全文获取类型
收费全文 | 329915篇 |
免费 | 3044篇 |
国内免费 | 933篇 |
专业分类
化学 | 164769篇 |
晶体学 | 5374篇 |
力学 | 15531篇 |
综合类 | 7篇 |
数学 | 38464篇 |
物理学 | 109747篇 |
出版年
2021年 | 3132篇 |
2020年 | 3330篇 |
2019年 | 3760篇 |
2018年 | 5198篇 |
2017年 | 5439篇 |
2016年 | 7368篇 |
2015年 | 4139篇 |
2014年 | 7028篇 |
2013年 | 15904篇 |
2012年 | 12375篇 |
2011年 | 14824篇 |
2010年 | 11012篇 |
2009年 | 10913篇 |
2008年 | 13233篇 |
2007年 | 13191篇 |
2006年 | 12137篇 |
2005年 | 10520篇 |
2004年 | 9832篇 |
2003年 | 8685篇 |
2002年 | 8672篇 |
2001年 | 10393篇 |
2000年 | 7655篇 |
1999年 | 5967篇 |
1998年 | 4973篇 |
1997年 | 4811篇 |
1996年 | 4480篇 |
1995年 | 3864篇 |
1994年 | 3820篇 |
1993年 | 3701篇 |
1992年 | 4096篇 |
1991年 | 4306篇 |
1990年 | 4096篇 |
1989年 | 4008篇 |
1988年 | 3779篇 |
1987年 | 3917篇 |
1986年 | 3683篇 |
1985年 | 4629篇 |
1984年 | 4681篇 |
1983年 | 3885篇 |
1982年 | 3973篇 |
1981年 | 3697篇 |
1980年 | 3647篇 |
1979年 | 3913篇 |
1978年 | 3901篇 |
1977年 | 3906篇 |
1976年 | 3879篇 |
1975年 | 3675篇 |
1974年 | 3615篇 |
1973年 | 3650篇 |
1972年 | 2603篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
We study initial boundary value problems for linear scalar evolutionpartial differential equations, with spatial derivatives ofarbitrary order, posed on the domain {t > 0, 0 < x <L}. We show that the solution can be expressed as an integralin the complex k-plane. This integral is defined in terms ofan x-transform of the initial condition and a t-transform ofthe boundary conditions. The derivation of this integral representationrelies on the analysis of the global relation, which is an algebraicrelation defined in the complex k-plane coupling all boundaryvalues of the solution. For particular cases, such as the case of periodic boundaryconditions, or the case of boundary value problems for even-orderPDEs, it is possible to obtain directly from the global relationan alternative representation for the solution, in the formof an infinite series. We stress, however, that there existinitial boundary value problems for which the only representationis an integral which cannot be written as an infinite series.An example of such a problem is provided by the linearized versionof the KdV equation. Similarly, in general the solution of odd-orderlinear initial boundary value problems on a finite intervalcannot be expressed in terms of an infinite series. 相似文献
162.
We obtain exponential upper bounds for tails of distributions of generalized L-statistics based on a sample from an exponential distribution. We prove the asymptotic normality of generalized L-statistics based on a sample from the uniform distribution on [0,1] and of L-statistics with decomposed kernels (without any restrictions on the sample distribution type). 相似文献
163.
The first stage in a multi-attribute value analysis is the development of a hierarchical structure of the attributes of the problem. This paper reports the process of developing such a structure for the problem of choosing a suitable mode of transport for radioactive waste. The initial hierarchy of attributes went through several stages of development as new insights emerged about the nature of the problem. Some of the reasons behind this restructuring are discussed, and several important questions about the structuring process are formulated. 相似文献
164.
S. F. Dubinin V. E. Arkhipov S. G. Teploukhov V. D. Parkhomenko 《Physics of the Solid State》2003,45(11):2147-2151
The {1/2, 0, 1/2} nuclear superstructure in an La0.93Sr0.07MnO3 manganite orthorhombic crystal is revealed using thermal-neutron diffraction. It is demonstrated that this superlattice belongs to the class of distortion-type structures and is directly associated with a 1/16-type ordering of Mn4+ and Mn3+ ions in a collinear ferromagnetic phase of the La0.93Sr0.07MnO3 manganite. 相似文献
165.
达草灭对莱茵衣藻(Chlamydomonas reinhardtii) 品系遗传后效应的研究 总被引:1,自引:0,他引:1
通过将莱菌衣藻(Chlamydomonas reinhardtii)6种达草灭抗性突变株分别与野生型株、丧失合成叶绿素b能力的cbnI-43等基因突变株和精氨酸依赖型突变株杂交对其后代进行四分析与随机分析,发现在Nfr-4-Nfr-7突变株中达草灭抗性状只有单一核基因遗传的性质,而在Nfr-1、Nfr-3~Nfr-7抗性株的抗性性状都是由同一个nfr-1基因(norflurazon resisanse)的突变所决定的,而Nfr-4抗性株的抗性性状是由另一滚突变等位基因nfr-2所决定的。在Nfr-1和Nfr-3抗性株中除了nfr-1基因的突变还有nfr-3基因突变的参与。 相似文献
166.
O. Perru F. Ibrahim O. Bajeat C. Bourgeois F. Clapier E. Cottereau C. Donzaud M. Ducourtieux S. Galès D. Guillemaud-Mueller C. Lau H. Lefort F. Le Blanc A. C. Mueller J. Obert N. Pauwels J. C. Potier F. Pougheon J. Proust B. Roussière J. Sauvage O. Sorlin D. Verney 《Physics of Atomic Nuclei》2003,66(8):1421-1427
The PARRNe facility has been used to produce neutron-rich isotopes 83,84Gaby the ISOL method. Their decay has been studied, and β-γ coincidence and γ-γ coincidence data were collected as a function of time. The first two excited levels in 83Ge and the first excited level in 84Ge have been measured for the first time. 相似文献
167.
Lobanovsky L. S. Troyanchuk I. O. 《Journal of Experimental and Theoretical Physics》2003,96(2):331-334
Journal of Experimental and Theoretical Physics - The magnetoresistance effect in the SmCu3Mn4O12 compound with a perovskite-like structure is investigated for the first time. It is found that an... 相似文献
168.
A self-consistent, completely quantum calculation of the structure of the inner crust of neutron stars is carried out in the Wigner-Seitz approximation with a realistic phenomenological nuclear energy functional, where pair correlations of neutrons and protons are included in the explicit form. It has been shown that the superfluidity of neutrons and protons affects the structure of the ground state of the crust. 相似文献
169.
We examine several interesting relationships and expressions involving Fourier-Feynman transform, convolution product and
first variation for functionals in the Fresnel class F(B) of an abstract Wiener space B. We also prove a translation theorem and Parseval's identity for the analytic Feynman integral.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
170.
The interaction between multiple incompressible air jets has been studied numerically and experimentally. The numerical predictions have been first validated using experimental data for a single jet configuration. The spreading features of five unequal jets in the configuration of one larger central jet surrounded by four smaller equi‐distant jets, have been studied, for different lateral spacing ratios of 1.5, 2.0 and 2.5 and a central jet Reynolds number of 1.24×105 (corresponding to a Mach number of 0.16). Flow of five equal jets has also been simulated, for the sake of comparison. The jet interactions commence at an axial distance of about 3–4 diameters and complete by an axial distance of about 10 diameters for the lowest spacing ratio of 1.5. For larger spacing ratios, the length required for the start and completion of jet interaction increase. Peripheral jets bend more towards the central jet and merge at a smaller distance, when their sizes are smaller than that of the central jet. The entrainment ratio for multiple jets is higher than that for a single jet. Excellent agreement is observed between the experimental data and theoretical predictions for both mean flow field and turbulent quantities, at regions away from the jet inlet. The potential core length and initial jet development, however, are not predicted very accurately due to differences in the assumed and actual velocity profiles at the jet inlet. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献