全文获取类型
收费全文 | 304448篇 |
免费 | 2846篇 |
国内免费 | 994篇 |
专业分类
化学 | 149754篇 |
晶体学 | 4846篇 |
力学 | 15411篇 |
综合类 | 19篇 |
数学 | 52746篇 |
物理学 | 85512篇 |
出版年
2021年 | 1896篇 |
2020年 | 2217篇 |
2019年 | 2469篇 |
2018年 | 12745篇 |
2017年 | 12645篇 |
2016年 | 10091篇 |
2015年 | 3521篇 |
2014年 | 4640篇 |
2013年 | 11027篇 |
2012年 | 11390篇 |
2011年 | 19361篇 |
2010年 | 11989篇 |
2009年 | 12290篇 |
2008年 | 14454篇 |
2007年 | 16481篇 |
2006年 | 7819篇 |
2005年 | 8098篇 |
2004年 | 7621篇 |
2003年 | 7559篇 |
2002年 | 6329篇 |
2001年 | 7006篇 |
2000年 | 5392篇 |
1999年 | 4074篇 |
1998年 | 3254篇 |
1997年 | 3176篇 |
1996年 | 3102篇 |
1995年 | 2919篇 |
1994年 | 2741篇 |
1993年 | 2581篇 |
1992年 | 3230篇 |
1991年 | 3132篇 |
1990年 | 3044篇 |
1989年 | 3086篇 |
1988年 | 3078篇 |
1987年 | 3065篇 |
1986年 | 2948篇 |
1985年 | 3717篇 |
1984年 | 3731篇 |
1983年 | 2932篇 |
1982年 | 3055篇 |
1981年 | 3107篇 |
1980年 | 2883篇 |
1979年 | 3233篇 |
1978年 | 3194篇 |
1977年 | 3273篇 |
1976年 | 3124篇 |
1975年 | 2820篇 |
1974年 | 2762篇 |
1973年 | 2759篇 |
1967年 | 1943篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Tapan K. Chattopadhyay Rex A Palmer Daruka Mahadevan 《Journal of chemical crystallography》1995,25(4):195-199
The crystal and molecular structure of pindolol, 1-(1H indol-4-yloxy)-3-[(1-methylethyl)amino]-2-propanol, has been determined by direct methods. Crystals are tetragonal,
,a=b=15.809(4),c=11.246(2) Å,Z=8,D
c=1.174 mg m–3. The finalR-factor for 2271 reflections withI>2(I) is 0.038. Refinement by full-matrix least-squares on F2 also enabled the absolute configuration of the structure to be established. The molecule is essentially planar, including much of the side-chain which is stabilized by the existence of two intramolecular H-bonds, between the ethyl oxygen and OH group, and between the OH and side-chain amide groups, respectively. The crystal structure is formed by three intermolecular hydrogen bonds including two side-chain-side-chain interactions, between ethyl oxygen to amide and OH to amide, and an interaction between the side-chain OH to indole NH. 相似文献
992.
This note was inspired by McKenzie's recent paper [8] whose main result is a characterization of categorical equivalence (for short category equivalence) between varieties. Here we use this result to define category equivalent clones and to describe all clones category equivalent to maximal clones. If one is interested in maximal clones only up to category equivalence it is sufficient to consider very simple maximal clones, essentially the same as considered in Jablonski's early papers about maximal clones [6]. The results we have found encourage us in our feeling that category equivalence could be a useful tool in clone theory.Dedicated to the memory of Alan Day.Presented by J. Sichler. 相似文献
993.
K. Coolsaet 《Combinatorica》1995,15(4):481-487
Several properties of graphs with ==2,a
2=4 are studied. It is proved that such graphs are locally unions of triangles, hexagons or heptagons. As a consequence, a distance regular graph with intersection array (13,10,7;1,2,7) does not exist. 相似文献
994.
K. Wilderotter 《Ukrainian Mathematical Journal》1995,47(9):1334-1340
The even-dimensional Kolmogorov widthsd
2n
, Gel'fand widthsd
2n
, and linear widths 2n ofà inL
q
andC are determined exactly. We show that all threen-widths are equal and give a characterization of the widths in terms of Blaschke products.Published in Ukrainskii Matematicheskii Zhurnal, Vol. 47, No. 9, pp. 1170–1175, September, 1995. 相似文献
995.
A. K. Motovilov 《Theoretical and Mathematical Physics》1995,104(2):989-1007
A study is made of the spectral problem (A+V(z)=z, in which the main HamiltonianA is a self-adjoint operator of fairly general nature, while the perturbationV(z)=–B(A–z)–1
B* depends on the energyz as the resolvent of some other self-adjoint operatorA. It is assumed that the operatorB has a finite Hilbert—Schmidt norm and, in addition, that the spectra of the operatorsA andA are separated. Conditions are formulated under which it is possible to replace the perturbationV(z) by an energy-independent potentialW such that the HamiltonianH=A+W has the same spectrum (more precisely, part of the spectrum) and the same eigenfunctions as the original spectral problem. Completeness and orthogonality theorems are proved for the systems of eigenfunctions of the operatorH=A+W. A scattering theory is constructed for the HamiltonianH in the case when the operatorA has a continuous spectrum. Applications of the results to the few-body problem are discussed.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 104, No. 2, pp. 281–303, August, 1995. 相似文献
996.
For any fixed
we construct an orthonormal Schauder basis
for C[-1,1] consisting of algebraic polynomials
with
The orthogonality is with respect to the Chebyshev weight. 相似文献
997.
W. U. Boeglin 《Czechoslovak Journal of Physics》1995,45(4-5):295-335
Coincidence experiments with electrons provide new information on the structure of nucleons and nuclei. Using new CW accelerators, kinematic regions can be explored with high precision which have not been accessible previously. The equipment and the necessary steps in the analysis of (e,ep) experiments will be discussed and illustrated with new data taken at the MAMI facility.Lectures given at the Indian-Summer School on Electron Scattering of Nucleons and Nuclei, Prague (Czech Republic), September 1994. 相似文献
998.
K. Daum W. Rhode P. Bareyre R. Barloutaud G. Chardin B. Degrange J. Ernwein B. Kuznik H. Meyer L. Mosca L. Moscoso O. Perdereau M. Schubnell S. Tisserant Y. Wei 《Zeitschrift fur Physik C Particles and Fields》1995,66(3):417-428
The combined analysis of the final event set of data on neutrino interactions inside the detector, upward going stopping muons and horizontal muons recorded in the Fréjus experiment is presented. The absolute atmospheric neutrino spectra in the energy range
for electron neutrinos and
for muon neutrinos are determined. Based on the parameterization of Volkova for thev
µ
a spectral index of =2.66±0.05 is obtained from the ratio of horizontal muons over upward going stopping muons and from the measurement of the energy loss of horizontal muons inside the detector. The neutrino spectra are compared with various flux calculations. They do not show any evidence for neutrino oscillations in agreement with earlier analyses of the Fréjus data.Now atUniversity of Michigan, Ann Arbor, USA 相似文献
999.
A. Laurinavi?ius K. Rep?as A. -R. Va?kevi?ius 《International Journal of Infrared and Millimeter Waves》1995,16(7):1217-1222
Power-voltage and frequency characteristics of power heads for 90–120 GHz TE10-mode millimeter waves are presented. Operation of the power heads is based on thermo-e.m.f. of hot charge carriers in silicon. The head has been tested both in the pulsed and continuous generation regime. The experiments were carried out in the power range of 2·10–3–4 W. In the pulse regime, the shortest pulse duration was 1s. 相似文献
1000.