.d. standard normal variables, then $F_{n^{-1/2}A_{k,n}}$ converges weakly in probability to the uniform distribution over the circle with center at (0,0) and radius $r=\exp(\mathbb{E}[\log\sqrt{E}_{1}])$ . 相似文献
215.
Ambresh Shivaji Subhadip Mitra Pankaj Agrawal 《The European Physical Journal C - Particles and Fields》2012,72(3):1922
In order to solve the hierarchy problem, several extra-dimensional models have received considerable attention. We have considered
a process where a Higgs boson is produced in association with a KK-graviton (G
KK) at the LHC. At the leading order, this process occurs through the gluon fusion mechanism gg→hG
KK via a quark loop. We compute the cross section and examine some features of this process in the ADD model. We find that the
quark in the loop does not decouple in the large quark-mass limit just as in the case of gg→h process. We compute the cross section of this process for the case of the RS model also. We examine the feasibility of this
process being observed at the LHC. 相似文献
216.
Sau SC Santra S Sen TK Mandal SK Koley D 《Chemical communications (Cambridge, England)》2012,48(4):555-557
Palladium complexes bearing abnormal N-heterocyclic carbene were used as catalysts in Suzuki-Miyaura cross coupling of aryl chlorides at 25 °C. The catalyst remained active for 10 successive catalytic runs and can activate 4-chlorotoluene at 25 °C with 0.01 mol% catalyst loading resulting in a TON of 9500 within 6 h. 相似文献
217.
Bappa Acherjee Arunanshu S. Kuar Souren Mitra Dipten Misra 《Optics & Laser Technology》2012,44(5):1281-1289
In this research, a systematic investigation on laser transmission contour welding process is carried out using finite element analysis (FEA) and design of experiments (DoE) techniques. First of all, a three-dimensional thermal model is developed to simulate the laser transmission contour welding process with a moving heat source. The commercial finite element code ANSYS® multi-physics is used to obtain the numerical results by implementing a volumetric Gaussian heat source, and combined convection–radiation boundary conditions. Design of experiments together with regression analysis is then employed to plan the experiments and to develop mathematical models based on simulation results. Four key process parameters, namely power, welding speed, beam diameter, and carbon black content in absorbing polymer, are considered as independent variables, while maximum temperature at weld interface, weld width, and weld depths in transparent and absorbing polymers are considered as dependent variables. Sensitivity analysis is performed to determine how different values of an independent variable affect a particular dependent variable. 相似文献
218.
The effects of multivalent metal ions (Cu(2+)/Zn(2+)/Al(3+)) on the aggregation of salmon calcitonin (sCT)--a therapeutic peptide used worldwide in the treatment of osteoporosis and Paget's disease--have been studied in vitro using NMR (both solution state and solid state), TEM, ThT-fluorescence, and FT-IR spectroscopy. Overall, the various results indicated that the metal-ions-induced conformational transitions in the peptide--mostly toward the β-sheet--facilitate the aggregation of sCT in solution. First, the solution NMR has been used to check the interaction between the peptide and the metal ions. Following this, the formation and characterization of calcitonin aggregates has been performed using TEM, solid state NMR, and FT-IR spectroscopy. The TEM and ThT-fluorescence results revealed that the sCT peptide incubated with Cu(2+) and Zn(2+) metal ions (in aqueous environment) forms globular aggregates, while that with Al(3+) ions forms fibrils. The solid state NMR and FT-IR studies revealed the presence of a substantial amount of β-sheet content in sCT aggregates (formed in the presence of these metal ions) compared to the monomeric sCT, indicating that the metal binding is concomitant with conformational changes. The present study becomes crucial while prescribing this drug peptide under physio-pathological conditions associated with an abnormal accumulation of metal ions (Cu(2+)/Zn(2+)/Al(3+)) in the body (i.e., abnormal metal ion homeostasis). 相似文献
219.
Dessingou J Tabbasum K Mitra A Hinge VK Rao CP 《The Journal of organic chemistry》2012,77(3):1406-1413
The structurally characterized lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene (L) exhibits high selectivity toward Hg(2+) among other biologically important metal ions, viz., Na(+), K(+), Ca(2+), Mg(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Ag(+) as studied by fluorescence, absorption, and ESI MS. L acts as a sensor for Hg(2+) by switch-off fluorescence and exhibits a lowest detectable concentration of 1.87 ± 0.1 ppm. The complex formed between L and Hg(2+) is found to be 1:1 on the basis of absorption and fluorescence titrations and was confirmed by ESI MS. The coordination features of the mercury complex of L were derived on the basis of DFT computations and found that the Hg(2+) is bound through an N(2)O(2) extending from both the arms to result in a distorted octahedral geometry with two vacant sites. The nanostructural features such as shape and size obtained using AFM and TEM distinguishes L from its Hg(2+) complex and were different from those of the simple mercuric perchlorate. L is also suited to sense pyrimidine bases by fluorescence quenching with a minimum detection limit of 1.15 ± 0.1 ppm in the case of cytosine. The nature of interaction of pyrimidine bases with L has been further studied by DFT computational calculations and found to have interactions through a hydrogen bonding and NH-π interaction between the host and the guest. 相似文献