全文获取类型
收费全文 | 15162篇 |
免费 | 2296篇 |
国内免费 | 3413篇 |
专业分类
化学 | 12680篇 |
晶体学 | 313篇 |
力学 | 689篇 |
综合类 | 344篇 |
数学 | 1571篇 |
物理学 | 5274篇 |
出版年
2024年 | 42篇 |
2023年 | 227篇 |
2022年 | 497篇 |
2021年 | 549篇 |
2020年 | 551篇 |
2019年 | 588篇 |
2018年 | 489篇 |
2017年 | 560篇 |
2016年 | 675篇 |
2015年 | 774篇 |
2014年 | 973篇 |
2013年 | 1271篇 |
2012年 | 1323篇 |
2011年 | 1429篇 |
2010年 | 1117篇 |
2009年 | 1068篇 |
2008年 | 1243篇 |
2007年 | 1143篇 |
2006年 | 1010篇 |
2005年 | 842篇 |
2004年 | 700篇 |
2003年 | 563篇 |
2002年 | 543篇 |
2001年 | 494篇 |
2000年 | 436篇 |
1999年 | 319篇 |
1998年 | 234篇 |
1997年 | 167篇 |
1996年 | 152篇 |
1995年 | 149篇 |
1994年 | 124篇 |
1993年 | 98篇 |
1992年 | 83篇 |
1991年 | 78篇 |
1990年 | 77篇 |
1989年 | 38篇 |
1988年 | 50篇 |
1987年 | 28篇 |
1986年 | 35篇 |
1985年 | 33篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1961年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
962.
963.
可见光化的半导体光催化剂 总被引:1,自引:0,他引:1
光解水制氢能否实用化取决于太阳光的有效利用率, 研究开发可见光化的光催化剂成为当前光催化剂研究中的重要课题.本文介绍了利用 光解水制氢的反应机理,综述了近年来半导体光催化剂在利用可见光方面的研究进展,重点描述了这些光催化剂的结构,并对该领域今后的研究方向进行了展望. 相似文献
964.
偶氮喹啉-镍离子配合物应用于HSO-4识别研究 总被引:4,自引:0,他引:4
考察了5-(4'-氰基苯)偶氮-8-羟基喹啉(1)-镍配合物的光谱特性并将其应用于阴离子识别研究中.研究结果表明,1-Ni2+金属配合物可选择性识别不同的阴离子,并对HSO-4具有独特的光谱响应.化合物1在乙腈中为无色溶液,与Ni2+可形成稳定常数为9.2×10 6mol-1·L的1∶1型红色配合物,在此配合物中加入HSO-4后,红色的溶液逐渐褪色,而加入CH3CO-2,F-和H2PO-4却产生增色效应,Cl-和Br-加入后主体溶液无明显颜色和光谱变化,据此建立了选择性识别HSO-4新体系,并探讨其作用机理. 相似文献
965.
Biosorption of copper(II) and zinc(II) from aqueous solution by Pseudomonas putida CZ1 总被引:1,自引:0,他引:1
Chen XC Wang YP Lin Q Shi JY Wu WX Chen YX 《Colloids and surfaces. B, Biointerfaces》2005,46(2):101-107
To study Pseudomonas putida CZ1, having high tolerance to copper and zinc on the removal of toxic metals from aqueous solutions, the biosorption of Cu(II) and Zn(II) by living and nonliving P. putida CZ1 were studied as functions of reaction time, initial pH of the solution and metal concentration. It was found that the optimum pH for Zn(II) removal by living and nonliving cells was 5.0, while it was 5.0 and 4.5, respectively, for Cu(II) removal. At the optimal conditions, metal ion biosorption was increased as the initial metal concentration increased. The adsorption data with respect to both metals provide an excellent fit to the Langmuir isotherm. The binding capacity of living cells is significantly higher than that of nonliving cells at tested conditions. It demonstrated that about 40-50% of the metals were actively taken up by P. putida CZ1, with the remainder being passively bound to the bacterium. Moreover, desorption efficiency of Cu(II) and Zn(II) by living cells was 72.5 and 45.6% under 0.1M HCl and it was 95.3 and 83.8% by nonliving cells, respectively. It may be due to Cu(II) and Zn(II) uptake by the living cells enhanced by intracellular accumulation. 相似文献
966.
967.
The crystal structure of ( [CuL (H2O) 2 ] (ClO4) 2 · 2H2O, CuL) (L = N- (5-sulfosalicylidene)-4' -bromoaniline) was determined by means of X-ray crystallography. The interaction between CuL and salmon sperm DNA in a 0. 1 mol/L HOAc-NaOAc buffer solution (pH 5.10) was investigated by cyclic voltammetry and UV-Vis spectroscopy. A couple of redox peaks of CuL in the cyclic voltammograms(CV) can be seen at the glassy carbon electrode. It was found that the peak current of CuL decreased significantly with a negative shift of the peak potential in the presence of DNA compared with that in the absence of DNA. In addition,the decreased absorbance of CuL was observed with increasing the concentration of DNA; the absorption spectrum of an ethidium bromide(EB)-DNA system inthe presence of CuL confirms that the binding mode of CuL to DNA is different from the intercalation of EB with DNA. All the experimental results indicate that CuL can bind to DNA by electrostatic binding and form a 1:1 association complex with a binding constant of 2.72×104 L/mol. 相似文献
968.
In the present paper, we describe a microfluidics-based sensing system for nonelectroactive anions under negative separation electric field by mounting a single carbon fiber disk working electrode (WE) in the end part of a poly(dimethylsiloxane) microchannel. In contrast to work in a positive separation electric field described in our previous paper (Anal. Chem. 2004, 76, 6902-6907), here the electrochemical reduction reaction at the WE is not coupled with the separation high-voltage (HV) system, whereas the electrochemical oxidation reaction at the WE is coupled with the separation HV system. The electroactive indicator is the carbon fiber WE itself but not dissolved oxygen. This provides a convenient and sensitive means for the determination of nonelectroactive anions by amperometry. The influences of separation voltage, detection potential, and the distance between the WE and the separation channel outlet on the response of the detector have been investigated. The present detection mode is successfully used to electrochemically detect F-, Cl-, SO4(2-), CH3COO-, H2PO4-. Based on the preliminary results, a detection limit of 2 microM and a dynamic range up to three orders of magnitude for Cl- could be achieved. 相似文献
969.
A novel diterpene derivative, 5-methyl-5-(4,8,12-trimethyl-tridecyl)-dihydro-furan-2-one (1) and a new chromone, 5-hydroxy-7-methoxy-3-methyl-chromen-4-one (2), along with a known compound, phytol (3) have been isolated from the aerial parts of Hypericum perforatum. Their structures were established on the basis of spectroscopic analysis and by comparison with published values. 相似文献
970.
Positioning isolation and biochemical analysis of single DNA molecules based on nanomanipulation and single-molecule PCR 总被引:8,自引:0,他引:8
Lü JH Li HK An HJ Wang GH Wang Y Li MQ Zhang Y Hu J 《Journal of the American Chemical Society》2004,126(36):11136-11137
Recently, the isolation and biochemical analysis of DNA at the single-molecule level has been recognized as very important for genetic research and clinical analysis. A unique technique for the positioning, dissection, and isolation of single DNA molecules using atomic force microscopy (AFM) has been demonstrated. Full-length genome DNA molecules were first deposited and stretched by a modified "molecular combing" technique onto a 3-aminopropyl triethoxysilane-coated mica substrate. A single DNA fragment was dissected from one of those genome DNA strands with the AFM tip at the desired position, and then isolated (or picked up) after a special operation called "kneading". All the operations including imaging, dissection, and isolation could be carried out with one tip. The isolated DNA fragment on the AFM tip could be successfully amplified by single-molecule PCR. 相似文献