全文获取类型
收费全文 | 77704篇 |
免费 | 519篇 |
国内免费 | 112篇 |
专业分类
化学 | 41282篇 |
晶体学 | 1261篇 |
力学 | 3277篇 |
综合类 | 1篇 |
数学 | 7828篇 |
物理学 | 24686篇 |
出版年
2022年 | 629篇 |
2021年 | 873篇 |
2020年 | 965篇 |
2019年 | 1104篇 |
2018年 | 1596篇 |
2017年 | 1686篇 |
2016年 | 2148篇 |
2015年 | 1022篇 |
2014年 | 1719篇 |
2013年 | 3268篇 |
2012年 | 2896篇 |
2011年 | 3279篇 |
2010年 | 2638篇 |
2009年 | 2636篇 |
2008年 | 2997篇 |
2007年 | 2875篇 |
2006年 | 2767篇 |
2005年 | 2432篇 |
2004年 | 2237篇 |
2003年 | 2073篇 |
2002年 | 2134篇 |
2001年 | 2234篇 |
2000年 | 1623篇 |
1999年 | 1252篇 |
1998年 | 1125篇 |
1997年 | 1036篇 |
1996年 | 891篇 |
1995年 | 831篇 |
1994年 | 811篇 |
1993年 | 811篇 |
1992年 | 864篇 |
1991年 | 933篇 |
1990年 | 877篇 |
1989年 | 905篇 |
1988年 | 816篇 |
1987年 | 767篇 |
1986年 | 739篇 |
1985年 | 864篇 |
1984年 | 961篇 |
1983年 | 818篇 |
1982年 | 834篇 |
1981年 | 746篇 |
1980年 | 701篇 |
1979年 | 768篇 |
1978年 | 892篇 |
1977年 | 913篇 |
1976年 | 808篇 |
1975年 | 774篇 |
1974年 | 790篇 |
1973年 | 760篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
P. Laggner O. Kratky W. H. Palm A. Holasek 《Monatshefte für Chemie / Chemical Monthly》1971,102(6):1729-1744
Zusammenfassung Schweineserum-Albumin wurde nach sorgfältiger Reinigung bei den pH-Werten 7,0, 5,1 und 3,7 mit Hilfe der Röntgenkleinwinkelstreuung untersucht. Es wurde bei allen Messungen praktisch dasselbe Molekulargewicht gefunden: der Mittelwert liegt bei 70 300±2 500. Die Ermittlung der Streumassenradien ergab bei pH 7,0 und pH 5,1 ähnliche Werte (33,0 Å bzw. 31,1 Å), bei pH 3,7 dagegen einen Wert von 37,8 Å. Die Formbestimmung ergab bei pH 7,0 und pH 5,1 identische Achsenverhältnisse (0,75 : 1 : 2), während bei pH 3,7 ein solches von 0,2 : 1 : 1 gefunden wurde.
Herrn Prof. Dr.H. Nowotny gewidmet. 相似文献
X-ray small-angle scattering investigations on solutions of porcine serum albumin at differentpH-values
Higly purified samples of porcine serum albumin were measured by the X-ray small-angle scattering method at pH 7.0, 5.1, and 3.7. The molecular weight is found to be the same in all three cases: the mean value is 70 300±2 500. The radius of gyration is 31.1 Å and 33.0 Å at pH 5.1 and 7.0 resp., whereas at pH 3.7 a value of 37.8 Å is found. The determination of the molecular conformation yields a similar axial ratio at pH 5.1 and pH 7.0 of 0.75 : 1 : 2; at pH 3,7 we find an axial ratio of 0.2 : 1 : 1 to be consistent with the scattering curves.
Herrn Prof. Dr.H. Nowotny gewidmet. 相似文献
992.
Ab initio calculations of the structure, force field, frequencies and intensities of normal modes of the LiBeF3 molecule have been carried out, using basis sets of Huzinaga and Dunning in a double-zeta contraction. The calculated results are compared with the infrared spectrum of LiBeF3 in an inert matrix obtained by Snelson et al. 相似文献
993.
V. G. Granik A. G. Sukhoruchkin N. S. Kuryatov V. P. Pakhomov O. S. Anisimova R. G. Glushkov 《Chemistry of Heterocyclic Compounds》1973,9(7):880-883
The diethyl acetal of N-methylpiperidin-2-one has been synthesized and its reactions with compounds having active CH2 and CH3 groups have been studied. In the reaction of diethyl acetal of N-methylpiperidin-2-one with malonic ester, in addition to the condensation product, ethylmalonic ester is formed. The reaction of the acetal with benzoic acid leads to O-alkylation and the formation of ethyl benzoate.For communication IV, see [2].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 954–957, July, 1973. 相似文献
994.
H. Durchschlag O. Kratky O. F. Olaj J. W. Breitenbach 《Journal of polymer science. Part A, Polymer chemistry》1973,11(6):1327-1338
Small-angle x-ray investigations on poly-o-bromostyrene in benzene solution at extremely high resolution (corresponding to a Bragg's value of 3200 Å) proved to be able to link together the ranges covered by small-angle x-ray scattering and light scattering. On the other hand, there are problems encountered in molecular weight determination of chain molecules, since both methods at extremely small angles and at finite concentrations reach the limits of particle scattering. The differing results obtained by means of the two methods for the molecular weight of a rather high molecular weight sample of poly-o-bromostyrene are ascribed to entangelements stabilized by dipole–dipole interactions. These, due to the differing Bragg's angles and concentration ranges in the two methods, affect the experimental results to a different degree. 相似文献
995.
The reflectivity and transmitivity of a spatially dispersive crystal for S-polarized incident light are calculated for a microscopical model in which the interaction among the crystal planes is assumed to fall exponentially with distance. The angle of incidence is arbitrary and the deduced formulae are valid from X-ray to the visible light region. The generalization to the more complicated models is briefly discussed. For solving the problem an algebraic formulation of the Ewald dynamical theory of diffraction is used. 相似文献
996.
I. Espe B. Skaali P. O. Tjøm S. M. Lee M. Rozkoš B. Elbek 《Czechoslovak Journal of Physics》1980,30(4):395-416
The experimental data have been compared with the result of extensive compound nucleus calculations based on the statistical theory. The shapes and the absolute cross sections for the high energy parts of the proton- and -spectra are reproduced with a level density parametera 0·11 A MeV–1 and a moment of inertiaJ1·3J
rig. The same parameters fairly well reproduce the angular distributions corresponding to the high energy parts of the spectra whereas deviations between theory and experiment are observed for the lower energies where particles emitted by higher order processes contribute. The observed total cross section for emission of an -particle is 500 mb or 1·7 times calculated value. For protons the corresponding numbers are 2313 mb and 3·0. The increase in cross section is ascribed to the process in which several particles are evaporated. Various methods are discussed for determination of the average orbital angular momentum of the emitted particle or the average spin of the daughter nucleus.On leave fromFaculty of Matematics and Physics, Charles University, Prague, Czechoslovakia. 相似文献
997.
Zusammenfassung Bisher waren die Untersuchungen über Erwartungswert-Streuungs-effiziente Wertpapiermischungen auf den Fall nichtsingulärer Kovarianzmatrizen beschränkt. Der Fall singulärer Kovarianzmatrizen war bisher nicht konstruktiv behandelt worden. Es wird in dem vorstehenden Papier in einem allgemeinen Ansatz, der auch den Fall singulärer Kovarianzmatrizen zuläßt, die allgemeine Gültigkeit des Separationstheorems und des Zwei-Fonds-Theorems nachgewiesen.
Summary Previous studies of mean-variance-efficient portfolios got constructive results in the case of non-singular covariance matrices only, singular covariance matrices were not treated in a constructional way. The present paper proves the Separation Theorem and the Two-Fonds-Theorem within a general framework including the case of singular covariance matrices.相似文献
998.
K. Huckert R. Rhode O. Roglin R. Weber 《Mathematical Methods of Operations Research》1980,24(1):47-60
Summary A mixed integer multiple criteria model is formulated for scheduling problems. Its solution is obtained by an interactive method based on the Tchebycheff-approximation. For solving greater problems some modifications are discussed at the end of the paper, which are essentially based on the notion of heuristic efficiency.
Zusammenfassung Da bei Ablaufplanungsproblemen häufig mehrere Zielsetzungen zu beachten sind, wird im folgenden Beitrag hierzu ein gemischt-ganzzahliges multikriterielles Entscheidungsmodell formuliert. Seine Lösung erfolgt mit Hilfe eines interaktiven Verfahrens. Zur numerischen Lösung größerer Problemstellungen sind einzelne Verfahrensmodifikationen erforderlich, die im wesentlichen auf dem im letzten Abschnitt eingeführten Begriff der heuristischen Effizienz aufbauen.相似文献
999.
N. G. Basov V. F. Belyan G. P. Zhilkin V. S. Zvezdin V. S. Krasovskii O. N. Krokhin B. V. Kruglov A. V. Kutsenko Yu. N. Ol'shevskii N. V. Pletnev Yu. V. Senat-skii G. V. Sklizkov L. K. Subbotin S. I. Fedotov N. N. Shermet'evskii 《Journal of Russian Laser Research》1980,1(1):38-62
The concrete object of the investigation is the alignment of the high-power 12-channel Del'fin neodymium-glass laser facility. The objects of the alignment are the optical channel of the laser installation, the system for pointing and focusing the laser radiation on the target, the system for positioning the target in the focal volume, and the system for monitoring the optical quality of the elements of the laser installation and laser beams and also the conditions of the target irradiation in the vacuum chamber. The list of requirements that must be satisfied by the alignment beams, the possible sources of alignment beams, the makeup of the apparatus, and the methods of aligning the laser facility are considered. The principles and the actual systems of automatic alignment of the optical elements are described, as are the operating models of the automatized units. The problem of simulating the working laser beams by the alignment beams and the possibility of automatizing the control of the spatial and angular characteristics of the laser radiation are discussed. The system for controlling the alignment processes by means of a laser is considered, as is also a scheme for incorporating the automatized alignment subsystem in the overall system for the automation of the Del'fln facility.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 103, pp. 52–83, 1978. 相似文献
1000.
O. P. Vinogradov 《Mathematical Notes》1977,22(4):809-811
A class of weakly aging distribution functions is introduced and a number of properties of this class are derived. It is proved in particular that a random variable , having a weakly aging distribution function, can be written as a sum of two independent random variables, one of which has exponential distribution with a parameter equal to the modulus of the singular point of Me–s nearest the coordinate origin.Translated from Matematicheskie Zametki, Vol. 22, No. 4, pp. 571–574, October, 1977. 相似文献