全文获取类型
收费全文 | 1357299篇 |
免费 | 29238篇 |
国内免费 | 7781篇 |
专业分类
化学 | 681891篇 |
晶体学 | 20434篇 |
力学 | 74984篇 |
综合类 | 105篇 |
数学 | 242068篇 |
物理学 | 374836篇 |
出版年
2021年 | 13499篇 |
2020年 | 15908篇 |
2019年 | 16046篇 |
2018年 | 13211篇 |
2016年 | 28020篇 |
2015年 | 20816篇 |
2014年 | 30374篇 |
2013年 | 74333篇 |
2012年 | 38551篇 |
2011年 | 36072篇 |
2010年 | 37553篇 |
2009年 | 39720篇 |
2008年 | 35388篇 |
2007年 | 31321篇 |
2006年 | 36900篇 |
2005年 | 29720篇 |
2004年 | 30538篇 |
2003年 | 28815篇 |
2002年 | 29785篇 |
2001年 | 29548篇 |
2000年 | 25553篇 |
1999年 | 22861篇 |
1998年 | 21139篇 |
1997年 | 21095篇 |
1996年 | 21138篇 |
1995年 | 19180篇 |
1994年 | 18625篇 |
1993年 | 18192篇 |
1992年 | 18389篇 |
1991年 | 18641篇 |
1990年 | 17912篇 |
1989年 | 17914篇 |
1988年 | 17497篇 |
1987年 | 17481篇 |
1986年 | 16417篇 |
1985年 | 22823篇 |
1984年 | 23955篇 |
1983年 | 20075篇 |
1982年 | 21692篇 |
1981年 | 20940篇 |
1980年 | 20282篇 |
1979年 | 20617篇 |
1978年 | 21789篇 |
1977年 | 21471篇 |
1976年 | 21179篇 |
1975年 | 19940篇 |
1974年 | 19565篇 |
1973年 | 20061篇 |
1972年 | 14527篇 |
1967年 | 12779篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
892.
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
893.
The correlation between the parameters of the Agrawal-Thodos equation, the fundamentalconstants of a substance are established. A modified equation is proposed, in which the minimum set of easily measurable properties of the substance is used as input data. 相似文献
894.
Shunin D. G. Filippova A. G. Okhotina N. A. Liakumovich A. G. Samuilov Ya. D. 《Russian Journal of Applied Chemistry》2002,75(6):1020-1023
Procedures are discussed for production of rubber-bitumen compounds based on spent rubber items. A possibility of using these binders for paving is studied experimentally. 相似文献
895.
Tony Forbes. 《Mathematics of Computation》2002,71(237):449-452
We describe a successful search for a sequence of fifteen consecutive integers, each the product of exactly four prime factors. Fifteen is best possible.
896.
This paper deals with mathematical human resource planning; more specifically, it suggests a new model for a manpower‐planning system. In general, we study a k‐classed hierarchical system where the workforce demand at each time period is satisfied through internal mobility and recruitment. The motivation for this work is based on various European Union incentives, which promote regional or local government assistance programs that could be exploited by firms not only for hiring and training newcomers, but also to improve the skills and knowledge of their existing personnel. In this respect, in our augmented mobility model we establish a new ‘training/standby’ class, which serves as a manpower inventory position for potential recruits. This class, which may very well be internal or external to the system, is incorporated into the framework of a non‐homogeneous Markov chain model. Furthermore, cost objectives are employed using the goal‐programming approach, under different operating assumptions, in order to minimize the operational cost in the presence of system's constraints and regulations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
897.
C.J. Wu 《Applied Acoustics》2002,63(10):1143-1154
This work formulates the double-layer structural-acoustic coupling problem for cylindrical shell by using a combination of the wave-number domain approach (WDA) and the boundary integral equation (BIE). Expressions for the spectral radial velocity of the outer surface of a finite fluid-filled/submerged (FFS) cylindrical thin shell are formulated by means of the transfer matrix equation in wave-number domain. It is shown that the spectral variables on the inner surface of the shell are related to those on the outer surface of the shell. The far field sound radiation from this kind of shell is numerically evaluated for various fluid cases. An experimental verification is performed, and a good correlation between the theoretical results and the experimental results shows that the theoretical study work in this paper is correct. 相似文献
898.
Using Brown's construction (J. Algebra 15 (1970) 103) of an exact 6-term sequence for a fibration of groupoids we show how an exact 9-term sequence can be associated to a fibration of bigroupoids. Applications to topology and algebra are given. 相似文献
899.
A Hodge structure V of weight k on which a CM field acts defines, under certain conditions, a Hodge structure of weight , its half twist. In this paper we consider hypersurfaces in projective space with a cyclic automorphism which defines an
action of a cyclotomic field on a Hodge substructure in the cohomology. We determine when the half twist exists and relate
it to the geometry and moduli of the hypersurfaces. We use our results to prove the existence of a Kuga-Satake correspondence
for certain cubic 4-folds.
Received: 25 August 2000; in final form: 8 January 2001 / Published online: 18 January 2002 相似文献
900.
ON THE UNIQUENESS OF THE WEAK SOLUTIONS OF A QUASILINEAR HYPERBOLIC SYSTEM WITH A SINGULAR SOURCE TERM 下载免费PDF全文
This paper is a continuation of the authors'previous paper[1].In this paper the authorsprove,assuming additional conditions on the initial data,some results about the existence anduniqueness of the entropy weak solutions of the Cauchy problem for the singular hyperbolicsystem a_t+(au)_x_2au/x=0,u_t+1/2(a~2+u~2)_x=0,x>0,t≥0. 相似文献