全文获取类型
收费全文 | 46433篇 |
免费 | 7003篇 |
国内免费 | 4428篇 |
专业分类
化学 | 32541篇 |
晶体学 | 524篇 |
力学 | 2451篇 |
综合类 | 233篇 |
数学 | 4886篇 |
物理学 | 17229篇 |
出版年
2024年 | 159篇 |
2023年 | 869篇 |
2022年 | 1541篇 |
2021年 | 1674篇 |
2020年 | 1765篇 |
2019年 | 1790篇 |
2018年 | 1501篇 |
2017年 | 1373篇 |
2016年 | 2131篇 |
2015年 | 2069篇 |
2014年 | 2578篇 |
2013年 | 3305篇 |
2012年 | 3969篇 |
2011年 | 4131篇 |
2010年 | 2702篇 |
2009年 | 2631篇 |
2008年 | 3004篇 |
2007年 | 2684篇 |
2006年 | 2467篇 |
2005年 | 2006篇 |
2004年 | 1658篇 |
2003年 | 1391篇 |
2002年 | 1355篇 |
2001年 | 1089篇 |
2000年 | 840篇 |
1999年 | 875篇 |
1998年 | 708篇 |
1997年 | 656篇 |
1996年 | 688篇 |
1995年 | 572篇 |
1994年 | 504篇 |
1993年 | 421篇 |
1992年 | 398篇 |
1991年 | 322篇 |
1990年 | 309篇 |
1989年 | 232篇 |
1988年 | 187篇 |
1987年 | 144篇 |
1986年 | 176篇 |
1985年 | 175篇 |
1984年 | 111篇 |
1983年 | 113篇 |
1982年 | 78篇 |
1981年 | 69篇 |
1980年 | 59篇 |
1979年 | 39篇 |
1976年 | 38篇 |
1975年 | 37篇 |
1974年 | 48篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
提出用溶胶粒子表面修饰方法,结合溶胶凝胶技术制备无机催化膜.该方法的基本原理是利用合适的金属配合物在胶粒表面的吸附作用,经溶胶凝胶过程,将活性组分结合到无机膜中.实验测定结果表明:(NiEDTA)2-,VO-3,MoO2-4,(Pd(NH3)4)2+,PdCl2-4,PtCl2-6和RhCl3-6可用来修饰AlOOH溶胶.以Pd/γAl2O3催化膜的制备为例,经三次溶胶凝胶过程,可制得无裂缺的厚度为9μm的Pd/γAl2O3催化膜,膜材料的平均孔直径为6nm,Pd被均匀地分布在膜的顶层,其平均粒径为23nm. 相似文献
3.
Jun-tao Chang Joerg Evers Marian O. Scully M. Suhail Zubairy 《量子光学学报》2006,12(B08):77-77
We propose a scheme to obtain the distance of two identical atoms placed inside the standing wave field by monitoring the collective resonance fluorescence spectrum emitted by the two particles. We find three different parameter ranges, depending on the distance of the atoms as compared to the transition wavelength. For large interparticle distances, dipole-dipole coupling is negligible, and the main system evolution arises from the interaction with the standing wave field. In the small-distance limit, the dynamics is dominated by the dipole-dipole interaction. Finally, in the intermediate region, a rich interplay of the various couplings arises, which however is lifted for strong driving laser fields. The present measurement procedure allows us to distinguish the three cases. In each of the cases, we show how to determine the distance of the two particles and their respective positions relative to the nodes of the standing wave field with fractional-wavelength precision. 相似文献
4.
赵志伟 《光谱学与光谱分析》2002,22(6):895-897
在化学发光分析中,常常要用到碱性条件下鲁米诺与过氧化氢的反应系统,通过催化剂辣根过氧化物酶使反应顺利进行。如果再加入适当的增强剂,则灵敏度提高且发光时间延长,可改善测定的重现性。实验证明,对位酚类衍生物,如:对叔丁基苯酚,对甲苯酚的发光增强作用明显,其发光效率可上升几十倍,发光时间也获得有效延长。 相似文献
5.
Qian-shun Chang Bo-ling GuoInstitute of Applied Mathematics Academy of Mathematics System Sciences Chinese Academy of Sciences Beijing ChinaInstitute of Applied Physics Computational Mathematics Beijing China 《应用数学学报(英文版)》2002,18(2):201-214
Abstract In this paper, a dissipative Zakharov equations are discretized by difference method.We make priorestimates for the algebric system of equations. It is proved that for each mesh size,there exist attractors forthe discretized system.The bounds of the Hausdorff dimensions of the discrete attractors are obtained,and thevarious bounds are dependent of the mesh sizes. 相似文献
6.
A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively. 相似文献
7.
This paper proposes two constructive heuristics for the well-known single-level uncapacitated dynamic lot-sizing problem. The proposed heuristics, called net least period cost (nLPC) and nLPC(i), are developed by modifying the average period cost concept from Silver and Meal's heuristic, commonly known as least period cost (LPC). An improved tie-breaking stopping rule and a locally optimal decision rule are proposed in the second heuristic to enhance performance. We test the effectiveness of the proposed heuristics by using 20 benchmarking test problems frequently used in the literature. Furthermore, we perform a large-scale simulation study involving three factors, 50 experimental conditions, and 100?000 randomly generated problems to evaluate the proposed heuristics against LPC and six other well-known constructive heuristics in the literature. The simulation results show that both nLPC and nLPC(i) produce average holding and setup costs lower than or equal to those of LPC in every one of the 50 experimental conditions. The proposed heuristics also outperform each of the six other heuristics evaluated in all experimental conditions, without an increase in computational requirements. Lastly, considering that both nLPC and nLPC(i) are fairly simple for practitioners to understand and that lot-sizing heuristics have been commonly used in practice, there should be a very good chance for practical applications of the proposed heuristics. 相似文献
8.
9.
10.
Fiber-optic reflex sensor for in-line production measurement 总被引:1,自引:0,他引:1
The paper describes experiments concerning distance measurement with fiber-optic sensor and improvement of the measurement principle. The sensor probe was well-designed with a small structure and multi-function. The novel optical fiber probe arrangement as well as the possibilities of use for complex measurement problems are explained using the measurement of an internal screw thread as an example. The experimental results show that the measurement uncertainty of the thread minor diameter can reach ±10 μm, and the stability of the measurement system is better than 0.07%. 相似文献