全文获取类型
收费全文 | 1989篇 |
免费 | 56篇 |
国内免费 | 7篇 |
专业分类
化学 | 1614篇 |
晶体学 | 31篇 |
力学 | 31篇 |
数学 | 64篇 |
物理学 | 312篇 |
出版年
2022年 | 20篇 |
2021年 | 15篇 |
2020年 | 25篇 |
2019年 | 27篇 |
2018年 | 17篇 |
2016年 | 34篇 |
2015年 | 35篇 |
2014年 | 42篇 |
2013年 | 122篇 |
2012年 | 95篇 |
2011年 | 111篇 |
2010年 | 80篇 |
2009年 | 68篇 |
2008年 | 117篇 |
2007年 | 96篇 |
2006年 | 112篇 |
2005年 | 105篇 |
2004年 | 83篇 |
2003年 | 88篇 |
2002年 | 114篇 |
2001年 | 36篇 |
2000年 | 23篇 |
1999年 | 31篇 |
1998年 | 18篇 |
1997年 | 24篇 |
1996年 | 26篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 22篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 16篇 |
1985年 | 42篇 |
1984年 | 29篇 |
1983年 | 17篇 |
1982年 | 29篇 |
1981年 | 20篇 |
1980年 | 29篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 20篇 |
1975年 | 16篇 |
1974年 | 9篇 |
1973年 | 15篇 |
1972年 | 9篇 |
排序方式: 共有2052条查询结果,搜索用时 15 毫秒
991.
Kato Y Okada S Atobe K Endo T Haraguchi K 《Analytical and bioanalytical chemistry》2012,404(1):197-206
A number of bioactive brominated secondary metabolites, including hydroxylated polybrominated diphenyl ethers, have been isolated from algae, sponges, and bacteria. In the present study, a screening method using liquid-chromatography tandem mass spectrometry was developed for the identification and selective determination of dihydroxy (diOH), hydroxy-methoxy (OH-MeO), and dimethoxy (diMeO) analogs of tetra- to hexa-BDEs in marine biota. In negative atmospheric pressure chemical ionization (APCI) mode, diOH and OH-MeO analogs provided intense [M-H](-) ions, whereas diMeO analogs provided characteristic [M-Br+O](-) and [M-CH(3)](-) ions. This enabled the diOH-, OH-MeO-, and diMeO-PBDEs to be distinguished using selected reaction monitoring transitions in the APCI source. Recoveries of 2'-OH-6-MeO-2,3',4,5'-tetra-BDE in spiked marine samples were 84 ± 5 %, with a limit of quantification at 9.1 ng mL(-1) (signal-to-noise ratio = 10). The developed method was used to analyze two sponge species collected from Palau, Micronesia; the concentration ratio of diOH-tetra-BDE:OH-MeO-tetra-BDE was 10:1 for the Lamellodysidea sp., whereas it was 1:30 for the Callyspongia sp. 相似文献
992.
We prepared single crystals of basic copper formate Cu2(OH)3HCO2 ( 1) by hydrolysis of formate anions in an aqueous solution of copper formate. X‐ray structure analysis showed that this material has a two‐dimensional triangular lattice network with S=1/2. The temperature dependence of magnetic susceptibility revealed antiferromagnetic ordering at 5.4 K. A spin‐flop transition was observed at about 20 kOe at 2 K, thereby indicating metamagnetic‐like behavior. The saturation magnetization was almost one‐half of the theoretical value at 2 K under 70 kOe. The magnetic behaviors of 1 were also discussed with regard to its crystal structure. The preparation method presented herein is convenient and available for single crystal growth of metal hydroxide derivatives with various anions. 相似文献
993.
J Han J Zhu Y Li X Yu S Wang G Wu H Xie SC Vogel F Izumi K Momma Y Kawamura Y Huang JB Goodenough Y Zhao 《Chemical communications (Cambridge, England)》2012,48(79):9840-9842
The evolution of the Li-ion displacements in the 3D interstitial pathways of the cubic garnet-type Li(7)La(3)Zr(2)O(12), cubic Li(7)La(3)Zr(2)O(12), was investigated with high-temperature neutron diffraction (HTND) from RT to 600 °C; the maximum-entropy method (MEM) was applied to estimate the Li nuclear-density distribution. Temperature-driven Li displacements were observed; the displacements indicate that the conduction pathways in the garnet framework are restricted to diffusion through the tetrahedral sites of the interstitial space. 相似文献
994.
3-Aminoquinoline/α-cyano-4-hydroxycinnamic acid (3AQ/CHCA) is a liquid matrix (LM), which was reported by Kumar et al. in 1996 for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. It is a viscous liquid and has some advantages of durability of ion generation by a self-healing surface and quantitative performance. In this study, we found a novel aspect of 3AQ/CHCA as a MALDI matrix, which converges hydrophilic material into the center of the droplet of analyte-3AQ/CHCA mixture on a MALDI sample target well during the process of evaporation of water derived from analyte solvent. This feature made it possible to separate not only the buffer components, but also the peptides and oligosaccharides from one another within 3AQ/CHCA. The MALDI imaging analyses of the analyte-3AQ/CHCA droplet indicated that the oligosaccharides and the peptides were distributed in the center and in the whole area around the center of 3AQ/CHCA, respectively. This 'on-target separation' effect was also applicable to glycoprotein digests such as ribonuclease B. These features of 3AQ/CHCA liquid matrix eliminate the requirement for pretreatment, and reduce sample handling losses thus resulting in the improvement of throughput and sensitivity. 相似文献
995.
This study addresses Bezout equations over bivariate polynomial matrices, where the relationship between two variables is described by a real entire function. This paper proposes a solution method that makes optimal use of minor primeness to reduce such Bezout equations to simple equations over univariate scalar polynomials. The proposed solution method requires only matrix calculations, thus making it very useful, especially in the absence of modern computer algebra systems. 相似文献
996.
Mikami K Wakabayashi K Yusa Y Aikawa K 《Chemical communications (Cambridge, England)》2006,(22):2365-2367
The chirality of an achiral benzophenone-based rhodium complex can be controlled by chiral diamines to afford significantly high enantioselectivity in the catalytic asymmetric transfer hydrogenation of ketones (up to 99% ee, 99% yield). 相似文献
997.
Koichi Mitsudo 《Tetrahedron letters》2006,47(29):5147-5150
N-Glycosylation of 2,3-dideoxy-1-[(2-pyridylmethyl)thio]glycosides (1a) using several activators is described. NBS-promoted glycosylation reaction utilizing either the α- or β-thiodideoxyglycoside proceeded smoothly at −78 °C to give the corresponding dideoxynucleoside in a β-selective manner, presumably through a common glycosyl donor. 相似文献
998.
We investigate the cosmological moduli problem by studying a modulus decay in detail and find that the branching ratio of the gravitino production is generically of O(0.01-1), which causes another cosmological disaster. Consequently, the cosmological moduli problem cannot be solved simply by making the modulus mass heavier than 100 TeV. We also illustrate our results by explicitly calculating the branching ratio into the gravitinos in the mixed modulus-anomaly model. 相似文献
999.
Application of the HPLC hyphenated techniques of LC-MS, LC-NMR and solvent-elimination LC-IR was demonstrated by the identification of the degradation products of a third generation cephalosporin antibiotic, cefpodoxime proxetil, in solid state, drug formulation and solution. Molecular weight and fragment information were obtained by LC-MS, and detailed structural information was confirmed by LC-NMR. Information on the carboxyl functional group obtained by solvent-elimination LC-IR was useful for confirmation of the ester hydrolysis. The degradation products were successfully identified without complicated isolation or purification processes. 相似文献
1000.
Fukutsu N Sakamaki Y Kawasaki T Saito K Nakazawa H 《Chemical & pharmaceutical bulletin》2006,54(10):1469-1472
Cross-contamination is a critical issue for pharmaceutical manufacturing, especially for beta-lactam antibiotics. Thus, an analytical method for the simultaneous determination of beta-lactam antibiotics cefmetazole (CMZ) and cefpodoxime proxetil (CPDXPR) contaminants in non-beta-lactam pharmaceuticals was developed using high-performance liquid chromatography-tandem mass spectrometry. The developed method was found to be sensitive at the detection limit of 0.002 ppm for both compounds. Mean recoveries of CMZ and CPDXPR from olmesartan medoxomil (OLM) tablets were 96.7 to 102.2% and 88.9 to 94.2%, respectively. The developed method was successfully applied for the verification of CMZ and CPDXPR contamination to actually manufactured OLM tablets. 相似文献