全文获取类型
收费全文 | 140697篇 |
免费 | 22387篇 |
国内免费 | 15485篇 |
专业分类
化学 | 99555篇 |
晶体学 | 1461篇 |
力学 | 8440篇 |
综合类 | 921篇 |
数学 | 17346篇 |
物理学 | 50846篇 |
出版年
2024年 | 294篇 |
2023年 | 2524篇 |
2022年 | 3800篇 |
2021年 | 4604篇 |
2020年 | 5224篇 |
2019年 | 4894篇 |
2018年 | 4289篇 |
2017年 | 4033篇 |
2016年 | 6444篇 |
2015年 | 6060篇 |
2014年 | 7550篇 |
2013年 | 10169篇 |
2012年 | 12206篇 |
2011年 | 12961篇 |
2010年 | 8697篇 |
2009年 | 8636篇 |
2008年 | 9363篇 |
2007年 | 8340篇 |
2006年 | 7794篇 |
2005年 | 6619篇 |
2004年 | 5546篇 |
2003年 | 4488篇 |
2002年 | 4310篇 |
2001年 | 3399篇 |
2000年 | 2863篇 |
1999年 | 2897篇 |
1998年 | 2454篇 |
1997年 | 2312篇 |
1996年 | 2392篇 |
1995年 | 1968篇 |
1994年 | 1704篇 |
1993年 | 1499篇 |
1992年 | 1358篇 |
1991年 | 1214篇 |
1990年 | 989篇 |
1989年 | 806篇 |
1988年 | 591篇 |
1987年 | 507篇 |
1986年 | 533篇 |
1985年 | 457篇 |
1984年 | 326篇 |
1983年 | 268篇 |
1982年 | 219篇 |
1981年 | 167篇 |
1980年 | 133篇 |
1979年 | 64篇 |
1978年 | 63篇 |
1977年 | 69篇 |
1976年 | 57篇 |
1974年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
121.
122.
123.
Mariusz Marć Marek Tobiszewski Bożena Zabiegała Miguel de la Guardia Jacek Namieśnik 《Analytica chimica acta》2015
This review summarizes the different tools and concepts that are commonly applied in air quality monitoring. The monitoring of atmosphere is extremely important as the air quality is an important problem for large communities. Main requirements for analytical devices used for monitoring include a long period of autonomic operation and portability. These instruments, however, are often characterized by poor analytical performance. Monitoring networks are the most common tools used for monitoring, so large-scale monitoring programmes are summarized here. Biomonitoring, as a cheap and convenient alternative to traditional sample collection, is becoming more and more popular, although its main drawback is the lack of standard procedures. Telemonitoring is another approach to air monitoring, which offers some interesting opportunities, such as ease of coverage of large or remote areas, constituting a complementary approach to traditional strategies; however, it requires huge costs. 相似文献
124.
125.
126.
Design and development of a two‐dimensional system based on hydrophilic and reversed‐phase liquid chromatography with on‐line sample treatment for the simultaneous separation of excreted xenobiotics and endogenous metabolites in urine 下载免费PDF全文
Diego García‐Gómez Encarnación Rodríguez‐Gonzalo Rita Carabias‐Martínez 《Biomedical chromatography : BMC》2015,29(8):1190-1196
In the present work we describe a two‐dimensional liquid chromatographic system (2D‐LC) with detection by mass spectrometry (MS) for the simultaneous separation of endogenous metabolites of clinical interest and excreted xenobiotics deriving from exposure to toxic compounds. The 2D‐LC system involves two orthogonal chromatographic modes, hydrophilic interaction liquid chromatography (HILIC) to separate polar endogenous metabolites and reversed‐phase (RP) chromatography to separate excreted xenobiotics of low and intermediate polarity. Additionally, the present proposal has the novelty of incorporating an on‐line sample treatment based on the use of restricted access materials (RAMs), which permits the direct injection of urine samples into the system. The work is focused on the instrumental coupling, studying all possible options and attempting to circumvent the problems of solvent incompatibility between the RAM device and the two chromatographic columns, HILIC and RP. The instrumental configuration developed, RAM‐HILIC‐RPLC‐MS/MS, allows the simultaneous assessment of urinary metabolites of clinical interest and excreted compounds derived from exposure to toxic agents with minimal sample manipulation. Thus, it may be of interest in areas such as occupational and environmental toxicology in order to explore the possible relationship between the two types of compounds. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
127.
DFT mechanistic study of the H2‐assisted chain transfer copolymerization of propylene and p‐methylstyrene catalyzed by zirconocene complex 下载免费PDF全文
Cheng‐Gen Zhang Shu‐Yuan Yu Liaoyun Zhang Huayi Li Zhi‐Xiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2015,53(4):576-585
DFT computations have been performed to investigate the mechanism of H2‐assisted chain transfer strategy to functionalize polypropylene via Zr‐catalyzed copolymerization of propylene and p‐methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2‐insertion over 2,1‐insertion both kinetically and thermodynamically, explaining the observed 1,2‐insertion regioselectivity for propylene insertion. (ii) The 2,1‐inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2‐insertion. The observation of 2,1‐insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H2 can react with the deactivated [Zr]?pMS?PPn facilely, which displace functionalized pMS?PPn chain and regenerate [Zr]? H active catalyst to continue copolymerization. The effects of counterions are also discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 576–585 相似文献
128.
Zhang Kailun Wu Hongjuan Wang Tian Yao Meng Xie Jixing Jiao Yunhong 《Journal of Thermal Analysis and Calorimetry》2021,145(6):3067-3075
Journal of Thermal Analysis and Calorimetry - A phosphazene-based flame retardant (PBFA) was synthesized by hexachlorocyclotriphosphazene and N-aminoethylpiperazine. To improve the flame retardancy... 相似文献
129.
Rong Yin Jihui Zhang Xudong Shang 《Mathematical Methods in the Applied Sciences》2020,43(15):8736-8752
This paper is dedicated to studying the following Schrödinger–Poisson system Under some different assumptions on functions V(x), K(x), a(x) and f(u), by using the variational approach, we establish the existence of positive ground state solutions. 相似文献
130.