全文获取类型
收费全文 | 8745篇 |
免费 | 353篇 |
国内免费 | 61篇 |
专业分类
化学 | 5876篇 |
晶体学 | 47篇 |
力学 | 218篇 |
数学 | 1791篇 |
物理学 | 1227篇 |
出版年
2023年 | 71篇 |
2022年 | 119篇 |
2021年 | 238篇 |
2020年 | 162篇 |
2019年 | 200篇 |
2018年 | 163篇 |
2017年 | 143篇 |
2016年 | 318篇 |
2015年 | 270篇 |
2014年 | 309篇 |
2013年 | 529篇 |
2012年 | 626篇 |
2011年 | 693篇 |
2010年 | 421篇 |
2009年 | 446篇 |
2008年 | 568篇 |
2007年 | 578篇 |
2006年 | 529篇 |
2005年 | 477篇 |
2004年 | 388篇 |
2003年 | 270篇 |
2002年 | 271篇 |
2001年 | 112篇 |
2000年 | 98篇 |
1999年 | 82篇 |
1998年 | 66篇 |
1997年 | 69篇 |
1996年 | 99篇 |
1995年 | 52篇 |
1994年 | 55篇 |
1993年 | 52篇 |
1992年 | 69篇 |
1991年 | 47篇 |
1990年 | 42篇 |
1989年 | 38篇 |
1988年 | 34篇 |
1987年 | 30篇 |
1986年 | 38篇 |
1985年 | 53篇 |
1984年 | 48篇 |
1983年 | 32篇 |
1982年 | 36篇 |
1981年 | 30篇 |
1980年 | 28篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1975年 | 9篇 |
1974年 | 14篇 |
1971年 | 12篇 |
排序方式: 共有9159条查询结果,搜索用时 31 毫秒
171.
Luis Paris 《Geometriae Dedicata》1993,45(2):171-176
We denote by the complement of the complexification of a real arrangement of hyperplanes. It is known that there is a certain technical property, called property D, on real arrangements of hyperplanes such that: if a real arrangement of hyperplanes is simplicial then has property D, and if has property D then is aK(, 1) space. Our main goal is to prove that: if has property D then is simplicial. We also prove that a quasi-simplicial arrangement is always simplicial. 相似文献
172.
Jorge A. León 《Applied Mathematics and Optimization》1993,27(3):313-327
Let (X,l,) be a measure space, letW be a cylindrical Hilbert-Wiener process, and let be an anticipating integrable process-valued function onX. We prove, under natural assumptions on, that there exists a measurable version Yx,x X, of the anticipating integral of(x) such that the integral x Yx(dx) is a version of the anticipating integral of X
(x)(dx). We apply this anticipating Fubini theorem to study solutions of a class of stochastic evolution equations in Hilbert space. 相似文献
173.
Luis P. Chimento 《General Relativity and Gravitation》1993,25(10):979-989
The general solution to the semiclassical backreaction equation is found for conformally invariant free quantum fields in spatially flat homogeneous and isotropic spacetime with Cosmological constant and with no classical source when the ratio of the renormalisation parameters/=9/4. It contains a two-parameter family of bouncing solutions that avoid the singularity. There are several one-parameter families which do not have particle horizons. The stability of these solutions is investigated and it is found that they are stable when and have different signs. However, when both parameters have the same sign the set of stable solutions is restricted by the condition 0 < < 1/9. In both cases these solutions have a final de Sitter stage. 相似文献
174.
Luis O. Pimentel 《International Journal of Theoretical Physics》1993,32(6):979-984
The Weyl equation (massless Dirac equation) is studied in a family of exact solutions of the Einstein equations whose material content is a perfect fluid with stiff equation of state (p=) and which are of Bianchi type I. The field equation is solved exactly for some members of the family. 相似文献
175.
Using a version of density-functional theory which combines Onsager approximation and fundamental-measure theory for spatially nonuniform phases, we have studied the phase diagram of freely rotating hard rectangles and hard discorectangles. We find profound differences in the phase behavior of these models, which can be attributed to their different packing properties. Interestingly, bimodal orientational distribution functions are found in the nematic phase of hard rectangles, which cause a certain degree of biaxial order, albeit metastable with respect to spatially ordered phases. This feature is absent in discorectangles, which always show unimodal behavior. This result may be relevant in the light of recent experimental results which have confirmed the existence of biaxial phases. We expect that some perturbation of the particle shapes (either a certain degree of polydispersity or even bimodal dispersity in the aspect ratios) may actually destabilize spatially ordered phases thereby stabilizing the biaxial phase. 相似文献
176.
Del Pópolo MG Lynden-Bell RM Kohanoff J 《The journal of physical chemistry. B》2005,109(12):5895-5902
Ab initio molecular dynamics simulations have been performed for the first time on the room-temperature organic ionic liquid dimethyl imidazolium chloride [DMIM][Cl] using density functional theory. The aim is to compare the local liquid structure with both that obtained from two different classical force fields and from neutron scattering experiments. The local structure around the cation shows significant differences compared to both the classical calculations and the neutron results. In particular, and unlike in the gas-phase ion pair, chloride ions tend to be located near a ring C-H proton in a position suggesting hydrogen bonding. The results are used to suggest ways in which the classical potentials may be improved. 相似文献
177.
[reaction: see text] A new nonchain 5-endo radical cyclization starting with xanthates was exploited in a short synthesis of (+/-)-alpha-lycorane and the erythrina ring system. 相似文献
178.
José Luis Baeza 《Tetrahedron letters》2007,48(21):3689-3693
To investigate the ability of 2-alkyl-2-carboxy-azetidines (Azx) to induce reverse turns when incorporated into peptides, RCO-Azx-l-Ala-NHMe dipeptide derivatives were selected as simplified tetrapeptide models, in which the azetidine residue is incorporated at the i + 1 position. Molecular modelling, 1H NMR and FTIR studies showed the high tendency of the model tetrapeptides to adopt γ-turn conformations, indicating that these azetidine-containing amino acids could serve as general γ-turn promoters. 相似文献
179.
Gámiz-Gracia L Cuadros-Rodrı́guez L Almansa-López E Soto-Chinchilla JJ Garcı́a-Campaña AM 《Talanta》2003,60(2-3):523-534
A new formal strategy in the multidimensional optimisation of the experimental variables affecting the chemiluminescence (CL) detection in flow injection analysis (FIA) is proposed here. The strategy implies several steps, being the most significant: selection of the variables to be studied and their experimental domain; use of a screening design to detect significant variables and interactions into the experimental region; study of the main effect of variables and second-order interactions; and finally application of a Draper-Lin small composite design (orthogonal) to obtain the optimum values of the significant variables. The methodology is applied to the determination of methylamine by FIA based on the use of the peroxyoxalate CL (PO-CL) reaction. Considering the high number of experiments required due to the different chemical and instrumental variables to be taken account and their adequate compatibility to obtain maximum sensitivity, the methodology offers a rigorous study of the main effects and interactions, achieving a reduction of experimental work. 相似文献
180.
Arturo Zizumbo Rosa Maria Félix-Navarro Jorge Cervantes-Jáuregui Felípe Avalos-Belmontes 《Silicon Chemistry》2005,2(5-6):265-269
Electrochemical formation of poly(phenylmethylsilane) in a divided cell containing a Teflon® neutral membrane was studied. The electrolysis of dichlorosilanes was carried out in a solution containing tetrahydrofuran + hexamethylphosphoramide as the solvent, tetrabutylammonium perchlorate as the support electrolyte and stainless steel as the cathode, with Pt and graphite as the resistant anodes or stainless steel as the sacrificial anode. Polysilanes with a number-average molecular weight in the range from 2,600 to 130,000 g/mol were obtained, depending on the conditions used. 相似文献