全文获取类型
收费全文 | 10429篇 |
免费 | 1710篇 |
国内免费 | 2029篇 |
专业分类
化学 | 7991篇 |
晶体学 | 121篇 |
力学 | 632篇 |
综合类 | 150篇 |
数学 | 1321篇 |
物理学 | 3953篇 |
出版年
2024年 | 31篇 |
2023年 | 243篇 |
2022年 | 436篇 |
2021年 | 471篇 |
2020年 | 497篇 |
2019年 | 484篇 |
2018年 | 385篇 |
2017年 | 414篇 |
2016年 | 572篇 |
2015年 | 580篇 |
2014年 | 617篇 |
2013年 | 850篇 |
2012年 | 784篇 |
2011年 | 874篇 |
2010年 | 658篇 |
2009年 | 615篇 |
2008年 | 706篇 |
2007年 | 584篇 |
2006年 | 546篇 |
2005年 | 507篇 |
2004年 | 417篇 |
2003年 | 353篇 |
2002年 | 404篇 |
2001年 | 320篇 |
2000年 | 277篇 |
1999年 | 233篇 |
1998年 | 181篇 |
1997年 | 130篇 |
1996年 | 152篇 |
1995年 | 112篇 |
1994年 | 132篇 |
1993年 | 100篇 |
1992年 | 74篇 |
1991年 | 94篇 |
1990年 | 90篇 |
1989年 | 42篇 |
1988年 | 40篇 |
1987年 | 29篇 |
1986年 | 34篇 |
1985年 | 37篇 |
1984年 | 15篇 |
1983年 | 18篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1971年 | 1篇 |
1957年 | 3篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
A series of novel monooxazoline-Schiff base ligands 1 has been successfully synthesized. The Cu(I)–1a complex showed excellent catalytic activities with up to 83% ee for the asymmetric α-chlorination of β-keto esters. 相似文献
993.
Broadband Convergence of 40 GHz-ROF and 10-Gb/s WDM-PON Systems in the Duplex Access Network
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A broadly converged 40G-ROF and 10-Gb/s WDM-PON multi-service access system is proposed and exper- imentally demonstrated. This scheme consists of an integrated system of 40G-ROF and 10-Gb/s WDM-PON simultaneously transmitting independent 2.5-Gb/s wireless and 10-Gb/s wire signal. At the base station, it employs a remodulation scheme, which is achieved by remodulating the upstream OOK signal on the DPSK downstream signal, to reduce the cost of the base station. The transmission experiment is carried out over a 25-km-long single mode fiber (SMF-28). The results show that the sensitivities of downstream PON and ROF signal are -14.5 dBm and -21.5 dBm, respectively, and the sensitivity of upstream signal is -25.3 dBm. 相似文献
994.
Meijuan Yu Shulei Tian Wangsheng Chu Dongliang Chen Qi Wang Ziyu Wu 《Journal of synchrotron radiation》2009,16(4):528-532
The evaporation aerosols produced during the vitrification process of municipal solid waste incinerators (MSWI) fly ash represent a potential environmental risk owing to their high content of heavy metals. In this research, high‐temperature heating processes were carried out on fly ashes collected from bag houses in a Chinese MSWI plant and the secondary fly ashes (SFA) were separately collected at three high temperatures (1273 K, 1423 K and 1523 K) below the melting range. Elemental analysis showed that high contents of both zinc and chlorine were present in these SFA samples and, according to the standard of the heavy metals industrial grade of ore, SFAs can be re‐used as metallurgical raw materials or rich ore. Moreover, as shown by XAS analysis and for different high temperatures, zinc environments in the three SFA samples were characterized by the same local structure of the zinc chloride. As a consequence, a zinc recycling procedure can be easily designed based on the configuration information. 相似文献
995.
Ag3PW12O40 and Ag4SiW12O40 showed high activity and stability in the synthesis of diethylene glycol ethyl ether with diethylene glycol and ethanol, on which the conversion is 80.2% and 78.4%, respectively, and the selectivity of diethylene glycol ether is 75.4% and 80.6%, respectively. After the third reaction cycle, Ag3PW12O40 and Ag4SiW12O40) still showed higher activity and selectivity, on which the conversion is 72. 6% and 77.5% respectively. But the activity of Ag3PMo12O40 is lower, the conversion is only 21.0%. IR, XRD, TG and n‐butylamine titrimetry showed that the catalysis may be connected with two kinds of acidic centers owned by heteropoly acidic salt. 相似文献
996.
In the fifties, Calderón established a formal relation between symbol and kernel distribution, but it is difficult to establish an intrinsic relation. The Calderón-Zygmund (C-Z) school studied the C-Z operators, and Hörmander, Kohn and Nirenberg, et al. studied the symbolic operators. Here we apply a refinement of the Littlewood-Paley (L-P) decomposition, analyse under new wavelet bases, to characterize both symbolic operators spaces \({\text{OP}}S^{m}_{{1,\delta }} \) and kernel distributions spaces with other spaces composed of some almost diagonal matrices, then get an isometric between \({\text{OP}}S^{m}_{{1,\delta }} \) and kernel distribution spaces 相似文献
997.
High aspect-ratio, single crystal BaWO4 nanowires with diameters as small as 3.5 nm and lengths up to more than 50 microns were synthesized in catanionic reverse micelles formed by an equimolar mixture of two surfactants: undecylic acid and decylamine. 相似文献
998.
A stable paramagnetic calix[4]arene(III) bearing two nitroxide groups on the upper rim is synthesized, which exhibits a strong intramolecular spin-spin exchange interaction and is found to be able to undergo reversible conformational transitions upon heating. 相似文献
999.
Aubert B Boutigny D Gaillard JM Hicheur A Karyotakis Y Lees JP Robbe P Tisserand V Palano A Chen GP Chen JC Qi ND Rong G Wang P Zhu YS Eigen G Reinertsen PL Stugu B Abbott B Abrams GS Borgland AW Breon AB Brown DN Button-Shafer J Cahn RN Clark AR Gill MS Gritsan AV Groysman Y Jacobsen RG Kadel RW Kadyk J Kerth LT Kluth S Kolomensky YG Kral JF LeClerc C Levi ME Liu T Lynch G Meyer AB Momayezi M Oddone PJ Perazzo A Pripstein M Roe NA Romosan A Ronan MT Shelkov VG Telnov AV Wenzel WA Zisman MS 《Physical review letters》2002,88(10):101805
The branching fractions of the exclusive decays B0-->K(*0)gamma and B+-->K(*+)gamma are measured from a sample of (22.74+/-0.36)x10(6) BB decays collected with the BABAR detector at the PEP-II asymmetric e(+)e(-) collider. We find B (B0-->K(*0)gamma) = [4.23+/-0.40(stat)+/-0.22(syst)]x10(-5), B(B+-->K(*+)gamma) = [3.83+/-0.62(stat)+/-0.22(syst)]x10(-5) and constrain the CP-violating charge asymmetry to be -0.170K(*)gamma)<0.082 at 90% C.L. 相似文献
1000.
Qi JH Zhang XY Zhang RS Liu MC Hu ZD Xue HF Fan BT 《SAR and QSAR in environmental research》2000,11(2):117-131
It is proposed for the first time a method of prediction of the programmed-temperature retention times of components of naphthas in capillary gas chromatography using artificial neural networks. People are used to predict the programmed-temperature retention time using many formulas such as the integral formula, which requires that four parameters must be determined by calculation or experiments. However the results obtained by the formula are not so good to meet the demand of industry. In order to predict retention time accurately and conveniently, artificial neural networks using five-fold cross-validation and leave-20%-out methods have been applied. Only two parameters: density and isothermal retention index were used as input vectors. The average RMS error for predicted values of five different networks was 0.18, whereas the RMS error of predictions by the integral formula was 0.69. Obviously, the predictions by neural networks were much better than predictions by the formula, and neural networks need fewer parameters than the formula. So neural networks can successfully and conveniently solve the problem of predictions of programmed-temperature retention times, and provide useful data for analysis of naphthas in petrochemical industry. 相似文献