全文获取类型
收费全文 | 2751篇 |
免费 | 398篇 |
国内免费 | 317篇 |
专业分类
化学 | 2090篇 |
晶体学 | 38篇 |
力学 | 149篇 |
综合类 | 26篇 |
数学 | 298篇 |
物理学 | 865篇 |
出版年
2024年 | 8篇 |
2023年 | 54篇 |
2022年 | 105篇 |
2021年 | 117篇 |
2020年 | 147篇 |
2019年 | 123篇 |
2018年 | 93篇 |
2017年 | 95篇 |
2016年 | 144篇 |
2015年 | 138篇 |
2014年 | 142篇 |
2013年 | 210篇 |
2012年 | 216篇 |
2011年 | 245篇 |
2010年 | 153篇 |
2009年 | 152篇 |
2008年 | 185篇 |
2007年 | 158篇 |
2006年 | 109篇 |
2005年 | 101篇 |
2004年 | 92篇 |
2003年 | 98篇 |
2002年 | 103篇 |
2001年 | 81篇 |
2000年 | 73篇 |
1999年 | 53篇 |
1998年 | 39篇 |
1997年 | 32篇 |
1996年 | 30篇 |
1995年 | 20篇 |
1994年 | 23篇 |
1993年 | 15篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 17篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1959年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有3466条查询结果,搜索用时 15 毫秒
1.
Monomeric sarcosine oxidase (mSOx) fusion with the silaffin peptide, R5, designed previously for easy protein production in low resource areas, was used in a biosilification process to form an enzyme layer electrode biosensor. mSOx is a low activity enzyme (10–20 U/mg) requiring high amounts of enzyme to obtain an amperometric biosensor signal, in the clinically useful range <1 mM sarcosine, especially since the Km is >10 mM. An amperometric biosensor model was fitted to experimental data to investigate dynamic range. mSOx constructs were designed with 6H (6×histidine) and R5 (silaffin) peptide tags and compared with native mSOx. Glutaraldehyde (GA) cross‐linked proteins retained ~5 % activity for mSOx and mSOx‐6H and only 0.5 % for mSOx‐R5. In contrast R5 catalysed biosilification on (3‐mercaptopropyl) trimethoxysilane (MPTMS) and tetramethyl orthosilicate (TMOS) particles created a ‘self‐immobilisation’ matrix retaining 40 % and 76 % activity respectively. The TMOS matrix produced a thick layer (>500 μm) on a glassy carbon electrode with a mediated current due to sarcosine in the clinical range for sarcosinemia (0–1 mM). The mSOx‐R5 fusion protein was also used to catalyse biosilification in the presence of creatinase and creatininase, entrapping all three enzymes. A mediated GC enzyme linked current was obtained with dynamic range available for creatinine determination of 0.1–2 mM for an enzyme layer ~800 nm. 相似文献
2.
The acoustic and perceptive characteristics of discourse units, including clauses, simple sentences, compound sentences and paragraphs, were studied. The acoustic characteristics were based on the analysis of a speech corpus consisted of ten monologues. The Perceived Boundary Strength (PBS) of the monologues was labeled on a five-point scale by 25 participants. The main results are as follows: (1) There is a significant difference in the PBS of clauses (corresponding to intonational phrase), sentences (including simple sentences and compound sentences) and paragraphs. But the PBS of simple sentences and compound sentences is the same, and the pitch reset and pause are also not significantly different between these two kinds of boundaries. (2) The pitch-based cue used to distinguish clauses, sentences and paragraphs appears to be the difference between pre- and post-boundary syllables, but not simply the pitch value of either syllable alone. (3) Declination mainly occurs within intonational phrases, whereas there is no consistent global declination in sentences or in paragraphs. (4) Pauses are longer and more varied at the boundary of larger discourse units. Moreover, there is a significant positive correlation between pause duration and degree of pitch reset at clause boundaries, but not at sentence or paragraph boundaries. 相似文献
3.
Gujie Qian S. Baccaro M. Falconieri Jiafang Bei A. Cecilia Guorong Chen 《Journal of Non》2008,354(40-41):4626-4629
Glasses in SiO2–ZnO–BaO system with the different ZnO/BaO ratio were studied. In some cases, BaF2 was introduced to substitute for BaO on the equal base. Photoluminescent spectra showed that ZnO in glass matrices behaved somewhat differently from ZnO crystals. Especially, the introduction of fluorine ions led to dramatic shift of UV emission band of glasses closer to that of ZnO crystals. Raman spectral analysis provided consistent results. In particular, Raman bands in the high frequency region are sensitive to effects of different ZnO/BaO or BaF2/BaO ratio on structure of glasses. 相似文献
4.
5.
用传统的预测效度估计法估计高考预测效度,其估计值往往偏低。为此,本文应用回归分析中混合估计理论提出了高考预测效度的混合估计。这种估计是预测效度的无偏估计,并解决了预测效度估计值偏低的问题。 相似文献
6.
Zhengqian Luo Guoyong Sun Zhiping Cai Miaoling Si Qibo Li 《Optics Communications》2007,277(1):118-124
In this paper, continuous wave Yb3+-doped double-clad fiber lasers (DCFLs) with linear-cavity are investigated theoretically and numerically using the rate equations. Under the steady state conditions, the simplified analytic solutions of Yb3+-doped DCFLs under considering the scattering loss are deduced in the strongly pump condition. Compared with the known analytic solutions in published literatures, our analytic solutions are more accurate, especially, at higher reflectivity of output mirror. In addition, a fast and stable algorithm based on the Newton-Raphson method is proposed to simulate numerically Yb3+-doped DCFLs. The results by simplified analytic solutions are in good agreement with those by the numerical simulation. Moreover, we have performed the optimization of an Yb3+-doped DCFL using the simplified analytic solutions and the numerical simulations, respectively. 相似文献
7.
8.
低温太阳热能与化学链燃烧相结合控制CO2分离动力系统 总被引:3,自引:1,他引:2
本文探索并提出控制CO2分离的低温太阳热能与清洁合成燃料甲醇-三氧化二铁化学链燃烧相结合的新颖能源动力系统。基于图象(?)分析方法,明确地指出甲醇化学链燃烧能量释放过程燃烧堋损失减小和低温太阳热能品位提升的机理。从能源有效利用和环境相容出发,研究和揭示化学链燃烧与太阳能有机整合共同减小CO2分离能耗的特性规律。相比不分离常规联合循环,新系统(?)效率提高约6.2个百分点;与分离CO2的联合循环相比,新系统媚效率提高约14.2个百分点。同时,低温太阳热能热转功效率可达到22.5%。 相似文献
9.
10.
In this article a new technique was developed to fabricate scaffolds with a unique microstructure by solid–liquid separation in combination with particulate-leaching. Firstly, the effects of polymer concentration, quenching temperature on the porous morphology and the mechanical property of obtained scaffolds during solid–liquid separation have been investigated. Then, salt granules as porogen were introduced into the solid–liquid phase separation to produce the unique pore structure of the scaffold. The pore diameter of the scaffold could be controlled with the particulate size and the wall of pores possessed special microstructure, which enhanced the pore interconnectivity. The cell culture results confirmed that a good interconnectivity of the scaffold prepared by the improved solid–liquid separation was useful for nutrition transportation and cell proliferation. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献