全文获取类型
收费全文 | 311982篇 |
免费 | 2007篇 |
国内免费 | 772篇 |
专业分类
化学 | 133219篇 |
晶体学 | 3913篇 |
力学 | 18611篇 |
综合类 | 7篇 |
数学 | 66249篇 |
物理学 | 92762篇 |
出版年
2019年 | 1242篇 |
2018年 | 18380篇 |
2017年 | 18971篇 |
2016年 | 11270篇 |
2015年 | 3174篇 |
2014年 | 2886篇 |
2013年 | 6901篇 |
2012年 | 12086篇 |
2011年 | 26309篇 |
2010年 | 15674篇 |
2009年 | 16152篇 |
2008年 | 21252篇 |
2007年 | 26305篇 |
2006年 | 5967篇 |
2005年 | 13053篇 |
2004年 | 9180篇 |
2003年 | 8974篇 |
2002年 | 6208篇 |
2001年 | 4744篇 |
2000年 | 3913篇 |
1999年 | 2785篇 |
1998年 | 2483篇 |
1997年 | 2363篇 |
1996年 | 2326篇 |
1995年 | 2127篇 |
1994年 | 2063篇 |
1993年 | 1916篇 |
1992年 | 2132篇 |
1991年 | 2262篇 |
1990年 | 2051篇 |
1989年 | 2063篇 |
1988年 | 2012篇 |
1987年 | 1911篇 |
1986年 | 1833篇 |
1985年 | 2360篇 |
1984年 | 2493篇 |
1983年 | 2067篇 |
1982年 | 2231篇 |
1981年 | 2108篇 |
1980年 | 2047篇 |
1979年 | 2188篇 |
1978年 | 2353篇 |
1977年 | 2138篇 |
1976年 | 2209篇 |
1975年 | 2101篇 |
1974年 | 2139篇 |
1973年 | 2184篇 |
1972年 | 1412篇 |
1971年 | 1250篇 |
1968年 | 1189篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
201.
F. G. Gerasimato 《Journal of Mathematical Sciences》1991,57(5):3381-3383
We propose a simplified method of determining the integral characteristics of the opening of a parachute which makes it possible to compute the maximal stress on a parachute and the trajectory parameters of the motion of the load in the region of the opening of the parachute, and to determine the size of the portion of the canopy at the time of maximal stress.Translated fromDinamicheskie Sistemy, No. 6, 1987, pp. 38–41. 相似文献
202.
M. B. Wright 《The Journal of the Operational Research Society》1989,40(2):187-192
This paper addresses a problem common to all railway networks. Given a fixed train timetable and locomotives (or other forms of traction) of various types, each train must be allocated a locomotive. This paper examines the use of stochastic algorithms for such a problem. Two types of algorithm are used—a simple ‘local improvement’ method, performed successively from randomly chosen starting points, and a ‘simulated annealing’ approach. Both are found to give considerably better results than a deterministic method in current use, and the annealing approach is probably the better stochastic method. 相似文献
203.
204.
Vijaya Gracias Alan F. Gasiecki Joel D. Moore Irini Akritopoulou-Zanze Stevan W. Djuric 《Tetrahedron letters》2006,47(50):8977-8980
A general method for the preparation of diaza-spirocycles is reported. This method used an olefin metathesis in order to construct the desired spirocyclic framework. Beginning with commercially available protected amino ketones, this strategy ultimately produced pharmacologically relevant diaza-scaffolds in an efficient and high-yielding process. 相似文献
205.
M. F. Gamal' 《Journal of Mathematical Sciences》2006,134(4):2263-2271
We consider a class of C·0-contractions that is a generalization of the class of C·0-contractions with finite defect indices. Some results of Uchigama and Wu for C·0-contractions with finite defect indices are generalized: the lattices of hyperinvariant subspaces of such a contraction T
is isomorphic to that of its Jordan model and is generated by subspaces of the form Ker ϕ(T) and Ran ϕ(T), where ϕ ∈ H∞. The form of the inverse to an isomorphism of the invariant subspace lattices given by an intertwining quasiaffinity is also
studied. Next, for C·0-contractions in question, the characteristic disc related to the lattice of invariant subspaces is computed. Bibliography:
13 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 315, 2004, pp. 48–62. 相似文献
206.
Kurenkov V. F. Zaitseva O. A. Kirdyashova G. N. 《Russian Journal of Applied Chemistry》2002,75(4):641-644
The kinetics of radical copolymerization of acrylamide with lithium, sodium, and potassium 2-acrylamido-2-methylpropanesulfonates in concentrated aqueous solutions in the presence of potassium persulfate as initiating agent at pH 9 and 50°C was studied by dilatometry. 相似文献
207.
In this paper we suggest a unique model for estimating the operating cost of each of three waste-collection systems. Under the traditional system, which is widely used, waste is typically collected in plastic bags and a three-man crew is needed on each vehicle. The other two systems require a one-man crew for vehicle collecting street containers. The side-loader system with fixed body automatically empties street containers into the vehicle body and empties the load at the disposal site. The side-loader system with demountable body allows the separation of the waste collection phase from transport to the disposal site, since the vehicle body can be demounted. We also present two case studies and show how the estimation of operating costs is a critical issue in decisions regarding the type of system to be used for waste collection. 相似文献
208.
We consider the problem of contact of two elastic wedges and assume that only the vertices of the wedges touch before loading. After loading, the edges of both wedges come in contact near their common vertex. We reduce the constructed system of dual integral equations to a Fredholm integral equation of the second kind with difference kernel given on the semiaxis. We analytically solve the Fredholm equation by reducing it to the boundary-value Riemann problem for analytic functions. We obtain an analytic expression for contact stresses. 相似文献
209.
The behaviour of correlation functions of d=1$ interacting fermionic systems is determined by a small number of critical indices. We prove that one of them is exactly
zero. As a consequence, the behavior of the Fourier transform of the density-density correlation at zero momentum is qualitatively
unaffected by the interaction, contrary to what happens at , if is the Fermi momentum. The result is obtained by implementing Ward identities in a Renormalization Group approach.
Received: 12 November 2001 / Accepted: 25 February 2002?Published online: 2 October 2002 相似文献
210.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime. 相似文献