全文获取类型
收费全文 | 18295篇 |
免费 | 2605篇 |
国内免费 | 2447篇 |
专业分类
化学 | 13368篇 |
晶体学 | 251篇 |
力学 | 947篇 |
综合类 | 235篇 |
数学 | 2226篇 |
物理学 | 6320篇 |
出版年
2024年 | 34篇 |
2023年 | 191篇 |
2022年 | 428篇 |
2021年 | 497篇 |
2020年 | 515篇 |
2019年 | 596篇 |
2018年 | 523篇 |
2017年 | 517篇 |
2016年 | 822篇 |
2015年 | 841篇 |
2014年 | 1087篇 |
2013年 | 1360篇 |
2012年 | 1476篇 |
2011年 | 1642篇 |
2010年 | 1244篇 |
2009年 | 1270篇 |
2008年 | 1418篇 |
2007年 | 1296篇 |
2006年 | 1222篇 |
2005年 | 1085篇 |
2004年 | 909篇 |
2003年 | 719篇 |
2002年 | 863篇 |
2001年 | 575篇 |
2000年 | 509篇 |
1999年 | 336篇 |
1998年 | 219篇 |
1997年 | 159篇 |
1996年 | 158篇 |
1995年 | 112篇 |
1994年 | 97篇 |
1993年 | 81篇 |
1992年 | 95篇 |
1991年 | 68篇 |
1990年 | 44篇 |
1989年 | 51篇 |
1988年 | 43篇 |
1987年 | 29篇 |
1986年 | 24篇 |
1985年 | 34篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1978年 | 20篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Let
d−1{(x1,…,xd)
d:x21+···+x2d=1} be the unit sphere of the d-dimensional Euclidean space
d. For r>0, we denote by Brp (1p∞) the class of functions f on
d−1 representable in the formwhere dσ(y) denotes the usual Lebesgue measure on
d−1,
and Pλk(t) is the ultraspherical polynomial.For 1p,q∞, the Kolmogorov N-width of Brp in Lq(
d−1) is given bythe left-most infimum being taken over all N-dimensional subspaces XN of Lq(
d−1).The main result in this paper is that for r2(d−1)2,where ANBN means that there exists a positive constant C, independent of N, such that C−1ANBNCAN.This extends the well-known Kashin theorem on the asymptotic order of the Kolmogorov widths of the Sobolev class of the periodic functions. 相似文献
32.
33.
Jong Chan Lee Jin Young Park So Young Yoon Yong Hun Bae Seung Jun Lee 《Tetrahedron letters》2004,45(1):191-193
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described. 相似文献
34.
In the ever fusion experiments in SWIP, pellet forming process was carried out through adjusting relative devices by staff member in site, which will make every pellet-forming process slight distinction and will result in pellet difference in shape, size and intensity. In the intervals of HL-2A discharges, staff member have to go site to accomplish the pellet-forming process, this wastes human power and increase the potential danger. So it is necessary to develop a remote control system to perform the pellet-forming process. The control system needs have the features of real-time, reliability and be easy to operate and maintain. 相似文献
35.
YBa2Cu3O7-x (YBCO) bulk is one of the most important high temperature superconducting materials for magnetic levitation applications, because it has a high magnetic irreversibility field Hirr at liquid nitrogen temperature, and can grow into large grains. The levitation force of YBCO bulk is proportional to the critical current density (Jc) and grain radius (r)[1], so higher Jc and r are appreciated for YBCO bulks to achieve higher levitation force. Now single-domain YBCO bulks up to s… 相似文献
36.
Deposition of Hydrogen-Free Silicon Nitride Thin Films by Microwave ECR plasma Enhanced Magnetron Sputtering at Room Temperature 下载免费PDF全文
Hydrogen-free silicon nitride (SiNx) films were deposited at room temperature by microwave electron cyclotron resonance (MW-ECR) plasma enhanced unbalance magnetron sputtering system. Both Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy are used to study the bonding type and the change of bonding structures of the silicon nitride films. The results indicate that the chemical structure and composition of SiNx films deposited by this technique depend strongly on the N2 flow rates, the stoichiometric SiNx film, which has the highest hardness of 22.9 GPa, could be obtained at lower N2 flow rate of 4 sccm. 相似文献
37.
The inhomogeneous Dirichlet problems concerning divergence form elliptic equations are studied. Optimal regularity requirements on the coefficients and domains for the W1,p theory, 1 < p < ∞, are obtained. The principal coefficients are supposed to be in the John‐Nirenberg space with small BMO seminorms. The domain is a Reifenberg domain. These conditions for the W1,p theory not only weaken the requirements on the coefficients but also lead to a more general geometric condition on the domains. In fact, these domains might have fractal dimensions. © 2004 Wiley Periodicals, Inc. 相似文献
38.
The first α‐diimine nickel(I) complex having a chloro bridge is reported. The centrosymmetric dinuclear structure of {[ArN?C(Me)C(Me)?NAr]NiCl}2[Ar?2,6?C6H3(i‐Pr)2] features two chelating α‐diimine ligands and two bridged chlorine atoms, so that a distorted tetrahedral N2Cl2 coordination geometry for nickel results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
39.
40.
GM(1,1)的周期修正模型及其在泉水流量预测中的应用 总被引:6,自引:2,他引:4
本文阐述了 GM( 1 ,1 )的残差周期修正模型 ,并将它应用于山西神头泉的流量预测中 ,建立了神头泉流量的 GM( 1 ,1 )周期修正模型 ,对其流量进行了预测 ,为神头泉域岩溶水资源开发利用和保护提供了科学依据 相似文献