全文获取类型
收费全文 | 22975篇 |
免费 | 2225篇 |
国内免费 | 2482篇 |
专业分类
化学 | 17799篇 |
晶体学 | 177篇 |
力学 | 1313篇 |
综合类 | 151篇 |
数学 | 2700篇 |
物理学 | 5542篇 |
出版年
2024年 | 19篇 |
2023年 | 216篇 |
2022年 | 344篇 |
2021年 | 592篇 |
2020年 | 707篇 |
2019年 | 653篇 |
2018年 | 580篇 |
2017年 | 708篇 |
2016年 | 839篇 |
2015年 | 789篇 |
2014年 | 929篇 |
2013年 | 1646篇 |
2012年 | 1651篇 |
2011年 | 1221篇 |
2010年 | 1029篇 |
2009年 | 1172篇 |
2008年 | 1280篇 |
2007年 | 1439篇 |
2006年 | 1347篇 |
2005年 | 1178篇 |
2004年 | 1204篇 |
2003年 | 978篇 |
2002年 | 803篇 |
2001年 | 674篇 |
2000年 | 665篇 |
1999年 | 649篇 |
1998年 | 550篇 |
1997年 | 606篇 |
1996年 | 359篇 |
1995年 | 421篇 |
1994年 | 371篇 |
1993年 | 314篇 |
1992年 | 298篇 |
1991年 | 268篇 |
1990年 | 235篇 |
1989年 | 172篇 |
1988年 | 148篇 |
1987年 | 107篇 |
1986年 | 85篇 |
1985年 | 85篇 |
1984年 | 80篇 |
1983年 | 41篇 |
1982年 | 58篇 |
1981年 | 34篇 |
1980年 | 33篇 |
1979年 | 26篇 |
1978年 | 16篇 |
1977年 | 14篇 |
1976年 | 10篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
在异源四倍体棉种中现已鉴定出22个芽黄突变体、26个芽黄基因,其中V1与V7、V2之间存在着部分同源关系。重叠牙黄基因V16V17的遗传主式独特,单体1测验的分离世代F2和BC恢复产生了黄化的单体株。鉴于杂中子生产现状,俄系统阐述了以芽黄作为指示性进行棉花杂种优势利用的可行性。 相似文献
102.
本应用自己合成的联萘20-冠-6作为活性载体,进行了五羟色胺分子选择性电极研究。电极在10^-^5-10^-^2mol/L浓度范围内对五羟色胺具有稳定的线性响应,平均斜率为63mV/PC,检测下限为2.7×10^-^6mol/L。 相似文献
103.
104.
105.
The hydrocarbon discovery prediction problem is important to firms having to make decisions about the deployment of scarce exploration resources. Traditional methods for estimating the discovery rate rely on the completion of time consuming simulation experiments. A rapid approximation that does not require the completion of simulation exists and has been shown to have some promise as a prediction tool. This paper investigates the accuracy of the approximation method under a wide variety of distributional and drilling efficiency assumptions. The results indicate that the approximation produces predictions close to those of simulation under most of the tested conditions. This suggests that resource exploration firms could conveniently use the method for a wide variety of planning purposes without incurring the same costs in time and personnel required for simulation. 相似文献
106.
This contribution discusses the phenomena of retrograde condensation of one or two liquids. It w1 be shown that both phenomena can be well understood. Also the relation of retrograde condensation of one liquid phase with the condensation behavior of natural gas will be discussed. Similarly that of two liquid phases with multiple phase behavior occurring in low temperature reservoir fluids will be pointed out. 相似文献
107.
108.
Simple expressions are given for the mean delay, mean waiting time, and mean busy period length in a multiplexer. Data streams with active periods having a general distribution are permitted, and the data rate during the active periods can be random. Data can also arrive in batches. The key restrictions of the model are that the sources are independent, idle periods are exponentially distributed, and a source generates at least enough data during an active period to keep the server busy throughout the period. The exact formulas allow evaluation of the error in approximations such as a heavy traffic diffusion approximation.Both continuous and discrete time models are considered. The discrete-time model includes that studied by Viterbi and subsequently generalized by Neuts. The Pollaczek-Khinchine formula for the mean amount of work in anM/GI/1 queue is retrieved as a limiting case.Preliminary version presented at IEEE INFOCOM, San Francisco, April 1993. 相似文献
109.
J. Teixeira 《Il Nuovo Cimento D》1994,16(9):1433-1437
Summary The dynamics of water molecules occupying very small volumes can be probed by incoherent quasi-elastic neutron scattering.
We summarise some results obtained with wet samples of porous silica and hydrated proteins. The movements of the molecules
in the vicinity of the substrate are extremely reduced as compared to those of bulk water at the same temperature. Almost
only rotational movements subsist and the local diffusion is of the order of that observed in deeply supercooled water.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
110.
具有非局部边界条件的奇摄动反应扩散问题 总被引:2,自引:0,他引:2
本文研究了一类具有非局部边界条件的奇摄动反应扩散初始边值问题.在适当的条件下,利用比较定理讨论了问题解的渐近性态. 相似文献