全文获取类型
收费全文 | 16582篇 |
免费 | 391篇 |
国内免费 | 137篇 |
专业分类
化学 | 11352篇 |
晶体学 | 134篇 |
力学 | 511篇 |
数学 | 2538篇 |
物理学 | 2575篇 |
出版年
2022年 | 135篇 |
2021年 | 152篇 |
2020年 | 218篇 |
2019年 | 203篇 |
2018年 | 187篇 |
2017年 | 150篇 |
2016年 | 320篇 |
2015年 | 274篇 |
2014年 | 312篇 |
2013年 | 785篇 |
2012年 | 769篇 |
2011年 | 1040篇 |
2010年 | 490篇 |
2009年 | 441篇 |
2008年 | 851篇 |
2007年 | 889篇 |
2006年 | 936篇 |
2005年 | 864篇 |
2004年 | 784篇 |
2003年 | 717篇 |
2002年 | 685篇 |
2001年 | 231篇 |
2000年 | 203篇 |
1999年 | 162篇 |
1998年 | 191篇 |
1997年 | 199篇 |
1996年 | 235篇 |
1995年 | 179篇 |
1994年 | 187篇 |
1993年 | 150篇 |
1992年 | 153篇 |
1991年 | 159篇 |
1990年 | 135篇 |
1989年 | 118篇 |
1988年 | 150篇 |
1987年 | 148篇 |
1986年 | 109篇 |
1985年 | 213篇 |
1984年 | 236篇 |
1983年 | 169篇 |
1982年 | 241篇 |
1981年 | 223篇 |
1980年 | 227篇 |
1979年 | 206篇 |
1978年 | 200篇 |
1977年 | 182篇 |
1976年 | 182篇 |
1975年 | 152篇 |
1974年 | 164篇 |
1973年 | 156篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
K.J. Liu M. Miyake P.E. James H.M. Swartz 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,133(2):291-298
Carbon based paramagnetic materials are frequently used for EPR oximetry, especiallyin vivo,but the EPR spectra of these materials often have more than one paramagnetic center and/or relatively low signal intensity. To determine whether the multi-components of carbon based materials could be separated and enriched in the active component, we used density gradient centrifugation to separate the materials into several fractions. We studied two types of coals, gloxy and Pocahontas, and found these materials to have large density distribution. The separated density fractions had very different EPR spectra and intensities. The active component from the coal material had a more homogeneous EPR signal and significantly increased EPR signal intensity, whereas for India ink, only slight changes were observed. This result can be very useful in the development of better probes for EPR oximetry. 相似文献
42.
James H. Liu 《Semigroup Forum》2002,66(1):63-67
We provide a counterexample to some recent publications concerning the existence of the mild solutions of the non-local evolution equations, and indicate that in the study of the non-local evolution equations, the operators from which the mild solutions may be derived are in general not compact, thus those fixed point theorems requiring the compactness of the operators are not applicable. 相似文献
43.
James E. Keesling Yuli B. Rudyak 《Proceedings of the American Mathematical Society》2007,135(8):2629-2631
We discuss which groups can be realized as the fundamental groups of compact Hausdorff spaces. In particular, we prove that the claim ``every group can be realized as the fundamental group of a compact Hausdorff space' is consistent with the Zermelo-Fraenkel-Choice set theory.
44.
This paper discusses recent trends in the field of reverse engineering, particularly those highlighted at the Second Working
Conference on Reverse Engineering, held in July 1995. The trends observed include increased orientation toward tasks, grounding
in complex real-world applications, guidance from empirical study, analysis of non-code sources, and increased formalization.
The paper also summarizes open research issues and provides pointers to future events and sources of information in this area. 相似文献
45.
In many metrics of physical interest, the gravitational field can be represented as an optical medium with an effective index of refraction. We show that, in such a metric, the orbits of both massive and massless particles are governed by a variational principle which involves the index of refraction and which assumes the form of Fermat's principle or of Maupertuis's principle. From this variational principle we derive exact equations of motion of Newtonian form which govern both massless and massive particles. These equations of motion are applied to some problems of physical interest. 相似文献
46.
LetX
1,X
2, ... be a sequence of independent random variables with common lattice distribution functionF having zero mean, and let (S
n
) be the random walk of partial sums. The strong law of large numbers (SLLN) implies that for any and >0
\alpha + \varepsilon n {\text{for some }}n \geqq m\} $$
" align="middle" vspace="20%" border="0"> 相似文献
47.
S. Bamidele Sanni H. Behm Paul T. Beurskens E. Kayode Adesogan James I. Durodola 《Journal of chemical crystallography》1988,18(5):575-582
A new cytotoxic macrocyclic diterpenoid named Japodagrol, C20H28O4, has been isolated from the ornamental plantJatropha podagrica, family Euphorbiaceae, grown in Nigeria. The structure of the title compound, C20H28O4, was solved by X-ray analysis.M
r
=332.44, monoclinic space groupC2,a=23.285(4),b=6.5105(12),c=12.505(3) Å,=98.504(17),V=1874.8 Å3,Z=4,D
c
=1.178 Mg/m3. CuK radiation (graphite crystal monochromator, =1.54184 A), (CuK)=6.13 cm–1,F(000)=720,T=290 K. Final conventionalR factor=0.035,R
w
=0.038 for 3349 observed reflections. The structure was solved with the programDirdif. The 5-membered ring is closed to a half-chair form. The compound contains inter- and intramolecular hydrogen bonds. 相似文献
48.
A critical review of known results about the permanence conditions for the null character of the solutions to the (vacuum) Maxwell equations, is presented. Concomitants of the electromagnetic field and the metric tensor are constructed, which give the principal directions of the field in covariant form. The known permanence conditions are generalized in order to includeall the (local) null fields; the above concomitants allow these conditions to be explicitly formulated in terms of the electromagnetic field.Supported in part by Conselleria de Cultura, Educació i Ciència de la Generalitat Valenciana. 相似文献
49.
50.
Abstract From April 1982 to April 1986 we used photodynamic therapy to treat 192 patients with various malignancies. In all, 172 injections of hematoporphyrin derivative and 135 injections of dihematoporphyrin ether were made intravenously to sensitize the tumors; 684 photodynamic treatments were given using a tunable dye argon laser system for the light source. The technical problems of the light source and delivery systems are presented and the efficacy of therapy is analyzed. 相似文献
|