全文获取类型
收费全文 | 1930篇 |
免费 | 61篇 |
国内免费 | 19篇 |
专业分类
化学 | 1497篇 |
晶体学 | 32篇 |
力学 | 30篇 |
数学 | 146篇 |
物理学 | 305篇 |
出版年
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 20篇 |
2020年 | 11篇 |
2019年 | 38篇 |
2018年 | 23篇 |
2017年 | 15篇 |
2016年 | 30篇 |
2015年 | 44篇 |
2014年 | 40篇 |
2013年 | 118篇 |
2012年 | 110篇 |
2011年 | 139篇 |
2010年 | 70篇 |
2009年 | 75篇 |
2008年 | 141篇 |
2007年 | 136篇 |
2006年 | 133篇 |
2005年 | 130篇 |
2004年 | 109篇 |
2003年 | 84篇 |
2002年 | 99篇 |
2001年 | 28篇 |
2000年 | 29篇 |
1999年 | 24篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 26篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 11篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 14篇 |
1985年 | 25篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1973年 | 11篇 |
排序方式: 共有2010条查询结果,搜索用时 140 毫秒
991.
Takao Komatsu 《Czechoslovak Mathematical Journal》2007,57(3):919-932
Many new types of Hurwitz continued fractions have been studied by the author. In this paper we show that all of these closed
forms can be expressed by using confluent hypergeometric functions 0
F1(;c;z). In the application we study some new Hurwitz continued fractions whose closed form can be expressed by using confluent
hypergeometric functions.
This research was supported in part by the Grant-in-Aid for Scientific research (C) (No. 18540006), the Japan Society for
the Promotion of Science. 相似文献
992.
Dr. Koji Numasawa Prof. Kenjiro Hanaoka Naoko Saito Prof. Yoshifumi Yamaguchi Takayuki Ikeno Honami Echizen Dr. Masahiro Yasunaga Dr. Toru Komatsu Dr. Tasuku Ueno Prof. Masayuki Miura Prof. Tetsuo Nagano Prof. Yasuteru Urano 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(15):6071-6076
Folate receptors (FRs) are membrane proteins involved in folic acid uptake, and the alpha isoform (FR-α) is overexpressed in ovarian and endometrial cancer cells. For fluorescence imaging of FRs in vivo, the near-infrared (NIR) region (650–900 nm), in which tissue penetration is high and autofluorescence is low, is optimal, but existing NIR fluorescent probes targeting FR-α show high non-specific tissue adsorption, and require prolonged washout to visualize tumors. We have designed and synthesized a new NIR fluorescent probe, FolateSiR-1 , utilizing a Si-rhodamine fluorophore having a carboxy group at the benzene moiety, coupled to a folate ligand moiety through a negatively charged tripeptide linker. This probe exhibits very low background fluorescence and afforded a tumor-to-background ratio (TBR) of up to 83 in FR-expressing tumor-bearing mice within 30 min. Thus, FolateSiR-1 has the potential to contribute to the research in the field of biology and the clinical medicine. 相似文献
993.
Synthesis of 3‐(ω‐Hydroxyalkoxy)isobenzofuran‐1(3H)‐ones by Trifluoroacetic Acid‐Mediated Lactonization of tert‐Butyl 2‐(1,3‐Dioxol‐2‐yl)‐ or 2‐(1,3‐Dioxan‐2‐yl)benzoates
下载免费PDF全文
![点击此处可从《Helvetica chimica acta》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An efficient two‐step method for the preparation of 3‐(2‐hydroxyethoxy)‐ or 3‐(3‐hydroxypropoxy)isobenzofuran‐1(3H)‐ones 3 has been developed. Thus, the reaction of 1‐(1,3‐dioxol‐2‐yl)‐ or 1‐(1,3‐dioxan‐2‐yl)‐2‐lithiobenzenes, generated in situ by the treatment of 1‐bromo‐2‐(1,3‐dioxol‐2‐yl)‐ or 1‐bromo‐2‐(1,3‐dioxan‐2‐yl)benzenes 1 with BuLi in THF at ?78°, with (Boc)2O afforded tert‐butyl 2‐(1,3‐dioxol‐2‐yl)‐ or 2‐(1,3‐dioxan‐2‐yl)benzoates 2 , which can subsequently undergo facile lactonization on treatment with CF3COOH (TFA) in CH2Cl2 at 0° to give the desired products in reasonable yields. 相似文献
994.
Hitoshi Tamiaki Kazuhiro Fukai Hideki Shimazu Sunao Shoji 《Photochemistry and photobiology》2014,90(1):121-128
Zinc complex of pyropheophorbide‐b, a derivative of chlorophyll‐b, was covalently dimerized through ethylene glycol diester. The synthetic homo‐dyad was axially ligated with two methanol molecules from the β‐face and both the diastereomerically coordinating methanol species were hydrogen bonded with the keto‐carbonyl groups of the neighboring chlorin in a complex. The resulting folded conformer in a solution was confirmed by visible, 1H NMR and IR spectra. All the synthetic zinc chlorin homo‐ and hetero‐dyads consisting of pyropheophorbides‐a, b and/or d took the above methanol‐locked and π–π stacked supramolecules in 1% (v/v) methanol and benzene to give redmost (Qy) electronic absorption band(s) at longer wavelengths than those of the corresponding monomeric chlorin composites. The other zinc chlorin and bacteriochlorin homo‐dyads completely formed similar folded conformers in the same solution, while zinc inverse chlorin and porphyrin homo‐dyads partially took such supramolecules. The J‐type aggregation to folded conformers and the redshift values of composite Qy bands were dependent on the electronic and steric factors of porphyrinoid moieties in dyads. 相似文献
995.
Stereoselective Construction of 1,3‐Disilylcyclopentane Derivatives by Scandium‐Catalyzed [3+2] Cycloaddition of Allylsilanes to β‐Silylenones
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Kazuhiro Okamoto Eisuke Tamura Prof. Dr. Kouichi Ohe 《Angewandte Chemie (International ed. in English)》2014,53(38):10195-10199
The Sc(OTf)3‐catalyzed [3+2] cycloaddition of allylsilanes to β‐silyl‐α,β‐unsaturated ketones (β‐silylenones) has been developed to form five‐membered syn‐1,3‐disilylketones diastereoselectively through the rearrangement of the silicon substituents on the allylsilane. Stabilization of the carbocation intermediates by a double silicon effect plays a key role in directing the course of the reaction to favor the [3+2] cycloaddition pathway over simple allylation. 相似文献
996.
Masashi Shigenobu Kazuhiro Takenaka Hiroaki Sasai 《Angewandte Chemie (International ed. in English)》2015,54(33):9572-9576
A palladium‐catalyzed direct arylation of isoxazoles with aryl iodides has been achieved. The C H bond at the 5‐position is activated selectively to give coupling products in moderate to good yields. This direct arylation was applied to the synthesis of a spiro‐type chiral ligand, which proved to be most effective to the palladium‐catalyzed tandem cyclization of a dialkenyl alcohol. 相似文献
997.
Kazuki Komatsu Koji Munakata Kazuyuki Matsubayashi Yoshiya Uwatoko Yoshihiko Yokoyama Kazumasa Sugiyama 《高压研究》2015,35(3):254-262
Zirconium-based bulk metallic glass (Zr-based BMG) has outstanding properties as a cylinder material for piston-cylinder high pressure apparatuses and is especially useful for neutron scattering. The piston-cylinder consisting of a Zr-based BMG cylinder with outer/inner diameters of 8.8/2.5?mm sustains pressures up to 1.81?GPa and ruptured at 2.0?GPa, with pressure values determined by the superconducting temperature of lead. The neutron attenuation of Zr-based BMG is similar to that of TiZr null-scattering alloy and more transparent than that of CuBe alloy. No contamination of sharp Bragg reflections is observed in the neutron diffraction pattern for Zr-based BMG. The magnetic susceptibility of Zr-based BMG is similar to that of CuBe alloy; this leads to a potential application for measurements of magnetic properties under pressure. 相似文献
998.
Kazuhiro Kobayashi Hideo Tanaka Koujirou Tanaka Keiichi Yoneda Osamu Morikawa Hisatoshi Konishi 《合成通讯》2013,43(23):4277-4291
The reaction of 1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione with various alkenes or terminal alkynes in the presence of cerium(IV) ammonium nitrate (CAN) afforded the corresponding 5,6-dihydrofuro[2,3-d]pyrimidine-2,4(1H,3H)-diones or furo[2,3-d]pyrimidine-2,4(1H,3H)-diones in moderate to good yields. 相似文献
999.
The first preparation of acridin‐9(10H)‐ones carrying a tertiary thiocarbamoyl group at C(10), i.e., N,N‐dialkyl‐9‐oxoacridine‐10(9H)‐carbothioamides 9 , is described. The method is based on the reaction of (2‐halophenyl)(2‐isothiocyanatophenyl)methanones 7 , prepared from (2‐aminophenyl)(2‐halophenyl)methanones 5 by a convenient three‐step sequence, with secondary amines in DMF at room temperature to generate the corresponding thiourea derivatives 8 in situ, which are treated with NaH at 100–120° to provide the desired products in one‐pot reactions in generally good yields. 相似文献
1000.
A convenient procedure for the synthesis of 2,N,N‐trisubstituted 1H‐indole‐1‐carbothioamides from 2‐(acylmethyl)phenyl isocyanides has been developed. Thus, these isocyanides are converted into (Z)‐ [1‐alkyl (or phenyl)‐2‐(2‐isothiocyanatophenyl)ethenyl] 1,1‐dimethylethyl carbonates via an easy two‐step sequence. Treatment with secondary amines gave thiourea intermediates which afforded with CF3COOH (TFA) the desired products in fair‐to‐good yields. 相似文献