全文获取类型
收费全文 | 2946篇 |
免费 | 50篇 |
国内免费 | 10篇 |
专业分类
化学 | 1976篇 |
晶体学 | 12篇 |
力学 | 64篇 |
数学 | 410篇 |
物理学 | 544篇 |
出版年
2021年 | 24篇 |
2020年 | 33篇 |
2019年 | 34篇 |
2016年 | 44篇 |
2015年 | 45篇 |
2014年 | 57篇 |
2013年 | 91篇 |
2012年 | 98篇 |
2011年 | 117篇 |
2010年 | 79篇 |
2009年 | 75篇 |
2008年 | 95篇 |
2007年 | 91篇 |
2006年 | 107篇 |
2005年 | 91篇 |
2004年 | 82篇 |
2003年 | 81篇 |
2002年 | 100篇 |
2001年 | 51篇 |
2000年 | 52篇 |
1999年 | 59篇 |
1998年 | 36篇 |
1997年 | 37篇 |
1996年 | 41篇 |
1995年 | 50篇 |
1994年 | 38篇 |
1993年 | 51篇 |
1992年 | 41篇 |
1991年 | 47篇 |
1990年 | 37篇 |
1989年 | 37篇 |
1988年 | 26篇 |
1987年 | 43篇 |
1986年 | 35篇 |
1985年 | 45篇 |
1984年 | 51篇 |
1983年 | 22篇 |
1982年 | 38篇 |
1981年 | 35篇 |
1980年 | 47篇 |
1979年 | 33篇 |
1978年 | 45篇 |
1977年 | 54篇 |
1976年 | 42篇 |
1975年 | 45篇 |
1974年 | 49篇 |
1973年 | 49篇 |
1972年 | 30篇 |
1971年 | 29篇 |
1970年 | 26篇 |
排序方式: 共有3006条查询结果,搜索用时 15 毫秒
1.
2.
Simen Gjelseth Antonsen Arne Joakim C. Bunkan Tomas Mikoviny Yngve Stenstrøm Armin Wisthaler 《Molecular physics》2020,118(15)
The kinetics of the O3, OH and NO3 radical reactions with diazomethane were studied in smog chamber experiments employing long-path FTIR and PTR-ToF-MS detection. The rate coefficients were determined to be k CH2NN+O3?=?(3.2?±?0.4)?×?10?17 and k CH2NN+OH?=?(1.68?±?0.12)?×?10?10 cm3 molecule?1 s?1 at 295?±?3?K and 1013?±?30 hPa, whereas the CH2NN?+?NO3 reaction was too fast to be determined in the static smog chamber experiments. Formaldehyde was the sole product observed in all the reactions. The experimental results are supported by CCSD(T*)-F12a/aug-cc-pVTZ//M062X/aug-cc-pVTZ calculations showing the reactions to proceed exclusively via addition to the carbon atom. The atmospheric fate of diazomethane is discussed. 相似文献
3.
The rotational spectra of the deuterium cyanide isotopic species DCN, D13CN, DC15N, and D13C15N were recorded in the vibrational ground and first excited bending state (v2=1) up to 2 THz. The R-branch transitions from J=3←2 to J=13←12 were measured with sub-Doppler resolution. These very high resolution (∼70 kHz) and precise (±3-10 kHz) saturation dip measurements allowed for resolving the underlying hyperfine structure due to the 14N nucleus in DCN and D13CN for transitions as high as J=10←9. Additional high JR-branch (J=25←24 to J=28←27) transitions around 2 THz and direct l-type (ΔJ=0, J=19 to J=25) transitions from 66 to 118 GHz were recorded in Doppler-limited resolution. For the ground state of D13C15N, the J=1←0 transition was measured for the first time. The transition frequency accuracies for the other deuterated species were significantly improved. These new experimental data, together with the available infrared rovibrational data and previously measured direct l-type transitions, were subjected to a global least squares analysis for each isotopomer. This yielded precise sets of molecular constants for the ground and first excited vibrational states, including the nuclear quadrupole and magnetic spin-rotation coupling constants of the 14N nucleus for DCN and D13CN. The hyperfine structure due to the D, 13C, and 15N nuclei have not been resolved, but led to a broadening of the observed saturation dips. 相似文献
4.
B. Pignataro L. Chi S. Gao B. Anczykowski C. Niemeyer M. Adler H. Fuchs 《Applied Physics A: Materials Science & Processing》2002,74(3):447-452
Self-assembled oligomeric nanostructures consisting of bisbiotinylated DNA fragments connected by the protein streptavidin
(STV) are studied by dynamic scanning force microscopy (SFM) operating in air. A comparison of the images taken in repulsive
and attractive regimes is systematically made on DNA and STV structures. Stable and reproducible SFM images are obtained in
the attractive regime by using a special feedback circuit, called Q-control. On the other hand, when SFM is operating in the
repulsive regime, deformation of the structures that reduce the resolution and the image quality are clearly observable. The
heights of both DNA and STV have been measured as a function of the tip/molecule interaction forces. This study offers the
possibility to suggest a different mechanical behavior of DNA with respect to STV.
Received: 24 July 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002 相似文献
5.
Fr. Hernler R. Pfeningberger F. Pregl K. Fuchs C. Mai H. Hurts 《Analytical and bioanalytical chemistry》1938,112(11-12):421-425
6.
Stefan Pitsch Sebastian Wendeborn Ramanarayanan Krishnamurthy Armin Holzner Mark Minton Martin Bolli Christian Miculca Norbert Windhab Ronald Micura Michael Stanek Bernhard Jaun Albert Eschenmoser 《Helvetica chimica acta》2003,86(12):4270-4363
Pyranosyl‐RNA (‘p‐RNA’ ) is an oligonucleotide system isomeric to natural RNA and composed of the very same building blocks as RNA. Its generational, chemical, and informational properties are deemed to be those of an alternative nucleic acid system that could have been a candidate in Nature's evolutionary choice of the molecular basis of genetic function. We consider the study of the chemistry of p‐RNA as etiologically relevant in the sense that knowledge of its structural, chemical, and informational properties on the chemical level offers both a perspective and reference points for the recognition of specific structural assets of the RNA structure that made it the (supposedly) superior system among possible alternatives and, therefore, the system that became part of biology as we know it today. The paper describes the chemical synthesis of β‐d‐ (and L )‐ribopyranosyl‐(4′→2′)‐oligonucleotide sequences, presents a resume of their structural and chemical properties, and cautiously discusses what we may and may not have learned from the pyranosyl isomer of RNA with respect to the conundrum of RNA's origin. 相似文献
7.
Martin Fuchs 《manuscripta mathematica》1989,63(4):381-419
We prove an extension theorem for Sobolev functions which plays an important role in the partial regularity theory of vector valued functions which minimize degenerate variational integrals subject to some nonlinear side conditions in the image space. 相似文献
8.
9.
Technical cellulose-2.5-acetates (CA 2.5) were characterized regarding their carbohydrate composition in comparison to the raw material. The association of the CA 2.5 samples in acetone was studied by size exclusion chromatography (SEC) using various acetone grades and styrene divinylbenzene copolymer columns. In HPLC grade acetone with and without addition of 1% water up to three different pre-humps eluted in front of the main fraction of the polymer. The evaluation of the main peak by light scattering measurements resulted in high molar masses indicating that for these technical CA 2.5 samples even the main fraction is not dissolved without association. No pre-humps or association phenomena were observed after addition of 1 ppm LiBr to HPLC grade acetone or with p.a. grade acetone. In addition pre-hump enriched and pre-hump free fractions were isolated by fractionated precipitation. The carbohydrate composition of these fractions was determined and correlated with their association pattern in SEC investigations. 相似文献
10.