全文获取类型
收费全文 | 45467篇 |
免费 | 4945篇 |
国内免费 | 7665篇 |
专业分类
化学 | 35140篇 |
晶体学 | 1912篇 |
力学 | 2261篇 |
综合类 | 317篇 |
数学 | 2231篇 |
物理学 | 10727篇 |
无线电 | 5489篇 |
出版年
2024年 | 120篇 |
2023年 | 453篇 |
2022年 | 883篇 |
2021年 | 1003篇 |
2020年 | 1324篇 |
2019年 | 1192篇 |
2018年 | 1050篇 |
2017年 | 1300篇 |
2016年 | 1765篇 |
2015年 | 1755篇 |
2014年 | 2184篇 |
2013年 | 3219篇 |
2012年 | 3698篇 |
2011年 | 2692篇 |
2010年 | 2262篇 |
2009年 | 2765篇 |
2008年 | 2976篇 |
2007年 | 3092篇 |
2006年 | 2864篇 |
2005年 | 2591篇 |
2004年 | 2537篇 |
2003年 | 2208篇 |
2002年 | 2290篇 |
2001年 | 1503篇 |
2000年 | 1530篇 |
1999年 | 1213篇 |
1998年 | 1071篇 |
1997年 | 874篇 |
1996年 | 868篇 |
1995年 | 758篇 |
1994年 | 718篇 |
1993年 | 545篇 |
1992年 | 554篇 |
1991年 | 332篇 |
1990年 | 271篇 |
1989年 | 209篇 |
1988年 | 200篇 |
1987年 | 134篇 |
1986年 | 124篇 |
1985年 | 136篇 |
1984年 | 109篇 |
1983年 | 87篇 |
1982年 | 81篇 |
1981年 | 74篇 |
1980年 | 72篇 |
1979年 | 72篇 |
1978年 | 55篇 |
1977年 | 56篇 |
1974年 | 43篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
B. L. Tumanskii 《Russian Chemical Bulletin》1996,45(10):2267-2278
The results of ESR spectroscopic studies of radical reactions of fullerenes are presented. Reactivities of radicals of various chemical natures with respect to C60 and C70, delocalization of the unpaired electron in monofullerenyl radicals, and their reactivity are considered. The examples of dynamic effects in the ESR spectra of fullerenyl radicals, associated with the hindered rotation of the attached radicals, are presented. Characteristic features of the structures of the spin adducts resulting from polyaddition of free radicals to fullerenes and of fullerenyl radicals containing 2-bonded metaIloco mplexes are discussed.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2396–2406, October, 1996. 相似文献
992.
Mamoru Sato Yukiteru Katsube Masaaki Katai Jun' ichi Katakawa Tadahiro Tetsumi 《Journal of chemical crystallography》1996,26(2):153-156
The crystal and molecular structure of a grayanotoxin III derivative, 6-0-acetylgrayanotoxin III is presented. The crystal is orthorhombic, space group P212121, witha=15.582(3),b=21.304(3),c=6.339(3)Å,V=2104(1) Å3
Z=4. The structure was solved by direct methods and refined by full matrix least-squares methods to a finalR=0.047 for 1763 independent reflections withF
0>3 (F
0) The molecule is based on a tetracyclic structure consisting of two five-membered, one six-membered, and one seven-membered ring with various conformations. 相似文献
993.
R. de Gelder J. M. M. Smits W. A. J. Starmans L. Thijs B. Zwanenburg 《Journal of chemical crystallography》1996,26(9):639-642
The crystal and molecular structure of a new azetidine-2-carboxylic amide derivative is described. The structure was solved by direct methods and refined by least squares methods toR1=0.0393 for 4264 reflections (withI>2(I)) The structure consists of two independent molecules which are chemically the same with slight differences in geometry. Crystal data: C17H24N2O, monoclinic, space groupP21,a=8.3782(4),b=20.0342(13),c=9.7769(8) Å, =109.687(6)°,V=1545.1(2)Å3,Z=4. 相似文献
994.
In this paper estimation of the probabilities of a multinomial distribution has been studied. The five estimators considered are: unrestricted estimator (UE), restricted estimator (RE) (under model ), preliminary test estimator (PTE) based on a test of the model , shrinkage estimator (SE) and the positive-rule shrinkage estimator (PRSE). Asymptotic distributions of these estimators are given under Pitman alternatives and the asymptotic risk under a quadratic loss has been evaluated. The relative performance of the five estimators is then studied with respect to their asymptotic distributional risks (ADR). It is seen that neither of the preliminary test and shrinkage estimators dominates the other, though each fares well relative to the other estimators. However, the positive rule estimator is recommended for use for dimension 3 or more while the PTE is recommended for dimension less than 3. 相似文献
995.
Lucifer yellow and lissamine rhodamine sulfonyl hydrazine were used as the donor and the receptor, respectively, for Förster energy transfer measurements to determine the location of the subunit in the native Na,K-ATPase from pig kidney. It was found that (1) the subunits are located in one functional complex, i.e., the dimer ()2 appears to be the functional complex of Na,K-ATPase, and (2) the subunits in the functional enzyme complex in the membrane are not located next to each other but are rather well separated. The distance between fluorophores covalently attached to the subunits was found to be 5.3 nm. 相似文献
996.
Summary A simple and quantitative method for the preparation and high performance liquid chromatography (HPLC) of N-acylated fluoroquinolones has been developed. The acylation procedure was performed with four different acid anhydrides and found to be applicable to several fluoroquinolones. The acylated derivatives were chromatographed directly on a Nucleosil C18 column without the necessity of further sample manipulation. Detector response for the N-acetyl derivatives of norfloxacin, ciprofloxacin, sarafloxacin, and temafloxacin was linear to at least 50 g/mL. The retention behavior of the N-acyl derivatives can be predicted by the length of the carbon chain of the amide. 相似文献
997.
A nearly stoichiometric SrCoO3 phase had been prepared up to now only using high oxygen pressure. A new method for preparing fully stoichiometric SrCoO3 has been proposed using electrochemical oxidation. Brownmillerite-type SrCoO2.50 is oxidized into a completely stoichiometric perovskite at a potential of 500 mV for 180 hours at room temperature in alkaline media (1 M KOH). The oxidized phase has a cubic unit cell (a=383.5 pm). It is metallic and, at temperatures below T=280 K, it shows ferromagnetic behavior. The magnetic moment at 0 K is 2.1 μB. The physical properties of SrCoO3.00 have been explained in terms of partial occupancy of a σ*e band. 相似文献
998.
乙基苯基二氯化锡与2-羟基萘醛缩对甲氧基苯胺Schiff碱1∶1配合物的合成和晶体结构刘宝殿,包明,孙振刚,贺庆林,邢彦,贾恒庆,林永华(东北师范大学化学系,长春,130024)(中国科学院长春应用化学研究所,长春)关键词乙基苯基二氯化锡,Schif... 相似文献
999.
Reaction of the isodicyclopentadienide anion and its dehydro congener with Fe(II) leads to a stereochemically homogeneous ferrocene derivative in each instance. Through chemical correlation and X-ray analysis, above-plane complexation is established for both halves within the two sandwich compounds. 相似文献
1000.
A study on the ductile deformation domain of the brittle fault in the shallow level ofthe crust is a new probe field for the modern structural geology. Taking the southern Jiang-su Province area as an example the orientation measurement of quartz crystals, the com-positional texture observation of three pressure sensitive minerals and the rheological param-eter determination of dislocation densities, etc. have been demonstrated and analysed basedon typical samples in the present paper. In addition, their generation mechanisms arealso discussed from the cataclastic rheology, the dynamic differentiation and the simpleshearing, specially, from the Ode strength theory. Finally, a generative relationship betweenthe ductile deformation domain of the brittle fault system, in the regional layer--slip andthe formation of the stratabound ore deposit is shown as well. 相似文献