全文获取类型
收费全文 | 319578篇 |
免费 | 2616篇 |
国内免费 | 868篇 |
专业分类
化学 | 140638篇 |
晶体学 | 4343篇 |
力学 | 18293篇 |
综合类 | 3篇 |
数学 | 66531篇 |
物理学 | 93254篇 |
出版年
2021年 | 1285篇 |
2020年 | 1538篇 |
2019年 | 1636篇 |
2018年 | 18521篇 |
2017年 | 19124篇 |
2016年 | 11702篇 |
2015年 | 3587篇 |
2014年 | 3363篇 |
2013年 | 7423篇 |
2012年 | 12781篇 |
2011年 | 26949篇 |
2010年 | 16085篇 |
2009年 | 16427篇 |
2008年 | 21817篇 |
2007年 | 26666篇 |
2006年 | 6656篇 |
2005年 | 13489篇 |
2004年 | 9815篇 |
2003年 | 9645篇 |
2002年 | 6824篇 |
2001年 | 6207篇 |
2000年 | 4808篇 |
1999年 | 3499篇 |
1998年 | 2572篇 |
1997年 | 2575篇 |
1996年 | 2631篇 |
1995年 | 2353篇 |
1994年 | 2269篇 |
1993年 | 2091篇 |
1992年 | 2517篇 |
1991年 | 2583篇 |
1990年 | 2416篇 |
1989年 | 2392篇 |
1988年 | 2359篇 |
1987年 | 2341篇 |
1986年 | 2143篇 |
1985年 | 2663篇 |
1984年 | 2672篇 |
1983年 | 2144篇 |
1982年 | 2189篇 |
1981年 | 2024篇 |
1980年 | 2001篇 |
1979年 | 2306篇 |
1978年 | 2400篇 |
1977年 | 2211篇 |
1976年 | 2146篇 |
1975年 | 2033篇 |
1974年 | 1990篇 |
1973年 | 2053篇 |
1972年 | 1345篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
171.
P Vincent A BrioudeC Journet S RabasteS.T Purcell J Le BrusqJ.C Plenet 《Journal of Non》2002,311(2):130-137
We report here the successful inclusion of carbon nanotubes (CNs) into a TiO2 matrix prepared by a sol-gel method. The presence of CNs in the sol-gel matrix and the structure of the film were analyzed principally by transmission electron microscopy. Complementary information about the behavior of embedded carbon nanotubes versus heat treatment and ion irradiation were obtained by X-ray photoelectron spectroscopy. The elaboration of an inorganic matrix containing embedded carbon nanotubes leads to a new nanocomposite. The possible applications of this nanocomposite are discussed. 相似文献
172.
173.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
174.
Richard T. Hammond 《General Relativity and Gravitation》1991,23(9):973-980
It is shown that torsion can be built from two independent vector fields, and that these vector fields obey, for the Lagrangian chosen, the equations of electromagnetism with magnetic charge from the two photon formalism. The equation of motion follows from the Bianchi identity ofU
4 spacetime, and finally the interpretation of these fields is discussed. 相似文献
175.
We consider a randomized version of the greedy algorithm for finding a large matching in a graph. We assume that the next edge is always randomly chosen from those remaining. We analyze the performance of this algorithm when the input graph is fixed. We show that there are graphs for which this Randomized Greedy Algorithm (RGA) usually only obtains a matching close in size to that guaranteed by worst-case analysis (i.e., half the size of the maximum). For some classes of sparse graphs (e.g., planar graphs and forests) we show that the RGA performs significantly better than the worst-case. Our main theorem concerns forests. We prove that the ratio to maximum here is at least 0.7690…, and that this bound is tight. 相似文献
176.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 51, No. 2, pp. 212–217, August, 1989. 相似文献
177.
Palle E. T. Jorgensen 《Mathematische Zeitschrift》1989,201(4):455-476
Work supported in part by the NSF 相似文献
178.
A firm's logistics cost, including shipping and inventory-carrying, is a substantial percentage of its sales. Nevertheless, typical inventory-control methods ignore or insufficiently represent the shipping cost. This paper describes a recursive algorithm that determines the reorder cycle-time that minimizes total logistics cost. It allows for a realistic accounting of shipping cost, which is modelled here as a function of shipping distance and weight. The algorithm uses a relaxation procedure to identify a suitable initial approximation to the optimal order cycle-time and then, through a series of recursive steps, moves to the optimal result. We demonstrate the algorithm with a single item, with a group of items that share a common order cycle, and with multi-items when item demands are random variables. Experience with this algorithm indicates that it converges to the optimal result in a very few steps. 相似文献
179.
Graham Smith 《The Journal of the Operational Research Society》1989,40(9):761-770
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation. 相似文献
180.
The Cauchy Problem for the relativistic Vlasov-Maxwell equations is studied in three space dimensions. It is assumed that the initial data satisfy the required constraints and have compact support. If in addition the data have sufficiently smallC
2 norm, then a uniqueC
1 solution to this system is shown to exist on all of spacetime.Research supported in part by NSF DMS 85-20662 and NSF DMS 84-20957 相似文献