全文获取类型
收费全文 | 36452篇 |
免费 | 4718篇 |
国内免费 | 8624篇 |
专业分类
化学 | 36811篇 |
晶体学 | 535篇 |
力学 | 1605篇 |
综合类 | 345篇 |
数学 | 1376篇 |
物理学 | 9122篇 |
出版年
2024年 | 21篇 |
2023年 | 329篇 |
2022年 | 550篇 |
2021年 | 929篇 |
2020年 | 1373篇 |
2019年 | 1104篇 |
2018年 | 1139篇 |
2017年 | 1291篇 |
2016年 | 1691篇 |
2015年 | 1686篇 |
2014年 | 2086篇 |
2013年 | 3437篇 |
2012年 | 2466篇 |
2011年 | 2641篇 |
2010年 | 2216篇 |
2009年 | 2556篇 |
2008年 | 2629篇 |
2007年 | 2828篇 |
2006年 | 2700篇 |
2005年 | 2541篇 |
2004年 | 2304篇 |
2003年 | 2075篇 |
2002年 | 1428篇 |
2001年 | 1054篇 |
2000年 | 949篇 |
1999年 | 813篇 |
1998年 | 671篇 |
1997年 | 696篇 |
1996年 | 560篇 |
1995年 | 525篇 |
1994年 | 488篇 |
1993年 | 416篇 |
1992年 | 394篇 |
1991年 | 252篇 |
1990年 | 163篇 |
1989年 | 172篇 |
1988年 | 127篇 |
1987年 | 85篇 |
1986年 | 53篇 |
1985年 | 90篇 |
1984年 | 59篇 |
1983年 | 28篇 |
1982年 | 44篇 |
1981年 | 28篇 |
1980年 | 20篇 |
1979年 | 17篇 |
1977年 | 8篇 |
1976年 | 15篇 |
1974年 | 6篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
1.
2.
3.
Synthesis of trialkyl semithioglycolurils from alkylthiourea-glyoxal cyclic adducts and dialkylureas
《Mendeleev Communications》2022,32(6):771-773
Condensation of 1-alkyl-4,5-dihydroxyimidazolidine-2-thiones (monoalkylthiourea-glyoxal cyclic adducts) with 1,3-dialkylureas affords novel 1,4,6-trialkylsemithio- glycolurils having non-substituted NH group linked to C=S function. Such compounds can be accessed in two-stage one-pot reaction sequence from alkylthioureas and glyoxal followed by treatment of the resulting adduct with 1,3-dialkylureas 相似文献
4.
Applied Mathematics and Mechanics - Mechanical models of residually stressed fibre-reinforced solids, which do not resist bending, have been developed in the literature. However, in some residually... 相似文献
5.
《Mendeleev Communications》2022,32(1):105-108
A mixed-metal 1D coordination polymer [CaCu(HBTC)2(H2O)8]n (where H3BTC – benzene-1,3,5-tric arboxylic acid) was obtained in a solvothermal synthesis of a well-known copper-containing metal–organic framework [Cu3(BTC)2(H2O)3]n (HKUST-1) in autoclaves 3D-printed from commercial polypropylene. This material was a source of calcium ions, apparently, leaking from a colorant (calcium carbonate) promoted by glacial acetic acid as a modulator used to produce large single crystals of HKUST-1. This finding was confirmed by elemental analysis and a model experiment that resulted in a new calcium-based 1D coordination polymer [Ca(H2BTC)2(H2O)5]n under the same solvothermal conditions with no copper or calcium salts put into a 3D-printed autoclave. 相似文献
6.
Behnam Mohammadi 《中国物理C(英文版)》2022,46(2):023107-023107-8
In this study, the heavy to heavy decay of \begin{document}$ B^0_s\rightarrow D^{*+}D^- $\end{document} ![]()
![]()
is evaluated through the factorization approach by using the final state interaction as an effective correction. Under the factorization approach, this decay mode occurs only through the annihilation process, so a small amount is produced. Feynman's rules state that six meson pairs can be assumed for the intermediate states before the final meson pairs are produced. By taking into account the effects of twelve final state interaction diagrams in the calculations, a significant correction is obtained. These effects correct the value of the branching ratio obtained by the pure factorization approach from \begin{document}$ (2.41\pm1.37)\times10^{-5} $\end{document} ![]()
![]()
to \begin{document}$ (8.27\pm2.23)\times10^{-5} $\end{document} ![]()
![]()
. The value obtained for the branching ratio of the \begin{document}$ B^0_s\rightarrow D^{*+}D^- $\end{document} ![]()
![]()
decay is consistent with the experimental results. 相似文献
7.
Reza Kordnezhadian Bing-Yu Li Armir Zogu Dr. Joachim Demaerel Prof. Dr. Wim M. De Borggraeve Dr. Ermal Ismalaj 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201491
Pentafluorosulfanyl (SF5)-containing compounds and corresponding analogs are a highly valuable class of fluorine-containing building blocks owing to their unique properties. The reason for that is the set of peculiar and tremendously beneficial characteristics they can impart on molecules once introduced onto them. Despite this, their application in distinct scientific fields remains modest, given the extremely harsh reaction conditions needed to access such compounds. The recent synthetic approaches via S−F, and C−SF5 bond formation as well as the use of SF5-containing building blocks embody a “stairway-to-heaven” loophole in the synthesis of otherwise-inaccessible chemical scaffolds only a few years ago. Herein, we report and evaluate the properties of the SF5 group and analogs, by summarizing synthetic methodologies available to access them as well as following applications in material science and medicinal chemistry since 2015. 相似文献
8.
Dr. Yoko Hasegawa Dr. Thomas Cantin Dr. Jonathan Decaens Dr. Samuel Couve-Bonnaire Prof. Dr. André B. Charette Prof. Dr. Thomas Poisson Prof. Dr. Philippe Jubault 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(47):e202201438
The first diastereo- and enantioselective cyclopropanation reactions of electron-deficient allenes with donor-acceptor and diacceptor diazo reagents are described. The desired enantioenriched alkylidenecyclopropanes (ACPs) were obtained in high yields with high diastereo- and enantioselectivities in the presence of Rh2((S)-TCPTAD)4 or Rh2((R)-BTPCP)4 catalysts (up to 95 % yield, >95 : 5 d.r. and 99 : 1 e.r.). This methodology gave a direct access to ACPs bearing multiple electron-deficient substituents and allows to further expand the availability of ACPs chemistry. Interestingly, during the examination of the scope of this reaction, the asymmetric intramolecular C−H insertion reaction into tert-butyl group was observed as a side reaction with up to 94 : 6 e.r. 相似文献
9.
Yuanbo Gao Tingting Yang Xueli Wang Jizong Chen Yong He 《Journal of polymer science. Part A, Polymer chemistry》2022,60(10):1610-1623
Two series of novel alternating copolyoxamides (PAnT-alt-n2 and PAn2-alt-62) are synthesized via solution/solid-state polycondensation (SSP). The alternating structures are analyzed carefully with 1H NMR and 13C NMR spectra. The melting behaviors, thermal stabilities, crystal structures and crystallinities are systematically evaluated by DSC, TGA and WAXD. The results reveal that these alternating copolyoxamides possess almost perfect alternating chain structures and have high melting temperature (Tm > 270 °C), high crystallinity (Xc > 32%) and high decomposition temperature (T5 > 405 °C) as well as low saturated water absorption (<3.5 wt%), which suggests that they have high potential as engineering plastic of high heat resistant. 相似文献
10.
Prof. Dr. Erika Nakashima Prof. PhD Hisashi Yamamoto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(35):e202103989
Since the global peptide drug market demand has been predicted to increase, highly efficient and inexpensive mass scale peptides are required. However, the production process raises questions about the cost of energy input, scale-up production, raw materials, and solvents treatment. This paper introduces 2 methods for the 2–4 mer oligopeptides bond formation for batch reaction utilizing 50–100 mol% of a mild Brønsted acid under the mild condition. One of the methods has been capably adapted to flow synthesis at room temperature using organic solvents with boiling points below 100 °C. The method applies the tert-butoxycarbonyl amino methoxy group, forming the desired dipeptide without solvent at mild temperatures. Furthermore, the conversion of the carboxylic acid leaving the group to phenyl ester promotes peptide bond formation, and the reaction were applied to di, tri, and tetrapeptide bond formation in excellent yield without notable racemization at ambient temperature (up to >99 % yield and 99 : 1 dr). Finally, this study proposes this new production method to overcome the limited scale-up production by reaction device scale: liquid phase biomimetic catalytic peptide flow synthesis utilizing a mild Brønsted acid. 相似文献