全文获取类型
收费全文 | 41719篇 |
免费 | 3206篇 |
国内免费 | 2540篇 |
专业分类
化学 | 21000篇 |
晶体学 | 198篇 |
力学 | 1349篇 |
综合类 | 817篇 |
数学 | 12032篇 |
物理学 | 12069篇 |
出版年
2023年 | 332篇 |
2022年 | 510篇 |
2021年 | 1495篇 |
2020年 | 965篇 |
2019年 | 1078篇 |
2018年 | 810篇 |
2017年 | 914篇 |
2016年 | 1121篇 |
2015年 | 1116篇 |
2014年 | 1570篇 |
2013年 | 2817篇 |
2012年 | 1793篇 |
2011年 | 2016篇 |
2010年 | 1917篇 |
2009年 | 2517篇 |
2008年 | 2658篇 |
2007年 | 2830篇 |
2006年 | 2209篇 |
2005年 | 1457篇 |
2004年 | 1365篇 |
2003年 | 1435篇 |
2002年 | 1338篇 |
2001年 | 1262篇 |
2000年 | 966篇 |
1999年 | 806篇 |
1998年 | 787篇 |
1997年 | 539篇 |
1996年 | 569篇 |
1995年 | 534篇 |
1994年 | 539篇 |
1993年 | 548篇 |
1992年 | 574篇 |
1991年 | 380篇 |
1990年 | 325篇 |
1989年 | 272篇 |
1988年 | 306篇 |
1987年 | 269篇 |
1986年 | 261篇 |
1985年 | 372篇 |
1984年 | 290篇 |
1983年 | 174篇 |
1982年 | 339篇 |
1981年 | 527篇 |
1980年 | 493篇 |
1979年 | 531篇 |
1978年 | 429篇 |
1977年 | 317篇 |
1976年 | 279篇 |
1974年 | 88篇 |
1973年 | 175篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Anton Schiela 《Numerical Functional Analysis & Optimization》2019,40(1):85-118
We propose a cubic regularization algorithm that is constructed to deal with nonconvex minimization problems in function space. It allows for a flexible choice of the regularization term and thus accounts for the fact that in such problems one often has to deal with more than one norm. Global and local convergence results are established in a general framework. 相似文献
93.
Jianglin Zhao Yong Yan Lizhuang Huang Run Yang 《Mathematical Methods in the Applied Sciences》2019,42(11):3831-3847
This paper deals with a diffusive toxin producing phytoplankton‐zooplankton model with maturation delay. By analyzing eigenvalues of the characteristic equation associated with delay parameter, the stability of the positive equilibrium and the existence of Hopf bifurcation are studied. Explicit results are derived for the properties of bifurcating periodic solutions by means of the normal form theory and the center manifold reduction for partial functional differential equations. Numerical simulations not only agree with the theoretical analysis but also exhibit the complex behaviors such as the period‐3, 5, 6, 7, 8, 11, and 12 solutions, cascade of period‐doubling bifurcation in period‐2, 4, quasi‐periodic solutions, and chaos. The key observation is that time delay may control harmful algae blooms (HABs). Moreover, numerical simulations show that the chaotic states induced by the period‐doubling bifurcation are purely temporal, which is stationary in space and oscillatory in time. The investigations may provide some new insights on harmful phytoplankton blooms. 相似文献
94.
Balázs Gerencsér 《Stochastic Processes and their Applications》2019,129(9):3570-3584
The paper concerns a particular example of the Gibbs sampler and its mixing efficiency. Coordinates of a point are rerandomized in the unit square to approach a stationary distribution with density proportional to for with some large parameter .Diaconis conjectured the mixing time of this process to be which we confirm in this paper. This improves on the currently known estimate. 相似文献
95.
96.
Haijuan Zhi Zhenwei Li Yanping Deng Peng Qi Jinjun Hou Wen Deng Jinle Cheng Wanying Wu Dean Guo 《Biomedical chromatography : BMC》2019,33(2)
Salvia miltiorrhiza, one of the most well‐known herbal medicines, is commonly used for the treatment of coronary heart diseases in China. Besides traditional decoction slices (TDS), another relatively new product of S. miltiorrhiza, ultrafine granular powder (UGP; D90 < 45 μm), is also increasingly being used. In this paper, a UHPLC‐LTQ‐Orbitrap MS technique was developed for a metabolite profile study after oral administration of UGP and TDS of S. miltiorrhiza. The results showed that the number of in vivo absorbed compounds from UGP was much greater than that from TDS, and different types of products from S. miltiorrhiza will have different metabolic processes in vivo. Furthermore, a UHPLC‐Q‐Trap MS/MS method for simultaneously determining four tanshinones (tanshinone IIA, dihydrotanshinone I, tanshinone I and cryptotanshinone) was established and applied to assess the pharmacokinetics of the two types of products. All of the analytes displayed significant higher area under the concentration–time curve and peak concentration after oral administration of UGP than after TDS, indicating that ultrafine powder product could improve the bioavailability and absorption of cryptotanshinon,tanshinone II A,dihydrotanshinonE I and tanshinone I in vivo. The present study provides scientific information for further exploration of the pharmacology of these two types of S. miltiorrhiza and offers a reference for clinical administration of S. miltiorrhiza. 相似文献
97.
Fereshteh K. Yousefi Ali Jannesari Shahla Pazokifard Mohammad Reza Saeb Alison J. Scott Alexander Penlidis 《大分子反应工程》2019,13(4)
Ternary monomer reactivity ratios of triisopropylsilyl acrylate (SiA), methyl methacrylate (MMA), and n‐butyl acrylate (BA), as common monomers in self‐polishing coatings (SPCs) binders are obtained using experimental data collected from free radical bulk polymerization at 70 °C. Different terpolymerizations at low and medium‐high conversions are performed at optimized feed compositions. Estimations are made using the error‐in‐variables model (EVM) framework, applying the recast form of the Alfrey–Goldfinger (AG) model and a direct numerical integration (DNI) approach to the collected data. Estimations from individual low and medium‐high conversion data are compared to those found with the combined data (full conversion range data). The highest certainty in point estimates are obtained with analysis of the full conversion range data. Furthermore, the reactivity ratios determined from the combined data fall between those found with analysis of individual low and medium‐high conversion data, another corroboration of reliable data collection. Reactivity ratios determined from analysis of the combined data (rSiA/MMA = 0.4185, rMMA/SiA = 1.3754, rSiA/BA = 0.8739, rBA/SiA = 0.5736, rBA/MMA = 0.3692, rMMA/BA = 1.7919) are used in the recast AG model to predict cumulative terpolymer composition as a function of conversion. The experimental data and model prediction show satisfactory agreement. 相似文献
98.
Let K and S be locally compact Hausdorff spaces and let X be a strictly convex Banach space of finite dimension at least 2. In this paper, we prove that if there exists an isomorphism T from onto satisfying then K and S are homeomorphic. Here denotes the Schäffer constant of X. Even for the classical cases , and , this result is the X‐valued Banach–Stone theorem via isomorphism with the largest distortion that is known so far, namely . On the other hand, it is well known that this result is not true for , even though K and S are compact Hausdorff spaces. 相似文献
99.
Yasuhito Tanaka 《Operations Research Letters》2019,47(5):406-409
We study a dynamic free-entry oligopoly with sluggish entry and exit of firms under general demand and cost functions. We show that the number of firms in a steady-state open-loop solution for a dynamic free-entry oligopoly is smaller than that at static equilibrium and that the number of firms in a steady-state memoryless closed-loop solution is larger than that in an open-loop solution. 相似文献
100.
Bilender P. Allahverdiev 《Mathematical Methods in the Applied Sciences》2019,42(1):229-236
In this study, maximal dissipative second‐order dynamic operators on semi‐infinite time scale are studied in the Hilbert space , that the extensions of a minimal symmetric operator in limit‐point case. We construct a self‐adjoint dilation of the dissipative operator together with its incoming and outgoing spectral representations so that we can determine the scattering function of the dilation as stated in the scheme of Lax‐Phillips. Moreover, we construct a functional model of the dissipative operator and identify its characteristic function in terms of the Weyl‐Titchmarsh function of a self‐adjoint second‐order dynamic operator. Finally, we prove the theorems on completeness of the system of root functions of the dissipative and accumulative dynamic operators. 相似文献