全文获取类型
收费全文 | 5335篇 |
免费 | 573篇 |
国内免费 | 702篇 |
专业分类
化学 | 5048篇 |
晶体学 | 19篇 |
力学 | 251篇 |
综合类 | 102篇 |
数学 | 549篇 |
物理学 | 641篇 |
出版年
2024年 | 11篇 |
2023年 | 58篇 |
2022年 | 107篇 |
2021年 | 174篇 |
2020年 | 203篇 |
2019年 | 173篇 |
2018年 | 130篇 |
2017年 | 167篇 |
2016年 | 223篇 |
2015年 | 208篇 |
2014年 | 229篇 |
2013年 | 316篇 |
2012年 | 451篇 |
2011年 | 269篇 |
2010年 | 247篇 |
2009年 | 298篇 |
2008年 | 371篇 |
2007年 | 308篇 |
2006年 | 326篇 |
2005年 | 285篇 |
2004年 | 274篇 |
2003年 | 241篇 |
2002年 | 241篇 |
2001年 | 148篇 |
2000年 | 149篇 |
1999年 | 130篇 |
1998年 | 122篇 |
1997年 | 112篇 |
1996年 | 101篇 |
1995年 | 90篇 |
1994年 | 74篇 |
1993年 | 71篇 |
1992年 | 50篇 |
1991年 | 49篇 |
1990年 | 42篇 |
1989年 | 23篇 |
1988年 | 16篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有6610条查询结果,搜索用时 15 毫秒
91.
Qingde Zhang Yisheng Tan Caihong Yang Yizhuo Han Jun Shamoto Noritatsu Tsubaki 《天然气化学杂志》2007,16(3):322-325
The attractive utilization route for one-step catalytic oxidation of dimethyl ether to dimethoxymethane was successfully carried out over the H3PW12O40(40%)/SiO2 catalyst, modified by Cs, K, Ni, and V. The Cs modification of H3PW12O40(40%)/SiO2 gave the most promising result of 20% dimethyl ether conversion and 34.8% dimethoxymethane selectivity. Dimethoxymethane could be synthe- sized via methoxy groups decomposed from dimethyl ether through the synergistic effect between the acid sites and the redox sites of Cs modified H3PW12O40(40%)/SiO2. 相似文献
92.
Surface plasmon resonance (SPR) has been successfully applied for the simple, rapid, and label-free assay of various biomolecules. This assay evaluates a novel wavelength modulation SPR biosensor for the detection of tetanus toxin. The wavelength modulation SPR biosensor is designed based on fixing the incident angle of light and measuring the reflected intensities in the resonance wavelength range spanning 400-800 nm simultaneously. Tetanus toxin (TeNT), one of the most potent toxins known, is synthesized as a 150 kDa single polypeptide chain. The SPR biosensor has been shown to be capable of directly detecting concentration of tetanus toxin as low as 0.028 Lf ml−1. Under selected experimental conditions, the SPR biosensor has a good reproducibility, sensitivity and reversibility. The results illustrate how wavelength modulation SPR biosensor can be used to detect biomolecular interactions. 相似文献
93.
J. Sereikaité D. Iljasevičiené G. Dienys H. Danilčenko V. Gavrilova 《Applied biochemistry and biotechnology》1993,43(2):153-160
Ascorbate oxidase fromCucurbita sp. was isolated by ammonium sulfate precipitation and DEAE-dextran-silochrome column chromatography. The thermal and pH stabilities
of the purified enzyme were investigated. TheK
M forl-ascorbic acid (1.5 mM) and chlorohydroquinone (0.37 mM) was determined. Substrate specificity of ascorbate oxidase was investigated and compared with those of laccases fromCoriolus hirsutus andCerrena maxima. Ascorbate oxidase was covalently bound to a polymeric membrane and used in an enzyme electrode for ascorbic acid. 相似文献
94.
95.
将改进的基本度量理论与热力学微扰理论相结合,提出了胶体/高分子系统排空相互作用的IRDFT理论。该理论解释了在实际胶体系统中起重要作用的排斥体积效应和高分子链内相关性的竞争机制。应用该IRDFT,分别以线性链状和环状结构的高分子及其单体为排空元,计算了不同排空元条件下的胶体间排空相互作用。研究表明:对于絮凝破坏,自由环状高分子具有更大的优势。 相似文献
96.
A rapid microtiter plate assay for the detection of inhibitors of the Na+, K+-ATPase has been developed. The assay is based on the measurement of inorganic phosphate released from the substrate, ATP,
and has been designed to be carried out in the individual wells of a microtiter plate. Since the production of inorganic phosphate
is determined colorimetrically, multiple samples can be tested simultaneously using a microtiter plate reader. This microtiter
plate assay is particularly useful for screening large numbers of samples, such as microbial culture supernatants. 相似文献
97.
98.
Toshiyuki Chikuma Yoko ShimabukuroTakeya Iguchi Akira TanakaKyoji Taguchi Takeshi KatoMitsune Yamaguchi Hiroshi Hojo 《Analytica chimica acta》2002,457(2):157-164
A rapid and sensitive assay for the determination of Dns-His-Lys-Arg-His-Lys cleaving enzyme activity is reported. This assay is based on fluorimetric detection of a dansylated dipeptide, 5-dimethylaminonaphthalene-1-sulfonyl-His-Lys, enzymatically formed from the substrate 5-dimethylaminonaphthalene-1-sulfonyl-His-Lys-Arg-His-d-Lys, after separation by high-performance liquid chromatography (HPLC) using a C-18 reversed-phase column by isocratic elution. This assay is sensitive enough to measure 5-dimethylaminonaphthalene-1-sulfonyl-His-Lys at concentrations as low as 7 pmol, and yields highly reproducible results and requires less than 9.0 min per sample for separation and quantitation. The optimum pH for Dns-His-Lys-Arg-His-Lys cleaving enzyme activity was 7.5-8.0. The Michaelis constant (Km) and the maximum velocity (Vmax) values were 33.3 μM and 47.07 pmol/(μg h), respectively with the use of enzyme extract obtained from bovine pituitary. By using this assay, axonal transport of this enzyme activity was observed 48 h after double ligations of rat sciatic nerves. The high sensitivity and selectivity of this assay would be useful for clarification of the physiological role of this enzyme. 相似文献
99.
QIAN Baogong 《高分子科学》1988,(2):97-116
For the mechanism of isothermal bulk crystallization of high polymers, beside the nucleation and growth steps, the unimpingement of growing crystal aggregates should be taken into account for the modification of the Avrami equation. Starting from Poisson distribution function of growing crystal aggregates, the probability of the unimpinging ones should be P(0)+P(1), then the Q-modified Avrami equation thus derived can be expressed aswhere V0 represents the volume fraction of crystal aggregates at crystallization time t at a given temperature, while the exponent n on t relates to the mode of nucleation and growth, and K_q is the corresponding shape factor. This Q-modified one is verified satisfactory by the isothermal bulk crystallization of lanthanidecatalytically polymerized polybutadiene (Ln-PB), polyisoprene (Ln-PIR) and their copolymers (LnPB/IR). Furthermore, the proposed mechanism is well identified by the change of morphological state during the course of crystallization of the corresponding east film of Ln-PB TR (92/8) at-60°(Fig. 1).Upon examination of the influence of the number of entanglement on crystallization rate, it reveals the existence of two stages of entanglementation, the primary and the secondary ones (Fig. 19)The equation for dependence of molecular weight and entanglement on bulk crystallization rate has been derived as Eq. 13 or 18 for Ln-PB, and verified by the experimental rate data of well fractionated Ln-PB samples crystallized at -9.1 to -15℃(Fig.20). 相似文献
100.
Transition state analogues (TSAs) have long been regarded as ideal templates for the preparation of catalytically active synthetic imprinted polymers. In the current work, however, a new type of molecularly imprinted polymer (MIP) was synthesized with the substrate (homovanillic acid, HVA) as the template and hemin introduced as the catalytic center, with the use of plural functional monomers to prepare the active sites. The MIP successfully mimicked natural peroxidase, suggesting that it may not be imperative to employ a TSA as the template when preparing enzyme-like imprinted polymers and that the imprinted polymer matrix provided an advantageous microenvironment around the catalytic center (hemin), essentially similar to that supplied by apo-proteins in natural enzymes. Significantly, by taking advantage of the special structure of hemin and multiple-site interactions provided by several functional monomers, the intrinsic difficulties for MIPs in recognizing template molecules in polar solutions were overcome. The newly developed polymer showed considerable recognizing ability toward HVA, catalytic activity, substrate specificity and also stability, which are the merits lacked by the natural peroxidase. Meanwhile, the ease of recovery and reuse the MIP implies the potential for industrial application. 相似文献