全文获取类型
收费全文 | 15072篇 |
免费 | 453篇 |
国内免费 | 31篇 |
专业分类
化学 | 10098篇 |
晶体学 | 49篇 |
力学 | 259篇 |
数学 | 2353篇 |
物理学 | 2797篇 |
出版年
2020年 | 178篇 |
2019年 | 142篇 |
2018年 | 121篇 |
2017年 | 129篇 |
2016年 | 306篇 |
2015年 | 276篇 |
2014年 | 294篇 |
2013年 | 554篇 |
2012年 | 591篇 |
2011年 | 695篇 |
2010年 | 451篇 |
2009年 | 372篇 |
2008年 | 643篇 |
2007年 | 620篇 |
2006年 | 616篇 |
2005年 | 602篇 |
2004年 | 486篇 |
2003年 | 419篇 |
2002年 | 403篇 |
2001年 | 308篇 |
2000年 | 230篇 |
1999年 | 210篇 |
1998年 | 224篇 |
1997年 | 206篇 |
1996年 | 215篇 |
1995年 | 220篇 |
1994年 | 196篇 |
1993年 | 258篇 |
1992年 | 202篇 |
1991年 | 181篇 |
1990年 | 166篇 |
1989年 | 180篇 |
1988年 | 180篇 |
1987年 | 216篇 |
1986年 | 202篇 |
1985年 | 223篇 |
1984年 | 239篇 |
1983年 | 203篇 |
1982年 | 199篇 |
1981年 | 208篇 |
1980年 | 193篇 |
1979年 | 197篇 |
1978年 | 187篇 |
1977年 | 163篇 |
1976年 | 181篇 |
1975年 | 145篇 |
1974年 | 125篇 |
1973年 | 130篇 |
1971年 | 96篇 |
1970年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
A. Türler H. W. Gäggeler D. T. Jost P. Armbruster W. Brüchle H. Folger F. P. Heßberger S. Hofmann G. Münzenberg V. Ninov M. Schädel K. Sümmerer J. V. Kratz U. Scherer 《Zeitschrift für Physik A Hadrons and Nuclei》1988,331(3):363-364
The isotope254No was produced in the fusion reaction48Ca +208Pb. Using the velocity filter SHIP and radiochemical techniques it was found that the nuclide254No with a half-life of 55 s decays byα, EC, and spontaneous-fission. Deduced partial half-lives are (61±2) s forα-decay, (550 ?160 +370 ) s for EC and [2.2 ?1.0 +2.0 ]×104 s for spontaneous fission. 相似文献
132.
I. Miesiąc K. Schügerl J. Szymanowski 《Journal of Radioanalytical and Nuclear Chemistry》1992,163(1):181-191
Potassium leakage was studied in liquid membrane systems containing various emulsifiers and compared with emulsion, stability in the storage test. The effects of various parameters upon emulsion stability and the leakage of standard traces are discussed. The transfer of cations can be caused by emulsion breaking, by transport with the specific carrier and/or with surfactants used as emulsifiers. The latter case becomes especially important when hydrophilic surfactants, e.g. ones containing polyoxyethylene chains, are present in liquid membranes. In systems containing hydrophobic emulsifiers the transfer of potassium is relatively low. In each case considered the effect of emulsifiers upon the transfer of the standard tracer should be checked prior to using the leakage test to characterize emulsion stability. 相似文献
133.
134.
M. Steyer K. A. Stankov H. Mizoguchi B. Ouyang F. P. Schäfer 《Applied physics. B, Lasers and optics》1989,49(4):331-337
An X-ray preionized, discharge-pumped XeCl laser with a variable beam cross-section of up to 6×6 cm2 is described. It uses flat electrodes and the beam width is determined by X-ray collimation. Its operation characteristics concerning reduced electric field strength (E/p) and X-ray dose are discussed in detail. The inductance of the discharge loop is minimized using a water capacitor arrangement. A very high specific optical power (90 MW/l) is achieved in an active volume of 1.2 l. The pulse energy exceeds 5 J in a 45 ns pulse (FWHM). Komatsu Ltd., Manda 1200, Hiratsuka-shi, Kanagawa 254, Japan Institute of Optics and Fine Mechanics, Department of Plasma Physics, Academia Sinica, Shanghai, P.R. China 相似文献
135.
B. Freisinger U. Kogelschatz J. H. Schäfer J. Uhlenbusch W. Viöl 《Applied physics. B, Lasers and optics》1989,49(2):121-129
Ozone is generated in pure oxygen (p5 kPa), synthetic air (p7 kPa) and oxygen-argon mixtures (p3 kPa) by irradiation of these gases with the VUV light of a repetitively pulsed (f
L15 Hz) F2-laser at =157.6 nm with maximum about 4 mJ/pulse. An absorption photometer measurement operating at 253.7 nm (Hg line) determines the ozone concentration as a function of oxygen and/or additive gas pressure, the repetition frequency of the laser and the wall temperature of the reaction chamber. The temporal development of the ozone concentration as a function of these parameters is calculated by means of rate equations for the species O(3
P), O2(X
3
g
–
), O3(1
A
1), O(1
D), O2(a
1g), O2(b
1
g
+
) and vibrationally excited O
3
*
(1
A
1) and the photon distribution. The maximum concentration of O3 in the sealed-off chamber reaches 1.6% in pure O2, 4.1% in air and 1.2% in a 1:5 O2-Ar mixture at 3 kPa. The annihilation of O3 by the wall and temperature dependent volume processes (300 KT395 K) is studied and the experimental and theoretical results are compared. 相似文献
136.
Dirk Lützenkirchen‐Hecht Kay Rohrmann Thomas Stöcker Wolfgang Thiel 《Surface and interface analysis : SIA》2007,39(11):845-851
Different ink‐jet printed paper materials were investigated using X‐ray photoelectron spectroscopy (XPS) yielding the elemental composition of the near‐surface region of the papers. We found significant differences with respect to the detected elements and their atomic concentrations in the different inks studied here. Two different groups of inks could be identified by means of a lower ratio of the O and C atomic concentrations and lower concentrations in specific trace elements like Mg, Na and Si. High‐resolution spectra of C 1s and O 1s core levels allowed a detailed determination of the chemical state of the respective elements. On the basis of a detailed deconvolution of these XPS signals, significant differences between all the investigated ink‐jet printed papers were found, thereby allowing their discrimination. The applicability of the measurements and, more generally, the XPS technique for forensic investigations of paper are discussed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
137.
Naumann W 《The Journal of chemical physics》2005,123(6):64505
Fluorescence quenching by excimer formation is studied on the assumption that the excimer formation and dissociation can be modeled as overdamped motion in an attractive potential (classical potential models). An approach to the zeroth-order, concentration-independent quenching constants is proposed which starts from a mean reaction-time ansatz and reduces the calculation essentially to the solution of the eigenvalue problem for the Smoluchowski operator which describes the excimer equilibration. For a square-well potential model it is shown that a quenching constant expansion in terms of relaxation modes, truncated at the kinetic level, gives a satisfactory approximation of the recently obtained exact zeroth-order result under defined conditions. It is demonstrated how this two-mode approach can be applied for a quenching constant estimation if the excimer formation and dissociation are modeled by more realistic interaction potentials, as for instance, Morse- or Gaussian-type ones. 相似文献
138.
C. Fischbacher K.-U. Jagemann K. Danzer U. A. Müller L. Papenkordt J. Schüler 《Analytical and bioanalytical chemistry》1997,359(1):78-82
Partial least-squares regression (PLS) and radial basis function (RBF) networks are used to compute calibration models for non-invasive blood glucose determination by NIR diffuse reflectance spectroscopy. A model computation shows that even extremely small deviations of the spectra induce increased prediction errors. Since the spectral contribution of blood glucose is much smaller than deviations resulting from the non-invasive measuring process a method based on Pearson’s correlation coefficient can be used for evaluating the quality of the recorded spectra during the prediction step. Another method is based on the leverage values from the hat matrix of the RBF network. Both methods lead to a significant decrease in prediction error. 相似文献
139.
Wolfgang Werner 《Fresenius' Journal of Analytical Chemistry》1992,342(10):783-786
Summary Systematic quality assurance, e.g. in accordance with the provisions of ISO 9000, requires not only the targeted use of quality as a management tool, but also a revised attitude to operational procedures. Although sophisticated checking of the final results of a procedure (e.g. results of analyses, sales products, reports) meets the legal requirements and often also the customers' requirements, this misses the chance of being able to influence the quality of a final result at the earliest possible stage. It is then only possible subsequently to take the uneconomic decision as to whether the result of the work is useable or must be discarded or the object reworked. Within quality assurance, all operations are to be considered as processes with the aim of arriving at a statistically controlled process. The advantages of statistical process control are explained by way of examples from analytical procedures and production. The status of internal audits is explained as it interrelates with process control. 相似文献
140.