全文获取类型
收费全文 | 13503篇 |
免费 | 752篇 |
国内免费 | 1131篇 |
专业分类
化学 | 2116篇 |
晶体学 | 67篇 |
力学 | 249篇 |
综合类 | 216篇 |
数学 | 6550篇 |
物理学 | 1070篇 |
综合类 | 5118篇 |
出版年
2024年 | 13篇 |
2023年 | 67篇 |
2022年 | 202篇 |
2021年 | 223篇 |
2020年 | 246篇 |
2019年 | 309篇 |
2018年 | 295篇 |
2017年 | 273篇 |
2016年 | 284篇 |
2015年 | 327篇 |
2014年 | 466篇 |
2013年 | 729篇 |
2012年 | 638篇 |
2011年 | 720篇 |
2010年 | 709篇 |
2009年 | 828篇 |
2008年 | 826篇 |
2007年 | 944篇 |
2006年 | 870篇 |
2005年 | 683篇 |
2004年 | 677篇 |
2003年 | 596篇 |
2002年 | 531篇 |
2001年 | 450篇 |
2000年 | 475篇 |
1999年 | 432篇 |
1998年 | 369篇 |
1997年 | 341篇 |
1996年 | 279篇 |
1995年 | 206篇 |
1994年 | 208篇 |
1993年 | 184篇 |
1992年 | 168篇 |
1991年 | 112篇 |
1990年 | 126篇 |
1989年 | 102篇 |
1988年 | 77篇 |
1987年 | 70篇 |
1986年 | 41篇 |
1985年 | 39篇 |
1984年 | 47篇 |
1983年 | 18篇 |
1982年 | 33篇 |
1981年 | 32篇 |
1980年 | 28篇 |
1979年 | 34篇 |
1978年 | 27篇 |
1977年 | 15篇 |
1976年 | 7篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 291 毫秒
891.
The strong consistency of least squares estimates in multiple regression models is established under minimal assumptions on the design and weak dependence and moment restrictions on the errors. 相似文献
892.
The asymptotic properties of maximum likelihood estimates of a vector ARMAX system are considered under general conditions, relating to the nature of the exogenous variables and the innovation sequence and to the form of the parameterization of the rational transfer functions, from exogenous variables and innovations to the output vector. The exogenous variables are assumed to be such that the sample serial covariances converge to limits. The innovations are assumed to be martingale differences and to be nondeterministic in a fairly weak sense. Stronger conditions ensure that the asymptotic distribution of the estimates has the same covariance matrix as for Gaussian innovations but these stronger conditions are somewhat implausible. With each ARMAX structure may be associated an integer (the McMillan degree) and all structures for a given value of this integer may be topologised as an analytic manifold. Other parameterizations and topologisations of spaces of structures as analytic manifolds may also be considered and the presentation is sufficiently general to cover a wide range of these. Greater generality is also achieved by allowing for general forms of constraints. 相似文献
893.
甘蓝型杂交油菜"蜀杂9号"种子纯度的RAPD鉴定 总被引:4,自引:0,他引:4
通过50个随机引物对“蜀杂9号”亲本进行RAPD扩增,选出了两个能在父、母本间产生多态性扩增的随机引物S18和S31,在杂种F,代中验证了它们的特异性和稳定性,证明随机引物S18和S31能分别在F1代中稳定扩增出父本和母本的特异标记片段S18750与S31550.对该引物的RAPD-PCR的反应体系优化后,对“蜀杂9号”父、母本和杂种F1代的单株进行了随机检测,结果表明这两个RAPD标记配合使用能稳定可靠地鉴定甘蓝型杂交油菜“蜀杂9号”种子的纯度. 相似文献
894.
Expression of lysine-rich protein gene and analysis of lysine content in transgenic wheat 总被引:2,自引:0,他引:2
MENGChaomin CHENXuqing LIANGRongqi YANGFengping ZHANGLiquan ZHANGXiaodong CHENTianyou S.S.M.Sun 《科学通报(英文版)》2004,49(19):2053-2057
Expression vector pBPC102, which carries winged bean lysine-rich protein (wblrp) gene and dihydropicolinate synthase (DHDPS) gene, was transferred into hexaploid winter wheat cv. Jinghua No.l, Jing411, You899 and Yangnongl5 explants of immature inflorescence and immature embryos by particle bombardment. More than 100 transgenic plants were obtained under the selection of s-(2-aminoethyl)-L-cysteine (AEC). Confirmed transgenic plants of To and TI generation by PCR and PCR-Southern blotting analyses showed successful integration of wblrp gene into wheat genome. Analysis of transgenic plant lines of T2 by Northern dot-blotting showed good expression of wblrp gene in offspring seed. The content of free lysine in leaves, contents of bound lysine and total proteins in seeds of T2 transgenie wheat lines were determined and analyzed. Among 34 tested transgenic lines, levels of free lysine content in leaves of 9 transgenic lines are 2~3times higher than un-trans-formed wild-type cultivars. Among 17 analyzed transgenic lines, bound lysine content of 4 transgenic lines is more than 10% higher than that of wild-type cultivars. Our research suggests that introducing wblrp gene into wheat is an effective way to improve its nutrition quality. 相似文献
895.
制备了[(Fe/Pt/Fe)/Ag]n多层膜,研究了不同温度退火后的微结构和磁特性.实验结果表明温度高于400℃退火后,样品开始形成L10相的FePt纳米颗粒与Ag基体的复合结构.ΔM曲线的测量表明FePt颗粒之间不存在交换作用,非常清楚地说明非磁基体Ag有效地隔离了FePt磁性颗粒.有序相的低温合成可能和多层膜结构所造成的界面扩散以及Ag层引入的界面缺陷有关,同时,Ag原子较强的迁移性以及FePt与Ag之间表面自由能的显著差异,使FePt纳米颗粒被Ag隔离.
关键词:
L10相
FePt
交换作用 相似文献
896.
Let L(x, v) be a Lagrangian which is convex and superlinear in the velocity variable v, and let H(x, p) be the associated Hamiltonian. Conditions are obtained under which every viscosity solution
of the Hamilton-Jacobi equation
is an action function in the large, i.e.,
for all
Received: 13 June 2003 相似文献
897.
We consider the Cauchy problem for the 2×2 nonstrictly hyperbolic system
898.
This paper is concerned with the existence, smoothness and attractivity of invariant manifolds for evolutionary processes on general Banach spaces when the nonlinear perturbation has a small global Lipschitz constant and locally Ck-smooth near the trivial solution. Such a nonlinear perturbation arises in many applications through the usual cut-off procedure, but the requirement in the existing literature that the nonlinear perturbation is globally Ck-smooth and has a globally small Lipschitz constant is hardly met in those systems for which the phase space does not allow a smooth cut-off function. Our general results are illustrated by and applied to partial functional differential equations for which the phase space (where r>0 and being a Banach space) has no smooth inner product structure and for which the validity of variation-of-constants formula is still an interesting open problem. 相似文献
899.
900.
Very few Banach spaces E are known for which the lattice of closed ideals in the Banach algebra of all (bounded, linear) operators on E is fully understood. Indeed, up to now the only such Banach spaces are, up to isomorphism, Hilbert spaces and the sequence spaces c0 and ?p for 1?p<∞. We add a new member to this family by showing that there are exactly four closed ideals in for the Banach space E?(⊕?2n)c0, that is, E is the c0-direct sum of the finite-dimensional Hilbert spaces ?21,?22,…,?2n,… . 相似文献