全文获取类型
收费全文 | 1221篇 |
免费 | 56篇 |
国内免费 | 4篇 |
专业分类
化学 | 923篇 |
晶体学 | 10篇 |
力学 | 40篇 |
数学 | 50篇 |
物理学 | 258篇 |
出版年
2023年 | 10篇 |
2022年 | 38篇 |
2021年 | 27篇 |
2020年 | 36篇 |
2019年 | 40篇 |
2018年 | 42篇 |
2017年 | 58篇 |
2016年 | 46篇 |
2015年 | 42篇 |
2014年 | 42篇 |
2013年 | 112篇 |
2012年 | 86篇 |
2011年 | 101篇 |
2010年 | 42篇 |
2009年 | 42篇 |
2008年 | 40篇 |
2007年 | 53篇 |
2006年 | 44篇 |
2005年 | 33篇 |
2004年 | 30篇 |
2003年 | 15篇 |
2002年 | 21篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 14篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 3篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1974年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有1281条查询结果,搜索用时 15 毫秒
1.
P. R. Latthe P. S. Shinge Bharati V. Badami P. B. Patil S. N. Holihosur 《Journal of Chemical Sciences》2006,118(3):249-256
3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a-h), 4,4′-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a-l). Compounds (5a-l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a-l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a-l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been
found to be more toxic against fourth instar larvae ofAedes aegypti, in particular, then-butyl derivative (3e). 相似文献
2.
Properties of nonparametric estimators of autocovariance for stationary random fields 总被引:1,自引:0,他引:1
Summary We introduce nonparametric estimators of the autocovariance of a stationary random field. One of our estimators has the property that it is itself an autocovatiance. This feature enables the estimator to be used as the basis of simulation studies such as those which are necessary when constructing bootstrap confidence intervals for unknown parameters. Unlike estimators proposed recently by other authors, our own do not require assumptions such as isotropy or monotonicity. Indeed, like nonparametric function estimators considered more widely in the context of curve estimation, our approach demands only smoothness and tail conditions on the underlying curve or surface (here, the autocovariance), and moment and mixing conditions on the random field. We show that by imposing the condition that the estimator be a covariance function we actually reduce the numerical value of integrated squared error. 相似文献
3.
The present paper reports the dislocation unpinning model of acoustic emission (AE) from alkali halide crystals. Equations
are derived for the strain dependence of the transient AE pulse rate, peak value of the AE pulse rate and the total number
of AE pulse emitted. It is found that the AE pulse rate should be maximum for a particular strain of the crystals. The peak
value of the AE pulse rate should depend on the volume and strain rate of the crystals, and also on the pinning time of dislocations.
Since the pinning time of dislocations decreases with increasing strain rate, the AE pulse rate should be weakly dependent
on the strain rate of the crystals. The total number of AE should increase linearly with deformation and then it should attain
a saturation value for the large deformation. By measuring the strain dependence of the AE pulse rate at a fixed strain rate,
the time constantτ
s for surface annihilation of dislocations and the pinning timeτ
p of the dislocations can be determined. A good agreement is found between the theoretical and experimental results related
to the AE from alkali halide crystals. 相似文献
4.
5.
Abhimanyu O. Patil Stephen Zushma Robert T. Stibrany Steven P. Rucker Louise M. Wheeler 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):2095-2106
Novel nickel(II) bisbenzimidazole complexes were prepared via a three‐step synthetic procedure consisting of aniline/diacid condensation, ligand N‐alkylation, and metal complexation. The complexes were characterized by X‐ray crystallography and found to possess a pseudotetrahedral geometry. Upon activation with methylaluminoxane, these nickel bisbenzimidazoles did not polymerize simple olefins (e.g., ethylene, propylene, and 1‐butene) but were found to carry out the rapid and efficient polymerization of norbornene. The polynorbornene products were characterized by gel permeation chromatography/light scattering, 13C NMR, and IR, and their Mark–Houwink and dn/dc parameters were determined. The molecular weights of the polynorbornenes were very high (weight‐average molecular weight = 587,000–797,000 g/mol). 13C NMR suggested that the polymerization occurred via vinyl addition (i.e., a 2,3‐linked polymer); no ring‐opened product was observed. Thermogravimetric analysis indicated that the polynorbornenes were stable up to 400 °C under nitrogen. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2095–2106, 2003 相似文献
6.
Dilip H. Dagade Rajendra R. KumbharSandip R. Sabale Kesharsingh J. Patil 《Fluid Phase Equilibria》2007
In the present communication, we report the studies concerning liquid–liquid–solid equilibria for the ternary system sodium thiosulphate (Na2S2O3) + ethanol + water at ambient pressure and at room temperature (303 ± 2 K). The solubility data of Na2S2O3 are reported for solutions in water, ethanol and solutions of varying concentrations of ethanol in water. The phase diagram for the said system is developed, described and compared with similar system K2CO3 + methanol + water. These results have been explained in terms of structural properties of aqueous ethanol solutions and further discussed in terms of the effect of ions to cause phase separation. 相似文献
7.
8.
9.
More D. H. Pawar N. S. Dewang P. M. Patil S. L. Mahulikar P. P. 《Russian Journal of General Chemistry》2004,74(2):217-218
Various thymyl ethers and esters have been synthesized by reactions of thymol with alkyl halides and acid chlorides, respectively, in aqueous medium under environmentally benign conditions using micro-wave irradiation. The products are important as potent pest managing agents. 相似文献
10.
S. K. Patil A. G. Godbole R. Swarup 《Journal of Radioanalytical and Nuclear Chemistry》1980,60(1):31-44
Synergistic extraction studies on Np(VI) and Pu(VI) have been carried out as a part of the programme on the synergistic extraction
of hexavalent actinides. Extraction of Np(VI) and Pu(VI) were carried out by mixtures of HTTA and TBP in benzene from aqueous
perchlorate and nitrate media. Equilibrium constant values for the various reaction equilibria involved were calculated from
the data obtained by using slope-ratio as well as Job’s method. The extraction of Np(VI) by the synergistic mixture from 1M
nitric acid indicated that the species NpO2 (TTA) (NO3). TBP was not involved in the extraction. The log values of KA, KAB and βAB were −1.5, 2.92 and 4.43, respectively for Np(VI) and −1.63, 2.50 and 4.13 respectively for Pu(VI). 相似文献