全文获取类型
收费全文 | 158375篇 |
免费 | 10509篇 |
国内免费 | 17899篇 |
专业分类
化学 | 96915篇 |
晶体学 | 1436篇 |
力学 | 8538篇 |
综合类 | 2089篇 |
数学 | 36970篇 |
物理学 | 40835篇 |
出版年
2024年 | 157篇 |
2023年 | 1211篇 |
2022年 | 2141篇 |
2021年 | 3144篇 |
2020年 | 3617篇 |
2019年 | 3746篇 |
2018年 | 3158篇 |
2017年 | 4379篇 |
2016年 | 4786篇 |
2015年 | 4154篇 |
2014年 | 5851篇 |
2013年 | 10971篇 |
2012年 | 9047篇 |
2011年 | 8119篇 |
2010年 | 6915篇 |
2009年 | 9612篇 |
2008年 | 10167篇 |
2007年 | 10578篇 |
2006年 | 9640篇 |
2005年 | 8283篇 |
2004年 | 7625篇 |
2003年 | 6802篇 |
2002年 | 7717篇 |
2001年 | 5185篇 |
2000年 | 4937篇 |
1999年 | 4567篇 |
1998年 | 4088篇 |
1997年 | 3346篇 |
1996年 | 2892篇 |
1995年 | 2681篇 |
1994年 | 2401篇 |
1993年 | 2024篇 |
1992年 | 1923篇 |
1991年 | 1398篇 |
1990年 | 1195篇 |
1989年 | 1065篇 |
1988年 | 896篇 |
1987年 | 702篇 |
1986年 | 628篇 |
1985年 | 641篇 |
1984年 | 642篇 |
1983年 | 337篇 |
1982年 | 541篇 |
1981年 | 551篇 |
1980年 | 467篇 |
1979年 | 438篇 |
1978年 | 354篇 |
1977年 | 281篇 |
1976年 | 218篇 |
1973年 | 144篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
研究一类脉冲时滞抛物型偏微分方程组解的振动性,利用一阶脉冲时滞微分不等式获得了该类方程组在两类不同边值条件下所有解振动的若干充分条件.所得结果充分反映了脉冲和时滞在振动中的影响作用. 相似文献
992.
In the paper we indicate an error made in the proof of the main result of the paper [M.A. Darwish, On quadratic integral equation of fractional orders, J. Math. Anal. Appl. 311 (2005) 112-119]. Moreover, we provide correct proof of a slightly modified version of the mentioned result. The main tool used in our proof is the technique associated with the Hausdorff measure of noncompactness. 相似文献
993.
General limit theorems are established for l~p-valued Gaussian random fields indexed by a multidimensional parameter,which contain both almost sure moduli of continuity and limits of large increments for the l~p-valued Gaussian random fields under(?)explicit conditions. 相似文献
994.
D. Boilley A. Marchix B. Jurado K. -H. Schmidt 《The European Physical Journal A - Hadrons and Nuclei》2007,33(1):47-52
We propose a new formula for the saddle-to-scission time that is more general that the one based on Kramers' approach. Its
validity and applicability is then studied in detail. Such a formula is useful for the evaluation of the fission time of very
heavy nuclei. 相似文献
995.
Andrea Vietri 《Graphs and Combinatorics》2007,23(1):111-121
We analyse 3-subset difference families of Z2d+1⊕Z2d+1 arising as reductions (mod 2d+1) of particular families of 3-subsets of Z⊕Z. The latter structures, namely perfect d-families, can be viewed as 2-dimensional analogues of difference triangle sets having the least scope. Indeed, every perfect d-family is a set of base blocks which, under the natural action of the translation group Z⊕Z, cover all edges {(x,y),(x′,y′)} such that |x−x′|, |y−y′|≤d. In particular, such a family realises a translation invariant (G,K3)-design, where V(G)=Z⊕Z and the edges satisfy the above constraint. For that reason, we regard perfect families as part of the hereby defined translation designs, which comprise and slightly generalise many structures already existing in the literature. The geometric context allows
some suggestive additional definitions. The main result of the paper is the construction of two infinite classes of d-families. Furthermore, we provide two sporadic examples and show that a d-family may exist only if d≡0,3,8,11 (mod 12). 相似文献
996.
Yozo Miura Hiroyuki Dote Hiroyuki Kubonishi Kenichi Fukuda Tomoko Saka 《Journal of polymer science. Part A, Polymer chemistry》2007,45(6):1159-1169
A dendritic macroinitiator having 16 TEMPO‐based alkoxyamines, Star‐16 , was prepared by the reaction of a dendritic macroinitiator having eight TEMPO‐based alkoxyamines, [G‐3]‐OH , with 4,4′‐bis(chlorocarbonyl)biphenyl. The nitroxide‐mediated radical polymerization (NMRP) of styrene (St) from Star‐16 gave 16‐arm star polymers with PDI of 1.19–1.47, and NMPR of 4‐vinylpyridine from the 16‐arm star polymer gave 16‐arm star diblock copolymers with PDI of 1.30–1.43. The ring‐opening polymerization of ε‐caprolactone from [G‐3]‐OH and the subsequent NMRP of St gave AB8 9‐miktoarm star copolymers with PDI of 1.30–1.38. The benzyl ether linkages of the 16‐arm star polymers and the AB8 9‐miktoarm star copolymers were cleaved by treating with Me3SiI, and the resultant poly(St) arms were investigated by size exclusion chromatography (SEC). The SEC results showed PDIs of 1.23–1.28 and 1.18–1.22 for the star polymers and miktoarm stars copolymers, respectively, showing that they have well‐controlled poly(St) arms. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1159–1169, 2007. 相似文献
997.
Reaction of arenesulfonylimines of methyl trifluoropyruvate with 1,3-C,N-and-N,N-binucleophiles led to a variety of N-sulfonylated fluorine-containing heterocycles, including the fused ones.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2171–2175, November, 2007. 相似文献
998.
N-Acylalkylation of neutral and anionic N-nucleophiles with α-halocarbonyl compounds was investigated by quantum chemical methods
in terms of the density functional theory and by experimental methods for 2,3-dihydroimidazo[2,1-b]quinazolin-1(10)H-5-one, its N-anion, and simpler model structures. High reactivity of these reagents is determined primarily by stabilization
of transition states (TS) by bridge bonds involving halogen or nitrogen atoms rather than by conjugation, as has been commonly
accepted. Bridged TS are formed by both the substitution mechanism S
N
2 and the addition-elimination mechanism. α-Haloalkyl-substituted zwitterions, which are potential intermediates of stepwise
N-acylalkylation of neutral N-nucleophiles, do not exist in the isolated state, but they are rather efficiently stabilized
upon solvation. These zwitterions, as well as analogous O-anions generated from anionic N-nucleophiles, can serve as intermediates
of N-acylalkylation, as was demonstrated by localization of the corresponding TS.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1150–1164, June, 2007. 相似文献
999.
The adsorption behavior (capacity, density distribution and packing density) and the isosteric heat versus loading in a slit pore whose walls contain defective graphene layers are investigated in this paper. The defective wall is characterized by the extent and size of the defect. Simulation results obtained with the Grand Canonical Monte Carlo method reveal complex patterns of isosteric heat, and this complex behavior is a result of the interplay between three factors: (i) the surface heterogeneity (solid-fluid interaction, sites with varying degree of affinity), (ii) fluid-fluid interaction and (iii) the overlapping of potentials exerted by the two defective walls. We illustrate this with argon adsorption in pores of various sizes, and results obtained from the simulation agree qualitatively with the experimental data at 77 K on Saran microporous S600H and micro-mesoporous S84 charcoals of Beebe et al. [R.A. Beebe, B. Millard, J. Cynarski, J. Am. Chem. Soc. 75 (1953) 839]. The S600H was found to contain pores predominantly in the neighborhood of 7 Å with 30% of defect and a defective size of 2.84 Å. This is consistent with the argument made by Beebe et al. that this sample is a microporous solid and most pores can accommodate only one layer. The other sample, S84, has larger pores than S600H, and it is found that it has a wider pore size distribution and the pore width is centered at about 12 Å. 相似文献
1000.
Ignacio Villanueva 《Mathematische Nachrichten》2003,250(1):98-103
We clarify and prove in a simpler way a result of Taskinen about symmetric operators on C(Kn), K an uncountable metrizable compact space. To do this we prove that, for any compact space K and any n ∈ ?, the symmetric injective n–tensor product of C(K), , is complemented in C(BC(K)*), a result of independent interest. The techniques we develop allow us to extend the result in several directions. We also show that the hypothesis of metrizability and uncountability cannot be removed. 相似文献