全文获取类型
收费全文 | 846篇 |
免费 | 24篇 |
国内免费 | 12篇 |
专业分类
化学 | 486篇 |
晶体学 | 1篇 |
力学 | 23篇 |
数学 | 176篇 |
物理学 | 196篇 |
出版年
2022年 | 6篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2016年 | 21篇 |
2015年 | 13篇 |
2014年 | 16篇 |
2013年 | 32篇 |
2012年 | 30篇 |
2011年 | 47篇 |
2010年 | 11篇 |
2009年 | 12篇 |
2008年 | 31篇 |
2007年 | 24篇 |
2006年 | 42篇 |
2005年 | 36篇 |
2004年 | 33篇 |
2003年 | 31篇 |
2002年 | 37篇 |
2001年 | 22篇 |
2000年 | 28篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 14篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 15篇 |
1975年 | 14篇 |
1974年 | 7篇 |
1973年 | 8篇 |
1972年 | 7篇 |
1971年 | 6篇 |
1968年 | 6篇 |
排序方式: 共有882条查询结果,搜索用时 15 毫秒
21.
Alexandra Alimova A. Katz Rakhi Podder Glenn Minko Hul Wei R. R. Alfano Paul Gottlieb 《Photochemistry and photobiology》2004,80(1):41-46
Native fluorescence spectroscopy was used for in situ investigations of two lipid‐containing bacteriophages from the cystovirus family as well as their Pseudomonad host cells. Both the viruses φ6 and φ12 and their bacterial host proteins contain the amino acid tryptophan (trp), which is the predominant fluorophore in UV. Within proteins, trp's structural environment differs, and the differences are reflected in their spectroscopic signatures. It was observed that the peak of the trp emission from both viruses was at 330 nm, a significantly shorter wavelength than trp in either the Pseudomonad host cells or the amino acid's chemical form. This allowed us to monitor the viral attachment process and subsequent lytic release of progeny virus particles by measurement of the trp emission spectra during the infection process. This work demonstrates that fluorescence may offer a novel tool to detect viruses and monitor viral infection of cells and may be part of a biodefense application. 相似文献
22.
Condensation of 3,4-dichloro-6-[(trimethylsilyl)oxy] pyridazine ( 3 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-β- D -ribofuranose ( 4 ), by the stannic chloride catalyzed procedure, has furnished 3,4-dichloro-1-(2,3,5-tri-O-benzoyl-β- D -ribofuranosyl) pyridazin-6-one ( 5 ). Nucleophilic displacement of the chloro groups and removal of the benzoyl blocking groups from 5 has furnished 3-chloro-4-methoxy-, 3,4-dimethoxy-, 4-amino-3-chloro-, 3-chloro-4-methylamino-, 3-chloro-4-hydroxy-, and 4-hydroxy-3-methoxy-1-β- D -ribofuranosylpyridazin-6-one. An unusual reaction of 5 with dimethylamine is reported. Condensation of 4,5-dichloro-3-nitro-6-[(trimethylsilyl)oxy]pyridazine with 4 yielded 4,5-dichloro-3-nitro-1-(2,3,5-tri-O-benzoyl-β- D -ribofuranosyl)pyridazin-6-one ( 24 ). Nucleophilic displacement of the aromatic nitro groups from 24 is discussed. Condensation of 3 with 3,5-di-O-p-toluoyl 2-deoxy- D -erythro-pentofuranosyl chloride ( 28 ) afforded an α, β mixture of 2-deoxy nucleosides. The synthesis of certain 3-substituted pyridazine 2′-deoxy necleosides are reported. 相似文献
23.
24.
Michael Woolman Jimmy Qiu Claudia M. Kuzan-Fischer Isabelle Ferry Delaram Dara Lauren Katz Fowad Daud Megan Wu Manuela Ventura Nicholas Bernards Harley Chan Inga Fricke Mark Zaidi Brad G. Wouters James T. Rutka Sunit Das Jonathan Irish Robert Weersink Howard J. Ginsberg David A. Jaffray Arash Zarrine-Afsar 《Chemical science》2020,11(33):8723
Integration between a hand-held mass spectrometry desorption probe based on picosecond infrared laser technology (PIRL-MS) and an optical surgical tracking system demonstrates in situ tissue pathology from point-sampled mass spectrometry data. Spatially encoded pathology classifications are displayed at the site of laser sampling as color-coded pixels in an augmented reality video feed of the surgical field of view. This is enabled by two-way communication between surgical navigation and mass spectrometry data analysis platforms through a custom-built interface. Performance of the system was evaluated using murine models of human cancers sampled in situ in the presence of body fluids with a technical pixel error of 1.0 ± 0.2 mm, suggesting a 84% or 92% (excluding one outlier) cancer type classification rate across different molecular models that distinguish cell-lines of each class of breast, brain, head and neck murine models. Further, through end-point immunohistochemical staining for DNA damage, cell death and neuronal viability, spatially encoded PIRL-MS sampling is shown to produce classifiable mass spectral data from living murine brain tissue, with levels of neuronal damage that are comparable to those induced by a surgical scalpel. This highlights the potential of spatially encoded PIRL-MS analysis for in vivo use during neurosurgical applications of cancer type determination or point-sampling in vivo tissue during tumor bed examination to assess cancer removal. The interface developed herein for the analysis and the display of spatially encoded PIRL-MS data can be adapted to other hand-held mass spectrometry analysis probes currently available.Integration between a hand-held mass spectrometry desorption probe based on picosecond infrared laser technology (PIRL-MS) and an optical surgical tracking system demonstrates in situ tissue pathology from point-sampled mass spectrometry data. 相似文献
25.
The mechanism of the anesthetic process is of interest both to the clinician and to the pharmacologist. However, this is still an unsettled issue and a multitude of models have been proposed for the process. Noticing that most models propose either a molecular perturbation by the agents or an effect on some colligative property, we explore in this article the thermodynamical consequences of these postulations. Comparison of these with experimental findings is then made. The comparison shows the inconsistency of many of the models with the facts: (i) it refutes the long accepted conviction, culminated in the unitary hypothesis, that general anesthetics act not at a particular receptor site but invariably on all. Some consequences of this finding are demonstrated. (ii) it implies that a simple phospholipid medium is not feasible as an anesthetic site. (iii) it infers that proteins do have the properties required from anesthetic sites.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday 相似文献
26.
Oleg A. Raitman Andrei B. Kharitonov Maya Zayats Eugenii Katz Itamar Willner 《Analytica chimica acta》2004,504(1):101-111
Crosslinked films consisting of the acrylamide-acrylamidophenylboronic acid copolymer that are imprinted with recognition sites for β-nicotinamide adenine dinucleotide (NAD+), β-nicotinamide adenine dinucleotide phosphate NADP+, and their reduced forms (NAD(P)H), are assembled on Au-coated glass supports. The binding of the oxidized cofactors NAD+ or NADP+ or the reduced cofactors NADH or NADPH to the respective imprinted sites results in the swelling of the polymer films through the uptake of water. Surface plasmon resonance (SPR) spectroscopy is employed to follow the binding of the different cofactors to the respective imprinted sites. The imprinted recognition sites reveal selectivity towards the association of the imprinted cofactors. The method enables the analysis of the NAD(P)+ and NAD(P)H cofactors in the concentration range of 1×10−6 to 1×10−3 M. The cofactor-imprinted films associated with the Au-coated glass supports act as active interfaces for the characterization of biocatalyzed transformations that involve the cofactor-dependent enzymes. This is exemplified with the characterization of the biocatalyzed oxidation of lactate to pyruvate in the presence of NAD+ and lactate dehydrogenase using the NADH-imprinted polymer film. 相似文献
27.
S. J. Pearton U. K. Chakrabarti A. Katz A. P. Perley W. S. Hobson M. Geva 《Plasma Chemistry and Plasma Processing》1991,11(4):405-422
A systematic study has been performed of the dry etching characteristics of GaAs, Al0.3Ga0.7As, and GaSb in chlorine-based electron cyclotron resonance (ECR) discharges. The gas mixtures investigated were CCl2F2/O2, CHCl2F/O2, and PCl3. The etching rates of all three materials increase rapidly with applied RF power, while the addition of the microwave power at moderate levels (150 W) increases the etch rates by 20–80%. In the microwave discharges, the etch rates decrease with increasing pressure, but at 1 m Torr it is possible to obtain usable rates for self-bias voltages 100 V. Of the Freon-based mixtures, CHCl2F provides the least degradation of optical (photoluminescence) and electrical (diode ideality factors and Schottky barrier heights) properties of GaAs as a result of dry etching. Smooth surface morphologies are obtained on all three materials provided the microwave power is limited to 200 W. Above this power, there is surface roughening evident with all of the gas mixtures investigated. 相似文献
28.
The glycoprotein (G) of vesicular stomatitis virus (VSV) is synthesized on membrane-bound polyribosomes. Approximately 30 min after its synthesis, it reaches the surface plasma membrane where it is incorporated into budding virus. The first part of this paper focuses on the 2 intracellular, membrane-bound, glycosylated forms of the glycoprotein which are intermediates in its biogenesis. All glycosylation and processing is completed in the smooth microsome fraction before the protein reaches the surface. Next, we turn to the mechanism by which G is synthesized on membrane-bound polyribosomes. All of the G mRNA is bound to membranes, and studies with puromycin suggest that this attachment of G mRNA is mediated by the nascent glycoprotein chain. After its synthesis G is a transmembrane protein with about 30 amino acids at the carboxyl terminus remaining on the cytoplasmic side of the endoplasmic reticulum. Since 95% of the glycoprotein, containing the carbohydrate residues, is resistant to attack by external proteases, it appears to be within the lumen of the endoplasmic reticulum or embedded within the lipid bilayer. Finally, we show that synthesis, glycosylation, and proper asymmetric insertion of G into the ER can be achieved in cell-free extracts. Both glycosylation of G and proper insertion into the ER membrane in this cell-free system require concomitant protein synthesis. 相似文献
29.
Mikhail Katz 《Geometriae Dedicata》1991,40(2):171-190
We study the critical points of the diameter functional on the n-fold Cartesian product of the complex projective plane C
P
2 with the Fubini-Study metric. Such critical points arise in the calculation of a metric invariant called the filling radius, and are akin to the critical points of the distance function. We study a special family of such critical points, P
kC
P
1C
P
2, k=1,2... We show that P
k is a local minimum of by verifying the positivity of the Hessian of (a smooth approximation to) at P
k. For this purpose, we use Shirokov's law of cosines and the holonomy of the normal bundle of C
P
1C
P
2. We also exhibit a critical point of , given by a subset which is not contained in any totally geodesic submanifold of C
P
2. 相似文献
30.
G. T. Jones R. W. L. Jones B. W. Kennedy D. R. O. Morrison M. M. Mobayyen S. Wainstein M. Aderholz D. Hantke E. Hoffmann U. F. Katz J. Kern N. Schmitz W. Wittek H. P. Borner G. Myatt D. Radojicic S. Burke 《Zeitschrift fur Physik C Particles and Fields》1991,51(2):205-208
Using data obtained with the bubble chamber BEBC at CERN, the inclusivef 2 (1270) meson production invp and \(\bar vp\) charged current reactions is studied. It is found thatf 2 production occurs mainly in events with a hadronic invariant massW?7 GeV. In these events, the averagef 2 multiplicity is about half the average ρO multiplicity, and thex F andp T 2 distributions of thef 2 agree in shape with those of the ρO. The predictions of a semi-empirical model (Wells model) are in accord with the measured multiplicities atW>7 GeV, whereas at lowerW the model predicts too largef 2 multiplicities. 相似文献