全文获取类型
收费全文 | 386204篇 |
免费 | 8413篇 |
国内免费 | 5906篇 |
专业分类
化学 | 195361篇 |
晶体学 | 4811篇 |
力学 | 20360篇 |
综合类 | 381篇 |
数学 | 57731篇 |
物理学 | 121879篇 |
出版年
2021年 | 3230篇 |
2020年 | 3886篇 |
2019年 | 4152篇 |
2018年 | 12465篇 |
2017年 | 13004篇 |
2016年 | 10163篇 |
2015年 | 5250篇 |
2014年 | 6747篇 |
2013年 | 13380篇 |
2012年 | 15859篇 |
2011年 | 24772篇 |
2010年 | 16385篇 |
2009年 | 16315篇 |
2008年 | 21782篇 |
2007年 | 24608篇 |
2006年 | 11873篇 |
2005年 | 15957篇 |
2004年 | 12240篇 |
2003年 | 11352篇 |
2002年 | 9692篇 |
2001年 | 9058篇 |
2000年 | 7108篇 |
1999年 | 5144篇 |
1998年 | 4465篇 |
1997年 | 4172篇 |
1996年 | 4060篇 |
1995年 | 3615篇 |
1994年 | 3784篇 |
1993年 | 3558篇 |
1992年 | 3732篇 |
1991年 | 3860篇 |
1990年 | 3642篇 |
1989年 | 3471篇 |
1988年 | 3349篇 |
1987年 | 3265篇 |
1986年 | 3245篇 |
1985年 | 4103篇 |
1984年 | 4136篇 |
1983年 | 3500篇 |
1982年 | 3721篇 |
1981年 | 3441篇 |
1980年 | 3195篇 |
1979年 | 3489篇 |
1978年 | 3736篇 |
1977年 | 3675篇 |
1976年 | 3828篇 |
1975年 | 3498篇 |
1974年 | 3603篇 |
1973年 | 3692篇 |
1972年 | 2941篇 |
排序方式: 共有10000条查询结果,搜索用时 525 毫秒
991.
A method employing a wide pore polymeric reversed phase column has been developed for the separation of most of the chlorophylls and related compounds previously described as occurring in marine microalgae. The high selectivity toward molecular shape of this kind of stationary phase has enabled compounds of very similar structure, such as chlorophylls c1, c2 and Mg-divinylpheoporphyrin a5 monomethyl ester, and chlorophyll a and the phytol-substituted chlorophyll c-like pigments, which commonly coelute on monomeric bonded phases, to be resolved in a single run. Some of these pigments, formerly thought to be a single compound, have, in fact, been demonstrated to be groups of two or more. The method has been successfully applied to both algal cultures and natural sea water samples. When visible light absorbance detection was used, the method proved suitable for separation of various carotenoids. 相似文献
992.
993.
G. Garcia-Belmonte J. Bisquert L. M. Navarro J. R. Jurado F. M. B. Marques 《Ionics》1995,1(5-6):377-383
In ionic conductors, long range-migrating charges are a main cause of polarization processes. This has complicated, up to
date, the study of ionic thermocurrents (ITC) in solid electrolytes. However, the method is appealing, as it probes directly
charge-formation phenomena that are important both from a scientific point of view and for applications.
This work reports on the observation of ITC in solid electrolytes. Under appropriate experimental conditions, the ITC response
of a zirconia sample electroded with platinum is a reproducible one, thus opening the way to a new characterization method
that may complement other well established methods, such as Impedance Spectroscopy and a number of electrochemical techniques.
The general trends of the response, which is composed of two well resolved ITC peaks, is discussed. One of them, taking place
at higher temperatures, conforms to the standard shape of a first order kinetics depolarization process.
Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995 相似文献
994.
995.
A PULSED LASER AND PULSE RADIOLYSIS STUDY OF AMPHIPHILIC CHLOROPHYLL DERIVATIVES WITH PDT ACTIVITY TOWARD MALIGNANT MELANOMA 总被引:1,自引:0,他引:1
L. Fiedor A. A. Gorman I. Hamblett V. Rosenbach-Belkin Y. Salomon A. Scherz I. Tregub 《Photochemistry and photobiology》1993,58(4):506-511
Two amphiphilic derivatives of chlorophyll, which have high potential as photodynamic therapy sensitizers for malignant melanoma have been investigated by a combination of laser flash photolysis and pulse radiolysis. It is shown that direct excitation of monomeric forms of these molecules in both hydrophilic and hydrophobic environments produces significant yields of the corresponding triplet states, which have been characterized in terms of spectral and kinetic parameters. In both environments, scavenging of the triplets by oxygen produces singlet oxygen, O2 (l Δ8 ), with essentially unit efficiency as evidenced by time-resolved IR luminescence measurements. 相似文献
996.
O. A. Rakitin E. A. Khaibullina T. I. Godovikova V. A. Ogurtsov L. I. Khimel'nitskii 《Chemistry of Heterocyclic Compounds》1993,29(8):952-954
Previously unreported furoxanenitrolic acids have been synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1117–1119, August, 1993. 相似文献
997.
The micro element content of food is an important quality index due to the action of these elements on human health. In this
article, we discuss how to ensure the reliability of analytical data on micro elements in order to truly represent the condition
of food. Sampling, treatment of the analytical sample, selection of the analytical method, standard solution, and certified
reference material, blank test, calibration of the instrument and equipment, application of the quality control chart, assessment
of the final analytical result, and quality assurance system are briefly described.
Received: 5 July 2001 Accepted: 19 November 2001 相似文献
998.
999.
L. A. Sakhnovich 《Functional Analysis and Its Applications》2002,36(3):205-211
The conjecture according to which the mean energy of an equilibrium system in quantum theory exceeds the mean energy of the corresponding classical system is considered. It is rigorously proved that the conjecture holds for the potential well. The estimates for the mean energy of the potential well at high and low temperatures are of special interest. 相似文献
1000.
Yu. V. Belovitskaya I. V. Pekov E. R. Gobechiya N. A. Yamnova Yu. K. Kabalov N. V. Chukanov J. Schneider 《Crystallography Reports》2002,47(2):223-228
The crystal structures of two ancylite specimens from Khibiny massif (the Kola Peninsula, Russia)—ancylite-(Ce) from alkali hydrothermalites (Sr1.01Ca0.02Ba0.01)Σ1.04(Ce0.52La0.28Nd0.11Pr0.04 Sm0.01)Σ0.96(CO3)2(OH0.83F0.13)Σ0.96 · 0.9H2O and ancylite-(Ce) from carbonatites—have (Sr0.80Ca0.05Ba0.01)Σ0.86(Ce0.62La0.40Nd0.09Pr0.03) Σ1.14(CO3)2(OH0.99F0.15)Σ1.14 · 1.0H2O been refined by the Rietveld method. A focusing STOE-STADIP diffractometer with a bent Ge(111) primary monochromator was used (λ MoK α 1 radiation, 2.16° < 2θ < 54.98°; reflection number 237–437). All the computations for ancylite from alkali hydrothermalites were performed within the sp. gr. Pmc21, a = 5.0634(1) Å, b = 8.5898(1) Å, c = 7.2781(1) Å, V = 316.55(1) Å3, R wp = 1.90; the computations for ancylite from carbonatites were performed within the sp. gr. Pmcn, a = 5.0577(1) Å, b = 8.5665(2) Å, c = 7.3151(2) Å, V = 316.94(1) Å3, R wp = 2.38 in the anisotropic approximation of thermal vibrations of cations and oxygen atoms. 相似文献