全文获取类型
收费全文 | 43715篇 |
免费 | 2757篇 |
国内免费 | 2499篇 |
专业分类
化学 | 21464篇 |
晶体学 | 438篇 |
力学 | 2276篇 |
综合类 | 168篇 |
数学 | 10845篇 |
物理学 | 13780篇 |
出版年
2023年 | 324篇 |
2022年 | 414篇 |
2021年 | 565篇 |
2020年 | 672篇 |
2019年 | 738篇 |
2018年 | 1726篇 |
2017年 | 1956篇 |
2016年 | 1451篇 |
2015年 | 1329篇 |
2014年 | 1394篇 |
2013年 | 1767篇 |
2012年 | 4487篇 |
2011年 | 3713篇 |
2010年 | 2796篇 |
2009年 | 2550篇 |
2008年 | 1587篇 |
2007年 | 1480篇 |
2006年 | 1403篇 |
2005年 | 5081篇 |
2004年 | 4448篇 |
2003年 | 2732篇 |
2002年 | 987篇 |
2001年 | 668篇 |
2000年 | 413篇 |
1999年 | 502篇 |
1998年 | 376篇 |
1997年 | 296篇 |
1996年 | 256篇 |
1995年 | 226篇 |
1994年 | 190篇 |
1993年 | 178篇 |
1992年 | 272篇 |
1991年 | 254篇 |
1990年 | 221篇 |
1989年 | 187篇 |
1988年 | 170篇 |
1987年 | 96篇 |
1986年 | 82篇 |
1985年 | 83篇 |
1984年 | 56篇 |
1983年 | 44篇 |
1982年 | 42篇 |
1979年 | 36篇 |
1976年 | 83篇 |
1975年 | 39篇 |
1974年 | 43篇 |
1973年 | 51篇 |
1972年 | 43篇 |
1969年 | 39篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Improved sample wettability was obtained by oxygen plasma functionalization of pyrolytic graphite. The samples were exposed to highly dissociated oxygen plasma with the density of 1 × 1016 m−3, the electron temperature of about 5.5 eV and the density of neutral oxygen atoms of 8 × 1021 m−3 for 20 s. The surface wettability was measured by a contact angle of water drop. The contact angle dropped from original 112° down to about 1°. The functional groups were detected by XPS analyses. The survey spectrum showed a substantial increase of oxygen concentration on the surface, while high-resolution analyses showed additional oxygen was bonded onto the graphite surface in the form of C-O polar functional group responsible for the increase of the surface energy. 相似文献
112.
本文用COSY,CHCOR等二维核磁共振技术对TRANILAST,2[]3-(3.4-二甲基苯基)1-氧代-2-丙烯基]氨基]苯甲到进行了~1H、~(13)C NMR谱数据分析及归属,并结合~(13)C弛豫时间T_1 及变温实验对合成产品进行了结构鉴定. 相似文献
113.
Yong LU Hong WANG Ye LIU Ming Yuan HE 《中国化学快报》2006,17(10):1397-1400
Recently, miniature H2 generator to power fuel cells for portable/micro electronic devices and passenger propulsion has been the focus of intense research activities1-3. One of the strategies is to find simple CO-free H2 production with novel microreactor… 相似文献
114.
Z.G. Xiao R.J. HuH.Y. Wu G.M. JinZ.Y. Li L.M. DuanH.W. Wang B.G. ZhangS.F. Wang Z.Y. WeiH.S. Xu Y.T. ZhuS.L. Li F. FuX.H. Yuan Z.Q. Feng 《Physics letters. [Part B]》2006
The inclusive reduced velocity correlation functions of the intermediate mass fragments were measured in the reactions of 36Ar + 112,124Sn at 35 MeV/u. The anti-correlation is observed to be stronger in 36Ar + 124Sn system than that in 36Ar + 112Sn. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three body Coulomb repulsive trajectory model is employed to calculate the emission time scale of the IMFs for the two systems. The time scale is 150 fm/c in 36Ar + 112Sn and 120 fm/c in the 36Ar + 124Sn, respectively. 相似文献
115.
Kj?rand Iversen Per Nilsson 《International Journal of Computers for Mathematical Learning》2007,12(2):113-133
This paper focuses on the different ways in which students in lower secondary school (14–16 year olds) experience compound
random events, presented to them in the form of combined junctions. A carefully designed ICT environment was developed enabling
the students to interact with different representations of such structures. Data for the analysis was gathered from two interview
sessions. The analysis of the interaction is based on constructivist principles on learning; i.e. we adopted a student-oriented
perspective, taking into consideration the different ways students try to make sense of chance encounters.
Our results show how some students give priority to geometrical and physical concerns, and we discuss how seeking causal explanations
of random phenomena may have encouraged this. With respect to numerically oriented models a division strategy appears to stand
out as the preferred one. 相似文献
116.
117.
Piotr Ko?cielniak 《Topology and its Applications》2007,154(9):1951-1955
Let M be a compact manifold with dimM?2. We prove that some iteration of the generic homeomorphism on M is semiconjugated to the shift map and has infinite topological entropy (Theorem 1.1). 相似文献
118.
Covering numbers of precompact symmetric convex subsets of Hilbert spaces are investigated. Lower bounds are derived for sets containing orthogonal subsets with norms of their elements converging to zero sufficiently slowly. When these sets are convex hulls of sets with power-type covering numbers, the bounds are tight. The arguments exploit properties of generalized Hadamard matrices. The results are illustrated by examples from machine learning, neurocomputing, and nonlinear approximation. 相似文献
119.
We give counterexamples to the following conjecture of Auslander: given a finitely generated module M over an Artin algebra Λ, there exists a positive integer nM such that for all finitely generated Λ-modules N, if ExtΛi(M,N)=0 for all i?0, then ExtΛi(M,N)=0 for all i?nM. Some of our examples moreover yield homologically defined classes of commutative local rings strictly between the class of local complete intersections and the class of local Gorenstein rings. 相似文献
120.
New Kamenev-type oscillation criteria for second-order nonlinear differential equations with damping 总被引:1,自引:0,他引:1
Yuan Gong Sun 《Journal of Mathematical Analysis and Applications》2004,291(1):341-351
Some new oscillation criteria are established for the nonlinear damped differential equation (r(t)y′)′+p(t)y′+q(t)f(y)=0 that are different from most known ones in the sense that they are based on a class of new functions Φ(t,s,r) defined in the sequel. Our results are sharper than some previous results which can be seen by the examples at the end of this paper. 相似文献