首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2235篇
  免费   89篇
  国内免费   36篇
化学   1698篇
晶体学   2篇
力学   21篇
数学   74篇
物理学   370篇
无线电   195篇
  2025年   32篇
  2024年   44篇
  2023年   46篇
  2022年   73篇
  2021年   61篇
  2020年   34篇
  2019年   12篇
  2018年   20篇
  2017年   23篇
  2016年   22篇
  2015年   21篇
  2014年   36篇
  2013年   15篇
  2012年   204篇
  2011年   298篇
  2010年   66篇
  2009年   35篇
  2008年   198篇
  2007年   206篇
  2006年   193篇
  2005年   170篇
  2004年   84篇
  2003年   68篇
  2002年   75篇
  2001年   54篇
  2000年   52篇
  1999年   32篇
  1998年   32篇
  1997年   15篇
  1996年   23篇
  1995年   21篇
  1994年   16篇
  1993年   18篇
  1992年   12篇
  1991年   15篇
  1990年   18篇
  1989年   2篇
  1988年   2篇
  1985年   2篇
  1984年   1篇
  1983年   3篇
  1982年   1篇
  1981年   3篇
  1980年   1篇
  1974年   1篇
排序方式: 共有2360条查询结果,搜索用时 15 毫秒
1.
2.
The molecular structure and binding, as well as infrared and electronic spectroscopic properties for the title complex Cu(mnt)(dmbpy)(mnt(2-)=maleonitriledithiolate, dmbpy=4,4'-dimethyl-2,2'-bipyridine) were studied in this paper. With semi-empirical PM3 and non-empirical DFT (B3LYP/6-311G*) methods, the molecular geometry of the complex was optimized and corresponding vibrational spectra in the gaseous state were obtained. The calculated results derived from DFT were more reasonable than those from PM3. The point group of Cu(mnt)(dmbpy) in isolated gaseous state was C(2), in which Cu(II) adopted a distorted tetrahedral geometry and the dihedral angle between the N(2)Cu and S(2)Cu planes was about 29.814 degrees. And a complete assignment to the IR spectra of such a complicated molecule was exhibited. With ZINDO/S method an electronic spectrum was calculated. The results showed that the calculated values generally agreed with the observed ones. And a detailed explain was made on its electronic spectra.  相似文献   
3.
Xu S  Sun L  Fang Z 《Talanta》1992,39(6):581-587
The slotted quartz has been applied to flow-injection flame atomic-absorption spectrometry (FI-FAAS) showing several important advantages. The tube life was improved by a factor of 5-6 compared to conventional continuous aspiration. Flow impact systems were found not to be necessary in the applications so that larger enhancement factors may be achieved without sacrifice in precision. For 1.0 mg/l. copper, 1.0 mg/l. lead, 0.1 mg/l. cadmium and 1.0 mg/l. gold sensitivity enhancement factors of 3.1, 5.5, 5.3 and 4.0 were obtained with precisions of 1.3%, 1.1%, 1.6% and 1.7% RSD (n = 11) respectively. Application of the slotted quartz tube FI-FAAS method to the determination of heavy metals in urine has shown improved tolerance to interfering matrices. Recoveries obtained by spiking undiluted urine samples with 0.1 mg/l. copper and lead, and 0.01 mg/l. cadmium were in the range 100-102%.  相似文献   
4.
5.
Cloud providers(e.g.,Google,Alibaba,Amazon)own large-scale datacenter networks that comprise thousands of switches and links.A loadbalancing mechanism is supposed to effectively utilize the bisection bandwidth.Both Equal-Cost Multi-Path(ECMP),the canonical solution in practice,and alternatives come with performance limitations or significant deployment challenges.In this work,we propose Closer,a scalable load balancing mechanism for cloud datacenters.Closer complies with the evaluation of technology including the deployment of Clos-based topologies,overlays for network virtualization,and virtual machine(VM)clusters.We decouple the system into centralized route calculation and distributed route decision to guarantee its flexibility and stability in large-scale networks.Leveraging In-band Network Telemetry(INT)to obtain precise link state information,a simple but efficient algorithm implements a weighted ECMP at the edge of fabric,which enables Closer to proactively map the flows to the appropriate path and avoid the excessive congestion of a single link.Closer achieves 2 to 7 times better flow completion time(FCT)at 70%network load than existing schemes that work with same hardware environment.  相似文献   
6.
尽管亚洲地区连接器市场争剧烈,1995年三季度起需求又下跌,但是计算机连接器制造商对其前景是乐观的。当前,连接器正在向更小的中心距和压配合连接器方向发展。在中国内地和中国台湾地区的高档产品中,采用液晶聚合物(LCP)绝缘的和镀金的连接器已变得普遍。由于原材料价格稳定和同行业竞争  相似文献   
7.
We experimentally evaluate and correct the non-equivalence between electrical and radiative heating of solar irradiance absolute radiometer to compensate the systematic error of radiant power measurement at ambient pressure. A relative difference of the order of 0.08%-0.27% between electrical and radiative heating sensitivities is shown, and the resulting non-equivalence correction factor is calculated. The radiant power measurement equation is modified using the non-equivalence correction factor, a systematic deviation of 0.19% of radiant power measurement is hence eliminated.  相似文献   
8.
We report a determination of the B(0)(d)-&B_(0)(d) mixing parameter Deltam(d) based on the time evolution of dilepton yields in Upsilon(4S) decays. The measurement is based on a 5.9 fb(-1) data sample collected by the Belle detector at KEKB. The proper-time difference distributions for same-sign and opposite-sign dilepton events are simultaneously fitted to an expression containing Deltam(d) as a free parameter. Using both muons and electrons, we obtain Deltam(d) = 0.463+/-0.008 (stat)+/-0.016 (syst) ps(-1). This is the first determination of Deltam(d) from time evolution measurements at the Upsilon(4S). We also place limits on possible CPT violations.  相似文献   
9.
Zong W  Liu R  Sun F  Teng Y  Fang X  Chai J 《Journal of fluorescence》2011,21(3):1249-1254
To identify and eliminate the inner filter effects (IFEs), prepositive and side cells containing absorbents are fixed beside the fluorescer contained cell. In this way, excitation and emission lights can be quenched by primary and secondary outer filter effects respectively, depending on absorbent concentration and cell length. Herein the quenching of emission fluorescence caused by IFEs can be equally reduced by outer filter effects (OFEs) and the interference of IFEs was eliminated. This approach was experimentally used for identifying the interaction mode and mechanism between BSA and nanoAg. Results showed that the quenching of BSA fluorescence and synchronous fluorescence mainly attributes to IFEs, instead of static/dynamic fluorescent quenching. In view of the above, the elimination of the interference of IFEs by the design of OFEs plays an important part in the precise application of fluorescence detector.  相似文献   
10.
The vascular tree of the retina is likely the most representative and stable feature for eye fundus images in registration. Based on the reconstructed vascular tree, we propose an elastic matching algorithm to register pairs of fundus images. The identified vessels are thinned and approximated using short line segments of equal length that results a set of elements. The set of elements corresponding to one vascular tree are elastically deformed to optimally match the set of elements of another vascular tree, with the guide of an energy function to finally establish pixel relationship between both vascular trees. The mapped positions of pixels in the transformed retinal image are computed to be the sum of their original locations and corresponding displacement vectors. For the purpose of performance comparison, a weak affine model based fast chamfer matching technique is proposed and implemented. Experiment results validated the effectiveness of the elastic matching algorithm and its advantage over the weak affine model for registration of retinal fundus images.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号