全文获取类型
收费全文 | 8607篇 |
免费 | 249篇 |
国内免费 | 45篇 |
专业分类
化学 | 5482篇 |
晶体学 | 96篇 |
力学 | 172篇 |
数学 | 1472篇 |
物理学 | 1679篇 |
出版年
2023年 | 49篇 |
2022年 | 72篇 |
2021年 | 109篇 |
2020年 | 119篇 |
2019年 | 120篇 |
2018年 | 152篇 |
2017年 | 137篇 |
2016年 | 257篇 |
2015年 | 236篇 |
2014年 | 253篇 |
2013年 | 521篇 |
2012年 | 508篇 |
2011年 | 534篇 |
2010年 | 374篇 |
2009年 | 323篇 |
2008年 | 423篇 |
2007年 | 445篇 |
2006年 | 430篇 |
2005年 | 372篇 |
2004年 | 340篇 |
2003年 | 242篇 |
2002年 | 238篇 |
2001年 | 149篇 |
2000年 | 159篇 |
1999年 | 111篇 |
1998年 | 108篇 |
1997年 | 96篇 |
1996年 | 105篇 |
1995年 | 65篇 |
1994年 | 82篇 |
1993年 | 68篇 |
1992年 | 75篇 |
1991年 | 74篇 |
1990年 | 65篇 |
1989年 | 75篇 |
1988年 | 56篇 |
1987年 | 56篇 |
1986年 | 56篇 |
1985年 | 52篇 |
1984年 | 56篇 |
1983年 | 41篇 |
1982年 | 46篇 |
1981年 | 57篇 |
1979年 | 46篇 |
1978年 | 46篇 |
1977年 | 36篇 |
1976年 | 48篇 |
1973年 | 45篇 |
1959年 | 35篇 |
1958年 | 42篇 |
排序方式: 共有8901条查询结果,搜索用时 326 毫秒
51.
Matrix-Investigations on Monomeric Copper(I) Chloride and its Complexes with N2 and PN Ligands. IR Spectroscopic Results and ab-initio Calculation In solid argon the reaction of monomeric CuCl with N2 yields ClCuN2. On the basis of two absorptions in the ir-spectrum and their corresponding isotopic shifts (14/15N) and with the help of a normal coordinate analysis, linearity of the molecule has been deduced. These results are confirmed by large scale ab-initio Calculations (CPF, MP2). Reaction of monomeric CuCl with molecular PN under matrix condition is shown to give rise to new absorptions in the IR spectrum which arev assigned to a linear molecule ClCuNP. 相似文献
52.
I. Mohammed-Ziegler B. Por M. Kubinyi A. Grofcsik A. Grün I. Bitter 《Journal of Molecular Structure》2003,650(1-3):39-44
The complex formation between chromogenic capped calix 4 arene derivatives comprising indophenol indicator group(s), and aliphatic amines has been studied by UV/Vis spectroscopy. The equilibrium constants have been determined in ethanol, and—for one ligand—also in dimethylsulfoxide. The results have been interpreted in terms of various types of host–guest interactions and of steric effects. 相似文献
53.
Wolf Johannes MÜller 《Monatshefte für Chemie / Chemical Monthly》1927,48(1-2):61-70
Zusammenfassung Es wurde an Hand des Zahlenmaterials meiner Arbeit »Über die Passivierung speziell des Eisens« a. a. O. gezeigt, da\ man unter BerÜcksichtigung der Zeiterscheinungen Stromspannungskurven fÜr die Passivierung des Eisens erhält, welche aus zwei ästen bestehen. Von diesen entspricht der eine dem Verhalten des aktiven, der andere dem Verhalten des passiven Metalles. Die frÜheren, ohne BerÜcksichtigung der Zeitverhältnisse von verschiedenen Forschern aufgestellten Kurven entsprechen mehr oder weniger Zufallswerten, geben das Verhalten eines Metalles, das aktiv und passiv auftreten kann, nicht vollständig wieder und sind als Grundlage theoretischer Diskussionen unzureichend. 相似文献
54.
Solichová D Melichar B Klejna M Jurašková B Královská L Bláha V Zd'ánský P Zadák Z 《Talanta》2003,60(2-3):459-465
Twelve self-sustaining nonagenarians, 10 women and two men, aged 94+/-3 years, and eight institutionalised nonagenarians, eight women, aged 91+/-1 year as well as 11 control subjects, seven women and four men, aged 84+/-5 years entered the study. Urinary neopterin, an indicator of systemic immune activation, and serum thiobarbituric acid reactive substances (TBARS), a marker of lipoperoxidation, were determined initially, and collection of the blood and urine samples was repeated at 3-month interval. Neopterin was measured in the urine specimens by reversed-phase high performance liquid chromatography. A C(18) reversed-phase column 3.3x150 mm, 5 mum-diameter packing Separon SGX was used. Potassium phosphate buffer (15 mmol l(-1), pH 6.4) at flow rate of 0.8 ml min(-1) was used as mobile phase. After centrifugation (5 min, 1300xg) and diluting 100 mul of urine specimens with 1.0 ml of mobile phase containing 2 g of disodium-EDTA per litre, a 20 mul sample was injected on a column. Neopterin was identified by its native fluorescence (353 nm excitation, 438 nm emission). Creatinine was determined by Jaffé kinetic reaction after dilution of sample 1:50 (v/v). The concentration of neopterin in urine was expressed as neopterin/creatinine ratio (mumol mol(-1) creatinine). TBARS were determined spectrofluorometrically using LS-5 spectrofluorimeter (excitation wavelength 528 nm, emission wavelength 558 nm) after extraction with n-butanol treatment with thiobarbituric acid. The significance of differences between nonagenarians and control group was examined by ANOVA-Kruskal-Wallis tests, using statistical software NCSS 6.0.21 (Kaysville, UT, 1996). The decision on significance was based on P=0.05. Urinary neopterin was significantly higher in institutionalised compared to self-sustaining subjects and controls (625+/-565 vs. 203+/-63 mumol mol(-1) creatinine, and 198+/-128 mumol mol(-1) creatinine, respectively, P=0.006). The serum TBARS were higher in both groups of nonagenarians (3.23+/-1.16 mumol l(-1) and 2.69+/-0.39 vs. 2.12+/-0.83 mumol l(-1) for the self-sustaining, institutionalised and controls, respectively, P=0.023). We conclude that the fluorimetric determinations of urinary neopterin and serum TBARS can be useful for the monitoring health status in the elderly patients. 相似文献
55.
This study compared the fracture strength of Class II slot cavities restored with polymerizable restorative materials. Sixty, caries-free, posterior teeth were divided into five groups of 12 teeth. The Class II slot cavities were prepared. The teeth were restored with two packable composites (Filtek P60, Surefil), a microhybrid composite (Filtek Z250)and two ormocer (Definite, Admira). The restorations were then subjected to fracture resistance tests. The marginal ridges of the restorations were loaded at an angle of 13.5° to the long axis of the tooth in an Universal Testing Machine until failure. Analysis of mean forces indicated that, Filtek P60, Surefil and Filtek Z250 exhibited better performance than Definite and Admira. The tested resin composites differed in their mechanical properties. This study suggested that fracture behavior were highly influenced by the filler system. Overall, Filtek P60, Surefil, Filtek Z250, demonstrated good fracture resistance. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
56.
57.
Zólomy A. Berceli T. Járó G. Hilt A. Marozsák T. 《Optical and Quantum Electronics》1998,30(11-12):969-983
Optical and Quantum Electronics - A new approach for the design and construction of low noise broadband optical receivers is presented utilizing distributed amplification based on hybrid integrated... 相似文献
58.
Katalin E. Kövér Dušan Uhr?&#x;n Victor J. Hruby 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):162-168
A pulsed field gradient version of the sensitivity-enhanced 2D TOCSY experiment is proposed which yields high-quality spectra with improved sensitivity and a minimum of two scans pert1increment. For rapid acquisition of 1D TOCSY spectra, the 1D DPFGSE–TOCSY experiment was modified to include phase-encoded multiple-selective excitation followed by a simple spectral editing. Combination of these two building blocks is used in a sensitivity-enhanced 2D analog of the 3D TOCSY–TOCSY experiment which provides an efficient tool for resolving severely overlapped signals of oligomers in short experimental time. 相似文献
59.
In this paper we describe the general forms of all (nonlinear) continuous functionals on the sets of positive definite, positive semi-definite and Hermitian matrices which are multiplicative on the commuting elements. As a consequence, we obtain some new characterizations of the determinant on those classes of matrices.
60.
Lubomír Kubáček 《Mathematica Slovaca》2007,57(1):59-82
In some situations estimates of unknown parameters must be corrected by additional measurements. It is in principle no problem
to calculate the corrected estimates, however, it is of more interest to find formulae for correction itself. The formulae
enable us to design an additional experiment and to judge its usefulness.
The aim of the paper is to find such formulae for several situations.
Supported by the grant of the Council of Czech Government MSM 6 198 959 214. 相似文献