全文获取类型
收费全文 | 12802篇 |
免费 | 419篇 |
国内免费 | 1723篇 |
专业分类
化学 | 8593篇 |
晶体学 | 129篇 |
力学 | 173篇 |
综合类 | 193篇 |
数学 | 1639篇 |
物理学 | 4217篇 |
出版年
2023年 | 100篇 |
2022年 | 153篇 |
2021年 | 135篇 |
2020年 | 164篇 |
2019年 | 184篇 |
2018年 | 137篇 |
2017年 | 188篇 |
2016年 | 194篇 |
2015年 | 175篇 |
2014年 | 288篇 |
2013年 | 784篇 |
2012年 | 587篇 |
2011年 | 590篇 |
2010年 | 543篇 |
2009年 | 826篇 |
2008年 | 857篇 |
2007年 | 959篇 |
2006年 | 821篇 |
2005年 | 719篇 |
2004年 | 638篇 |
2003年 | 501篇 |
2002年 | 436篇 |
2001年 | 390篇 |
2000年 | 1175篇 |
1999年 | 835篇 |
1998年 | 774篇 |
1997年 | 210篇 |
1996年 | 228篇 |
1995年 | 208篇 |
1994年 | 189篇 |
1993年 | 166篇 |
1992年 | 157篇 |
1991年 | 108篇 |
1990年 | 66篇 |
1989年 | 57篇 |
1988年 | 41篇 |
1987年 | 40篇 |
1986年 | 21篇 |
1985年 | 43篇 |
1984年 | 27篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 42篇 |
1980年 | 22篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1974年 | 12篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This article deals with Leibniz's reception of Descartes' “geometry.” Leibnizian mathematics was based on five fundamental notions: calculus, characteristic, art of invention, method, and freedom. On the basis of methodological considerations Leibniz criticized Descartes' restriction of geometry to objects that could be given in terms of algebraic (i.e., finite) equations: “Descartes's mind was the limit of science.” The failure of algebra to solve equations of higher degree led Leibniz to develop linear algebra, and the failure of algebra to deal with transcendental problems led him to conceive of a science of the infinite. Hence Leibniz reconstructed the mathematical corpus, created new (transcendental) notions, and redefined known notions (equality, exactness, construction), thus establishing “a veritable complement of algebra for the transcendentals”: infinite equations, i.e., infinite series, became inestimable tools of mathematical research. 相似文献
62.
??We study the linear quadratic optimal stochastic control problem which is jointly driven by Brownian motion and L\'{e}vy processes. We prove that the new affine stochastic differential adjoint equation exists an inverse process by applying the profound section theorem. Applying for the Bellman's principle of quasilinearization and a monotone iterative convergence method, we prove the existence and uniqueness of the solution of the backward Riccati differential equation. Finally, we prove that the optimal feedback control exists, and the value function is composed of the initial value of the solution of the related backward Riccati differential equation and the related adjoint equation. 相似文献
63.
First, this paper deals with lagrangean heuristics for the 0-1 bidimensional knapsack problem. A projected subgradient algorithm is performed for solving a lagrangean dual of the problem, to improve the convergence of the classical subgradient algorithm. Secondly, a local search is introduced to improve the lower bound on the value of the biknapsack produced by lagrangean heuristics. Thirdly, a variable fixing phase is embedded in the process. Finally, the sequence of 0-1 one-dimensional knapsack instances obtained from the algorithm are solved by using reoptimization techniques in order to reduce the total computational time effort. Computational results are presented. 相似文献
64.
不同方法制备的CO2-3替换磷灰石固溶体晶体化学的FTIR研究 总被引:1,自引:0,他引:1
采用不同方法制备了CO2-3替换的磷灰石固溶体,利用FTIR结合XRD对其进行了晶体化学研究,结果表明均相沉淀法制备的碳羟磷灰石(CHAP)属B型替换且替换方式是[CO3·OH]四面体替换[PO4]四面体;固相离子交换法制备的CHAP属A型替换且替换方式是[CO3]三角形配位体替换通道位置的OH-;固相反应法制备的碳氟磷灰石(CFAP)属B型替换,其替换方式是[CO3·F]四面体替换[PO4]四面体;sol-gel法制备的CHAP属AB混合型替换,其Ψ3分裂为Ψ3-1,Ψ3F,Ψ3-4.高斯函数法拟合表明Ψ3F峰是A型替换的Ψ3-2与B型替换的Ψ3-3的叠合.当WCO2-3<3.34%时,随CO2-3含量增加,A型替换量增大,且当WCO2-3=3.34%时达最大值,当3.34%<WCO2-3<7.52%时,随CO2-3含量增加,B型替换量增大,且当WCO2-3= 7.52%时亦到饱和. 相似文献
65.
利用莫尔条纹的准正弦特性的三维轮廓术 总被引:5,自引:0,他引:5
分析了两个矩形光栅迭合产生的莫尔条纹的光强分布特性,通过选择适当的光栅参数,可得到一个近似的正弦分划板,并把它用于三维面形测量中,实验结果表明,这种方法简单,易于自动处理,有广泛的实用价值。 相似文献
66.
M. A. Macrì C. Del Gratta L. Di Donato S. Di Luzio G. L. Romani S. Della Penna A. Pasquarelli 《Il Nuovo Cimento D》1994,16(5):425-432
Summary A preliminary study is here reported on a new potential marker for biomagnetic measurements. The marker consists of superparamagnetic
polymer microspheres which were detected in the presence of external steady magnetic fields by means of an r.f.-SQUID magnetometer.
The particles were prepared in samples differing in the concentration value and immersed in a homogeneous magnetic field of
variable intensity. A simple model was taken into account for the distribution of the microspheres in the samples, so that
the theoretical values were compared to the marker field values measured by the biomagnetic sensor. The overall sensitivity
of the experimental apparatus and the minimum concentration value of the marker were then estimated. 相似文献
67.
68.
69.
W.T. Ingram 《Topology and its Applications》2006,153(10):1530-1539
70.
A. S. Peregudov L. N. Usatova E. I. Smyslova E. I. Fedin D. N. Kravtsov 《Russian Chemical Bulletin》1995,44(8):1513-1519
It has been shown by the19F NMR method that the relative polarities of nitrogenelement bonds in 2-(4-fluorophenyl)benzimidazole and its PhHg and PPh3Au derivatives increase in the order N-H19F NMR. It has been found that these reactions occur by a bimolecular associative mechanism and that the N-H bond is substantially less reactive than the N-Hg and N-Au bonds, which have identical reactivities within the limits of sensitivity of the method used.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1574–1580, August, 1995.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No. 93-03-5528). 相似文献