全文获取类型
收费全文 | 58340篇 |
免费 | 20658篇 |
国内免费 | 1924篇 |
专业分类
化学 | 65733篇 |
晶体学 | 210篇 |
力学 | 3194篇 |
综合类 | 75篇 |
数学 | 4334篇 |
物理学 | 7376篇 |
出版年
2024年 | 415篇 |
2023年 | 4294篇 |
2022年 | 2025篇 |
2021年 | 3037篇 |
2020年 | 5150篇 |
2019年 | 2881篇 |
2018年 | 2769篇 |
2017年 | 1089篇 |
2016年 | 6316篇 |
2015年 | 6177篇 |
2014年 | 5828篇 |
2013年 | 6223篇 |
2012年 | 4618篇 |
2011年 | 2457篇 |
2010年 | 4345篇 |
2009年 | 4239篇 |
2008年 | 2076篇 |
2007年 | 1673篇 |
2006年 | 952篇 |
2005年 | 831篇 |
2004年 | 581篇 |
2003年 | 474篇 |
2002年 | 460篇 |
2001年 | 387篇 |
2000年 | 328篇 |
1999年 | 353篇 |
1998年 | 293篇 |
1997年 | 322篇 |
1996年 | 347篇 |
1995年 | 407篇 |
1994年 | 271篇 |
1993年 | 358篇 |
1992年 | 249篇 |
1991年 | 212篇 |
1990年 | 180篇 |
1989年 | 177篇 |
1988年 | 199篇 |
1980年 | 203篇 |
1979年 | 184篇 |
1978年 | 191篇 |
1977年 | 309篇 |
1976年 | 361篇 |
1975年 | 456篇 |
1974年 | 471篇 |
1973年 | 284篇 |
1972年 | 370篇 |
1971年 | 355篇 |
1970年 | 541篇 |
1969年 | 413篇 |
1968年 | 456篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Lan-Lan Zhang Dr. Wen-Ke Miao Dr. Li-Jun Ren Yu-Kun Yan Dr. Yue Lin Prof. Wei Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(58):13396-13401
Organic polymers and inorganic clusters belong to two different disciplines and have completely different properties and structures. When a cluster is attached to the backbone of a polymer as a pendant, the resultant hybrid polymers (polyclusters) exhibit unique behaviours totally different from those of conventional polymers owing to the nanoscale size of the cluster and its particular interactions. Herein, the aggregation of a poly(polyoxometalate)—a polynorbornene backbone with inorganic polyoxometalate cluster pendants—upon addition of a non-solvent to its dilute solution is reported. A three-dimensional network of tangled and snake-like nanothreads was observed. Direct visualisation of individual nanoscale clusters enabled identification of single chains within the nanothreads. These observations suggest that during the process of aggregation, the hybrid polymer forms curved or extended chains as a consequence of an armouring effect in which the collapsed cluster pendants wrap around the backbone. The collapse occurs because they become less soluble in the solvent/non-solvent mixture. The extended chains then become entwined and form nanoropes consisting of multiple chains wound around each other. This study provides a deeper understanding of the nature of polyclusters and should also prove useful for their future development and application. 相似文献
72.
Hideaki Murasugi Dr. Shohei Kumagai Dr. Hiroaki Iguchi Prof. Dr. Masahiro Yamashita Dr. Shinya Takaishi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(42):9885-9891
Crystal structures of a series of organic–inorganic hybrid gold iodide perovskites, formulated as A2[AuII2][AuIIII4] [A=methylammonium (MA) ( 1 ) and formamidinium (FA) ( 2 )], A′2[I3]1−x[AuII2]x[AuIIII4] [A′=imidazolium (IMD) ( 3 ), guanidinium (GUA) ( 4 ), dimethylammonium (DMA) ( 5 ), pyridinium (PY) ( 6 ), and piperizinium (PIP) ( 7 )], systematically changed depending on the cation size. In addition, triiodide (I3−) ions were partly incorporated into the AuI2− sites of 3 – 7 , whereas they were not incorporated into those of 1 and 2 . Such a difference comes from the size of the organic cation. Optical absorption spectra showed characteristic intervalence charge-transfer bands from AuI to AuIII species, and the optical band gap increased as the size of the cation became larger. 相似文献
73.
Minoru Koyama Dr. Takafumi Kawakami Dr. Takashi Okazoe Prof. Dr. Kyoko Nozaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(46):10913-10917
Methacrylic esters, represented by methyl methacrylate (MMA), are widely used as commodity chemicals. Here, the one-pot synthesis of methacrylic esters from acetone, a haloform and alcohols in the presence of an organic base is described. Using DBU as the organic base for the reaction of acetone, chloroform and methanol in acetonitrile afforded MMA in 66 % yield. When the solvent was replaced by benzonitrile, the product MMA was successfully purified by distillation. Applicability of this process to various alcohols was also investigated to show ethyl, phenyl, CF3CH2, and n-C6F13CH2CH2 esters were obtained in moderate yields. The use of bromoform instead of chloroform resulted in the improvement of the yield, for example, methyl and n-C6F13CH2CH2 esters up to 81 and 70 %, respectively. The reaction with deuterated starting materials acetone-d6 and MeOH-d4, with DBU in acetonitrile afforded deuterated MMA (MMA-d8) in 70 % yield. 相似文献
74.
Ji-Dong Lou Chun-Ling Gao Li Li Zhi-Gang Fang 《Monatshefte für Chemie / Chemical Monthly》2006,41(10):1071-1074
A new procedure for the selective oxidation of alcohols to the corresponding aldehydes and ketones with potassium permanganate
supported on aluminum silicate at room temperature under solvent-free conditions and shaking is reported. 相似文献
75.
76.
间歇式高速同步相机新型全数字化微机控制系统 总被引:2,自引:2,他引:0
本文提出了一种间歇式高速同步相机的全新设计方法,介绍了系统的工作原理,硬件,软件设计以及核心控制算法,最后给出了实际应用结果。 相似文献
77.
78.
79.
Guofen Yu Yuanci Gao Shenggang Liu Wenxiang Wang Jin Wu 《International Journal of Infrared and Millimeter Waves》2002,23(8):1261-1269
Analysis of the field distributions in a single biological cell under electromagnetic wave is given. With Debye approximation, the dielectric relaxation of each part of the cell, including the extracellular and cellular media, the cell membrane and the nuclear membrane, was taken into account. Making use of some typical parameters for a cell, the voltage across nuclear and cytoplasma membranes under electromagnetic waves are calculated up to millimeter wave frequency range. The calculated result indicates that it is unlikely to generate electroporation by present available millimeter wave sources. 相似文献
80.
Dr. H. Schmieg Prof. Dr. P. Vielsack 《Archive of Applied Mechanics (Ingenieur Archiv)》1987,57(6):446-458
Übersicht Betrachtet wird ein zwangserregtes Zweikörpersystem mit wechselnden Bindungen infolge trockener Reibung. Stationäre Bewegungen werden als Grenzfall instationärer Einschwingvorgänge berechnet. Abhängig von den Systemparametern ergeben sich drei typische Bewegungsformen. Ihnen entsprechen dauernde Haftzustände, wechselnde Haft-Gleitzustände oder dauernde Gleitzustände an der Berührfläche beider Körper.
Intermittant constraints in a two-body-system with dry friction
Summary An externally excited two-body-system with intermittant constraints due to dry friction is considered. Stationary motions are calculated as limit cases of instationary transients. Depending on the parameters of the system, three typical modes are of interest. These correspond to permanent sticking, slipstick behaviour, or to permanent slipping in the contact surface of the bodies, respectively.相似文献