全文获取类型
收费全文 | 6511篇 |
免费 | 179篇 |
国内免费 | 25篇 |
专业分类
化学 | 5041篇 |
晶体学 | 77篇 |
力学 | 115篇 |
数学 | 500篇 |
物理学 | 982篇 |
出版年
2022年 | 58篇 |
2021年 | 56篇 |
2020年 | 76篇 |
2019年 | 95篇 |
2018年 | 58篇 |
2017年 | 44篇 |
2016年 | 115篇 |
2015年 | 108篇 |
2014年 | 146篇 |
2013年 | 311篇 |
2012年 | 352篇 |
2011年 | 385篇 |
2010年 | 212篇 |
2009年 | 204篇 |
2008年 | 398篇 |
2007年 | 414篇 |
2006年 | 431篇 |
2005年 | 362篇 |
2004年 | 322篇 |
2003年 | 299篇 |
2002年 | 275篇 |
2001年 | 92篇 |
2000年 | 80篇 |
1999年 | 75篇 |
1998年 | 55篇 |
1997年 | 89篇 |
1996年 | 87篇 |
1995年 | 45篇 |
1994年 | 62篇 |
1993年 | 56篇 |
1992年 | 51篇 |
1991年 | 52篇 |
1990年 | 36篇 |
1989年 | 32篇 |
1988年 | 43篇 |
1987年 | 45篇 |
1986年 | 40篇 |
1985年 | 88篇 |
1984年 | 91篇 |
1983年 | 41篇 |
1982年 | 86篇 |
1981年 | 81篇 |
1980年 | 76篇 |
1979年 | 76篇 |
1978年 | 69篇 |
1977年 | 57篇 |
1976年 | 63篇 |
1975年 | 42篇 |
1974年 | 46篇 |
1973年 | 64篇 |
排序方式: 共有6715条查询结果,搜索用时 0 毫秒
991.
Masaki Kita Tomoyuki Koyama Hiroshi Matsumoto Daisuke Uemura 《Tetrahedron letters》2005,46(49):8583-8585
The muricid gastropods genus Drupella are known to be voracious coral predator. Outbreaks of them have accelerated significant destruction on coral reefs, but its precise mechanism is poorly understood. Here, we describe the identification of montiporic acids C (1) and A (2) isolated from sea water extracts of the coral Montipora sp., which showed potent feeding-attractant activity toward D. cornus. 相似文献
992.
Prabhu VM Vogt BD Wu WL Douglas JF Lin EK Satija SK Goldfarb DL Ito H 《Langmuir : the ACS journal of surfaces and colloids》2005,21(15):6647-6651
The depth profile of the counterion concentration within thin polyelectrolyte films was measured in situ using contrast variant specular neutron reflectivity to characterize the initial swelling stage of the film dissolution. We find substantial counterion depletion near the substrate and enrichment near the periphery of the film extending into the solution. These observations challenge our understanding of the charge distribution in polyelectrolyte films and are important for understanding film dissolution in medical and technological applications. 相似文献
993.
Yao K Imai Y Shi L Dong A Adachi Y Nishikubo K Abe E Tateyama H 《Journal of colloid and interface science》2005,285(1):259-266
A novel strategy for the synthesis of layered organosilica is demonstrated. The ionic interaction between the anionic group of a surfactant (sodium dodecyl sulfate) and the cationic organic group of an organosilane (3-aminopropyltrimethoxysilane, ATMS) under acidic conditions was utilized to create a layered organosilica at room temperature. The inorganic part of the organosilica layer was an Si-O hexagonal sheet, and organofunctional groups were alternately arranged on both sides of the sheet. The layered structure of the ATMS organosilica was retained after the removal of the surfactant with chloride anion. The properties of the layered ATMS organosilica were investigated. The layered ATMS-Cl organosilica is stable and possesses a definite layer structure in water or ethanol. Various kinds of anions can be intercalated in the interlayer space of the layered ATMS organosilicas and the layer was expanded dependent on the intercalated anions. The structure of the layered ATMS organosilica was well retained during the intercalation processes. 相似文献
994.
The photochemistry of 3-methyl-2-(1-naphthyl)-2H-azirine (1a) was investigated by the direct observation of reactive intermediates in matrixes at 10 K and by the characterization of reaction products in solutions. As already reported, the photolysis of the azirine 1a with the short-wavelength light (>300 nm) caused the C-C bond cleavage of the 2H-azirine ring to produce the nitrile ylide 2. However, the products derived from the C-N bond cleavage were exclusively obtained in the irradiation of 1a with the long-wavelength light (366 nm) both in matrixes and in solutions. When 1a was irradiated in the presence of O(2) with the long-wavelength light, acetonitrile oxide (6) was produced through the capture of the biradical 4 generated by the C-N bond cleavage of 1a with O(2). An introduction of a nitro group into the naphthyl ring of 1a resulted in an acceleration of the decomposition in the long-wavelength irradiation and an extension of the wavelength region where the products derived from the C-N bond cleavage were selectively obtained. On the basis of molecular orbital calculations with the INDO/S method, the reason for the wavelength-dependent selective C-C and C-N bond cleavage of the azirine ring of 1a is discussed. 相似文献
995.
Yuko?Ogihara Richard?L.?SmithJr.Email author Hiroshi?Inomata Kunio?Arai 《Cellulose (London, England)》2005,12(6):595-606
Direct observations of the heating of microcrystalline cellulose (230 DP) in water at temperatures up to 410 °C and at pressures
up to 700 MPa were made with a batch-type microreactor. Cellulose particles were found to dissolve with water over temperatures
ranging from 315 to 355 °C at high pressures. Dissolution temperatures depended on water density and decreased from about
350 °C at a water density of 560 kg/m3 to a minimum of around 320 °C at a water density of 850 kg/m3. At densities greater than 850 kg/m3, the dissolution temperatures increased and reached a value of about 347 °C at 980 kg/m3. The cellulose dissolution temperatures were independent of heating rates for values ranging from 10 to 17 °C/s. The low
dependence of dissolution temperatures on the heating rates is strong evidence for simultaneous dissolution and reaction of
the cellulose. Different phenomena occurred depending on water density. At low densities, particles turned transparent and
seemed to dissolve into the aqueous phase from the surface. From 670 to 850 kg/m3, the cellulose particles visibly swelled just before completely collapsing and dissolving into the aqueous phase. The swelling
probably increased water accessibility and particle surface area and thus lead to the lower dissolution temperatures observed.
From 850 to 1000 kg/m3, the particles required longer times to dissolve and many fine brown-like particles were generated as the particles dissolved.
FT-IR spectra of the residues were analyzed. Residues formed from heating cellulose at high densities still retained some
cellulose character whereas those as low densities had little cellulose character, especially in the O–H stretching vibration
region. 相似文献
996.
Nikaido H 《Chemistry & biology》2005,12(5):507-509
A recent issue of Cell published two papers resulting from the collaboration between the Kahne and Silhavy laboratories [1,2]. These studies, possibly initiated as an effort to identify the target of action of vancomycin with lipophilic substitutions, resulted in the discovery of a protein complex involved in the assembly of outer membrane proteins. 相似文献
997.
Nakade H Ilker MF Jordan BJ Uzun O Lapointe NL Coughlin EB Rotello VM 《Chemical communications (Cambridge, England)》2005,(26):3271-3273
The regular arrangement of complementary diaminopyridine-thymine (DAP-THY) on alternating copolymers permits cooperative binding events and the effective formation of well-controlled micrometre-scale aggregates. 相似文献
998.
Ijima Y Matoishi K Terao Y Doi N Yanagawa H Ohta H 《Chemical communications (Cambridge, England)》2005,(7):877-879
The introduction of two mutations (G74C/C188S) based on the estimated reaction mechanism resulted in the inversion of enantioselectivity of arylmalonate decarboxylase, which catalyses the asymmetric decarboxylation of arylmethylmalonate to give optically active arylpropionate. 相似文献
999.
1000.