全文获取类型
收费全文 | 4214篇 |
免费 | 161篇 |
国内免费 | 19篇 |
专业分类
化学 | 2869篇 |
晶体学 | 28篇 |
力学 | 110篇 |
数学 | 474篇 |
物理学 | 913篇 |
出版年
2023年 | 40篇 |
2022年 | 35篇 |
2021年 | 65篇 |
2020年 | 116篇 |
2019年 | 98篇 |
2018年 | 68篇 |
2017年 | 41篇 |
2016年 | 107篇 |
2015年 | 83篇 |
2014年 | 90篇 |
2013年 | 177篇 |
2012年 | 280篇 |
2011年 | 351篇 |
2010年 | 131篇 |
2009年 | 116篇 |
2008年 | 238篇 |
2007年 | 227篇 |
2006年 | 227篇 |
2005年 | 176篇 |
2004年 | 159篇 |
2003年 | 117篇 |
2002年 | 98篇 |
2001年 | 56篇 |
2000年 | 61篇 |
1999年 | 28篇 |
1998年 | 47篇 |
1996年 | 43篇 |
1995年 | 36篇 |
1994年 | 51篇 |
1993年 | 70篇 |
1992年 | 56篇 |
1991年 | 51篇 |
1990年 | 41篇 |
1989年 | 48篇 |
1988年 | 41篇 |
1987年 | 34篇 |
1986年 | 37篇 |
1985年 | 50篇 |
1984年 | 37篇 |
1983年 | 37篇 |
1982年 | 31篇 |
1981年 | 36篇 |
1980年 | 31篇 |
1979年 | 35篇 |
1978年 | 33篇 |
1977年 | 31篇 |
1976年 | 34篇 |
1975年 | 37篇 |
1974年 | 35篇 |
1973年 | 44篇 |
排序方式: 共有4394条查询结果,搜索用时 62 毫秒
991.
Lead phosphate quantitatively coprecipitates trace amounts of Ag(I), Cd(II), Cr(III), Cu(II), Mn(II), Th(IV), U(VI) and Zr(IV).
The trace elements are determined in the precipitate by instrumental neutron activation analysis (INAA); detection limits
are given. The practical application to the determination of U and Th is described. 相似文献
992.
A RP-HPLC method that allows the separation of several types of phenolic compounds present in grapes and wines by direct injection of samples, using a binary gradient with solvents free of salts and photodiode array detection is described. Results show that more than 15 different phenolic molecules with antioxidant properties (flavan-3-ols, anthocyanins, cinnamic acid derivatives, flavonol derivatives and trans-resveratrol) may be separated in a single run by direct injection of red wine. The method is also valuable for the analysis of these compounds in white wine and in skins, seeds and pulp extracts of red and white grapes. 相似文献
993.
Marcos Ramos A Meskers SC Beckers EH Prince RB Brunsveld L Janssen RA 《Journal of the American Chemical Society》2004,126(31):9630-9644
A novel donor-bridge-acceptor system has been synthesized by covalently linking a p-phenylene vinylene oligomer (OPV) and a perylene diimid (PERY) at opposite ends of a m-phenylene ethynylene oligomer (FOLD) of twelve phenyl rings, containing nonpolar (S)-3,7-dimethyl-1-octanoxy side chains. For comparison, model compounds have been prepared in which either the donor or acceptor is absent. In chloroform, the oligomeric bridge is in a random coil conformation. Upon addition of an apolar solvent (heptane) the oligomeric bridge first folds into a helical stack and subsequently intermolecular self-assembly of the stacks into columnar architectures occurs. Photoexcitation in the random coil conformation, where the interaction between the donor and acceptor chromophores is small, results only in long-range intramolecular energy transfer in which the OPV singlet-excited state is transformed into the PERY singlet-excited state. In the folded conformation of the bridge, donor and acceptor are closer and their enhanced interaction favors the formation the OPV(*)(+)-FOLD-PERY(*)(-) charge-separated state upon photoexcitation. As a result, the extent of photoinduced charge separation depends on the degree of folding of the bridge between donor and acceptor and therefore on the apolar nature of the medium. As a consequence, and contrary to conventional photoinduced charge separation processes, the formation of the OPV(*)(+)-FOLD-PERY(*)(-) charge-separated state is more favored in apolar media. 相似文献
994.
Kevin R. Chalek Xinning Dong Fei Tong Ryan A. Kudla Lingyan Zhu Adam D. Gill Wenwen Xu Chen Yang Joshua D. Hartman Alviclr Magalhes Rabih O. Al-Kaysi Ryan C. Hayward Richard J. Hooley Gregory J. O. Beran Christopher J. Bardeen Leonard J. Mueller 《Chemical science》2021,12(1):453
Crystals composed of photoreactive molecules represent a new class of photomechanical materials with the potential to generate large forces on fast timescales. An example is the photodimerization of 9-tert-butyl-anthracene ester (9TBAE) in molecular crystal nanorods that leads to an average elongation of 8%. Previous work showed that this expansion results from the formation of a metastable crystalline product. In this article, it is shown how a novel combination of ensemble oriented-crystal solid-state NMR, X-ray diffraction, and first principles computational modeling can be used to establish the absolute unit cell orientations relative to the shape change, revealing the atomic-resolution mechanism for the photomechanical response and enabling the construction of a model that predicts an elongation of 7.4%, in good agreement with the experimental value. According to this model, the nanorod expansion does not result from an overall change in the volume of the unit cell, but rather from an anisotropic rearrangement of the molecular contents. The ability to understand quantitatively how molecular-level photochemistry generates mechanical displacements allows us to predict that the expansion could be tuned from +9% to −9.5% by controlling the initial orientation of the unit cell with respect to the nanorod axis. This application of NMR-assisted crystallography provides a new tool capable of tying the atomic-level structural rearrangement of the reacting molecular species to the mechanical response of a nanostructured sample.NMR crystallography establishes absolute unit-cell orientations relative to the shape change, revealing the atomic-resolution mechanism for the nanorod''s photomechanical response. 相似文献
995.
Real-time multicolor DNA detection with chemoresponsive diffraction gratings and nanoparticle probes
Bailey RC Nam JM Mirkin CA Hupp JT 《Journal of the American Chemical Society》2003,125(44):13541-13547
We report a real-time DNA detection method that utilizes single-strand DNA-modified nanoparticle probes and micropatterned chemoresponsive diffraction gratings interrogated simultaneously at multiple laser wavelengths. The surface-bound nanoparticle probe based assay with the chemoresponsive diffraction grating signal transduction scheme results in an experimentally simple DNA detection protocol, displaying attributes of both detection methodologies: the high sensitivity and selectivity afforded by nanoparticle probes and the experimental simplicity, wavelength-dependent resonant enhancement features, and miniaturization potential provided by the diffraction-based sensing technology. 相似文献
996.
Phillips ST Piersanti G Rüth M Gubernator N van Lengerich B Bartlett PA 《Organic letters》2004,6(24):4483-4485
The synthesis of @-tide beta-strand peptidomimetics has been improved such that oligomers now can be obtained from solution- and solid-phase synthesis protocols approaching the efficiency and flexibility of peptide chemistry. These methods enable the synthesis of @-tide oligomers with a variety of amino acids and with lengths up to 13 units. [reaction: see text] 相似文献
997.
The fluorescence behaviour of a series of acenaphthylene/methyl methacrylate copolymers covering a wide range of intramolecular chromophore compositions has been examined using pulsed laser excitation. The decay of emission intensity in the region of monomer fluorescence could be described only by the use of triple exponential functions. The data have been discussed in terms of the existence of two temporally distinct monomeric species in addition to an excimer. 相似文献
998.
Ryan D Madder Chu-Young Kim Pooja P Chandra Jeffrey B Doyon Teaster A Baird Carol A Fierke David W Christianson Judith G Voet Ahamindra Jain 《The Journal of organic chemistry》2002,67(2):582-584
QSAR has been used to elucidate the origin of the hydrophobicity and binding affinity of a small library of fluoroaromatic inhibitors of F131V carbonic anhydrase II. Our analysis predicted the presence of a twisted amide conformation for several bound inhibitors, which we confirmed crystallographically. We also determined that the hydrophobicity of the inhibitors as a whole results from the fragment hydrophobicities of their fluorobenzyl rings, corrected for field effects and the presence of an intramolecular F.H contact in solution. The loss of this interaction on binding to the enzyme makes the affinity sensitive to the same terms, but with the opposite dependence on the F.H contact. In the case of the four inhibitors bound as twisted amides, this F.H contact must be retained to some extent in the bound state in order for their affinities to be consistent with our QSAR analysis of the entire set of 17 molecules. 相似文献
999.
Bhirud VA Panjabi G Salvi SN Phillips BL Gates BC 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6173-6181
[Os5C(CO)14]2- was synthesized on the surface of MgO by reductive carbonylation of adsorbed Os3(CO)12 at 548 K and 1 bar. The supported species were characterized by infrared (IR), 13C NMR, and extended X-ray absorption fine structure (EXAFS) spectroscopies. The IR and EXAFS data are consistent with the presence of [Os5C(CO)14]2-, formed in a yield of about 65%, along with smaller osmium carbonyl clusters. As the supported clusters were decarbonylated in flowing He or H2, they were characterized by IR and EXAFS spectroscopies, which indicate that the decarbonylation was complete after each treatment at 573 K. The EXAFS data characterizing the sample treated in He determine an Os-Os first-shell coordination number of 3.4, matching that of [Os5C(CO)14]2- and indicating that the Os5C frame was retained after decarbonylation in He. Treatment of MgO-supported [Os5C(CO)14]2- in H2 at 573 K resulted in the formation of aggregated osmium clusters larger than Os5C. The catalytic activity of Os5C for toluene hydrogenation was found to be an order of magnitude less than that of the aggregated osmium clusters, which are metallic in character. 相似文献
1000.