全文获取类型
收费全文 | 50074篇 |
免费 | 6929篇 |
国内免费 | 5402篇 |
专业分类
化学 | 16258篇 |
晶体学 | 1274篇 |
力学 | 10521篇 |
综合类 | 696篇 |
数学 | 15391篇 |
物理学 | 18265篇 |
出版年
2024年 | 105篇 |
2023年 | 486篇 |
2022年 | 950篇 |
2021年 | 1184篇 |
2020年 | 1419篇 |
2019年 | 1266篇 |
2018年 | 1306篇 |
2017年 | 1800篇 |
2016年 | 2099篇 |
2015年 | 1624篇 |
2014年 | 2569篇 |
2013年 | 3796篇 |
2012年 | 3154篇 |
2011年 | 3465篇 |
2010年 | 2994篇 |
2009年 | 3306篇 |
2008年 | 3172篇 |
2007年 | 3217篇 |
2006年 | 2913篇 |
2005年 | 2688篇 |
2004年 | 2354篇 |
2003年 | 2109篇 |
2002年 | 1869篇 |
2001年 | 1567篇 |
2000年 | 1498篇 |
1999年 | 1378篇 |
1998年 | 1223篇 |
1997年 | 1039篇 |
1996年 | 872篇 |
1995年 | 744篇 |
1994年 | 678篇 |
1993年 | 585篇 |
1992年 | 575篇 |
1991年 | 416篇 |
1990年 | 346篇 |
1989年 | 274篇 |
1988年 | 260篇 |
1987年 | 176篇 |
1986年 | 126篇 |
1985年 | 138篇 |
1984年 | 129篇 |
1983年 | 64篇 |
1982年 | 102篇 |
1981年 | 77篇 |
1980年 | 43篇 |
1979年 | 67篇 |
1978年 | 52篇 |
1977年 | 48篇 |
1976年 | 21篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 890 毫秒
1.
《Mendeleev Communications》2022,32(5):597-600
Calorimetric monitoring of the autoclave reaction N2O4 + C2H4 at –85 to +10 °C under argon pressure 10–30 bar revealed that the exothermic chemical reaction started at temperatures above –52 °C at 10 bar, whereas an intensive exothermic reaction started at –85 °C and pressure of 30 bar. IR study showed that oligo/polynitroethylene was formed at 30 bar, while carbonyl and hydroxy compound as well as nitrate R–ONO2 formation occurred upon processing at 10 bar. 相似文献
2.
Dan Chen Kaixin Du Xiaochen Niu Hongwei Zhang Xue Zhang Yu Tang Jianchun Zhao 《Biomedical chromatography : BMC》2022,36(3):e5288
Amlexanox, an anti-inflammatory and anti-allergic agent, has been widely used clinically for the treatment of canker sores, asthma, and allergic rhinitis. Recently, amlexanox has received considerable attention in curing nonalcoholic fatty liver diseases and hepatitis virus infection. Herein, we first established a sensitive high-performance liquid chromatography-tandem mass spectrum (LC–MS/MS) method for the determination of amlexanox in rat plasma. Propranolol was used as the internal standard (IS). Using a simple protein precipitation method, the amlexanox and IS were separated with Capcell Pak C18 column (2.0 × 50 mm, 5 μm) and eluted with water and acetonitrile each containing 0.1% formic acid using gradient elution condition at a flow rate of 0.4 mL·min−1. Amlexanox and IS were detected by a triple quadrupole mass in multiple reactive monitoring (MRM) under the transitions of m/z 299.2 → 281.2 and m/z 259.9 → 116.1 with positive electrospray ionization, respectively. The calibration curves of amlexanox were established with the range of 50 to 2000 ng·mL−1 (r2 > 0.99). The validation method consisted of selectivity, accuracy, precision, carryover effect, matrix effect, recovery, dilution effect, and stability. The fully validated method was successfully applied to the pharmacokinetic study of amlexanox in Wistar rats. 相似文献
3.
This paper is concerned with the Cauchy problem on the Boltzmann equation without angular cutoff assumption for hard potential in the whole space. When the initial data is a small perturbation of a global Maxwellian, the global existence of solution to this problem is proved in unweighted Sobolev spaces with . But if we want to obtain the optimal temporal decay estimates, we need to add the velocity weight function, in this case the global existence and the optimal temporal decay estimate of the Boltzmann equation are all established. Meanwhile, we further gain a more accurate energy estimate, which can guarantee the validity of the assumption in Chen et al. (0000). 相似文献
4.
5.
6.
7.
Sol-gel method has been used for the synthesis of biocompatible superparamagnetic nanoferrites of AFeO2 (A = Li, Na, K, Ca). Structural study of the nanoferrites reveals that LiFeO2 exhibits cubic phase on the other hand NaFeO2, KFeO2, CaFeO2 nanoparticles possess orthorhombic phase. Transmission electron microscopy (TEM) suggests that synthesized nanoferrites are nano-sized with spherical morphology. Optical properties confirm that nanoferrites emit and absorb light in a visible range of the electromagnetic spectrum. International Commission on Illumination (CIE) study discloses that the nanoparticles can be used to produce light of various colors. Magnetic study reveals that the nanoferrites exhibit superparamagnetic nature with high values of saturation magnetization 40.26 emu/g, 41.69 emu/g, 57.16 emu/g, and 43.66 emu/g, respectively for LiFeO2, NaFeO2, KFeO2, and CaFeO2. Biocompatibility study of the nanoferrites has been performed using Sulforhodamine B (SRB) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The reason behind the observed properties and behavior has been discussed. 相似文献
8.
A liquid dewetting method for the determination of the viscoelastic properties of ultrathin polymer films has been extended to study thickness effects on the properties of ultrathin polycarbonate (PC) films. PC films with film thicknesses ranging from 4 to 299 nm were placed on glycerol at temperatures from below the macroscopic glass transition temperature (Tg) to above it with the dewetting responses being monitored. It is found that the isothermal creep results for films of the same thickness, but dewetted at different temperatures can be superposed into one master curve, which is consistent with the fact of PC being a thermorheologically simple material. Furthermore, the results show that the Tg of PC thin films is thickness dependent, but the dependence is weaker than the results for freely standing films and similar to literature data for PC films supported on rigid substrates. It was also found that the rubbery plateau region for the PC films stiffens dramatically, but still less than what has been observed for freely standing polycarbonate films. The rubbery stiffening is discussed in terms of a recently reported model that relates macroscopic segmental dynamics with the stiffening. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1559–1566 相似文献
9.
10.
The biodegradability of phtalic acid esters in marine and freshwater environments was characterized by their binding free energy with corresponding degrading enzymes. According to comprehensive biodegradation effects weights, the binding free energy values were converted into dimensionless efficacy coefficient using ratio normalization method. Then, considering comprehensive dual biodegradation effects value and the structural parameters of PAEs in both marine and freshwater environments, a 3D-QSAR pharmacophore model was constructed, five PAE derivatives (DBP−COOH, DBP−CHO, DBP−OH, DINP−NH2, and DINP−NO2) were screened out based on their environmental friendliness, functionality and stability. The prediction of biodegradation effects on five PAE derivatives by biodegradation models in marine and freshwater environment increased by 15.90 %, 15.84 %, 27.21 %, 12.33 %, and 8.32 %, and 21.57 %, 15.21 %, 20.99 %, 15.10 %, and 9.74 %, respectively. By simulating the photodegradation path of the PAE derivative molecular, it was found that DBP−OH can generate .OH and provides free radicals for the photodegradation of microplastics in the environment. 相似文献