全文获取类型
收费全文 | 20239篇 |
免费 | 3424篇 |
国内免费 | 2314篇 |
专业分类
化学 | 14625篇 |
晶体学 | 262篇 |
力学 | 1238篇 |
综合类 | 189篇 |
数学 | 2096篇 |
物理学 | 7567篇 |
出版年
2024年 | 41篇 |
2023年 | 448篇 |
2022年 | 507篇 |
2021年 | 677篇 |
2020年 | 815篇 |
2019年 | 789篇 |
2018年 | 638篇 |
2017年 | 605篇 |
2016年 | 940篇 |
2015年 | 923篇 |
2014年 | 1078篇 |
2013年 | 1382篇 |
2012年 | 1829篇 |
2011年 | 1908篇 |
2010年 | 1257篇 |
2009年 | 1113篇 |
2008年 | 1309篇 |
2007年 | 1291篇 |
2006年 | 1138篇 |
2005年 | 1017篇 |
2004年 | 735篇 |
2003年 | 631篇 |
2002年 | 576篇 |
2001年 | 433篇 |
2000年 | 415篇 |
1999年 | 481篇 |
1998年 | 360篇 |
1997年 | 377篇 |
1996年 | 320篇 |
1995年 | 297篇 |
1994年 | 307篇 |
1993年 | 246篇 |
1992年 | 196篇 |
1991年 | 198篇 |
1990年 | 177篇 |
1989年 | 113篇 |
1988年 | 86篇 |
1987年 | 89篇 |
1986年 | 61篇 |
1985年 | 44篇 |
1984年 | 43篇 |
1983年 | 24篇 |
1982年 | 25篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1975年 | 2篇 |
1957年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Jiang Zhankui A. Persson L. Sturesson S. Svanberg 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,21(4):315-322
In the recently introduced high-contrast transmission version of saturated absorption laser spectroscopy, narrow signals are obtained from dense atomic samples subject to strong pumping. A study of possible systematic shifts of the signals in this domain of rather extreme experimental conditions was performed in order to assess the validity of spectroscopic data obtained with this technique. Certain signal components were found to be slightly shifted while others were not. Further, a theoretical study of the behaviour of overlapping signals in the high-contrast regime is presented. In particular, the question of whether structures buried under the natural linewidth could be resolved is addressed. 相似文献
192.
ICP激发光源以其独特的功能使ICP/AES技术在稀土分析中的应用日益广泛,在一定程度上取代了经典的直流电弧光谱法,但应指出,由于常规雾化器的低雾化效率(≤5%)和试样的高倍稀释,ICP/AES技术的实际检测能力的改善并不明显,本文用ICP光谱法测定了 相似文献
193.
194.
Nicole Fietkau Fran?ois G Chevallier Li Jiang Timothy G J Jones Richard G Compton 《Chemphyschem》2006,7(10):2162-2167
The size of a glass sphere positioned in the center of a microdisk electrode is determined by using a simple electrochemical procedure and is confirmed, additionally, by a microscopical measurement of the sphere at the time of the electrochemical measurement. The cyclic voltammetric response of the naked electrode and of the electrode with the sphere positioned in its center is recorded over a wide range of scan rates (0.002-1.5 V s(-1)). The size of the sphere is then determined by comparison of the experimental voltammogram with simulations for each individual scan rate. 相似文献
195.
Zou JW Jiang YJ Guo M Hu GX Zhang B Liu HC Yu QS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(2):740-751
Ab initio calculations have been performed on a series of complexes formed between halogen-containing molecules and ammonia to gain a deeper insight into the nature of halogen bonding. It appears that the dihalogen molecules form the strongest halogen-bonded complexes with ammonia, followed by HOX; the charge-transfer-type contribution has been demonstrated to dominate the halogen bonding in these complexes. For the complexes involving carbon-bound halogen molecules, our calculations clearly indicate that electrostatic interactions are mainly responsible for their binding energies. Whereas the halogen-bond strength is significantly enhanced by progressive fluorine substitution, the substitution of a hydrogen atom by a methyl group in the CH(3)X...NH(3) complex weakened the halogen bonding. Moreover, remote substituent effects have also been noted in the complexes of halobenzenes with different para substituents. The influence of the hybridization state of the carbon atom bonded to the halogen atom has also been examined and the results reveal that halogen-bond strengths decrease in the order HC triple bond CX > H(2)C=CHX approximately O=CHX approximately C(6)H(5)X > CH(3)X. In addition, several excellent linear correlations have been established between the interaction energies and both the amount of charge transfer and the electrostatic potentials corresponding to an electron density of 0.002 au along the R-X axis; these correlations provide good models with which to evaluate the electron-accepting abilities of the covalently bonded halogen atoms. Finally, some positively charged halogen-bonded systems have been investigated and the effect of the charge has been discussed. 相似文献
196.
Lingjun Chou Yingchun Cai Bing Zhang Jianzhong Niu Shengfu Ji Shuben Li 《Reaction Kinetics and Catalysis Letters》2002,76(2):311-315
Na-Mn-W/SiO2 catalysts were prepared and their catalytic performance for oxidative coupling of methane (OCM) was evaluated in a stainless-steel microreactor at elevated pressure. The results show that a CH4 conversion of 15.1% with a C2+ selectivity of 71.8% was obtained under 750oC, 1.0×105h-1 GHSV, CH4/O2 ratio of 8 and 1.0 MPa. Moreover, 17.3% CH4 conversion with 51.6% C2 selectivity and 23.6% C3-C4 selectivity was obtained under 750oC, 2.0×105h-1 GHSV, CH4/O2 ratio of 8 and 1.0 MPa. 相似文献
197.
FT-IR and Raman spectroscopic study of hydrated rubidium (cesium) borates and alkali double borates 总被引:1,自引:0,他引:1
Zhu Lixia Yue Tao Wang Jiang Gao Shiyang 《Russian Journal of Inorganic Chemistry》2007,52(11):1786-1792
FT-IR and Raman spectra of five hydrated alkali borates and five hydrated alkali double borates have been recorded at room
temperature in the range 400 to 4000 cm−1, and analyzed. Fundamental vibrational modes have been identified and assignments tentatively made in comparison with the
work of Janda and Heller, and Li Jun.
The text was submitted by the authors in English. 相似文献
198.
Huang M Jin Y Jiang H Sun X Chen H Liu B Wang E Dong S 《The journal of physical chemistry. B》2005,109(32):15264-15271
Multiple-deposited Pt overlayer modified Pt nanoparticle (MD-Pt overlayer/PtNPs) films were deliberately constructed on glassy carbon electrodes through alternately multiple underpotential deposition (UPD) of Ag followed redox replacement reaction by Pt (II) cations. The linear and regular growth of the films characterized by cyclic voltammetry was observed. Atomic force spectroscopy (AFM) provides the surface morphology of the nanostructured Pt films. Rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry demonstrate that the MD-Pt overlayer/PtNPs films can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated 0.1 M H(2)SO(4). Thus-prepared Pt films behave as novel nanostructured electrocatalysts for dioxygen reduction and hydrogen evolution reaction (HER) with enhanced electrocatalytic activities, in terms of both reduction peak potential and peak current, when compared to that of the bulk polycrystalline Pt electrode. Additionally, it is noted that after multiple replacement cycles, the electrocatalytic activities improved remarkably, although the increased amount of Pt is very low in comparison to that of pre-modified PtNPs due to the intrinsic feature of the UPD-redox replacement technique. In other words, the electrocatalytic activities could be improved markedly without using very much Pt by the technique of tailoring the catalytic surface. These features may provide an interesting way to produce Pt catalysts with a reliable catalytic performance as well as a reduction in cost. 相似文献
199.
200.
Shujiang Tu Bo Jiang Hong Jiang Yan Zhang Runhong Jia Junyong Zhang Qingqing Shao Chunmei Li Dianxiang Zhou Longji Cao 《Tetrahedron》2007,63(25):5406-5414
Reaction of arylidenemalononitriles, 1,3-indanedione, and mercaptoacetic acid or 4-methylbenzenethiol is successfully carried out using microwave heating. It is an efficient and promising synthetic strategy to build the indenopyridine skeleton. 相似文献