全文获取类型
收费全文 | 5057篇 |
免费 | 167篇 |
国内免费 | 33篇 |
专业分类
化学 | 3073篇 |
晶体学 | 38篇 |
力学 | 127篇 |
数学 | 698篇 |
物理学 | 1321篇 |
出版年
2023年 | 40篇 |
2022年 | 70篇 |
2021年 | 68篇 |
2020年 | 85篇 |
2019年 | 101篇 |
2018年 | 75篇 |
2017年 | 71篇 |
2016年 | 128篇 |
2015年 | 100篇 |
2014年 | 111篇 |
2013年 | 232篇 |
2012年 | 245篇 |
2011年 | 285篇 |
2010年 | 169篇 |
2009年 | 146篇 |
2008年 | 232篇 |
2007年 | 263篇 |
2006年 | 238篇 |
2005年 | 225篇 |
2004年 | 173篇 |
2003年 | 150篇 |
2002年 | 123篇 |
2001年 | 85篇 |
2000年 | 78篇 |
1999年 | 76篇 |
1998年 | 44篇 |
1997年 | 60篇 |
1996年 | 67篇 |
1995年 | 61篇 |
1994年 | 63篇 |
1993年 | 81篇 |
1992年 | 79篇 |
1991年 | 50篇 |
1990年 | 48篇 |
1989年 | 53篇 |
1988年 | 51篇 |
1987年 | 47篇 |
1986年 | 45篇 |
1985年 | 54篇 |
1984年 | 55篇 |
1983年 | 37篇 |
1982年 | 42篇 |
1981年 | 58篇 |
1980年 | 53篇 |
1979年 | 44篇 |
1978年 | 47篇 |
1977年 | 46篇 |
1976年 | 48篇 |
1974年 | 31篇 |
1973年 | 40篇 |
排序方式: 共有5257条查询结果,搜索用时 46 毫秒
101.
102.
103.
Belz J Cousins RD Diwan MV Eckhause M Ecklund KM Hancock AD Highland VL Hoff C Hoffmann GW Irwin GM Kane JR Kettell SH Klein JR Kuang Y Lang K Martin R May M McDonough J Molzon WR Riley PJ Ritchie JL Schwartz AJ Trandafir A Ware B Welsh RE White SN Witkowski MT Wojcicki SG Worm S 《Physical review letters》1996,76(18):3277-3280
104.
Inclusion-exclusion: Exact and approximate 总被引:1,自引:0,他引:1
It is often required to find the probability of the union of givenn eventsA
1
,...,A
n
. The answer is provided, of course, by the inclusion-exclusion formula: Pr(A
i
)=
i
–
i<j
Pr(A
i
A
j
)±.... Unfortunately, this formula has exponentially many terms, and only rarely does one manage to carry out the exact calculation. From a computational point of view, finding the probability of the union is an intractable, #P-hard problem, even in very restricted cases. This state of affairs makes it reasonable to seek approximate solutions that are computationally feasible. Attempts to find such approximate solutions have a long history starting already with Boole [1]. A recent step in this direction was taken by Linial and Nisan [4] who sought approximations to the probability of the union, given the probabilities of allj-wise intersections of the events forj=1,...k. The developed a method to approximate Pr(A
i
), from the above data with an additive error of exp
. In the present article we develop an expression that can be computed in polynomial time, that, given the sums |S|=j
Pr(
iS
A
i
) forj=1,...k, approximates Pr(A
i
) with an additive error of exp
. This error is optimal, up to the logarithmic factor implicit in the
notation.The problem of enumerating satisfying assignments of a boolean formula in DNF formF=v
l
m
C
i
is an instance of the general problem that had been extensively studied [7]. HereA
i
is the set of assignments that satisfyC
i
, and Pr(
iS
A
i
)=a
S
/2n where
iS
C
i
is satisfied bya
S
assignments. Judging from the general results, it is hard to expect a decent approximation ofF's number of satisfying assignments, without knowledge of the numbersa
S
for, say, all cardinalities
. Quite surprisingly, already the numbersa
S
over |S|log(n+1)uniquely determine the number of satisfying assignments for F.We point out a connection between our work and the edge-reconstruction conjecture. Finally we discuss other special instances of the problem, e.g., computing permanents of 0,1 matrices, evaluating chromatic polynomials of graphs and for families of events whose VC dimension is bounded.Work supported in part by a grant of the Binational Israel-US Science Foundation.Work supported in part by a grant of the Binational Israel-US Science Foundation and by the Israel Science Foundation. 相似文献
105.
106.
107.
108.
N. Kukhtarev G. Dovgalenko J. Shultz G. Salamo E. J. Sharp B. A. Wechsler M. B. Klein 《Applied Physics A: Materials Science & Processing》1993,56(4):303-305
We report the first measurement of the photo-galvanic circular current antisymmetric tensor component in BaTiO3: Co. The measurement gives a value of this coefficient, for extraordinary beam amplification, of 4×10–9 A/W using a nonstationary measurement technique at a wavelength of 0.632 m.Professor N. Kukhtarev is on leave from the Institute of Physics in the Ukraine and is supported by the NSFDr. G. Dovgalenko is on leave from the IRPA Rotor-Control research laboratory of the Ukraine and is supported by the University of Arkansas 相似文献
109.
110.
For benzenoid hydrocarbons the distribution of pi-electrons amongst rings is characterized in the context of Randis mode of assignment attending to the different Kekulé structures. In particular the mean and mean deviation from the mean are considered, and the benzenoids which achieve maximum deviation are identified. 相似文献