全文获取类型
收费全文 | 656篇 |
免费 | 40篇 |
国内免费 | 43篇 |
专业分类
化学 | 84篇 |
晶体学 | 2篇 |
力学 | 17篇 |
综合类 | 3篇 |
数学 | 283篇 |
物理学 | 54篇 |
综合类 | 296篇 |
出版年
2023年 | 3篇 |
2022年 | 16篇 |
2021年 | 18篇 |
2020年 | 17篇 |
2019年 | 15篇 |
2018年 | 14篇 |
2017年 | 10篇 |
2016年 | 15篇 |
2015年 | 14篇 |
2014年 | 27篇 |
2013年 | 44篇 |
2012年 | 30篇 |
2011年 | 24篇 |
2010年 | 24篇 |
2009年 | 35篇 |
2008年 | 29篇 |
2007年 | 46篇 |
2006年 | 44篇 |
2005年 | 40篇 |
2004年 | 33篇 |
2003年 | 26篇 |
2002年 | 22篇 |
2001年 | 27篇 |
2000年 | 18篇 |
1999年 | 29篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1995年 | 5篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有739条查询结果,搜索用时 196 毫秒
701.
MichaelJohnO'Hara 《科学通报(英文版)》2004,49(17):1788-1800
The outcome of the Apollo lunar exploration program 1969-1974 was a model of lunar petrogenesis which ignored the probability of selective volatilisation of gases and alkalis from fire-fountaining lunar basalts. It overlooked the fact that the average compositions of the erupted basalts were those of plagioclase-saturated and low-pressure cotectic liquids on eruption, clearly indicating that they were not primary magmas. The basalts may have undergone evolution by gabbro fractionation within the lunar crust, perhaps in large lava lakes now solidified as the lunar maria. The existing model involving a global magma ocean and plagioclase flotation to form the lunar crust arises solely from the incorrect assumption that the basalts are primary magmas. The plagioclase flotation hypothesis requires the presence of a significant positive europium anomaly in the lunar highland crust, and was founded upon its alleged presence. However, that positive anomaly is neither established by the original data set nor by the much broader current data set. Critical observations, and experiments which will advance the debate are suggested, and alternative interpretations outlined. 相似文献
702.
为保护臭氧层,《蒙特利尔议定书》规定CFC-12为首批禁用物质,因此,寻找其替代物的工作日益紧迫。针对目前各种替代物的不足之处,运用多目标决策分析方法,筛选出一种新的绿色环保制冷剂“清华2号”(THR02),其热物理性能和循环参数与CFC-12非常接近,并进行了压缩机、润滑油和冰箱的性能试验以及循环的变工况模拟分析。结果表明THR02具有以下特点:不破坏臭氧层,温室效应低,不燃无毒,适用于原制冷系统、压缩机与冷冻油,热工性能好,可直接灌注,长期替代CFC-12,且可进一步替代HFC-134a。 相似文献
703.
Alejandra?A.?Silva-MorenoEmail author Francisco?J.?S?nchez-MarinEmail author 《Optical Review》2003,10(4):216-220
Psychophysical experiments were done with hearing and deaf subjects, children and adults to investigate their visual performance when detecting a moving stimulus. Our experiments were done under the Two-Alternative-Forced Choice paradigm, using images with Gaussian noise of known energy as background and moving stimuli of predetermined energies. We confirm the results of better visual performance of deaf adults obtained in previous experiments with static stimuli. In this study, unexpectedly, deaf children also obtained higher performance indexes for relatively high signal energies, when compared to hearing counterparts. Also unexpectedly, in the last experiments, all deaf adults obtained 100% of correct responses while none of the hearing subjects achieved that. Our results suggest a kind of compensation effect in deaf people. 相似文献
704.
Nikolaos C. Kourogenis 《Journal of Mathematical Analysis and Applications》2003,287(2):348-364
In this paper, we study second order differential inclusions in with a maximal monotone term and generalized boundary conditions. The nonlinear differential operator need not be necessary homogeneous and incorporates as a special case the one-dimensional p-Laplacian. The generalized boundary conditions incorporate as special cases well-known problems such as the Dirichlet (Picard), Neumann and periodic problems. As application to the proven results we obtain existence theorems for both “convex” and “nonconvex” problems when the maximal monotone term A is defined everywhere and when not (case of variational inequalities). 相似文献
705.
J. Gwinner 《Journal of Optimization Theory and Applications》1985,47(3):321-336
An extension lemma, which is equivalent to the generalized Gordan's theorem of the alternative, due to Fan, Glicksberg, and Hoffman, is applied to present a duality theory for a general class of homogeneous programs, with and without a constraint qualification of Slater type. In addition, an existence theorem for optimal solutions of homogeneous programs is given.The author thanks an anonymous referee for valuable suggestions about an earlier draft of this paper. 相似文献
706.
丁协平 《四川师范大学学报(自然科学版)》1991,(2)
作者在没有线性结构的 H-空间内证明了某些重合点定理,推广了江嘉禾,Lassonde,Park,Brow-der,Ben-El-Mechaiekh-Dequire-Granas,Simons,Ko-Tan 和 Takahashi 等人的结果。应用所得的重合点定理,证明了某些新的择一型定理和函数取值于 Riesz 空间的极小极大不等式,推广了 Fan,Park,Las-sonde,Browder,Kim,lohvidov,Bardaro-Ceppitelli 等人的相应结果. 相似文献
707.
Taka-Aki Shiraishi 《Annals of the Institute of Statistical Mathematics》1986,38(1):513-522
Summary The alternative hypothesis of translated scale for the classical non-parametric hypothesis of equality of two distribution
functions in the two-sample problem is extended to a scale-alternative including contamination. The asymptotic power of rank
tests and the two-sampleF-test under contiguous sequences of the alternatives is derived and asymptotic relative efficiency of these rank tests with
respect to theF-test is investigated. It is found that some of the rank tests have reasonably high asymptotic powers satisfied enough. 相似文献
708.
本文对非定常的Stokes方程的初边值问题证明了Phragmen-Lindelof二择性原理,即证明Stokes流函数的能量,随着与带状区域有限端距离的增加必定或者按指数率增长或者按指数率衰减.对能量衰减情况建立了Stokes流速度的最大模的点点估计.并提出求全能量上界的方法. 相似文献
709.
710.
A necessary and sufficient condition is established for an optimal solution of a primal vector optimization problem to be an optimal solution of its reciprocal. Such a condition is developed and analyzed in the Pareto case, the strong case, and the lexicographic case. We detail these results for ordinary (i.e., scalar) optimization problems. 相似文献