全文获取类型
收费全文 | 977篇 |
免费 | 106篇 |
国内免费 | 141篇 |
专业分类
化学 | 764篇 |
晶体学 | 4篇 |
力学 | 72篇 |
综合类 | 10篇 |
数学 | 156篇 |
物理学 | 218篇 |
出版年
2024年 | 2篇 |
2023年 | 21篇 |
2022年 | 24篇 |
2021年 | 26篇 |
2020年 | 36篇 |
2019年 | 45篇 |
2018年 | 30篇 |
2017年 | 32篇 |
2016年 | 53篇 |
2015年 | 51篇 |
2014年 | 30篇 |
2013年 | 45篇 |
2012年 | 82篇 |
2011年 | 80篇 |
2010年 | 54篇 |
2009年 | 65篇 |
2008年 | 65篇 |
2007年 | 56篇 |
2006年 | 60篇 |
2005年 | 52篇 |
2004年 | 34篇 |
2003年 | 26篇 |
2002年 | 20篇 |
2001年 | 26篇 |
2000年 | 23篇 |
1999年 | 32篇 |
1998年 | 28篇 |
1997年 | 23篇 |
1996年 | 27篇 |
1995年 | 24篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有1224条查询结果,搜索用时 31 毫秒
91.
Accurate calculation of the almost singular double surface integrals is essential for successful solutions of the magnetic field integral equation (MFIE) by method of moments (MoM) using Rao–Wilton–Glisson (RWG) basis functions, especially for the scattering analysis of small conducting objects. In this paper, an accurate singularity extraction technique to avoid logarithmic singularity of the integration on the testing triangles is used for the MFIE. The numerical examples of several small sharp-edged conducting objects demonstrate that accuracy of the MFIE is improved with the use of the new technique. In addition, the MFIE converges much faster than the electric field integral equation (EFIE) when iterative equation solvers are employed, which means high efficiency and a suitable choice for very low frequency small sharp-edged conducting object problems using this new singularity extraction technique. 相似文献
92.
对基于工业CT图像重构的网格模型进行网格简化时,大多数现有网格模型简化算法会丢失特征,出现网格质量不好的问题。因此提出一种网格模型保特征简化方法,该方法用三角形折叠法对原始模型进行简化,当简化后模型的平均二面角角度误差达到允许误差后,再使用边折叠法对模型进行简化。在三角形折叠法中提出了利用被折叠三角形的法向量、各个顶点的高斯曲率及其在周边三角形上的投影确定该三角形的折叠点,利用局部体积误差与二面角角度误差的无因次化和确定折叠代价的方法;在边折叠法中提出了将二面角角度误差引入到二次误差测度(QEM)法的折叠代价中的改进QEM法。实验结果表明:与其他算法相比,该方法能够生成保特征、高质量、低几何误差的网格模型。 相似文献
93.
Pentacyclic lactam acceptor unit TPTI invented by our group is proved to be a good building block for efficient D‐A copolymers used in organic solar cells. Here, two D‐A copolymers PBTTPTI and PTTTPTI are developed by copolymerizing TPTI with 2,2′‐bithiophene (BT) or thieno[3,2‐b]thiophene (TT). PBTTPTI and PTTTPTI exhibit good solubility and strong interchain π–π interaction even in dilute solution. They possess deep HOMO levels (ca. ‐5.3 eV), partial crystallinity, and good hole mobilities. Blending with PC71BM, PBTTPTI and PTTTPTI give decent power conversion efficiencies (PCE) up to 6.83% and 5.86%, with outstanding fill factors (FF) of 74.3% and 71.3%, respectively.
94.
Lili Wang ;Shisheng Hu ;Liming Yang ;Zijian Sun ;Jue Zhu ;Huawei Lai ;Yuanyuan Ding 《Acta Mechanica Solida Sinica》2014,27(4):331-344
The split Hopkinson pressure bar(SHPB) technique and the wave propagation inverse analysis(WPIA) technique are both extensively used to experimentally investigate the impact behavior of materials, although neither of them alone provides a fully satisfactory analysis. In the present paper, attention is given to new experimental techniques by incorporating a damagemodified constitutive model into the SHPB technique and combining the Hopkinson pressure bar(HPB) technique with WPIA. First, to distinguish the response due to dynamic constitutive behavior and the response due to dynamic damage evolution, the SHPB method incorporating a damage-modified constitutive model is developed, including an explicit damage-modified Zhu–Wang–Tang model and an implicit damage-modified constitutive model. Second, when the SHPB results become invalid, a method of combining new Lagrange inverse analyses with the HPB technique is developed, including cases of the HPB arranged in front of a long specimen and behind the specimen. As examples of these new methods, typical results are given for nonlinear viscoelastic polymers and concretes considering damage evolution, a super-elastic Ti–Ni alloy with phase transformation and an aluminum foam with shock waves propagating within it. 相似文献
95.
ASYMPTOTIC ANALYSIS OF DYNAMIC PROBLEMS FOR LINEARLY ELASTIC SHELLS-JUSTIFICATION OF EQUATIONS FOR DYNAMIC FLEXURAL SHELLS 总被引:3,自引:0,他引:3
XIAO Liming 《数学年刊B辑(英文版)》2001,22(1):13-22
61. IntroductionIn this paper) or,P,a,T,' take their values in the set {1, 2}; i, i, k, l,' take their valuesin the set {1, 2, 3}.In [1] under appropriate conditions on the body force density and the middle surfaceof elastic shells, starting from the three-dimensional dynamic equations of elastic shells wehave given the justification of two-dimensional dynamic equations of membrane shells. Inthis paper, under different assumptions on the body force density and the middle surfaceof elastic… 相似文献
96.
Yuefang Wu Junzhi Wang Jingwen Wu Huirong Yan Chengming Lei Jinjiang Sun Liming Wang 《中国科学 数学(英文版)》2001,44(4):536-544
Using the newly installed SIS receiving system on the 13.7 m telescope at Qinghai Station of PMO, United Radio Astronomy of CAS, CO isotope13CO J= 1-0 and C18O J= 1-0 lines were observed for three sources S241, S39 and ON3. Results show that the three sources have massive cores, of which the size is ~ 2-5 pc, masses are ~ 103- 104M⊙. The widths of lines are also larger than those in low mass cores. And high velocity characteristics were observed for all the sources. The VLSR distribution presents rotation of the core in ON3. And all the three cores contain deeply embedded forming massive stars. The young stellar objects in S241 and ON3 seem to be moving away from their birth sites. 相似文献
97.
Tsao George T. Xia Liming Cao Ningjun Gong Cheng S. 《Applied biochemistry and biotechnology》2000,84(1-9):743-749
Aspergillus niger NRRL3 was cultivated in a moist wheat bran and ground corncob solid medium supplemented with inorganic minerals for the production
of cellobiase (β-1,4-glucosidase, EC 3.2.1.21). With this method, A. niger NRRL3 was able to produce a high concentration of cellobiase (215 IU/gofsolid substrate) after 96 h of incubation. Temperature
and moisture content affected final cellobiase titers. The best conditions for cell obiase production from solid substrate
by A. niger NRRL3 were determined to be 70% moisture and 35°C. 相似文献
98.
液相色谱紫外法测定鸡肉中三种硝基咪唑残留量 总被引:3,自引:0,他引:3
建立了测定鸡肉中二甲硝咪唑、罗硝唑、甲硝唑残留量的方法。以二氯甲烷提取,硅胶固相萃取净化,液相色谱紫外法检测。样品添加10μg/kg,50μg/kg,平均回收率为78%~91%,相对标准偏差为6.4%~10.1%。 相似文献
99.
高黎明 《数学年刊A辑(中文版)》2014,35(4):435-450
讨论了一类含双参变量的两点时滞微分及差分方程的多重解,主要方法是基于Bonanno创立的变分法,得到了一些新的结论. 相似文献
100.
The emergence of B2B spot markets has greatly facilitated spot trading and impacted supply chain structures as well as the way commercial transactions take place between firms in many industries. While providing new opportunities, the B2B spot market also exposes participants to a price risk. This new business landscape raises some important questions on how the supplier and manufacturer should change their sales channel and procurement strategies and tailor their decisions to this changing environment. In this paper, we study the channel-choice, pricing and ordering/production decisions of the risk-averse supplier and manufacturer in a two-tier supply chain with a B2B spot market. Our analysis shows that, to benefit from the B2B spot market and control the risk exposure, the upstream supplier should develop an integrated channel-choice and pricing strategy. When the supplier adopts a dual-channel strategy, the equilibrium contract price decreases in the supplier’s risk attitude, but increases in the demand uncertainty. However, it first decreases and then increases in the manufacturer’s risk attitude and spot price volatility. We conclude that rather than simply being a second channel, the B2B spot market provides a strategic tool to supply chain members to achieve an advantageous position in their contract trading. 相似文献