全文获取类型
收费全文 | 144407篇 |
免费 | 23891篇 |
国内免费 | 14456篇 |
专业分类
化学 | 97198篇 |
晶体学 | 1434篇 |
力学 | 9679篇 |
综合类 | 993篇 |
数学 | 17982篇 |
物理学 | 55468篇 |
出版年
2024年 | 332篇 |
2023年 | 2851篇 |
2022年 | 4115篇 |
2021年 | 4808篇 |
2020年 | 5611篇 |
2019年 | 5187篇 |
2018年 | 4697篇 |
2017年 | 4191篇 |
2016年 | 6589篇 |
2015年 | 6378篇 |
2014年 | 7785篇 |
2013年 | 10283篇 |
2012年 | 12646篇 |
2011年 | 13254篇 |
2010年 | 8841篇 |
2009年 | 8681篇 |
2008年 | 9169篇 |
2007年 | 8195篇 |
2006年 | 7752篇 |
2005年 | 6436篇 |
2004年 | 5043篇 |
2003年 | 3923篇 |
2002年 | 3579篇 |
2001年 | 3122篇 |
2000年 | 2811篇 |
1999年 | 3184篇 |
1998年 | 2771篇 |
1997年 | 2595篇 |
1996年 | 2644篇 |
1995年 | 2273篇 |
1994年 | 2049篇 |
1993年 | 1786篇 |
1992年 | 1560篇 |
1991年 | 1387篇 |
1990年 | 1141篇 |
1989年 | 940篇 |
1988年 | 703篇 |
1987年 | 619篇 |
1986年 | 584篇 |
1985年 | 531篇 |
1984年 | 337篇 |
1983年 | 282篇 |
1982年 | 233篇 |
1981年 | 165篇 |
1980年 | 118篇 |
1979年 | 56篇 |
1978年 | 57篇 |
1977年 | 52篇 |
1975年 | 57篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
141.
Aequationes mathematicae - We discuss equivalence conditions for the non-existence of non-trivial meromorphic solutions to the Fermat Diophantine equation $$f^m(z)+g^n(z)=1$$ with integers $$m,n\ge... 相似文献
142.
143.
144.
He Haidong Yang Haifeng Zhou Longpeng Chen Tianchi 《Journal of Russian Laser Research》2015,36(3):292-299
Ni–Co alloys have a wide range of applications in various fields owning to their excellent physical, chemical, and mechanical properties. In this paper, we prepare Ni–Co alloy coatings on 316L stain steel surfaces by electroplating. We present a novel approach utilizing a nanosecond laser to induce microtextures on Ni–Co alloy coatings. We study experimentally the effects of laser power and scanning rate on the surface morphologies of Ni–Co alloy coatings. The results indicate that the shape and size of induced microtextures can be controlled by the laser power and scanning rate. The size of grains increases with increase in the work current of the laser (WCL) at a certain scanning rate. With the WCL constant, the size of grains decreases with increase in scanning rate while their average height increases. It is a simple and easily-controlled method for the fabrication of microstructures on Ni–Co alloy coatings, which has promising applications in investigations of the properties of microtextured surfaces, such as friction, adhesion, and wetting. 相似文献
145.
Metabolic profiles of dioscin in rats revealed by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
He Zhu Jin‐Di Xu Qian Mao Hong Shen Ming Kong Jian‐Ping Chen Song‐Lin Li 《Biomedical chromatography : BMC》2015,29(9):1415-1421
Dioscin (DIS), one of the most abundant bioactive steroidal saponins in Dioscorea sp., is used as a complementary medicine to treat coronary disease and angina pectoris in China. Although the pharmacological activities and pharmacokinetics of DIS have been well demonstrated, information regarding the final metabolic fates is very limited. This study investigated the in vivo metabolic profiles of DIS after oral administration by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry method. The structures of the metabolites were identified and tentatively characterized by means of comparing the molecular mass, retention time and fragmentation pattern of the analytes with those of the parent compound. A total of eight metabolites, including seven phase I and one phase II metabolites, were detected and tentatively identified for the first time. Oxidation, deglycosylation and glucuronidation were found to be the major metabolic processes of the compound in rats. In addition, a possible metabolic pathway on the biotransformation of DIS in vivo was proposed. This study provides valuable and new information on the metabolism of DIS, which will be helpful for further understanding its mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
146.
147.
In this paper,we investigate the non-autonomous Hamilton-Jacobi equation ■ where H is 1-periodic with respect to t and M is a compact Riemannian manifold without boundary.We obtain the viscosity solution denoted by T_(t_0)~tφ(x) and show T_(t_0)~tφ(x) converges uniformly to a time-periodic viscosity solution u~*(x,t) of ?_tu+H(t,x,?_xu,u)=0. 相似文献
148.
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
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
149.
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
150.
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