全文获取类型
收费全文 | 402840篇 |
免费 | 1989篇 |
国内免费 | 696篇 |
专业分类
化学 | 186319篇 |
晶体学 | 5943篇 |
力学 | 23618篇 |
综合类 | 16篇 |
数学 | 60870篇 |
物理学 | 128759篇 |
出版年
2020年 | 3254篇 |
2019年 | 4082篇 |
2018年 | 11898篇 |
2017年 | 12386篇 |
2016年 | 10554篇 |
2015年 | 4152篇 |
2014年 | 6843篇 |
2013年 | 13826篇 |
2012年 | 13962篇 |
2011年 | 21916篇 |
2010年 | 15366篇 |
2009年 | 15873篇 |
2008年 | 19917篇 |
2007年 | 22498篇 |
2006年 | 10908篇 |
2005年 | 13710篇 |
2004年 | 11252篇 |
2003年 | 10846篇 |
2002年 | 9576篇 |
2001年 | 9510篇 |
2000年 | 7236篇 |
1999年 | 5342篇 |
1998年 | 4734篇 |
1997年 | 4657篇 |
1996年 | 4426篇 |
1995年 | 3872篇 |
1994年 | 3919篇 |
1993年 | 3876篇 |
1992年 | 4126篇 |
1991年 | 4478篇 |
1990年 | 4355篇 |
1989年 | 4431篇 |
1988年 | 4242篇 |
1987年 | 4252篇 |
1986年 | 3978篇 |
1985年 | 5077篇 |
1984年 | 5151篇 |
1983年 | 4375篇 |
1982年 | 4439篇 |
1981年 | 4295篇 |
1980年 | 3970篇 |
1979年 | 4565篇 |
1978年 | 4692篇 |
1977年 | 4790篇 |
1976年 | 4894篇 |
1975年 | 4565篇 |
1974年 | 4434篇 |
1973年 | 4722篇 |
1972年 | 3680篇 |
1971年 | 3407篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Three new cytotoxic polyacetylenes, PQ-1 (1), PQ-2 (2) and PQ-3 (3), have been isolated from Panax quinquefolium. The structures of these acetylenes were determined by analyses of their 1H-1H and 1H-13C COSY spectra. All these compounds exhibited strong cytotoxic activities against leukemia cells (L 1210) in tissue culture. 相似文献
72.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
73.
74.
75.
A. N. Troflmchuk 《Journal of Mathematical Sciences》1991,57(5):3407-3409
We develop a method of computing the nonsteady-state and free oscillations of a framed elastic structure situated on an elastic base and containing an ideal compressible fluid. The solution uses the method of integral transforms in conjunction with the method of orthogonal polynomials. In the transform space the problem reduces to systems of linear algebraic equations. The Fourier transform is applied to return to the original space. Examples of the computation are given.Translated fromDinamicheskie Sistemy, No. 6, 1987, pp. 69–72. 相似文献
76.
We consider the solution of integral equations in problems of three-dimensional electromagnetic fields in piecewise-homogeneous media. An algorithm is proposed for analytical isolation of singularities in the kernel and the density of the integral equation of potential theory for the case of complex boundary surfaces.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 56, pp. 14–17, 1985 相似文献
77.
I. L. Davies K. E. Markides M. L. Lee M. W. Raynor K. D. Bartle 《Journal of separation science》1989,12(4):193-207
Although coupled liquid chromatographygas chromatography (LC-GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC-GC applications have been published in the last two years (1987–88) alone. This review categorizes LC-GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled-column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on-line trace enrichment-GC) have also been included in this review. 相似文献
78.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 51, No. 2, pp. 212–217, August, 1989. 相似文献
79.
A firm's logistics cost, including shipping and inventory-carrying, is a substantial percentage of its sales. Nevertheless, typical inventory-control methods ignore or insufficiently represent the shipping cost. This paper describes a recursive algorithm that determines the reorder cycle-time that minimizes total logistics cost. It allows for a realistic accounting of shipping cost, which is modelled here as a function of shipping distance and weight. The algorithm uses a relaxation procedure to identify a suitable initial approximation to the optimal order cycle-time and then, through a series of recursive steps, moves to the optimal result. We demonstrate the algorithm with a single item, with a group of items that share a common order cycle, and with multi-items when item demands are random variables. Experience with this algorithm indicates that it converges to the optimal result in a very few steps. 相似文献
80.