全文获取类型
收费全文 | 29299篇 |
免费 | 4732篇 |
国内免费 | 3609篇 |
专业分类
化学 | 12995篇 |
晶体学 | 346篇 |
力学 | 1897篇 |
综合类 | 402篇 |
数学 | 7724篇 |
物理学 | 14276篇 |
出版年
2024年 | 62篇 |
2023年 | 285篇 |
2022年 | 596篇 |
2021年 | 681篇 |
2020年 | 862篇 |
2019年 | 804篇 |
2018年 | 765篇 |
2017年 | 868篇 |
2016年 | 1130篇 |
2015年 | 999篇 |
2014年 | 1398篇 |
2013年 | 2825篇 |
2012年 | 1555篇 |
2011年 | 1947篇 |
2010年 | 1668篇 |
2009年 | 1938篇 |
2008年 | 1985篇 |
2007年 | 1979篇 |
2006年 | 1841篇 |
2005年 | 1681篇 |
2004年 | 1397篇 |
2003年 | 1425篇 |
2002年 | 1262篇 |
2001年 | 991篇 |
2000年 | 1001篇 |
1999年 | 864篇 |
1998年 | 696篇 |
1997年 | 609篇 |
1996年 | 562篇 |
1995年 | 424篇 |
1994年 | 400篇 |
1993年 | 322篇 |
1992年 | 296篇 |
1991年 | 249篇 |
1990年 | 157篇 |
1989年 | 175篇 |
1988年 | 128篇 |
1987年 | 98篇 |
1986年 | 94篇 |
1985年 | 116篇 |
1984年 | 92篇 |
1983年 | 39篇 |
1982年 | 72篇 |
1981年 | 54篇 |
1980年 | 39篇 |
1979年 | 46篇 |
1978年 | 24篇 |
1977年 | 29篇 |
1976年 | 22篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
171.
The use of liquid fuels such as kerosene is of interest for the pulse detonation engine (PDE). Within this context, the aim
of this work, which is a preliminary study, was to show the feasibility to initiate a detonation in air with liquid-fuel pyrolysis
products, using energies and dimensions of test facility similars to those of PDEs. Therefore, two liquids fuels have been
compared, JP10, which is a synthesis fuel generally used in the field of missile applications, and decane, which is one of
the major components of standard kerosenes (F-34, Jet A1, ...). The thermal degradation of these fuels was studied with two
pyrolysis processes, a batch reactor and a flow reactor. The temperatures varied from 600°C to 1,000°C and residence times
for the batch reactor and the flow reactor were, respectively, between 10–30 s and 0.1–2 s. Subsequently, the detonability
of synthetic gaseous mixtures, which was a schematisation of the decomposition state after the pyrolysis process, has been
studied. The detonability study, regarding nitrogen dilution and equivalence ratio, was investigated in a 50 mm-diameter,
2.5 m-long detonation tube. These dimensions are compatible with applications in the aircraft industry and, more particularly,
in PDEs. Therefore, JP10 and decane were compared to choose the best candidate for liquid-fuel PDE studies.
This paper was based on work that was presented at the 20th International Colloquium on the Dynamics of Explosions and Reactive
Systems, Montreal, Canada, July 31 – August 5, 2005. 相似文献
172.
In the present paper, a new two-parameter inverted equation of state (EOS) is developed which is found to be working very
well in the high-pressure region. To check its success and validity, this EOS has been applied in a number of solids. The
computed volume compression is found to be in very good agreement with the experimental data in the whole range of pressure
in all the solids. The minimum and the maximum pressure range used in the present study is 0–320 kbar and 0–3000 kbar, respectively. 相似文献
173.
Rolando Cavazos-Cadena 《Annals of Operations Research》1991,28(1):169-184
We consider a class of Markov decision processes withfinite state and action spaces which, essentially, is determined by the following condition: The state space isirreducible under the action of any stationary policy. However, except by this restriction, the transition law iscompletely unknown to the controller. In this context, we find a set of policies under which thefrequency estimators of the transition law are strongly consistent and then, this result is applied to constructadaptive asymptotically discount-optimal policies.Dedicated to Professor Truman O. Lewis, on the occasion of his sixtieth birthdayThis research was supported in part by the Third World Academy of Sciences (TWAS) under Grant TWAS RG MP 898-152, and in part by the Consejo Nacional de Ciencia y Tecnología (CONACYT) under Grant A128CCOEO550 (MT-2). 相似文献
174.
Ekatherina A. Karatsuba 《Numerical Algorithms》2007,45(1-4):127-137
A new approach to the study of the Jaynes–Cummings sum, which determines the atomic inversion in quantum model of a single
two-level atom interacting with a single mode of the quantized radiation field, based on the number theory theorems on approximation
of trigonometric sums is presented.
相似文献
175.
强色指数的一个新的上界 总被引:1,自引:0,他引:1
给出了图的强色指数的一个新的上界,并指出几类恰好达到该上界的图,从而改进了Erodoes和Nesetri的强色指数猜想,在某种意义上证明了这个猜想。 相似文献
176.
PURE STATE APPROACH TO C(x)_αZ_nLIBINGREN;LINQING(InstituteofMathematics,AcademiaSinica,Beijing100080,China.Projectsupportedbyth?.. 相似文献
177.
An efficient synthesis approach is developed which permits thecalculation of the steady-state frequency response of an assembly whichis comprised of linear components and nonlinear joints. Receptancematrices are used to characterize the linear components, which permitscondensation of the system to just the joint degrees-of-freedom.Furthermore, the calculated nonlinear joint forces are then used tostudy the power flow in the assembly, as well as detailed dynamicbehavior within the components. Integrated into the technique is acontinuation scheme which permits efficient parametric studies. 相似文献
178.
Hilbert空间上线性算子的Drazin可逆性 总被引:1,自引:0,他引:1
主要研究了Hilbert空间上两个Drazin可逆算子和的Drazin可逆性.同时,对上三角算子矩阵的Drazin可逆性也给出了详细的讨论. 相似文献
179.
A general framework is developed to treat inverse problems with parameters that are random fields. It involves a sampling
method that exploits the sensitivity derivatives of the control variable with respect to the random parameters. As the sensitivity
derivatives are computed only at the mean values of the relevant parameters, the related extra cost of the present method
is a fraction of the total cost of the Monte Carlo method. The effectiveness of the method is demonstrated on an example problem
governed by the Burgers equation with random viscosity. It is specifically shown that this method is two orders of magnitude
more efficient compared to the conventional Monte Carlo method. In other words, for a given number of samples, the present
method yields two orders of magnitude higher accuracy than its conventional counterpart. 相似文献
180.
复方单硝酸异山梨酯-阿司匹林双缓释微丸胶囊的研制(Ⅱ) 总被引:2,自引:0,他引:2
以乙基纤维素、丙烯酸树脂Ⅱ和丙烯酸树脂Ⅲ为骨架材料分别制备单硝酸异山梨酯和阿司匹林混合骨架缓释微丸,并通过包薄膜衣进一步控制药物的释放。通过测定微丸的释放度对处方工艺进行评价,选择最佳微丸灌装胶囊.胶囊中两种药物均达到良好的缓释效果。符合中国药典对缓释制剂的要求.其体外释放过程同时符合Higuchi方程和一级释药方程,R^2值均在0.995以上。 相似文献