全文获取类型
收费全文 | 658299篇 |
免费 | 5313篇 |
国内免费 | 1496篇 |
专业分类
化学 | 320434篇 |
晶体学 | 9250篇 |
力学 | 35763篇 |
综合类 | 24篇 |
数学 | 97161篇 |
物理学 | 202476篇 |
出版年
2021年 | 5634篇 |
2020年 | 6102篇 |
2019年 | 6971篇 |
2018年 | 13428篇 |
2017年 | 13728篇 |
2016年 | 15053篇 |
2015年 | 7277篇 |
2014年 | 11847篇 |
2013年 | 26656篇 |
2012年 | 22872篇 |
2011年 | 31031篇 |
2010年 | 22141篇 |
2009年 | 22319篇 |
2008年 | 28643篇 |
2007年 | 30437篇 |
2006年 | 21163篇 |
2005年 | 21505篇 |
2004年 | 18976篇 |
2003年 | 17765篇 |
2002年 | 16743篇 |
2001年 | 17194篇 |
2000年 | 13369篇 |
1999年 | 10177篇 |
1998年 | 8865篇 |
1997年 | 8675篇 |
1996年 | 8209篇 |
1995年 | 7381篇 |
1994年 | 7326篇 |
1993年 | 7125篇 |
1992年 | 7496篇 |
1991年 | 8093篇 |
1990年 | 7715篇 |
1989年 | 7698篇 |
1988年 | 7475篇 |
1987年 | 7276篇 |
1986年 | 6961篇 |
1985年 | 8880篇 |
1984年 | 9201篇 |
1983年 | 7794篇 |
1982年 | 8081篇 |
1981年 | 7586篇 |
1980年 | 7155篇 |
1979年 | 7831篇 |
1978年 | 8136篇 |
1977年 | 7994篇 |
1976年 | 8011篇 |
1975年 | 7685篇 |
1974年 | 7471篇 |
1973年 | 7866篇 |
1972年 | 5839篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Koval'chukova O. V. Kuz'mina N. E. Strashnova S. B. Palkina K. K. Mordovina N. I. Zaitsev B. E. Nikitin S. V. 《Russian Journal of Coordination Chemistry》2003,29(2):123-128
Complexes of scandium, yttrium, and lanthanum nitrates with 3-chloro-9-hydroxy-2,4-dimethylpyrido[1,2-a]pyrimidinium perchlorate (HL1ClO4) and 9-hydroxy-2,4-dimethylpyrido[1,2-a]pyrimidinium perchlorate (HL2ClO4) were obtained. Their composition was formulated as Sc(LClO4)2(NO3) and M(LClO4)2(NO3)2 (L = L1 or L2; M = Y or La); structures for the complexes obtained were proposed. The crystal and molecular structure of HL1ClO4 was determined. Dissociation and complexation of HL1ClO4 and HL2ClO4 in aqueous ethanol were studied using the spectroscopic method. Ligand dissociation and complexation constants were calculated. It was shown that a chlorine-containing organic ligand only slightly changes the composition and stability of the metal complexes. 相似文献
992.
L. S. Azhgirey V. V. Arkhipov S. V. Afanasiev V. K. Bondarev V. N. Zhmyro L. S. Zolin V. I. Ivanov A. Yu. Isupov A. A. Kartamyshev V. A. Kashirin V. I. Kolesnikov V. A. Kuznetsov V. P. Ladygin N. B. Ladygina A. G. Litvinenko S. G. Reznikov P. A. Rukoyatkin A. Yu. Semenov I. A. Semenova G. D. Stoletov G. Filipov A. N. Khrenov N. P. Yudin 《Physics of Atomic Nuclei》2003,66(4):690-699
The invariant differential cross section, the tensor analyzing power A yy , and the vector analyzing power A y for the reaction 9Be(d, p)X are measured at an initial deuteron momentum of 4.5 GeV/c and a proton detection angle of about 80 mrad. The data obtained for the differential cross section are consistent with the results of measurements at 3.5 and 5.78 GeV/c and a proton emission angle of 2.5°. The values found for the tensor analyzing power A yy are compared with similar data obtained previously for the deuteron-fragmentation process occurring on a carbon target at various values of the initial deuteron momentum and leading to proton emission at zero angle. The data on the differential cross section for the reaction 9Be(d, p)X can be satisfactorily described within the relativistic impulse approximation by using standard deuteron wave functions; however, the approach based on this conceptual framework proves to be inadequate in dealing with data on the tensor analyzing power. These results indicate that it is necessary either to change the method for describing the relativistic deuteron or to take into account additional mechanisms. 相似文献
993.
994.
The general stability of single-layer cylindrical grids is studied in linear and nonlinear formulations. Dependence of the general buckling load on the geometry and stiffness parameters of a grid is established in an analytical form. Such grids are numerically analyzed for stability. It is established that the general buckling load is much less than the local buckling load. Typical general buckling modes are found. It is shown that such grids are weakly sensitive to imperfections 相似文献
995.
Willem A.L. van Otterlo 《Tetrahedron letters》2004,45(26):5091-5094
Contrary to literature reports, bromination of 3-hydroxybenzaldehyde can afford both 2-bromo-5-hydroxybenzaldehyde and 2-bromo-3-hydroxybenzaldehyde, but 4-bromo-3-hydroxybenzaldehyde was not detected. 2-Bromo-3-hydroxybenzaldehyde was converted into 2-(benzyloxy)-1-bromo-5-methoxy-7-methylnaphthalene. X-ray crystallographic analysis supports the identity of 2-bromo-3-hydroxybenzaldehyde. 相似文献
996.
Howard Anton and Robert C. Busby, John Wiley & Sons, Inc., 2002. 相似文献
997.
Residuals have long been used in frequency domain parameter estimation methods to model the influence of out-of-band modes but, typically, as a fixed set of no more than two or three terms. Recently, a systematic approach to the use of residual polynomials has led to the development of a generalized residual model. The use of a generalized residual model with rational fraction polynomial frequency domain parameter estimation methods allows the contribution of out-of-band modes to be included without increasing the model order and creating additional computational poles. Of particular interest is the use of the generalized residual for single-degree-of-freedom (s.d.o.f.) techniques, which generally do not consider the residual effects and suffer accordingly. With the use of generalized residuals, it becomes possible to properly account for nearby modes and also extract accurate residues with an s.d.o.f. algorithm. The development of the generalized residual polynomial model is outlined and a new s.d.o.f. frequency domain algorithm with generalized residuals is developed. 相似文献
998.
Nickel complexes 1–4 ligated with 2,9-disubstituted-1,10-phenanthroline were synthesized and characterized by FT-IR spectra and elemental analysis.
The molecular structure of complex 2 was confirmed by X-ray crystal diffraction analysis. Activated with methylaluminoxane (MAO), those complexes showed moderate
activities for ethylene oligomerization.
Published in Kinetika i Kataliz, 2007, Vol. 48, No. 5, pp. 710–714.
This article was submitted by the authors in English. 相似文献
999.
Guangchang Zhou Jibao He Issifu I. Harruna 《Journal of polymer science. Part A, Polymer chemistry》2007,45(18):4204-4210
Amphiphilic tris(2,2′‐bipyridine)ruthenium‐cored star‐shaped polymers consisting of one polystyrene block and two poly(N‐isopropylacrylamide) blocks were prepared by the “arm‐first” method in which RAFT polymerization and nonconvalent ligand–metal complexation were employed. The prepared amphiphilic star‐shaped metallopolymers are able to form micelles in water. The size and distribution of the micelles were studied by dynamic light scattering and transmission electron microscopy techniques. Preliminary studies indicate that the polymer concentration and the hydrophilic poly(N‐isopropylacrylamide) block length can affect the morphologies of the formed metal‐interfaced core–shell micelles in water. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4204–4210, 2007 相似文献
1000.
Fabrina R S Bentlin Fábio A Duarte Valderi L Dressler Dirce Pozebon 《Analytical sciences》2007,23(9):1097-1101
This work deals with As determination in marine sediment using ultrasound for sample preparation. It is shown that As can be quantitatively extracted from marine sediment using 20% (v/v) HCl and sonication. The slurry is centrifuged and the analyte is determined in the supernatant by hydride generation atomic absorption spectrometry (HG AAS). A flow injection (FI) system is employed for hydride generation, with 0.5% (m/v) NaBH(4) used as reducdant and a 20% (v/v) HCl used as sample carrier. The limit of quantification is 1.6 microg g(-1) of As, which is based on 800 microl of sample solution and 0.200 g of sample mass in a volume of 50 mL. Certified and non certified marine sediment samples were analyzed; the results were in accordance with the certified or reference values. Speciation analysis by HPLC-ICP-MS showed that As(V) is the only detectable As species present in the supernatant of the centrifuged sample. 相似文献