全文获取类型
收费全文 | 11164篇 |
免费 | 378篇 |
国内免费 | 85篇 |
专业分类
化学 | 7823篇 |
晶体学 | 66篇 |
力学 | 162篇 |
数学 | 1641篇 |
物理学 | 1935篇 |
出版年
2023年 | 64篇 |
2022年 | 98篇 |
2021年 | 128篇 |
2020年 | 221篇 |
2019年 | 189篇 |
2018年 | 113篇 |
2017年 | 87篇 |
2016年 | 295篇 |
2015年 | 233篇 |
2014年 | 286篇 |
2013年 | 523篇 |
2012年 | 568篇 |
2011年 | 655篇 |
2010年 | 393篇 |
2009年 | 347篇 |
2008年 | 585篇 |
2007年 | 582篇 |
2006年 | 599篇 |
2005年 | 555篇 |
2004年 | 448篇 |
2003年 | 342篇 |
2002年 | 408篇 |
2001年 | 200篇 |
2000年 | 204篇 |
1999年 | 171篇 |
1998年 | 173篇 |
1997年 | 165篇 |
1996年 | 170篇 |
1995年 | 147篇 |
1994年 | 162篇 |
1993年 | 147篇 |
1992年 | 126篇 |
1991年 | 119篇 |
1990年 | 101篇 |
1989年 | 84篇 |
1988年 | 73篇 |
1987年 | 75篇 |
1985年 | 127篇 |
1984年 | 111篇 |
1983年 | 80篇 |
1982年 | 119篇 |
1981年 | 105篇 |
1980年 | 86篇 |
1979年 | 104篇 |
1978年 | 100篇 |
1977年 | 88篇 |
1976年 | 102篇 |
1975年 | 72篇 |
1974年 | 63篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Summary In general, solid particles liquify when they are exposed to air laden with the vapor of a liquid in which they are soluble. There are exceptions, however, which may be explained by assuming the formation of a solvate.
On the occasion of the hundredth return ofFriedrich Emich's birthday.
The authors wish to express their appreciation to ProfessorO. F. Steinbach for his suggestions and advice. 相似文献
Zusammenfassung Feste Teilchen verflüssigen sich im allgemeinen, wenn sie Luft ausgesetzt sind, die mit dem Dampf einer Flüssigkeit geladen ist, in der sie löslich sind. Es wurden aber Ausnahmen gefunden, die möglicherweise durch die Bildung von Solvaten erklärt werden können.
Résumé Généralement, les particules solides se liquéfient si elles sont exposées à l'air chargé de la vapeur d'un liquide dans lequel elles sont solubles. Il existe cependant des exceptions que l'on peut expliquer en supposant la formation de solvates.
On the occasion of the hundredth return ofFriedrich Emich's birthday.
The authors wish to express their appreciation to ProfessorO. F. Steinbach for his suggestions and advice. 相似文献
32.
Hafnium tetrachloride reacts with the tris(trimethylsilyl)silyl potassium tmen adduct (1) to form a [tris(trimethylsilyl)silyl]trichlorohafnium tmen complex (2); reaction of 2 with 2,6-dimethylphenylisonitrile leads to insertion into the silicon hafnium bond (4). 相似文献
33.
34.
Solid-liquid phase-transfer glycosylation (KOH, tris[2-(2-methoxyethoxy)ethye]amine ( = TDA-1), MeCN) of pyrrolo[2,3-d]pyrimidines such as 3a and 3b with an equimolar amount of 5-O-[(1,1 -dimethylethyl)dimethylsilyl]-2,3-O-(1-methylethylidene)-α-D -ribofuranosyl chloride (1) [6] gave the protected β-D -nucleosides 4a and 4b , respectively, stereoselectively (Scheme). The β-D -anomer 2 [6] yielded the corresponding α-D -nucleosides 5a and 5b with traces of the β-D -compounds. The 6-substituted 7-deazapurine nucleosides 6a , 7a , and 8 were converted into tubercidin (10) or its α-D -anomer (11) . Spin-lattice relaxation measurements of anomeric ribonucleosides revealed that T1 values of H? C(8) in the α-D -series are significantly increased compared to H? C(8) in the β-D -series while the opposite is true for T1 of H? C(1′). 15N-NMR data of 6-substituted 7-deazapurine D -ribofuranosides were assigned and compared with those of 2′-deoxy compounds. Furthermore, it was shown that 7-deaza-2′deoxyadenosine ( = 2′-deoxytubercidin; 12 ) is protonated at N(1), whereas the protonation site of 7-deaza-2′-deoxyguanosine ( 20 ) is N(3). 相似文献
35.
J. W. Petersen G. Weyer S. Damgaard H. L. Nielsen 《Zeitschrift für Physik B Condensed Matter》1980,38(4):313-326
Single crystalline and polycrystalline -tin has been implanted at room temperature with 80-keV ions of radioactive119m
Sn,119Sb, and119m
Te. The radioactive nuclei decay to the Mössbauer level of119Sn. Mössbauer spectra of the emitted 24-keV radiation have been measured for different source temperatures by resonance counting techniques. Five individual lines in the spectra are characterized mainly by their isomer shifts and Debye temperatures. From these parameters the radiogenic119Sn atoms are concluded to be located in regular substitutional and interstitial lattice sites and in defect complexes. Simple models for the defects are proposed: A Sn-vacancy pair consists of Sn atoms on (nearly) substitutional sites with a dangling bond into an adjacent vacancy. In a complex oxygen-containing defect the Sn atoms have approximately a 5s
2 configuration withp-bonds to two nearest neighbour atoms. Sn atoms, having an atomic 5s
2 5p
2 configuration and large vibrational amplitudes, are concluded to be in non-bonding regular interstitial sites. For special implantation conditions minor fractions of SnO2 molecules are formed in the bulk. The interstitial119Sn and the119Sn-vacancy pairs are proposed to represent elementary point defects in -tin. Conclusions are also drawn concerning the lattice location and the defects created in the implantation process of the implanted parent isotopes. 相似文献
36.
Dr. Frank Piefke 《Monatshefte für Mathematik》1980,89(1):45-56
We continue our investigations started in a paper with the same title. The -length of a curve defined in this paper can be written as an integral along the curve. Furthermore, we determine necessary and sufficient conditions for the existence of a measure of orientated lines which generates a given non-symmetric pseudo-metric.
Herrn Prof. Dr. H.-J. Kanold zum 65. Geburtstag gewidmet 相似文献
Herrn Prof. Dr. H.-J. Kanold zum 65. Geburtstag gewidmet 相似文献
37.
Frank J.S. Wang 《Stochastic Processes and their Applications》1977,5(2):173-193
Consider a population consisting of one type of individual living in a fixed region with area A. In [8], we constructed a stochastic population model in which the death rate is affected by the age of the individual and the birth rate is affected by the population density PA(t), i.e., the population size divided by the area A of the given region. In [8], we proposed a continuous deterministic model which in general is a nonlinear Volterra type integral equation and proved that under appropriate conditions the sequence PA(t) would converge to the solution P(t) of our integral equation in the sense that .In this paper, we obtain a “central limit theorem” for the random element √A(PA(t)?P(t)). We prove that under appropriate conditions √A(PA(t)?P(t)) will converge to a Gaussian process. (See Theorem 3.4 for the explicit formula of this Gaussian process.) 相似文献
38.
The analysis of microbial communities is of increasing importance in life sciences and bioengineering. Traditional techniques of investigations like culture or cloning methods suffer from many disadvantages. They are unable to give a complete qualitative and quantitative view of the total amount of microorganisms themselves, their interactions among each other and with their environment. Obviously, the determination of static or dynamic balances among microorganisms is of fast growing interest. The generation of species specific and fluorescently labeled 16S ribosomal DNA (rDNA) fragments by the terminal restriction fragment length polymorphism (T-RFLP) technique is a suitable tool to overcome the problems other methods have. For the separation of these fragments polyacrylamide gel sequencers are preferred as compared to capillary sequencers using linear polymers until now because of their higher electrophoretic resolution and therefore sizing accuracy. But modern capillary sequencers, especially multicapillary sequencers, offer an advanced grade of automation and an increased throughput necessary for the investigation of complex communities in long-time studies. Therefore, we adapted a T-RFLP technique to an automated high-throughput multicapillary electrophoresis device (ABI 3100 Genetic Analysis) with regard to a precise qualitative and quantitative characterization of microbial communities. 相似文献
39.
Frank Herwig Köhler Hans Jürgen Kalder Ernst Otto Fischer 《Journal of organometallic chemistry》1975,85(2):C19-C22
Carbon-13 NMR data are reported for trimethyltin derivatives containing ERn groups where E C, Si, Ge, Sn, N, O and S including a series of cyclic amines with ring sizes from three to seven. Coupling constant values for the homologous series of fourth group derivatives give goood correlations with the electronegativity of E. The observation of the two-bond, ¦ 2J(119SnE13C) ¦ couplings only in the derivatives containing bulky R groups is rationalized by a bimolecular exchange of ERn groups in the concentrated solutions studied. 相似文献
40.
The enthalpies of dilution of lithium, sodium, potassium, and magnesium chloride and sulfate solutions in the range 0.1 to 1.0 m have been measured at 30°C with a microcalorimeter. The relative apparent enthalpies φL of these solutions have been determined with the aid of an extended form of the Debye-Hückel limiting law $$\phi _L = S_H I^{1/2} [1/(1 + I^{1/2} ) - (\sigma /3)] + {\rm B}{\rm I} + CI^{3/2} $$ whereS H is the limiting-law slope, σ = 3/I3/2 × [(1+I1/2 ? 1/(1+I1/2 ? 2 ln (2+I1/2)], andB andC are empirical constants. This equation fits the experimental results to within a standard deviation of 2 cal-mole?1 for all the salts. The measured φL for the MgSO4 solutions were compared to those calculated using the additivity principle, φL(MgCl2) + φL(Na2SO4) ? 2φL(NaCl), and the extended Debye-Hückel equation. The results of this comparison have been used to calculate the ΔH A o for the formation of MgSO 4 0 . A value of ΔH A o = 1.15 to 1.36 was obtained, depending upon the φL estimates for the free ions Mg2+ and SO 4 2? . The results are briefly discussed and compared to the results obtained by other workers. 相似文献