全文获取类型
收费全文 | 1965篇 |
免费 | 375篇 |
国内免费 | 700篇 |
专业分类
化学 | 1453篇 |
晶体学 | 108篇 |
力学 | 100篇 |
综合类 | 106篇 |
数学 | 349篇 |
物理学 | 924篇 |
出版年
2024年 | 3篇 |
2023年 | 17篇 |
2022年 | 64篇 |
2021年 | 74篇 |
2020年 | 65篇 |
2019年 | 48篇 |
2018年 | 71篇 |
2017年 | 76篇 |
2016年 | 61篇 |
2015年 | 102篇 |
2014年 | 130篇 |
2013年 | 151篇 |
2012年 | 126篇 |
2011年 | 162篇 |
2010年 | 161篇 |
2009年 | 173篇 |
2008年 | 210篇 |
2007年 | 166篇 |
2006年 | 176篇 |
2005年 | 151篇 |
2004年 | 108篇 |
2003年 | 91篇 |
2002年 | 91篇 |
2001年 | 102篇 |
2000年 | 112篇 |
1999年 | 79篇 |
1998年 | 34篇 |
1997年 | 26篇 |
1996年 | 32篇 |
1995年 | 17篇 |
1994年 | 29篇 |
1993年 | 24篇 |
1992年 | 22篇 |
1991年 | 13篇 |
1990年 | 20篇 |
1989年 | 3篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有3040条查询结果,搜索用时 15 毫秒
61.
To reduce low-frequency noise of the water-filled pipeline system,a compact flexible micro-perforated muffler with a flexible back cavity(FMPMFBC) is proposed.The flexible pipe wall is made of a rubber-cord composite material.A numerical solution for the transmission loss is derived.Firstly,the flexible micro-perforated panel(FMPP) is equivalent to a flexible porous material based on Biot-Allard porous-elastic theory.Then,a periodic structural unit of the aramid fabric cloth is established with the two-scale method,and the equivalent stiffness matrix is obtained.Besides,a multi-layer composite model for the flexible pipe wall is constructed according to the lamination theory.Coupling with the internal sound field,the transmission loss of the FMPMFBC is calculated.On a water-filled impedance tube,the transmission loss curves of the FMPMFBC prototypes are measured with the two source-location method,and compared with those of a flexible micro-perforated muffler with a rigid back cavity(FMPMRBC)and an expansion muffler.Theoretical results are experimentally verified.The FMPMFBC is a hybrid muffler combining reflection with dissipation,capable of attenuating broadband lowfrequency noise.The transmission loss of prototype B2 in the frequency bands of [40 300] Hz and [40 1200] Hz is 36 dB and 30 dB,respectively,while the transmission loss of the same-sized expansion muffler in the corresponding frequency bands is 7 dB and 11 dB,respectively. 相似文献
62.
��ѧ�ۣ����������κ�����˻����� �� 《核聚变与等离子体物理》2020,39(4):359-364
Based on the structure design and characteristics of the sealing welding of tritium-breeding blanket cap runner, the ultrasonic microscopic detection technology is studied. The testing parameters and the applicability of the method are determined. The JSR DPR500 ultrasonic microscopic detection system is selected to study the testing parameters. The characteristics of the probe parameters and the focus of the sound beam in the ultrasonic microscopy detection are analyzed. Different parameters and water layer thicknesses are used to improve the detection sensitivity. The problem that the small defects in the sealing welding of cap runner are difficult to detect is solved. 相似文献
63.
64.
65.
66.
67.
合成了含Fe2+的脂氧合酶模型化合物[Fe(CTB)Cl]Cl.3CH3CH2OH.H2O(CTB为N,N,N,'N'-四(2'-苯并咪唑甲基)邻二胺反式-环己烷).该配合物属单斜晶系,P21/n空间群.晶胞参数a=1.12938(7)nm,b=1.49004(9)nm,c=2.69346(17)nm,β=91.9530(10),°V=4.5300(5)nm3,Z=4;R=0.0602,wR=0.1629.中心离子Fe2+只与六齿配体CTB的3个苯并咪唑的3-位氮和两个烷胺氮配位,氯离子占据着第六配位位点,整个配合物呈变形八面体构型.该化合物可催化亚油酸氧化断链成丙二醛(酸)、壬烯醛和壬醛酸等低分子醛和ω-氧酸. 相似文献
68.
69.
通过采用水热晶化与荷电复合分散法制备γ-AlOOH、R-TiO2和α-Al2O3纳米晶体粉末,利用TEM和激光粒度分析仪等手段研究了纳米颗粒水热晶化与荷电复合分散的分散效果及其工艺条件,并探讨了金属氧化物纳米颗粒水热晶化与荷电复合分散机理。结果表明,晶化与荷电复合分散可明显改善金属氧化物纳米颗粒在液相中的分散稳定性,所制得的AlOOH、TiO2和Al2O3纳米颗粒在水中分散放置24 h后的透光率的变化率D24还可分别保持为94.1%、87.7%和82.2%;在水中分散后的粒径分布统计的平均粒径分别为67、70和143 nm。 相似文献
70.
A molecular structural characterization (MSC) method called reduced molecular electronegativity-distance vector (MEDVR) was used to describe the molecular structures of 55 components of meconopsis integrifolia flowers. By use of stepwise multiple regression (SMR) and partial least square (PLS) methods, a model with the correlation coefficient (R1) of 0.987 and the standard deviation (SD1) of 1.377 could be obtained. Then through multiple linear regression (MLR), another model with the correlation coefficient (R2) of 0.989 and standard deviation (SD2) of 1.395 could be constructed. Furthermore, in virtue of variable screening by the stepwise multiple regression technique (SMR), 8 vectors were selected to build up another model with its correlation coefficient (R3) and standard deviation (SD3) of 0.989 and 1.366, respectively. Then all the three models were evaluated by performing cross-validation with the leave-one-out (LOO) procedure, and the correlation coefficients (QCV) were 0.981, 0.976 and 0.979, respectively. The results show that the models constructed could provide estimation stability and favorable predictive ability. 相似文献