全文获取类型
收费全文 | 3813篇 |
免费 | 126篇 |
国内免费 | 13篇 |
专业分类
化学 | 2207篇 |
晶体学 | 22篇 |
力学 | 84篇 |
数学 | 475篇 |
物理学 | 1164篇 |
出版年
2023年 | 27篇 |
2022年 | 47篇 |
2021年 | 63篇 |
2020年 | 79篇 |
2019年 | 84篇 |
2018年 | 30篇 |
2017年 | 40篇 |
2016年 | 91篇 |
2015年 | 97篇 |
2014年 | 97篇 |
2013年 | 120篇 |
2012年 | 166篇 |
2011年 | 196篇 |
2010年 | 99篇 |
2009年 | 112篇 |
2008年 | 181篇 |
2007年 | 155篇 |
2006年 | 160篇 |
2005年 | 163篇 |
2004年 | 114篇 |
2003年 | 88篇 |
2002年 | 77篇 |
2001年 | 69篇 |
2000年 | 51篇 |
1999年 | 36篇 |
1998年 | 30篇 |
1997年 | 46篇 |
1996年 | 67篇 |
1995年 | 65篇 |
1994年 | 59篇 |
1993年 | 74篇 |
1992年 | 45篇 |
1991年 | 26篇 |
1990年 | 31篇 |
1989年 | 38篇 |
1988年 | 34篇 |
1987年 | 30篇 |
1986年 | 38篇 |
1985年 | 28篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 27篇 |
1981年 | 23篇 |
1980年 | 30篇 |
1978年 | 25篇 |
1975年 | 30篇 |
1968年 | 50篇 |
1967年 | 117篇 |
1966年 | 110篇 |
1965年 | 71篇 |
排序方式: 共有3952条查询结果,搜索用时 9 毫秒
51.
Netto-Ferreira JC Lhiaubet-Vallet V de Oliveira Bernardes B Ferreira AB Miranda MA 《Photochemistry and photobiology》2009,85(1):153-159
The photochemical reactivity of β-lapachone ( 1 ), nor -β-lapachone ( 2 ) and 1,2-naphthoquinone ( 3 ) towards amino acids and nucleobases or nucleosides has been examined employing the nanosecond laser flash photolysis technique. Excitation (λ = 355 nm) of degassed solutions of 1 – 3 , in acetonitrile, resulted in the formation of their corresponding triplet excited states. These transients were efficiently quenched by l -tryptophan, l -tryptophan methyl ester, l -tyrosine, l -tyrosine methyl ester and l -cysteine ( k q ≈ 109 L mol−1 s−1 ). For l -tryptophan, l -tyrosine and their methyl esters new transients were formed in the quenching process, which were assigned to the corresponding radical pair resulting from an initial electron transfer from the amino acids or their esters to the excited quinone, followed by a fast proton transfer. No measurable quenching rate constants could be observed in the presence of thymine and thymidine. On the other hand, efficient rate constants were obtained when 1 – 3 were quenched by 2'-deoxyguanosine ( k q ≈ 109 L mol−1 s−1 ). The quantum efficiency of singlet oxygen (1 O2 ) formation from 1 to 3 was determined employing time-resolved near-IR emission studies upon laser excitation and showed considerably high values in all cases (ΦΔ = 0.6), which are fully in accord with the ππ* character of these triplets in acetonitrile. 相似文献
52.
Obermaier C Jankowski V Schmutzler C Bauer J Wildgruber R Infanger M Köhrle J Krause E Weber G Grimm D 《Electrophoresis》2005,26(11):2109-2116
The method of preparing protein mixtures for electrophoretic analysis of membrane-associated cell proteins was improved. By sonication, about one-half of the proteins of thyroid cells were released into the supernatant, while the other half preferentially comprising membrane proteins still remained in cell fragments, which could be sedimented by centrifugation. After sonication, even those proteins which remained in cell fragments, could completely be dissolved by free-flow isoelectric focusing media. They migrated through the free-flow electrophoresis chamber without forming precipitates. Because of these improvements, it was possible to show that the two thyroid cancer cell lines ML-1 and ONCO-DG1 express cytokeratin 8 at similar rates, but cytokeratins 7 and 18 differently. In addition, the presence of inorganic pyrophosphatase, tubulin-beta-5, and tubulin-beta-1 chains in human thyroid cells was proved for the first time. 相似文献
53.
This work deals with the synthesis of piperidine and hydroxypiperidine analogs of nucleosides. Starting from commercially available 3-hydroxypiperidine, proline or 4-hydroxyproline, a series of piperidine derivatives of both purine and pyrimidine nucleobases was prepared. Various methods of nucleobase attachment were evaluated. The prepared compounds were tested for cytostatic, antibacterial, and antiviral properties but no significant activity was found. 相似文献
54.
By means of the stimulated Raman effect one may produce in H2, D2, and in several other gases, a substantial population in the ν = 1 state. Subsequent to the pulse excitation v---v energy transfers rapidly generate a vibrational distribution which is approximately equivalent to (3–4) × 103°K. Then, in H2 + D2 mixtures metathetic reactions occur. Here we report on a computer simulation of an experiment described elsewhere, designed to estimate whether a measurable fraction of the hydrogen molecules reach the upper vibrational level and dissociate. Solutions of the coupled differential equations show that the anticipated hydrogen atom concentrations are too low by a factor of 107-108 to account for the observed H/D exchanges. These calculations also show that the conventional phenomenological rate equation for dissociation does not apply to this highly non-thermal distribution. 相似文献
55.
An infrared spectral investigation of a number of pyrimidine and pyrimidone hexachloroantimonates is reported. Typical aromatic absorption bands found in pyrimidinium salts were absent in the pyrimidone cations. 2-And 4-Pyrimidone hexachloroantimonates, as well as their N-methyl- and N,N'-dimethyl derivatives, exhibit intense carbonyl absorption bands between 1720–1729 cm?1 (solid state) which corroborates N-protonation of pyrimidones. 相似文献
56.
The partial Lossen degradation of the hydroxamic acid group at C-4 or C-5 of sodium 4,5-thiazoledicarbohydroxamate (IIIb) and its 2-methyl analog (IIIe) initiated a multicoursed reaction which furnished a mixture of thiazolo[4,5-d]- and thiazolo[5,4-d]-N-hydroxyuracils. The isomer distribution was sensitive to the solvent systems in which these reactions were carried out. The structure of the isomers so obtained was established by chemical and spectral methods. 相似文献
57.
58.
Dominik Schumacher Dr. Jonas Helma Anselm F. L. Schneider Prof. Dr. Heinrich Leonhardt Prof. Dr. Christian P. R. Hackenberger 《Angewandte Chemie (International ed. in English)》2018,57(9):2314-2333
Nanobodies can be seen as next‐generation tools for the recognition and modulation of antigens that are inaccessible to conventional antibodies. Due to their compact structure and high stability, nanobodies see frequent usage in basic research, and their chemical functionalization opens the way towards promising diagnostic and therapeutic applications. In this Review, central aspects of nanobody functionalization are presented, together with selected applications. While early conjugation strategies relied on the random modification of natural amino acids, more recent studies have focused on the site‐specific attachment of functional moieties. Such techniques include chemoenzymatic approaches, expressed protein ligation, and amber suppression in combination with bioorthogonal modification strategies. Recent applications range from sophisticated imaging and mass spectrometry to the delivery of nanobodies into living cells for the visualization and manipulation of intracellular antigens. 相似文献
59.
60.
C.H. Ziener T. Kampf P.M. Jakob W.R. Bauer 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2010,202(1):38-42
The diffusion in the magnetic dipolar field around a sphere is considered. The diffusion is restricted to the space between two concentric spheres, where the inner sphere is the source of the magnetic dipolar field. Analytical expressions for the CPMG transverse relaxation rate as well as the free induction decay and the spin echo time evolution are given in the Gaussian approximation. The influence of the inter-echo time is analyzed. The limiting cases of small and large inter-echo times as well as the short and long time behavior are evaluated. 相似文献