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991.
A unique feature of synthetic helical polymers for the detection and amplification of chirality is briefly described in this article. In sharp contrast to host-guest and supramolecular systems that use small synthetic receptor molecules, chirality can be significantly amplified in a helical polymer, such as poly(phenylacetylene)s with functional pendants, which enable the detection of a tiny imbalance in biologically important chiral molecules through a noncovalent bonding interaction with high cooperativity. The rational design of polymeric receptors can be possible by using chromophoric helical polymers combined with functional groups as the pendants, which target particular chiral guest molecules for developing a highly efficient chirality-sensing system. The chirality sensing of other small molecular and supramolecular systems is also briefly described for comparison. 相似文献
992.
报道一种新的测定寡糖链糖体亚谱的NMR方法, 称为MMDY混合脉冲梯度选择一维HOHAHA法. 本方法采用MMDY混合脉冲与双梯度自旋回波脉冲相结合, 为解决高度重叠的1H NMR谱图分析困难提供了有力手段. 本方法的主要特点是: 采用双梯度自旋回波脉冲进行选择激发, 与差谱为基础的选择激发方法相比不但可节省测定时间, 而且谱图干净, 没有差谱伪峰; MMDY混合脉冲的磁化接力相干转移非常有效, 远程磁化转移信号的灵敏度高, 对于偶合常数大约为1 Hz的微弱偶合自旋体系, 如阿拉伯糖和鼠李糖, 也能够得到完整的亚谱; 梯度脉冲只是用于相干路径选择, 灵敏度比较高, 并且纯吸收形的高质量亚谱不经过复杂的Z-滤波步骤就可以快速得到, 因此比较适用于常规样品分析. 以苷类化合物为例讨论本方法的特点以及在谱峰高度的寡糖结构测定中的应用. 相似文献
993.
WANG Wen-Zhi FAN Neng-Ting 《结构化学》2002,21(6):634-636
<正>The title compound 4-(dichloroacetyl)-1-oxa-4-azaspiro[4. 5] decane (CAS number 71526-07-3, C10H15Cl2NO2, Mr= 252.13) was obtained by the reaction of dichloroacetic acid with 1-oxa-4-azaspiro[4. 5] decane. The crystal is of monoclinic, space group P21ln with the unit cell constants: a = 5.9619(4),b= 10.0066(8), c = 20.0986(4) A,β = 90.194(3)°, V= 1199(4) A3,Z = 4, Dc= 1.397 g/cm3, F(000) = 528, μ(MoKα) = 0.522 mm-1, R = 0.0611 and wR = 0.1656 for 1276 observed reflections (I > 2σ(I)). X-ray analysis reveals that the cyclohexyl adopts a chair conformation and the compound is a chiral one. 相似文献
994.
995.
毛细管电泳研究和应用的最新进展 总被引:5,自引:1,他引:5
以作者所在实验室近期工作为主线,结合第五届国际毛细管电泳学术报告会(1993.1.25-28,Orlando,USA)的有关背景情况,介绍了近年来高性能毛细管电泳在应用、技术和理论方面研究工作的进展。 相似文献
996.
997.
奎宁与钴(Ⅱ)手性络合物用于前手性酮的不对称催化还原 总被引:2,自引:0,他引:2
奎宁与钴(Ⅱ)手性络合物用于前手性酮的不对称催化还原刘湘*李纪国张正(无锡轻工大学化工系无锡214036)(南京大学化学系南京)关键词手性络合物,不对称还原,前手性芳香酮1996-10-25收稿,1997-04-22修回前手性酮的不对称催化还原作为光... 相似文献
998.
Partial acylation of (R,S)-3,7-dimethyloctan-1-ol (1) and (R,S)-7-methoxy-3,7-dimethyloctan-1-ol (2) with vinyl acetate catalyzed by the lipase fromCandida cylindracea affords in good yields the correspondingS-configured acetates with 92–98% enantiomeric excess (ee). Under similar conditions, racemic α-cyclogeraniol (3), drim-7-en-11-ol, methyl 4-(3-hydroxy-2-methylpropyl)benzoate, and
its η6-chromium(tricarbonyl) complex (6) are acylated with rather poor (and, for the two latter, opposite) enantioselectivity, whereas
(R,S)-2,4∶3,5-di-O-benzylidenexylitol remains unaffected. Racemic isoborneol (8) and 2-nitro-1-phenylethanol also remain almost or completely
unconverted. Attempts to perform enantioselective acylation of alcohols 3 and 8 with Ac2O in the presence of porcine pancreatic lipase (PPL) proved equally unsuccessful. By contrast, the PPL-catalyzed acylation
of alcohol 6 with vinyl acetate at 17% conversion affords the levorotatory acetate (S)-6a withca. 100%ee. PPL-Mediated partial acylation of (R,S)-pantolactone with Ac2O, followed by mild deacylation of the resultingR acetate, gives (R)-(-)-pantolactone of 97% enantiomeric purity in 60% overall yield.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 175–186, January, 1997. 相似文献
999.
Chiral ligand (A)‐N,N′‐Bis(2‐hydroxy‐3,5‐di‐tert‐butyl‐arylmethyl)‐1,1′‐binaphthalene‐2,2′‐diamine derived from the reduction of Schiff base (R)‐2,2′‐bis (3,5‐di‐tert‐butyl‐2‐hydroxybenzylideneamino)‐1, 1′‐binaphthyl with LiAlH4, is fairly effective in the asymmetric addition reaction of diethylzinc to aldehydes by which good yields (46%‐94%) of the corresponding sec‐alcohols can be obtained in moderate ee (51%‐79%) with R configuration for a variety of aldehydes. 相似文献
1000.
Jürgen Dnnecke Wilfried A. Knig Olle Gyllenhaal Jrgen Vessman Christian Schulze 《Journal of separation science》1994,17(11):779-783
Heptakis(2,6-di-O-methyl-3-O-pentyl) (2-O-methyl-6-O-oct-1-enyl-3-O-pentyl)-γ-cyclodextrin was immobilized to narrow-bore fused silica capillaries after selective modification. One tert-butyldimethylsilyl group was introduced into octakis-(2-O-methyl-3-O-pentyl)-γ-cyclodextrin in order to get a pure monofunctionalized cyclodextrin derivative. During synthesis the tert-butyldimethylsilyl group was replaced by an anchoring group to bind the cyclodextrin to a polysiloxane. After thermal immobilization of the modified polysiloxane this new chiral stationary phase was applied in GC and SFC. High efficiency separations were obtained in GC. In SFC very polar compounds could be chromatographed at low temperatures resulting in higher separation factors as compared to GC. 相似文献