全文获取类型
收费全文 | 26295篇 |
免费 | 4452篇 |
国内免费 | 3809篇 |
专业分类
化学 | 19064篇 |
晶体学 | 422篇 |
力学 | 1753篇 |
综合类 | 304篇 |
数学 | 3256篇 |
物理学 | 9757篇 |
出版年
2024年 | 41篇 |
2023年 | 436篇 |
2022年 | 626篇 |
2021年 | 853篇 |
2020年 | 958篇 |
2019年 | 975篇 |
2018年 | 891篇 |
2017年 | 881篇 |
2016年 | 1190篇 |
2015年 | 1276篇 |
2014年 | 1469篇 |
2013年 | 1959篇 |
2012年 | 2278篇 |
2011年 | 2387篇 |
2010年 | 1700篇 |
2009年 | 1716篇 |
2008年 | 1877篇 |
2007年 | 1734篇 |
2006年 | 1633篇 |
2005年 | 1298篇 |
2004年 | 1098篇 |
2003年 | 918篇 |
2002年 | 1000篇 |
2001年 | 880篇 |
2000年 | 642篇 |
1999年 | 597篇 |
1998年 | 474篇 |
1997年 | 322篇 |
1996年 | 335篇 |
1995年 | 318篇 |
1994年 | 267篇 |
1993年 | 245篇 |
1992年 | 177篇 |
1991年 | 186篇 |
1990年 | 184篇 |
1989年 | 147篇 |
1988年 | 115篇 |
1987年 | 100篇 |
1986年 | 78篇 |
1985年 | 78篇 |
1984年 | 34篇 |
1983年 | 37篇 |
1982年 | 28篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1973年 | 9篇 |
1936年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
21.
22.
23.
Numerical Algorithms - A singularly perturbed Volterra integro-differential equation with an integrable singularity in the integral term is considered. The upwind difference method is used to... 相似文献
24.
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
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
25.
26.
Dr. Feifan Wang Jie Tian Dr. Mengzhu Li Dr. Weizhen Li Dr. Lifang Chen Xiaozhi Liu Dr. Jian Li Aidaer Muhetaer Prof. Dr. Qi Li Prof. Dr. Yuan Wang Prof. Dr. Lin Gu Prof. Dr. Ding Ma Prof. Dr. Dongsheng Xu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(21):8280-8286
Fully utilizing solar energy for catalysis requires the integration of conversion mechanisms and therefore delicate design of catalyst structures and active species. Herein, a MOF crystal engineering method was developed to controllably synthesize a copper–ceria catalyst with well-dispersed photoactive Cu-[O]-Ce species. Using the preferential oxidation of CO as a model reaction, the catalyst showed remarkably efficient and stable photoactivated catalysis, which found practical application in feed gas treatment for fuel cell gas supply. The coexistence of photochemistry and thermochemistry effects contributes to the high efficiency. Our results demonstrate a catalyst design approach with atomic or molecular precision and a combinatorial photoactivation strategy for solar energy conversion. 相似文献
27.
Dongping Wang Jie Dong Wenjing Fan Prof. Dr. Xiang-Ai Yuan Prof. Dr. Jian Han Prof. Dr. Jin Xie 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(22):8508-8512
An unprecedented Mn(I)-catalyzed selective hydroarylation and hydroalkenylation of unsaturated amides with commercially available organic boronic acids is reported. Alkenyl boronic acids have been successfully employed for the first time in Mn(I)-catalyzed carbon–carbon bond formation. A wide array of β-alkenylated amide products can be obtained in moderate to good yields, which offers practical access to five- and six-membered lactams. This protocol has predictable regio- and chemoselectivity, excellent functional group compatibility and ease of operation in air, representing a significant step-forward towards manganese-catalyzed C−C coupling. 相似文献
28.
29.
Kai Xu Zhenchang Tang Yan Zhang Wanshu Li Haiou Li Lihui Wang Liming Liu Honghang Wang Feng Chi Xiaowen Zhang 《Current Applied Physics》2019,19(10):1076-1081
Germanium dioxide (GeO2) aqueous solutions are facilely prepared and the corresponding anode buffer layers (ABLs) with solution process are demonstrated. Atomic force microscopy, X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy measurements show that solution-processed GeO2 behaves superior film morphology and enhanced work function. Using GeO2 as ABL of organic light-emitting diodes (OLEDs), the visible device with tris(8-hydroxy-quinolinato)aluminium as emitter gives maximum luminous efficiency of 6.5 cd/A and power efficiency of 3.5 lm/W, the ultraviolet device with 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole as emitter exhibits short-wavelength emission with peak of 376 nm, full-width at half-maximum of 42 nm, maximum radiance of 3.36 mW/cm2 and external quantum efficiency of 1.5%. The performances are almost comparable to the counterparts with poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) as ABL. The current, impedance, phase and capacitance as a function of voltage characteristics elucidate that the GeO2 ABL formed from appropriate concentration of GeO2 aqueous solution favors hole injection enhancement and accordingly promoting device performance. 相似文献
30.
Here, we report a new strategy for rapid synthesis of branched peptide by side-chain hydrazide ligation at Asn. The hydrazide was converted to thioester at Asn side chain by NaNO2 and thiol reagent, and sequential ligation with an N-terminus Cys-peptide efficiently afforded the branched peptide. A branched cyclic peptide was successfully synthesized by side-chain ligation with a two-Cys-peptide and formation of a disulfide bond. This approach provides a new way for expeditious synthesis of branched peptides and facilitates the design of neopeptides as functional bio-mimics. 相似文献