全文获取类型
收费全文 | 63203篇 |
免费 | 5300篇 |
国内免费 | 11080篇 |
专业分类
化学 | 49433篇 |
晶体学 | 2059篇 |
力学 | 718篇 |
综合类 | 444篇 |
数学 | 12666篇 |
物理学 | 14263篇 |
出版年
2024年 | 172篇 |
2023年 | 1008篇 |
2022年 | 1849篇 |
2021年 | 1854篇 |
2020年 | 1948篇 |
2019年 | 1953篇 |
2018年 | 1671篇 |
2017年 | 1967篇 |
2016年 | 2002篇 |
2015年 | 1807篇 |
2014年 | 2470篇 |
2013年 | 5787篇 |
2012年 | 3661篇 |
2011年 | 4407篇 |
2010年 | 3707篇 |
2009年 | 4313篇 |
2008年 | 4345篇 |
2007年 | 4452篇 |
2006年 | 4026篇 |
2005年 | 3351篇 |
2004年 | 3171篇 |
2003年 | 2656篇 |
2002年 | 2238篇 |
2001年 | 1828篇 |
2000年 | 1695篇 |
1999年 | 1454篇 |
1998年 | 1213篇 |
1997年 | 1068篇 |
1996年 | 950篇 |
1995年 | 1012篇 |
1994年 | 897篇 |
1993年 | 716篇 |
1992年 | 655篇 |
1991年 | 491篇 |
1990年 | 360篇 |
1989年 | 300篇 |
1988年 | 254篇 |
1987年 | 188篇 |
1986年 | 174篇 |
1985年 | 215篇 |
1984年 | 176篇 |
1983年 | 86篇 |
1982年 | 139篇 |
1981年 | 170篇 |
1980年 | 136篇 |
1979年 | 128篇 |
1978年 | 117篇 |
1977年 | 94篇 |
1976年 | 74篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Vibsanin O, isolated from the leaves and twigs of Viburnum awabuki, is an unprecedented bicyclic diterpenoid. The structures of vibsanin O was established by extensive analysis of spectroscopic data. 相似文献
102.
103.
Pedro lvarez‐Boo Jos Sergio Casas Alfonso Castieiras María Delfina Couce Eduardo Freijanes Eva Novoa Jos Sordo 《应用有机金属化学》2003,17(9):725-729
Reaction of dichloro‐ and dibromodimethyltin(IV) with 2‐(pyrazol‐1‐ylmethyl)pyridine (PMP) afforded [SnMe2Cl2(PMP)] and [SnMe2Br2(PMP)] respectively. The new complexes were characterized by elemental analysis and mass spectrometry and by IR, Raman and NMR (1H, 13C) spectroscopies. Structural studies by X‐ray diffraction techniques show that the compounds consist of discrete units with the tin atom octahedrally coordinated to the carbon atoms of the two methyl groups in a trans disposition (Sn? C = 2.097(5), 2.120(5) Å and 2.110(6), 2.121(6) Å in the chloro and in the bromo compounds respectively), two cis halogen atoms (Sn? Cl = 2.4908(16), 2.5447(17) Å; Sn? Br = 2.6875(11), 2.7464(9) Å) and the two donor atoms of the ligand (Sn? N = 2.407(4), 2.471(4) Å and 2.360(5), 2.455(5) Å). In both cases, the Sn? N(pyridine) bond length is markedly longer than the Sn? N(pyrazole) distance. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
104.
在氨性溶液中,光照射对ZnTPPS的形成影响很大。光-极谱试验表明:光电流(i_p)与浓度(c)间有以下的关系:对Zn(NH_3)_4~(2+),i_p∝C_((Zn)(NH_3)_4)~(2+)_~(1/2),对H_2TPPS,i_p∝C_(H_2TPPS),ZnTPPS络合物还原波的i_p不明显。本文对其差异性和光电流产生的原因做了初步探讨。 相似文献
105.
A conjecture of Toft [17] asserts that any 4-critical graph (or equivalently, every 4-chromatic graph) contains a fully odd subdivision ofK
4. We show that if a graphG has a degree three nodev such thatG-v is 3-colourable, then eitherG is 3-colourable or it contains a fully oddK
4. This resolves Toft's conjecture in the special case where a 4-critical graph has a degree three node, which is in turn used to prove the conjecture for line-graphs. The proof is constructive and yields a polynomial algorithm which given a 3-degenerate graph either finds a 3-colouring or exhibits a subgraph that is a fully odd subdivision ofK
4. (A graph is 3-degenerate if every subgraph has some node of degree at most three.) 相似文献
106.
We deal with the q-numerical radius of weighted unilateral and bilateral shift operators. In particular, the q-numerical radius of weighted shift operators with periodic weights is discussed and computed. 相似文献
107.
Libor Barto 《Journal of Pure and Applied Algebra》2007,211(3):721-731
A category is said to be alg-universal if every category of universal algebras can be fully embedded into it. We prove here that the category of varieties and interpretations, or in other words, the category of abstract clones and clone homomorphisms, is alg-universal. 相似文献
108.
In this article, a kind of auxiliary design BSA* for constructing BSAs is introduced and studied. Two powerful recursive constructions on BSAs from 3‐IGDDs and BSA*s are exploited. Finally, the necessary and sufficient conditions for the existence of a BSA(v, 3, λ; α) with α = 2, 3 are established. © 2006 Wiley Periodicals, Inc. J Combin Designs 15: 61–76, 2007 相似文献
109.
Martin A. Bos Bertus Dunnewind Ton van Vliet 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):95-105
Interfacial rheological properties and their suitability for foam production and stability of two vegetable proteins were studied and compared to β-casein. Proteins used ranged from flexible to rigid/globular in the order of β-casein, gliadin and soy glycinin. Experiments were performed at pH 6.7. Network forming properties were characterised by the surface dilational modulus (determined with the ring trough) and the critical falling film length (Lstill) at which a stagnant protein film will break. Gliadin had the highest dilational modulus, followed by glycinin and β-casein, whereas glycinin formed the strongest film against fracture in the overflowing cylinder. The rate of decrease in the surface tension was studied at the air–water (Wilhelmy plate method) and the oil–water interface (bursting membrane) and the dynamic surface tension during compression and expansion in the caterpillar. Gliadin had the lowest equilibrium interfacial tensions and β-casein the lowest dynamic surface tension during expansion. Hardly any foam could be formed at a concentration of 0.1 g/l by shaking. At a concentration of 1.4 g/l most foam was formed by β-casein, followed by gliadin and glycinin. It seems that in the first place the rate of adsorption is important for foam formation. For the vegetable proteins, adsorption was slow. This resulted in lower foamability, especially for glycinin. 相似文献
110.
In this paper we first give a lower bound on multiplicities for Buchsbaum homogeneous k-algebras A in terms of the dimension d, the codimension c, the initial degree q, and the length of the local cohomology modules of A. Next, we introduce the notion of Buchsbaum k-algebras with minimal multiplicity of degree q, and give several characterizations for those rings. In particular, we will show that those algebras have linear free resolutions. Further, we will give many examples of those algebras. 相似文献