全文获取类型
收费全文 | 8946篇 |
免费 | 1124篇 |
国内免费 | 346篇 |
专业分类
化学 | 753篇 |
晶体学 | 14篇 |
力学 | 1032篇 |
综合类 | 324篇 |
数学 | 5486篇 |
物理学 | 2807篇 |
出版年
2024年 | 22篇 |
2023年 | 90篇 |
2022年 | 296篇 |
2021年 | 269篇 |
2020年 | 187篇 |
2019年 | 205篇 |
2018年 | 226篇 |
2017年 | 340篇 |
2016年 | 444篇 |
2015年 | 294篇 |
2014年 | 544篇 |
2013年 | 601篇 |
2012年 | 488篇 |
2011年 | 543篇 |
2010年 | 430篇 |
2009年 | 570篇 |
2008年 | 585篇 |
2007年 | 595篇 |
2006年 | 480篇 |
2005年 | 433篇 |
2004年 | 374篇 |
2003年 | 316篇 |
2002年 | 296篇 |
2001年 | 252篇 |
2000年 | 226篇 |
1999年 | 194篇 |
1998年 | 182篇 |
1997年 | 158篇 |
1996年 | 135篇 |
1995年 | 104篇 |
1994年 | 71篇 |
1993年 | 82篇 |
1992年 | 71篇 |
1991年 | 38篇 |
1990年 | 44篇 |
1989年 | 28篇 |
1988年 | 30篇 |
1987年 | 23篇 |
1986年 | 29篇 |
1985年 | 29篇 |
1984年 | 28篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1959年 | 5篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
水资源可再生能力综合评价的遗传加权物元模型 总被引:6,自引:0,他引:6
为了科学地计算水资源可再生能力评价指标的权重 ,使评价方法具有可操作性 ,采用主、客观相结合的赋权基点法 ,以全局收敛的格雷码加速遗传算法为工具来确定权重 ,并结合物元分析理论 ,建立了一种新的评价模型——遗传加权物元模型 .文中给出了该模型实施的详细步骤 ,对黄河流域 9个行政分区的水资源可再生能力进行了综合评价 ,取得了较好的效果 . 相似文献
912.
A pair of primal-dual integer programs is constructed for a class of problems motivated by a generalization of the concept of greatest common divisor. The primal-dual formulation is based on a number-theoretic, rather than a Lagrangian, duality property; consequently, it avoids the dualitygap common to Lagrangian duals in integer programming.This research was partially supported by the National Science Foundation, Grant No. DCR-74-20584 相似文献
913.
Hwangseo Park 《Journal of computational chemistry》2010,31(5):897-903
Backbone–backbone hydrogen bonds (BBHBs) are one of the most abundant interactions at the interface of protein–protein complex. Here, we propose an angle‐dependent potential energy function for BBHB based on density functional theory (DFT) calculations and the operation of a genetic algorithm to find the optimal parameters in the potential energy function. The angular part of the energy funtion is assumed to be the product of the power series of sine and cosine functions with respect to the two angles associated with BBHB. Two radial functions are taken into account in this study: Morse and Leonard‐Jones 12‐10 potential functions. Of these two functions under consideration, the former is found to be more accurate than the latter in terms of predicting the binding energies obtained from DFT calculations. The new HB potential function also compares well with the knowledge‐based potential derived by applying Boltzmann statistics for a variety of protein–protein complexes in protein data bank. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
914.
《Stochastic Processes and their Applications》2019,129(12):5278-5311
In this paper, we study the problem of sampling from a given probability density function that is known to be smooth and strongly log-concave. We analyze several methods of approximate sampling based on discretizations of the (highly overdamped) Langevin diffusion and establish guarantees on its error measured in the Wasserstein-2 distance. Our guarantees improve or extend the state-of-the-art results in three directions. First, we provide an upper bound on the error of the first-order Langevin Monte Carlo (LMC) algorithm with optimized varying step-size. This result has the advantage of being horizon free (we do not need to know in advance the target precision) and to improve by a logarithmic factor the corresponding result for the constant step-size. Second, we study the case where accurate evaluations of the gradient of the log-density are unavailable, but one can have access to approximations of the aforementioned gradient. In such a situation, we consider both deterministic and stochastic approximations of the gradient and provide an upper bound on the sampling error of the first-order LMC that quantifies the impact of the gradient evaluation inaccuracies. Third, we establish upper bounds for two versions of the second-order LMC, which leverage the Hessian of the log-density. We provide non asymptotic guarantees on the sampling error of these second-order LMCs. These guarantees reveal that the second-order LMC algorithms improve on the first-order LMC in ill-conditioned settings. 相似文献
915.
916.
917.
In this paper.by using the two-space method,homogenizedequations for steady heat conduction in the composite ma-terial cylinders with dilutely-distributed elliptic cylin-ders of impurities are derived.and the ezplicit ezpres-sions for the corresponding effective heat conductivity ofthose which are concerned are obtained.It is also shownthat the macroscopic heat conduction is anisotropic whenthe cross-sections of the impurity cylinders are unidirec-tionally oriented and isotropic when the angular distribu-tion of the cross-sections is uniform. 相似文献
918.
Régis Brugiere et Pierre Lucasson 《辐射效应与固体损伤》2013,168(1):55-57
The nature of the electron bombarded aluminium electrical recovery process has been studied by combining quenches with irradiations. Measured Frenkel pair formation rates per incident electrons as well as annealing kinetics emphasize the role of impurity interstitial trapping. 相似文献
919.
能量色散X荧光分析(EDXRF)过程中,存在吸收增强效应影响分析准确性的问题。利用EDXRF测量Fe、Ni、Zn三种元素与Cu的六组伪二元系样品,根据实验结果对元素间的影响特征和影响程度进行了分析。并利用La-chance-Trail算法得到三组元素间的影响因子数值,Cu和Fe以及Cu和Zn之间的影响效应随元素含量变化较明显,分别在0.38~0.70和0.43~0.65之间,Cu和Ni之间的影响效应不明显。对Cu-Zn二元系中Cu含量实际计算结果相对误差均在5%以内。 相似文献
920.
High-contrast imaging provided by a coronagraph is critical for the direction imaging of the Earth-like planet orbiting its
bright parent star. A major limitation for such direct imaging is the speckle noise that is induced from the wave-front error
of an optical system. We derive an algorithm for the wave-front measurement directly from 3 focal plane images. The 3 images
are achieved through a deformable mirror to provide specific phases for the optics system. We introduce an extra amplitude
modulation on one deformable mirror configuration to create an uncorrelated wave-front, which is a critical procedure for
wave-front sensing. The simulation shows that the reconstructed wave-front is consistent with the original wave-front theoretically,
which indicates that such an algorithm is a promising technique for the wave-front measurement for the high-contrast imaging.
Supported by the National Natural Science Foundation of China (Grant No. 10873024) 相似文献