全文获取类型
收费全文 | 5407篇 |
免费 | 692篇 |
国内免费 | 564篇 |
专业分类
化学 | 3946篇 |
晶体学 | 78篇 |
力学 | 221篇 |
综合类 | 49篇 |
数学 | 1047篇 |
物理学 | 1322篇 |
出版年
2023年 | 55篇 |
2022年 | 129篇 |
2021年 | 162篇 |
2020年 | 189篇 |
2019年 | 234篇 |
2018年 | 221篇 |
2017年 | 174篇 |
2016年 | 301篇 |
2015年 | 279篇 |
2014年 | 315篇 |
2013年 | 397篇 |
2012年 | 405篇 |
2011年 | 426篇 |
2010年 | 317篇 |
2009年 | 295篇 |
2008年 | 379篇 |
2007年 | 325篇 |
2006年 | 281篇 |
2005年 | 254篇 |
2004年 | 226篇 |
2003年 | 227篇 |
2002年 | 261篇 |
2001年 | 199篇 |
2000年 | 119篇 |
1999年 | 86篇 |
1998年 | 53篇 |
1997年 | 34篇 |
1996年 | 30篇 |
1995年 | 20篇 |
1994年 | 24篇 |
1993年 | 24篇 |
1992年 | 10篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 18篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1973年 | 6篇 |
1972年 | 6篇 |
排序方式: 共有6663条查询结果,搜索用时 15 毫秒
991.
Diastereo‐ and Enantioselective Copper(I)‐Catalyzed Intermolecular [3+2] Cycloaddition of Azomethine Ylides with β‐Trifluoromethyl β,β‐Disubstituted Enones 下载免费PDF全文
Zhan‐Ming Zhang Bing Xu Shan Xu Prof. Dr. Hai‐Hong Wu Prof. Dr. Junliang Zhang 《Angewandte Chemie (International ed. in English)》2016,55(21):6324-6328
Reported herein is an asymmetric [3+2] cycloaddition reaction of azomethine ylides with β‐trifluoromethyl β,β‐disubstituted enones, a reaction which is enabled by a Ming‐Phos‐derived copper(I) catalyst (Ming‐Phos=chiral sulfinamide monophosphines, Figure 2 ). This method provides scalable and efficient access to the highly substituted pyrrolidines with a trifluoromethylated, all‐carbon quaternary stereocenter in good yields with up to greater than 20:1 d.r. and 98 % ee. The reaction has a broad substrate scope and tolerates a wide range of functional groups. 相似文献
992.
Isolating Reactions at the Picoliter Scale: Parallel Control of Reaction Kinetics at the Liquid–Liquid Interface 下载免费PDF全文
Gia Chuong Phan‐Quang Hiang Kwee Lee Prof. Xing Yi Ling 《Angewandte Chemie (International ed. in English)》2016,55(29):8304-8308
Miniaturized liquid–liquid interfacial reactors offer enhanced surface area and rapid confinement of compounds of opposite solubility, yet they are unable to provide in situ reaction monitoring at a molecular level at the interface. A picoreactor operative at the liquid–liquid interface is described, comprising plasmonic colloidosomes containing Ag octahedra strategically assembled at the water‐in‐decane emulsion interface. The plasmonic colloidosomes isolate ultrasmall amounts of solutions (<200 pL), allowing parallel monitoring of multiple reactions simultaneously. Using the surface‐enhanced Raman spectroscopy (SERS) technique, in situ monitoring of the interfacial protonation of dimethyl yellow (p‐dimethylaminoazobenzene (DY)) is performed, revealing an apparent rate constant of 0.09 min?1 for the first‐order reaction. The presence of isomeric products with similar physical properties is resolved, which would otherwise be indiscernible by other analytical methods. 相似文献
993.
Electrochemical C−H/N−H Functionalization for the Synthesis of Highly Functionalized (Aza)indoles 下载免费PDF全文
Zhong‐Wei Hou Zhong‐Yi Mao Huai‐Bo Zhao Yared Yohannes Melcamu Prof. Dr. Xin Lu Dr. Jinshuai Song Prof. Dr. Hai‐Chao Xu 《Angewandte Chemie (International ed. in English)》2016,55(32):9168-9172
Indoles and azaindoles are among the most important heterocycles because of their prevalence in nature and their broad utility in pharmaceutical industry. Reported herein is an unprecedented noble‐metal‐ and oxidant‐free electrochemical method for the coupling of (hetero)arylamines with tethered alkynes to synthesize highly functionalized indoles, as well as the more challenging azaindoles. 相似文献
994.
Modifying the 5′‐Cap for Click Reactions of Eukaryotic mRNA and To Tune Translation Efficiency in Living Cells 下载免费PDF全文
Josephin M. Holstein Lea Anhäuser Prof. Dr. Andrea Rentmeister 《Angewandte Chemie (International ed. in English)》2016,55(36):10899-10903
The 5′‐cap is a hallmark of eukaryotic mRNAs and plays fundamental roles in RNA metabolism, ranging from quality control to export and translation. Modifying the 5′‐cap may thus enable modulation of the underlying processes and investigation or tuning of several biological functions. A straightforward approach is presented for the efficient production of a range of N7‐modified caps based on the highly promiscuous methyltransferase Ecm1. We show that these, as well as N2‐modified 5′‐caps, can be used to tune translation of the respective mRNAs both in vitro and in cells. Appropriate modifications allow subsequent bioorthogonal chemistry, as demonstrated by intracellular live‐cell labeling of a target mRNA. The efficient and versatile N7 manipulation of the mRNA cap makes mRNAs amenable to both modulation of their biological function and intracellular labeling, and represents a valuable addition to the chemical biology toolbox. 相似文献
995.
Pham Bich Ngoc Thanh Binh Pham Hai Dang Nguyen Thu Trang Tran Hoang Ha Chu Van Minh Chau 《Natural product research》2016,30(12):1360-1365
One new β-carboline alkaloid 7-methoxy-(9H-β-carbolin-1-il)-(E)-1-propenoic acid (1) together with 9-methoxycanthin-6-one (2) and 9-hydroxycanthin-6-one (3) were isolated from the hairy-root cultures of Eurycoma longifolia. The effects of these compounds on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW264.7 cells were investigated. Compound 1 strongly inhibited the production of NO while 2 and 3 having weak or inactive effect. Consistently, compound 1 decreased the expression of cyclooxygenase-2 and inducible nitric oxide synthase. 相似文献
996.
Nguyen Phuong Hanh Nguyen Huu Toan Phan Nguyen Thi Dieu Thuan Tran Thi Hong Hanh Le Thi Vien Nguyen Phuong Thao 《Natural product research》2016,30(18):2071-2076
Six iridoid derivatives (1–6), including two new compounds myrmecodoides A and B (1 and 2), were isolated from the ant-plant Myrmecodia tuberosa. Their structures were determined on the basis of spectroscopic data (1H and 13C NMR, HSQC, HMBC, 1H-1H COSY, NOESY and HR-ESI-MS) and by comparison with the literature values. Among isolates, 3 and 4 exhibit weak antibacterial effect against Staphylococcus aureus subsp. aureus with MIC value of 100.0 μg/mL. 相似文献
997.
Yin-Di Zhu Jing-Yi Zhang Peng-Fei Li Hai-Feng Wu Nai-Liang Zhu Hai Jiang 《Natural product research》2016,30(9):1075-1080
Two new abietane diterpenoid glycosides, named clinopoditerpenes B (1) and C (2), were isolated from Clinopodium chinese. The structures of the new compounds were determined on the basis of extensive spectral analysis. Compound 1 exhibited cardioprotective effect against H2O2-induced apoptosis in H9c2 cells. 相似文献
998.
Some subgradient extragradient type algorithms for solving split feasibility and fixed point problems 下载免费PDF全文
In this paper, we consider the split feasibility problem (SFP) in infinite‐dimensional Hilbert spaces and propose some subgradient extragradient‐type algorithms for finding a common element of the fixed‐point set of a strict pseudocontraction mapping and the solution set of a split feasibility problem by adopting Armijo‐like stepsize rule. We derive convergence results under mild assumptions. Our results improve some known results from the literature. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
999.
Nguyen Le Hoang Anh 《Numerical Functional Analysis & Optimization》2016,37(7):823-838
In this article, we introduce a notion of higher-order radial epiderivative for set-valued maps and study its properties. A generalized concept of higher-order strict minimizers in set-valued optimization is proposed as well. By virtue of the radial epiderivative, we establish a mixed dual problem, and then weak, strong, and converse duality theorems are obtained in dealing with generalized strict minimizers. 相似文献
1000.
We study an optimal control problem with quadratic objective functional for the three dimensional Navier-Stokes-Voigt equations in bounded domains. We show the existence of optimal solutions, the necessary optimality conditions and the sufficient optimality conditions. The second-order optimality conditions obtained in the article seem to be optimal. 相似文献