全文获取类型
收费全文 | 114119篇 |
免费 | 6707篇 |
国内免费 | 6790篇 |
专业分类
化学 | 53212篇 |
晶体学 | 1482篇 |
力学 | 8440篇 |
综合类 | 526篇 |
数学 | 35870篇 |
物理学 | 28086篇 |
出版年
2024年 | 93篇 |
2023年 | 653篇 |
2022年 | 1089篇 |
2021年 | 1300篇 |
2020年 | 1514篇 |
2019年 | 1592篇 |
2018年 | 11508篇 |
2017年 | 11450篇 |
2016年 | 7677篇 |
2015年 | 2737篇 |
2014年 | 2642篇 |
2013年 | 3289篇 |
2012年 | 7139篇 |
2011年 | 13965篇 |
2010年 | 8446篇 |
2009年 | 8603篇 |
2008年 | 9396篇 |
2007年 | 11300篇 |
2006年 | 2628篇 |
2005年 | 3262篇 |
2004年 | 2992篇 |
2003年 | 3138篇 |
2002年 | 2205篇 |
2001年 | 1304篇 |
2000年 | 1170篇 |
1999年 | 849篇 |
1998年 | 689篇 |
1997年 | 555篇 |
1996年 | 579篇 |
1995年 | 453篇 |
1994年 | 388篇 |
1993年 | 308篇 |
1992年 | 240篇 |
1991年 | 238篇 |
1990年 | 197篇 |
1989年 | 170篇 |
1988年 | 149篇 |
1987年 | 134篇 |
1986年 | 129篇 |
1985年 | 113篇 |
1984年 | 69篇 |
1983年 | 64篇 |
1982年 | 69篇 |
1981年 | 47篇 |
1980年 | 55篇 |
1979年 | 59篇 |
1978年 | 42篇 |
1914年 | 45篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
In mononuclear HgI2[(C5H4N)3N], mercury is tetrahedrally coordinated by two nitrogen atoms of a tris(2‐pyridyl)amine ligand and two iodides. The coordination moieties are connected by weak intermolecular Hg(II)···I interactions to give a one‐dimensional structure. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
162.
Howard Robinson 《Acta Analytica》2005,20(3):7-10
Nicholas Nathan tries to resist the current version of the causal argument for sense-data in two ways. First he suggests that,
on what he considers to be the correct re-construction of the argument, it equivocates on the sense of proximate cause. Second
he defends a form of disjunctivism, by claiming that there might be an extra mechanism involved in producing veridical hallucination,
that is not present in perception. I argue that Nathan’s reconstruction of the argument is not the appropriate one, and that,
properly interpreted, the argument does not equivocate on proximate cause. Furthermore, I claim that his postulation of a
modified mechanism for hallucinations is implausibly ad hoc. 相似文献
163.
Chris Pollett 《Archive for Mathematical Logic》2003,42(5):469-488
The paper establishes lower bounds on the provability of 𝒟=NP and the MRDP theorem in weak fragments of arithmetic. The
theory I
5
E
1
is shown to be unable to prove 𝒟=NP. This non-provability result is used to show that I
5
E
1
cannot prove the MRDP theorem. On the other hand it is shown that I
1
E
1
proves 𝒟 contains all predicates of the form (∀i≤|b|)P(i,x)^Q(i,x) where ^ is =, <, or ≤, and I
0
E
1
proves 𝒟 contains all predicates of the form (∀i≤b)P(i,x)=Q(i,x). Here P and Q are polynomials. A conjecture is made that 𝒟 contains NLOGTIME. However, it is shown that this conjecture would not be sufficient
to imply 𝒟=N P. Weak reductions to equality are then considered as a way of showing 𝒟=NP. It is shown that the bit-wise less than predicate,
≤2, and equality are both co-NLOGTIME complete under FDLOGTIME reductions. This is used to show that if the FDLOGTIME functions
are definable in 𝒟 then 𝒟=N P.
Received: 13 July 2001 / Revised version: 9 April 2002 /
Published online: 19 December 2002
Key words or phrases: Bounded Arithmetic – Bounded Diophantine Complexity 相似文献
164.
165.
Xiao Qi ZHENG Yong Hui WANG Qing Xiang GUO* Li YANG You Cheng LIU Department of Chemistry University of Science Technology of China Hefei National Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2003,(8)
As artificial enzymes, the binding constants of cyclodextrins (CDs) and their substrates are expected to be high1. For this purpose, many kinds of bridged cyclodextrin dimers2 whose two cyclodextrins are linked by various spacers have been constructed. It was of interest to make the dimers, whose binding constants would exceed 108dm3/mol3. Up to date, the bridged cyclodextrin dimers have been extensively studied as enzyme models and as molecular receptors4-6. Recently, we synthesized a brid… 相似文献
166.
Grégory Duby 《Archive for Mathematical Logic》2003,42(5):435-447
This paper generalizes results of F. K?rner from [4] where she established the existence of maximal automorphisms (i.e. automorphisms
moving all non-algebraic elements). An ω-maximal automorphism is an automorphism whose powers are maximal automorphisms. We
prove that any structure has an elementary extension with an ω-maximal automorphism. We also show the existence of ω-maximal
automorphisms in all countable arithmetically saturated structures. Further we describe the pairs of tuples (ˉa,ˉb) for which there is an ω-maximal automorphism mapping ˉa to ˉb.
Received: 12 December 2001 /
Published online: 10 October 2002
Supported by the ``Fonds pour la Formation à la Recherche dans l'Industrie et dans l'Agriculture'
Mathematics Subject Classification (2000): Primary: 03C50; Secondary: 03C57
Key words or phrases: Automorphism – Recursively saturated structure 相似文献
167.
This paper analyzes the compromise social choice correspondence derived from the τ-value of digraph games. Monotonicity of
this correspondence is shown. A connection between several properties of social choice correspondences based on game theoretical
solutions and game theoretical properties of the underlying solutions is given. Applications to several game theoretic solutions
are provided. 相似文献
168.
169.
LiuYuqi LiZhigang YahYakun 《Acta Mechanica Solida Sinica》2004,17(1):58-64
By using the Finite Element Inverse Approach based on the Hill quadratic anisotrop-ically yield criterion and the quadrilateral element, a fast analyzing software-FASTAMP for the sheet metal forming is developed. The blank shapes of three typical stampings are simulated and compared with numerical results given by the AUTOFORM software and experimental results, respectively. The comparison shows that the FASTAMP can predict blank shape and strain distribution of the stamping more precisely and quickly than those given by the traditional methods and the AUTOFORM. 相似文献
170.
A technique is described for the measurement of all components of mean velocity and Reynolds stresses, in a complex turbulent flow where achieving coincidence data acquisition is difficult. The method is based on data recorded using four orientations of the laser probe. It is shown that the measurement errors are not the same for all the components of the Reynolds tensor, but they are sufficiently small to give a good accuracy. An application to a turbomachinery flow is given to illustrate the method. 相似文献