全文获取类型
收费全文 | 313793篇 |
免费 | 4290篇 |
国内免费 | 1085篇 |
专业分类
化学 | 170605篇 |
晶体学 | 4457篇 |
力学 | 13029篇 |
综合类 | 7篇 |
数学 | 36262篇 |
物理学 | 94808篇 |
出版年
2020年 | 1983篇 |
2019年 | 1954篇 |
2018年 | 1965篇 |
2017年 | 1875篇 |
2016年 | 3858篇 |
2015年 | 3235篇 |
2014年 | 4421篇 |
2013年 | 13976篇 |
2012年 | 10728篇 |
2011年 | 13363篇 |
2010年 | 8270篇 |
2009年 | 8255篇 |
2008年 | 12336篇 |
2007年 | 12571篇 |
2006年 | 12213篇 |
2005年 | 11154篇 |
2004年 | 10034篇 |
2003年 | 8848篇 |
2002年 | 8700篇 |
2001年 | 10109篇 |
2000年 | 7710篇 |
1999年 | 6115篇 |
1998年 | 4894篇 |
1997年 | 4733篇 |
1996年 | 4773篇 |
1995年 | 4363篇 |
1994年 | 4114篇 |
1993年 | 3940篇 |
1992年 | 4431篇 |
1991年 | 4293篇 |
1990年 | 4011篇 |
1989年 | 3830篇 |
1988年 | 4120篇 |
1987年 | 3784篇 |
1986年 | 3677篇 |
1985年 | 5317篇 |
1984年 | 5395篇 |
1983年 | 4377篇 |
1982年 | 4753篇 |
1981年 | 4793篇 |
1980年 | 4545篇 |
1979年 | 4663篇 |
1978年 | 4665篇 |
1977年 | 4644篇 |
1976年 | 4597篇 |
1975年 | 4508篇 |
1974年 | 4356篇 |
1973年 | 4524篇 |
1972年 | 2569篇 |
1971年 | 1879篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
941.
The dependence of cross sections on the colour state of the colliding hadrons is investigated within the Low-Nussinov model of two-gluon exchange. The total cross sections for colour-octet hadrons are practically constant as functions of the hadronic radii, while they tend to zero when the radii of the colour-singlet hadrons approach zero. The slope parameter of the differential clastic cross sections for small momentum transfers is rather insensitive to the colour structure of the colliding hadrons. The integrated colour exchange cross section is calculated. 相似文献
942.
J. Kircher M. Cardona M. Alouani S. Gopalan O. Jepsen O. K. Andersen
E. Kaldis
J. Karpinski S. Rusieki 《Physica C: Superconductivity and its Applications》1992,200(3-4):413-417We report results of ellipsometric measurements of the dielectric tensor of YBa2Cu4O8 as well as calculations employing density functional theory in the local density approximation (LDA). For the computation of the one-electron eigenvalues and states the linear-muffin-tin-orbital method (LMTO) was used. Measured and calculated results show good agreement. In particular, the calculation predicts different band structures for YBa2Cu3O7 and YBa2Cu4O8 in the vicinity of the Fermi energy which lead to significant differences in the optical spectra. One such difference is a region of small ε2 in the near infrared which is a fingerprint of the high (relative to the top of the highest fully occupied band) Fermi energy as compared to the situation in YBa2Cu3O7. Our experimental results confirm the theoretical findings. 相似文献
943.
K. J. Ellis R. J. Shypailo H. -P. Sheng W. G. Pond 《Journal of Radioanalytical and Nuclear Chemistry》1992,157(1):159-168
Characteristic gamma-rays are emitted promptly by elements during exposure to neutrons. These emissions enable a radioanalytical analysis of the body's composition of protein (nitrogen), water (hydrogen), and fat (carbon). We have used this method in vivo to determine the body composition of obese and lean pigs (10 to 20 kg body wt) fed an altered cholesterol diet. 相似文献
944.
945.
G A van't Klooster F M Woutersen-van Nijnanten H J Kolker J Noordhoek A S van Miert 《Journal of chromatography. A》1992,579(1):158-164
Ethylmorphine N-demethylation is used as a marker pathway in studies of rat cytochrome P450 3A and 2C11 biotransformations. At present, microsomal activities are generally measured by a colorimetric determination of the formed formaldehyde. In the present study, a high-performance liquid chromatographic method of separating and quantifying both the N-demethylated (norethylmorphine) and the O-de-ethylated (morphine) metabolites is described. Either samples are extracted with ethyl acetate or proteins are precipitated with zinc sulphate-barium hydroxide. Separation is achieved on a CN reversed-phase column, using a mobile phase of phosphate buffer (pH 4.5)-acetonitrile (90:10, v/v). At a flow-rate of 1.5 ml/min, the analysis time is 30 min. The limit of detection (ultraviolet, 210 nm) for ethylmorphine and its metabolites is 0.5 micrograms/ml. 相似文献
946.
Muscarine, oxazole, thiazole, imidazole and peptide alkaloids and other miscellaneous alkaloids. 总被引:1,自引:0,他引:1
J R Lewis 《Natural product reports》1992,9(1):81-101
947.
D. J. Hartfiel 《Linear and Multilinear Algebra》1994,36(4):293-304
In this paper we consider the nonnegative matrix system ciA+uiB=ci+1 where the nonnegative matrix A is allowed to vary, within bounds. The cone control problem is to find a nonnegative matrix B such that if Ci is a nonnegative vector in a specified cone, then there is a nonnegative vector ui such that ci+1 is in that cone. We extend this problem to input control by finding a B such that the cone, generated by the rows of B, is as small as possible. Thus, the percent distribution of ∣uiB∣ through the states of the sustem by uiB is either constant or varies little. 相似文献
948.
949.
Applied Biochemistry and Biotechnology - In summary, it appears that the microbial reduction process is clearly not competitive with conventional SO2-reduction techniques when glucose (DE95 corn... 相似文献
950.
The authors study concentration profiles of solutes undergoingequilibrium absorption in the vicinity of a water well. Forthe case of a contamination event, the limit problem of vanishingwell radius, which is of self-similar nature, is analysed indetail. Existence, uniqueness, and qualitative properties ofsolutions of the corresponding ordinary differential equationsare shown. Some numerical examples are also presented. 相似文献