全文获取类型
收费全文 | 47951篇 |
免费 | 5026篇 |
国内免费 | 6660篇 |
专业分类
化学 | 44144篇 |
晶体学 | 1558篇 |
力学 | 809篇 |
综合类 | 241篇 |
数学 | 2083篇 |
物理学 | 10802篇 |
出版年
2024年 | 86篇 |
2023年 | 528篇 |
2022年 | 1475篇 |
2021年 | 1342篇 |
2020年 | 1585篇 |
2019年 | 1442篇 |
2018年 | 1197篇 |
2017年 | 1517篇 |
2016年 | 1818篇 |
2015年 | 1690篇 |
2014年 | 2129篇 |
2013年 | 3918篇 |
2012年 | 2614篇 |
2011年 | 3013篇 |
2010年 | 2688篇 |
2009年 | 2985篇 |
2008年 | 3053篇 |
2007年 | 3041篇 |
2006年 | 2869篇 |
2005年 | 2681篇 |
2004年 | 2507篇 |
2003年 | 2102篇 |
2002年 | 2616篇 |
2001年 | 1395篇 |
2000年 | 1293篇 |
1999年 | 1107篇 |
1998年 | 962篇 |
1997年 | 798篇 |
1996年 | 915篇 |
1995年 | 912篇 |
1994年 | 603篇 |
1993年 | 503篇 |
1992年 | 427篇 |
1991年 | 295篇 |
1990年 | 189篇 |
1989年 | 196篇 |
1988年 | 180篇 |
1987年 | 107篇 |
1986年 | 115篇 |
1985年 | 119篇 |
1984年 | 91篇 |
1983年 | 57篇 |
1982年 | 61篇 |
1981年 | 65篇 |
1980年 | 63篇 |
1979年 | 53篇 |
1978年 | 43篇 |
1977年 | 30篇 |
1971年 | 49篇 |
1970年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA) and polystyrene-polyacrylonitrile copolymer (PS-AN), containing various embedded transition-metal complexes, have been studied by FTIR microscopy. The spatial distributions of the transition-metal carbonyl complexes throughout the thin organic polymer films have been determined by a two-dimensional IR mapping procedure. The spectral variations observed in the distribution of the metal carbonyls throughout the different polymer films are discussed. The IR data show that the technique used to prepare the organometallic-embedded thin films (viz. freeze-drying of solutions followed by hot mechanical pressing of the residues) does in general lead to homogeneous films which may eventually find industrial application, e.g. as membrane sensors for small molecules. 相似文献
103.
104.
以Nd:MgO:LiNbO_3同时兼作激活介质和非线性光学材料,研究自倍频激光器。用小型氙灯泵浦,在室温下获得二次谐波激光(0.547μm) 阈值小于4.8'J,最大输出400μJ/shot,工作温度范围大于20℃~45℃,无光损伤。 相似文献
105.
微微秒自动调谐参量激光的研究 总被引:3,自引:3,他引:0
采用一对MgO:LiNbO_3角度调谐覆盖了红近外波段0.7~2.2μm,并配以自动波长扫描。文中分析了影响脉冲宽度与线宽的因素,与实验结果相吻合。脉宽<30ps,线宽~1nm(简并波长附近~10nm),单脉冲峰功率达MW级,参量光总能量转换效率达5.4%。 相似文献
106.
停流—荧光动力学分析法测定痕量钛的研究 总被引:3,自引:1,他引:2
利用自行组装的停流-荧光动力学分析仪,采用停流法汇合流体动力注入技术,研究了钛与3.5-二溴水杨基荧光酮的荧光增强动力学反应性质,讨论了流速、进样时间对方法灵敏度和精密度的影响,提出了一个快速、简便、精确测定钛的分析方法,并用于稀土样品及合成样品中痕量钛的测定.方法检测限为8×10~(-3)ppm,大多数元素的干扰均可用动力学方法消除. 相似文献
107.
108.
E. S. Dy H. Kasai 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):241-245
We study the interaction between tin(II) porphyrin (SnPor) with platinum and
non-precious Group 8B metals (iron, cobalt and nickel) by density functional
theory and discuss the electronic properties of the resulting products. We
also model the interaction of the resulting compounds with water where
applicable. Our studies indicate that, SnPor-Ni possesses electronic
properties similar to SnPor-Pt, suggesting that it may possess similar
photocatalytic properties for reduction reactions, such as converting water
to hydrogen gas. 相似文献
109.
A palladium‐TPPTS catalyst heterogenized on KF/alumina has been shown to be effective and recyclable for the selective formation of monooctadienylxylopyranosides via the telomerization of butadiene with D ‐xylose. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
110.
Let G(x,y) and GD(x,y) be the Green functions of rotationally invariant symmetric α-stable process in Rd and in an open set D, respectively, where 0<α<2. The inequality GD(x,y)GD(y,z)/GD(x,z)?c(G(x,y)+G(y,z)) is a very useful tool in studying (local) Schrödinger operators. When the above inequality is true with c=c(D)∈(0,∞), then we say that the 3G theorem holds in D. In this paper, we establish a generalized version of 3G theorem when D is a bounded κ-fat open set, which includes a bounded John domain. The 3G we consider is of the form GD(x,y)GD(z,w)/GD(x,w), where y may be different from z. When y=z, we recover the usual 3G. The 3G form GD(x,y)GD(z,w)/GD(x,w) appears in non-local Schrödinger operator theory. Using our generalized 3G theorem, we give a concrete class of functions belonging to the non-local Kato class, introduced by Chen and Song, on κ-fat open sets. As an application, we discuss relativistic α-stable processes (relativistic Hamiltonian when α=1) in κ-fat open sets. We identify the Martin boundary and the minimal Martin boundary with the Euclidean boundary for relativistic α-stable processes in κ-fat open sets. Furthermore, we show that relative Fatou type theorem is true for relativistic stable processes in κ-fat open sets. The main results of this paper hold for a large class of symmetric Markov processes, as are illustrated in the last section of this paper. We also discuss the generalized 3G theorem for a large class of symmetric stable Lévy processes. 相似文献