全文获取类型
收费全文 | 53914篇 |
免费 | 1441篇 |
国内免费 | 17篇 |
专业分类
化学 | 31617篇 |
晶体学 | 359篇 |
力学 | 910篇 |
综合类 | 1篇 |
数学 | 10616篇 |
物理学 | 11869篇 |
出版年
2023年 | 369篇 |
2022年 | 351篇 |
2021年 | 558篇 |
2020年 | 737篇 |
2019年 | 693篇 |
2018年 | 1065篇 |
2017年 | 999篇 |
2016年 | 1895篇 |
2015年 | 1598篇 |
2014年 | 1586篇 |
2013年 | 3485篇 |
2012年 | 3193篇 |
2011年 | 3087篇 |
2010年 | 2048篇 |
2009年 | 1754篇 |
2008年 | 2594篇 |
2007年 | 2389篇 |
2006年 | 2084篇 |
2005年 | 2086篇 |
2004年 | 1835篇 |
2003年 | 1548篇 |
2002年 | 1348篇 |
2001年 | 1060篇 |
2000年 | 1067篇 |
1999年 | 776篇 |
1998年 | 610篇 |
1997年 | 536篇 |
1996年 | 675篇 |
1995年 | 507篇 |
1994年 | 574篇 |
1993年 | 544篇 |
1992年 | 568篇 |
1991年 | 475篇 |
1990年 | 537篇 |
1989年 | 439篇 |
1988年 | 436篇 |
1987年 | 404篇 |
1986年 | 386篇 |
1985年 | 532篇 |
1984年 | 516篇 |
1983年 | 403篇 |
1982年 | 429篇 |
1981年 | 424篇 |
1980年 | 351篇 |
1979年 | 361篇 |
1978年 | 352篇 |
1977年 | 327篇 |
1976年 | 369篇 |
1975年 | 341篇 |
1974年 | 339篇 |
排序方式: 共有10000条查询结果,搜索用时 27 毫秒
61.
Castiñeiras A Sicilia-Zafra AG González-Pérez JM Choquesillo-Lazarte D Niclós-Gutiérrez J 《Inorganic chemistry》2002,41(26):6956-6958
By reaction of Cu(2)CO(3)(OH)(2), 2-benzylmalonic acid (H(2)Bzmal), and 1,10-phenanthroline (phen), [Cu(Bzmal)(phen)(H(2)O)] x 3H(2)O (compound 1) has been obtained and characterized by thermal, spectral, magnetic, and X-ray diffraction methods. The molecular structure of 1 is remarkably similar to that of [Cu(Bzmal)(bipy)(H(2)O)] x 2H(2)O (compound 2, bipy = 2,2'-bipyridine). In both complexes, the aryl(Bzmal) ring produces an unexpected pi,pi-stacking interaction with the Cu(II)-(aromatic alpha,alpha'-diimine) chelate ring, at an average distance d(pi)(-)(pi) of 3.40 A, involving roughly parallel and smoothly slipped rings. This insight is discussed as new structural evidence for metalloaromaticity of Cu(II)-(aromatic alpha,alpha'-diimine) chelate rings. Interestingly, 1 recognizes itself by a weak intermolecular pi,pi-stacking interaction between aryl(Bzmal) ligands to give pairs of complex molecules. In contrast, there is an intermolecular pyridyl-pyridyl pi,pi-stacking interaction also forming pairs of complex molecules in 2. 相似文献
62.
S. Mlinkó I. Gács K. Payer J. Ottinger E. Dobis 《Journal of Radioanalytical and Nuclear Chemistry》1977,35(2):321-331
In this paper an automatic apparatus designed for the radioactivity measurement of14C-labelled organic compounds in the gaseous phase is described. The labelled organic compounds are combusted in a mixture
of argon and oxygen. After combustion the oxygen content of the gas is eliminated by passing it through a copper packing.
The water and heteroelements present are also removed and the radioactive carbon dioxide gas is swept by argon carrier gas
into a piston-type counter tube. In the counter tube the piston forming a dividing wall moves forward in accordance with the
rate of combustion and sweeping, and thus sucks the gases leaving the combustion tube into the effective tube volume. The
anode wire is carried by a reel located in the piston and a spring device ensures its stretched state. At the end of the sweeping
period methane is fed into the counter tube and the activity of the argon—methane—carbon dioxide mixture is measured in the
limited proportional region. Manual and automatic operation is possible. The piston-type counter tube provides possibility
for strandardization by means of extrapolation and for measurement of absolute activities. 相似文献
63.
The effect of substituted hydroxybenzophenone, benzotriazole and organic metal complexes on the photooxidation of PP films has been studied. It has been established that NiDBTC added in 1.0 wt. % is the most effective photostabilizer.While in the case of other stabilizers there is a slight increase in the Co content even during the induction period, with the application of NiDBTC practically no oxidation can be observed before the stabilizer completely disappears. This means that NiDBTC inhibits the photooxidation of the polymer even in low concentration.
, - . , Ni, 1,0 . %. . , Ni , . , Ni .相似文献
64.
L. Ulická 《Journal of Thermal Analysis and Calorimetry》1986,31(2):333-342
The thermal reactivities of KHV6O16·3H2O and Cd(HV6O16)2·12H2O were investigated. By means of IR spectroscopy and X-ray phase analysis it was found that, after dehydration, both compounds decompose to vanadium pentoxide and the corresponding metavanadate. Potassium metavanadate and vanadium pentoxide react together to form bronzes of different compositions. In contrast, vanadium pentoxide and cadmium metavanadate are the predominant components of the reaction products obtained within the temperature range from 300° to 800°C. 相似文献
65.
J. Sztatisz S. Gál L. Fodor E. Pungor 《Journal of Thermal Analysis and Calorimetry》1977,12(3):351-360
The melting and crystallization of sorbitol were investigated with the DSC method and thermal microscopy. Sorbitol was found to have two crystalline modifications (confirmed by X-ray diffraction) with different melting points, while rapid cooling of molten sorbitol resulted in an amorphous form. The effect of inoculation on the crystallization of the melt was studied too. Powders of both crystalline modifications were used for this purpose. A new technological process for rapid crystallization of molten sorbitol has been worked out on the basis of the thermal analysis results. 相似文献
66.
A. Gosman P. Podhájecký J. Sedláček 《Journal of Radioanalytical and Nuclear Chemistry》1976,30(1):293-298
This paper presents the method of double labelling in the study of the kinetics of homogeneous isotope exchange reactions.
This method was tested by the determination of the Sn(II)−Sn(IV) exchange rate in hydrochloric acid medium. The system was
labelled by the tracer119mSn [initially in the Sn(IV) state]; when the isotope equilibrium was established, Sn(IV) was again labelled by tracer113Sn. The separation of Sn(II) and Sn(IV) in the given time of exchange was performed by the extraction of Sn(IV)-hydroxyquinolate
into chloroform. The specific activities of the separated components were determined from the ratio of113Sn and119mSn activities. The exchange rate was calculated from the time dependence of specific activities. The advantage and possibilities
of the method of double labelling in the study of isotope exchange are discussed. 相似文献
67.
H. Kalász 《Chromatographia》1984,18(11):628-632
Summary The effect of the vapor phase and other special influences on thin-layer chromatography have been investigated. Comparisons were made of the relationships of time vs. developing distance and flow rate vs. efficiency using a planar arrangement of the thin-layer. Covering the layer facilitates the reproducibility and of the migration front but the most effective optimization step for thin-layer chromatography is provided by forced-flow of the mobile phase. It is suggested that planar chromatography with a covered sorbent layer and using a pressurised solvent stream should be calledforced-flow thin-layer chromtatography. 相似文献
68.
Copolymers of 1,2,2,2-tetrachloroethyl esters of unsaturated acids and halogenated N-phenyl maleimides with styrene were pyrolyzed; volatile products were analyzed with a mass spectrometer combined with a gas chromatograph. Hydrogen halide and carbon dioxide in the volatile products were determined during the thermal decomposition of copolymers in glass ampoules; the acyl chloride groups were determined in the residues. The thermal decomposition of copolymers of tetrachloroethyl esters with styrene sets in at ca. 230° by the release of chloral from the copolymer and splitting of some of the CCl bonds in the copolymer. The decomposition of copolymers of styrene with halogenated N-phenyl maleimides starts above 300° by depolymerization of the polystyrene chain sections and by splitting of some of the carbon-halogen bonds. At 310 and 500° for copolymers of tetrachloroethyl esters and at 500° for halogenated N-phenyl maleimides, there is radical dehydrohalogenation of the copolymers, with depolymerization of polystyrene blocks and splitting of carbon-carbon bonds in the main chain. 相似文献
69.
θ-Conditions, the temperature coefficient of unperturbed dimensions of the macromolecules and the thermodynamic interaction parameters ψ and κ were determined for solutions of poly(methyl methacrylate) in 2-alkoxyethanols (methoxy, ethoxy and butoxy). The results for this series of solvents fit the data reported for other solvents and dln . The dependence of parameters ψ and κ exhibited deviations from the theoretical dependence, mainly near the limiting value ψ = 0.5. 相似文献
70.
In this paper we suggest to consider the spatial distribution of the Born-Oppenheimer nonadiabatic coupling terms as fields which are created by sources, located at degeneracy points, and which can be derived using the ordinary mathematical tools of field theory. It is shown that the curl-divergence equations as formed within a given Hilbert space [M. Baer, Chem. Phys. Lett. 35, 112 (1975)] can be converted into a set of inhomogeneous coupled Poisson equations which are solved for a given set of boundary conditions. The method is applied to the three-state Hilbert subspace of the H(3) system. The numerical results are compared with ab initio calculations for which a very encouraging fit is found. 相似文献