全文获取类型
收费全文 | 209646篇 |
免费 | 32599篇 |
国内免费 | 22584篇 |
专业分类
化学 | 140180篇 |
晶体学 | 2358篇 |
力学 | 13602篇 |
综合类 | 1376篇 |
数学 | 26744篇 |
物理学 | 80569篇 |
出版年
2024年 | 655篇 |
2023年 | 3752篇 |
2022年 | 6799篇 |
2021年 | 7499篇 |
2020年 | 7779篇 |
2019年 | 7643篇 |
2018年 | 7019篇 |
2017年 | 6541篇 |
2016年 | 9719篇 |
2015年 | 9552篇 |
2014年 | 11713篇 |
2013年 | 15383篇 |
2012年 | 18219篇 |
2011年 | 18837篇 |
2010年 | 12857篇 |
2009年 | 12513篇 |
2008年 | 13358篇 |
2007年 | 12079篇 |
2006年 | 11246篇 |
2005年 | 9570篇 |
2004年 | 7368篇 |
2003年 | 5829篇 |
2002年 | 5368篇 |
2001年 | 4527篇 |
2000年 | 3992篇 |
1999年 | 4335篇 |
1998年 | 3741篇 |
1997年 | 3466篇 |
1996年 | 3567篇 |
1995年 | 3059篇 |
1994年 | 2810篇 |
1993年 | 2315篇 |
1992年 | 2066篇 |
1991年 | 1869篇 |
1990年 | 1515篇 |
1989年 | 1137篇 |
1988年 | 919篇 |
1987年 | 757篇 |
1986年 | 731篇 |
1985年 | 613篇 |
1984年 | 442篇 |
1983年 | 338篇 |
1982年 | 281篇 |
1981年 | 204篇 |
1980年 | 138篇 |
1979年 | 79篇 |
1978年 | 58篇 |
1976年 | 59篇 |
1975年 | 60篇 |
1974年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Recently, molecular imaging has been rapidly developed to studyphysiological and pathological processes in vivo at the cellularand molecular levels. Among molecular imaging modalities, opticalimaging has attracted a major attention for its unique advantages.In this paper, we establish a mathematical framework for multispectralbioluminescence tomography (BLT) that allows simultaneous studiesof multiple optical reporters. We show solution existence, uniquenessand continuous dependence on data as well as the limiting behaviourswhen the regularization parameter approaches zero or when thepenalty parameter approaches infinity. Then, we propose twonumerical schemes for multispectral BLT and derive error estimatesfor the corresponding solutions. 相似文献
62.
The crystal and molecular structure of the complex containing cobalt-carbon and iron-sulfur cluster cores, (μ-p-CH3C6H4C2S) (μ-n-C3H7S)Fe2(CO)6Co2(CO)6, has been determined by X-ray diffraction method. The crystals are triclinic, space group P&1bar;, with a — 9.139(2), b=9.610(1), c-17.183(2) Å, α = 84.36(1), β-89.45(1), γ=88.15(1)°, V-1501.0 Å3; Z=2, Dc=1.74 g/cm3. R=0.072, Rw=0.081. The results of the structure determination show a cobalt-carbon cluster core formed through the reaction of (μ-p-CH3C6H4C2S)(μ-n-C3H7S)Fe2(CO)6 with Co2(CO)8. In the cobalt-carbon cluster core, the bond length of the original C≡C lengthened to 1.324 Å which is close to the typical value of carbon-carbon double bond. The groups connecting the carbons of the cluster core are in cis position and lie on the opposite side of cobalt atoms. In this complex, the conformation of —SC3H7 is e-type, while that of —SC2C6H4CH3 is a-type. 相似文献
63.
A new chemiluminescence method for the determination of carbamazepine (CBZ) has been developed. The method is based on the chemiluminescence produced in the reaction of tris(2,2'-bipyridine)ruthenium(III) and CBZ in an acidic medium. The chemiluminescence intensity was enhanced by organic solvents in the reaction system. Under the optimum experimental conditions, the calibration curve was linear over the range 4.0 x 10(-3)-8.6 x 10(-7) mol/L for CBZ. The detection limit (S/N = 3) was 2.5 x 10(-7) mol/L and the relative standard deviation of six replicate measurements was 2.6% for 4.0 x 10(-4) mol/L of CBZ. The possible reaction mechanism were also discussed. The chemiluminescence method was successfully applied to assay the CBZ contents in pharmaceutical tablets. 相似文献
64.
本文利用比较原理以及一种特殊变换研究了一类非线性退化方程的混合问题,得到了这类复杂问题解的渐进性质。 相似文献
65.
溃坝问题的间断有限元方法 总被引:2,自引:0,他引:2
本文研究90年代初提出的Runge-Kutta间断Galerkin有限元方法,给出该方法的精度分析,通过经典算例验证该方法处理间断问题、捕捉锐利波形的能力,并将其推广到求解浅水问题.针对坝底无摩擦,无坡度的理想情形进行讨论,给出方溃坝和圆溃坝问题的数值模拟结果. 相似文献
66.
Various problems associated with optimal path planning for mobile observers such as mobile robots equipped with cameras to obtain maximum visual coverage of a surface in the three-dimensional Euclidean space are considered. The existence of solutions to these problems is discussed first. Then, optimality conditions are derived by considering local path perturbations. Numerical algorithms for solving the corresponding approximate problems are proposed. Detailed solutions to the optimal path planning problems for a few examples are given. 相似文献
67.
本文给出多目标规划有效解适应鞍点准则的一个新的判别法 ,它不使用凸性的几何术语及凸分析中的概念。最后给出单目标规划的一个相应的判别法 相似文献
68.
Chi-Kwong Li Ilya M. Spitkovsky 《Journal of Mathematical Analysis and Applications》2003,282(1):329-340
Existence of the fractional powers is established in Banach algebra setting, in terms of the numerical ranges of elements involved. The behavior of the spectra and (for Hermitian ∗-algebras satisfying some additional hypotheses) the ∗-numerical range under taking these powers also is investigated. 相似文献
69.
Zhen‐Feng Chen Hong‐Li Zhou Hong Liang Yan Li Ren‐Gen Xiong Xiao‐Zeng You 《应用有机金属化学》2003,17(11):883-884
The centrosymmetric binuclear structure of [Pb2(H‐Norf)2(ONO2)4]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
70.
Numerical studies were conducted to investigate the natural convection heat transfer around a uniformly heated thin plate
with arbitrary inclination in an infinite space. The numerical approach was based on the finite volume technique with a nonstaggered
grid arrangement. For handling the pressure–velocity coupling the SIMPLE-algorithm was used. QUICK scheme and first order
upwind scheme were employed for discretization of the momentum and energy convective terms respectively. Plate width and heating
rate were used to vary the modified Rayleigh number over the range of 4.8×106 to 1.87×108. Local and average heat transfer characteristics were compared with regarding to the inclination angle. The empirical expressions
for local and average Nusselt number were correlated. It has been found that for inclination angle less than 10∘, the flow and heat transfer characteristics are complicated and the average Nusselt number can not be correlated by one equation
while for inclination angle larger than 10∘, the average Nusselt number can be correlated into an elegant correlation.
Received on 18 April 2001 / Published online: 29 November 2001 相似文献