全文获取类型
收费全文 | 34759篇 |
免费 | 620篇 |
国内免费 | 136篇 |
专业分类
化学 | 19562篇 |
晶体学 | 237篇 |
力学 | 1109篇 |
综合类 | 9篇 |
数学 | 5061篇 |
物理学 | 9537篇 |
出版年
2022年 | 412篇 |
2021年 | 508篇 |
2020年 | 499篇 |
2019年 | 457篇 |
2018年 | 530篇 |
2017年 | 469篇 |
2016年 | 809篇 |
2015年 | 685篇 |
2014年 | 765篇 |
2013年 | 1536篇 |
2012年 | 1589篇 |
2011年 | 1874篇 |
2010年 | 1090篇 |
2009年 | 1015篇 |
2008年 | 1582篇 |
2007年 | 1524篇 |
2006年 | 1411篇 |
2005年 | 1793篇 |
2004年 | 1850篇 |
2003年 | 1333篇 |
2002年 | 975篇 |
2001年 | 776篇 |
2000年 | 728篇 |
1999年 | 483篇 |
1998年 | 400篇 |
1997年 | 411篇 |
1996年 | 509篇 |
1995年 | 426篇 |
1994年 | 420篇 |
1993年 | 470篇 |
1992年 | 463篇 |
1991年 | 411篇 |
1990年 | 321篇 |
1989年 | 307篇 |
1988年 | 307篇 |
1987年 | 354篇 |
1986年 | 320篇 |
1985年 | 415篇 |
1984年 | 391篇 |
1983年 | 323篇 |
1982年 | 348篇 |
1981年 | 352篇 |
1980年 | 333篇 |
1979年 | 312篇 |
1978年 | 326篇 |
1977年 | 287篇 |
1976年 | 264篇 |
1975年 | 267篇 |
1974年 | 251篇 |
1973年 | 243篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
C. de Duve 《Fresenius' Journal of Analytical Chemistry》1970,252(4-5):346-348
Summary Some recent developments in the field of tissue fractionation are briefly reviewed. Separation techniques have been improved considerably, thanks mainly to the construction of various automatic rotors for density gradient centrifugation. Progress has also been made in the analysis of the fractions, through automation of biochemical techniques, and especially through the use of quantitative morphological methods.
Trennverfahren subcellularer Teilchen
Zusammenfassung Ein Überblick über neuere Entwicklungen auf dem Gebiet der Gewebefraktionierung wird angegeben. Die Trennverfahren konnten wesentlich verbessert werden, hauptsächlich durch die Konstruktion verschiedener automatischer Rotoren zum Zentrifugieren mit Dichtegradient. Auch die Analyse der Fraktionen wurde durch Automation biochemischer Verfahren und besonders durch den Einsatz quantitativer morphologischer Methoden weitgehend verbessert.相似文献
132.
B. E. Krisyuk A. A. Popov G. E. Zaikov F. de Candia V. Vittoria R. Russo 《Colloid and polymer science》1987,265(3):220-225
The static modulus of elasticity (E) and the correlation time of rotation (
c
) of 2,-2,6,6-tetramethylpiperidine-1-oxyl are studied as a function of the temperature (210<T <350°K) for oriented films of isotactic polypropylene and polyethylene of high and low density.E and
c
change both upon heating and polymer orientation; this result indicates that sample properties are influenced by the microstructure of the amorphous phase where probes are localized. 相似文献
133.
134.
135.
Christian C. Van de Sande Syed Zahoor Ahmad Friedrich Borchers Karsten Levsen 《Journal of mass spectrometry : JMS》1978,13(11):666-670
Gaseous protonated aziridine ions are produced at the threshold from β-phenoxyethylamine molecular ions. The evidence for this is collisional activation spectra, using various precursors (including labelled analogues) under electron impact and field ionization conditions. Partial conversion to the acyclic \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH = }\mathop {\rm N}\limits^ + {\rm H}_{\rm 2} $\end{document} isomer occurs at higher electron energies and is rationalized by means of a potential energy surface constructed from energetic data. 相似文献
136.
Augustin de Castries 《Tetrahedron》2007,63(41):10330-10336
Azamacrocycles bearing four arylsulfonyl or arylsulfinyl pendant arms have been synthesised with good yields through nucleophilic addition of 1,4,8,11-tetraazacyclotetradecane (cyclam) to phenylvinylsulfone, phenylvinylsulfoxide or (R)-tolylvinylsulfoxide in isopropanol/water media. The crystal structure of the tetraethylsulfonylphenyl substituted macrocycle has been determined by X-ray crystallography. Preliminary studies of the coordination properties of these functionalised macrocyles towards Cu(II) and Eu(III) indicate that pendant sulfoxide groups act as oxygen donor coordinating groups. 相似文献
137.
Metabolic profiling of urinary organic acids by single and multicolumn capillary gas chromatography 总被引:1,自引:0,他引:1
M F Lefevere B J Verhaeghe D H Declerck J F Van Bocxlaer A P De Leenheer R M De Sagher 《Journal of chromatographic science》1989,27(1):23-29
High-resolution gas chromatography (HRGC) and gas chromatography/mass spectrometry (GC/MS) are the techniques of choice to determine the retention indices of more than 200 organic acids as their trimethylsilyl (TMS) or oxime-trimethylsilyl derivatives. Several types of apolar and semipolar fused-silica capillary columns (OV-1, SE-52, and OV-1701), used to analyze and separate organic acids isolated from urine samples, are evaluated. 相似文献
138.
Summary After a brief introduction of the subject, the paper focusses on the first step in any optimization procedure: the delineation
of the parameter space, wherein the global optimum is to be found. For organic modifier optimization in reversed-phase liquid
chromatography it is shown that the necessary information can be derived from a single water-methanol gradient. It first yields
an estimate of the total number of solutes in the sample, which is vital to define the peak capacity needed to achieve separation
at a certain confidence level. Next, the gradient allows the prediction of suitable isocratic methanol binary solvents, and
transfer rules formulate the iso-eluotropic composition of the common binary solvents (tetrahydrofuran and acetonitrile).
Because all predictions are based on a statistical analysis of a limited data base, attention is given to the practical situation
where an actual sample deviates from the average solute behaviour. Such deviations are revealed in the first isocratic run
and can be used to arrive at a better estimate of solute retention. 相似文献
139.
L. D'Haenens C. C. Van De Sande M. Schelfaut M. Vandewalle 《Journal of mass spectrometry : JMS》1987,22(6):330-333
The chemical ionization (CI) mass spectra of the 2-tert-butyl-substituted 1,3-cyclopentane- and 1,3-cyclohexanediol diacetates and dimethyl ethers have been determined using isobutane and methane as reagent gases. From the differences in the spectra of these compounds, it clearly follows that steric and conformational effects are expresssed in the CI mass spectra. The relative impact of these effects, however, is strongly dependent on diol derivatization and 2-alkyl substitution. 相似文献
140.
H. J. de Vega H. Eichenherr J. M. Maillet 《Communications in Mathematical Physics》1984,92(4):507-524
We investigate the algebras of the non-local charges and their generating functionals (the monodromy matrices) in classical and quantum non-linear models. In the case of the classical chiral models it turns out that there exists no definition of the Poisson bracket of two monodromy matrices satisfying antisymmetry and the Jacobi identity. Thus, the classical non-local charges do not generate a Lie algebra. In the case of the quantum O(N) non-linear model, we explicitly determine the conserved quantum monodromy operator from a factorization principle together withP,T, and O(N) invariance. We give closed expressions for its matrix elements between asymptotic states in terms of the known two-particleS-matrix. The quantumR-matrix of the model is found. The quantum non-local charges obey a quadratic Lie algebra governed by a Yang-Baxter equation.Laboratoire associé au CNRS No. LA 280 相似文献