全文获取类型
收费全文 | 21442篇 |
免费 | 3336篇 |
国内免费 | 4106篇 |
专业分类
化学 | 17427篇 |
晶体学 | 338篇 |
力学 | 1029篇 |
综合类 | 310篇 |
数学 | 2321篇 |
物理学 | 7459篇 |
出版年
2024年 | 37篇 |
2023年 | 342篇 |
2022年 | 573篇 |
2021年 | 717篇 |
2020年 | 815篇 |
2019年 | 852篇 |
2018年 | 667篇 |
2017年 | 693篇 |
2016年 | 927篇 |
2015年 | 1060篇 |
2014年 | 1249篇 |
2013年 | 1690篇 |
2012年 | 1833篇 |
2011年 | 2040篇 |
2010年 | 1534篇 |
2009年 | 1433篇 |
2008年 | 1633篇 |
2007年 | 1472篇 |
2006年 | 1362篇 |
2005年 | 1185篇 |
2004年 | 954篇 |
2003年 | 782篇 |
2002年 | 766篇 |
2001年 | 693篇 |
2000年 | 572篇 |
1999年 | 457篇 |
1998年 | 366篇 |
1997年 | 270篇 |
1996年 | 282篇 |
1995年 | 279篇 |
1994年 | 236篇 |
1993年 | 197篇 |
1992年 | 139篇 |
1991年 | 161篇 |
1990年 | 131篇 |
1989年 | 96篇 |
1988年 | 101篇 |
1987年 | 57篇 |
1986年 | 54篇 |
1985年 | 43篇 |
1984年 | 35篇 |
1983年 | 31篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
123.
124.
排气全燃型联合循环设计点性能简明估计公式 总被引:1,自引:0,他引:1
排气全燃型联合循环设计点性能简明估计公式蔡睿贤(中国科学院工程热物理研究所北京10O080)关键词:排气全燃型联合循环,热力分析主要符号表Hu燃料热值L燃料理论空气量l比功P单位能量价格R燃气轮机与蒸汽轮机的功率比α过量空气系数β摩尔燃料系数△增量η... 相似文献
125.
谢家麟 庄杰佳 黄永章 张令翊 林绍波 赵春农 李立华 吴钢 王钢 李承泽 傅恩生 苏憬 钟元元 王言山 李永贵 应润杰 杨学平 李有猛 韩斌 吴庆武 张玉珍 潘卫民 王建伟 张黎文 郭康柱 畅祥云 李亚南 戴立盛 徐金强 陆辉华 汪伯嗣 任廉重 田瑞生 《中国物理 C》1994,18(8):763-768
北京自由电子激光(BFEL)装置于1993年底在10.68μm处实现了饱和振荡.输出激光能量为3mJ,饱和平顶宽度2μs.对应饱和振荡平均功率为210kW(宏脉冲),峰值功率约为20MW,比自发辐射高8个量级,单程小讯号净增益为24%,转换效率为0.45%,与理论预期结果相符.光束质量接近衍射极限.目前装置可工作于9-11μm. 相似文献
126.
Three-dimensional astigmatic resonators, typical examples of which are the resonators bounded by cylindrical-spherical mirrors and cylindrical-cylindrical mirrors oriented at an arbitrary crossed angle, are investigated in detail by using a complex curvature tensor concept and generalized tensor ABCD law. Computerized numerical calculations illustrate some interesting characteristics of these astigmatic resonators. 相似文献
127.
The present paper covers three silabridged hafnocene dichlorides(1, 2 and 3) prepared by sequential reactions of α, ω-dichloropermethyl polysilane with cyclopentadienyl sodium, n-butyl lithium and hafnium tetrachloride. Their structures were characterized by elemental analyses, UV, 1H(13C) NMR and MS. Furthermore the crystal and molecular structures of 1 and 2 were determined by X-ray diffraction method. The crystal of 1 is monoclinic, space group C2/c with a=1. 3401(4), b=0. 9977(3), c = 1. 0922(4) nm; β=94. 07(1)° V=3. 6342 nm3, Z = 2, Dc = 2.155 g·cm-3. The final deviation factor R = 0. 064. The crystal of 2 is monoclinic, space group P21/c with a=0.0847(1), b=1.5181(1), c=2.9824(2) nm; β= 94. 07(1)°? V=3.634 nm3; Dc= l. 805 g·cm-3. The final deviation factor R = 0. 033. The relationship between the silabridged structure and spectral properties is also discussed. 相似文献
128.
We describe one convenient synthesis route to boron nitride (BN) nanotube by the reaction of boron powder, iron oxide, and ammonium chloride at 600 °C for 12 h. Characterized by XRD, FTIR, XPS, TEM and SAED, the composition and morphology of the products are confirmed. The possible reaction mechanism is also discussed. 相似文献
129.
ZhengBin Zhang Chunying Liu Peifeng Li Zhenzhen Wu Cai Lin Huawei Huang Lei Xing Liansheng Liu 《Frontiers of Chemistry in China》2006,1(1):86-97
Many food algae and red tide algae were cultivated in the f/2 medium, and the nitric oxide (NO) concentration of the medium
and the cell density were determined. The experiments on algae were conducted when different concentrations of NO were added
into the medium using two methods. The results show that low concentrations of NO were self-produced by marine algae during
the exponential growth period and were about nmol/L level. But at the end of the period, i.e., 2 or 3 days before the cell
density reaches the maximum, an NO peak appeared, with the NO concentration reaching 10 nmol/L. The NO threshold concentration
exists according to the influence of exogenous NO on the marine phytoplankton growth. One type is the threshold concentration
that can promote algae growth, and its value is between 10 and 1 nmol level, or even lower. The other type can inhibit the
phytoplankton growth, which is about μmol level or higher. The results indicate that red tide algae are far more sensitive
to NO than are food algae. The fundamental experimental outcome above may provide a new clue for red tide chemical forecast
by inspecting the NO change. 相似文献
130.
蔡建平 《Annals of Differential Equations》2004,20(1):14-20
This paper investigates the periodic boundary value problems for a class of second order functional differential equations. The monotone iterative technique and the maximum principle are applied to obtain the existence of maximal and minimal solutions. 相似文献