全文获取类型
收费全文 | 4176篇 |
免费 | 93篇 |
国内免费 | 12篇 |
专业分类
化学 | 2549篇 |
晶体学 | 21篇 |
力学 | 89篇 |
数学 | 680篇 |
物理学 | 942篇 |
出版年
2021年 | 43篇 |
2020年 | 32篇 |
2019年 | 44篇 |
2018年 | 39篇 |
2017年 | 29篇 |
2016年 | 77篇 |
2015年 | 57篇 |
2014年 | 65篇 |
2013年 | 204篇 |
2012年 | 166篇 |
2011年 | 177篇 |
2010年 | 99篇 |
2009年 | 74篇 |
2008年 | 163篇 |
2007年 | 165篇 |
2006年 | 174篇 |
2005年 | 201篇 |
2004年 | 156篇 |
2003年 | 152篇 |
2002年 | 129篇 |
2001年 | 86篇 |
2000年 | 83篇 |
1999年 | 68篇 |
1998年 | 44篇 |
1997年 | 65篇 |
1996年 | 76篇 |
1995年 | 64篇 |
1994年 | 51篇 |
1993年 | 57篇 |
1992年 | 68篇 |
1991年 | 52篇 |
1990年 | 67篇 |
1989年 | 57篇 |
1988年 | 64篇 |
1987年 | 31篇 |
1986年 | 46篇 |
1985年 | 87篇 |
1984年 | 80篇 |
1983年 | 61篇 |
1982年 | 79篇 |
1981年 | 68篇 |
1980年 | 75篇 |
1979年 | 50篇 |
1978年 | 64篇 |
1977年 | 61篇 |
1976年 | 47篇 |
1975年 | 55篇 |
1974年 | 45篇 |
1973年 | 50篇 |
1972年 | 25篇 |
排序方式: 共有4281条查询结果,搜索用时 15 毫秒
1.
Monomeric sarcosine oxidase (mSOx) fusion with the silaffin peptide, R5, designed previously for easy protein production in low resource areas, was used in a biosilification process to form an enzyme layer electrode biosensor. mSOx is a low activity enzyme (10–20 U/mg) requiring high amounts of enzyme to obtain an amperometric biosensor signal, in the clinically useful range <1 mM sarcosine, especially since the Km is >10 mM. An amperometric biosensor model was fitted to experimental data to investigate dynamic range. mSOx constructs were designed with 6H (6×histidine) and R5 (silaffin) peptide tags and compared with native mSOx. Glutaraldehyde (GA) cross‐linked proteins retained ~5 % activity for mSOx and mSOx‐6H and only 0.5 % for mSOx‐R5. In contrast R5 catalysed biosilification on (3‐mercaptopropyl) trimethoxysilane (MPTMS) and tetramethyl orthosilicate (TMOS) particles created a ‘self‐immobilisation’ matrix retaining 40 % and 76 % activity respectively. The TMOS matrix produced a thick layer (>500 μm) on a glassy carbon electrode with a mediated current due to sarcosine in the clinical range for sarcosinemia (0–1 mM). The mSOx‐R5 fusion protein was also used to catalyse biosilification in the presence of creatinase and creatininase, entrapping all three enzymes. A mediated GC enzyme linked current was obtained with dynamic range available for creatinine determination of 0.1–2 mM for an enzyme layer ~800 nm. 相似文献
2.
3.
It is known that a distance-regular graph with valency k at least three admits at most two Qpolynomial structures. We show that all distance-regular graphs with diameter four and valency at least three admitting two Q-polynomial structures are either dual bipartite or almost dual bipartite. By the work of Dickie(1995) this implies that any distance-regular graph with diameter d at least four and valency at least three admitting two Q-polynomial structures is, provided it is not a Hadamard graph, either the cube H(d, 2)with d even, the half cube 1/2H(2d + 1, 2), the folded cube?H(2d + 1, 2), or the dual polar graph on [2A2d-1(q)]with q 2 a prime power. 相似文献
4.
TGA, DTA and DSC analyses indicate that benzotriazole is significantly more stable thermally than 1,2,3-triazole. 相似文献
5.
Stuart P. RomerilVictor Lee Jack E. Baldwin Timothy D.W. ClaridgeBarbara Odell 《Tetrahedron letters》2003,44(42):7757-7761
The absolute configuration of the marine sponge alkaloid pyrinodemin A is established by organic synthesis. 相似文献
6.
Jack Harrowfield Dominique Matt 《Journal of inclusion phenomena and macrocyclic chemistry》2004,50(3-4):133-150
The problems involved in identifying and quantifying labile interactions considered to influence complex compound structures are highlighted through the assessment of four different families of metal complexes for which extensive crystallographic data are available. Modification of the charge distribution within a ligand molecule as a result of coordination is one factor with a number of ramifications. A detailed analysis of evidence for both intra- and inter-molecular attractions in dimethylsulfoxide complexes of metal perchlorates is used to provide a basis for the consideration of weak interactions between complex ions involving forces including phenyl-group attractions, hydrogen bonding and cavity inclusion. 相似文献
7.
Several models have been developed in order to categorize the numerous expressions that people use in order to describe their emotional experiences. The focus of the present study is on one of these theoretical classifications proposed by Pekrun (1992) specifically concerning emotions which are directly related to learning and achievement in mathematics. In his model, emotions are classified according to their valence (positive vs. negative) and their level of activation. In testing the assumptions of this model, we investigated students' enjoyment, anxiety, anger and boredom experienced before, during, and after the completion of a math test. Correspondence analyses which were used to generate a graphical illustration of structural interrelationships between these emotions provide empirical support for the theoretical classification. 相似文献
8.
9.
LetBr(K) denote the Brauer group of a fieldK andPS(K) the projective Schur subgroup.
1. LetK be a finitely generated infinite field. ThenPS(K)=Br(K) if and only ifK is a global field.
2.|LetK be a finitely generated infinite field, and letK((t)) denote the field of formal power series int overK. ThenPS(K((t)))=Br(K((t))) if and only ifK=ℚ. 相似文献
10.
The results of Monte Carlo simulations of the beta dose rate to enamel are presented. The dose rates are the most comprehensive to date, incorporating the beta spectrum from 21 different radionuclides, all internal conversion and Auger electrons, the majority of the bremsstrahlung radiation, effects due to radon loss in the uranium series, and variations in the moisture content of the sediment. Applications to a new dating technique in archaeology using electron spin resonance and beta-gradient isochrons are discussed. 相似文献