全文获取类型
收费全文 | 150592篇 |
免费 | 5812篇 |
国内免费 | 4467篇 |
专业分类
化学 | 88593篇 |
晶体学 | 2452篇 |
力学 | 6211篇 |
综合类 | 301篇 |
数学 | 15031篇 |
物理学 | 48283篇 |
出版年
2021年 | 1409篇 |
2020年 | 1683篇 |
2019年 | 1710篇 |
2018年 | 1537篇 |
2017年 | 1523篇 |
2016年 | 2505篇 |
2015年 | 2239篇 |
2014年 | 2922篇 |
2013年 | 6787篇 |
2012年 | 5766篇 |
2011年 | 6887篇 |
2010年 | 4653篇 |
2009年 | 4325篇 |
2008年 | 5845篇 |
2007年 | 5752篇 |
2006年 | 5697篇 |
2005年 | 5285篇 |
2004年 | 4415篇 |
2003年 | 3920篇 |
2002年 | 3785篇 |
2001年 | 4209篇 |
2000年 | 3237篇 |
1999年 | 2669篇 |
1998年 | 2234篇 |
1997年 | 2179篇 |
1996年 | 2065篇 |
1995年 | 2023篇 |
1994年 | 1774篇 |
1993年 | 1700篇 |
1992年 | 1894篇 |
1991年 | 1872篇 |
1990年 | 1793篇 |
1989年 | 1768篇 |
1988年 | 1751篇 |
1987年 | 1725篇 |
1986年 | 1646篇 |
1985年 | 2182篇 |
1984年 | 2280篇 |
1983年 | 1905篇 |
1982年 | 2229篇 |
1981年 | 2031篇 |
1980年 | 2079篇 |
1979年 | 2065篇 |
1978年 | 2189篇 |
1977年 | 2092篇 |
1976年 | 2116篇 |
1975年 | 2053篇 |
1974年 | 1896篇 |
1973年 | 2104篇 |
1972年 | 1282篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
H.O.U. Fynbo Y. Prezado J. Äystö U.C. Bergmann M.J.G. Borge P. Dendooven W. Huang J. Huikari H. Jeppesen P. Jones B. Jonson M. Meister G. Nyman M. Oinonen K. Riisager O. Tengblad I.S. Vogelius Y. Wang L. Weissman K.W. Rolander 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):135-138
962.
This paper describes a methodology for allocating resources in hospitals. The methodology uses two linear goal-programming models. One model sets case mix and volume for physicians, while holding service costs fixed; the other translates case mix decisions into a commensurate set of practice changes for physicians. The models allow decision makers to set case mix and case costs in such a way that the institution is able to break even, while preserving physician income and minimizing disturbance to practice. The models also permit investigation of trade-offs between case mix and physician practice parameters. Results are presented from a decision-making scenario facing the surgical division of Toronto's Mount Sinai Hospital after the announcement of a 3-year, 18% reduction in funding. 相似文献
963.
N.P. Somasiri W.K. Toh X. Chen I.D. Robertson A.A. Rezazadeh 《International Journal of Infrared and Millimeter Waves》2002,23(12):1777-1785
This paper describes numerical modelling of a dual band multi-layered microstrip patch antenna operating at 35GHz on an in-house semi-insulating GaAs substrate. The simulated and measured resonant frequencies at both lower and upper resonant frequencies will be compared to check the accuracy of the different numerical modelling techniques. 相似文献
964.
965.
Tevian Dray Corinne A. Manogue Robin W. Tucker 《General Relativity and Gravitation》1991,23(8):967-971
We consider the (massless) scalar field on 2-dimensional manifolds whose metric changes signature and which admit a spacelike isometry. Choosing the wave equation so that there will be a conserved Klein-Gordon product implicitly determines the junction conditions one needs to impose in order to obtain global solutions. The resulting mix of positive and negative frequencies produced by the presence of Euclidean regions depends only on the total width of the regions, and not on the detailed form of the metric.This essay received honorable mention in the 1991 competition of the Gravity Research Foundation. 相似文献
966.
967.
Gerald W. Evans Robert Fairbairn 《The Journal of the Operational Research Society》1989,40(11):971-981
A 0-1 integer linear programme for the selection and scheduling of US National Aeronautics and Space Administration (NASA) missions over a long planning horizon is presented. This model was formulated to allow a higher-level user-interaction with an advanced missions database currently being developed. The model implicitly considers the multi-objective nature of the problem, which results from the desire to maximize benefits in several categories as well as from the desire to minimize cost. In addition, the model allows the planner much flexibility in the selection process. This is accomplished by allowing the planner the ability to specify long- or short-term budget constraints, precursor/follow-on mission requirements, or any number of other idiosyncratic constraints which might be of importance in the decision process. Small example problems are solved in order to illustrate the approach, and areas for further research are discussed. 相似文献
968.
It is shown, using a Born-Oppenheimer model, that the four-body Efimov effect may occur in a system consisting of three identical heavy particles and one light particle, if the light-heavy interaction leads to a zeroenergy two-heavy-one-light bound state. 相似文献
969.
讨论具有无穷时滞中立型泛函微分方程$ \frac{\rm d}{{\rm d}t}\left(x(t)-\int_{-\infty}^{0}g(s,x(t+s)){\rm d}s\right) =A(t,x(t))x(t)+f(t,x_t)$的周期解问题,利用重合度理论中的延拓定理得到了周期解的存在性和唯一性条件;特别地,当$g(s,x)\equiv 0, A(t,x)=A(t)$时, 给出了存在唯一稳定周期解的条件. 相似文献
970.
Binyuan Liu Yang Li Boo‐Gyo Shin Do Yeung Yoon IL Kim Li Zhang Weidong Yan 《Journal of polymer science. Part A, Polymer chemistry》2007,45(15):3391-3399
Three novel functionalized polynorbornenes (PNB) with pendant dimethyl carboxylate group (carboxylates—acetate, propionate, and butyrate) are synthesized as a vinyl‐type with a palladium (II) catalyst in high yield. The effects of size of substitutents, molar ratio of monomer to catalyst, solvent polarity, reaction time, and temperature on the polymerization of exo‐norbornene dimethyl propionate were systematically investigated. The low molar ratio and temperature, as well as high polarity of solvent, and long reaction time, are favorable for the enhancement of the monomer conversion, especially, the solvent have an obvious effect on the catalyst activity. The resulting poly(cis‐norbornene‐exo‐2,3‐dimethyl carboxylates) (PNB‐dimethyl carboxylates) show good solubility in common organic solvent and high thermal stability up to 360 °C. The glass transition temperature was detected by DMA at 331, 324, and 318 °C for acetate, propionate, and butyrate, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3391–3399, 2007 相似文献