全文获取类型
收费全文 | 1355篇 |
免费 | 45篇 |
国内免费 | 7篇 |
专业分类
化学 | 563篇 |
晶体学 | 20篇 |
力学 | 65篇 |
数学 | 262篇 |
物理学 | 497篇 |
出版年
2023年 | 11篇 |
2022年 | 12篇 |
2021年 | 30篇 |
2020年 | 34篇 |
2019年 | 38篇 |
2018年 | 41篇 |
2017年 | 31篇 |
2016年 | 53篇 |
2015年 | 37篇 |
2014年 | 60篇 |
2013年 | 83篇 |
2012年 | 87篇 |
2011年 | 104篇 |
2010年 | 88篇 |
2009年 | 69篇 |
2008年 | 61篇 |
2007年 | 74篇 |
2006年 | 37篇 |
2005年 | 48篇 |
2004年 | 28篇 |
2003年 | 28篇 |
2002年 | 22篇 |
2001年 | 13篇 |
2000年 | 18篇 |
1999年 | 18篇 |
1998年 | 9篇 |
1997年 | 13篇 |
1996年 | 26篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1974年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有1407条查询结果,搜索用时 109 毫秒
991.
Khanra S Biswas B Golze C Büchner B Kataev V Weyhermüller T Chaudhuri P 《Dalton transactions (Cambridge, England : 2003)》2007,(4):481-487
A tetranuclear complex [Cr(III)Mn(II)(3)(PyA)(6)Cl(3)] 1 containing pyridine-2-aldoximato monoanion, PyA, has been structurally and magnetochemically characterized. The compound is a rare example of a tetranuclear star-shaped metal topology containing pyridine-2-aldoximato ligands. Static magnetic studies have demonstrated very weak antiferromagnetic exchange interactions between the paramagnetic centers (S(Cr) = 3/2 and S(Mn) = 5/2) resulting in closely spaced low-lying levels, which undergo splitting and crossing. Preliminary high-field EPR measurements (20 < nu < 388 GHz) indicate the presence of zero-field splitting D of the order of 0.7 cm(-1). 相似文献
992.
We report here a robust automated active site detection, docking, and scoring (AADS) protocol for proteins with known structures. The active site finder identifies all cavities in a protein and scores them based on the physicochemical properties of functional groups lining the cavities in the protein. The accuracy realized on 620 proteins with sizes ranging from 100 to 600 amino acids with known drug active sites is 100% when the top ten cavity points are considered. These top ten cavity points identified are then submitted for an automated docking of an input ligand/candidate molecule. The docking protocol uses an all atom energy based Monte Carlo method. Eight low energy docked structures corresponding to different locations and orientations of the candidate molecule are stored at each cavity point giving 80 docked structures overall which are then ranked using an effective free energy function and top five structures are selected. The predicted structure and energetics of the complexes agree quite well with experiment when tested on a data set of 170 protein-ligand complexes with known structures and binding affinities. The AADS methodology is implemented on an 80 processor cluster and presented as a freely accessible, easy to use tool at http://www.scfbio-iitd.res.in/dock/ActiveSite_new.jsp . 相似文献
993.
We perform linear stability analysis of solvent density modes in the presence of nonpolar solute-solvent interaction in a nonpolar solvent. The dominant instability given by the maximum positive eigenvalue of the stability matrix provides the time scale of the solvent rearrangement around a solute. Our theory predicts two long time scales for both in normal nonpolar and supercritical fluids. We discuss the existing experimental results on nonpolar solvation dynamics in light of our prediction. 相似文献
994.
A. C. Gomes G. Biswas B. P. Mukhopadhyay Y. Iitaka Asok Banerjee 《Journal of chemical crystallography》1994,24(6):383-386
The structure of di(2-Methylbenzotriazole) sulphate, (C7N3H9)2SO4, has been solved by X-ray diffraction methods. The compound crystallises in triclinic space group P
witha=6.986(1),b=18.914(1),c=6.990(1) Å, =95.083 (1), =115.56 (1) and =84.93(1)o, respectively.M
r=362.36,F(000)=380,Z=2,D
m=1.45 mg m–3, finalR=0.060,R
w=0.064. The structure was solved by direct methods (SHELXS86) and refined by least-squares methods. Dimers of planar 2-Methylbenzotriazole (MBT) molecules form stacks, one along thea-axis and the other parallel to thec-axis. The SO
4
–2
ions are confined by the two sets of stacks and are responsible for holding them together. The structure is mainly stabilized by the stacking forces. The average interplanar distances in any stack are 3.281 Å, within a dimer, and 3.361 Å, between the dimers. 相似文献
995.
Dr. Jean‐Nicolas Desrosiers Liana Hie Dr. Soumik Biswas Dr. Olga V. Zatolochnaya Dr. Sonia Rodriguez Dr. Heewon Lee Dr. Nelu Grinberg Dr. Nizar Haddad Dr. Nathan K. Yee Prof. Neil K. Garg Dr. Chris H. Senanayake 《Angewandte Chemie (International ed. in English)》2016,55(39):11921-11924
A nickel‐catalyzed Heck cyclization for the construction of quaternary stereocenters is reported. This transformation is demonstrated in the synthesis of 3,3‐disubstituted oxindoles, which are prevalent motifs seen in numerous biologically active molecules. The method shows broad scope, proceeds in synthetically useful yields, and provides a rare means to construct stereochemically complex frameworks by nonprecious‐metal catalysis. 相似文献
996.
Sudipta?Saha S.?K.?Mohanta Sayani?Biswas R.?Palit S.?N.?MishraEmail author 《Hyperfine Interactions》2016,237(1):121
The magnetic hyperfine field of Ba in ferromagnetic Ni has been measured by time differential perturbed angular distribution technique using the 13 ns 10+ isomeric state in 132Ba as probe which was populated in the reaction 12C(124Sn, 4n) 132Ba at beam energy of 60 MeV. The hyperfine field extracted from the observed Larmor precession frequency comes out to be ?84(5) kG. Our experimental results show good agreement with theoretical calculations performed within local density approximation of the density functional theory. The hyperfine field data presented here would be useful towards accurate determination of g-factor in other high spin states in Ba isotopes. 相似文献
997.
In this paper, we transform a continuous-time predator-prey model with Beddington–DeAngelis functional response into a discrete-time model by nonstandard finite difference scheme (NSFD). The NSFD model shows complete dynamic consistency with its continuous counterpart for any step size. However, the discrete model of same continuous system obtained by Euler forward method shows dynamic inconsistency for larger step size. Extensive numerical simulations have been done to compare the dynamics of NSFD system and Euler system. Our analysis reveals that dynamics of NSFD model is independent of the step-size, whereas the dynamics of the standard discrete model completely depends on the step-size and produces spurious dynamics like chaos. 相似文献
998.
Polypyromellitimides have been synthesized from carbazole and N-benzylcarbazole by a two-step procedure involving ring-opening polyaddition with pyromellitic dianhydride and subsequent thermal cyclodehydration. The physicochemical, thermal and dielectric properties of the polymers have been studied. The various N-substituents, such as N-methyl and N-benzyl groups of the carbazole moieties, exert some influence on the overall thermal and dielectric properties of the polyimides. The influence has been rationalized in terms of gross structural characteristics. 相似文献
999.
High-performance capillary electrophoresis (HPCE) was evaluated as a potential technique for the regulatory analysis of commercial dosage forms of insulin. A comparison was made to a liquid chromatographic analysis presently being proposed as an official monograph in the United States Pharmacopeia. The salient points of this comparison were accuracy, precision and ease of use. Both authentic (i.e. single blind, spiked) samples and commercial pharmaceutical formulations (injections) were examined. Chromatographic analyses of both commercial formulations and authentic samples were characterized by good precision, with accuracy being supported by results from authentic (spiked) samples. Conventional HPCE (by which is meant a non-micellar electrolyte used with an uncoated, unmodified fused-silica capillary) achieved reasonable accuracy, but less than impressive precision, when applied to authentic samples. When used for commercial formulations, this type of HPCE did not produce a level of accuracy suitable for regulatory purposes, even with the use of an internal standard. 相似文献
1000.
Muhammad A. Motin Tapan K. Biswas Entazul M. Huque 《Monatshefte für Chemie / Chemical Monthly》2003,134(4):475-487
Summary. Density and viscosity of NaNO3 and KNO3 in aqueous and in H2O-urea solutions were determined as a function of electrolyte concentrations at 308, 313, 318, 323, and 328 K, respectively.
The apparent molal volume (φ
v
) of the electrolytes were found to be linear functions of the square root of the solute molality (b). The φ
v
and data were fitted to the Masson equation [1] by the least square method to obtain the apparent molar volume at infinite dilution (φ
v
^), which is practically equal to the partial molar volume . The viscosity coefficients A and B were calculated on the basis of the viscosity of the solutions and the solvent concerned using the Jones–Dole [2] equation. The activation parameters for viscous flow (ΔG
≠, ΔS
≠, and ΔH
≠) were calculated according to Eyring [3]. The values of for the two systems were also calculated from B-coefficient data. The results were found to be of opposite nature in the two electrolyte systems. Where sodium nitrate showed
structure making behaviour both in aqueous and in H2O-urea solutions, KNO3 showed structure breaking behaviour in aqueous solutions and structure making behaviour in 5 molal H2O-urea solutions in the studied temperature range. The behaviour of these two electrolytes in aqueous binary and in aqueous-urea
ternary systems are discussed in terms of charge, size, and hydrogen bonding effects.
Corresponding author. E-mail: chemistry_ru@yahoo.com
Received January 24, 2002; accepted (revised) April 5, 2002 相似文献